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gnunet - GNUnet


GNUnet in its current version is the result of almost 20 years of work from many contributors. So far, most contributions were made by volunteers or people paid to do fundamental research. At this stage, GNUnet remains an experimental system where significant parts of the software lack a reasonable degree of professionalism in its implementation. Furthermore, we are aware of a significant number of existing bugs and critical design flaws, as some unfortunate early design decisions remain to be rectified. There are still known open problems; GNUnet remains an active research project.

The project was started in 2001 when some initial ideas for improving Freenet’s file-sharing turned out to be too radical to be easily realized within the scope of the existing Freenet project. We lost our first contributor on 11.9.2001 as the contributor realized that privacy may help terrorists. The rest of the team concluded that it was now even more important to fight for civil liberties. The first release was called “GNet” – already with the name GNUnet in mind, but without the blessing of GNU we did not dare to call it GNUnet immediately. A few months after the first release we contacted the GNU project, happily agreed to their governance model and became an official GNU package.

Within the first year, we created GNU libextractor, a helper library for meta data extraction which has been used by a few other projects as well. 2003 saw the emergence of pluggable transports, the ability for GNUnet to use different mechanisms for communication, starting with TCP, UDP and SMTP (support for the latter was later dropped due to a lack of maintenance). In 2005, the project first started to evolve beyond the original file-sharing application with a first simple P2P chat. In 2007, we created GNU libmicrohttpd to support a pluggable transport based on HTTP. In 2009, the architecture was radically modularized into the multi-process system that exists today. Coincidentally, the first version of the ARM service (ARM: Automatic Restart Manager) was implemented a day before systemd was announced. From 2009 to 2014 work progressed rapidly thanks to a significant research grant from the Deutsche Forschungsgesellschaft. This resulted in particular in the creation of the R5N DHT, CADET, ATS and the GNU Name System. In 2010, GNUnet was selected as the basis for the secushare online social network, resulting in a significant growth of the core team. In 2013, we launched GNU Taler to address the challenge of convenient and privacy-preserving online payments. In 2015, the pretty Easy privacy (pEp) project announced that they will use GNUnet as the technology for their meta-data protection layer, ultimately resulting in GNUnet e.V. entering into a formal long-term collaboration with the pEp Foundation. In 2016, Taler Systems SA, a first startup using GNUnet technology, was founded with support from the community.

GNUnet is not merely a technical project, but also a political mission: like the GNU project as a whole, we are writing software to achieve political goals with a focus on the human right of informational self-determination. Putting users in control of their computing has been the core driver of the GNU project. With GNUnet we are focusing on informational self-determination for collaborative computing and communication over networks.

The Internet is shaped as much by code and protocols as it is by its associated political processes (IETF, ICANN, IEEE, etc.). Similarly its flaws are not limited to the protocol design. Thus, technical excellence by itself will not suffice to create a better network. We also need to build a community that is wise, humble and has a sense of humor to achieve our goal to create a technical foundation for a society we would like to live in.

Project governance

GNUnet, like the GNU project and many other free software projects, follows the governance model of a benevolent dictator. This means that ultimately, the GNU project appoints the GNU maintainer and can overrule decisions made by the GNUnet maintainer. Similarly, the GNUnet maintainer can overrule any decisions made by individual developers. Still, in practice neither has happened in the last 20 years for GNUnet, and we hope to keep it that way.

The current maintainers of GNUnet are:

  • Christian Grothoff
  • Martin Schanzenbach

The GNUnet project is supported by GNUnet e.V., a German association where any developer can become a member. GNUnet e.V. serves as a legal entity to hold the copyrights to GNUnet. GNUnet e.V. may also choose to pay for project resources, and can collect donations as well as choose to adjust the license of the software (with the constraint that it has to remain free software). In 2018 we switched from GPL3 to AGPL3, in practice these changes do not happen very often.


The primary goal of the GNUnet project is to provide a reliable, open, non-discriminating and censorship-resistant system for information exchange. We value free speech above state interests and intellectual monopoly. GNUnet’s long-term goal is to serve as a development platform for the next generation of Internet protocols.

Participants are encouraged to contribute at least as much resources (storage, bandwidth) to the network as they consume, so that their participation does not have a negative impact on other users.

Design Principles

These are the GNUnet design principles, in order of importance:

  • GNUnet must be implemented as Free Software — This means that you have the four essential freedoms: to run the program, to study and change the program in source code form, to redistribute exact copies, and to distribute modified versions. (
  • GNUnet must minimize the amount of personally identifiable information exposed.
  • GNUnet must be fully distributed and resilient to external attacks and rogue participants.
  • GNUnet must be self-organizing and not depend on administrators or centralized infrastructure.
  • GNUnet must inform the user which other participants have to be trusted when establishing private communications.
  • GNUnet must be open and permit new peers to join.
  • GNUnet must support a diverse range of applications and devices.
  • GNUnet must use compartmentalization to protect sensitive information.
  • The GNUnet architecture must be resource efficient.
  • GNUnet must provide incentives for peers to contribute more resources than they consume.

Privacy and Anonymity

The GNUnet protocols minimize the leakage of personally identifiable information of participants and do not allow adversaries to control, track, monitor or censor users activities. The GNUnet protocols also make it as hard as possible to disrupt operations by participating in the network with malicious intent.

Analyzing participant’s activities becomes more difficult as the number of peers and applications that generate traffic on the network grows, even if the additional traffic generated is not related to anonymous communication. This is one of the reasons why GNUnet is developed as a peer-to-peer framework where many applications share the lower layers of an increasingly complex protocol stack. The GNUnet architecture encourages many different forms of peer-to-peer applications.


Wherever possible GNUnet allows the peer to adjust its operations and functionalities to specific use cases. A GNUnet peer running on a mobile device with limited battery for example might choose not to relay traffic for other participants.

For certain applications like file-sharing GNUnet allows participants to trade degrees of anonymity in exchange for increased efficiency. However, it is not possible for any user’s efficiency requirements to compromise the anonymity of any other user.

Key Concepts

In this section, the fundamental concepts of GNUnet are explained. Most of them are also described in our research papers. First, some of the concepts used in the GNUnet framework are detailed. The second part describes concepts specific to anonymous file-sharing.


Almost all peer-to-peer communications in GNUnet are between mutually authenticated peers. The authentication works by using ECDHE, that is a DH (Diffie—Hellman) key exchange using ephemeral elliptic curve cryptography. The ephemeral ECC (Elliptic Curve Cryptography) keys are signed using ECDSA. The shared secret from ECDHE is used to create a pair of session keys (using HKDF) which are then used to encrypt the communication between the two peers using both 256-bit AES (Advanced Encryption Standard) and 256-bit Twofish (with independently derived secret keys). As only the two participating hosts know the shared secret, this authenticates each packet without requiring signatures each time. GNUnet uses SHA-512 (Secure Hash Algorithm) hash codes to verify the integrity of messages.

In GNUnet, the identity of a host is its public key. For that reason, man-in-the-middle attacks will not break the authentication or accounting goals. Essentially, for GNUnet, the IP of the host has nothing to do with the identity of the host. As the public key is the only thing that truly matters, faking an IP, a port or any other property of the underlying transport protocol is irrelevant. In fact, GNUnet peers can use multiple IPs (IPv4 and IPv6) on multiple ports — or even not use the IP protocol at all (by running directly on layer 2).

GNUnet uses a special type of message to communicate a binding between public (ECC) keys to their current network address. These messages are commonly called HELLOs or peer advertisements. They contain the public key of the peer and its current network addresses for various transport services. A transport service is a special kind of shared library that provides (possibly unreliable, out-of-order) message delivery between peers. For the UDP and TCP transport services, a network address is an IP and a port. GNUnet can also use other transports (HTTP, HTTPS, WLAN, etc.) which use various other forms of addresses. Note that any node can have many different active transport services at the same time, and each of these can have a different addresses. Binding messages expire after at most a week (the timeout can be shorter if the user configures the node appropriately). This expiration ensures that the network will eventually get rid of outdated advertisements.

For more information, refer to the following paper:

Ronaldo A. Ferreira, Christian Grothoff, and Paul Ruth. A Transport Layer Abstraction for Peer-to-Peer Networks Proceedings of the 3rd International Symposium on Cluster Computing and the Grid (GRID 2003), 2003. (

Accounting to Encourage Resource Sharing

Most distributed P2P networks suffer from a lack of defenses or precautions against attacks in the form of freeloading. While the intentions of an attacker and a freeloader are different, their effect on the network is the same; they both render it useless. Most simple attacks on networks such as Gnutella involve flooding the network with traffic, particularly with queries that are, in the worst case, multiplied by the network.

In order to ensure that freeloaders or attackers have a minimal impact on the network, GNUnet’s file-sharing implementation (FS) tries to distinguish good (contributing) nodes from malicious (freeloading) nodes. In GNUnet, every file-sharing node keeps track of the behavior of every other node it has been in contact with. Many requests (depending on the application) are transmitted with a priority (or importance) level. That priority is used to establish how important the sender believes this request is. If a peer responds to an important request, the recipient will increase its trust in the responder: the responder contributed resources. If a peer is too busy to answer all requests, it needs to prioritize. For that, peers do not take the priorities of the requests received at face value. First, they check how much they trust the sender, and depending on that amount of trust they assign the request a (possibly lower) effective priority. Then, they drop the requests with the lowest effective priority to satisfy their resource constraints. This way, GNUnet’s economic model ensures that nodes that are not currently considered to have a surplus in contributions will not be served if the network load is high.

For more information, refer to the following paper: Christian Grothoff. An Excess-Based Economic Model for Resource Allocation in Peer-to-Peer Networks. Wirtschaftsinformatik, June 2003. (


Adversaries (malicious, bad actors) outside of GNUnet are not supposed to know what kind of actions a peer is involved in. Only the specific neighbor of a peer that is the corresponding sender or recipient of a message may know its contents, and even then application protocols may place further restrictions on that knowledge. In order to ensure confidentiality, GNUnet uses link encryption, that is each message exchanged between two peers is encrypted using a pair of keys only known to these two peers. Encrypting traffic like this makes any kind of traffic analysis much harder. Naturally, for some applications, it may still be desirable if even neighbors cannot determine the concrete contents of a message. In GNUnet, this problem is addressed by the specific application-level protocols. See for example the following sections: Anonymity, see How file-sharing achieves Anonymity, and see Deniability.


Providing anonymity for users is the central goal for the anonymous file-sharing application. Many other design decisions follow in the footsteps of this requirement. Anonymity is never absolute. While there are various scientific metrics (Claudia Díaz, Stefaan Seys, Joris Claessens, and Bart Preneel. Towards measuring anonymity. 2002. ( that can help quantify the level of anonymity that a given mechanism provides, there is no such thing as “complete anonymity”.

GNUnet’s file-sharing implementation allows users to select for each operation (publish, search, download) the desired level of anonymity. The metric used is based on the amount of cover traffic needed to hide the request.

While there is no clear way to relate the amount of available cover traffic to traditional scientific metrics such as the anonymity set or information leakage, it is probably the best metric available to a peer with a purely local view of the world, in that it does not rely on unreliable external information or a particular adversary model.

The default anonymity level is 1, which uses anonymous routing but imposes no minimal requirements on cover traffic. It is possible to forego anonymity when this is not required. The anonymity level of 0 allows GNUnet to use more efficient, non-anonymous routing.

How file-sharing achieves Anonymity

Contrary to other designs, we do not believe that users achieve strong anonymity just because their requests are obfuscated by a couple of indirections. This is not sufficient if the adversary uses traffic analysis. The threat model used for anonymous file sharing in GNUnet assumes that the adversary is quite powerful. In particular, we assume that the adversary can see all the traffic on the Internet. And while we assume that the adversary can not break our encryption, we assume that the adversary has many participating nodes in the network and that it can thus see many of the node-to-node interactions since it controls some of the nodes.

The system tries to achieve anonymity based on the idea that users can be anonymous if they can hide their actions in the traffic created by other users. Hiding actions in the traffic of other users requires participating in the traffic, bringing back the traditional technique of using indirection and source rewriting. Source rewriting is required to gain anonymity since otherwise an adversary could tell if a message originated from a host by looking at the source address. If all packets look like they originate from one node, the adversary can not tell which ones originate from that node and which ones were routed. Note that in this mindset, any node can decide to break the source-rewriting paradigm without violating the protocol, as this only reduces the amount of traffic that a node can hide its own traffic in.

If we want to hide our actions in the traffic of other nodes, we must make our traffic indistinguishable from the traffic that we route for others. As our queries must have us as the receiver of the reply (otherwise they would be useless), we must put ourselves as the receiver of replies that actually go to other hosts; in other words, we must indirect replies. Unlike other systems, in anonymous file-sharing as implemented on top of GNUnet we do not have to indirect the replies if we don’t think we need more traffic to hide our own actions.

This increases the efficiency of the network as we can indirect less under higher load. Refer to the following paper for more: Krista Bennett and Christian Grothoff. GAP — practical anonymous networking. In Proceedings of Designing Privacy Enhancing Technologies, 2003. (

How messaging provided Anonymity

While the file-sharing tries to achieve anonymity through hiding actions in other traffic, the messaging service provides a weaker form of protection against identification.

The messaging service allows the use of an anonymous ego for the signing and verification process of messages instead of a unique ego. This anonymous ego is a publicly known key pair which is shared between all peers in GNUnet.

Using this ego only ensures that individual messages alone can’t identify its sender inside of a messenger room. It should be clarified that the route of the traffic for each message can still be tracked to identify the senders peer inside of a messenger room if the threat agent controls certain peers hosting the room.

Also opening a room in the messenger service will potentially match your peer identity with the internal member identity from the messenger service. So despite using the anonymous ego you can reveal your peer identity. This means to decrease the chance of being identified, it is recommended to enter rooms but you should not open them for others.


Even if the user that downloads data and the server that provides data are anonymous, the intermediaries may still be targets. In particular, if the intermediaries can find out which queries or which content they are processing, a strong adversary could try to force them to censor certain materials.

With the file-encoding used by GNUnet’s anonymous file-sharing, this problem does not arise. The reason is that queries and replies are transmitted in an encrypted format such that intermediaries cannot tell what the query is for or what the content is about. Mind that this is not the same encryption as the link-encryption between the nodes. GNUnet has encryption on the network layer (link encryption, confidentiality, authentication) and again on the application layer (provided by gnunet-publish, gnunet-download, gnunet-search and gnunet-fs-gtk).

Refer to the following paper for more: Christian Grothoff, Krista Grothoff, Tzvetan Horozov, and Jussi T. Lindgren. An Encoding for Censorship-Resistant Sharing. 2009. (

Peer Identities

Peer identities are used to identify peers in the network and are unique for each peer. The identity for a peer is simply its public key, which is generated along with a private key when the peer is started for the first time. While the identity is binary data, it is often expressed as an ASCII string. For example, the following is a peer identity as you might see it in various places:


You can find your peer identity by running gnunet-peerinfo -s.

Zones in the GNU Name System (GNS Zones)

GNS zones are similar to those of DNS zones, but instead of a hierarchy of authorities to governing their use, GNS zones are controlled by a private key. When you create a record in a DNS zone, that information is stored in your nameserver. Anyone trying to resolve your domain then gets pointed (hopefully) by the centralised authority to your nameserver. Whereas GNS, being fully decentralized by design, stores that information in DHT. The validity of the records is assured cryptographically, by signing them with the private key of the respective zone.

Anyone trying to resolve records in a zone of your domain can then verify the signature of the records they get from the DHT and be assured that they are indeed from the respective zone. To make this work, there is a 1:1 correspondence between zones and their public-private key pairs. So when we talk about the owner of a GNS zone, that’s really the owner of the private key. And a user accessing a zone needs to somehow specify the corresponding public key first.

For more information, refer to the following paper:

Matthias Wachs, Martin Schanzenbach, and Christian Grothoff. A Censorship-Resistant, Privacy-Enhancing and Fully Decentralized Name System. In proceedings of 13th International Conference on Cryptology and Network Security (CANS 2014). 2014.


Egos are your “identities” in GNUnet. Any user can assume multiple identities, for example to separate their activities online. Egos can correspond to “pseudonyms” or “real-world identities”. Technically an ego is first of all a key pair of a public- and private-key.


This guide is intended for those who want to install GNUnet from source. For instructions on how to install GNUnet as a binary package please refer to the official documentation of your operating system or package manager.

For understanding this guide properly it is important to know that there are two different ways of running GNUnet:

  • the single-user setup
  • the multi-user setup

The latter variant has a better security model and requires extra preparation before running make install and a different configuration. Beginners who want to quickly try out GNUnet can use the single-user setup.


GNUnet needs few libraries and applications for being able to run and another few optional ones for using certain features. Preferably they should be installed with a package manager.

The mandatory libraries and applications are

  • autoconf 2.59 or above (when building from git)
  • automake 1.11.1 or above (when building from git)
  • recutils 1.0 or above (when building from git)
  • gettext
  • glibc (read below, other libcs work)
  • GnuTLS 3.2.12 or above, recommended to be linked against libunbound
  • GNU make 4.0 or higher (other make implementations do work)
  • iptables (on Linux systems)
  • libtool 2.2 or above
  • libltdl (part of libtool)
  • libgcrypt 1.6 or above
  • libidn2 or libidn
  • libmicrohttpd 0.9.63 or above
  • libunistring
  • libjansson
  • libjose (optional, for reclaimID)
  • libgmp
  • libgnurl or libcurl (libcurl has to be linked to GnuTLS) 7.35.0 or above
  • Texinfo 5.2 or above (for building the documentation)
  • Texlive 2012 or above (for building the documentation, and for gnunet-bcd)
  • makeinfo 4.8 or above
  • pkgconf (or pkg-config)
  • zlib

Glibc is required for certain NSS features:

One mechanism of integrating GNS with legacy applications via NSS is
not available if this is disabled. But applications that don't use the
glibc for NS resolution won't work anyway with this, so little is lost
on *BSD systems.
GNS via direct use or via the HTTP or DNS proxies is unaffected.

Other libcs should work, the resulting builds just don’t include the glibc NSS specific code. One example is the build against NetBSD’s libc as detailed in

In addition GNUnet needs at least one of these three databases (at the minimum sqlite3)

  • sqlite + libsqlite 3.8 or above (the default, requires no further configuration)
  • postgres + libpq
  • mysql + libmysqlclient

These are the dependencies only required for certain features

  • miniupnpc (for traversing NAT boxes more reliably)
  • libnss
  • libopus (for running the GNUnet conversation telephony application)
  • libogg (for running the GNUnet conversation telephony application)
  • gstreamer OR libpulse (for running the GNUnet conversation telephony application)
  • bluez (for bluetooth support)
  • libextractor (optional but highly recommended, read below)
  • texi2mdoc (for automatic mdoc generation)
  • perl5 for some utilities (which are not installed)

About libextractor being optional:

While libextractor ("LE") is optional, it is recommended to build gnunet
against it. If you install it later, you won't benefit from libextractor.
If you are a distributor, we recommend to split LE into basis + plugins
rather than making LE an option as an afterthought by the user.  LE
itself is very small, but its dependency chain on first, second, third
etc level can be big.  There is a small effect on privacy if your LE
build differs from one which includes all plugins (plugins are build as
shared objects): if users publish a directory with a mixture of file
types (for example mpeg, jpeg, png, gif) the configuration of LE could
leak which plugins are installed for which filetypes are not providing
more details.  However, this leak is just a minor concern.

These are the test-suite requirements:

  • python3.6 or higher
  • gnunet (installation first)
  • some core-utils: which(1), bc(1), curl(1), sed(1), awk(1), etc.
  • a shell (very few Bash scripts, the majority are POSIX sh scripts)

These are runtime requirements:

  • nss (the certutil binary, for gnunet-gns-proxy-setup-ca)
  • openssl (openssl binary, for gnunet-gns-proxy-setup-ca)

Getting the Source Code

You can either download the source code using git (you obviously need git installed) or as an archive.

Using git type

The archive can be found at Extract it using a graphical archive tool or tar:

tar xf gnunet-0.17.1-26-g233ec6111.tar.gz

In the next chapter we will assume that the source code is available in the home directory at ~/gnunet.

Create user and groups for the system services

For single-user setup this section can be skipped

The multi-user setup means that there are system services, which are run once per machine as a dedicated system user (called gnunet) and user services which can be started by every user who wants to use GNUnet applications. The user services communicate with the system services over unix domain sockets. To gain permissions to read and write those sockets the users running GNUnet applications will need to be in the gnunet group. In addition the group gnunetdns may be needed (see below).

Create user gnunet who is member of the group gnunet (automatically created) and specify a home directory where the GNUnet services will store persistent data such as information about peers.

$ sudo useradd --system --home-dir /var/lib/gnunet --create-home gnunet

Now add your own user to the gnunet group:

$ sudo usermod -aG gnunet <user>

Create a group gnunetdns. This allows using setgid in a way that only the DNS service can run the gnunet-helper-dns binary. This is only needed if system-wide DNS interception will be used. For more information see Configuring system-wide DNS interception.

$ sudo groupadd gnunetdns

Preparing and Compiling the Source Code

For preparing the source code for compilation a bootstrap script and configure has to be run from the source code directory. When running configure, options can be specified to customize the compilation and installation process. For details execute:

$ ./configure --help

The following example configures the installation prefix /usr/local and disables building the documentation

$ cd ~/gnunet
$ ./bootstrap
$ ./configure --prefix=/usr/local --disable-documentation

After running the bootstrap script and configure successfully the source code can be compiled and the compiled binaries can be installed using:

$ make
$ make install

The latter command may need to be run as root (or with sudo) because some binaries need the suid bit set. Without that some features (e.g. the VPN service, system-wide DNS interception, NAT traversal using ICMP) will not work.

NSS plugin (optional)

NOTE: The installation of the NSS plugin is only necessary if GNS resolution shall be used with legacy applications (that only support DNS) and if you cannot do not want to use the DNS2GNS service.

One important library is the GNS plugin for NSS (the name services switch) which allows using GNS (the GNU name system) in the normal DNS resolution process. Unfortunately NSS expects it in a specific location (probably /lib) which may differ from the installation prefix (see --prefix option in the previous section). This is why the plugin has to be installed manually.

Find the directory where nss plugins are installed on your system, e.g.:

$ ls -l /lib/libnss_*

Copy the GNS NSS plugin to that directory:

cp ~/gnunet/src/gns/nss/.libs/ /lib

Now, to activate the plugin, you need to edit your /etc/nsswitch.conf where you should find a line like this:

hosts: files mdns4_minimal [NOTFOUND=return] dns mdns4

The exact details may differ a bit, which is fine. Add the text gns [NOTFOUND=return] after files:

hosts: files gns [NOTFOUND=return] mdns4_minimal [NOTFOUND=return] dns mdns4

Installing the GNS Certificate Authority (Optional)

NOTE: Installing the GNS certificate authority is only necessary if GNS shall be used in a browser and if you cannot or do not want to use the DNS2GNS service.

The GNS Certificate authority can provide TLS certificates for GNS names while downloading webpages from legacy webservers. This allows browsers to use HTTPS in combinations with GNS name resolution.

To install it execute the GNS CA-setup script. So far Firefox and Chromium are supported.

$ gnunet-gns-proxy-setup-ca

A local proxy server, that takes care of the name resolution and provides certificates on-the-fly needs to be started:

$ /usr/lib/gnunet/libexec/gnunet-gns-proxy

Now GNS should work in browsers that are configured to use a SOCKS proxy on localhost:7777.

Minimal configuration

GNUnet needs a configuration file to start (see Config file format). For the single-user setup an empty file is sufficient:

$ touch ~/.config/gnunet.conf

For the multi-user setup we need an extra config file for the system services. The default location is /etc/gnunet.conf. The minimal content of that file which activates the system services roll is:


The config file for the user services (~/.config/gnunet.conf) needs the opposite configuration to activate the user services roll:



This tutorial is supposed to give a first introduction for users trying to do something real with GNUnet. Installation and configuration are specifically outside of the scope of this tutorial. Instead, we start by briefly checking that the installation works, and then dive into uncomplicated, concrete practical things that can be done with the framework provided by GNUnet.

In short, this chapter of the “GNUnet Reference Documentation” will show you how to use the various peer-to-peer applications of the GNUnet system. As GNUnet evolves, we will add new sections for the various applications that are being created.

Comments on the content of this chapter, and extensions of it are always welcome.

Starting and stopping

Prior to using any GNUnet-based application, one has to start a node:

$ gnunet-arm -s

To stop GNUnet:

$ gnunet-arm -e

You can usually find the logs under ~/.cache/gnunet and all files such as databases and private keys in ~/.local/share/gnunet.

The list of running services can be displayed using the -I option. It should look similar to this example:

$ gnunet-arm -I
Running services:
topology (gnunet-daemon-topology)
nat (gnunet-service-nat)
vpn (gnunet-service-vpn)
gns (gnunet-service-gns)
cadet (gnunet-service-cadet)
namecache (gnunet-service-namecache)
hostlist (gnunet-daemon-hostlist)
revocation (gnunet-service-revocation)
ats (gnunet-service-ats)
peerinfo (gnunet-service-peerinfo)
zonemaster (gnunet-service-zonemaster)
zonemaster-monitor (gnunet-service-zonemaster-monitor)
dht (gnunet-service-dht)
namestore (gnunet-service-namestore)
set (gnunet-service-set)
statistics (gnunet-service-statistics)
nse (gnunet-service-nse)
fs (gnunet-service-fs)
peerstore (gnunet-service-peerstore)
core (gnunet-service-core)
rest (gnunet-rest-server)
transport (gnunet-service-transport)
datastore (gnunet-service-datastore)

For the multi-user setup first the system services need to be started as the system user, i.e. the user gnunet needs to execute gnunet-arm -s. This should be done by the system’s init system. Then the user who wants to start GNUnet applications has to run gnunet-arm -s, too. It is recommended to automate this, e.g. using the user’s crontab.

First, you should launch the peer information tool. You can do this from the command-line by typing:

$ gnunet-peerinfo

Once you have done this, you will see a list of known peers. If hardly any peers are listed, there is likely a problem with your network configuration. You can also check directly connected peers with:

$ gnunet-core

This should return (at least) one established connection peer. Otherwise, again, there is likely a problem with your network configuration.

The GNU Name System

The GNU Name System (GNS) is secure and decentralized naming system. It allows its users to register names as top-level domains (TLDs) and resolve other namespaces within their TLDs.

GNS is designed to provide:

  • Censorship resistance
  • Query privacy
  • Secure name resolution
  • Compatibility with DNS

For the initial configuration and population of your GNS installation, please follow the GNS setup instructions. The remainder of this chapter will provide some background on GNS and then describe how to use GNS in more detail.

Unlike DNS, GNS does not rely on central root zones or authorities. Instead any user administers their own root and can can create arbitrary name value mappings. Furthermore users can delegate resolution to other users’ zones just like DNS NS records do. Zones are uniquely identified via public keys and resource records are signed using the corresponding public key. Delegation to another user’s zone is done using special PKEY records and petnames. A petname is a name that can be freely chosen by the user. This results in non-unique name-value mappings as www.bob to one user might be www.friend for someone else.

Start Zones

In the default configuration, there are two zones defined and shipped with GNUnet:

The first is “”, which points to the authoritate zone of the GNUnet project. It can be used to resolve, for example, “”.

“.pin” is another default zone which points to a special zone also managed by Users may register submodomains on a first-come first-served-basis at

Use gnunet-config -s gns to view the GNS configuration, including all configured zones that are operated by other users. The respective configuration entry names start with a “.”, e.g. “.pin”.

You can configure any number of top-level domains, and point them to the respective zones of your friends! For this, simply obtain the respective public key (you will learn how below) and extend the configuration:

$ gnunet-config -s gns -o .myfriend -V PUBLIC_KEY

Zones and Egos

In GNUnet, identity management is about managing egos. Egos can correspond to pseudonyms or real-world identities. If you value your privacy, you are encouraged to use separate egos for separate activities.

Technically, an ego is first of all a public-private key pair, and thus egos also always correspond to a GNS zone. Egos are managed by the IDENTITY service. Note that this service has nothing to do with the peer identity. The IDENTITY service essentially stores the private keys under human-readable names, and keeps a mapping of which private key should be used for particular important system functions.

You probably should create at least one zone of your own. You can create any number of zones using the gnunet-identity tool using:

$ gnunet-identity --create="myzone"

Henceforth, on your system you control the TLD “myzone”.

All of your zones can be listed (displayed) using the gnunet-identity command line tool as well:

$ gnunet-identity --display

Maintaining Zones

Now you can add (or edit, or remove) records in your GNS zone using the gnunet-namestore-gtk GUI or using the gnunet-namestore command-line tool. In either case, your records will be stored in an SQL database under control of the gnunet-service-namestore. Note that if multiple users use one peer, the namestore database will include the combined records of all users. However, users will not be able to see each other’s records if they are marked as private.

To provide a short example for editing your own zone, suppose you have your own web server with the IP Then you can put an A record (A records in DNS are for IPv4 IP addresses) into your local zone “myzone” using the command:

$ gnunet-namestore -z myzone -a -n www -t A -V -e 1d

Similar commands will work for other types of DNS and GNS records, the syntax largely depending on the type of the record. Naturally, most users may find editing the zones using the gnunet-namestore-gtk GUI to be easier.

Each zone in GNS has a public-private key. Usually, gnunet-namestore and gnunet-setup will access your private key as necessary, so you do not have to worry about those. What is important is your public key (or rather, the hash of your public key), as you will likely want to give it to others so that they can securely link to you.

A central operation in GNS is the ability to securely delegate to other zones. Basically, by adding a delegation you make all of the names from the other zone available to yourself. This section describes how to create delegations.

Suppose you have a friend who you call ’bob’ who also uses GNS. You can then delegate resolution of names to Bob’s zone by adding a PKEY record to their local zone:

$ gnunet-namestore -a -n bob --type PKEY -V XXXX -e 1d -z myzone

Note that “XXXX” in the command above must be replaced with the hash of Bob’s public key (the output your friend obtained using the gnunet-identity command from the previous section and told you, for example by giving you a business card containing this information as a QR code).

Assuming Bob has an “A” record for their website under the name of “www” in his zone, you can then access Bob’s website under “www.bob.myzone” — as well as any (public) GNS record that Bob has in their zone by replacing www with the respective name of the record in Bob’s zone.

Furthermore, if Bob has themselves a (public) delegation to Carol’s zone under “carol”, you can access Carol’s records under “NAME.carol.bob.myzone” (where “NAME” is the name of Carol’s record you want to access).

Resolving GNS records

Next, you should try resolving your own GNS records. The method we found to be the most uncomplicated is to do this by explicitly resolving using gnunet-gns. For this exercise, we will assume that you used the string “gnu” for the pseudonym (or label) of your GNS zone. If you used something else, replace “.gnu” with your real pseudonym in the examples below.

In the shell, type:

$ gnunet-gns -u
Got `A' record: ...

That shows that resolution works, once GNS is integrated with the application.

Integration with Browsers (DNS2GNS service)

Most OSes allow you to either modify your /etc/resolv.conf directly or through resolvectl. We are going to configure the dns2gns service in order to translate DNS name queries by applications to GNS name queries where applicable and else fall back to DNS.

Optionally, you may want to configure your dns2gns service to run on a non-priviledged port like 5353. But, in case you are going to edit /etc/resolv.conf directly, the dns2gns service MUST run on port 53 as you cannot specify the port number. A $FALLBACK_DNS variable should be a DNS server you trust such as your local router:

$ gnunet-config -s dns2gns -o OPTIONS -V "-d $FALLBACK_DNS -p 5252"
$ gnunet-arm -i dns2gns # Make sure the service is started

If you edit your resolv.conf directly, it should contain and entry like this:


In any case, it is very likely that the method of modification of your resolver is OS specific. Recently, the combination of NetworkManager and systemd-resolved is becoming increasingly popular.

If you use resolvectl and systemd-resolved you can temporarily set the nameserver like this:

$ resolvectl $INTERFACE

Where $INTERFACE is your network interface such as eth0.

In order to automatically set the DNS2GNS server if it is running already you can use NetworkManager-dispatcher. First, enable it:

$ sudo systemctl enable NetworkManager-dispatcher.service
$ sudo systemctl start NetworkManager-dispatcher.service

Then, create a script /etc/NetworkManager/dispatch.h/

if [ "$interface" = "eth0" ]; then

case $status in
if nc -u -z 5353; then
resolvectl dns $interface
esac fi

Make sure the script is owned by root and executable:

$ sudo root:root /etc/NetworkManager/dispatch.d/
$ sudo +x /etc/NetworkManager/dispatch.d/

You can test accessing this website using your browser or curl:

$ curl

Note that “” is a domain that also exists in DNS and for which the GNUnet project webservers can provide trusted TLS certificates. When using non-DNS names with GNS or aliases, this may result in issues when accessing HTTPS websites with browsers. In order learn how to provide relief for this issue, read on.

Integration with Browsers (SOCKS proxy)

While we recommend integrating GNS using the DNS2GNS service or the NSSwitch plugin, you can also integrate GNS directly with your browser via the gnunet-gns-proxy. This method can have the advantage that the proxy can validate TLS/X.509 records and thus strengthen web security; however, the proxy is still a bit brittle, so expect subtle failures. We have had reasonable success with Chromium, and various frustrations with Firefox in this area recently.

The first step is to start the proxy. As the proxy is (usually) not started by default, this is done as a unprivileged user using gnunet-arm -i gns-proxy. Use gnunet-arm -I as a unprivileged user to check that the proxy was actually started. (The most common error for why the proxy may fail to start is that you did not run gnunet-gns-proxy-setup-ca during installation.) The proxy is a SOCKS5 proxy running (by default) on port 7777. Thus, you need to now configure your browser to use this proxy. With Chromium, you can do this by starting the browser as a unprivileged user using chromium –proxy-server=“socks5://localhost:7777” For Firefox (or Icecat), select “Edit-Preferences” in the menu, and then select the “Advanced” tab in the dialog and then “Network”:

Here, select “Settings…” to open the proxy settings dialog. Select “Manual proxy configuration” and enter localhost with port 7777 under SOCKS Host. Furthermore, set the checkbox “Proxy DNS when using SOCKS v5” at the bottom of the dialog. Finally, push “OK”.

You must also go to about:config and change the browser.fixup.alternate.enabled option to false, otherwise the browser will autoblunder an address like www.gnu to If you want to resolve @ in your own TLDs, you must additionally set browser.fixup.dns_first_use_for_single_words to true.

After configuring your browser, you might want to first confirm that it continues to work as before. (The proxy is still experimental and if you experience “odd” failures with some webpages, you might want to disable it again temporarily.) Next, test if things work by typing “http://test.gnu/” into the URL bar of your browser. This currently fails with (my version of) Firefox as Firefox is super-smart and tries to resolve “http://www.test.gnu/” instead of “test.gnu”. Chromium can be convinced to comply if you explicitly include the “http://” prefix — otherwise a Google search might be attempted, which is not what you want. If successful, you should see a simple website.

Note that while you can use GNS to access ordinary websites, this is more an experimental feature and not really our primary goal at this time. Still, it is a possible use-case and we welcome help with testing and development.

Creating a Business Card

Before we can really use GNS, you should create a business card. Note that this requires having LaTeX installed on your system. If you are using a Debian GNU/Linux based operating system, the following command should install the required components. Keep in mind that this requires 3GB of downloaded data and possibly even more when unpacked. On a GNU Guix based system texlive 2017 has returns a DAG size of 5032.4 MiB. The packages which are confirmed to be required are:

  • texlive-units
  • texlive-labels
  • texlive-pst-barcode
  • texlive-luatex85
  • texlive-preview
  • texlive-pdfcrop
  • texlive-koma-script

We welcome any help in identifying the required components of the TexLive Distribution. This way we could just state the required components without pulling in the full distribution of TexLive.

apt-get install texlive-full

Start creating a business card by clicking the “Copy” button in gnunet-namestore-gtk. Next, you should start the gnunet-bcd program (in the terminal, on the command-line). You do not need to pass any options, and please be not surprised if there is no output:

$ gnunet-bcd # does not return

Then, start a browser and point it to http://localhost:8888/ where gnunet-bcd is running a Web server!

First, you might want to fill in the “GNS Public Key” field by right-clicking and selecting “Paste”, filling in the public key from the copy you made in gnunet-namestore-gtk. Then, fill in all of the other fields, including your GNS NICKname. Adding a GPG fingerprint is optional. Once finished, click “Submit Query”. If your LaTeX installation is incomplete, the result will be disappointing. Otherwise, you should get a PDF containing fancy 5x2 double-sided translated business cards with a QR code containing your public key and a GNUnet logo. We’ll explain how to use those a bit later. You can now go back to the shell running gnunet-bcd and press CTRL-C to shut down the Web server.

Be Social

Next, you should print out your business card and be social. Find a friend, help them install GNUnet and exchange business cards with them. Or, if you’re a desperate loner, you might try the next step with your own card. Still, it’ll be hard to have a conversation with yourself later, so it would be better if you could find a friend. You might also want a camera attached to your computer, so you might need a trip to the store together.

Before we get started, we need to tell gnunet-qr which zone it should import new records into. For this, run:

$ gnunet-identity -s namestore -e NAME

where NAME is the name of the zone you want to import records into. In our running example, this would be “gnu”.

Henceforth, for every business card you collect, simply run:

$ gnunet-qr

to open a window showing whatever your camera points at. Hold up your friend’s business card and tilt it until the QR code is recognized. At that point, the window should automatically close. At that point, your friend’s NICKname and their public key should have been automatically imported into your zone.

Assuming both of your peers are properly integrated in the GNUnet network at this time, you should thus be able to resolve your friends names. Suppose your friend’s nickname is “Bob”. Then, type

$ gnunet-gns -u test.bob

to check if your friend was as good at following instructions as you were.

Backup of Identities and Egos

One should always backup their files, especially in these SSD days (our team has suffered 3 SSD crashes over a span of 2 weeks). Backing up peer identity and zones is achieved by copying the following files:

The peer identity file can be found in ~/.local/share/gnunet/private_key.ecc.

The private keys of your egos are stored in the directory ~/.local/share/gnunet/identity/egos/. They are stored in files whose filenames correspond to the zones’ ego names. These are probably the most important files you want to backup from a GNUnet installation.

Note: All these files contain cryptographic keys and they are stored without any encryption. So it is advisable to backup encrypted copies of them.


Now, in the situation of an attacker gaining access to the private key of one of your egos, the attacker can create records in the respective GNS zone and publish them as if you published them. Anyone resolving your domain will get these new records and when they verify they seem authentic because the attacker has signed them with your key.

To address this potential security issue, you can pre-compute a revocation certificate corresponding to your ego. This certificate, when published on the P2P network, flags your private key as invalid, and all further resolutions or other checks involving the key will fail.

A revocation certificate is thus a useful tool when things go out of control, but at the same time it should be stored securely. Generation of the revocation certificate for a zone can be done through gnunet-revocation. For example, the following command (as unprivileged user) generates a revocation file revocation.dat for the zone zone1: gnunet-revocation -f revocation.dat -R zone1

The above command only pre-computes a revocation certificate. It does not revoke the given zone. Pre-computing a revocation certificate involves computing a proof-of-work and hence may take up to 4 to 5 days on a modern processor. Note that you can abort and resume the calculation at any time. Also, even if you did not finish the calculation, the resulting file will contain the signature, which is sufficient to complete the revocation process even without access to the private key. So instead of waiting for a few days, you can just abort with CTRL-C, backup the revocation certificate and run the calculation only if your key actually was compromised. This has the disadvantage of revocation taking longer after the incident, but the advantage of saving a significant amount of energy. So unless you believe that a key compromise will need a rapid response, we urge you to wait with generating the revocation certificate. Also, the calculation is deliberately expensive, to deter people from doing this just for fun (as the actual revocation operation is expensive for the network, not for the peer performing the revocation).

To avoid TL;DR ones from accidentally revocating their zones, we are not giving away the command, but it is uncomplicated: the actual revocation is performed by using the -p option of gnunet-revocation.

What’s next?

This may seem not like much of an application yet, but you have just been one of the first to perform a decentralized secure name lookup (where nobody could have altered the value supplied by your friend) in a privacy-preserving manner (your query on the network and the corresponding response were always encrypted). So what can you really do with this? Well, to start with, you can publish your GnuPG fingerprint in GNS as a “CERT” record and replace the public web-of-trust with its complicated trust model with explicit names and privacy-preserving resolution. Also, you should read the next chapter of the tutorial and learn how to use GNS to have a private conversation with your friend. Finally, help us with the next GNUnet release for even more applications using this new public key infrastructure.

Resource Records

GNS supports the majority of the DNS records as defined in RFC 1035. Additionally, GNS defines some new record types the are unique to the GNS system. For example, GNS-specific resource records are used to give petnames for zone delegation, revoke zone keys and provide some compatibility features.

For some DNS records, GNS does extended processing to increase their usefulness in GNS. In particular, GNS introduces special names referred to as “zone relative names”. Zone relative names are allowed in some resource record types (for example, in NS and CNAME records) and can also be used in links on webpages. Zone relative names end in “.+” which indicates that the name needs to be resolved relative to the current authoritative zone. The extended processing of those names will expand the “.+” with the correct delegation chain to the authoritative zone (replacing “.+” with the name of the location where the name was encountered) and hence generate a valid GNS name.

The GNS currently supports the record types as defined in GANA. In addition, GNS supports DNS record types, such as A, AAAA or TXT.

For a complete description of the records, please refer to the specification at LSD0001.

In the following, we discuss GNS records with specific behaviour or special handling in GNUnet.


GNS allows easy access to services provided by the GNUnet Virtual Public Network. When the GNS resolver encounters a VPN record it will contact the VPN service to try and allocate an IPv4/v6 address (if the queries record type is an IP address) that can be used to contact the service.


I want to provide access to the VPN service “web.gnu.” on port 80 on peer ABC012: Name: www; RRType: VPN; Value: 80 ABC012 web.gnu.

The peer ABC012 is configured to provide an exit point for the service “web.gnu.” on port 80 to it’s server running locally on port 8080 by having the following lines in the gnunet.conf configuration file:

TCP_REDIRECTS = 80:localhost4:8080

Synchronizing with legacy DNS

If you want to support GNS but the master database for a zone is only available and maintained in DNS, GNUnet includes the gnunet-zoneimport tool to monitor a DNS zone and automatically import records into GNS. Today, the tool does not yet support DNS AF(X)R, as we initially used it on the “.fr” zone which does not allow us to perform a DNS zone transfer. Instead, gnunet-zoneimport reads a list of DNS domain names from stdin, issues DNS queries for each, converts the obtained records (if possible) and stores the result in the namestore.

The zonemaster service then takes the records from the namestore, publishes them into the DHT which makes the result available to the GNS resolver. In the GNS configuration, non-local zones can be configured to be intercepted by specifying “.tld = PUBLICKEY” in the configuration file in the “[gns]” section.

Note that the namestore by default also populates the namecache. This pre-population is cryptographically expensive. Thus, on systems that only serve to import a large (millions of records) DNS zone and that do not have a local gns service in use, it is thus advisable to disable the namecache by setting the option “DISABLE” to “YES” in section “[namecache]”.

Migrating an existing DNS zone into GNS

Ascension is a tool to migrate existing DNS zones into GNS.

Compared to the gnunet-zoneimport tool it strictly uses AXFR or IXFR depending on whether or not there exists a SOA record for the zone. If that is the case it will take the serial as a reference point and request the zone. The server will either answer the IXFR request with a correct incremental zone or with the entire zone, which depends on the server configuration.

Before you can migrate any zone though, you need to start a local GNUnet peer. To migrate the Syrian top level domain - one of the few top level domains that support zone transfers - into GNS use the following command:

$ ascension sy. -n -p

The -p flag will tell GNS to put these records on the DHT so that other users may resolve these records by using the public key of the zone.

Once the zone is migrated, Ascension will output a message telling you, that it will refresh the zone after the time has elapsed. You can resolve the names in the zone directly using GNS or if you want to use it with your browser, check out the GNS manual section. Configuring the GNU Name System. To resolve the records from another system you need the respective zones PKEY. To get the zones public key, you can run the following command:

$ gnunet-identity -dqe sy

Where “sy” is the name of the zone you want to migrate.

You can share the PKEY of the zone with your friends. They can then resolve records in the zone by doing a lookup replacing the zone label with your PKEY:

$ gnunet-gns -t SOA -u "$PKEY"

The program will continue to run as a daemon and update once the refresh time specified in the zones SOA record has elapsed.

DNSCurve style records are supported in the latest release and they are added as a PKEY record to be referred to the respective GNS public key. Key distribution is still a problem but provided someone else has a public key under a given label it can be looked up.

There is an unofficial Debian package called python3-ascension that adds a system user ascension and runs a GNUnet peer in the background.

Ascension-bind is also an unofficial Debian package that on installation checks for running DNS zones and whether or not they are transferable using DNS zone transfer (AXFR). It asks the administrator which zones to migrate into GNS and installs a systemd unit file to keep the zone up to date. If you want to migrate different zones you might want to check the unit file from the package as a guide.


The re:claimID Identity Provider (IdP) is a decentralized IdP service. It allows its users to manage and authorize third parties to access their identity attributes such as email or shipping addresses.

It basically mimics the concepts of centralized IdPs, such as those offered by Google or Facebook. Like other IdPs, reclaimID features an (optional) OpenID Connect 1.0-compliant protocol layer that can be used for websites to integrate reclaimID as an Identity Provider with little effort.

Managing Attributes

Before adding attributes to an identity, you must first create an ego:

$ gnunet-identity --create="user"

Henceforth, you can manage a new user profile of the user "user".

To add an email address to your user profile, simply use the gnunet-reclaim command line tool:


$ gnunet-reclaim -e "user" -a "email" -V "username@example.gnunet"

All of your attributes can be listed using the gnunet-reclaim command line tool as well:

$ gnunet-reclaim -e "user" -D

Currently, and by default, attribute values are interpreted as plain text. In the future there might be more value types such as X.509 certificate credentials.

Managing Credentials

Attribute values may reference a claim in a third party attested credential. Such a credential can have a variety of formats such as JSON-Web-Tokens or X.509 certificates. Currently, reclaimID only supports JSON-Web-Token credentials.

To add a credential to your user profile, invoke the gnunet-reclaim command line tool as follows:

$ gnunet-reclaim -e "user"\


All of your credentials can be listed using the gnunet-reclaim command line tool as well:

$ gnunet-reclaim -e "user" --credentials

In order to add an attribe backed by a credential, specify the attribute value as the claim name in the credential to reference along with the credential ID:

$ gnunet-reclaim -e "user"\


Sharing Attributes with Third Parties

If you want to allow a third party such as a website or friend to access to your attributes (or a subset thereof) execute:

$ TICKET=$(gnunet-reclaim -e "user"\

-r "$RP_KEY"\
-i "attribute1,attribute2,...")

The command will return a "ticket" string. You must give $TICKET to the requesting third party.

$RP_KEY is the public key of the third party and "attribute1,attribute2,..." is a comma-separated list of attribute names, such as "email,name,...", that you want to share.

The third party may retrieve the key in string format for use in the above call using "gnunet-identity":

$ RP_KEY=$(gnunet-identity -d | grep "relyingparty" | awk '{print $3}')

The third party can then retrieve your shared identity attributes using:

$ gnunet-reclaim -e "relyingparty" -C "ticket"

Where "relyingparty" is the name for the identity behind $RP_KEY that the requesting party is using. This will retrieve and list the shared identity attributes. The above command will also work if the user is currently offline since the attributes are retrieved from GNS. Further, $TICKET can be re-used later to retrieve up-to-date attributes in case "friend" has changed the value(s). For instance, because his email address changed.

To list all given authorizations (tickets) you can execute:

$ gnunet-reclaim -e "user" -T

Revoking Authorizations of Third Parties

If you want to revoke the access of a third party to your attributes you can execute:

$ gnunet-reclaim -e "user" -R $TICKET

This will prevent the third party from accessing the attribute in the future. Please note that if the third party has previously accessed the attribute, there is not way in which the system could have prevented the thiry party from storing the data. As such, only access to updated data in the future can be revoked. This behaviour is _exactly the same_ as with other IdPs.

OpenID Connect

There is an API for use with re:claimID. However, its use is quite complicated to setup.

The token endpoint is protected using HTTP basic authentication. You can authenticate using any username and the password configured under:

$ gnunet-config -s reclaim-rest-plugin -o OIDC_CLIENT_SECRET

The authorize endpoint is protected using a Cookie which can be obtained through a request against the login endpoint. This functionality is meant to be used in the context of the OpenID Connect authorization flow to collect user consent interactively. Without a Cookie, the authorize endpoint redirects to a URI configured under:

$ gnunet-config -s reclaim-rest-plugin -o ADDRESS

The token endpoint is protected using OAuth2 and expects the grant which is retrieved from the authorization endpoint according to the standard.

The userinfo endpoint is protected using OAuth2 and expects a bearer access token which is retrieved from a token request.

In order to make use of OpenID Connect flows as a user, you need to install the browser plugin:

  • Firefox Add-on
  • Chrome Web Store

In order to create and register an OpenID Connect client as a relying party, you need to execute the following steps:

$ gnunet-identity -C <client_name>
$ gnunet-namestore -z <client_name> -a -n "@" -t RECLAIM_OIDC_REDIRECT -V <redirect_uri> -e 1d -p
$ gnunet-namestore -z <client_name> -a -n "@" -t RECLAIM_OIDC_CLIENT -V "My OIDC Client" -e 1d -p

The "client_id" for use in OpenID Connect is the public key of the client as displayed using:

$ gnunet-identity -d grep "relyingparty" | awk '{print $3}'

The RECLAIM_OIDC_REDIRECT record contains your website redirect URI. You may use any globally unique DNS or GNS URI. The RECLAIM_OIDC_CLIENT record represents the client description which whill be displayed to users in an authorization request.

Any website or relying party must use the authorization endpoint https://api.reclaim/openid/authorize in its authorization redirects, e.g.

<a href="https://api.reclaim/openid/authorize?client_id=<PKEY>\

&scope=openid email\

This will direct the user's browser onto his local reclaimID instance. After giving consent, you will be provided with the OpenID Connect authorization code according to the specifications at your provided redirect URI.

The ID Tokens issues by the token endpoints are signed using HS512 with the shared secret configured under:

$ gnunet-config -s reclaim-rest-plugin -o JWT_SECRET

The authorization code flow optionally supports Proof Key for Code Exchange. If PKCE is used, the client does not need to authenticate against the token endpoint.

Providing Third Party Attestation

If you are running an identity provider (IdP) service you may be able to support providing credentials for re:claimID users. IdPs can issue JWT credentials as long as they support OpenID Connect and OpenID Connect Discovery.

In order to allow users to import attributes through the re:claimID user interface, you need to register the following public OAuth2/OIDC client:

  • client_id: reclaimid
  • client_secret: none
  • redirect_uri: https://ui.reclaim (The URI of the re:claimID webextension)
  • grant_type: authorization_code with PKCE (RFC7636)
  • scopes: all you want to offer.
  • id_token: JWT

When your users add an attribute with name "email" which supports webfinger discovery they will be prompted with the option to retrieve the OpenID Connect ID Token through the user interface.


This chapter documents the GNUnet file-sharing application. The original file-sharing implementation for GNUnet was designed to provide anonymous file-sharing. However, over time, we have also added support for non-anonymous file-sharing (which can provide better performance). Anonymous and non-anonymous file-sharing are quite integrated in GNUnet and, except for routing, share most of the concepts and implementation. There are three primary file-sharing operations: publishing, searching and downloading. For each of these operations, the user specifies an anonymity level. If both the publisher and the searcher/downloader specify “no anonymity”, non-anonymous file-sharing is used. If either user specifies some desired degree of anonymity, anonymous file-sharing will be used.

After a short introduction, we will first look at the various concepts in GNUnet’s file-sharing implementation. Then, we will discuss specifics as to how they impact users that publish, search or download files.


The command gnunet-search can be used to search for content on GNUnet. The format is:

$ gnunet-search [-t TIMEOUT] KEYWORD

The -t option specifies that the query should timeout after approximately TIMEOUT seconds. A value of zero (“0”) is interpreted as no timeout, which is the default. In this case, gnunet-search will never terminate (unless you press CTRL-C).

If multiple words are passed as keywords, they will all be considered optional. Prefix keywords with a “+” to make them mandatory.

Note that searching using:

$ gnunet-search Das Kapital

is not the same as searching for

$ gnunet-search "Das Kapital"

as the first will match files shared under the keywords “Das” or “Kapital” whereas the second will match files shared under the keyword “Das Kapital”.

Search results are printed like this:

gnunet-download -o "COPYING" gnunet://fs/chk/PGK8M...3EK130.75446

The whole line is the command you would have to enter to download the file. The first argument passed to -o is the suggested filename (you may change it to whatever you like). It is followed by the key for decrypting the file, the query for searching the file, a checksum (in hexadecimal) finally the size of the file in bytes.


In order to download a file, you need the whole line returned by gnunet-search. You can then use the tool gnunet-download to obtain the file:

$ gnunet-download -o <FILENAME> <GNUNET-URL>

FILENAME specifies the name of the file where GNUnet is supposed to write the result. Existing files are overwritten. If the existing file contains blocks that are identical to the desired download, those blocks will not be downloaded again (automatic resume).

If you want to download the GPL from the previous example, you do the following:

$ gnunet-download -o "COPYING" gnunet://fs/chk/PGK8M...3EK130.75446

If you ever have to abort a download, you can continue it at any time by re-issuing gnunet-download with the same filename. In that case, GNUnet will not download blocks again that are already present.

GNUnet’s file-encoding mechanism will ensure file integrity, even if the existing file was not downloaded from GNUnet in the first place.

You may want to use the -V switch to turn on verbose reporting. In this case, gnunet-download will print the current number of bytes downloaded whenever new data was received.


The command gnunet-publish can be used to add content to the network. The basic format of the command is:

$ gnunet-publish [-n] [-k KEYWORDS]* [-m TYPE:VALUE] FILENAME

For example:

$ gnunet-publish -m "description:GNU License" -k gpl -k test -m "mimetype:text/plain" COPYING

The option -k is used to specify keywords for the file that should be inserted. You can supply any number of keywords, and each of the keywords will be sufficient to locate and retrieve the file. Please note that you must use the -k option more than once – one for each expression you use as a keyword for the filename.

The -m option is used to specify meta-data, such as descriptions. You can use -m multiple times. The TYPE passed must be from the list of meta-data types known to libextractor. You can obtain this list by running extract -L. Use quotes around the entire meta-data argument if the value contains spaces. The meta-data is displayed to other users when they select which files to download. The meta-data and the keywords are optional and may be inferred using GNU libextractor.

gnunet-publish has a few additional options to handle namespaces and directories. Refer to the man-page for details.

Indexing vs Inserting

By default, GNUnet indexes a file instead of making a full copy. This is much more efficient, but requires the file to stay unaltered at the location where it was when it was indexed. If you intend to move, delete or alter a file, consider using the option -n which will force GNUnet to make a copy of the file in the database.

Since it is much less efficient, this is strongly discouraged for large files. When GNUnet indexes a file (default), GNUnet does not create an additional encrypted copy of the file but just computes a summary (or index) of the file. That summary is approximately two percent of the size of the original file and is stored in GNUnet’s database. Whenever a request for a part of an indexed file reaches GNUnet, this part is encrypted on-demand and send out. This way, there is no need for an additional encrypted copy of the file to stay anywhere on the drive. This is different from other systems, such as Freenet, where each file that is put online must be in Freenet’s database in encrypted format, doubling the space requirements if the user wants to preserve a directly accessible copy in plaintext.

Thus indexing should be used for all files where the user will keep using this file (at the location given to gnunet-publish) and does not want to retrieve it back from GNUnet each time. If you want to remove a file that you have indexed from the local peer, use the tool gnunet-unindex to un-index the file.

The option -n may be used if the user fears that the file might be found on their drive (assuming the computer comes under the control of an adversary). When used with the -n flag, the user has a much better chance of denying knowledge of the existence of the file, even if it is still (encrypted) on the drive and the adversary is able to crack the encryption (e.g. by guessing the keyword).


For better results with filesharing it is useful to understand the following concepts. In addition to anonymous routing GNUnet attempts to give users a better experience in searching for content. GNUnet uses cryptography to safely break content into smaller pieces that can be obtained from different sources without allowing participants to corrupt files. GNUnet makes it difficult for an adversary to send back bogus search results. GNUnet enables content providers to group related content and to establish a reputation. Furthermore, GNUnet allows updates to certain content to be made available. This section is supposed to introduce users to the concepts that are used to achieve these goals.


A file in GNUnet is just a sequence of bytes. Any file-format is allowed and the maximum file size is theoretically 2^64 - 1 bytes, except that it would take an impractical amount of time to share such a file. GNUnet itself never interprets the contents of shared files, except when using GNU libextractor to obtain keywords.


Keywords are the most simple mechanism to find files on GNUnet. Keywords are case-sensitive and the search string must always match exactly the keyword used by the person providing the file. Keywords are never transmitted in plaintext. The only way for an adversary to determine the keyword that you used to search is to guess it (which then allows the adversary to produce the same search request). Since providing keywords by hand for each shared file is tedious, GNUnet uses GNU libextractor to help automate this process. Starting a keyword search on a slow machine can take a little while since the keyword search involves computing a fresh RSA key to formulate the request.


A directory in GNUnet is a list of file identifiers with meta data. The file identifiers provide sufficient information about the files to allow downloading the contents. Once a directory has been created, it cannot be changed since it is treated just like an ordinary file by the network. Small files (of a few kilobytes) can be inlined in the directory, so that a separate download becomes unnecessary.

Directories are shared just like ordinary files. If you download a directory with gnunet-download, you can use gnunet-directory to list its contents. The canonical extension for GNUnet directories when stored as files in your local file-system is ".gnd". The contents of a directory are URIs and meta data. The URIs contain all the information required by gnunet-download to retrieve the file. The meta data typically includes the mime-type, description, a filename and other meta information, and possibly even the full original file (if it was small).

Egos and File-Sharing

When sharing files, it is sometimes desirable to build a reputation as a source for quality information. With egos, publishers can (cryptographically) sign files, thereby demonstrating that various files were published by the same entity. An ego thus allows users to link different publication events, thereby deliberately reducing anonymity to pseudonymity.

Egos used in GNUnet's file-sharing for such pseudonymous publishing also correspond to the egos used to identify and sign zones in the GNU Name System. However, if the same ego is used for file-sharing and for a GNS zone, this will weaken the privacy assurances provided by the anonymous file-sharing protocol.

Note that an ego is NOT bound to a GNUnet peer. There can be multiple egos for a single user, and users could (theoretically) share the private keys of an ego by copying the respective private keys.


A namespace is a set of files that were signed by the same ego. Today, namespaces are implemented independently of GNS zones, but in the future we plan to merge the two such that a GNS zone can basically contain files using a file-sharing specific record type.

Files (or directories) that have been signed and placed into a namespace can be updated. Updates are identified as authentic if the same secret key was used to sign the update.


Advertisements are used to notify other users about the existence of a namespace. Advertisements are propagated using the normal keyword search. When an advertisement is received (in response to a search), the namespace is added to the list of namespaces available in the namespace-search dialogs of gnunet-fs-gtk and printed by gnunet-identity. Whenever a namespace is created, an appropriate advertisement can be generated. The default keyword for the advertising of namespaces is "namespace".

Anonymity level

The anonymity level determines how hard it should be for an adversary to determine the identity of the publisher or the searcher/downloader. An anonymity level of zero means that anonymity is not required. The default anonymity level of "1" means that anonymous routing is desired, but no particular amount of cover traffic is necessary. A powerful adversary might thus still be able to deduce the origin of the traffic using traffic analysis. Specifying higher anonymity levels increases the amount of cover traffic required.

The specific numeric value (for anonymity levels above 1) is simple: Given an anonymity level L (above 1), each request FS makes on your behalf must be hidden in L-1 equivalent requests of cover traffic (traffic your peer routes for others) in the same time-period. The time-period is twice the average delay by which GNUnet artificially delays traffic.

While higher anonymity levels may offer better privacy, they can also significantly hurt performance.

Content Priority

Depending on the peer's configuration, GNUnet peers migrate content between peers. Content in this sense are individual blocks of a file, not necessarily entire files. When peers run out of space (due to local publishing operations or due to migration of content from other peers), blocks sometimes need to be discarded. GNUnet first always discards expired blocks (typically, blocks are published with an expiration of about two years in the future; this is another option). If there is still not enough space, GNUnet discards the blocks with the lowest priority. The priority of a block is decided by its popularity (in terms of requests from peers we trust) and, in case of blocks published locally, the base-priority that was specified by the user when the block was published initially.


When peers migrate content to other systems, the replication level of a block is used to decide which blocks need to be migrated most urgently. GNUnet will always push the block with the highest replication level into the network, and then decrement the replication level by one. If all blocks reach replication level zero, the selection is simply random.

Namespace Management

The gnunet-identity tool can be used to create egos. By default, gnunet-identity --display simply lists all locally available egos.

Creating Egos

With the --create=NICK option it can also be used to create a new ego. An ego is the virtual identity of the entity in control of a namespace or GNS zone. Anyone can create any number of egos. The provided NICK name automatically corresponds to a GNU Name System domain name. Thus, henceforth name resolution for any name ending in ".NICK" will use the NICK's zone. You should avoid using NICKs that collide with well-known DNS names.

Currently, the IDENTITY subsystem supports two types of identity keys: ECDSA and EdDSA. By default, ECDSA identities are creates with ECDSA keys. In order to create an identity with EdDSA keys, you can use the --eddsa flag.

Deleting Egos

With the -D NICK option egos can be deleted. Once the ego has been deleted it is impossible to add content to the corresponding namespace or zone. However, the existing GNS zone data is currently not dropped. This may change in the future.

Deleting the pseudonym does not make the namespace or any content in it unavailable.

File-Sharing URIs

GNUnet (currently) uses four different types of URIs for file-sharing. They all begin with "gnunet://fs/". This section describes the four different URI types in detail.

For FS URIs empty KEYWORDs are not allowed. Quotes are allowed to denote whitespace between words. Keywords must contain a balanced number of double quotes. Doubles quotes can not be used in the actual keywords. This means that the string '""foo bar""' will be turned into two OR-ed keywords 'foo' and 'bar', not into '"foo bar"'.

Encoding of hash values in URIs

Most URIs include some hash values. Hashes are encoded using base32hex (RFC 2938).

chk-uri .. _Content-Hash-Key-_0028chk_0029:

Content Hash Key (chk)

A chk-URI is used to (uniquely) identify a file or directory and to allow peers to download the file. Files are stored in GNUnet as a tree of encrypted blocks. The chk-URI thus contains the information to download and decrypt those blocks. A chk-URI has the format "gnunet://fs/chk/KEYHASH.QUERYHASH.SIZE". Here, "SIZE" is the size of the file (which allows a peer to determine the shape of the tree), KEYHASH is the key used to decrypt the file (also the hash of the plaintext of the top block) and QUERYHASH is the query used to request the top-level block (also the hash of the encrypted block).

loc-uri .. _Location-identifiers-_0028loc_0029:

Location identifiers (loc)

For non-anonymous file-sharing, loc-URIs are used to specify which peer is offering the data (in addition to specifying all of the data from a chk-URI). Location identifiers include a digital signature of the peer to affirm that the peer is truly the origin of the data. The format is "gnunet://fs/loc/KEYHASH.QUERYHASH.SIZE.PEER.SIG.EXPTIME". Here, "PEER" is the public key of the peer (in GNUnet format in base32hex), SIG is the RSA signature (in GNUnet format in base32hex) and EXPTIME specifies when the signature expires (in milliseconds after 1970).

ksk-uri .. _Keyword-queries-_0028ksk_0029:

Keyword queries (ksk)

A keyword-URI is used to specify that the desired operation is the search using a particular keyword. The format is simply "gnunet://fs/ksk/KEYWORD". Non-ASCII characters can be specified using the typical URI-encoding (using hex values) from HTTP. "+" can be used to specify multiple keywords (which are then logically "OR"-ed in the search, results matching both keywords are given a higher rank): "gnunet://fs/ksk/KEYWORD1+KEYWORD2". ksk-URIs must not begin or end with the plus ('+') character. Furthermore they must not contain '++'.

sks-uri .. _Namespace-content-_0028sks_0029:

Namespace content (sks)

Please note that the text in this subsection is outdated and needs to be rewritten for version 0.10! This especially concerns the terminology of Pseudonym/Ego/Identity.

Namespaces are sets of files that have been approved by some (usually pseudonymous) user --- typically by that user publishing all of the files together. A file can be in many namespaces. A file is in a namespace if the owner of the ego (aka the namespace's private key) signs the CHK of the file cryptographically. An SKS-URI is used to search a namespace. The result is a block containing meta data, the CHK and the namespace owner's signature. The format of a sks-URI is "gnunet://fs/sks/NAMESPACE/IDENTIFIER". Here, "NAMESPACE" is the public key for the namespace. "IDENTIFIER" is a freely chosen keyword (or password!). A commonly used identifier is "root" which by convention refers to some kind of index or other entry point into the namespace.

Virtual Public Network

Using the GNUnet Virtual Public Network (VPN) application you can tunnel IP traffic over GNUnet. Moreover, the VPN comes with built-in protocol translation and DNS-ALG support, enabling IPv4-to-IPv6 protocol translation (in both directions). This chapter documents how to use the GNUnet VPN.

The first thing to note about the GNUnet VPN is that it is a public network. All participating peers can participate and there is no secret key to control access. So unlike common virtual private networks, the GNUnet VPN is not useful as a means to provide a "private" network abstraction over the Internet. The GNUnet VPN is a virtual network in the sense that it is an overlay over the Internet, using its own routing mechanisms and can also use an internal addressing scheme. The GNUnet VPN is an Internet underlay --- TCP/IP applications run on top of it.

The VPN is currently only supported on GNU/Linux systems. Support for operating systems that support TUN (such as FreeBSD) should be easy to add (or might not even require any coding at all --- we just did not test this so far). Support for other operating systems would require re-writing the code to create virtual network interfaces and to intercept DNS requests.

The VPN does not provide good anonymity. While requests are routed over the GNUnet network, other peers can directly see the source and destination of each (encapsulated) IP packet. Finally, if you use the VPN to access Internet services, the peer sending the request to the Internet will be able to observe and even alter the IP traffic. We will discuss additional security implications of using the VPN later in this chapter.

Setting up an Exit node

Any useful operation with the VPN requires the existence of an exit node in the GNUnet Peer-to-Peer network. Exit functionality can only be enabled on peers that have regular Internet access. If you want to play around with the VPN or support the network, we encourage you to setup exit nodes. This chapter documents how to setup an exit node.

There are four types of exit functions an exit node can provide, and using the GNUnet VPN to access the Internet will only work nicely if the first three types are provided somewhere in the network. The four exit functions are:

  • DNS: allow other peers to use your DNS resolver
  • IPv4: allow other peers to access your IPv4 Internet connection
  • IPv6: allow other peers to access your IPv6 Internet connection
  • Local service: allow other peers to access a specific TCP or UDP service your peer is providing

By enabling "exit" in gnunet-setup and checking the respective boxes in the "exit" tab, you can easily choose which of the above exit functions you want to support.

Note, however, that by supporting the first three functions you will allow arbitrary other GNUnet users to access the Internet via your system. This is somewhat similar to running a Tor exit node. The Torproject has a nice article about what to consider if you want to do this here. We believe that generally running a DNS exit node is completely harmless.

The exit node configuration does currently not allow you to restrict the Internet traffic that leaves your system. In particular, you cannot exclude SMTP traffic (or block port 25) or limit to HTTP traffic using the GNUnet configuration. However, you can use your host firewall to restrict outbound connections from the virtual tunnel interface. This is highly recommended. In the future, we plan to offer a wider range of configuration options for exit nodes.

Note that by running an exit node GNUnet will configure your kernel to perform IP-forwarding (for IPv6) and NAT (for IPv4) so that the traffic from the virtual interface can be routed to the Internet. In order to provide an IPv6-exit, you need to have a subnet routed to your host's external network interface and assign a subrange of that subnet to the GNUnet exit's TUN interface.

When running a local service, you should make sure that the local service is (also) bound to the IP address of your EXIT interface (e.g. It will NOT work if your local service is just bound to loopback. You may also want to create a "VPN" record in your zone of the GNU Name System to make it easy for others to access your service via a name instead of just the full service descriptor. Note that the identifier you assign the service can serve as a passphrase or shared secret, clients connecting to the service must somehow learn the service's name. VPN records in the GNU Name System can make this easier.

Fedora and the Firewall

When using an exit node on Fedora 15, the standard firewall can create trouble even when not really exiting the local system! For IPv4, the standard rules seem fine. However, for IPv6 the standard rules prohibit traffic from the network range of the virtual interface created by the exit daemon to the local IPv6 address of the same interface (which is essentially loopback traffic, so you might suspect that a standard firewall would leave this traffic alone). However, as somehow for IPv6 the traffic is not recognized as originating from the local system (and as the connection is not already "established"), the firewall drops the traffic. You should still get ICMPv6 packets back, but that's obviously not very useful.

Possible ways to fix this include disabling the firewall (do you have a good reason for having it on?) or disabling the firewall at least for the GNUnet exit interface (or the respective IPv4/IPv6 address range). The best way to diagnose these kinds of problems in general involves setting the firewall to REJECT instead of DROP and to watch the traffic using wireshark (or tcpdump) to see if ICMP messages are generated when running some tests that should work.

Setting up VPN node for protocol translation and tunneling

The GNUnet VPN/PT subsystem enables you to tunnel IP traffic over the VPN to an exit node, from where it can then be forwarded to the Internet. This section documents how to setup VPN/PT on a node. Note that you can enable both the VPN and an exit on the same peer. In this case, IP traffic from your system may enter your peer's VPN and leave your peer's exit. This can be useful as a means to do protocol translation. For example, you might have an application that supports only IPv4 but needs to access an IPv6-only site. In this case, GNUnet would perform 4to6 protocol translation between the VPN (IPv4) and the Exit (IPv6). Similarly, 6to4 protocol translation is also possible. However, the primary use for GNUnet would be to access an Internet service running with an IP version that is not supported by your ISP. In this case, your IP traffic would be routed via GNUnet to a peer that has access to the Internet with the desired IP version.

Setting up an entry node into the GNUnet VPN primarily requires you to enable the "VPN/PT" option in "gnunet-setup". This will launch the "gnunet-service-vpn", "gnunet-service-dns" and "gnunet-daemon-pt" processes. The "gnunet-service-vpn" will create a virtual interface which will be used as the target for your IP traffic that enters the VPN. Additionally, a second virtual interface will be created by the "gnunet-service-dns" for your DNS traffic. You will then need to specify which traffic you want to tunnel over GNUnet. If your ISP only provides you with IPv4 or IPv6-access, you may choose to tunnel the other IP protocol over the GNUnet VPN. If you do not have an ISP (and are connected to other GNUnet peers via WLAN), you can also choose to tunnel all IP traffic over GNUnet. This might also provide you with some anonymity. After you enable the respective options and restart your peer, your Internet traffic should be tunneled over the GNUnet VPN.

The GNUnet VPN uses DNS-ALG to hijack your IP traffic. Whenever an application resolves a hostname (like ''), the "gnunet-daemon-pt" will instruct the "gnunet-service-dns" to intercept the request (possibly route it over GNUnet as well) and replace the normal answer with an IP in the range of the VPN's interface. "gnunet-daemon-pt" will then tell "gnunet-service-vpn" to forward all traffic it receives on the TUN interface via the VPN to the original destination.

For applications that do not use DNS, you can also manually create such a mapping using the gnunet-vpn command-line tool. Here, you specify the desired address family of the result (e.g. "-4"), and the intended target IP on the Internet (e.g. "-i") and "gnunet-vpn" will tell you which IP address in the range of your VPN tunnel was mapped.

gnunet-vpn can also be used to access "internal" services offered by GNUnet nodes. So if you happen to know a peer and a service offered by that peer, you can create an IP tunnel to that peer by specifying the peer's identity, service name and protocol (--tcp or --udp) and you will again receive an IP address that will terminate at the respective peer's service.


The GNUnet Messenger subsystem allows decentralized message-based communication inside of so called rooms. Each room can be hosted by a variable amount of peers. Every member of a room has the possibility to host the room on its own peer. A peer allows any amount of members to join a room. The amount of members in a room is not restricted.

Messages in a room will be distributed between all peers hosting the room or being internally (in context of the messenger service) connected to a hosting peer. All received or sent messages will be stored on any peer locally which is hosting the respective room or is internally connected to such a hosting peer.

The Messenger service is built on the CADET subsystem to make internal connections between peers using a reliable and encrypted transmission. Additionally the service uses a discrete padding to few different sizes. So kinds of messages and potential content can't be identified by the size of traffic from any attacker being unable to break the encryption of the transmission layer.

Another feature is additional end-to-end encryption for selected messages which uses the public key of another member (the receiver) to encrypt the message. Therefore it is ensured that only the selected member can read its content. This will also use additional padding.

Current state

Currently there is only a simplistic CLI application available to use the messenger service. You can use this application with the gnunet-messenger command.

This application was designed for testing purposes and it does not provide full functionality in the current state. It is planned to replace this CLI application in later stages with a fully featured one using a client-side library designed for messenger applications.

Entering a room

You can enter any room by its ROOMKEY and any PEERIDENTITY of a hosting peer. Optionally you can provide any IDENTITY which can represent a local ego by its name.

$ gnunet-messenger [-e IDENTITY] -d PEERIDENTITY -r ROOMKEY

A PEERIDENTITY gets entered in encoded form. You can get your own peer ID by using the gnunet-peerinfo command:

$ gnunet-peerinfo -s

A ROOMKEY gets entered in readable text form. The service will then hash the entered ROOMKEY and use the result as shared secret for transmission through the CADET submodule. You can also optionally leave out the '-r' parameter and the ROOMKEY to use the zeroed hash instead.

If no IDENTITY is provided you will not send any name to others, you will be referred as "anonymous" instead and use the anonymous ego. If you provide any IDENTITY a matching ego will be used to sign your messages. If there is no matching ego you will use the anonymous ego instead. The provided IDENTITY will be distributed as your name for the service in any case.

Opening a room

You can open any room in a similar way to entering it. You just have to leave out the '-d' parameter and the PEERIDENTITY of the hosting peer.

$ gnunet-messenger [-e IDENTITY] -r ROOMKEY

Providing ROOMKEY and IDENTITY is identical to entering a room. Opening a room will also make your peer to a host of this room. So others can enter the room through your peer if they have the required ROOMKEY and your peer ID.

If you want to use the zeroed hash as shared secret key for the room you can also leave it out as well:

$ gnunet-messenger

Messaging in a room

Once joined a room by entering it or opening it you can write text-based messages which will be distributed between all internally conntected peers. All sent messages will be displayed in the same way as received messages.

This relates to the internal handling of sent and received messages being mostly identical on application layer. Every handled message will be represented visually depending on its kind, content and sender. A sender can usually be identified by the encoded member ID or their name.

[17X37K] * 'anonymous' says: "hey"

Private messaging

As referred in the introduction the service allows sending private messages with additional end-to-end encryption. These messages will be visually represented by messages of the kind 'PRIVATE' in case they can't be decrypted with your used ego. Members who can't decrypt the message can potentially only identify its sender but they can't identify its receiver.

[17X37K] ~ message: PRIVATE

If they can be decrypted they will appear as their secret message instead but marked visually.

[17X37K] ** 'anonymous' says: "hey"

Currently you can only activate sending such encrypted text messages instead of usual text messages by adding the '-p' parameter:

$ gnunet-messenger [-e IDENTITY] -d PEERIDENTITY -r ROOMKEY -p

Notice that you can only send such encrypted messages to members who use an ego which is not publicly known as the anonymous ego to ensure transparency. If any user could decrypt these messages they would not be private. So as receiver of such messages the IDENTITY is required and it has to match a local ego.

Advanced Configuration

Config file format

In GNUnet realm, all components obey the same pattern to get configuration values. According to this pattern, once the component has been installed, the installation deploys default values in $prefix/share/gnunet/config.d/, in .conf files. In order to override these defaults, the user can write a custom .conf file and either pass it to the component at execution time, or name it gnunet.conf and place it under $HOME/.config/.

A config file is a text file containing sections, and each section contains its values. The right format follows:

value1 = string
value2 = 23
value21 = string
value22 = /path22

Throughout any configuration file, it is possible to use $-prefixed variables, like $VAR, especially when they represent filenames in in the filesystem. It is also possible to provide defaults values for those variables that are unset, by using the following syntax:


However, there are two ways a user can set $-prefixable variables: (a) by defining them under a [paths] section


or (b) by setting them in the environment

$ export VAR=/x

The configuration loader will give precedence to variables set under [path], though.

The utility 'gnunet-config', which gets installed along with GNUnet, serves to get and set configuration values without directly editing the .conf file. The option '-f' is particularly useful to resolve filenames, when they use several levels of $-expanded variables. See 'gnunet-config --help'.

Note that, in this stage of development, the file $HOME/.config/gnunet.conf can contain sections for all the components. .. _The-Single_002dUser-Setup:

The Single-User Setup

For the single-user setup, you do not need to do anything special and can just start the GNUnet background processes using gnunet-arm. By default, GNUnet looks in ~/.config/gnunet.conf for a configuration (or $XDG_CONFIG_HOME/gnunet.conf if $XDG_CONFIG_HOME is defined). If your configuration lives elsewhere, you need to pass the -c FILENAME option to all GNUnet commands.

Assuming the configuration file is called ~/.config/gnunet.conf, you start your peer using the gnunet-arm command (say as user gnunet) using:

gnunet-arm -c ~/.config/gnunet.conf -s

The "-s" option here is for "start". The command should return almost instantly. If you want to stop GNUnet, you can use:

gnunet-arm -c ~/.config/gnunet.conf -e

The "-e" option here is for "end".

Note that this will only start the basic peer, no actual applications will be available. If you want to start the file-sharing service, use (after starting GNUnet):

gnunet-arm -c ~/.config/gnunet.conf -i fs

The "-i fs" option here is for "initialize" the "fs" (file-sharing) application. You can also selectively kill only file-sharing support using

gnunet-arm -c ~/.config/gnunet.conf -k fs

Assuming that you want certain services (like file-sharing) to be always automatically started whenever you start GNUnet, you can activate them by setting "IMMEDIATE_START=YES" in the respective section of the configuration file (for example, "[fs]"). Then GNUnet with file-sharing support would be started whenever you enter:

gnunet-arm -c ~/.config/gnunet.conf -s

Alternatively, you can combine the two options:

gnunet-arm -c ~/.config/gnunet.conf -s -i fs

Using gnunet-arm is also the preferred method for initializing GNUnet from init.

Finally, you should edit your crontab (using the crontab command) and insert a line

@reboot gnunet-arm -c ~/.config/gnunet.conf -s

to automatically start your peer whenever your system boots.

The Multi-User Setup

This requires you to create a user gnunet and an additional group gnunetdns, prior to running make install during installation. Then, you create a configuration file /etc/gnunet.conf which should contain the lines:


Then, perform the same steps to run GNUnet as in the per-user configuration, except as user gnunet (including the crontab installation). You may also want to run gnunet-setup to configure your peer (databases, etc.). Make sure to pass -c /etc/gnunet.conf to all commands. If you run gnunet-setup as user gnunet, you might need to change permissions on /etc/gnunet.conf so that the gnunet user can write to the file (during setup).

Afterwards, you need to perform another setup step for each normal user account from which you want to access GNUnet. First, grant the normal user ($USER) permission to the group gnunet:

# adduser $USER gnunet

Then, create a configuration file in ~/.config/gnunet.conf for the $USER with the lines:


This will ensure that gnunet-arm when started by the normal user will only run services that are per-user, and otherwise rely on the system-wide services. Note that the normal user may run gnunet-setup, but the configuration would be ineffective as the system-wide services will use /etc/gnunet.conf and ignore options set by individual users.

Again, each user should then start the peer using gnunet-arm -s --- and strongly consider adding logic to start the peer automatically to their crontab.

Afterwards, you should see two (or more, if you have more than one USER) gnunet-service-arm processes running in your system.

Access Control for GNUnet

This chapter documents how we plan to make access control work within the GNUnet system for a typical peer. It should be read as a best-practice installation guide for advanced users and builders of binary distributions. The recommendations in this guide apply to POSIX-systems with full support for UNIX domain sockets only.

Note that this is an advanced topic. The discussion presumes a very good understanding of users, groups and file permissions. Normal users on hosts with just a single user can just install GNUnet under their own account (and possibly allow the installer to use SUDO to grant additional permissions for special GNUnet tools that need additional rights). The discussion below largely applies to installations where multiple users share a system and to installations where the best possible security is paramount.

A typical GNUnet system consists of components that fall into four categories:

User interfaces are not security sensitive and are supposed to be run and used by normal system users. The GTK GUIs and most command-line programs fall into this category. Some command-line tools (like gnunet-transport) should be excluded as they offer low-level access that normal users should not need.
System services should always run and offer services that can then be accessed by the normal users. System services do not require special permissions, but as they are not specific to a particular user, they probably should not run as a particular user. Also, there should typically only be one GNUnet peer per host. System services include the gnunet-service and gnunet-daemon programs; support tools include command-line programs such as gnunet-arm.
Some GNUnet components require root rights to open raw sockets or perform other special operations. These gnunet-helper binaries are typically installed SUID and run from services or daemons.
Some GNUnet services (such as the DNS service) can manipulate the service in deep and possibly highly security sensitive ways. For example, the DNS service can be used to intercept and alter any DNS query originating from the local machine. Access to the APIs of these critical services and their privileged helpers must be tightly controlled.


Shorten these subsection titles

Recommendation - Disable access to services via TCP

GNUnet services allow two types of access: via TCP socket or via UNIX domain socket. If the service is available via TCP, access control can only be implemented by restricting connections to a particular range of IP addresses. This is acceptable for non-critical services that are supposed to be available to all users on the local system or local network. However, as TCP is generally less efficient and it is rarely the case that a single GNUnet peer is supposed to serve an entire local network, the default configuration should disable TCP access to all GNUnet services on systems with support for UNIX domain sockets. Since GNUnet 0.9.2, configuration files with TCP access disabled should be generated by default. Users can re-enable TCP access to particular services simply by specifying a non-zero port number in the section of the respective service.

Recommendation - Run most services as system user gnunet

GNUnet's main services should be run as a separate user "gnunet" in a special group "gnunet". The user "gnunet" should start the peer using "gnunet-arm -s" during system startup. The home directory for this user should be /var/lib/gnunet and the configuration file should be /etc/gnunet.conf. Only the gnunet user should have the right to access /var/lib/gnunet (mode: 700).

Recommendation - Control access to services using group gnunet

Users that should be allowed to use the GNUnet peer should be added to the group "gnunet". Using GNUnet's access control mechanism for UNIX domain sockets, those services that are considered useful to ordinary users should be made available by setting "UNIX_MATCH_GID=YES" for those services. Again, as shipped, GNUnet provides reasonable defaults. Permissions to access the transport and core subsystems might additionally be granted without necessarily causing security concerns. Some services, such as DNS, must NOT be made accessible to the "gnunet" group (and should thus only be accessible to the "gnunet" user and services running with this UID).

Recommendation - Limit access to certain SUID binaries by group gnunet

Most of GNUnet's SUID binaries should be safe even if executed by normal users. However, it is possible to reduce the risk a little bit more by making these binaries owned by the group "gnunet" and restricting their execution to user of the group "gnunet" as well (4750).

Recommendation - Limit access to critical gnunet-helper-dns to group gnunetdns

A special group "gnunetdns" should be created for controlling access to the "gnunet-helper-dns". The binary should then be owned by root and be in group "gnunetdns" and be installed SUID and only be group-executable (2750). Note that the group "gnunetdns" should have no users in it at all, ever. The "gnunet-service-dns" program should be executed by user "gnunet" (via gnunet-service-arm) with the binary owned by the user "root" and the group "gnunetdns" and be SGID (2700). This way, only "gnunet-service-dns" can change its group to "gnunetdns" and execute the helper, and the helper can then run as root (as per SUID). Access to the API offered by "gnunet-service-dns" is in turn restricted to the user "gnunet" (not the group!), which means that only "benign" services can manipulate DNS queries using "gnunet-service-dns".

Differences between make install and these recommendations

The current build system does not set all permissions automatically based on the recommendations above. In particular, it does not use the group "gnunet" at all (so setting gnunet-helpers other than the gnunet-helper-dns to be owned by group "gnunet" must be done manually). Furthermore, 'make install' will silently fail to set the DNS binaries to be owned by group "gnunetdns" unless that group already exists (!). An alternative name for the "gnunetdns" group can be specified using the --with-gnunetdns=GRPNAME configure option.

Configuring the Friend-to-Friend (F2F) mode

GNUnet knows three basic modes of operation:

  • In standard "peer-to-peer" mode, your peer will connect to any peer.
  • In the pure "friend-to-friend" mode, your peer will ONLY connect to peers from a list of friends specified in the configuration.
  • Finally, in mixed mode, GNUnet will only connect to arbitrary peers if it has at least a specified number of connections to friends.

When configuring any of the F2F ("friend-to-friend") modes, you first need to create a file with the peer identities of your friends. Ask your friends to run

$ gnunet-peerinfo -sq

The resulting output of this command needs to be added to your friends file, which is simply a plain text file with one line per friend with the output from the above command.

You then specify the location of your friends file in the FRIENDS option of the "topology" section.

Once you have created the friends file, you can tell GNUnet to only connect to your friends by setting the FRIENDS-ONLY option (again in the "topology" section) to YES.

If you want to run in mixed-mode, set "FRIENDS-ONLY" to NO and configure a minimum number of friends to have (before connecting to arbitrary peers) under the "MINIMUM-FRIENDS" option.

If you want to operate in normal P2P-only mode, simply set MINIMUM-FRIENDS to zero and FRIENDS_ONLY to NO. This is the default.

Configuring the hostlist to bootstrap

After installing the software you need to get connected to the GNUnet network. The configuration file included in your download is already configured to connect you to the GNUnet network. In this section the relevant configuration settings are explained.

To get an initial connection to the GNUnet network and to get to know peers already connected to the network you can use the so called "bootstrap servers". These servers can give you a list of peers connected to the network. To use these bootstrap servers you have to configure the hostlist daemon to activate bootstrapping.

To activate bootstrapping, edit the [hostlist]-section in your configuration file. You have to set the argument -b in the options line:


Additionally you have to specify which server you want to use. The default bootstrapping server is "". [^] To set the server you have to edit the line "SERVERS" in the hostlist section. To use the default server you should set the lines to

To use bootstrapping your configuration file should include these lines:


Besides using bootstrap servers you can configure your GNUnet peer to receive hostlist advertisements. Peers offering hostlists to other peers can send advertisement messages to peers that connect to them. If you configure your peer to receive these messages, your peer can download these lists and connect to the peers included. These lists are persistent, which means that they are saved to your hard disk regularly and are loaded during startup.

To activate hostlist learning you have to add the -e switch to the OPTIONS line in the hostlist section:

OPTIONS = -b -e

Furthermore you can specify in which file the lists are saved. To save the lists in the file hostlists.file just add the line:

HOSTLISTFILE = hostlists.file

Best practice is to activate both bootstrapping and hostlist learning. So your configuration file should include these lines:

OPTIONS = -b -e

Configuration of the HOSTLIST proxy settings

The hostlist client can be configured to use a proxy to connect to the hostlist server.

The hostlist client supports the following proxy types at the moment:

  • HTTP and HTTP 1.0 only proxy
  • SOCKS 4/4a/5/5 with hostname

In addition authentication at the proxy with username and password can be configured.

To provide these options directly in the configuration, you can enter the following settings in the [hostlist] section of the configuration:

# Type of proxy server,
# Default: HTTP
# Hostname or IP of proxy server
# User name for proxy server
# User password for proxy server

Configuring your peer to provide a hostlist

If you operate a peer permanently connected to GNUnet you can configure your peer to act as a hostlist server, providing other peers the list of peers known to him.

Your server can act as a bootstrap server and peers needing to obtain a list of peers can contact it to download this list. To download this hostlist the peer uses HTTP. For this reason you have to build your peer with libgnurl (or libcurl) and microhttpd support.

To configure your peer to act as a bootstrap server you have to add the -p option to OPTIONS in the [hostlist] section of your configuration file. Besides that you have to specify a port number for the http server. In conclusion you have to add the following lines:

HTTPPORT = 12980

If your peer acts as a bootstrap server other peers should know about that. You can advertise the hostlist your are providing to other peers. Peers connecting to your peer will get a message containing an advertisement for your hostlist and the URL where it can be downloaded. If this peer is in learning mode, it will test the hostlist and, in the case it can obtain the list successfully, it will save it for bootstrapping.

To activate hostlist advertisement on your peer, you have to set the following lines in your configuration file:

HTTPPORT = 12981
OPTIONS = -p -a

With this configuration your peer will a act as a bootstrap server and advertise this hostlist to other peers connecting to it. The URL used to download the list will be

Please notice:

  • The hostlist is not human readable, so you should not try to download it using your webbrowser. Just point your GNUnet peer to the address!
  • Advertising without providing a hostlist does not make sense and will not work.

Configuring the datastore

The datastore is what GNUnet uses for long-term storage of file-sharing data. Note that long-term does not mean 'forever' since content does have an expiration date, and of course storage space is finite (and hence sometimes content may have to be discarded).

Use the QUOTA option to specify how many bytes of storage space you are willing to dedicate to GNUnet.

In addition to specifying the maximum space GNUnet is allowed to use for the datastore, you need to specify which database GNUnet should use to do so. Currently, you have the choice between sqLite, MySQL and Postgres.

Configuring the MySQL database

This section describes how to setup the MySQL database for GNUnet.

Note that the mysql plugin does NOT work with mysql before 4.1 since we need prepared statements. We are generally testing the code against MySQL 5.1 at this point.

Reasons for using MySQL

  • On up-to-date hardware where mysql can be used comfortably, this module will have better performance than the other database choices (according to our tests).
  • Its often possible to recover the mysql database from internal inconsistencies. Some of the other databases do not support repair.

Reasons for not using MySQL

  • Memory usage (likely not an issue if you have more than 1 GB)
  • Complex manual setup

Setup Instructions

  • In gnunet.conf set in section DATASTORE the value for DATABASE to mysql.
  • Access mysql as root:

$ mysql -u root -p

and issue the following commands, replacing $USER with the username that will be running gnunet-arm (so typically "gnunet"):

GRANT select,insert,update,delete,create,alter,drop,create temporary tables ON gnunet.* TO $USER@localhost;
SET PASSWORD FOR $USER@localhost=PASSWORD('$the_password_you_like');

In the $HOME directory of $USER, create a .my.cnf file with the following lines


That's it. Note that .my.cnf file is a slight security risk unless its on a safe partition. The $HOME/.my.cnf can of course be a symbolic link. Luckily $USER has only privileges to mess up GNUnet's tables, which should be pretty harmless.


You should briefly try if the database connection works. First, login as $USER. Then use:

$ mysql -u $USER
mysql> use gnunet;

If you get the message

Database changed

it probably works.

If you get

ERROR 2002: Can't connect to local MySQL server
through socket '/tmp/mysql.sock' (2)

it may be resolvable by

ln -s /var/run/mysqld/mysqld.sock /tmp/mysql.sock

so there may be some additional trouble depending on your mysql setup.

Performance Tuning

For GNUnet, you probably want to set the option


Code block not C, set appropriate language

innodb_flush_log_at_trx_commit = 0

for a rather dramatic boost in MySQL performance. However, this reduces the "safety" of your database as with this options you may loose transactions during a power outage. While this is totally harmless for GNUnet, the option applies to all applications using MySQL. So you should set it if (and only if) GNUnet is the only application on your system using MySQL.

Setup for running Testcases

If you want to run the testcases, you must create a second database "gnunetcheck" with the same username and password. This database will then be used for testing (make check).

Configuring the Postgres database

This text describes how to setup the Postgres database for GNUnet.

This Postgres plugin was developed for Postgres 8.3 but might work for earlier versions as well.

Reasons to use Postgres

  • Easier to setup than MySQL
  • Real database

Reasons not to use Postgres

  • Quite slow
  • Still some manual setup required

Manual setup instructions

  • In gnunet.conf set in section DATASTORE the value for DATABASE to postgres.
  • Access Postgres to create a user:

# su - postgres
$ createuser

and enter the name of the user running GNUnet for the role interactively. Then, when prompted, do not set it to superuser, allow the creation of databases, and do not allow the creation of new roles.

# su - postgres
$ createuser -d $GNUNET_USER

where $GNUNET_USER is the name of the user running GNUnet.

As that user (so typically as user "gnunet"), create a database (or two):

$ createdb gnunet
# this way you can run "make check"
$ createdb gnunetcheck

Now you should be able to start gnunet-arm.

Testing the setup manually

You may want to try if the database connection works. First, again login as the user who will run gnunet-arm. Then use:

$ psql gnunet # or gnunetcheck
gnunet=> \dt

If, after you have started gnunet-arm at least once, you get a gn090 table here, it probably works.

Configuring the datacache

The datacache is what GNUnet uses for storing temporary data. This data is expected to be wiped completely each time GNUnet is restarted (or the system is rebooted).

You need to specify how many bytes GNUnet is allowed to use for the datacache using the QUOTA option in the section [dhtcache]. Furthermore, you need to specify which database backend should be used to store the data. Currently, you have the choice between sqLite, MySQL and Postgres.

Configuring the file-sharing service

In order to use GNUnet for file-sharing, you first need to make sure that the file-sharing service is loaded. This is done by setting the START_ON_DEMAND option in section [fs] to "YES". Alternatively, you can run

$ gnunet-arm -i fs

to start the file-sharing service by hand.

Except for configuring the database and the datacache the only important option for file-sharing is content migration.

Content migration allows your peer to cache content from other peers as well as send out content stored on your system without explicit requests. This content replication has positive and negative impacts on both system performance and privacy.

FIXME: discuss the trade-offs. Here is some older text about it...

Setting this option to YES allows gnunetd to migrate data to the local machine. Setting this option to YES is highly recommended for efficiency. Its also the default. If you set this value to YES, GNUnet will store content on your machine that you cannot decrypt. While this may protect you from liability if the judge is sane, it may not (IANAL). If you put illegal content on your machine yourself, setting this option to YES will probably increase your chances to get away with it since you can plausibly deny that you inserted the content. Note that in either case, your anonymity would have to be broken first (which may be possible depending on the size of the GNUnet network and the strength of the adversary).

Configuring logging

Since version 0.9.0, logging in GNUnet is controlled via the -L and -l options. Using -L, a log level can be specified. With log level ERROR only serious errors are logged. The default log level is WARNING which causes anything of concern to be logged. Log level INFO can be used to log anything that might be interesting information whereas DEBUG can be used by developers to log debugging messages (but you need to run ./configure with --enable-logging=verbose to get them compiled). The -l option is used to specify the log file.

Since most GNUnet services are managed by gnunet-arm, using the -l or -L options directly is not possible. Instead, they can be specified using the OPTIONS configuration value in the respective section for the respective service. In order to enable logging globally without editing the OPTIONS values for each service, gnunet-arm supports a GLOBAL_POSTFIX option. The value specified here is given as an extra option to all services for which the configuration does contain a service-specific OPTIONS field.

GLOBAL_POSTFIX can contain the special sequence "{}" which is replaced by the name of the service that is being started. Furthermore, GLOBAL_POSTFIX is special in that sequences starting with "$" anywhere in the string are expanded (according to options in PATHS); this expansion otherwise is only happening for filenames and then the "$" must be the first character in the option. Both of these restrictions do not apply to GLOBAL_POSTFIX. Note that specifying % anywhere in the GLOBAL_POSTFIX disables both of these features.

In summary, in order to get all services to log at level INFO to log-files called SERVICENAME-logs, the following global prefix should be used:


Configuring the transport service and plugins

The transport service in GNUnet is responsible to maintain basic connectivity to other peers. Besides initiating and keeping connections alive it is also responsible for address validation.

The GNUnet transport supports more than one transport protocol. These protocols are configured together with the transport service.

The configuration section for the transport service itself is quite similar to all the other services

HOSTNAME = localhost
BINARY = gnunet-service-transport
#PREFIX = valgrind
PLUGINS = tcp udp
UNIXPATH = /tmp/gnunet-service-transport.sock

Different are the settings for the plugins to load PLUGINS. The first setting specifies which transport plugins to load.

transport-unix A plugin for local only communication with UNIX domain sockets. Used for testing and available on unix systems only. Just set the port

PORT = 22086

transport-tcp A plugin for communication with TCP. Set port to 0 for client mode with outbound only connections

# Use 0 to ONLY advertise as a peer behind NAT (no port binding)
PORT = 2086
# Maximum number of open TCP connections allowed

transport-udp A plugin for communication with UDP. Supports peer discovery using broadcasts.

PORT = 2086
MAX_BPS = 1000000

transport-http HTTP and HTTPS support is split in two part: a client plugin initiating outbound connections and a server part accepting connections from the client. The client plugin just takes the maximum number of connections as an argument.



The server has a port configured and the maximum number of connections. The HTTPS part has two files with the certificate key and the certificate file.

The server plugin supports reverse proxies, so a external hostname can be set using the EXTERNAL_HOSTNAME setting. The webserver under this address should forward the request to the peer and the configure port.

PORT = 1080

PORT = 4433
KEY_FILE = https.key
CERT_FILE = https.cert


The next section describes how to setup the WLAN plugin, so here only the settings. Just specify the interface to use:

# Name of the interface in monitor mode (typically monX)
# Real hardware, no testing

Configuring the WLAN transport plugin

The wlan transport plugin enables GNUnet to send and to receive data on a wlan interface. It has not to be connected to a wlan network as long as sender and receiver are on the same channel. This enables you to get connection to GNUnet where no internet access is possible, for example during catastrophes or when censorship cuts you off from the internet.

Requirements for the WLAN plugin

  • wlan network card with monitor support and packet injection (see
  • Linux kernel with mac80211 stack, introduced in 2.6.22, tested with 2.6.35 and 2.6.38
  • Wlantools to create the a monitor interface, tested with airmon-ng of the aircrack-ng package


There are the following options for the wlan plugin (they should be like this in your default config file, you only need to adjust them if the values are incorrect for your system)

# section for the wlan transport plugin
# interface to use, more information in the
# "Before starting GNUnet" section of the handbook.
# testmode for developers:
# 0 use wlan interface,
#1 or 2 use loopback driver for tests 1 = server, 2 = client

Before starting GNUnet

Before starting GNUnet, you have to make sure that your wlan interface is in monitor mode. One way to put the wlan interface into monitor mode (if your interface name is wlan0) is by executing:

sudo airmon-ng start wlan0

Here is an example what the result should look like:

Interface Chipset Driver
wlan0 Intel 4965 a/b/g/n iwl4965 - [phy0]
(monitor mode enabled on mon0)

The monitor interface is mon0 is the one that you have to put into the configuration file.

Limitations and known bugs

Wlan speed is at the maximum of 1 Mbit/s because support for choosing the wlan speed with packet injection was removed in newer kernels. Please pester the kernel developers about fixing this.

The interface channel depends on the wlan network that the card is connected to. If no connection has been made since the start of the computer, it is usually the first channel of the card. Peers will only find each other and communicate if they are on the same channel. Channels must be set manually, e.g. by using:

iwconfig wlan0 channel 1

Configuring HTTP(S) reverse proxy functionality using Apache or nginx

The HTTP plugin supports data transfer using reverse proxies. A reverse proxy forwards the HTTP request he receives with a certain URL to another webserver, here a GNUnet peer.

So if you have a running Apache or nginx webserver you can configure it to be a GNUnet reverse proxy. Especially if you have a well-known website this improves censorship resistance since it looks as normal surfing behaviour.

To do so, you have to do two things:

  • Configure your webserver to forward the GNUnet HTTP traffic
  • Configure your GNUnet peer to announce the respective address

As an example we want to use GNUnet peer running:

And we want the webserver to accept GNUnet traffic under The required steps are described here:

Reverse Proxy - Configure your Apache2 HTTP webserver

First of all you need mod_proxy installed.

Edit your webserver configuration. Edit /etc/apache2/apache2.conf or the site-specific configuration file.

In the respective server config,virtual host or directory section add the following lines:

ProxyTimeout 300
ProxyRequests Off
<Location /bar/ >

Reverse Proxy - Configure your Apache2 HTTPS webserver

We assume that you already have an HTTPS server running, if not please check how to configure a HTTPS host. An uncomplicated to use example is the example configuration file for Apache2/HTTPD provided in apache2/sites-available/default-ssl.

In the respective HTTPS server config,virtual host or directory section add the following lines:

SSLProxyEngine On
ProxyTimeout 300
ProxyRequests Off
<Location /bar/ >

More information about the apache mod_proxy configuration can be found in the Apache documentation.

Reverse Proxy - Configure your nginx HTTPS webserver

Since nginx does not support chunked encoding, you first of all have to install the chunkin module.

To enable chunkin add:

chunkin on;
error_page 411 = @my_411_error;
location @my_411_error {

Edit your webserver configuration. Edit /etc/nginx/nginx.conf or the site-specific configuration file.

In the server section add:

location /bar/ {
proxy_buffering off;
proxy_connect_timeout 5; # more than http_server
proxy_read_timeout 350; # 60 default, 300s is GNUnet's idle timeout
proxy_http_version 1.1; # 1.0 default
proxy_next_upstream error timeout invalid_header http_500 http_503 http_502 http_504;

Reverse Proxy - Configure your nginx HTTP webserver

Edit your webserver configuration. Edit /etc/nginx/nginx.conf or the site-specific configuration file.

In the server section add:

ssl_session_timeout 6m;
location /bar/
proxy_buffering off;
proxy_connect_timeout 5; # more than http_server
proxy_read_timeout 350; # 60 default, 300s is GNUnet's idle timeout
proxy_http_version 1.1; # 1.0 default
proxy_next_upstream error timeout invalid_header http_500 http_503 http_502 http_504;

Reverse Proxy - Configure your GNUnet peer

To have your GNUnet peer announce the address, you have to specify the EXTERNAL_HOSTNAME option in the [transport-http_server] section:


and/or [transport-https_server] section:


Now restart your webserver and your peer...

Blacklisting peers

Transport service supports to deny connecting to a specific peer of to a specific peer with a specific transport plugin using the blacklisting component of transport service. With blacklisting it is possible to deny connections to specific peers of to use a specific plugin to a specific peer. Peers can be blacklisted using the configuration or a blacklist client can be asked.

To blacklist peers using the configuration you have to add a section to your configuration containing the peer id of the peer to blacklist and the plugin if required.


To blacklist connections to P565... on peer AG2P... using tcp add:


too long?


verify whether these still produce errors in pdf output


To blacklist connections to P565... on peer AG2P... using all plugins add:


You can also add a blacklist client using the blacklist API. On a blacklist check, blacklisting first checks internally if the peer is blacklisted and if not, it asks the blacklisting clients. Clients are asked if it is OK to connect to a peer ID, the plugin is omitted.

On blacklist check for (peer, plugin)

  • Do we have a local blacklist entry for this peer and this plugin?
  • YES: disallow connection
  • Do we have a local blacklist entry for this peer and all plugins?
  • YES: disallow connection
  • Does one of the clients disallow?
  • YES: disallow connection

Configuration of the HTTP and HTTPS transport plugins

The client parts of the http and https transport plugins can be configured to use a proxy to connect to the hostlist server.

Both the HTTP and HTTPS clients support the following proxy types at the moment:

  • HTTP 1.1 proxy
  • SOCKS 4/4a/5/5 with hostname

In addition authentication at the proxy with username and password can be configured.

To configure these options directly in the configuration, you can configure the following settings in the [transport-http_client] and [transport-https_client] section of the configuration:

# Type of proxy server,
# Default: HTTP
# Hostname or IP of proxy server
# User name for proxy server
# User password for proxy server

Configuring the GNUnet VPN

Before configuring the GNUnet VPN, please make sure that system-wide DNS interception is configured properly as described in the section on the GNUnet DNS setup. see Configuring the GNU Name System, if you haven't done so already.

The default options for the GNUnet VPN are usually sufficient to use GNUnet as a Layer 2 for your Internet connection. However, what you always have to specify is which IP protocol you want to tunnel: IPv4, IPv6 or both. Furthermore, if you tunnel both, you most likely should also tunnel all of your DNS requests. You theoretically can tunnel "only" your DNS traffic, but that usually makes little sense.

The other options as shown on the gnunet-setup tool are:

IPv4 address for interface

This is the IPv4 address the VPN interface will get. You should pick a 'private' IPv4 network that is not yet in use for you system. For example, if you use already, you might use If you use already, then you might use If your system is not in a private IP-network, using any of the above will work fine. You should try to make the mask of the address big enough ( or, even better, to allow more mappings of remote IP Addresses into this range. However, even a mask will suffice for most users.

IPv6 address for interface

The IPv6 address the VPN interface will get. Here you can specify any non-link-local address (the address should not begin with fe80:). A subnet Unique Local Unicast (fd00::/8 prefix) that you are currently not using would be a good choice.

Configuring the GNUnet VPN DNS

To resolve names for remote nodes, activate the DNS exit option.

Configuring the GNUnet VPN Exit Service

If you want to allow other users to share your Internet connection (yes, this may be dangerous, just as running a Tor exit node) or want to provide access to services on your host (this should be less dangerous, as long as those services are secure), you have to enable the GNUnet exit daemon.

You then get to specify which exit functions you want to provide. By enabling the exit daemon, you will always automatically provide exit functions for manually configured local services (this component of the system is under development and not documented further at this time). As for those services you explicitly specify the target IP address and port, there is no significant security risk in doing so.

Furthermore, you can serve as a DNS, IPv4 or IPv6 exit to the Internet. Being a DNS exit is usually pretty harmless. However, enabling IPv4 or IPv6-exit without further precautions may enable adversaries to access your local network, send spam, attack other systems from your Internet connection and do other mischiefs that will appear to come from your machine. This may or may not get you into legal trouble. If you want to allow IPv4 or IPv6-exit functionality, you should strongly consider adding additional firewall rules manually to protect your local network and to restrict outgoing TCP traffic (e.g. by not allowing access to port 25). While we plan to improve exit-filtering in the future, you're currently on your own here. Essentially, be prepared for any kind of IP-traffic to exit the respective TUN interface (and GNUnet will enable IP-forwarding and NAT for the interface automatically).

Additional configuration options of the exit as shown by the gnunet-setup tool are:

IP Address of external DNS resolver

If DNS traffic is to exit your machine, it will be send to this DNS resolver. You can specify an IPv4 or IPv6 address.

IPv4 address for Exit interface

This is the IPv4 address the Interface will get. Make the mask of the address big enough ( or, even better, to allow more mappings of IP addresses into this range. As for the VPN interface, any unused, private IPv4 address range will do.

IPv6 address for Exit interface

The public IPv6 address the interface will get. If your kernel is not a very recent kernel and you are willing to manually enable IPv6-NAT, the IPv6 address you specify here must be a globally routed IPv6 address of your host.

Suppose your host has the address 2001:4ca0::1234/64, then using 2001:4ca0::1:0/112 would be fine (keep the first 64 bits, then change at least one bit in the range before the bitmask, in the example above we changed bit 111 from 0 to 1).

You may also have to configure your router to route traffic for the entire subnet (2001:4ca0::1:0/112 for example) through your computer (this should be automatic with IPv6, but obviously anything can be disabled).

Bandwidth Configuration

You can specify how many bandwidth GNUnet is allowed to use to receive and send data. This is important for users with limited bandwidth or traffic volume.

Configuring NAT

Most hosts today do not have a normal global IP address but instead are behind a router performing Network Address Translation (NAT) which assigns each host in the local network a private IP address. As a result, these machines cannot trivially receive inbound connections from the Internet. GNUnet supports NAT traversal to enable these machines to receive incoming connections from other peers despite their limitations.

In an ideal world, you can press the "Attempt automatic configuration" button in gnunet-setup to automatically configure your peer correctly. Alternatively, your distribution might have already triggered this automatic configuration during the installation process. However, automatic configuration can fail to determine the optimal settings, resulting in your peer either not receiving as many connections as possible, or in the worst case it not connecting to the network at all.

To manually configure the peer, you need to know a few things about your network setup. First, determine if you are behind a NAT in the first place. This is always the case if your IP address starts with "10.*" or "192.168.*". Next, if you have control over your NAT router, you may choose to manually configure it to allow GNUnet traffic to your host. If you have configured your NAT to forward traffic on ports 2086 (and possibly 1080) to your host, you can check the "NAT ports have been opened manually" option, which corresponds to the "PUNCHED_NAT" option in the configuration file. If you did not punch your NAT box, it may still be configured to support UPnP, which allows GNUnet to automatically configure it. In that case, you need to install the "upnpc" command, enable UPnP (or PMP) on your NAT box and set the "Enable NAT traversal via UPnP or PMP" option (corresponding to "ENABLE_UPNP" in the configuration file).

Some NAT boxes can be traversed using the autonomous NAT traversal method. This requires certain GNUnet components to be installed with "SUID" privileges on your system (so if you're installing on a system you do not have administrative rights to, this will not work). If you installed as 'root', you can enable autonomous NAT traversal by checking the "Enable NAT traversal using ICMP method". The ICMP method requires a way to determine your NAT's external (global) IP address. This can be done using either UPnP, DynDNS, or by manual configuration. If you have a DynDNS name or know your external IP address, you should enter that name under "External (public) IPv4 address" (which corresponds to the "EXTERNAL_ADDRESS" option in the configuration file). If you leave the option empty, GNUnet will try to determine your external IP address automatically (which may fail, in which case autonomous NAT traversal will then not work).

Finally, if you yourself are not behind NAT but want to be able to connect to NATed peers using autonomous NAT traversal, you need to check the "Enable connecting to NATed peers using ICMP method" box.

Peer configuration for distributors (e.g. Operating Systems)

The "GNUNET_DATA_HOME" in "[PATHS]" in /etc/gnunet.conf should be manually set to "/var/lib/gnunet/data/" as the default "~/.local/share/gnunet/" is probably not that appropriate in this case. Similarly, distributors may consider pointing "GNUNET_RUNTIME_DIR" to "/var/run/gnunet/" and "GNUNET_HOME" to "/var/lib/gnunet/". Also, should a distributor decide to override system defaults, all of these changes should be done in a custom /etc/gnunet.conf and not in the files in the config.d/ directory.

Given the proposed access permissions, the "gnunet-setup" tool must be run as use "gnunet" (and with option "-c /etc/gnunet.conf" so that it modifies the system configuration). As always, gnunet-setup should be run after the GNUnet peer was stopped using "gnunet-arm -e". Distributors might want to include a wrapper for gnunet-setup that allows the desktop-user to "sudo" (e.g. using gtksudo) to the "gnunet" user account and then runs "gnunet-arm -e", "gnunet-setup" and "gnunet-arm -s" in sequence.


This book is intended to be an introduction for programmers that want to extend the GNUnet framework. GNUnet is more than a simple peer-to-peer application.

For developers, GNUnet is:

  • developed by a community that believes in the GNU philosophy
  • Free Software (Free as in Freedom), licensed under the GNU Affero General Public License
  • A set of standards, including coding conventions and architectural rules
  • A set of layered protocols, both specifying the communication between peers as well as the communication between components of a single peer
  • A set of libraries with well-defined APIs suitable for writing extensions

In particular, the architecture specifies that a peer consists of many processes communicating via protocols. Processes can be written in almost any language. C, Java and Guile APIs exist for accessing existing services and for writing extensions. It is possible to write extensions in other languages by implementing the necessary IPC protocols.

GNUnet can be extended and improved along many possible dimensions, and anyone interested in Free Software and Freedom-enhancing Networking is welcome to join the effort. This Developer Handbook attempts to provide an initial introduction to some of the key design choices and central components of the system.

This part of the GNUnet documentation is far from complete, and we welcome informed contributions, be it in the form of new chapters, sections or insightful comments.


Licenses of contributions

GNUnet is a GNU package. All code contributions must thus be put under the GNU Affero Public License (AGPL). All documentation should be put under FSF approved licenses (see fdl).

By submitting documentation, translations, and other content to GNUnet you automatically grant the right to publish code under the GNU Public License and documentation under either or both the GNU Public License or the GNU Free Documentation License. When contributing to the GNUnet project, GNU standards and the GNU philosophy should be adhered to.


Link to copyright assignment.

We require a formal copyright assignment for GNUnet contributors to GNUnet e.V.; nevertheless, we do allow pseudonymous contributions. By signing the copyright agreement and submitting your code (or documentation) to us, you agree to share the rights to your code with GNUnet e.V.; GNUnet e.V. receives non-exclusive ownership rights, and in particular is allowed to dual-license the code. You retain non-exclusive rights to your contributions, so you can also share your contributions freely with other projects.

GNUnet e.V. will publish all accepted contributions under the AGPLv3 or any later version. The association may decide to publish contributions under additional licenses (dual-licensing).

We do not intentionally remove your name from your contributions; however, due to extensive editing it is not always trivial to attribute contributors properly. If you find that you significantly contributed to a file (or the project as a whole) and are not listed in the respective authors file or section, please do let us know.

Contributing to the Reference Manual


Move section to contrib.rst?


Update contrib section to reflect move to reStructuredText

  • When writing documentation, please use gender-neutral wording when referring to people, such as singular “they”, “their”, “them”, and so forth.
  • Keep line length below 74 characters, except for URLs. URLs break in the PDF output when they contain linebreaks.
  • Do not use tab characters (see chapter 2.1 texinfo manual)
  • Write texts in the third person perspective.

Contributing testcases

In the core of GNUnet, we restrict new testcases to a small subset of languages, in order of preference:

Portable Shell Scripts
Python (3.7 or later)

We welcome efforts to remove our existing Python 2.7 scripts to replace them either with portable shell scripts or, at your choice, Python 3.7 or later.

If you contribute new python based testcases, we advise you to not repeat our past misfortunes and write the tests in a standard test framework like for example pytest.

For writing portable shell scripts, these tools are useful:

Style Guide

This document contains normative rules for writing GNUnet code and naming conventions used throughout the project.

Naming conventions

Header files

For header files, the following suffixes should be used:

Suffix Usage
_lib Libraries without associated processes
_service Libraries using service processes
_plugin Plugin definition
_protocol structs used in network protocol

There exist a few exceptions to these rules within the codebase:

  • gnunet_config.h and gnunet_directories.h are automatically generated.
  • gnunet_common.h, which defines fundamental routines
  • platform.h, first included. .. I have no idea what that means
  • gettext.h, an external library.


For binary files, the following convention should be used:

Name format Usage
gnunet-service-xxx Service processes (with listen sockets)
gnunet-daemon-xxx Daemon processes (without listen sockets)
gnunet-helper-xxx[-yyy] SUID helper for module xxx
gnunet-yyy End-user command line tools Plugin for API xxx Library for API xxx


The convention is to define a macro on a per-file basis to manage logging:

#define LOG(kind,...)
[logging_macro] (kind, "[component_name]", __VA_ARGS__)

The table below indicates the substitutions which should be made for [component_name] and [logging_macro].

Software category [component_name] [logging_macro]
Services and daemons Directory name in GNUNET_log_setup GNUNET_log
Command line tools Full name in GNUNET_log_setup GNUNET_log
Service access libraries [directory_name] GNUNET_log_from
Pure libraries Library name (without lib or .so) GNUNET_log_from
Plugins [directory_name]-[plugin_name] GNUNET_log_from


Clear up terminology within the style guide (_lib, _service mapped to appropriate software categories)


Interpret and write configuration style


Exported symbols must be prefixed with GNUNET_[module_name]_ and be defined in [module_name].c. The only exceptions to this rule are symbols defined in gnunet_common.h.

Private symbols, including structs and macros, must not be prefixed. In addition, they must not be exported in a way that linkers could use them or other libraries might see them via headers. This means that they must never be declared in src/include, and only declared or defined in C source files or headers under src/[module_name].


Test cases and performance tests should follow the naming conventions test_[module-under-test]_[test_description].c and perf_[module-under-test]_[test_description].c, respectively.

In either case, if there is only a single test, [test_description] may be omitted.

src subdirectories

Subdirectories of src

Coding style


Examples should follow GNU Coding Standards?

This project follows the GNU Coding Standards.

Indentation is done with two spaces per level, never with tabs. Specific (though incomplete) indentation rules are defined in an uncrustify configuration file (in contrib) and are enforced by Git hooks.


Link to uncrustify config in contrib.

C99-style struct initialisation is acceptable and generally encouraged.


Clarify whether there are cases where C99-style struct init is discouraged?

As in all good C code, we care about symbol space pollution and thus use static to limit the scope where possible, even in the compilation unit that contains main.

Only one variable should be declared per line:

// bad
int i,j;
// good
int i;
int j;

This helps keep diffs small and forces developers to think precisely about the type of every variable.

Note that char * is different from const char* and int is different from unsigned int or uint32_t. Each variable type should be chosen with care.


libgnunetutil is the fundamental library that all GNUnet code builds upon. Ideally, this library should contain most of the platform dependent code (except for user interfaces and really special needs that only few applications have). It is also supposed to offer basic services that most if not all GNUnet binaries require. The code of libgnunetutil is in the src/util/ directory. The public interface to the library is in the gnunet_util.h header.

The functions provided by libgnunetutil fall roughly into the following categories (in roughly the order of importance for new developers):

  • logging (common_logging.c)
  • memory allocation (common_allocation.c)
  • endianness conversion (common_endian.c)
  • internationalization (common_gettext.c)
  • String manipulation (string.c)
  • file access (disk.c)
  • buffered disk IO (bio.c)
  • time manipulation (time.c)
  • configuration parsing (configuration.c)
  • command-line handling (getopt*.c)
  • cryptography (crypto_*.c)
  • data structures (container_*.c)
  • CPS-style scheduling (scheduler.c)
  • Program initialization (program.c)
  • Networking (network.c, client.c, server*.c, service.c)
  • message queuing (mq.c)
  • bandwidth calculations (bandwidth.c)
  • Other OS-related (os*.c, plugin.c, signal.c)
  • Pseudonym management (pseudonym.c)

It should be noted that only developers that fully understand this entire API will be able to write good GNUnet code.

Ideally, porting GNUnet should only require porting the gnunetutil library. More testcases for the gnunetutil APIs are therefore a great way to make porting of GNUnet easier.

System Architecture


FIXME: For those irritated by the textflow, we are missing images here, in the short term we should add them back, in the long term this should work without images or have images with alt-text.


Adjust image sizes so that they are less obtrusive.

GNUnet developers like LEGOs. The blocks are indestructible, can be stacked together to construct complex buildings and it is generally easy to swap one block for a different one that has the same shape. GNUnet’s architecture is based on LEGOs:

[image: service_lego_block] [image]

This chapter documents the GNUnet LEGO system, also known as GNUnet’s system architecture.

The most common GNUnet component is a service. Services offer an API (or several, depending on what you count as "an API") which is implemented as a library. The library communicates with the main process of the service using a service-specific network protocol. The main process of the service typically doesn’t fully provide everything that is needed — it has holes to be filled by APIs to other services.

A special kind of component in GNUnet are user interfaces and daemons. Like services, they have holes to be filled by APIs of other services. Unlike services, daemons do not implement their own network protocol and they have no API:

[image: daemon_lego_block] [image]

The GNUnet system provides a range of services, daemons and user interfaces, which are then combined into a layered GNUnet instance (also known as a peer).

[image: service_stack] [image]

Note that while it is generally possible to swap one service for another compatible service, there is often only one implementation. However, during development we often have a "new" version of a service in parallel with an "old" version. While the "new" version is not working, developers working on other parts of the service can continue their development by simply using the "old" service. Alternative design ideas can also be easily investigated by swapping out individual components. This is typically achieved by simply changing the name of the "BINARY" in the respective configuration section.

Key properties of GNUnet services are that they must be separate processes and that they must protect themselves by applying tight error checking against the network protocol they implement (thereby achieving a certain degree of robustness).

On the other hand, the APIs are implemented to tolerate failures of the service, isolating their host process from errors by the service. If the service process crashes, other services and daemons around it should not also fail, but instead wait for the service process to be restarted by ARM.


  • VPN and support services (DNS, PT, EXIT)
  • DATASTORE (only used by FS?)
  • MULTICAST and social services (PSYC, PSYCSTORE, SOCIAL)
  • GNS support services/applications (GNSRECORD, ZONEMASTER)

Internal dependencies


Break out into per-process information?

This section tries to give an overview of what processes a typical GNUnet peer running a particular application would consist of. All of the processes listed here should be automatically started by gnunet-arm -s. The list is given as a rough first guide to users for failure diagnostics. Ideally, end-users should never have to worry about these internal dependencies.

In terms of internal dependencies, a minimum file-sharing system consists of the following GNUnet processes (in order of dependency):

  • gnunet-service-arm
  • gnunet-service-resolver (required by all)
  • gnunet-service-statistics (required by all)
  • gnunet-service-peerinfo
  • gnunet-service-transport (requires peerinfo)
  • gnunet-service-core (requires transport)
  • gnunet-daemon-hostlist (requires core)
  • gnunet-daemon-topology (requires hostlist, peerinfo)
  • gnunet-service-datastore
  • gnunet-service-dht (requires core)
  • gnunet-service-identity
  • gnunet-service-fs (requires identity, mesh, dht, datastore, core)

A minimum VPN system consists of the following GNUnet processes (in order of dependency):

  • gnunet-service-arm
  • gnunet-service-resolver (required by all)
  • gnunet-service-statistics (required by all)
  • gnunet-service-peerinfo
  • gnunet-service-transport (requires peerinfo)
  • gnunet-service-core (requires transport)
  • gnunet-daemon-hostlist (requires core)
  • gnunet-service-dht (requires core)
  • gnunet-service-mesh (requires dht, core)
  • gnunet-service-dns (requires dht)
  • gnunet-service-regex (requires dht)
  • gnunet-service-vpn (requires regex, dns, mesh, dht)

A minimum GNS system consists of the following GNUnet processes (in order of dependency):

  • gnunet-service-arm
  • gnunet-service-resolver (required by all)
  • gnunet-service-statistics (required by all)
  • gnunet-service-peerinfo
  • gnunet-service-transport (requires peerinfo)
  • gnunet-service-core (requires transport)
  • gnunet-daemon-hostlist (requires core)
  • gnunet-service-dht (requires core)
  • gnunet-service-mesh (requires dht, core)
  • gnunet-service-dns (requires dht)
  • gnunet-service-regex (requires dht)
  • gnunet-service-vpn (requires regex, dns, mesh, dht)
  • gnunet-service-identity
  • gnunet-service-namestore (requires identity)
  • gnunet-service-gns (requires vpn, dns, dht, namestore, identity)

Subsystem stability

This page documents the current stability of the various GNUnet subsystems. Stability here describes the expected degree of compatibility with future versions of GNUnet.

For each subsystem we distinguish between compatibility on the P2P network level (communication protocol between peers), the IPC level (communication between the service and the service library) and the API level (stability of the API).

P2P compatibility is relevant in terms of which applications are likely going to be able to communicate with future versions of the network. IPC communication is relevant for the implementation of language bindings that re-implement the IPC messages. Finally, API compatibility is relevant to developers that hope to be able to avoid changes to applications built on top of the APIs of the framework.

The following table summarizes our current view of the stability of the respective protocols or APIs:


Make table automatically generated individual pages?

Subsystem P2P IPC C API
util n/a n/a stable
arm n/a stable stable
ats n/a unstable testing
block n/a n/a stable
cadet testing testing testing
consensus experimental experimental experimental
core stable stable stable
datacache n/a n/a stable
datastore n/a stable stable
dht stable stable stable
dns stable stable stable
dv testing testing n/a
exit testing n/a n/a
fragmentation stable n/a stable
fs stable stable stable
gns stable stable stable
hello n/a n/a testing
hostlist stable stable n/a
identity stable stable n/a
multicast experimental experimental experimental
mysql stable n/a stable
namestore n/a stable stable
nat n/a n/a stable
nse stable stable stable
peerinfo n/a stable stable
psyc experimental experimental experimental
pt n/a n/a n/a
regex stable stable stable
revocation stable stable stable
social experimental experimental experimental
statistics n/a stable stable
testbed n/a testing testing
testing n/a n/a testing
topology n/a n/a n/a
transport experimental experimental experimental
tun n/a n/a stable
vpn testing n/a n/a

Here is a rough explanation of the values:


0.10.x is outdated - rewrite “stable” to reflect a time-independent meaning.

No incompatible changes are planned at this time; for IPC/APIs, if there are incompatible changes, they will be minor and might only require minimal changes to existing code; for P2P, changes will be avoided if at all possible for the 0.10.x-series
No incompatible changes are planned at this time, but the code is still known to be in flux; so while we have no concrete plans, our expectation is that there will still be minor modifications; for P2P, changes will likely be extensions that should not break existing code
Changes are planned and will happen; however, they will not be totally radical and the result should still resemble what is there now; nevertheless, anticipated changes will break protocol/API compatibility
Changes are planned and the result may look nothing like what the API/protocol looks like today
Someone should think about where this subsystem headed
This subsystem does not implement a corresponding API/protocol

Basic Services

These services comprise a backbone of core services for peer-to-peer applications to use.

STATISTICS — Runtime statistics publication

In GNUnet, the STATISTICS subsystem offers a central place for all subsystems to publish unsigned 64-bit integer run-time statistics. Keeping this information centrally means that there is a unified way for the user to obtain data on all subsystems, and individual subsystems do not have to always include a custom data export method for performance metrics and other statistics. For example, the TRANSPORT system uses STATISTICS to update information about the number of directly connected peers and the bandwidth that has been consumed by the various plugins. This information is valuable for diagnosing connectivity and performance issues.

Following the GNUnet service architecture, the STATISTICS subsystem is divided into an API which is exposed through the header gnunet_statistics_service.h and the STATISTICS service gnunet-service-statistics. The gnunet-statistics command-line tool can be used to obtain (and change) information about the values stored by the STATISTICS service. The STATISTICS service does not communicate with other peers.

Data is stored in the STATISTICS service in the form of tuples (subsystem, name, value, persistence). The subsystem determines to which other GNUnet’s subsystem the data belongs. name is the name through which value is associated. It uniquely identifies the record from among other records belonging to the same subsystem. In some parts of the code, the pair (subsystem, name) is called a statistic as it identifies the values stored in the STATISTCS service.The persistence flag determines if the record has to be preserved across service restarts. A record is said to be persistent if this flag is set for it; if not, the record is treated as a non-persistent record and it is lost after service restart. Persistent records are written to and read from the file before shutdown and upon startup. The file is located in the HOME directory of the peer.

An anomaly of the STATISTICS service is that it does not terminate immediately upon receiving a shutdown signal if it has any clients connected to it. It waits for all the clients that are not monitors to close their connections before terminating itself. This is to prevent the loss of data during peer shutdown — delaying the STATISTICS service shutdown helps other services to store important data to STATISTICS during shutdown.


libgnunetstatistics is the library containing the API for the STATISTICS subsystem. Any process requiring to use STATISTICS should use this API by to open a connection to the STATISTICS service. This is done by calling the function GNUNET_STATISTICS_create(). This function takes the subsystem’s name which is trying to use STATISTICS and a configuration. All values written to STATISTICS with this connection will be placed in the section corresponding to the given subsystem’s name. The connection to STATISTICS can be destroyed with the function GNUNET_STATISTICS_destroy(). This function allows for the connection to be destroyed immediately or upon transferring all pending write requests to the service.

Note: STATISTICS subsystem can be disabled by setting DISABLE = YES under the [STATISTICS] section in the configuration. With such a configuration all calls to GNUNET_STATISTICS_create() return NULL as the STATISTICS subsystem is unavailable and no other functions from the API can be used.

Statistics retrieval

Once a connection to the statistics service is obtained, information about any other system which uses statistics can be retrieved with the function GNUNET_STATISTICS_get(). This function takes the connection handle, the name of the subsystem whose information we are interested in (a NULL value will retrieve information of all available subsystems using STATISTICS), the name of the statistic we are interested in (a NULL value will retrieve all available statistics), a continuation callback which is called when all of requested information is retrieved, an iterator callback which is called for each parameter in the retrieved information and a closure for the aforementioned callbacks. The library then invokes the iterator callback for each value matching the request.

Call to GNUNET_STATISTICS_get() is asynchronous and can be canceled with the function GNUNET_STATISTICS_get_cancel(). This is helpful when retrieving statistics takes too long and especially when we want to shutdown and cleanup everything.

Setting statistics and updating them

So far we have seen how to retrieve statistics, here we will learn how we can set statistics and update them so that other subsystems can retrieve them.

A new statistic can be set using the function GNUNET_STATISTICS_set(). This function takes the name of the statistic and its value and a flag to make the statistic persistent. The value of the statistic should be of the type uint64_t. The function does not take the name of the subsystem; it is determined from the previous GNUNET_STATISTICS_create() invocation. If the given statistic is already present, its value is overwritten.

An existing statistics can be updated, i.e its value can be increased or decreased by an amount with the function GNUNET_STATISTICS_update(). The parameters to this function are similar to GNUNET_STATISTICS_set(), except that it takes the amount to be changed as a type int64_t instead of the value.

The library will combine multiple set or update operations into one message if the client performs requests at a rate that is faster than the available IPC with the STATISTICS service. Thus, the client does not have to worry about sending requests too quickly.


As interesting feature of STATISTICS lies in serving notifications whenever a statistic of our interest is modified. This is achieved by registering a watch through the function GNUNET_STATISTICS_watch(). The parameters of this function are similar to those of GNUNET_STATISTICS_get(). Changes to the respective statistic’s value will then cause the given iterator callback to be called. Note: A watch can only be registered for a specific statistic. Hence the subsystem name and the parameter name cannot be NULL in a call to GNUNET_STATISTICS_watch().

A registered watch will keep notifying any value changes until GNUNET_STATISTICS_watch_cancel() is called with the same parameters that are used for registering the watch.

The STATISTICS Client-Service Protocol

Statistics retrieval

To retrieve statistics, the client transmits a message of type GNUNET_MESSAGE_TYPE_STATISTICS_GET containing the given subsystem name and statistic parameter to the STATISTICS service. The service responds with a message of type GNUNET_MESSAGE_TYPE_STATISTICS_VALUE for each of the statistics parameters that match the client request for the client. The end of information retrieved is signaled by the service by sending a message of type GNUNET_MESSAGE_TYPE_STATISTICS_END.

Setting and updating statistics

The subsystem name, parameter name, its value and the persistence flag are communicated to the service through the message GNUNET_MESSAGE_TYPE_STATISTICS_SET.

When the service receives a message of type GNUNET_MESSAGE_TYPE_STATISTICS_SET, it retrieves the subsystem name and checks for a statistic parameter with matching the name given in the message. If a statistic parameter is found, the value is overwritten by the new value from the message; if not found then a new statistic parameter is created with the given name and value.

In addition to just setting an absolute value, it is possible to perform a relative update by sending a message of type GNUNET_MESSAGE_TYPE_STATISTICS_SET with an update flag (GNUNET_STATISTICS_SETFLAG_RELATIVE) signifying that the value in the message should be treated as an update value.

Watching for updates

The function registers the watch at the service by sending a message of type GNUNET_MESSAGE_TYPE_STATISTICS_WATCH. The service then sends notifications through messages of type GNUNET_MESSAGE_TYPE_STATISTICS_WATCH_VALUE whenever the statistic parameter’s value is changed.

ATS — Automatic transport selection

ATS stands for "automatic transport selection", and the function of ATS in GNUnet is to decide on which address (and thus transport plugin) should be used for two peers to communicate, and what bandwidth limits should be imposed on such an individual connection.

To help ATS make an informed decision, higher-level services inform the ATS service about their requirements and the quality of the service rendered. The ATS service also interacts with the transport service to be appraised of working addresses and to communicate its resource allocation decisions. Finally, the ATS service’s operation can be observed using a monitoring API.

The main logic of the ATS service only collects the available addresses, their performance characteristics and the applications requirements, but does not make the actual allocation decision. This last critical step is left to an ATS plugin, as we have implemented (currently three) different allocation strategies which differ significantly in their performance and maturity, and it is still unclear if any particular plugin is generally superior.

TRANSPORT — Overlay transport management

This chapter documents how the GNUnet transport subsystem works. The GNUnet transport subsystem consists of three main components: the transport API (the interface used by the rest of the system to access the transport service), the transport service itself (most of the interesting functions, such as choosing transports, happens here) and the transport plugins. A transport plugin is a concrete implementation for how two GNUnet peers communicate; many plugins exist, for example for communication via TCP, UDP, HTTP, HTTPS and others. Finally, the transport subsystem uses supporting code, especially the NAT/UPnP library to help with tasks such as NAT traversal.

Key tasks of the transport service include:

  • Create our HELLO message, notify clients and neighbours if our HELLO changes (using NAT library as necessary)
  • Validate HELLOs from other peers (send PING), allow other peers to validate our HELLO’s addresses (send PONG)
  • Upon request, establish connections to other peers (using address selection from ATS subsystem) and maintain them (again using PINGs and PONGs) as long as desired
  • Accept incoming connections, give ATS service the opportunity to switch communication channels
  • Notify clients about peers that have connected to us or that have been disconnected from us
  • If a (stateful) connection goes down unexpectedly (without explicit DISCONNECT), quickly attempt to recover (without notifying clients) but do notify clients quickly if reconnecting fails
  • Send (payload) messages arriving from clients to other peers via transport plugins and receive messages from other peers, forwarding those to clients
  • Enforce inbound traffic limits (using flow-control if it is applicable); outbound traffic limits are enforced by CORE, not by us (!)
  • Enforce restrictions on P2P connection as specified by the blacklist configuration and blacklisting clients

Note that the term "clients" in the list above really refers to the GNUnet-CORE service, as CORE is typically the only client of the transport service.

Address validation protocol

This section documents how the GNUnet transport service validates connections with other peers. It is a high-level description of the protocol necessary to understand the details of the implementation. It should be noted that when we talk about PING and PONG messages in this section, we refer to transport-level PING and PONG messages, which are different from core-level PING and PONG messages (both in implementation and function).

The goal of transport-level address validation is to minimize the chances of a successful man-in-the-middle attack against GNUnet peers on the transport level. Such an attack would not allow the adversary to decrypt the P2P transmissions, but a successful attacker could at least measure traffic volumes and latencies (raising the adversaries capabilities by those of a global passive adversary in the worst case). The scenarios we are concerned about is an attacker, Mallory, giving a HELLO to Alice that claims to be for Bob, but contains Mallory’s IP address instead of Bobs (for some transport). Mallory would then forward the traffic to Bob (by initiating a connection to Bob and claiming to be Alice). As a further complication, the scheme has to work even if say Alice is behind a NAT without traversal support and hence has no address of her own (and thus Alice must always initiate the connection to Bob).

An additional constraint is that HELLO messages do not contain a cryptographic signature since other peers must be able to edit (i.e. remove) addresses from the HELLO at any time (this was not true in GNUnet 0.8.x). A basic assumption is that each peer knows the set of possible network addresses that it might be reachable under (so for example, the external IP address of the NAT plus the LAN address(es) with the respective ports).

The solution is the following. If Alice wants to validate that a given address for Bob is valid (i.e. is actually established directly with the intended target), she sends a PING message over that connection to Bob. Note that in this case, Alice initiated the connection so only Alice knows which address was used for sure (Alice may be behind NAT, so whatever address Bob sees may not be an address Alice knows she has). Bob checks that the address given in the PING is actually one of Bob’s addresses (ie: does not belong to Mallory), and if it is, sends back a PONG (with a signature that says that Bob owns/uses the address from the PING). Alice checks the signature and is happy if it is valid and the address in the PONG is the address Alice used. This is similar to the 0.8.x protocol where the HELLO contained a signature from Bob for each address used by Bob. Here, the purpose code for the signature is GNUNET_SIGNATURE_PURPOSE_TRANSPORT_PONG_OWN. After this, Alice will remember Bob’s address and consider the address valid for a while (12h in the current implementation). Note that after this exchange, Alice only considers Bob’s address to be valid, the connection itself is not considered ‘established’. In particular, Alice may have many addresses for Bob that Alice considers valid.

The PONG message is protected with a nonce/challenge against replay attacks (replay) and uses an expiration time for the signature (but those are almost implementation details).

NAT library .. _NAT-library:

NAT library

The goal of the GNUnet NAT library is to provide a general-purpose API for NAT traversal without third-party support. So protocols that involve contacting a third peer to help establish a connection between two peers are outside of the scope of this API. That does not mean that GNUnet doesn’t support involving a third peer (we can do this with the distance-vector transport or using application-level protocols), it just means that the NAT API is not concerned with this possibility. The API is written so that it will work for IPv6-NAT in the future as well as current IPv4-NAT. Furthermore, the NAT API is always used, even for peers that are not behind NAT — in that case, the mapping provided is simply the identity.

NAT traversal is initiated by calling GNUNET_NAT_register. Given a set of addresses that the peer has locally bound to (TCP or UDP), the NAT library will return (via callback) a (possibly longer) list of addresses the peer might be reachable under. Internally, depending on the configuration, the NAT library will try to punch a hole (using UPnP) or just "know" that the NAT was manually punched and generate the respective external IP address (the one that should be globally visible) based on the given information.

The NAT library also supports ICMP-based NAT traversal. Here, the other peer can request connection-reversal by this peer (in this special case, the peer is even allowed to configure a port number of zero). If the NAT library detects a connection-reversal request, it returns the respective target address to the client as well. It should be noted that connection-reversal is currently only intended for TCP, so other plugins must pass NULL for the reversal callback. Naturally, the NAT library also supports requesting connection reversal from a remote peer (GNUNET_NAT_run_client).

Once initialized, the NAT handle can be used to test if a given address is possibly a valid address for this peer (GNUNET_NAT_test_address). This is used for validating our addresses when generating PONGs.

Finally, the NAT library contains an API to test if our NAT configuration is correct. Using GNUNET_NAT_test_start before binding to the respective port, the NAT library can be used to test if the configuration works. The test function act as a local client, initialize the NAT traversal and then contact a gnunet-nat-server (running by default on and ask for a connection to be established. This way, it is easy to test if the current NAT configuration is valid.

Distance-Vector plugin

The Distance Vector (DV) transport is a transport mechanism that allows peers to act as relays for each other, thereby connecting peers that would otherwise be unable to connect. This gives a larger connection set to applications that may work better with more peers to choose from (for example, File Sharing and/or DHT).

The Distance Vector transport essentially has two functions. The first is "gossiping" connection information about more distant peers to directly connected peers. The second is taking messages intended for non-directly connected peers and encapsulating them in a DV wrapper that contains the required information for routing the message through forwarding peers. Via gossiping, optimal routes through the known DV neighborhood are discovered and utilized and the message encapsulation provides some benefits in addition to simply getting the message from the correct source to the proper destination.

The gossiping function of DV provides an up to date routing table of peers that are available up to some number of hops. We call this a fisheye view of the network (like a fish, nearby objects are known while more distant ones unknown). Gossip messages are sent only to directly connected peers, but they are sent about other knowns peers within the "fisheye distance". Whenever two peers connect, they immediately gossip to each other about their appropriate other neighbors. They also gossip about the newly connected peer to previously connected neighbors. In order to keep the routing tables up to date, disconnect notifications are propagated as gossip as well (because disconnects may not be sent/received, timeouts are also used remove stagnant routing table entries).

Routing of messages via DV is straightforward. When the DV transport is notified of a message destined for a non-direct neighbor, the appropriate forwarding peer is selected, and the base message is encapsulated in a DV message which contains information about the initial peer and the intended recipient. At each forwarding hop, the initial peer is validated (the forwarding peer ensures that it has the initial peer in its neighborhood, otherwise the message is dropped). Next the base message is re-encapsulated in a new DV message for the next hop in the forwarding chain (or delivered to the current peer, if it has arrived at the destination).

Assume a three peer network with peers Alice, Bob and Carol. Assume that

Alice <-> Bob and Bob <-> Carol

are direct (e.g. over TCP or UDP transports) connections, but that Alice cannot directly connect to Carol. This may be the case due to NAT or firewall restrictions, or perhaps based on one of the peers respective configurations. If the Distance Vector transport is enabled on all three peers, it will automatically discover (from the gossip protocol) that Alice and Carol can connect via Bob and provide a "virtual" Alice <-> Carol connection. Routing between Alice and Carol happens as follows; Alice creates a message destined for Carol and notifies the DV transport about it. The DV transport at Alice looks up Carol in the routing table and finds that the message must be sent through Bob for Carol. The message is encapsulated setting Alice as the initiator and Carol as the destination and sent to Bob. Bob receives the messages, verifies that both Alice and Carol are known to Bob, and re-wraps the message in a new DV message for Carol. The DV transport at Carol receives this message, unwraps the original message, and delivers it to Carol as though it came directly from Alice.

SMTP plugin .. _SMTP-plugin:

SMTP plugin



This section describes the new SMTP transport plugin for GNUnet as it exists in the 0.7.x and 0.8.x branch. SMTP support is currently not available in GNUnet 0.9.x. This page also describes the transport layer abstraction (as it existed in 0.7.x and 0.8.x) in more detail and gives some benchmarking results. The performance results presented are quite old and maybe outdated at this point. For the readers in the year 2019, you will notice by the mention of version 0.7, 0.8, and 0.9 that this section has to be taken with your usual grain of salt and be updated eventually.

  • Why use SMTP for a peer-to-peer transport?
  • SMTPHow does it work?
  • How do I configure my peer?
  • How do I test if it works?
  • How fast is it?
  • Is there any additional documentation?

Why use SMTP for a peer-to-peer transport?

There are many reasons why one would not want to use SMTP:

  • SMTP is using more bandwidth than TCP, UDP or HTTP
  • SMTP has a much higher latency.
  • SMTP requires significantly more computation (encoding and decoding time) for the peers.
  • SMTP is significantly more complicated to configure.
  • SMTP may be abused by tricking GNUnet into sending mail to non-participating third parties.

So why would anybody want to use SMTP?

  • SMTP can be used to contact peers behind NAT boxes (in virtual private networks).
  • SMTP can be used to circumvent policies that limit or prohibit peer-to-peer traffic by masking as "legitimate" traffic.
  • SMTP uses E-mail addresses which are independent of a specific IP, which can be useful to address peers that use dynamic IP addresses.
  • SMTP can be used to initiate a connection (e.g. initial address exchange) and peers can then negotiate the use of a more efficient protocol (e.g. TCP) for the actual communication.

In summary, SMTP can for example be used to send a message to a peer behind a NAT box that has a dynamic IP to tell the peer to establish a TCP connection to a peer outside of the private network. Even an extraordinary overhead for this first message would be irrelevant in this type of situation.

How does it work?

When a GNUnet peer needs to send a message to another GNUnet peer that has advertised (only) an SMTP transport address, GNUnet base64-encodes the message and sends it in an E-mail to the advertised address. The advertisement contains a filter which is placed in the E-mail header, such that the receiving host can filter the tagged E-mails and forward it to the GNUnet peer process. The filter can be specified individually by each peer and be changed over time. This makes it impossible to censor GNUnet E-mail messages by searching for a generic filter.

How do I configure my peer?

First, you need to configure procmail to filter your inbound E-mail for GNUnet traffic. The GNUnet messages must be delivered into a pipe, for example /tmp/gnunet.smtp. You also need to define a filter that is used by procmail to detect GNUnet messages. You are free to choose whichever filter you like, but you should make sure that it does not occur in your other E-mail. In our example, we will use X-mailer: GNUnet. The ~/.procmailrc configuration file then looks like this:

* ^X-mailer: GNUnet
# where do you want your other e-mail delivered to
# (default: /var/spool/mail/)
:0: /var/spool/mail/

After adding this file, first make sure that your regular E-mail still works (e.g. by sending an E-mail to yourself). Then edit the GNUnet configuration. In the section SMTP you need to specify your E-mail address under EMAIL, your mail server (for outgoing mail) under SERVER, the filter (X-mailer: GNUnet in the example) under FILTER and the name of the pipe under PIPE. The completed section could then look like this:

"X-mailer: GNUnet" PIPE = /tmp/gnunet.smtp


set highlighting for this code block properly.

Finally, you need to add smtp to the list of TRANSPORTS in the GNUNETD section. GNUnet peers will use the E-mail address that you specified to contact your peer until the advertisement times out. Thus, if you are not sure if everything works properly or if you are not planning to be online for a long time, you may want to configure this timeout to be short, e.g. just one hour. For this, set HELLOEXPIRES to 1 in the GNUNETD section.

This should be it, but you may probably want to test it first.

How do I test if it works?

Any transport can be subjected to some rudimentary tests using the gnunet-transport-check tool. The tool sends a message to the local node via the transport and checks that a valid message is received. While this test does not involve other peers and can not check if firewalls or other network obstacles prohibit proper operation, this is a great testcase for the SMTP transport since it tests pretty much nearly all of the functionality.

gnunet-transport-check should only be used without running gnunetd at the same time. By default, gnunet-transport-check tests all transports that are specified in the configuration file. But you can specifically test SMTP by giving the option --transport=smtp.

Note that this test always checks if a transport can receive and send. While you can configure most transports to only receive or only send messages, this test will only work if you have configured the transport to send and receive messages.

How fast is it?

We have measured the performance of the UDP, TCP and SMTP transport layer directly and when used from an application using the GNUnet core. Measuring just the transport layer gives the better view of the actual overhead of the protocol, whereas evaluating the transport from the application puts the overhead into perspective from a practical point of view.

The loopback measurements of the SMTP transport were performed on three different machines spanning a range of modern SMTP configurations. We used a PIII-800 running RedHat 7.3 with the Purdue Computer Science configuration which includes filters for spam. We also used a Xenon 2 GHZ with a vanilla RedHat 8.0 sendmail configuration. Furthermore, we used qmail on a PIII-1000 running Sorcerer GNU Linux (SGL). The numbers for UDP and TCP are provided using the SGL configuration. The qmail benchmark uses qmail’s internal filtering whereas the sendmail benchmarks relies on procmail to filter and deliver the mail. We used the transport layer to send a message of b bytes (excluding transport protocol headers) directly to the local machine. This way, network latency and packet loss on the wire have no impact on the timings. n messages were sent sequentially over the transport layer, sending message i+1 after the i-th message was received. All messages were sent over the same connection and the time to establish the connection was not taken into account since this overhead is minuscule in practice — as long as a connection is used for a significant number of messages.

Transport UDP TCP SMTP (Purdue s endmail) SMTP (RH 8.0) SMTP (SGL qmail)
11 bytes 31 ms 55 ms 781 s 77 s 24 s
407 bytes 37 ms 62 ms 789 s 78 s 25 s
1,221 bytes 46 ms 73 ms 804 s 78 s 25 s

The benchmarks show that UDP and TCP are, as expected, both significantly faster compared with any of the SMTP services. Among the SMTP implementations, there can be significant differences depending on the SMTP configuration. Filtering with an external tool like procmail that needs to re-parse its configuration for each mail can be very expensive. Applying spam filters can also significantly impact the performance of the underlying SMTP implementation. The microbenchmark shows that SMTP can be a viable solution for initiating peer-to-peer sessions: a couple of seconds to connect to a peer are probably not even going to be noticed by users. The next benchmark measures the possible throughput for a transport. Throughput can be measured by sending multiple messages in parallel and measuring packet loss. Note that not only UDP but also the TCP transport can actually loose messages since the TCP implementation drops messages if the write to the socket would block. While the SMTP protocol never drops messages itself, it is often so slow that only a fraction of the messages can be sent and received in the given time-bounds. For this benchmark we report the message loss after allowing t time for sending m messages. If messages were not sent (or received) after an overall timeout of t, they were considered lost. The benchmark was performed using two Xeon 2 GHZ machines running RedHat 8.0 with sendmail. The machines were connected with a direct 100 MBit Ethernet connection. Figures udp1200, tcp1200 and smtp-MTUs show that the throughput for messages of size 1,200 octets is 2,343 kbps, 3,310 kbps and 6 kbps for UDP, TCP and SMTP respectively. The high per-message overhead of SMTP can be improved by increasing the MTU, for example, an MTU of 12,000 octets improves the throughput to 13 kbps as figure smtp-MTUs shows. Our research paper [Transport2014] has some more details on the benchmarking results.

Bluetooth plugin .. _Bluetooth-plugin:

Bluetooth plugin

This page describes the new Bluetooth transport plugin for GNUnet. The plugin is still in the testing stage so don’t expect it to work perfectly. If you have any questions or problems just post them here or ask on the IRC channel.

  • What do I need to use the Bluetooth plugin transport?
  • BluetoothHow does it work?
  • What possible errors should I be aware of?
  • How do I configure my peer?
  • How can I test it?

What do I need to use the Bluetooth plugin transport?

If you are a GNU/Linux user and you want to use the Bluetooth transport plugin you should install the BlueZ development libraries (if they aren’t already installed). For instructions about how to install the libraries you should check out the BlueZ site ( If you don’t know if you have the necessary libraries, don’t worry, just run the GNUnet configure script and you will be able to see a notification at the end which will warn you if you don’t have the necessary libraries.


Change to unique title?

How does it work2?

The Bluetooth transport plugin uses virtually the same code as the WLAN plugin and only the helper binary is different. The helper takes a single argument, which represents the interface name and is specified in the configuration file. Here are the basic steps that are followed by the helper binary used on GNU/Linux:

  • it verifies if the name corresponds to a Bluetooth interface name
  • it verifies if the interface is up (if it is not, it tries to bring it up)
  • it tries to enable the page and inquiry scan in order to make the device discoverable and to accept incoming connection requests The above operations require root access so you should start the transport plugin with root privileges.
  • it finds an available port number and registers a SDP service which will be used to find out on which port number is the server listening on and switch the socket in listening mode
  • it sends a HELLO message with its address
  • finally it forwards traffic from the reading sockets to the STDOUT and from the STDIN to the writing socket

Once in a while the device will make an inquiry scan to discover the nearby devices and it will send them randomly HELLO messages for peer discovery.

What possible errors should I be aware of?

This section is dedicated for GNU/Linux users

Well there are many ways in which things could go wrong but I will try to present some tools that you could use to debug and some scenarios.

  • bluetoothd -n -d : use this command to enable logging in the foreground and to print the logging messages
  • hciconfig: can be used to configure the Bluetooth devices. If you run it without any arguments it will print information about the state of the interfaces. So if you receive an error that the device couldn’t be brought up you should try to bring it manually and to see if it works (use hciconfig -a hciX up). If you can’t and the Bluetooth address has the form 00:00:00:00:00:00 it means that there is something wrong with the D-Bus daemon or with the Bluetooth daemon. Use bluetoothd tool to see the logs
  • sdptool can be used to control and interrogate SDP servers. If you encounter problems regarding the SDP server (like the SDP server is down) you should check out if the D-Bus daemon is running correctly and to see if the Bluetooth daemon started correctly(use bluetoothd tool). Also, sometimes the SDP service could work but somehow the device couldn’t register its service. Use sdptool browse [dev-address] to see if the service is registered. There should be a service with the name of the interface and GNUnet as provider.
  • hcitool : another useful tool which can be used to configure the device and to send some particular commands to it.
  • hcidump : could be used for low level debugging


Fix name/referencing now that we’re using Sphinx.

How do I configure my peer2?

On GNU/Linux, you just have to be sure that the interface name corresponds to the one that you want to use. Use the hciconfig tool to check that. By default it is set to hci0 but you can change it.

A basic configuration looks like this:

# Name of the interface (typically hciX)
# Real hardware, no testing

In order to use the Bluetooth transport plugin when the transport service is started, you must add the plugin name to the default transport service plugins list. For example:

[transport] ...  PLUGINS = dns bluetooth ...

If you want to use only the Bluetooth plugin set PLUGINS = bluetooth

On Windows, you cannot specify which device to use. The only thing that you should do is to add bluetooth on the plugins list of the transport service.

How can I test it?

If you have two Bluetooth devices on the same machine and you are using GNU/Linux you must:

  • create two different file configuration (one which will use the first interface (hci0) and the other which will use the second interface (hci1)). Let’s name them peer1.conf and peer2.conf.
  • run gnunet-peerinfo -c peerX.conf -s in order to generate the peers private keys. The X must be replace with 1 or 2.
  • run gnunet-arm -c peerX.conf -s -i=transport in order to start the transport service. (Make sure that you have "bluetooth" on the transport plugins list if the Bluetooth transport service doesn’t start.)
  • run gnunet-peerinfo -c peer1.conf -s to get the first peer’s ID. If you already know your peer ID (you saved it from the first command), this can be skipped.
  • run gnunet-transport -c peer2.conf -p=PEER1_ID -s to start sending data for benchmarking to the other peer.

This scenario will try to connect the second peer to the first one and then start sending data for benchmarking.

If you have two different machines and your configuration files are good you can use the same scenario presented on the beginning of this section.

Another way to test the plugin functionality is to create your own application which will use the GNUnet framework with the Bluetooth transport service.

The implementation of the Bluetooth transport plugin

This page describes the implementation of the Bluetooth transport plugin.

First I want to remind you that the Bluetooth transport plugin uses virtually the same code as the WLAN plugin and only the helper binary is different. Also the scope of the helper binary from the Bluetooth transport plugin is the same as the one used for the WLAN transport plugin: it accesses the interface and then it forwards traffic in both directions between the Bluetooth interface and stdin/stdout of the process involved.

The Bluetooth plugin transport could be used both on GNU/Linux and Windows platforms.

  • Linux functionality
  • Pending Features

Linux functionality

In order to implement the plugin functionality on GNU/Linux I used the BlueZ stack. For the communication with the other devices I used the RFCOMM protocol. Also I used the HCI protocol to gain some control over the device. The helper binary takes a single argument (the name of the Bluetooth interface) and is separated in two stages:


‘THE INITIALIZATION’ should be in bigger letters or stand out, not starting a new section?


  • first, it checks if we have root privileges (Remember that we need to have root privileges in order to be able to bring the interface up if it is down or to change its state.).
  • second, it verifies if the interface with the given name exists.

    If the interface with that name exists and it is a Bluetooth interface:

  • it creates a RFCOMM socket which will be used for listening and call the open_device method

    On the open_device method:

  • creates a HCI socket used to send control events to the device
  • searches for the device ID using the interface name
  • saves the device MAC address
  • checks if the interface is down and tries to bring it UP
  • checks if the interface is in discoverable mode and tries to make it discoverable
  • closes the HCI socket and binds the RFCOMM one
  • switches the RFCOMM socket in listening mode
  • registers the SDP service (the service will be used by the other devices to get the port on which this device is listening on)

drops the root privileges

If the interface is not a Bluetooth interface the helper exits with a suitable error


The helper binary uses a list where it saves all the connected neighbour devices (neighbours.devices) and two buffers (write_pout and write_std). The first message which is send is a control message with the device’s MAC address in order to announce the peer presence to the neighbours. Here are a short description of what happens in the main loop:

  • Every time when it receives something from the STDIN it processes the data and saves the message in the first buffer (write_pout). When it has something in the buffer, it gets the destination address from the buffer, searches the destination address in the list (if there is no connection with that device, it creates a new one and saves it to the list) and sends the message.
  • Every time when it receives something on the listening socket it accepts the connection and saves the socket on a list with the reading sockets.
  • Every time when it receives something from a reading socket it parses the message, verifies the CRC and saves it in the write_std buffer in order to be sent later to the STDOUT.

So in the main loop we use the select function to wait until one of the file descriptor saved in one of the two file descriptors sets used is ready to use. The first set (rfds) represents the reading set and it could contain the list with the reading sockets, the STDIN file descriptor or the listening socket. The second set (wfds) is the writing set and it could contain the sending socket or the STDOUT file descriptor. After the select function returns, we check which file descriptor is ready to use and we do what is supposed to do on that kind of event. For example: if it is the listening socket then we accept a new connection and save the socket in the reading list; if it is the STDOUT file descriptor, then we write to STDOUT the message from the write_std buffer.

To find out on which port a device is listening on we connect to the local SDP server and search the registered service for that device.

You should be aware of the fact that if the device fails to connect to another one when trying to send a message it will attempt one more time. If it fails again, then it skips the message. Also you should know that the transport Bluetooth plugin has support forbroadcast messages.

Details about the broadcast implementation

First I want to point out that the broadcast functionality for the CONTROL messages is not implemented in a conventional way. Since the inquiry scan time is too big and it will take some time to send a message to all the discoverable devices I decided to tackle the problem in a different way. Here is how I did it:

  • If it is the first time when I have to broadcast a message I make an inquiry scan and save all the devices’ addresses to a vector.
  • After the inquiry scan ends I take the first address from the list and I try to connect to it. If it fails, I try to connect to the next one. If it succeeds, I save the socket to a list and send the message to the device.
  • When I have to broadcast another message, first I search on the list for a new device which I’m not connected to. If there is no new device on the list I go to the beginning of the list and send the message to the old devices. After 5 cycles I make a new inquiry scan to check out if there are new discoverable devices and save them to the list. If there are no new discoverable devices I reset the cycling counter and go again through the old list and send messages to the devices saved in it.


  • every time when I have a broadcast message I look up on the list for a new device and send the message to it
  • if I reached the end of the list for 5 times and I’m connected to all the devices from the list I make a new inquiry scan. The number of the list’s cycles after an inquiry scan could be increased by redefining the MAX_LOOPS variable
  • when there are no new devices I send messages to the old ones.

Doing so, the broadcast control messages will reach the devices but with delay.

NOTICE: When I have to send a message to a certain device first I check on the broadcast list to see if we are connected to that device. If not we try to connect to it and in case of success we save the address and the socket on the list. If we are already connected to that device we simply use the socket.

Pending features

Implement a testcase for the helper : The testcase consists of a program which emulates the plugin and uses the helper. It will simulate connections, disconnections and data transfers.

If you have a new idea about a feature of the plugin or suggestions about how I could improve the implementation you are welcome to comment or to contact me.

WLAN plugin

This section documents how the wlan transport plugin works. Parts which are not implemented yet or could be better implemented are described at the end.


TRANSPORT-NG — Next-generation transport management

The current GNUnet TRANSPORT architecture is rooted in the GNUnet 0.4 design of using plugins for the actual transmission operations and the ATS subsystem to select a plugin and allocate bandwidth. The following key issues have been identified with this design:

  • Bugs in one plugin can affect the TRANSPORT service and other plugins. There is at least one open bug that affects sockets, where the origin is difficult to pinpoint due to the large code base.
  • Relevant operating system default configurations often impose a limit of 1024 file descriptors per process. Thus, one plugin may impact other plugin’s connectivity choices.
  • Plugins are required to offer bi-directional connectivity. However, firewalls (incl. NAT boxes) and physical environments sometimes only allow uni-directional connectivity, which then currently cannot be utilized at all.
  • Distance vector routing was implemented in 209 but shortly afterwards broken and due to the complexity of implementing it as a plugin and dealing with the resource allocation consequences was never useful.
  • Most existing plugins communicate completely using cleartext, exposing metad data (message size) and making it easy to fingerprint and possibly block GNUnet traffic.
  • Various NAT traversal methods are not supported.
  • The service logic is cluttered with "manipulation" support code for TESTBED to enable faking network characteristics like lossy connections or firewewalls.
  • Bandwidth allocation is done in ATS, requiring the duplication of state and resulting in much delayed allocation decisions. As a result, often available bandwidth goes unused. Users are expected to manually configure bandwidth limits, instead of TRANSPORT using congestion control to adapt automatically.
  • TRANSPORT is difficult to test and has bad test coverage.
  • HELLOs include an absolute expiration time. Nodes with unsynchronized clocks cannot connect.
  • Displaying the contents of a HELLO requires the respective plugin as the plugin-specific data is encoded in binary. This also complicates logging.

Design goals of TNG

In order to address the above issues, we want to:

  • Move plugins into separate processes which we shall call communicators. Communicators connect as clients to the transport service.
  • TRANSPORT should be able to utilize any number of communcators to the same peer at the same time.
  • TRANSPORT should be responsible for fragmentation, retransmission, flow- and congestion-control. Users should no longer have to configure bandwidth limits: TRANSPORT should detect what is available and use it.
  • Commnunicators should be allowed to be uni-directional and unreliable. TRANSPORT shall create bi-directional channels from this whenever possible.
  • DV should no longer be a plugin, but part of TRANSPORT.
  • TRANSPORT should provide communicators help communicating, for example in the case of uni-directional communicators or the need for out-of-band signalling for NAT traversal. We call this functionality backchannels.
  • Transport manipulation should be signalled to CORE on a per-message basis instead of an approximate bandwidth.
  • CORE should signal performance requirements (reliability, latency, etc.) on a per-message basis to TRANSPORT. If possible, TRANSPORT should consider those options when scheduling messages for transmission.
  • HELLOs should be in a humman-readable format with monotonic time expirations.

The new architecture is planned as follows: [image]

TRANSPORT’s main objective is to establish bi-directional virtual links using a variety of possibly uni-directional communicators. Links undergo the following steps:

Communicator informs TRANSPORT A that a queue (direct neighbour) is available, or equivalently TRANSPORT A discovers a (DV) path to a target B.
TRANSPORT A sends a challenge to the target peer, trying to confirm that the peer can receive. FIXME: This is not implemented properly for DV. Here we should really take a validated DVH and send a challenge exactly down that path!
The other TRANSPORT, TRANSPORT B, receives the challenge, and sends back a response, possibly using a dierent path. If TRANSPORT B does not yet have a virtual link to A, it must try to establish a virtual link.
Upon receiving the response, TRANSPORT A creates the virtual link. If the response included a challenge, TRANSPORT A must respond to this challenge as well, eectively re-creating the TCP 3-way handshake (just with longer challenge values).


HELLOs change in three ways. First of all, communicators encode the respective addresses in a human-readable URL-like string. This way, we do no longer require the communicator to print the contents of a HELLO. Second, HELLOs no longer contain an expiration time, only a creation time. The receiver must only compare the respective absolute values. So given a HELLO from the same sender with a larger creation time, then the old one is no longer valid. This also obsoletes the need for the gnunet-hello binary to set HELLO expiration times to never. Third, a peer no longer generates one big HELLO that always contains all of the addresses. Instead, each address is signed individually and shared only over the address scopes where it makes sense to share the address. In particular, care should be taken to not share MACs across the Internet and confine their use to the LAN. As each address is signed separately, having multiple addresses valid at the same time (given the new creation time expiration logic) requires that those addresses must have exactly the same creation time. Whenever that monotonic time is increased, all addresses must be re-signed and re-distributed.

Priorities and preferences

In the new design, TRANSPORT adopts a feature (which was previously already available in CORE) of the MQ API to allow applications to specify priorities and preferences per message (or rather, per MQ envelope). The (updated) MQ API allows applications to specify one of four priority levels as well as desired preferences for transmission by setting options on an envelope. These preferences currently are:

  • GNUNET_MQ_PREF_UNRELIABLE: Disables TRANSPORT waiting for ACKS on unreliable channels like UDP. Now it is fire and forget. These messages then cannot be used for RTT estimates either.
  • GNUNET_MQ_PREF_LOW_LATENCY: Directs TRANSPORT to select the lowest-latency transmission choices possible.
  • GNUNET_MQ_PREF_CORK_ALLOWED: Allows TRANSPORT to delay transmission to group the message with other messages into a larger batch to reduce the number of packets sent.
  • GNUNET_MQ_PREF_GOODPUT: Directs TRANSPORT to select the highest goodput channel available.
  • GNUNET_MQ_PREF_OUT_OF_ORDER: Allows TRANSPORT to reorder the messages as it sees fit, otherwise TRANSPORT should attempt to preserve transmission order.

Each MQ envelope is always able to store those options (and the priority), and in the future this uniform API will be used by TRANSPORT, CORE, CADET and possibly other subsystems that send messages (like LAKE). When CORE sets preferences and priorities, it is supposed to respect the preferences and priorities it is given from higher layers. Similarly, CADET also simply passes on the preferences and priorities of the layer above CADET. When a layer combines multiple smaller messages into one larger transmission, the GNUNET_MQ_env_combine_options() should be used to calculate options for the combined message. We note that the exact semantics of the options may differ by layer. For example, CADET will always strictly implement reliable and in-order delivery of messages, while the same options are only advisory for TRANSPORT and CORE: they should try (using ACKs on unreliable communicators, not changing the message order themselves), but if messages are lost anyway (e.g. because a TCP is dropped in the middle), or if messages are reordered (e.g. because they took different paths over the network and arrived in a different order) TRANSPORT and CORE do not have to correct this. Whether a preference is strict or loose is thus dened by the respective layer.


The API for communicators is defined in gnunet_transport_communication_service.h. Each communicator must specify its (global) communication characteristics, which for now only say whether the communication is reliable (e.g. TCP, HTTPS) or unreliable (e.g. UDP, WLAN). Each communicator must specify a unique address prex, or NULL if the communicator cannot establish outgoing connections (for example because it is only acting as a TCP server). A communicator must tell TRANSPORT which addresses it is reachable under. Addresses may be added or removed at any time. A communicator may have zero addresses (transmission only). Addresses do not have to match the address prefix.

TRANSPORT may ask a communicator to try to connect to another address. TRANSPORT will only ask for connections where the address matches the communicator’s address prefix that was provided when the connection was established. Communicators should then attempt to establish a connection. No response is provided to TRANSPORT service on failure. The TRANSPORT service has to ask the communicator explicitly to retry.

If a communicator succeeds in establishing an outgoing connection for transmission, or if a communicator receives an incoming bi-directional connection, the communicator must inform the TRANSPORT service that a message queue (MQ) for transmission is now available. For that MQ, the communicator must provide the peer identity claimed by the other end, a human-readable address (for debugging) and a maximum transfer unit (MTU). A MTU of zero means sending is not supported, SIZE_MAX should be used for no MTU. The communicator should also tell TRANSPORT what network type is used for the queue. The communicator may tell TRANSPORT anytime that the queue was deleted and is no longer available.

The communicator API also provides for flow control. First, communicators exhibit back-pressure on TRANSPORT: the number of messages TRANSPORT may add to a queue for transmission will be limited. So by not draining the transmission queue, back-pressure is provided to TRANSPORT. In the other direction, communicators may allow TRANSPORT to give back-pressure towards the communicator by providing a non-NULL GNUNET_TRANSPORT_MessageCompletedCallback argument to the GNUNET_TRANSPORT_communicator_receive function. In this case, TRANSPORT will only invoke this function once it has processed the message and is ready to receive more. Communicators should then limit how much traffic they receive based on this backpressure. Note that communicators do not have to provide a GNUNET_TRANSPORT_MessageCompletedCallback; for example, UDP cannot support back-pressure due to the nature of the UDP protocol. In this case, TRANSPORT will implement its own TRANSPORT-to-TRANSPORT flow control to reduce the sender’s data rate to acceptable levels.

TRANSPORT may notify a communicator about backchannel messages TRANSPORT received from other peers for this communicator. Similarly, communicators can ask TRANSPORT to try to send a backchannel message to other communicators of other peers. The semantics of the backchannel message are up to the communicators which use them. TRANSPORT may fail transmitting backchannel messages, and TRANSPORT will not attempt to retransmit them.

HOSTLIST — HELLO bootstrapping and gossip

Peers in the GNUnet overlay network need address information so that they can connect with other peers. GNUnet uses so called HELLO messages to store and exchange peer addresses. GNUnet provides several methods for peers to obtain this information:

  • out-of-band exchange of HELLO messages (manually, using for example gnunet-peerinfo)
  • HELLO messages shipped with GNUnet (automatic with distribution)
  • UDP neighbor discovery in LAN (IPv4 broadcast, IPv6 multicast)
  • topology gossiping (learning from other peers we already connected to), and
  • the HOSTLIST daemon covered in this section, which is particularly relevant for bootstrapping new peers.

New peers have no existing connections (and thus cannot learn from gossip among peers), may not have other peers in their LAN and might be started with an outdated set of HELLO messages from the distribution. In this case, getting new peers to connect to the network requires either manual effort or the use of a HOSTLIST to obtain HELLOs.


The basic information peers require to connect to other peers are contained in so called HELLO messages you can think of as a business card. Besides the identity of the peer (based on the cryptographic public key) a HELLO message may contain address information that specifies ways to contact a peer. By obtaining HELLO messages, a peer can learn how to contact other peers.

Overview for the HOSTLIST subsystem

The HOSTLIST subsystem provides a way to distribute and obtain contact information to connect to other peers using a simple HTTP GET request. Its implementation is split in three parts, the main file for the daemon itself (gnunet-daemon-hostlist.c), the HTTP client used to download peer information (hostlist-client.c) and the server component used to provide this information to other peers (hostlist-server.c). The server is basically a small HTTP web server (based on GNU libmicrohttpd) which provides a list of HELLOs known to the local peer for download. The client component is basically a HTTP client (based on libcurl) which can download hostlists from one or more websites. The hostlist format is a binary blob containing a sequence of HELLO messages. Note that any HTTP server can theoretically serve a hostlist, the built-in hostlist server makes it simply convenient to offer this service.


The HOSTLIST daemon can:

  • provide HELLO messages with validated addresses obtained from PEERINFO to download for other peers
  • download HELLO messages and forward these message to the TRANSPORT subsystem for validation
  • advertises the URL of this peer’s hostlist address to other peers via gossip
  • automatically learn about hostlist servers from the gossip of other peers

HOSTLIST - Limitations

The HOSTLIST daemon does not:

  • verify the cryptographic information in the HELLO messages
  • verify the address information in the HELLO messages

Interacting with the HOSTLIST daemon

The HOSTLIST subsystem is currently implemented as a daemon, so there is no need for the user to interact with it and therefore there is no command line tool and no API to communicate with the daemon. In the future, we can envision changing this to allow users to manually trigger the download of a hostlist.

Since there is no command line interface to interact with HOSTLIST, the only way to interact with the hostlist is to use STATISTICS to obtain or modify information about the status of HOSTLIST:

$ gnunet-statistics -s hostlist

In particular, HOSTLIST includes a persistent value in statistics that specifies when the hostlist server might be queried next. As this value is exponentially increasing during runtime, developers may want to reset or manually adjust it. Note that HOSTLIST (but not STATISTICS) needs to be shutdown if changes to this value are to have any effect on the daemon (as HOSTLIST does not monitor STATISTICS for changes to the download frequency).

Hostlist security address validation

Since information obtained from other parties cannot be trusted without validation, we have to distinguish between validated and not validated addresses. Before using (and so trusting) information from other parties, this information has to be double-checked (validated). Address validation is not done by HOSTLIST but by the TRANSPORT service.

The HOSTLIST component is functionally located between the PEERINFO and the TRANSPORT subsystem. When acting as a server, the daemon obtains valid (validated) peer information (HELLO messages) from the PEERINFO service and provides it to other peers. When acting as a client, it contacts the HOSTLIST servers specified in the configuration, downloads the (unvalidated) list of HELLO messages and forwards these information to the TRANSPORT server to validate the addresses.

The HOSTLIST daemon

The hostlist daemon is the main component of the HOSTLIST subsystem. It is started by the ARM service and (if configured) starts the HOSTLIST client and server components.

GNUNET_MESSAGE_TYPE_HOSTLIST_ADVERTISEMENT If the daemon provides a hostlist itself it can advertise it’s own hostlist to other peers. To do so it sends a GNUNET_MESSAGE_TYPE_HOSTLIST_ADVERTISEMENT message to other peers when they connect to this peer on the CORE level. This hostlist advertisement message contains the URL to access the HOSTLIST HTTP server of the sender. The daemon may also subscribe to this type of message from CORE service, and then forward these kind of message to the HOSTLIST client. The client then uses all available URLs to download peer information when necessary.

When starting, the HOSTLIST daemon first connects to the CORE subsystem and if hostlist learning is enabled, registers a CORE handler to receive this kind of messages. Next it starts (if configured) the client and server. It passes pointers to CORE connect and disconnect and receive handlers where the client and server store their functions, so the daemon can notify them about CORE events.

To clean up on shutdown, the daemon has a cleaning task, shutting down all subsystems and disconnecting from CORE.

The HOSTLIST server

The server provides a way for other peers to obtain HELLOs. Basically it is a small web server other peers can connect to and download a list of HELLOs using standard HTTP; it may also advertise the URL of the hostlist to other peers connecting on CORE level.

The HTTP Server

During startup, the server starts a web server listening on the port specified with the HTTPPORT value (default 8080). In addition it connects to the PEERINFO service to obtain peer information. The HOSTLIST server uses the GNUNET_PEERINFO_iterate function to request HELLO information for all peers and adds their information to a new hostlist if they are suitable (expired addresses and HELLOs without addresses are both not suitable) and the maximum size for a hostlist is not exceeded (MAX_BYTES_PER_HOSTLISTS = 500000). When PEERINFO finishes (with a last NULL callback), the server destroys the previous hostlist response available for download on the web server and replaces it with the updated hostlist. The hostlist format is basically a sequence of HELLO messages (as obtained from PEERINFO) without any special tokenization. Since each HELLO message contains a size field, the response can easily be split into separate HELLO messages by the client.

A HOSTLIST client connecting to the HOSTLIST server will receive the hostlist as an HTTP response and the server will terminate the connection with the result code HTTP 200 OK. The connection will be closed immediately if no hostlist is available.

Advertising the URL

The server also advertises the URL to download the hostlist to other peers if hostlist advertisement is enabled. When a new peer connects and has hostlist learning enabled, the server sends a GNUNET_MESSAGE_TYPE_HOSTLIST_ADVERTISEMENT message to this peer using the CORE service.

HOSTLIST client .. _The-HOSTLIST-client:

The HOSTLIST client

The client provides the functionality to download the list of HELLOs from a set of URLs. It performs a standard HTTP request to the URLs configured and learned from advertisement messages received from other peers. When a HELLO is downloaded, the HOSTLIST client forwards the HELLO to the TRANSPORT service for validation.

The client supports two modes of operation:

  • download of HELLOs (bootstrapping)
  • learning of URLs


For bootstrapping, it schedules a task to download the hostlist from the set of known URLs. The downloads are only performed if the number of current connections is smaller than a minimum number of connections (at the moment 4). The interval between downloads increases exponentially; however, the exponential growth is limited if it becomes longer than an hour. At that point, the frequency growth is capped at (#number of connections * 1h).

Once the decision has been taken to download HELLOs, the daemon chooses a random URL from the list of known URLs. URLs can be configured in the configuration or be learned from advertisement messages. The client uses a HTTP client library (libcurl) to initiate the download using the libcurl multi interface. Libcurl passes the data to the callback_download function which stores the data in a buffer if space is available and the maximum size for a hostlist download is not exceeded (MAX_BYTES_PER_HOSTLISTS = 500000). When a full HELLO was downloaded, the HOSTLIST client offers this HELLO message to the TRANSPORT service for validation. When the download is finished or failed, statistical information about the quality of this URL is updated.


The client also manages hostlist advertisements from other peers. The HOSTLIST daemon forwards GNUNET_MESSAGE_TYPE_HOSTLIST_ADVERTISEMENT messages to the client subsystem, which extracts the URL from the message. Next, a test of the newly obtained URL is performed by triggering a download from the new URL. If the URL works correctly, it is added to the list of working URLs.

The size of the list of URLs is restricted, so if an additional server is added and the list is full, the URL with the worst quality ranking (determined through successful downloads and number of HELLOs e.g.) is discarded. During shutdown the list of URLs is saved to a file for persistence and loaded on startup. URLs from the configuration file are never discarded.


To start HOSTLIST by default, it has to be added to the DEFAULTSERVICES section for the ARM services. This is done in the default configuration.

For more information on how to configure the HOSTLIST subsystem see the installation handbook: Configuring the hostlist to bootstrap Configuring your peer to provide a hostlist

PEERINFO — Persistent HELLO storage

The PEERINFO subsystem is used to store verified (validated) information about known peers in a persistent way. It obtains these addresses for example from TRANSPORT service which is in charge of address validation. Validation means that the information in the HELLO message are checked by connecting to the addresses and performing a cryptographic handshake to authenticate the peer instance stating to be reachable with these addresses. Peerinfo does not validate the HELLO messages itself but only stores them and gives them to interested clients.

As future work, we think about moving from storing just HELLO messages to providing a generic persistent per-peer information store. More and more subsystems tend to need to store per-peer information in persistent way. To not duplicate this functionality we plan to provide a PEERSTORE service providing this functionality.

PEERINFO - Features

  • Persistent storage
  • Client notification mechanism on update
  • Periodic clean up for expired information
  • Differentiation between public and friend-only HELLO

PEERINFO - Limitations

Does not perform HELLO validation

DeveloperPeer Information

The PEERINFO subsystem stores these information in the form of HELLO messages you can think of as business cards. These HELLO messages contain the public key of a peer and the addresses a peer can be reached under. The addresses include an expiration date describing how long they are valid. This information is updated regularly by the TRANSPORT service by revalidating the address. If an address is expired and not renewed, it can be removed from the HELLO message.

Some peer do not want to have their HELLO messages distributed to other peers, especially when GNUnet’s friend-to-friend modus is enabled. To prevent this undesired distribution. PEERINFO distinguishes between public and friend-only HELLO messages. Public HELLO messages can be freely distributed to other (possibly unknown) peers (for example using the hostlist, gossiping, broadcasting), whereas friend-only HELLO messages may not be distributed to other peers. Friend-only HELLO messages have an additional flag friend_only set internally. For public HELLO message this flag is not set. PEERINFO does and cannot not check if a client is allowed to obtain a specific HELLO type.

The HELLO messages can be managed using the GNUnet HELLO library. Other GNUnet systems can obtain these information from PEERINFO and use it for their purposes. Clients are for example the HOSTLIST component providing these information to other peers in form of a hostlist or the TRANSPORT subsystem using these information to maintain connections to other peers.


During startup the PEERINFO services loads persistent HELLOs from disk. First PEERINFO parses the directory configured in the HOSTS value of the PEERINFO configuration section to store PEERINFO information. For all files found in this directory valid HELLO messages are extracted. In addition it loads HELLO messages shipped with the GNUnet distribution. These HELLOs are used to simplify network bootstrapping by providing valid peer information with the distribution. The use of these HELLOs can be prevented by setting the USE_INCLUDED_HELLOS in the PEERINFO configuration section to NO. Files containing invalid information are removed.

Managing Information

The PEERINFO services stores information about known PEERS and a single HELLO message for every peer. A peer does not need to have a HELLO if no information are available. HELLO information from different sources, for example a HELLO obtained from a remote HOSTLIST and a second HELLO stored on disk, are combined and merged into one single HELLO message per peer which will be given to clients. During this merge process the HELLO is immediately written to disk to ensure persistence.

PEERINFO in addition periodically scans the directory where information are stored for empty HELLO messages with expired TRANSPORT addresses. This periodic task scans all files in the directory and recreates the HELLO messages it finds. Expired TRANSPORT addresses are removed from the HELLO and if the HELLO does not contain any valid addresses, it is discarded and removed from the disk.

Obtaining Information

When a client requests information from PEERINFO, PEERINFO performs a lookup for the respective peer or all peers if desired and transmits this information to the client. The client can specify if friend-only HELLOs have to be included or not and PEERINFO filters the respective HELLO messages before transmitting information.

To notify clients about changes to PEERINFO information, PEERINFO maintains a list of clients interested in this notifications. Such a notification occurs if a HELLO for a peer was updated (due to a merge for example) or a new peer was added.

The PEERINFO Client-Service Protocol

To connect and disconnect to and from the PEERINFO Service PEERINFO utilizes the util client/server infrastructure, so no special messages types are used here.

To add information for a peer, the plain HELLO message is transmitted to the service without any wrapping. All pieces of information required are stored within the HELLO message. The PEERINFO service provides a message handler accepting and processing these HELLO messages.

When obtaining PEERINFO information using the iterate functionality specific messages are used. To obtain information for all peers, a struct ListAllPeersMessage with message type GNUNET_MESSAGE_TYPE_PEERINFO_GET_ALL and a flag include_friend_only to indicate if friend-only HELLO messages should be included are transmitted. If information for a specific peer is required a struct ListAllPeersMessage with GNUNET_MESSAGE_TYPE_PEERINFO_GET containing the peer identity is used.

For both variants the PEERINFO service replies for each HELLO message it wants to transmit with a struct ListAllPeersMessage with type GNUNET_MESSAGE_TYPE_PEERINFO_INFO containing the plain HELLO. The final message is struct GNUNET_MessageHeader with type GNUNET_MESSAGE_TYPE_PEERINFO_INFO. If the client receives this message, it can proceed with the next request if any is pending.


The PEERINFO API consists mainly of three different functionalities:

  • maintaining a connection to the service
  • adding new information to the PEERINFO service
  • retrieving information from the PEERINFO service

Connecting to the PEERINFO Service

To connect to the PEERINFO service the function GNUNET_PEERINFO_connect is used, taking a configuration handle as an argument, and to disconnect from PEERINFO the function GNUNET_PEERINFO_disconnect, taking the PEERINFO handle returned from the connect function has to be called.

Adding Information to the PEERINFO Service

GNUNET_PEERINFO_add_peer adds a new peer to the PEERINFO subsystem storage. This function takes the PEERINFO handle as an argument, the HELLO message to store and a continuation with a closure to be called with the result of the operation. The GNUNET_PEERINFO_add_peer returns a handle to this operation allowing to cancel the operation with the respective cancel function GNUNET_PEERINFO_add_peer_cancel. To retrieve information from PEERINFO you can iterate over all information stored with PEERINFO or you can tell PEERINFO to notify if new peer information are available.

Obtaining Information from the PEERINFO Service

To iterate over information in PEERINFO you use GNUNET_PEERINFO_iterate. This function expects the PEERINFO handle, a flag if HELLO messages intended for friend only mode should be included, a timeout how long the operation should take and a callback with a callback closure to be called for the results. If you want to obtain information for a specific peer, you can specify the peer identity, if this identity is NULL, information for all peers are returned. The function returns a handle to allow to cancel the operation using GNUNET_PEERINFO_iterate_cancel.

To get notified when peer information changes, you can use GNUNET_PEERINFO_notify. This function expects a configuration handle and a flag if friend-only HELLO messages should be included. The PEERINFO service will notify you about every change and the callback function will be called to notify you about changes. The function returns a handle to cancel notifications with GNUNET_PEERINFO_notify_cancel.

PEERSTORE — Extensible local persistent data storage

GNUnet’s PEERSTORE subsystem offers persistent per-peer storage for other GNUnet subsystems. GNUnet subsystems can use PEERSTORE to persistently store and retrieve arbitrary data. Each data record stored with PEERSTORE contains the following fields:

  • subsystem: Name of the subsystem responsible for the record.
  • peerid: Identity of the peer this record is related to.
  • key: a key string identifying the record.
  • value: binary record value.
  • expiry: record expiry date.


Subsystems can store any type of value under a (subsystem, peerid, key) combination. A "replace" flag set during store operations forces the PEERSTORE to replace any old values stored under the same (subsystem, peerid, key) combination with the new value. Additionally, an expiry date is set after which the record is *possibly* deleted by PEERSTORE.

Subsystems can iterate over all values stored under any of the following combination of fields:

  • (subsystem)
  • (subsystem, peerid)
  • (subsystem, key)
  • (subsystem, peerid, key)

Subsystems can also request to be notified about any new values stored under a (subsystem, peerid, key) combination by sending a "watch" request to PEERSTORE.


PEERSTORE implements the following components:

  • PEERSTORE service: Handles store, iterate and watch operations.
  • PEERSTORE API: API to be used by other subsystems to communicate and issue commands to the PEERSTORE service.
  • PEERSTORE plugins: Handles the persistent storage. At the moment, only an "sqlite" plugin is implemented.


libgnunetpeerstore is the library containing the PEERSTORE API. Subsystems wishing to communicate with the PEERSTORE service use this API to open a connection to PEERSTORE. This is done by calling GNUNET_PEERSTORE_connect which returns a handle to the newly created connection. This handle has to be used with any further calls to the API.

To store a new record, the function GNUNET_PEERSTORE_store is to be used which requires the record fields and a continuation function that will be called by the API after the STORE request is sent to the PEERSTORE service. Note that calling the continuation function does not mean that the record is successfully stored, only that the STORE request has been successfully sent to the PEERSTORE service. GNUNET_PEERSTORE_store_cancel can be called to cancel the STORE request only before the continuation function has been called.

To iterate over stored records, the function GNUNET_PEERSTORE_iterate is to be used. peerid and key can be set to NULL. An iterator callback function will be called with each matching record found and a NULL record at the end to signal the end of result set. GNUNET_PEERSTORE_iterate_cancel can be used to cancel the ITERATE request before the iterator callback is called with a NULL record.

To be notified with new values stored under a (subsystem, peerid, key) combination, the function GNUNET_PEERSTORE_watch is to be used. This will register the watcher with the PEERSTORE service, any new records matching the given combination will trigger the callback function passed to GNUNET_PEERSTORE_watch. This continues until GNUNET_PEERSTORE_watch_cancel is called or the connection to the service is destroyed.

After the connection is no longer needed, the function GNUNET_PEERSTORE_disconnect can be called to disconnect from the PEERSTORE service. Any pending ITERATE or WATCH requests will be destroyed. If the sync_first flag is set to GNUNET_YES, the API will delay the disconnection until all pending STORE requests are sent to the PEERSTORE service, otherwise, the pending STORE requests will be destroyed as well.

The CORE subsystem in GNUnet is responsible for securing link-layer communications between nodes in the GNUnet overlay network. CORE builds on the TRANSPORT subsystem which provides for the actual, insecure, unreliable link-layer communication (for example, via UDP or WLAN), and then adds fundamental security to the connections:

  • confidentiality with so-called perfect forward secrecy; we use ECDHE (Elliptic-curve Diffie—Hellman) powered by Curve25519 (Curve25519) for the key exchange and then use symmetric encryption, encrypting with both AES-256 (AES-256) and Twofish (Twofish)
  • authentication is achieved by signing the ephemeral keys using Ed25519 (Ed25519), a deterministic variant of ECDSA (ECDSA)
  • integrity protection (using SHA-512 (SHA-512) to do encrypt-then-MAC (encrypt-then-MAC))
  • Replay (replay) protection (using nonces, timestamps, challenge-response, message counters and ephemeral keys)
  • liveness (keep-alive messages, timeout)


CORE does not perform routing; using CORE it is only possible to communicate with peers that happen to already be "directly" connected with each other. CORE also does not have an API to allow applications to establish such "direct" connections — for this, applications can ask TRANSPORT, but TRANSPORT might not be able to establish a "direct" connection. The TOPOLOGY subsystem is responsible for trying to keep a few "direct" connections open at all times. Applications that need to talk to particular peers should use the CADET subsystem, as it can establish arbitrary "indirect" connections.

Because CORE does not perform routing, CORE must only be used directly by applications that either perform their own routing logic (such as anonymous file-sharing) or that do not require routing, for example because they are based on flooding the network. CORE communication is unreliable and delivery is possibly out-of-order. Applications that require reliable communication should use the CADET service. Each application can only queue one message per target peer with the CORE service at any time; messages cannot be larger than approximately 63 kilobytes. If messages are small, CORE may group multiple messages (possibly from different applications) prior to encryption. If permitted by the application (using the cork option), CORE may delay transmissions to facilitate grouping of multiple small messages. If cork is not enabled, CORE will transmit the message as soon as TRANSPORT allows it (TRANSPORT is responsible for limiting bandwidth and congestion control). CORE does not allow flow control; applications are expected to process messages at line-speed. If flow control is needed, applications should use the CADET service.

When is a peer connected ?

In addition to the security features mentioned above, CORE also provides one additional key feature to applications using it, and that is a limited form of protocol-compatibility checking. CORE distinguishes between TRANSPORT-level connections (which enable communication with other peers) and application-level connections. Applications using the CORE API will (typically) learn about application-level connections from CORE, and not about TRANSPORT-level connections. When a typical application uses CORE, it will specify a set of message types (from gnunet_protocols.h) that it understands. CORE will then notify the application about connections it has with other peers if and only if those applications registered an intersecting set of message types with their CORE service. Thus, it is quite possible that CORE only exposes a subset of the established direct connections to a particular application — and different applications running above CORE might see different sets of connections at the same time.

A special case are applications that do not register a handler for any message type. CORE assumes that these applications merely want to monitor connections (or "all" messages via other callbacks) and will notify those applications about all connections. This is used, for example, by the gnunet-core command-line tool to display the active connections. Note that it is also possible that the TRANSPORT service has more active connections than the CORE service, as the CORE service first has to perform a key exchange with connecting peers before exchanging information about supported message types and notifying applications about the new connection.


The CORE API (defined in gnunet_core_service.h) is the basic messaging API used by P2P applications built using GNUnet. It provides applications the ability to send and receive encrypted messages to the peer’s "directly" connected neighbours.

As CORE connections are generally "direct" connections, applications must not assume that they can connect to arbitrary peers this way, as "direct" connections may not always be possible. Applications using CORE are notified about which peers are connected. Creating new "direct" connections must be done using the TRANSPORT API.

The CORE API provides unreliable, out-of-order delivery. While the implementation tries to ensure timely, in-order delivery, both message losses and reordering are not detected and must be tolerated by the application. Most important, the core will NOT perform retransmission if messages could not be delivered.

Note that CORE allows applications to queue one message per connected peer. The rate at which each connection operates is influenced by the preferences expressed by local application as well as restrictions imposed by the other peer. Local applications can express their preferences for particular connections using the "performance" API of the ATS service.

Applications that require more sophisticated transmission capabilities such as TCP-like behavior, or if you intend to send messages to arbitrary remote peers, should use the CADET API.

The typical use of the CORE API is to connect to the CORE service using GNUNET_CORE_connect, process events from the CORE service (such as peers connecting, peers disconnecting and incoming messages) and send messages to connected peers using GNUNET_CORE_notify_transmit_ready. Note that applications must cancel pending transmission requests if they receive a disconnect event for a peer that had a transmission pending; furthermore, queuing more than one transmission request per peer per application using the service is not permitted.

The CORE API also allows applications to monitor all communications of the peer prior to encryption (for outgoing messages) or after decryption (for incoming messages). This can be useful for debugging, diagnostics or to establish the presence of cover traffic (for anonymity). As monitoring applications are often not interested in the payload, the monitoring callbacks can be configured to only provide the message headers (including the message type and size) instead of copying the full data stream to the monitoring client.

The init callback of the GNUNET_CORE_connect function is called with the hash of the public key of the peer. This public key is used to identify the peer globally in the GNUnet network. Applications are encouraged to check that the provided hash matches the hash that they are using (as theoretically the application may be using a different configuration file with a different private key, which would result in hard to find bugs).

As with most service APIs, the CORE API isolates applications from crashes of the CORE service. If the CORE service crashes, the application will see disconnect events for all existing connections. Once the connections are re-established, the applications will be receive matching connect events.

core client-service protocol .. _The-CORE-Client_002dService-Protocol:

The CORE Client-Service Protocol

This section describes the protocol between an application using the CORE service (the client) and the CORE service process itself.


When a client connects to the CORE service, it first sends a InitMessage which specifies options for the connection and a set of message type values which are supported by the application. The options bitmask specifies which events the client would like to be notified about. The options include:

No notifications
Peers connecting and disconnecting
All inbound messages (after decryption) with full payload
Just the MessageHeader of all inbound messages
All outbound messages (prior to encryption) with full payload
Just the MessageHeader of all outbound messages

Typical applications will only monitor for connection status changes.

The CORE service responds to the InitMessage with an InitReplyMessage which contains the peer’s identity. Afterwards, both CORE and the client can send messages.


The CORE will send ConnectNotifyMessages and DisconnectNotifyMessages whenever peers connect or disconnect from the CORE (assuming their type maps overlap with the message types registered by the client). When the CORE receives a message that matches the set of message types specified during the InitMessage (or if monitoring is enabled in for inbound messages in the options), it sends a NotifyTrafficMessage with the peer identity of the sender and the decrypted payload. The same message format (except with GNUNET_MESSAGE_TYPE_CORE_NOTIFY_OUTBOUND for the message type) is used to notify clients monitoring outbound messages; here, the peer identity given is that of the receiver.


When a client wants to transmit a message, it first requests a transmission slot by sending a SendMessageRequest which specifies the priority, deadline and size of the message. Note that these values may be ignored by CORE. When CORE is ready for the message, it answers with a SendMessageReady response. The client can then transmit the payload with a SendMessage message. Note that the actual message size in the SendMessage is allowed to be smaller than the size in the original request. A client may at any time send a fresh SendMessageRequest, which then superceeds the previous SendMessageRequest, which is then no longer valid. The client can tell which SendMessageRequest the CORE service’s SendMessageReady message is for as all of these messages contain a "unique" request ID (based on a counter incremented by the client for each request).

CORE Peer-to-Peer Protocol .. _The-CORE-Peer_002dto_002dPeer-Protocol:

The CORE Peer-to-Peer Protocol

EphemeralKeyMessage creation .. _Creating-the-EphemeralKeyMessage:

Creating the EphemeralKeyMessage

When the CORE service starts, each peer creates a fresh ephemeral (ECC) public-private key pair and signs the corresponding EphemeralKeyMessage with its long-term key (which we usually call the peer’s identity; the hash of the public long term key is what results in a struct GNUNET_PeerIdentity in all GNUnet APIs. The ephemeral key is ONLY used for an ECDHE (Elliptic-curve Diffie—Hellman) exchange by the CORE service to establish symmetric session keys. A peer will use the same EphemeralKeyMessage for all peers for REKEY_FREQUENCY, which is usually 12 hours. After that time, it will create a fresh ephemeral key (forgetting the old one) and broadcast the new EphemeralKeyMessage to all connected peers, resulting in fresh symmetric session keys. Note that peers independently decide on when to discard ephemeral keys; it is not a protocol violation to discard keys more often. Ephemeral keys are also never stored to disk; restarting a peer will thus always create a fresh ephemeral key. The use of ephemeral keys is what provides forward secrecy.

Just before transmission, the EphemeralKeyMessage is patched to reflect the current sender_status, which specifies the current state of the connection from the point of view of the sender. The possible values are:

  • KX_STATE_DOWN Initial value, never used on the network
  • KX_STATE_KEY_SENT We sent our ephemeral key, do not know the key of the other peer
  • KX_STATE_KEY_RECEIVED This peer has received a valid ephemeral key of the other peer, but we are waiting for the other peer to confirm it’s authenticity (ability to decode) via challenge-response.
  • KX_STATE_UP The connection is fully up from the point of view of the sender (now performing keep-alive)
  • KX_STATE_REKEY_SENT The sender has initiated a rekeying operation; the other peer has so far failed to confirm a working connection using the new ephemeral key

Establishing a connection

Peers begin their interaction by sending a EphemeralKeyMessage to the other peer once the TRANSPORT service notifies the CORE service about the connection. A peer receiving an EphemeralKeyMessage with a status indicating that the sender does not have the receiver’s ephemeral key, the receiver’s EphemeralKeyMessage is sent in response. Additionally, if the receiver has not yet confirmed the authenticity of the sender, it also sends an (encrypted)PingMessage with a challenge (and the identity of the target) to the other peer. Peers receiving a PingMessage respond with an (encrypted) PongMessage which includes the challenge. Peers receiving a PongMessage check the challenge, and if it matches set the connection to KX_STATE_UP.

Encryption and Decryption

All functions related to the key exchange and encryption/decryption of messages can be found in gnunet-service-core_kx.c (except for the cryptographic primitives, which are in util/crypto*.c). Given the key material from ECDHE, a Key derivation function (Key derivation function) is used to derive two pairs of encryption and decryption keys for AES-256 and TwoFish, as well as initialization vectors and authentication keys (for HMAC (HMAC)). The HMAC is computed over the encrypted payload. Encrypted messages include an iv_seed and the HMAC in the header.

Each encrypted message in the CORE service includes a sequence number and a timestamp in the encrypted payload. The CORE service remembers the largest observed sequence number and a bit-mask which represents which of the previous 32 sequence numbers were already used. Messages with sequence numbers lower than the largest observed sequence number minus 32 are discarded. Messages with a timestamp that is less than REKEY_TOLERANCE off (5 minutes) are also discarded. This of course means that system clocks need to be reasonably synchronized for peers to be able to communicate. Additionally, as the ephemeral key changes every 12 hours, a peer would not even be able to decrypt messages older than 12 hours.

Type maps

Once an encrypted connection has been established, peers begin to exchange type maps. Type maps are used to allow the CORE service to determine which (encrypted) connections should be shown to which applications. A type map is an array of 65536 bits representing the different types of messages understood by applications using the CORE service. Each CORE service maintains this map, simply by setting the respective bit for each message type supported by any of the applications using the CORE service. Note that bits for message types embedded in higher-level protocols (such as MESH) will not be included in these type maps.

Typically, the type map of a peer will be sparse. Thus, the CORE service attempts to compress its type map using gzip-style compression ("deflate") prior to transmission. However, if the compression fails to compact the map, the map may also be transmitted without compression (resulting in GNUNET_MESSAGE_TYPE_CORE_COMPRESSED_TYPE_MAP or GNUNET_MESSAGE_TYPE_CORE_BINARY_TYPE_MAP messages respectively). Upon receiving a type map, the respective CORE service notifies applications about the connection to the other peer if they support any message type indicated in the type map (or no message type at all). If the CORE service experience a connect or disconnect event from an application, it updates its type map (setting or unsetting the respective bits) and notifies its neighbours about the change. The CORE services of the neighbours then in turn generate connect and disconnect events for the peer that sent the type map for their respective applications. As CORE messages may be lost, the CORE service confirms receiving a type map by sending back a GNUNET_MESSAGE_TYPE_CORE_CONFIRM_TYPE_MAP. If such a confirmation (with the correct hash of the type map) is not received, the sender will retransmit the type map (with exponential back-off).

NSE — Network size estimation

NSE stands for Network Size Estimation. The NSE subsystem provides other subsystems and users with a rough estimate of the number of peers currently participating in the GNUnet overlay. The computed value is not a precise number as producing a precise number in a decentralized, efficient and secure way is impossible. While NSE’s estimate is inherently imprecise, NSE also gives the expected range. For a peer that has been running in a stable network for a while, the real network size will typically (99.7% of the time) be in the range of [2/3 estimate, 3/2 estimate]. We will now give an overview of the algorithm used to calculate the estimate; all of the details can be found in this technical report.


link to the report.


Some subsystems, like DHT, need to know the size of the GNUnet network to optimize some parameters of their own protocol. The decentralized nature of GNUnet makes efficient and securely counting the exact number of peers infeasible. Although there are several decentralized algorithms to count the number of peers in a system, so far there is none to do so securely. Other protocols may allow any malicious peer to manipulate the final result or to take advantage of the system to perform Denial of Service (DoS) attacks against the network. GNUnet’s NSE protocol avoids these drawbacks.

NSE security .. _Security:


The NSE subsystem is designed to be resilient against these attacks. It uses proofs of work to prevent one peer from impersonating a large number of participants, which would otherwise allow an adversary to artificially inflate the estimate. The DoS protection comes from the time-based nature of the protocol: the estimates are calculated periodically and out-of-time traffic is either ignored or stored for later retransmission by benign peers. In particular, peers cannot trigger global network communication at will.


The algorithm calculates the estimate by finding the globally closest peer ID to a random, time-based value.

The idea is that the closer the ID is to the random value, the more "densely packed" the ID space is, and therefore, more peers are in the network.


Suppose all peers have IDs between 0 and 100 (our ID space), and the random value is 42. If the closest peer has the ID 70 we can imagine that the average "distance" between peers is around 30 and therefore the are around 3 peers in the whole ID space. On the other hand, if the closest peer has the ID 44, we can imagine that the space is rather packed with peers, maybe as much as 50 of them. Naturally, we could have been rather unlucky, and there is only one peer and happens to have the ID 44. Thus, the current estimate is calculated as the average over multiple rounds, and not just a single sample.


Given that example, one can imagine that the job of the subsystem is to efficiently communicate the ID of the closest peer to the target value to all the other peers, who will calculate the estimate from it.

Target value

The target value itself is generated by hashing the current time, rounded down to an agreed value. If the rounding amount is 1h (default) and the time is 12:34:56, the time to hash would be 12:00:00. The process is repeated each rounding amount (in this example would be every hour). Every repetition is called a round.


The NSE subsystem has some timing control to avoid everybody broadcasting its ID all at one. Once each peer has the target random value, it compares its own ID to the target and calculates the hypothetical size of the network if that peer were to be the closest. Then it compares the hypothetical size with the estimate from the previous rounds. For each value there is an associated point in the period, let’s call it "broadcast time". If its own hypothetical estimate is the same as the previous global estimate, its "broadcast time" will be in the middle of the round. If its bigger it will be earlier and if its smaller (the most likely case) it will be later. This ensures that the peers closest to the target value start broadcasting their ID the first.

Controlled Flooding

When a peer receives a value, first it verifies that it is closer than the closest value it had so far, otherwise it answers the incoming message with a message containing the better value. Then it checks a proof of work that must be included in the incoming message, to ensure that the other peer’s ID is not made up (otherwise a malicious peer could claim to have an ID of exactly the target value every round). Once validated, it compares the broadcast time of the received value with the current time and if it’s not too early, sends the received value to its neighbors. Otherwise it stores the value until the correct broadcast time comes. This prevents unnecessary traffic of sub-optimal values, since a better value can come before the broadcast time, rendering the previous one obsolete and saving the traffic that would have been used to broadcast it to the neighbors.

Calculating the estimate

Once the closest ID has been spread across the network each peer gets the exact distance between this ID and the target value of the round and calculates the estimate with a mathematical formula described in the tech report. The estimate generated with this method for a single round is not very precise. Remember the case of the example, where the only peer is the ID 44 and we happen to generate the target value 42, thinking there are 50 peers in the network. Therefore, the NSE subsystem remembers the last 64 estimates and calculates an average over them, giving a result of which usually has one bit of uncertainty (the real size could be half of the estimate or twice as much). Note that the actual network size is calculated in powers of two of the raw input, thus one bit of uncertainty means a factor of two in the size estimate.


The NSE subsystem has the simplest API of all services, with only two calls: GNUNET_NSE_connect and GNUNET_NSE_disconnect.

The connect call gets a callback function as a parameter and this function is called each time the network agrees on an estimate. This usually is once per round, with some exceptions: if the closest peer has a late local clock and starts spreading its ID after everyone else agreed on a value, the callback might be activated twice in a round, the second value being always bigger than the first. The default round time is set to 1 hour.

The disconnect call disconnects from the NSE subsystem and the callback is no longer called with new estimates.


The callback provides two values: the average and the standard deviation of the last 64 rounds. The values provided by the callback function are logarithmic, this means that the real estimate numbers can be obtained by calculating 2 to the power of the given value (2average). From a statistics point of view this means that:

  • 68% of the time the real size is included in the interval [(2average-stddev), 2]
  • 95% of the time the real size is included in the interval [(2average-2*stddev, 2^average+2*stddev]
  • 99.7% of the time the real size is included in the interval [(2average-3*stddev, 2average+3*stddev]

The expected standard variation for 64 rounds in a network of stable size is 0.2. Thus, we can say that normally:

  • 68% of the time the real size is in the range [-13%, +15%]
  • 95% of the time the real size is in the range [-24%, +32%]
  • 99.7% of the time the real size is in the range [-34%, +52%]

As said in the introduction, we can be quite sure that usually the real size is between one third and three times the estimate. This can of course vary with network conditions. Thus, applications may want to also consider the provided standard deviation value, not only the average (in particular, if the standard variation is very high, the average maybe meaningless: the network size is changing rapidly).


Let’s close with a couple examples.

2^10 = 1024 peers. (The range in which we can be 95% sure is: [2^8, 2^12] = [256, 4096]. We can be very (>99.7%) sure that the network is not a hundred peers and absolutely sure that it is not a million peers, but somewhere around a thousand.)
2^22 = 4 Million peers. (The range in which we can be 99.7% sure is: [2^21.4, 2^22.6] = [2.8M, 6.3M]. We can be sure that the network size is around four million, with absolutely way of it being 1 million.)

To put this in perspective, if someone remembers the LHC Higgs boson results, were announced with "5 sigma" and "6 sigma" certainties. In this case a 5 sigma minimum would be 2 million and a 6 sigma minimum, 1.8 million.

The NSE Client-Service Protocol

As with the API, the client-service protocol is very simple, only has 2 different messages, defined in src/nse/nse.h:

  • GNUNET_MESSAGE_TYPE_NSE_START This message has no parameters and is sent from the client to the service upon connection.
  • GNUNET_MESSAGE_TYPE_NSE_ESTIMATE This message is sent from the service to the client for every new estimate and upon connection. Contains a timestamp for the estimate, the average and the standard deviation for the respective round.

When the GNUNET_NSE_disconnect API call is executed, the client simply disconnects from the service, with no message involved.

NSE Peer-to-Peer Protocol .. _The-NSE-Peer_002dto_002dPeer-Protocol:

The NSE Peer-to-Peer Protocol

GNUNET_MESSAGE_TYPE_NSE_P2P_FLOOD The NSE subsystem only has one message in the P2P protocol, the GNUNET_MESSAGE_TYPE_NSE_P2P_FLOOD message.

This message key contents are the timestamp to identify the round (differences in system clocks may cause some peers to send messages way too early or way too late, so the timestamp allows other peers to identify such messages easily), the proof of work used to make it difficult to mount a Sybil attack, and the public key, which is used to verify the signature on the message.

Every peer stores a message for the previous, current and next round. The messages for the previous and current round are given to peers that connect to us. The message for the next round is simply stored until our system clock advances to the next round. The message for the current round is what we are flooding the network with right now. At the beginning of each round the peer does the following:

  • calculates its own distance to the target value
  • creates, signs and stores the message for the current round (unless it has a better message in the "next round" slot which came early in the previous round)
  • calculates, based on the stored round message (own or received) when to start flooding it to its neighbors

Upon receiving a message the peer checks the validity of the message (round, proof of work, signature). The next action depends on the contents of the incoming message:

  • if the message is worse than the current stored message, the peer sends the current message back immediately, to stop the other peer from spreading suboptimal results
  • if the message is better than the current stored message, the peer stores the new message and calculates the new target time to start spreading it to its neighbors (excluding the one the message came from)
  • if the message is for the previous round, it is compared to the message stored in the "previous round slot", which may then be updated
  • if the message is for the next round, it is compared to the message stored in the "next round slot", which again may then be updated

Finally, when it comes to send the stored message for the current round to the neighbors there is a random delay added for each neighbor, to avoid traffic spikes and minimize cross-messages.

DHT — Distributed Hash Table

GNUnet includes a generic distributed hash table that can be used by developers building P2P applications in the framework. This section documents high-level features and how developers are expected to use the DHT. We have a research paper detailing how the DHT works. Also, Nate’s thesis includes a detailed description and performance analysis (in chapter 6). [R5N2011]


Confirm: Are “Nate’s thesis” and the “research paper” separate entities?

Key features of GNUnet’s DHT include:

  • stores key-value pairs with values up to (approximately) 63k in size
  • works with many underlay network topologies (small-world, random graph), underlay does not need to be a full mesh / clique
  • support for extended queries (more than just a simple ‘key’), filtering duplicate replies within the network (bloomfilter) and content validation (for details, please read the subsection on the block library)
  • can (optionally) return paths taken by the PUT and GET operations to the application
  • provides content replication to handle churn

GNUnet’s DHT is randomized and unreliable. Unreliable means that there is no strict guarantee that a value stored in the DHT is always found — values are only found with high probability. While this is somewhat true in all P2P DHTs, GNUnet developers should be particularly wary of this fact (this will help you write secure, fault-tolerant code). Thus, when writing any application using the DHT, you should always consider the possibility that a value stored in the DHT by you or some other peer might simply not be returned, or returned with a significant delay. Your application logic must be written to tolerate this (naturally, some loss of performance or quality of service is expected in this case).

Block library and plugins

What is a Block?

Blocks are small (< 63k) pieces of data stored under a key (struct GNUNET_HashCode). Blocks have a type (enum GNUNET_BlockType) which defines their data format. Blocks are used in GNUnet as units of static data exchanged between peers and stored (or cached) locally. Uses of blocks include file-sharing (the files are broken up into blocks), the VPN (DNS information is stored in blocks) and the DHT (all information in the DHT and meta-information for the maintenance of the DHT are both stored using blocks). The block subsystem provides a few common functions that must be available for any type of block.

libgnunetblock API .. _The-API-of-libgnunetblock:

The API of libgnunetblock

The block library requires for each (family of) block type(s) a block plugin (implementing gnunet_block_plugin.h) that provides basic functions that are needed by the DHT (and possibly other subsystems) to manage the block. These block plugins are typically implemented within their respective subsystems. The main block library is then used to locate, load and query the appropriate block plugin. Which plugin is appropriate is determined by the block type (which is just a 32-bit integer). Block plugins contain code that specifies which block types are supported by a given plugin. The block library loads all block plugins that are installed at the local peer and forwards the application request to the respective plugin.

The central functions of the block APIs (plugin and main library) are to allow the mapping of blocks to their respective key (if possible) and the ability to check that a block is well-formed and matches a given request (again, if possible). This way, GNUnet can avoid storing invalid blocks, storing blocks under the wrong key and forwarding blocks in response to a query that they do not answer.

One key function of block plugins is that it allows GNUnet to detect duplicate replies (via the Bloom filter). All plugins MUST support detecting duplicate replies (by adding the current response to the Bloom filter and rejecting it if it is encountered again). If a plugin fails to do this, responses may loop in the network.


The query format for any block in GNUnet consists of four main components. First, the type of the desired block must be specified. Second, the query must contain a hash code. The hash code is used for lookups in hash tables and databases and must not be unique for the block (however, if possible a unique hash should be used as this would be best for performance). Third, an optional Bloom filter can be specified to exclude known results; replies that hash to the bits set in the Bloom filter are considered invalid. False-positives can be eliminated by sending the same query again with a different Bloom filter mutator value, which parametrizes the hash function that is used. Finally, an optional application-specific "eXtended query" (xquery) can be specified to further constrain the results. It is entirely up to the type-specific plugin to determine whether or not a given block matches a query (type, hash, Bloom filter, and xquery). Naturally, not all xquery’s are valid and some types of blocks may not support Bloom filters either, so the plugin also needs to check if the query is valid in the first place.

Depending on the results from the plugin, the DHT will then discard the (invalid) query, forward the query, discard the (invalid) reply, cache the (valid) reply, and/or forward the (valid and non-duplicate) reply.

Sample Code

The source code in plugin_block_test.c is a good starting point for new block plugins — it does the minimal work by implementing a plugin that performs no validation at all. The respective shows how to build and install a block plugin.


In conclusion, GNUnet subsystems that want to use the DHT need to define a block format and write a plugin to match queries and replies. For testing, the GNUNET_BLOCK_TYPE_TEST block type can be used; it accepts any query as valid and any reply as matching any query. This type is also used for the DHT command line tools. However, it should NOT be used for normal applications due to the lack of error checking that results from this primitive implementation.

libgnunetdht libgnunetdht ———————————————-

The DHT API itself is pretty simple and offers the usual GET and PUT functions that work as expected. The specified block type refers to the block library which allows the DHT to run application-specific logic for data stored in the network.


When using GET, the main consideration for developers (other than the block library) should be that after issuing a GET, the DHT will continuously cause (small amounts of) network traffic until the operation is explicitly canceled. So GET does not simply send out a single network request once; instead, the DHT will continue to search for data. This is needed to achieve good success rates and also handles the case where the respective PUT operation happens after the GET operation was started. Developers should not cancel an existing GET operation and then explicitly re-start it to trigger a new round of network requests; this is simply inefficient, especially as the internal automated version can be more efficient, for example by filtering results in the network that have already been returned.

If an application that performs a GET request has a set of replies that it already knows and would like to filter, it can call GNUNET_DHT_get_filter_known_results with an array of hashes over the respective blocks to tell the DHT that these results are not desired (any more). This way, the DHT will filter the respective blocks using the block library in the network, which may result in a significant reduction in bandwidth consumption.



inconsistent use of “must” above it’s written “MUST”

In contrast to GET operations, developers must manually re-run PUT operations periodically (if they intend the content to continue to be available). Content stored in the DHT expires or might be lost due to churn. Furthermore, GNUnet’s DHT typically requires multiple rounds of PUT operations before a key-value pair is consistently available to all peers (the DHT randomizes paths and thus storage locations, and only after multiple rounds of PUTs there will be a sufficient number of replicas in large DHTs). An explicit PUT operation using the DHT API will only cause network traffic once, so in order to ensure basic availability and resistance to churn (and adversaries), PUTs must be repeated. While the exact frequency depends on the application, a rule of thumb is that there should be at least a dozen PUT operations within the content lifetime. Content in the DHT typically expires after one day, so DHT PUT operations should be repeated at least every 1-2 hours.


The DHT API also allows applications to monitor messages crossing the local DHT service. The types of messages used by the DHT are GET, PUT and RESULT messages. Using the monitoring API, applications can choose to monitor these requests, possibly limiting themselves to requests for a particular block type.

The monitoring API is not only useful for diagnostics, it can also be used to trigger application operations based on PUT operations. For example, an application may use PUTs to distribute work requests to other peers. The workers would then monitor for PUTs that give them work, instead of looking for work using GET operations. This can be beneficial, especially if the workers have no good way to guess the keys under which work would be stored. Naturally, additional protocols might be needed to ensure that the desired number of workers will process the distributed workload.

DHT Routing Options

There are two important options for GET and PUT requests:

peers should process the request, even if their peer ID is not closest to the key. For a PUT request, this means that all peers that a request traverses may make a copy of the data. Similarly for a GET request, all peers will check their local database for a result. Setting this option can thus significantly improve caching and reduce bandwidth consumption — at the expense of a larger DHT database. If in doubt, we recommend that this option should be used.
the path that a GET or a PUT request is taking through the overlay network. The resulting paths are then returned to the application with the respective result. This allows the receiver of a result to construct a path to the originator of the data, which might then be used for routing. Naturally, setting this option requires additional bandwidth and disk space, so applications should only set this if the paths are needed by the application logic.
the DHT’s peer discovery mechanism and should not be used by applications.
in the future offer performance improvements for clique topologies.

The DHT Client-Service Protocol

PUTting data into the DHT

To store (PUT) data into the DHT, the client sends a struct GNUNET_DHT_ClientPutMessage to the service. This message specifies the block type, routing options, the desired replication level, the expiration time, key, value and a 64-bit unique ID for the operation. The service responds with a struct GNUNET_DHT_ClientPutConfirmationMessage with the same 64-bit unique ID. Note that the service sends the confirmation as soon as it has locally processed the PUT request. The PUT may still be propagating through the network at this time.

In the future, we may want to change this to provide (limited) feedback to the client, for example if we detect that the PUT operation had no effect because the same key-value pair was already stored in the DHT. However, changing this would also require additional state and messages in the P2P interaction.

GETting data from the DHT

To retrieve (GET) data from the DHT, the client sends a struct GNUNET_DHT_ClientGetMessage to the service. The message specifies routing options, a replication level (for replicating the GET, not the content), the desired block type, the key, the (optional) extended query and unique 64-bit request ID.

Additionally, the client may send any number of struct GNUNET_DHT_ClientGetResultSeenMessages to notify the service about results that the client is already aware of. These messages consist of the key, the unique 64-bit ID of the request, and an arbitrary number of hash codes over the blocks that the client is already aware of. As messages are restricted to 64k, a client that already knows more than about a thousand blocks may need to send several of these messages. Naturally, the client should transmit these messages as quickly as possible after the original GET request such that the DHT can filter those results in the network early on. Naturally, as these messages are sent after the original request, it is conceivable that the DHT service may return blocks that match those already known to the client anyway.

In response to a GET request, the service will send struct GNUNET_DHT_ClientResultMessages to the client. These messages contain the block type, expiration, key, unique ID of the request and of course the value (a block). Depending on the options set for the respective operations, the replies may also contain the path the GET and/or the PUT took through the network.

A client can stop receiving replies either by disconnecting or by sending a struct GNUNET_DHT_ClientGetStopMessage which must contain the key and the 64-bit unique ID of the original request. Using an explicit "stop" message is more common as this allows a client to run many concurrent GET operations over the same connection with the DHT service — and to stop them individually.

Monitoring the DHT

To begin monitoring, the client sends a struct GNUNET_DHT_MonitorStartStop message to the DHT service. In this message, flags can be set to enable (or disable) monitoring of GET, PUT and RESULT messages that pass through a peer. The message can also restrict monitoring to a particular block type or a particular key. Once monitoring is enabled, the DHT service will notify the client about any matching event using struct GNUNET_DHT_MonitorGetMessages for GET events, struct GNUNET_DHT_MonitorPutMessage for PUT events and struct GNUNET_DHT_MonitorGetRespMessage for RESULTs. Each of these messages contains all of the information about the event.

The DHT Peer-to-Peer Protocol

Routing GETs or PUTs

When routing GETs or PUTs, the DHT service selects a suitable subset of neighbours for forwarding. The exact number of neighbours can be zero or more and depends on the hop counter of the query (initially zero) in relation to the (log of) the network size estimate, the desired replication level and the peer’s connectivity. Depending on the hop counter and our network size estimate, the selection of the peers maybe randomized or by proximity to the key. Furthermore, requests include a set of peers that a request has already traversed; those peers are also excluded from the selection.

PUTting data into the DHT

To PUT data into the DHT, the service sends a struct PeerPutMessage of type GNUNET_MESSAGE_TYPE_DHT_P2P_PUT to the respective neighbour. In addition to the usual information about the content (type, routing options, desired replication level for the content, expiration time, key and value), the message contains a fixed-size Bloom filter with information about which peers (may) have already seen this request. This Bloom filter is used to ensure that DHT messages never loop back to a peer that has already processed the request. Additionally, the message includes the current hop counter and, depending on the routing options, the message may include the full path that the message has taken so far. The Bloom filter should already contain the identity of the previous hop; however, the path should not include the identity of the previous hop and the receiver should append the identity of the sender to the path, not its own identity (this is done to reduce bandwidth).

GETting data from the DHT

A peer can search the DHT by sending struct PeerGetMessages of type GNUNET_MESSAGE_TYPE_DHT_P2P_GET to other peers. In addition to the usual information about the request (type, routing options, desired replication level for the request, the key and the extended query), a GET request also contains a hop counter, a Bloom filter over the peers that have processed the request already and depending on the routing options the full path traversed by the GET. Finally, a GET request includes a variable-size second Bloom filter and a so-called Bloom filter mutator value which together indicate which replies the sender has already seen. During the lookup, each block that matches they block type, key and extended query is additionally subjected to a test against this Bloom filter. The block plugin is expected to take the hash of the block and combine it with the mutator value and check if the result is not yet in the Bloom filter. The originator of the query will from time to time modify the mutator to (eventually) allow false-positives filtered by the Bloom filter to be returned.

Peers that receive a GET request perform a local lookup (depending on their proximity to the key and the query options) and forward the request to other peers. They then remember the request (including the Bloom filter for blocking duplicate results) and when they obtain a matching, non-filtered response a struct PeerResultMessage of type GNUNET_MESSAGE_TYPE_DHT_P2P_RESULT is forwarded to the previous hop. Whenever a result is forwarded, the block plugin is used to update the Bloom filter accordingly, to ensure that the same result is never forwarded more than once. The DHT service may also cache forwarded results locally if the "CACHE_RESULTS" option is set to "YES" in the configuration.


REGEX — Service discovery using regular expressions

Using the REGEX subsystem, you can discover peers that offer a particular service using regular expressions. The peers that offer a service specify it using a regular expressions. Peers that want to patronize a service search using a string. The REGEX subsystem will then use the DHT to return a set of matching offerers to the patrons.

For the technical details, we have Max’s defense talk and Max’s Master’s thesis.


An additional publication is under preparation and available to team members (in Git).


Missing links to Max’s talk and Master’s thesis

How to run the regex profiler

The gnunet-regex-profiler can be used to profile the usage of mesh/regex for a given set of regular expressions and strings. Mesh/regex allows you to announce your peer ID under a certain regex and search for peers matching a particular regex using a string. See szengel2012ms for a full introduction.

First of all, the regex profiler uses GNUnet testbed, thus all the implications for testbed also apply to the regex profiler (for example you need password-less ssh login to the machines listed in your hosts file).


Moreover, an appropriate configuration file is needed. In the following paragraph the important details are highlighted.

Announcing of the regular expressions is done by the gnunet-daemon-regexprofiler, therefore you have to make sure it is started, by adding it to the START_ON_DEMAND set of ARM:


Furthermore you have to specify the location of the binary:

# Location of the gnunet-daemon-regexprofiler binary.
BINARY = /home/szengel/gnunet/src/mesh/.libs/gnunet-daemon-regexprofiler
# Regex prefix that will be applied to all regular expressions and
# search string.

When running the profiler with a large scale deployment, you probably want to reduce the workload of each peer. Use the following options to do this.

# Force network size estimation
# Disable RC-file for Bloom filter? (for benchmarking with limited IO
# availability)
# Disable Bloom filter entirely
# Minimize proof-of-work CPU consumption by NSE


To finally run the profiler some options and the input data need to be specified on the command line.

gnunet-regex-profiler -c config-file -d log-file -n num-links \
-p path-compression-length -s search-delay -t matching-timeout \
-a num-search-strings hosts-file policy-dir search-strings-file


  • ... config-file means the configuration file created earlier.
  • ... log-file is the file where to write statistics output.
  • ... num-links indicates the number of random links between started peers.
  • ... path-compression-length is the maximum path compression length in the DFA.
  • ... search-delay time to wait between peers finished linking and starting to match strings.
  • ... matching-timeout timeout after which to cancel the searching.
  • ... num-search-strings number of strings in the search-strings-file.
  • ... the hosts-file should contain a list of hosts for the testbed, one per line in the following format:

  • ... the policy-dir is a folder containing text files containing one or more regular expressions. A peer is started for each file in that folder and the regular expressions in the corresponding file are announced by this peer.
  • ... the search-strings-file is a text file containing search strings, one in each line.

You can create regular expressions and search strings for every AS in the Internet using the attached scripts. You need one of the CAIDA routeviews prefix2as data files for this. Run <filename> <output path>

to create the regular expressions and <input path> <outfile>

to create a search strings file from the previously created regular expressions.

CADET — Confidential Ad-hoc Decentralized End-to-end Transport

The CADET subsystem in GNUnet is responsible for secure end-to-end communications between nodes in the GNUnet overlay network. CADET builds on the CORE subsystem, which provides for the link-layer communication, by adding routing, forwarding, and additional security to the connections. CADET offers the same cryptographic services as CORE, but on an end-to-end level. This is done so peers retransmitting traffic on behalf of other peers cannot access the payload data.

  • CADET provides confidentiality with so-called perfect forward secrecy; we use ECDHE powered by Curve25519 for the key exchange and then use symmetric encryption, encrypting with both AES-256 and Twofish
  • authentication is achieved by signing the ephemeral keys using Ed25519, a deterministic variant of ECDSA
  • integrity protection (using SHA-512 to do encrypt-then-MAC, although only 256 bits are sent to reduce overhead)
  • replay protection (using nonces, timestamps, challenge-response, message counters and ephemeral keys)
  • liveness (keep-alive messages, timeout)

Additional to the CORE-like security benefits, CADET offers other properties that make it a more universal service than CORE.

  • CADET can establish channels to arbitrary peers in GNUnet. If a peer is not immediately reachable, CADET will find a path through the network and ask other peers to retransmit the traffic on its behalf.
  • CADET offers (optional) reliability mechanisms. In a reliable channel traffic is guaranteed to arrive complete, unchanged and in-order.
  • CADET takes care of flow and congestion control mechanisms, not allowing the sender to send more traffic than the receiver or the network are able to process.


The CADET API (defined in gnunet_cadet_service.h) is the messaging API used by P2P applications built using GNUnet. It provides applications the ability to send and receive encrypted messages to any peer participating in GNUnet. The API is heavily based on the CORE API.

CADET delivers messages to other peers in "channels". A channel is a permanent connection defined by a destination peer (identified by its public key) and a port number. Internally, CADET tunnels all channels towards a destination peer using one session key and relays the data on multiple "connections", independent from the channels.

Each channel has optional parameters, the most important being the reliability flag. Should a message get lost on TRANSPORT/CORE level, if a channel is created with as reliable, CADET will retransmit the lost message and deliver it in order to the destination application.


To communicate with other peers using CADET, it is necessary to first connect to the service using GNUNET_CADET_connect. This function takes several parameters in form of callbacks, to allow the client to react to various events, like incoming channels or channels that terminate, as well as specify a list of ports the client wishes to listen to (at the moment it is not possible to start listening on further ports once connected, but nothing prevents a client to connect several times to CADET, even do one connection per listening port). The function returns a handle which has to be used for any further interaction with the service.


To connect to a remote peer, a client has to call the GNUNET_CADET_channel_create function. The most important parameters given are the remote peer’s identity (it public key) and a port, which specifies which application on the remote peer to connect to, similar to TCP/UDP ports. CADET will then find the peer in the GNUnet network and establish the proper low-level connections and do the necessary key exchanges to assure and authenticated, secure and verified communication. Similar to GNUNET_CADET_connect,GNUNET_CADET_create_channel returns a handle to interact with the created channel.


For every message the client wants to send to the remote application, GNUNET_CADET_notify_transmit_ready must be called, indicating the channel on which the message should be sent and the size of the message (but not the message itself!). Once CADET is ready to send the message, the provided callback will fire, and the message contents are provided to this callback.

Please note the CADET does not provide an explicit notification of when a channel is connected. In loosely connected networks, like big wireless mesh networks, this can take several seconds, even minutes in the worst case. To be alerted when a channel is online, a client can call GNUNET_CADET_notify_transmit_ready immediately after GNUNET_CADET_create_channel. When the callback is activated, it means that the channel is online. The callback can give 0 bytes to CADET if no message is to be sent, this is OK.


If a transmission was requested but before the callback fires it is no longer needed, it can be canceled with GNUNET_CADET_notify_transmit_ready_cancel, which uses the handle given back by GNUNET_CADET_notify_transmit_ready. As in the case of CORE, only one message can be requested at a time: a client must not call GNUNET_CADET_notify_transmit_ready again until the callback is called or the request is canceled.


When a channel is no longer needed, a client can call GNUNET_CADET_channel_destroy to get rid of it. Note that CADET will try to transmit all pending traffic before notifying the remote peer of the destruction of the channel, including retransmitting lost messages if the channel was reliable.

Incoming channels, channels being closed by the remote peer, and traffic on any incoming or outgoing channels are given to the client when CADET executes the callbacks given to it at the time of GNUNET_CADET_connect.


Finally, when an application no longer wants to use CADET, it should call GNUNET_CADET_disconnect, but first all channels and pending transmissions must be closed (otherwise CADET will complain).

RPS — Random peer sampling

In literature, Random Peer Sampling (RPS) refers to the problem of reliably [1] drawing random samples from an unstructured p2p network.

Doing so in a reliable manner is not only hard because of inherent problems but also because of possible malicious peers that could try to bias the selection.

It is useful for all kind of gossip protocols that require the selection of random peers in the whole network like gathering statistics, spreading and aggregating information in the network, load balancing and overlay topology management.

The approach chosen in the RPS service implementation in GNUnet follows the Brahms design.

The current state is "work in progress". There are a lot of things that need to be done, primarily finishing the experimental evaluation and a re-design of the API.

The abstract idea is to subscribe to connect to/start the RPS service and request random peers that will be returned when they represent a random selection from the whole network with high probability.

An additional feature to the original Brahms-design is the selection of sub-groups: The GNUnet implementation of RPS enables clients to ask for random peers from a group that is defined by a common shared secret. (The secret could of course also be public, depending on the use-case.)

Another addition to the original protocol was made: The sampler mechanism that was introduced in Brahms was slightly adapted and used to actually sample the peers and returned to the client. This is necessary as the original design only keeps peers connected to random other peers in the network. In order to return random peers to client requests independently random, they cannot be drawn from the connected peers. The adapted sampler makes sure that each request for random peers is independent from the others.


The high-level concept of Brahms is two-fold: Combining push-pull gossip with locally fixing a assumed bias using cryptographic min-wise permutations. The central data structure is the view - a peer’s current local sample. This view is used to select peers to push to and pull from. This simple mechanism can be biased easily. For this reason Brahms ‘fixes’ the bias by using the so-called sampler. A data structure that takes a list of elements as input and outputs a random one of them independently of the frequency in the input set. Both an element that was put into the sampler a single time and an element that was put into it a million times have the same probability of being the output. This is achieved with exploiting min-wise independent permutations. In the RPS service we use HMACs: On the initialisation of a sampler element, a key is chosen at random. On each input the HMAC with the random key is computed. The sampler element keeps the element with the minimal HMAC.

In order to fix the bias in the view, a fraction of the elements in the view are sampled through the sampler from the random stream of peer IDs.

According to the theoretical analysis of Bortnikov et al. this suffices to keep the network connected and having random peers in the view.

"Reliable" in this context means having no bias, neither spatial, nor temporal, nor through malicious activity.

Peer-to-Peer Set Operations

Many applications

SET — Peer to peer set operations (Deprecated)


The SET subsystem is in process of being replaced by the SETU and SETI subsystems, which provide basically the same functionality, just using two different subsystems. SETI and SETU should be used for new code.

The SET service implements efficient set operations between two peers over a CADET tunnel. Currently, set union and set intersection are the only supported operations. Elements of a set consist of an element type and arbitrary binary data. The size of an element’s data is limited to around 62 KB.

Local Sets

Sets created by a local client can be modified and reused for multiple operations. As each set operation requires potentially expensive special auxiliary data to be computed for each element of a set, a set can only participate in one type of set operation (either union or intersection). The type of a set is determined upon its creation. If a the elements of a set are needed for an operation of a different type, all of the set’s element must be copied to a new set of appropriate type.

Set Modifications

Even when set operations are active, one can add to and remove elements from a set. However, these changes will only be visible to operations that have been created after the changes have taken place. That is, every set operation only sees a snapshot of the set from the time the operation was started. This mechanism is not implemented by copying the whole set, but by attaching generation information to each element and operation.

Set Operations

Set operations can be started in two ways: Either by accepting an operation request from a remote peer, or by requesting a set operation from a remote peer. Set operations are uniquely identified by the involved peers, an application id and the operation type.

The client is notified of incoming set operations by set listeners. A set listener listens for incoming operations of a specific operation type and application id. Once notified of an incoming set request, the client can accept the set request (providing a local set for the operation) or reject it.

Result Elements

The SET service has three result modes that determine how an operation’s result set is delivered to the client:

  • Full Result Set. All elements of set resulting from the set operation are returned to the client.
  • Added Elements. Only elements that result from the operation and are not already in the local peer’s set are returned. Note that for some operations (like set intersection) this result mode will never return any elements. This can be useful if only the remove peer is actually interested in the result of the set operation.
  • Removed Elements. Only elements that are in the local peer’s initial set but not in the operation’s result set are returned. Note that for some operations (like set union) this result mode will never return any elements. This can be useful if only the remove peer is actually interested in the result of the set operation.



New sets are created with GNUNET_SET_create. Both the local peer’s configuration (as each set has its own client connection) and the operation type must be specified. The set exists until either the client calls GNUNET_SET_destroy or the client’s connection to the service is disrupted. In the latter case, the client is notified by the return value of functions dealing with sets. This return value must always be checked.

Elements are added and removed with GNUNET_SET_add_element and GNUNET_SET_remove_element.


Listeners are created with GNUNET_SET_listen. Each time time a remote peer suggests a set operation with an application id and operation type matching a listener, the listener’s callback is invoked. The client then must synchronously call either GNUNET_SET_accept or GNUNET_SET_reject. Note that the operation will not be started until the client calls GNUNET_SET_commit (see Section "Supplying a Set").


Operations to be initiated by the local peer are created with GNUNET_SET_prepare. Note that the operation will not be started until the client calls GNUNET_SET_commit (see Section "Supplying a Set").

Supplying a Set

To create symmetry between the two ways of starting a set operation (accepting and initiating it), the operation handles returned by GNUNET_SET_accept and GNUNET_SET_prepare do not yet have a set to operate on, thus they can not do any work yet.

The client must call GNUNET_SET_commit to specify a set to use for an operation. GNUNET_SET_commit may only be called once per set operation.

The Result Callback

Clients must specify both a result mode and a result callback with GNUNET_SET_accept and GNUNET_SET_prepare. The result callback with a status indicating either that an element was received, or the operation failed or succeeded. The interpretation of the received element depends on the result mode. The callback needs to know which result mode it is used in, as the arguments do not indicate if an element is part of the full result set, or if it is in the difference between the original set and the final set.

The SET Client-Service Protocol

Creating Sets

For each set of a client, there exists a client connection to the service. Sets are created by sending the GNUNET_SERVICE_SET_CREATE message over a new client connection. Multiple operations for one set are multiplexed over one client connection, using a request id supplied by the client.


Each listener also requires a separate client connection. By sending the GNUNET_SERVICE_SET_LISTEN message, the client notifies the service of the application id and operation type it is interested in. A client rejects an incoming request by sending GNUNET_SERVICE_SET_REJECT on the listener’s client connection. In contrast, when accepting an incoming request, a GNUNET_SERVICE_SET_ACCEPT message must be sent over the set that is supplied for the set operation.

Initiating Operations

Operations with remote peers are initiated by sending a GNUNET_SERVICE_SET_EVALUATE message to the service. The client connection that this message is sent by determines the set to use.

Modifying Sets

Sets are modified with the GNUNET_SERVICE_SET_ADD and GNUNET_SERVICE_SET_REMOVE messages.

Results and Operation Status

The service notifies the client of result elements and success/failure of a set operation with the GNUNET_SERVICE_SET_RESULT message.

Iterating Sets

All elements of a set can be requested by sending GNUNET_SERVICE_SET_ITER_REQUEST. The server responds with GNUNET_SERVICE_SET_ITER_ELEMENT and eventually terminates the iteration with GNUNET_SERVICE_SET_ITER_DONE. After each received element, the client must send GNUNET_SERVICE_SET_ITER_ACK. Note that only one set iteration may be active for a set at any given time.

The SET Intersection Peer-to-Peer Protocol

The intersection protocol operates over CADET and starts with a GNUNET_MESSAGE_TYPE_SET_P2P_OPERATION_REQUEST being sent by the peer initiating the operation to the peer listening for inbound requests. It includes the number of elements of the initiating peer, which is used to decide which side will send a Bloom filter first.

The listening peer checks if the operation type and application identifier are acceptable for its current state. If not, it responds with a GNUNET_MESSAGE_TYPE_SET_RESULT and a status of GNUNET_SET_STATUS_FAILURE (and terminates the CADET channel).

If the application accepts the request, the listener sends back a GNUNET_MESSAGE_TYPE_SET_INTERSECTION_P2P_ELEMENT_INFO if it has more elements in the set than the client. Otherwise, it immediately starts with the Bloom filter exchange. If the initiator receives a GNUNET_MESSAGE_TYPE_SET_INTERSECTION_P2P_ELEMENT_INFO response, it beings the Bloom filter exchange, unless the set size is indicated to be zero, in which case the intersection is considered finished after just the initial handshake.

The Bloom filter exchange

In this phase, each peer transmits a Bloom filter over the remaining keys of the local set to the other peer using a GNUNET_MESSAGE_TYPE_SET_INTERSECTION_P2P_BF message. This message additionally includes the number of elements left in the sender’s set, as well as the XOR over all of the keys in that set.

The number of bits ‘k’ set per element in the Bloom filter is calculated based on the relative size of the two sets. Furthermore, the size of the Bloom filter is calculated based on ‘k’ and the number of elements in the set to maximize the amount of data filtered per byte transmitted on the wire (while avoiding an excessively high number of iterations).

The receiver of the message removes all elements from its local set that do not pass the Bloom filter test. It then checks if the set size of the sender and the XOR over the keys match what is left of its own set. If they do, it sends a GNUNET_MESSAGE_TYPE_SET_INTERSECTION_P2P_DONE back to indicate that the latest set is the final result. Otherwise, the receiver starts another Bloom filter exchange, except this time as the sender.


Bloomfilter operations are probabilistic: With some non-zero probability the test may incorrectly say an element is in the set, even though it is not.

To mitigate this problem, the intersection protocol iterates exchanging Bloom filters using a different random 32-bit salt in each iteration (the salt is also included in the message). With different salts, set operations may fail for different elements. Merging the results from the executions, the probability of failure drops to zero.

The iterations terminate once both peers have established that they have sets of the same size, and where the XOR over all keys computes the same 512-bit value (leaving a failure probability of 2-511).

The SET Union Peer-to-Peer Protocol

The SET union protocol is based on Eppstein’s efficient set reconciliation without prior context. You should read this paper first if you want to understand the protocol.


Link to Eppstein’s paper!

The union protocol operates over CADET and starts with a GNUNET_MESSAGE_TYPE_SET_P2P_OPERATION_REQUEST being sent by the peer initiating the operation to the peer listening for inbound requests. It includes the number of elements of the initiating peer, which is currently not used.

The listening peer checks if the operation type and application identifier are acceptable for its current state. If not, it responds with a GNUNET_MESSAGE_TYPE_SET_RESULT and a status of GNUNET_SET_STATUS_FAILURE (and terminates the CADET channel).

If the application accepts the request, it sends back a strata estimator using a message of type GNUNET_MESSAGE_TYPE_SET_UNION_P2P_SE. The initiator evaluates the strata estimator and initiates the exchange of invertible Bloom filters, sending a GNUNET_MESSAGE_TYPE_SET_UNION_P2P_IBF.

During the IBF exchange, if the receiver cannot invert the Bloom filter or detects a cycle, it sends a larger IBF in response (up to a defined maximum limit; if that limit is reached, the operation fails). Elements decoded while processing the IBF are transmitted to the other peer using GNUNET_MESSAGE_TYPE_SET_P2P_ELEMENTS, or requested from the other peer using GNUNET_MESSAGE_TYPE_SET_P2P_ELEMENT_REQUESTS messages, depending on the sign observed during decoding of the IBF. Peers respond to a GNUNET_MESSAGE_TYPE_SET_P2P_ELEMENT_REQUESTS message with the respective element in a GNUNET_MESSAGE_TYPE_SET_P2P_ELEMENTS message. If the IBF fully decodes, the peer responds with a GNUNET_MESSAGE_TYPE_SET_UNION_P2P_DONE message instead of another GNUNET_MESSAGE_TYPE_SET_UNION_P2P_IBF.

All Bloom filter operations use a salt to mingle keys before hashing them into buckets, such that future iterations have a fresh chance of succeeding if they failed due to collisions before.

SETI — Peer to peer set intersections

The SETI service implements efficient set intersection between two peers over a CADET tunnel. Elements of a set consist of an element type and arbitrary binary data. The size of an element’s data is limited to around 62 KB.

Intersection Sets

Sets created by a local client can be modified (by adding additional elements) and reused for multiple operations. If elements are to be removed, a fresh set must be created by the client.

Set Intersection Modifications

Even when set operations are active, one can add elements to a set. However, these changes will only be visible to operations that have been created after the changes have taken place. That is, every set operation only sees a snapshot of the set from the time the operation was started. This mechanism is not implemented by copying the whole set, but by attaching generation information to each element and operation.

Set Intersection Operations

Set operations can be started in two ways: Either by accepting an operation request from a remote peer, or by requesting a set operation from a remote peer. Set operations are uniquely identified by the involved peers, an application id and the operation type.

The client is notified of incoming set operations by set listeners. A set listener listens for incoming operations of a specific operation type and application id. Once notified of an incoming set request, the client can accept the set request (providing a local set for the operation) or reject it.

Intersection Result Elements

The SET service has two result modes that determine how an operation’s result set is delivered to the client:

  • Return intersection. All elements of set resulting from the set intersection are returned to the client.
  • Removed Elements. Only elements that are in the local peer’s initial set but not in the intersection are returned.


Intersection Set API

New sets are created with GNUNET_SETI_create. Only the local peer’s configuration (as each set has its own client connection) must be provided. The set exists until either the client calls GNUNET_SET_destroy or the client’s connection to the service is disrupted. In the latter case, the client is notified by the return value of functions dealing with sets. This return value must always be checked.

Elements are added with GNUNET_SET_add_element.

Intersection Listeners

Listeners are created with GNUNET_SET_listen. Each time time a remote peer suggests a set operation with an application id and operation type matching a listener, the listener’s callback is invoked. The client then must synchronously call either GNUNET_SET_accept or GNUNET_SET_reject. Note that the operation will not be started until the client calls GNUNET_SET_commit (see Section "Supplying a Set").

Intersection Operations

Operations to be initiated by the local peer are created with GNUNET_SET_prepare. Note that the operation will not be started until the client calls GNUNET_SET_commit (see Section "Supplying a Set").

Supplying a Set for Intersection

To create symmetry between the two ways of starting a set operation (accepting and initiating it), the operation handles returned by GNUNET_SET_accept and GNUNET_SET_prepare do not yet have a set to operate on, thus they can not do any work yet.

The client must call GNUNET_SET_commit to specify a set to use for an operation. GNUNET_SET_commit may only be called once per set operation.

The Intersection Result Callback

Clients must specify both a result mode and a result callback with GNUNET_SET_accept and GNUNET_SET_prepare. The result callback with a status indicating either that an element was received, or the operation failed or succeeded. The interpretation of the received element depends on the result mode. The callback needs to know which result mode it is used in, as the arguments do not indicate if an element is part of the full result set, or if it is in the difference between the original set and the final set.

The SETI Client-Service Protocol

Creating Intersection Sets

For each set of a client, there exists a client connection to the service. Sets are created by sending the GNUNET_SERVICE_SETI_CREATE message over a new client connection. Multiple operations for one set are multiplexed over one client connection, using a request id supplied by the client.

Listeners for Intersection

Each listener also requires a separate client connection. By sending the GNUNET_SERVICE_SETI_LISTEN message, the client notifies the service of the application id and operation type it is interested in. A client rejects an incoming request by sending GNUNET_SERVICE_SETI_REJECT on the listener’s client connection. In contrast, when accepting an incoming request, a GNUNET_SERVICE_SETI_ACCEPT message must be sent over the set that is supplied for the set operation.

Initiating Intersection Operations

Operations with remote peers are initiated by sending a GNUNET_SERVICE_SETI_EVALUATE message to the service. The client connection that this message is sent by determines the set to use.

Modifying Intersection Sets

Sets are modified with the GNUNET_SERVICE_SETI_ADD message.

Intersection Results and Operation Status

The service notifies the client of result elements and success/failure of a set operation with the GNUNET_SERVICE_SETI_RESULT message.

The SETI Intersection Peer-to-Peer Protocol

The intersection protocol operates over CADET and starts with a GNUNET_MESSAGE_TYPE_SETI_P2P_OPERATION_REQUEST being sent by the peer initiating the operation to the peer listening for inbound requests. It includes the number of elements of the initiating peer, which is used to decide which side will send a Bloom filter first.

The listening peer checks if the operation type and application identifier are acceptable for its current state. If not, it responds with a GNUNET_MESSAGE_TYPE_SETI_RESULT and a status of GNUNET_SETI_STATUS_FAILURE (and terminates the CADET channel).

If the application accepts the request, the listener sends back a GNUNET_MESSAGE_TYPE_SETI_P2P_ELEMENT_INFO if it has more elements in the set than the client. Otherwise, it immediately starts with the Bloom filter exchange. If the initiator receives a GNUNET_MESSAGE_TYPE_SETI_P2P_ELEMENT_INFO response, it beings the Bloom filter exchange, unless the set size is indicated to be zero, in which case the intersection is considered finished after just the initial handshake.

The Bloom filter exchange in SETI

In this phase, each peer transmits a Bloom filter over the remaining keys of the local set to the other peer using a GNUNET_MESSAGE_TYPE_SETI_P2P_BF message. This message additionally includes the number of elements left in the sender’s set, as well as the XOR over all of the keys in that set.

The number of bits ‘k’ set per element in the Bloom filter is calculated based on the relative size of the two sets. Furthermore, the size of the Bloom filter is calculated based on ‘k’ and the number of elements in the set to maximize the amount of data filtered per byte transmitted on the wire (while avoiding an excessively high number of iterations).

The receiver of the message removes all elements from its local set that do not pass the Bloom filter test. It then checks if the set size of the sender and the XOR over the keys match what is left of its own set. If they do, it sends a GNUNET_MESSAGE_TYPE_SETI_P2P_DONE back to indicate that the latest set is the final result. Otherwise, the receiver starts another Bloom filter exchange, except this time as the sender.

Intersection Salt

Bloom filter operations are probabilistic: With some non-zero probability the test may incorrectly say an element is in the set, even though it is not.

To mitigate this problem, the intersection protocol iterates exchanging Bloom filters using a different random 32-bit salt in each iteration (the salt is also included in the message). With different salts, set operations may fail for different elements. Merging the results from the executions, the probability of failure drops to zero.

The iterations terminate once both peers have established that they have sets of the same size, and where the XOR over all keys computes the same 512-bit value (leaving a failure probability of 2-511).

SETU — Peer to peer set unions

The SETU service implements efficient set union operations between two peers over a CADET tunnel. Elements of a set consist of an element type and arbitrary binary data. The size of an element’s data is limited to around 62 KB.

Union Sets

Sets created by a local client can be modified (by adding additional elements) and reused for multiple operations. If elements are to be removed, a fresh set must be created by the client.

Set Union Modifications

Even when set operations are active, one can add elements to a set. However, these changes will only be visible to operations that have been created after the changes have taken place. That is, every set operation only sees a snapshot of the set from the time the operation was started. This mechanism is not implemented by copying the whole set, but by attaching generation information to each element and operation.

Set Union Operations

Set operations can be started in two ways: Either by accepting an operation request from a remote peer, or by requesting a set operation from a remote peer. Set operations are uniquely identified by the involved peers, an application id and the operation type.

The client is notified of incoming set operations by set listeners. A set listener listens for incoming operations of a specific operation type and application id. Once notified of an incoming set request, the client can accept the set request (providing a local set for the operation) or reject it.

Union Result Elements

The SET service has three result modes that determine how an operation’s result set is delivered to the client:

  • Locally added Elements. Elements that are in the union but not already in the local peer’s set are returned.
  • Remote added Elements. Additionally, notify the client if the remote peer lacked some elements and thus also return to the local client those elements that we are sending to the remote peer to be added to its union. Obtaining these elements requires setting the GNUNET_SETU_OPTION_SYMMETRIC option.


Union Set API

New sets are created with GNUNET_SETU_create. Only the local peer’s configuration (as each set has its own client connection) must be provided. The set exists until either the client calls GNUNET_SETU_destroy or the client’s connection to the service is disrupted. In the latter case, the client is notified by the return value of functions dealing with sets. This return value must always be checked.

Elements are added with GNUNET_SETU_add_element.

Union Listeners

Listeners are created with GNUNET_SETU_listen. Each time time a remote peer suggests a set operation with an application id and operation type matching a listener, the listener’s callback is invoked. The client then must synchronously call either GNUNET_SETU_accept or GNUNET_SETU_reject. Note that the operation will not be started until the client calls GNUNET_SETU_commit (see Section "Supplying a Set").

Union Operations

Operations to be initiated by the local peer are created with GNUNET_SETU_prepare. Note that the operation will not be started until the client calls GNUNET_SETU_commit (see Section "Supplying a Set").

Supplying a Set for Union

To create symmetry between the two ways of starting a set operation (accepting and initiating it), the operation handles returned by GNUNET_SETU_accept and GNUNET_SETU_prepare do not yet have a set to operate on, thus they can not do any work yet.

The client must call GNUNET_SETU_commit to specify a set to use for an operation. GNUNET_SETU_commit may only be called once per set operation.

The Union Result Callback

Clients must specify both a result mode and a result callback with GNUNET_SETU_accept and GNUNET_SETU_prepare. The result callback with a status indicating either that an element was received, transmitted to the other peer (if this information was requested), or if the operation failed or ultimately succeeded.

The SETU Client-Service Protocol

Creating Union Sets

For each set of a client, there exists a client connection to the service. Sets are created by sending the GNUNET_SERVICE_SETU_CREATE message over a new client connection. Multiple operations for one set are multiplexed over one client connection, using a request id supplied by the client.

Listeners for Union

Each listener also requires a separate client connection. By sending the GNUNET_SERVICE_SETU_LISTEN message, the client notifies the service of the application id and operation type it is interested in. A client rejects an incoming request by sending GNUNET_SERVICE_SETU_REJECT on the listener’s client connection. In contrast, when accepting an incoming request, a GNUNET_SERVICE_SETU_ACCEPT message must be sent over the set that is supplied for the set operation.

Initiating Union Operations

Operations with remote peers are initiated by sending a GNUNET_SERVICE_SETU_EVALUATE message to the service. The client connection that this message is sent by determines the set to use.

Modifying Union Sets

Sets are modified with the GNUNET_SERVICE_SETU_ADD message.

Union Results and Operation Status

The service notifies the client of result elements and success/failure of a set operation with the GNUNET_SERVICE_SETU_RESULT message.

The SETU Union Peer-to-Peer Protocol

The SET union protocol is based on Eppstein’s efficient set reconciliation without prior context. You should read this paper first if you want to understand the protocol.


Link to Eppstein’s paper!

The union protocol operates over CADET and starts with a GNUNET_MESSAGE_TYPE_SETU_P2P_OPERATION_REQUEST being sent by the peer initiating the operation to the peer listening for inbound requests. It includes the number of elements of the initiating peer, which is currently not used.

The listening peer checks if the operation type and application identifier are acceptable for its current state. If not, it responds with a GNUNET_MESSAGE_TYPE_SETU_RESULT and a status of GNUNET_SETU_STATUS_FAILURE (and terminates the CADET channel).

If the application accepts the request, it sends back a strata estimator using a message of type GNUNET_MESSAGE_TYPE_SETU_P2P_SE. The initiator evaluates the strata estimator and initiates the exchange of invertible Bloom filters, sending a GNUNET_MESSAGE_TYPE_SETU_P2P_IBF.

During the IBF exchange, if the receiver cannot invert the Bloom filter or detects a cycle, it sends a larger IBF in response (up to a defined maximum limit; if that limit is reached, the operation fails). Elements decoded while processing the IBF are transmitted to the other peer using GNUNET_MESSAGE_TYPE_SETU_P2P_ELEMENTS, or requested from the other peer using GNUNET_MESSAGE_TYPE_SETU_P2P_ELEMENT_REQUESTS messages, depending on the sign observed during decoding of the IBF. Peers respond to a GNUNET_MESSAGE_TYPE_SETU_P2P_ELEMENT_REQUESTS message with the respective element in a GNUNET_MESSAGE_TYPE_SETU_P2P_ELEMENTS message. If the IBF fully decodes, the peer responds with a GNUNET_MESSAGE_TYPE_SETU_P2P_DONE message instead of another GNUNET_MESSAGE_TYPE_SETU_P2P_IBF.

All Bloom filter operations use a salt to mingle keys before hashing them into buckets, such that future iterations have a fresh chance of succeeding if they failed due to collisions before.

VPN and VPN Support

GNS and GNS Support

The GNU Name System is a secure and censorship-resistant alternative to the Domain Name System (DNS) in common use for resolving domain names.

GNS — the GNU Name System

The GNU Name System (GNS) is a decentralized database that enables users to securely resolve names to values. Names can be used to identify other users (for example, in social networking), or network services (for example, VPN services running at a peer in GNUnet, or purely IP-based services on the Internet). Users interact with GNS by typing in a hostname that ends in a top-level domain that is configured in the “GNS” section, matches an identity of the user or ends in a Base32-encoded public key.

Videos giving an overview of most of the GNS and the motivations behind it is available here and here. The remainder of this chapter targets developers that are familiar with high level concepts of GNS as presented in these talks.


Link to videos and GNS talks?

GNS-aware applications should use the GNS resolver to obtain the respective records that are stored under that name in GNS. Each record consists of a type, value, expiration time and flags.

The type specifies the format of the value. Types below 65536 correspond to DNS record types, larger values are used for GNS-specific records. Applications can define new GNS record types by reserving a number and implementing a plugin (which mostly needs to convert the binary value representation to a human-readable text format and vice-versa). The expiration time specifies how long the record is to be valid. The GNS API ensures that applications are only given non-expired values. The flags are typically irrelevant for applications, as GNS uses them internally to control visibility and validity of records.

Records are stored along with a signature. The signature is generated using the private key of the authoritative zone. This allows any GNS resolver to verify the correctness of a name-value mapping.

Internally, GNS uses the NAMECACHE to cache information obtained from other users, the NAMESTORE to store information specific to the local users, and the DHT to exchange data between users. A plugin API is used to enable applications to define new GNS record types.


The GNS API itself is extremely simple. Clients first connect to the GNS service using GNUNET_GNS_connect. They can then perform lookups using GNUNET_GNS_lookup or cancel pending lookups using GNUNET_GNS_lookup_cancel. Once finished, clients disconnect using GNUNET_GNS_disconnect.

Looking up records

GNUNET_GNS_lookup takes a number of arguments:

be resolved. This can be any valid DNS or GNS hostname.
needs to specify the public key of the GNS zone against which the resolution should be done. Note that a key must be provided, the client should look up plausible values using its configuration, the identity service and by attempting to interpret the TLD as a base32-encoded public key.
to look for. While all records for the given name will be returned, this can be important if the client wants to resolve record types that themselves delegate resolution, such as CNAME, PKEY or GNS2DNS. Resolving a record of any of these types will only work if the respective record type is specified in the request, as the GNS resolver will otherwise follow the delegation and return the records from the respective destination, instead of the delegating record.
GNUNET_NO. Setting it to GNUNET_YES disables resolution via the overlay network.
their respective zones can automatically be learned and added to the "shorten zone". If this is desired, clients must pass the private key of the shorten zone. If NULL is passed, shortening is disabled.
the function to call with the result. It is given proc_cls, the number of records found (possibly zero) and the array of the records as arguments. proc will only be called once. After proc,> has been called, the lookup must no longer be canceled.

proc_cls The closure for proc.

Accessing the records

The libgnunetgnsrecord library provides an API to manipulate the GNS record array that is given to proc. In particular, it offers functions such as converting record values to human-readable strings (and back). However, most libgnunetgnsrecord functions are not interesting to GNS client applications.

For DNS records, the libgnunetdnsparser library provides functions for parsing (and serializing) common types of DNS records.

Creating records

Creating GNS records is typically done by building the respective record information (possibly with the help of libgnunetgnsrecord and libgnunetdnsparser) and then using the libgnunetnamestore to publish the information. The GNS API is not involved in this operation.

Future work

In the future, we want to expand libgnunetgns to allow applications to observe shortening operations performed during GNS resolution, for example so that users can receive visual feedback when this happens.


The libgnunetgnsrecord library is used to manipulate GNS records (in plaintext or in their encrypted format). Applications mostly interact with libgnunetgnsrecord by using the functions to convert GNS record values to strings or vice-versa, or to lookup a GNS record type number by name (or vice-versa). The library also provides various other functions that are mostly used internally within GNS, such as converting keys to names, checking for expiration, encrypting GNS records to GNS blocks, verifying GNS block signatures and decrypting GNS records from GNS blocks.

We will now discuss the four commonly used functions of the API. libgnunetgnsrecord does not perform these operations itself, but instead uses plugins to perform the operation. GNUnet includes plugins to support common DNS record types as well as standard GNS record types.

Value handling

GNUNET_GNSRECORD_value_to_string can be used to convert the (binary) representation of a GNS record value to a human readable, 0-terminated UTF-8 string. NULL is returned if the specified record type is not supported by any available plugin.

GNUNET_GNSRECORD_string_to_value can be used to try to convert a human readable string to the respective (binary) representation of a GNS record value.

Type handling

GNUNET_GNSRECORD_typename_to_number can be used to obtain the numeric value associated with a given typename. For example, given the typename "A" (for DNS A reocrds), the function will return the number 1. A list of common DNS record types is here. Note that not all DNS record types are supported by GNUnet GNSRECORD plugins at this time.

GNUNET_GNSRECORD_number_to_typename can be used to obtain the typename associated with a given numeric value. For example, given the type number 1, the function will return the typename "A".

GNS plugins

Adding a new GNS record type typically involves writing (or extending) a GNSRECORD plugin. The plugin needs to implement the gnunet_gnsrecord_plugin.h API which provides basic functions that are needed by GNSRECORD to convert typenames and values of the respective record type to strings (and back). These gnsrecord plugins are typically implemented within their respective subsystems. Examples for such plugins can be found in the GNSRECORD, GNS and CONVERSATION subsystems.

The libgnunetgnsrecord library is then used to locate, load and query the appropriate gnsrecord plugin. Which plugin is appropriate is determined by the record type (which is just a 32-bit integer). The libgnunetgnsrecord library loads all block plugins that are installed at the local peer and forwards the application request to the plugins. If the record type is not supported by the plugin, it should simply return an error code.

The central functions of the block APIs (plugin and main library) are the same four functions for converting between values and strings, and typenames and numbers documented in the previous subsection.

The GNS Client-Service Protocol

The GNS client-service protocol consists of two simple messages, the LOOKUP message and the LOOKUP_RESULT. Each LOOKUP message contains a unique 32-bit identifier, which will be included in the corresponding response. Thus, clients can send many lookup requests in parallel and receive responses out-of-order. A LOOKUP request also includes the public key of the GNS zone, the desired record type and fields specifying whether shortening is enabled or networking is disabled. Finally, the LOOKUP message includes the name to be resolved.

The response includes the number of records and the records themselves in the format created by GNUNET_GNSRECORD_records_serialize. They can thus be deserialized using GNUNET_GNSRECORD_records_deserialize.

Hijacking the DNS-Traffic using gnunet-service-dns

This section documents how the gnunet-service-dns (and the gnunet-helper-dns) intercepts DNS queries from the local system. This is merely one method for how we can obtain GNS queries. It is also possible to change resolv.conf to point to a machine running gnunet-dns2gns or to modify libc’s name system switch (NSS) configuration to include a GNS resolution plugin. The method described in this chapter is more of a last-ditch catch-all approach.

gnunet-service-dns enables intercepting DNS traffic using policy based routing. We MARK every outgoing DNS-packet if it was not sent by our application. Using a second routing table in the Linux kernel these marked packets are then routed through our virtual network interface and can thus be captured unchanged.

Our application then reads the query and decides how to handle it. If the query can be addressed via GNS, it is passed to gnunet-service-gns and resolved internally using GNS. In the future, a reverse query for an address of the configured virtual network could be answered with records kept about previous forward queries. Queries that are not hijacked by some application using the DNS service will be sent to the original recipient. The answer to the query will always be sent back through the virtual interface with the original nameserver as source address.

Network Setup Details

The DNS interceptor adds the following rules to the Linux kernel:

iptables -t mangle -I OUTPUT 1 -p udp --sport $LOCALPORT --dport 53 \
-j ACCEPT iptables -t mangle -I OUTPUT 2 -p udp --dport 53 -j MARK \
--set-mark 3 ip rule add fwmark 3 table2 ip route add default via \


FIXME: Rewrite to reflect display which is no longer content by line due to the < 74 characters limit.

Line 1 makes sure that all packets coming from a port our application opened beforehand ($LOCALPORT) will be routed normally. Line 2 marks every other packet to a DNS-Server with mark 3 (chosen arbitrarily). The third line adds a routing policy based on this mark 3 via the routing table.

Importing DNS Zones into GNS

This section discusses the challenges and problems faced when writing the Ascension tool. It also takes a look at possible improvements in the future.

Consider the following diagram that shows the workflow of Ascension:

[image: ascension] [image]

Further the interaction between components of GNUnet are shown in the diagram below:

DNS Conversion .. _Conversions-between-DNS-and-GNS:

Conversions between DNS and GNS

The differences between the two name systems lies in the details and is not always transparent. For instance an SRV record is converted to a BOX record which is unique to GNS.

This is done by converting to a BOX record from an existing SRV record:

# TTL class SRV priority weight port target 14000 IN SRV     0 0 5060
# TTL BOX flags port protocol recordtype priority weight port target
14000 BOX n 5060 6 33 0 0 5060

Other records that need to undergo such transformation is the MX record type, as well as the SOA record type.

Transformation of a SOA record into GNS works as described in the following example. Very important to note are the rname and mname keys.

# BIND syntax for a clean SOA record
   IN SOA (

2017030300 ; serial
3600 ; refresh
1800 ; retry
604800 ; expire
600 ) ; ttl # Recordline for adding the record $ gnunet-namestore -z -a -n  -t SOA -V \ \
2017030300,3600,1800,604800,600 -e 7200s

The transformation of MX records is done in a simple way.

# 3600 IN MX 10
$ gnunet-namestore -z -n mail -R 3600 MX n 10,mail

Finally, one of the biggest struggling points were the NS records that are found in top level domain zones. The intended behaviour for those is to add GNS2DNS records for those so that gnunet-gns can resolve records for those domains on its own. Those require the values from DNS GLUE records, provided they are within the same zone.

The following two examples show one record with a GLUE record and the other one does not have a GLUE record. This takes place in the ‘com’ TLD.

# 86400 IN A
# 86400 IN NS
$ gnunet-namestore -z com -n example -R 86400 GNS2DNS n \ # 86400 IN NS $ gnunet-namestore -z com -n example -R 86400 GNS2DNS n \

As you can see, one of the GNS2DNS records has an IP address listed and the other one a DNS name. For the first one there is a GLUE record to do the translation directly and the second one will issue another DNS query to figure out the IP of

A solution was found by creating a hierarchical zone structure in GNS and linking the zones using PKEY records to one another. This allows the resolution of the name servers to work within GNS while not taking control over unwanted zones.

Currently the following record types are supported:

  • A
  • AAAA
  • MX
  • NS
  • SRV
  • TXT

This is not due to technical limitations but rather a practical ones. The problem occurs with DNSSEC enabled DNS zones. As records within those zones are signed periodically, and every new signature is an update to the zone, there are many revisions of zones. This results in a problem with bigger zones as there are lots of records that have been signed again but no major changes. Also trying to add records that are unknown that require a different format take time as they cause a CLI call of the namestore. Furthermore certain record types need transformation into a GNS compatible format which, depending on the record type, takes more time.

Further a blacklist was added to drop for instance DNSSEC related records. Also if a record type is neither in the white list nor the blacklist it is considered as a loss of data and a message is shown to the user. This helps with transparency and also with contributing, as the not supported record types can then be added accordingly.

DNS Zone Size

Another very big problem exists with very large zones. When migrating a small zone the delay between adding of records and their expiry is negligible. However when working with big zones that easily have more than a few million records this delay becomes a problem.

Records will start to expire well before the zone has finished migrating. This is usually not a problem but can cause a high CPU load when a peer is restarted and the records have expired.

A good solution has not been found yet. One of the idea that floated around was that the records should be added with the s (shadow) flag to keep the records resolvable even if they expired. However this would introduce the problem of how to detect if a record has been removed from the zone and would require deletion of said record(s).

Another problem that still persists is how to refresh records. Expired records are still displayed when calling gnunet-namestore but do not resolve with gnunet-gns. Zonemaster will sign the expired records again and make sure that the records are still valid. With a recent change this was fixed as gnunet-gns to improve the suffix lookup which allows for a fast lookup even with thousands of local egos.

Currently the pace of adding records in general is around 10 records per second. Crypto is the upper limit for adding of records. The performance of your machine can be tested with the perf_crypto_* tools. There is still a big discrepancy between the pace of Ascension and the theoretical limit.

A performance metric for measuring improvements has not yet been implemented in Ascension.


The performance when migrating a zone using the Ascension tool is limited by a handful of factors. First of all ascension is written in Python3 and calls the CLI tools of GNUnet. This is comparable to a fork and exec call which costs a few CPU cycles. Furthermore all the records that are added to the same label are signed using the zones private key. This signing operation is very resource heavy and was optimized during development by adding the ‘-R’ (Recordline) option to gnunet-namestore which allows to specify multiple records using the CLI tool. Assuming that in a TLD zone every domain has at least two name servers this halves the amount of signatures needed.

Another improvement that could be made is with the addition of multiple threads or using asynchronous subprocesses when opening the GNUnet CLI tools. This could be implemented by simply creating more workers in the program but performance improvements were not tested.

Ascension was tested using different hardware and database backends. Performance differences between SQLite and postgresql are marginal and almost non existent. What did make a huge impact on record adding performance was the storage medium. On a traditional mechanical hard drive adding of records were slow compared to a solid state disk.

In conclusion there are many bottlenecks still around in the program, namely the single threaded implementation and inefficient, sequential calls of gnunet-namestore. In the future a solution that uses the C API would be cleaner and better.

Registering names using the FCFS daemon

This section describes FCFSD, a daemon used to associate names with PKEY records following a “First Come, First Served” policy. This policy means that a certain name can not be registered again if someone registered it already.

The daemon can be started by using gnunet-namestore-fcfsd, which will start a simple HTTP server on localhost, using a port specified by the HTTPORT value in its configuration.

Communication is performed by sending GET or POST requests to specific paths (“endpoints”), as described in the following sections.

The daemon will always respond with data structured using the JSON format. The fields to be expected will be listed for each endpoint.

The only exceptions are for the “root” endpoint (i.e. /) which will return a HTML document, and two other HTML documents which will be served when certain errors are encountered, like when requesting an unknown endpoint.

FCFSD GET requests .. _Obtaining-information-from-the-daemon:

Obtaining information from the daemon

To query the daemon, a GET request must be sent to these endpoints, placing parameters in the address as per the HTTP specification, like so:

GET /endpoint?param1=value&param2=value

Each endpoint will be described using its name (/endpoint in the example above), followed by the name of each parameter (like param1 and param2.)

This endpoint is used to query about the state of <name>, that is, whether it is available for registration or not.

The response JSON will contain two fields:

  • error
  • free

error can be either the string "true" or the string "false": when "true", it means there was an error within the daemon and the name could not be searched at all.

free can be either the string "true" or the string "false": when "true", the requested name can be registered.

FCFSD POST requests .. _Submitting-data-to-the-daemon:

Submitting data to the daemon

To send data to the daemon, a POST request must be sent to these endpoints, placing the data to submit in the body of the request, structured using the JSON format, like so:

POST /endpoint
Content-Type: application/json
{"param1": value1, "param2": value2, ...}

Each endpoint will be described using its name (/endpoint in the example above), followed by the name of each JSON field (like param1 and param2.)

This endpoint is used to register a new association between <name> and <key>.

For this operation to succeed, both <NAME> and <KEY> must not be registered already.

The response JSON will contain two fields:

  • error
  • message

error can be either the string "true" or the string "false": when "true", it means the name could not be registered. Clients can get the reason of the failure from the HTTP response code or from the message field.

message is a string which can be used by clients to let users know the result of the operation. It might be localized to the daemon operator’s locale.

Customizing the HTML output

In some situations, the daemon will serve HTML documents instead of JSON values. It is possible to configure the daemon to serve custom documents instead of the ones provided with GNUnet, by setting the HTMLDIR value in its configuration to a directory path.

Within the provided path, the daemon will search for these three files:

  • fcfsd-index.html
  • fcfsd-notfound.html
  • fcfsd-forbidden.html

The fcfsd-index.html file is the daemon’s “homepage”: operators might want to provide information about the service here, or provide a form with which it is possible to register a name.

The fcfsd-notfound.html file is used primarily to let users know they tried to access an unknown endpoint.

The fcfsd-forbidden.html file is served to users when they try to access an endpoint they should not access. For example, sending an invalid request might result in this page being served.

NAMECACHE — DHT caching of GNS results

The NAMECACHE subsystem is responsible for caching (encrypted) resolution results of the GNU Name System (GNS). GNS makes zone information available to other users via the DHT. However, as accessing the DHT for every lookup is expensive (and as the DHT’s local cache is lost whenever the peer is restarted), GNS uses the NAMECACHE as a more persistent cache for DHT lookups. Thus, instead of always looking up every name in the DHT, GNS first checks if the result is already available locally in the NAMECACHE. Only if there is no result in the NAMECACHE, GNS queries the DHT. The NAMECACHE stores data in the same (encrypted) format as the DHT. It thus makes no sense to iterate over all items in the NAMECACHE – the NAMECACHE does not have a way to provide the keys required to decrypt the entries.

Blocks in the NAMECACHE share the same expiration mechanism as blocks in the DHT – the block expires wheneever any of the records in the (encrypted) block expires. The expiration time of the block is the only information stored in plaintext. The NAMECACHE service internally performs all of the required work to expire blocks, clients do not have to worry about this. Also, given that NAMECACHE stores only GNS blocks that local users requested, there is no configuration option to limit the size of the NAMECACHE. It is assumed to be always small enough (a few MB) to fit on the drive.

The NAMECACHE supports the use of different database backends via a plugin API.


The NAMECACHE API consists of five simple functions. First, there is GNUNET_NAMECACHE_connect to connect to the NAMECACHE service. This returns the handle required for all other operations on the NAMECACHE. Using GNUNET_NAMECACHE_block_cache clients can insert a block into the cache. GNUNET_NAMECACHE_lookup_block can be used to lookup blocks that were stored in the NAMECACHE. Both operations can be canceled using GNUNET_NAMECACHE_cancel. Note that canceling a GNUNET_NAMECACHE_block_cache operation can result in the block being stored in the NAMECACHE — or not. Cancellation primarily ensures that the continuation function with the result of the operation will no longer be invoked. Finally, GNUNET_NAMECACHE_disconnect closes the connection to the NAMECACHE.

The maximum size of a block that can be stored in the NAMECACHE is GNUNET_NAMECACHE_MAX_VALUE_SIZE, which is defined to be 63 kB.

The NAMECACHE Client-Service Protocol

All messages in the NAMECACHE IPC protocol start with the struct GNUNET_NAMECACHE_Header which adds a request ID (32-bit integer) to the standard message header. The request ID is used to match requests with the respective responses from the NAMECACHE, as they are allowed to happen out-of-order.


The struct LookupBlockMessage is used to lookup a block stored in the cache. It contains the query hash. The NAMECACHE always responds with a struct LookupBlockResponseMessage. If the NAMECACHE has no response, it sets the expiration time in the response to zero. Otherwise, the response is expected to contain the expiration time, the ECDSA signature, the derived key and the (variable-size) encrypted data of the block.


The struct BlockCacheMessage is used to cache a block in the NAMECACHE. It has the same structure as the struct LookupBlockResponseMessage. The service responds with a struct BlockCacheResponseMessage which contains the result of the operation (success or failure). In the future, we might want to make it possible to provide an error message as well.


The NAMECACHE plugin API consists of two functions, cache_block to store a block in the database, and lookup_block to lookup a block in the database.


The lookup_block function is expected to return at most one block to the iterator, and return GNUNET_NO if there were no non-expired results. If there are multiple non-expired results in the cache, the lookup is supposed to return the result with the largest expiration time.


The cache_block function is expected to try to store the block in the database, and return GNUNET_SYSERR if this was not possible for any reason. Furthermore, cache_block is expected to implicitly perform cache maintenance and purge blocks from the cache that have expired. Note that cache_block might encounter the case where the database already has another block stored under the same key. In this case, the plugin must ensure that the block with the larger expiration time is preserved. Obviously, this can done either by simply adding new blocks and selecting for the most recent expiration time during lookup, or by checking which block is more recent during the store operation.

NAMESTORE — Storage of local GNS zones

The NAMESTORE subsystem provides persistent storage for local GNS zone information. All local GNS zone information are managed by NAMESTORE. It provides both the functionality to administer local GNS information (e.g. delete and add records) as well as to retrieve GNS information (e.g to list name information in a client). NAMESTORE does only manage the persistent storage of zone information belonging to the user running the service: GNS information from other users obtained from the DHT are stored by the NAMECACHE subsystem.

NAMESTORE uses a plugin-based database backend to store GNS information with good performance. Here sqlite, MySQL and PostgreSQL are supported database backends. NAMESTORE clients interact with the IDENTITY subsystem to obtain cryptographic information about zones based on egos as described with the IDENTITY subsystem, but internally NAMESTORE refers to zones using the ECDSA private key. In addition, it collaborates with the NAMECACHE subsystem and stores zone information when local information are modified in the GNS cache to increase look-up performance for local information.

NAMESTORE provides functionality to look-up and store records, to iterate over a specific or all zones and to monitor zones for changes. NAMESTORE functionality can be accessed using the NAMESTORE api or the NAMESTORE command line tool.


To interact with NAMESTORE clients first connect to the NAMESTORE service using the GNUNET_NAMESTORE_connect passing a configuration handle. As a result they obtain a NAMESTORE handle, they can use for operations, or NULL is returned if the connection failed.

To disconnect from NAMESTORE, clients use GNUNET_NAMESTORE_disconnect and specify the handle to disconnect.

NAMESTORE internally uses the ECDSA private key to refer to zones. These private keys can be obtained from the IDENTITY subsystem. Here egos can be used to refer to zones or the default ego assigned to the GNS subsystem can be used to obtained the master zone’s private key.

Editing Zone Information

NAMESTORE provides functions to lookup records stored under a label in a zone and to store records under a label in a zone.

To store (and delete) records, the client uses the GNUNET_NAMESTORE_records_store function and has to provide namestore handle to use, the private key of the zone, the label to store the records under, the records and number of records plus an callback function. After the operation is performed NAMESTORE will call the provided callback function with the result GNUNET_SYSERR on failure (including timeout/queue drop/failure to validate), GNUNET_NO if content was already there or not found GNUNET_YES (or other positive value) on success plus an additional error message.

Records are deleted by using the store command with 0 records to store. It is important to note, that records are not merged when records exist with the label. So a client has first to retrieve records, merge with existing records and then store the result.

To perform a lookup operation, the client uses the GNUNET_NAMESTORE_records_store function. Here it has to pass the namestore handle, the private key of the zone and the label. It also has to provide a callback function which will be called with the result of the lookup operation: the zone for the records, the label, and the records including the number of records included.

A special operation is used to set the preferred nickname for a zone. This nickname is stored with the zone and is automatically merged with all labels and records stored in a zone. Here the client uses the GNUNET_NAMESTORE_set_nick function and passes the private key of the zone, the nickname as string plus a the callback with the result of the operation.

Iterating Zone Information

A client can iterate over all information in a zone or all zones managed by NAMESTORE. Here a client uses the GNUNET_NAMESTORE_zone_iteration_start function and passes the namestore handle, the zone to iterate over and a callback function to call with the result. To iterate over all the zones, it is possible to pass NULL for the zone. A GNUNET_NAMESTORE_ZoneIterator handle is returned to be used to continue iteration.

NAMESTORE calls the callback for every result and expects the client to call GNUNET_NAMESTORE_zone_iterator_next to continue to iterate or GNUNET_NAMESTORE_zone_iterator_stop to interrupt the iteration. When NAMESTORE reached the last item it will call the callback with a NULL value to indicate.

Monitoring Zone Information

Clients can also monitor zones to be notified about changes. Here the clients uses the GNUNET_NAMESTORE_zone_monitor_start function and passes the private key of the zone and and a callback function to call with updates for a zone. The client can specify to obtain zone information first by iterating over the zone and specify a synchronization callback to be called when the client and the namestore are synced.

On an update, NAMESTORE will call the callback with the private key of the zone, the label and the records and their number.

To stop monitoring, the client calls GNUNET_NAMESTORE_zone_monitor_stop and passes the handle obtained from the function to start the monitoring.


FS — File sharing over GNUnet

This chapter describes the details of how the file-sharing service works. As with all services, it is split into an API (libgnunetfs), the service process (gnunet-service-fs) and user interface(s). The file-sharing service uses the datastore service to store blocks and the DHT (and indirectly datacache) for lookups for non-anonymous file-sharing. Furthermore, the file-sharing service uses the block library (and the block fs plugin) for validation of DHT operations.

In contrast to many other services, libgnunetfs is rather complex since the client library includes a large number of high-level abstractions; this is necessary since the FS service itself largely only operates on the block level. The FS library is responsible for providing a file-based abstraction to applications, including directories, meta data, keyword search, verification, and so on.

The method used by GNUnet to break large files into blocks and to use keyword search is called the "Encoding for Censorship Resistant Sharing" (ECRS). ECRS is largely implemented in the fs library; block validation is also reflected in the block FS plugin and the FS service. ECRS on-demand encoding is implemented in the FS service.


The documentation in this chapter is quite incomplete.

ECRS — Encoding for Censorship-Resistant Sharing

When GNUnet shares files, it uses a content encoding that is called ECRS, the Encoding for Censorship-Resistant Sharing. Most of ECRS is described in the (so far unpublished) research paper attached to this page. ECRS obsoletes the previous ESED and ESED II encodings which were used in GNUnet before version 0.7.0. The rest of this page assumes that the reader is familiar with the attached paper. What follows is a description of some minor extensions that GNUnet makes over what is described in the paper. The reason why these extensions are not in the paper is that we felt that they were obvious or trivial extensions to the original scheme and thus did not warrant space in the research report.


Find missing link to file system paper.

Namespace Advertisements


FIXME: all zeroses -> ?

An SBlock with identifier all zeros is a signed advertisement for a namespace. This special SBlock contains metadata describing the content of the namespace. Instead of the name of the identifier for a potential update, it contains the identifier for the root of the namespace. The URI should always be empty. The SBlock is signed with the content provider’s RSA private key (just like any other SBlock). Peers can search for SBlocks in order to find out more about a namespace.


GNUnet implements KSBlocks which are KBlocks that, instead of encrypting a CHK and metadata, encrypt an SBlock instead. In other words, KSBlocks enable GNUnet to find SBlocks using the global keyword search. Usually the encrypted SBlock is a namespace advertisement. The rationale behind KSBlocks and SBlocks is to enable peers to discover namespaces via keyword searches, and, to associate useful information with namespaces. When GNUnet finds KSBlocks during a normal keyword search, it adds the information to an internal list of discovered namespaces. Users looking for interesting namespaces can then inspect this list, reducing the need for out-of-band discovery of namespaces. Naturally, namespaces (or more specifically, namespace advertisements) can also be referenced from directories, but KSBlocks should make it easier to advertise namespaces for the owner of the pseudonym since they eliminate the need to first create a directory.

Collections are also advertised using KSBlocks.

File-sharing persistence directory structure

This section documents how the file-sharing library implements persistence of file-sharing operations and specifically the resulting directory structure. This code is only active if the GNUNET_FS_FLAGS_PERSISTENCE flag was set when calling GNUNET_FS_start. In this case, the file-sharing library will try hard to ensure that all major operations (searching, downloading, publishing, unindexing) are persistent, that is, can live longer than the process itself. More specifically, an operation is supposed to live until it is explicitly stopped.

If GNUNET_FS_stop is called before an operation has been stopped, a SUSPEND event is generated and then when the process calls GNUNET_FS_start next time, a RESUME event is generated. Additionally, even if an application crashes (segfault, SIGKILL, system crash) and hence GNUNET_FS_stop is never called and no SUSPEND events are generated, operations are still resumed (with RESUME events). This is implemented by constantly writing the current state of the file-sharing operations to disk. Specifically, the current state is always written to disk whenever anything significant changes (the exception are block-wise progress in publishing and unindexing, since those operations would be slowed down significantly and can be resumed cheaply even without detailed accounting). Note that if the process crashes (or is killed) during a serialization operation, FS does not guarantee that this specific operation is recoverable (no strict transactional semantics, again for performance reasons). However, all other unrelated operations should resume nicely.

Since we need to serialize the state continuously and want to recover as much as possible even after crashing during a serialization operation, we do not use one large file for serialization. Instead, several directories are used for the various operations. When GNUNET_FS_start executes, the master directories are scanned for files describing operations to resume. Sometimes, these operations can refer to related operations in child directories which may also be resumed at this point. Note that corrupted files are cleaned up automatically. However, dangling files in child directories (those that are not referenced by files from the master directories) are not automatically removed.

Persistence data is kept in a directory that begins with the "STATE_DIR" prefix from the configuration file (by default, "$SERVICEHOME/persistence/") followed by the name of the client as given to GNUNET_FS_start (for example, "gnunet-gtk") followed by the actual name of the master or child directory.

The names for the master directories follow the names of the operations:

  • "search"
  • "download"
  • "publish"
  • "unindex"

Each of the master directories contains names (chosen at random) for each active top-level (master) operation. Note that a download that is associated with a search result is not a top-level operation.

In contrast to the master directories, the child directories are only consulted when another operation refers to them. For each search, a subdirectory (named after the master search synchronization file) contains the search results. Search results can have an associated download, which is then stored in the general "download-child" directory. Downloads can be recursive, in which case children are stored in subdirectories mirroring the structure of the recursive download (either starting in the master "download" directory or in the "download-child" directory depending on how the download was initiated). For publishing operations, the "publish-file" directory contains information about the individual files and directories that are part of the publication. However, this directory structure is flat and does not mirror the structure of the publishing operation. Note that unindex operations cannot have associated child operations.

IDENTITY — Ego management

Identities of "users" in GNUnet are called egos. Egos can be used as pseudonyms ("fake names") or be tied to an organization (for example, "GNU") or even the actual identity of a human. GNUnet users are expected to have many egos. They might have one tied to their real identity, some for organizations they manage, and more for different domains where they want to operate under a pseudonym.

The IDENTITY service allows users to manage their egos. The identity service manages the private keys egos of the local user; it does not manage identities of other users (public keys). Public keys for other users need names to become manageable. GNUnet uses the GNU Name System (GNS) to give names to other users and manage their public keys securely. This chapter is about the IDENTITY service, which is about the management of private keys.

On the network, an ego corresponds to an ECDSA key (over Curve25519, using RFC 6979, as required by GNS). Thus, users can perform actions under a particular ego by using (signing with) a particular private key. Other users can then confirm that the action was really performed by that ego by checking the signature against the respective public key.

The IDENTITY service allows users to associate a human-readable name with each ego. This way, users can use names that will remind them of the purpose of a particular ego. The IDENTITY service will store the respective private keys and allows applications to access key information by name. Users can change the name that is locally (!) associated with an ego. Egos can also be deleted, which means that the private key will be removed and it thus will not be possible to perform actions with that ego in the future.

Additionally, the IDENTITY subsystem can associate service functions with egos. For example, GNS requires the ego that should be used for the shorten zone. GNS will ask IDENTITY for an ego for the "gns-short" service. The IDENTITY service has a mapping of such service strings to the name of the ego that the user wants to use for this service, for example "my-short-zone-ego".

Finally, the IDENTITY API provides access to a special ego, the anonymous ego. The anonymous ego is special in that its private key is not really private, but fixed and known to everyone. Thus, anyone can perform actions as anonymous. This can be useful as with this trick, code does not have to contain a special case to distinguish between anonymous and pseudonymous egos.


Connecting to the service

First, typical clients connect to the identity service using GNUNET_IDENTITY_connect. This function takes a callback as a parameter. If the given callback parameter is non-null, it will be invoked to notify the application about the current state of the identities in the system.

  • First, it will be invoked on all known egos at the time of the connection. For each ego, a handle to the ego and the user’s name for the ego will be passed to the callback. Furthermore, a void ** context argument will be provided which gives the client the opportunity to associate some state with the ego.
  • Second, the callback will be invoked with NULL for the ego, the name and the context. This signals that the (initial) iteration over all egos has completed.
  • Then, the callback will be invoked whenever something changes about an ego. If an ego is renamed, the callback is invoked with the ego handle of the ego that was renamed, and the new name. If an ego is deleted, the callback is invoked with the ego handle and a name of NULL. In the deletion case, the application should also release resources stored in the context.
  • When the application destroys the connection to the identity service using GNUNET_IDENTITY_disconnect, the callback is again invoked with the ego and a name of NULL (equivalent to deletion of the egos). This should again be used to clean up the per-ego context.

The ego handle passed to the callback remains valid until the callback is invoked with a name of NULL, so it is safe to store a reference to the ego’s handle.

Operations on Egos

Given an ego handle, the main operations are to get its associated private key using GNUNET_IDENTITY_ego_get_private_key or its associated public key using GNUNET_IDENTITY_ego_get_public_key.

The other operations on egos are pretty straightforward. Using GNUNET_IDENTITY_create, an application can request the creation of an ego by specifying the desired name. The operation will fail if that name is already in use. Using GNUNET_IDENTITY_rename the name of an existing ego can be changed. Finally, egos can be deleted using GNUNET_IDENTITY_delete. All of these operations will trigger updates to the callback given to the GNUNET_IDENTITY_connect function of all applications that are connected with the identity service at the time. GNUNET_IDENTITY_cancel can be used to cancel the operations before the respective continuations would be called. It is not guaranteed that the operation will not be completed anyway, only the continuation will no longer be called.

The anonymous Ego

A special way to obtain an ego handle is to call GNUNET_IDENTITY_ego_get_anonymous, which returns an ego for the "anonymous" user — anyone knows and can get the private key for this user, so it is suitable for operations that are supposed to be anonymous but require signatures (for example, to avoid a special path in the code). The anonymous ego is always valid and accessing it does not require a connection to the identity service.

Convenience API to lookup a single ego

As applications commonly simply have to lookup a single ego, there is a convenience API to do just that. Use GNUNET_IDENTITY_ego_lookup to lookup a single ego by name. Note that this is the user’s name for the ego, not the service function. The resulting ego will be returned via a callback and will only be valid during that callback. The operation can be canceled via GNUNET_IDENTITY_ego_lookup_cancel (cancellation is only legal before the callback is invoked).

Associating egos with service functions

The GNUNET_IDENTITY_set function is used to associate a particular ego with a service function. The name used by the service and the ego are given as arguments. Afterwards, the service can use its name to lookup the associated ego using GNUNET_IDENTITY_get.

The IDENTITY Client-Service Protocol

A client connecting to the identity service first sends a message with type GNUNET_MESSAGE_TYPE_IDENTITY_START to the service. After that, the client will receive information about changes to the egos by receiving messages of type GNUNET_MESSAGE_TYPE_IDENTITY_UPDATE. Those messages contain the private key of the ego and the user’s name of the ego (or zero bytes for the name to indicate that the ego was deleted). A special bit end_of_list is used to indicate the end of the initial iteration over the identity service’s egos.

The client can trigger changes to the egos by sending CREATE, RENAME or DELETE messages. The CREATE message contains the private key and the desired name. The RENAME message contains the old name and the new name. The DELETE message only needs to include the name of the ego to delete. The service responds to each of these messages with a RESULT_CODE message which indicates success or error of the operation, and possibly a human-readable error message.

Finally, the client can bind the name of a service function to an ego by sending a SET_DEFAULT message with the name of the service function and the private key of the ego. Such bindings can then be resolved using a GET_DEFAULT message, which includes the name of the service function. The identity service will respond to a GET_DEFAULT request with a SET_DEFAULT message containing the respective information, or with a RESULT_CODE to indicate an error.

REVOCATION — Ego key revocation

The REVOCATION subsystem is responsible for key revocation of Egos. If a user learns that their private key has been compromised or has lost it, they can use the REVOCATION system to inform all of the other users that their private key is no longer valid. The subsystem thus includes ways to query for the validity of keys and to propagate revocation messages.


When a revocation is performed, the revocation is first of all disseminated by flooding the overlay network. The goal is to reach every peer, so that when a peer needs to check if a key has been revoked, this will be purely a local operation where the peer looks at its local revocation list. Flooding the network is also the most robust form of key revocation — an adversary would have to control a separator of the overlay graph to restrict the propagation of the revocation message. Flooding is also very easy to implement — peers that receive a revocation message for a key that they have never seen before simply pass the message to all of their neighbours.

Flooding can only distribute the revocation message to peers that are online. In order to notify peers that join the network later, the revocation service performs efficient set reconciliation over the sets of known revocation messages whenever two peers (that both support REVOCATION dissemination) connect. The SET service is used to perform this operation efficiently.

Revocation Message Design Requirements

However, flooding is also quite costly, creating O(|E|) messages on a network with |E| edges. Thus, revocation messages are required to contain a proof-of-work, the result of an expensive computation (which, however, is cheap to verify). Only peers that have expended the CPU time necessary to provide this proof will be able to flood the network with the revocation message. This ensures that an attacker cannot simply flood the network with millions of revocation messages. The proof-of-work required by GNUnet is set to take days on a typical PC to compute; if the ability to quickly revoke a key is needed, users have the option to pre-compute revocation messages to store off-line and use instantly after their key has expired.

Revocation messages must also be signed by the private key that is being revoked. Thus, they can only be created while the private key is in the possession of the respective user. This is another reason to create a revocation message ahead of time and store it in a secure location.


The REVOCATION API consists of two parts, to query and to issue revocations.

Querying for revoked keys

GNUNET_REVOCATION_query is used to check if a given ECDSA public key has been revoked. The given callback will be invoked with the result of the check. The query can be canceled using GNUNET_REVOCATION_query_cancel on the return value.

Preparing revocations

It is often desirable to create a revocation record ahead-of-time and store it in an off-line location to be used later in an emergency. This is particularly true for GNUnet revocations, where performing the revocation operation itself is computationally expensive and thus is likely to take some time. Thus, if users want the ability to perform revocations quickly in an emergency, they must pre-compute the revocation message. The revocation API enables this with two functions that are used to compute the revocation message, but not trigger the actual revocation operation.

GNUNET_REVOCATION_check_pow should be used to calculate the proof-of-work required in the revocation message. This function takes the public key, the required number of bits for the proof of work (which in GNUnet is a network-wide constant) and finally a proof-of-work number as arguments. The function then checks if the given proof-of-work number is a valid proof of work for the given public key. Clients preparing a revocation are expected to call this function repeatedly (typically with a monotonically increasing sequence of numbers of the proof-of-work number) until a given number satisfies the check. That number should then be saved for later use in the revocation operation.

GNUNET_REVOCATION_sign_revocation is used to generate the signature that is required in a revocation message. It takes the private key that (possibly in the future) is to be revoked and returns the signature. The signature can again be saved to disk for later use, which will then allow performing a revocation even without access to the private key.

Issuing revocations

Given a ECDSA public key, the signature from GNUNET_REVOCATION_sign and the proof-of-work, GNUNET_REVOCATION_revoke can be used to perform the actual revocation. The given callback is called upon completion of the operation. GNUNET_REVOCATION_revoke_cancel can be used to stop the library from calling the continuation; however, in that case it is undefined whether or not the revocation operation will be executed.

The REVOCATION Client-Service Protocol

The REVOCATION protocol consists of four simple messages.

A QueryMessage containing a public ECDSA key is used to check if a particular key has been revoked. The service responds with a QueryResponseMessage which simply contains a bit that says if the given public key is still valid, or if it has been revoked.

The second possible interaction is for a client to revoke a key by passing a RevokeMessage to the service. The RevokeMessage contains the ECDSA public key to be revoked, a signature by the corresponding private key and the proof-of-work. The service responds with a RevocationResponseMessage which can be used to indicate that the RevokeMessage was invalid (e.g. the proof of work is incorrect), or otherwise to indicate that the revocation has been processed successfully.

The REVOCATION Peer-to-Peer Protocol

Revocation uses two disjoint ways to spread revocation information among peers. First of all, P2P gossip exchanged via CORE-level neighbours is used to quickly spread revocations to all connected peers. Second, whenever two peers (that both support revocations) connect, the SET service is used to compute the union of the respective revocation sets.

In both cases, the exchanged messages are RevokeMessages which contain the public key that is being revoked, a matching ECDSA signature, and a proof-of-work. Whenever a peer learns about a new revocation this way, it first validates the signature and the proof-of-work, then stores it to disk (typically to a file $GNUNET_DATA_HOME/revocation.dat) and finally spreads the information to all directly connected neighbours.

For computing the union using the SET service, the peer with the smaller hashed peer identity will connect (as a "client" in the two-party set protocol) to the other peer after one second (to reduce traffic spikes on connect) and initiate the computation of the set union. All revocation services use a common hash to identify the SET operation over revocation sets.

The current implementation accepts revocation set union operations from all peers at any time; however, well-behaved peers should only initiate this operation once after establishing a connection to a peer with a larger hashed peer identity.

MESSENGER — Room-based end-to-end messaging

The MESSENGER subsystem is responsible for secure end-to-end communication in groups of nodes in the GNUnet overlay network. MESSENGER builds on the CADET subsystem which provides a reliable and secure end-to-end communication between the nodes inside of these groups.

Additionally to the CADET security benefits, MESSENGER provides following properties designed for application level usage:

  • MESSENGER provides integrity by signing the messages with the users provided ego
  • MESSENGER adds (optional) forward secrecy by replacing the key pair of the used ego and signing the propagation of the new one with old one (chaining egos)
  • MESSENGER provides verification of a original sender by checking against all used egos from a member which are currently in active use (active use depends on the state of a member session)
  • MESSENGER offsers (optional) decentralized message forwarding between all nodes in a group to improve availability and prevent MITM-attacks
  • MESSENGER handles new connections and disconnections from nodes in the group by reconnecting them preserving an efficient structure for message distribution (ensuring availability and accountablity)
  • MESSENGER provides replay protection (messages can be uniquely identified via SHA-512, include a timestamp and the hash of the last message)
  • MESSENGER allows detection for dropped messages by chaining them (messages refer to the last message by their hash) improving accountability
  • MESSENGER allows requesting messages from other peers explicitly to ensure availability
  • MESSENGER provides confidentiality by padding messages to few different sizes (512 bytes, 4096 bytes, 32768 bytes and maximal message size from CADET)
  • MESSENGER adds (optional) confidentiality with ECDHE to exchange and use symmetric encryption, encrypting with both AES-256 and Twofish but allowing only selected members to decrypt (using the receivers ego for ECDHE)

Also MESSENGER provides multiple features with privacy in mind:

  • MESSENGER allows deleting messages from all peers in the group by the original sender (uses the MESSENGER provided verification)
  • MESSENGER allows using the publicly known anonymous ego instead of any unique identifying ego
  • MESSENGER allows your node to decide between acting as host of the used messaging room (sharing your peer’s identity with all nodes in the group) or acting as guest (sharing your peer’s identity only with the nodes you explicitly open a connection to)
  • MESSENGER handles members independently of the peer’s identity making forwarded messages indistinguishable from directly received ones ( complicating the tracking of messages and identifying its origin)
  • MESSENGER allows names of members being not unique (also names are optional)
  • MESSENGER does not include information about the selected receiver of an explicitly encrypted message in its header, complicating it for other members to draw conclusions from communication partners


The MESSENGER API (defined in gnunet_messenger_service.h) allows P2P applications built using GNUnet to communicate with specified kinds of messages in a group. It provides applications the ability to send and receive encrypted messages to any group of peers participating in GNUnet in a decentralized way ( without even knowing all peers’s identities).

MESSENGER delivers messages to other peers in "rooms". A room uses a variable amount of CADET "channels" which will all be used for message distribution. Each channel can represent an outgoing connection opened by entering a room with GNUNET_MESSENGER_enter_room or an incoming connection if the room was opened before via GNUNET_MESSENGER_open_room.

[image: messenger_room] [image]

To enter a room you have to specify the "door" (peer’s identity of a peer which has opened the room) and the key of the room (which is identical to a CADET "port"). To open a room you have to specify only the key to use. When opening a room you automatically distribute a PEER-message sharing your peer’s identity in the room.

Entering or opening a room can also be combined in any order. In any case you will automatically get a unique member ID and send a JOIN-message notifying others about your entry and your public key from your selected ego.

The ego can be selected by name with the initial GNUNET_MESSENGER_connect besides setting a (identity-)callback for each change/confirmation of the used ego and a (message-)callback which gets called every time a message gets sent or received in the room. Once the identity-callback got called you can check your used ego with GNUNET_MESSENGER_get_key providing only its public key. The function returns NULL if the anonymous ego is used. If the ego should be replaced with a newly generated one, you can use GNUNET_MESSENGER_update to ensure proper chaining of used egos.

Also once the identity-callback got called you can check your used name with GNUNET_MESSENGER_get_name and potentially change or set a name via GNUNET_MESSENGER_set_name. A name is for example required to create a new ego with GNUNET_MESSENGER_update. Also any change in ego or name will automatically be distributed in the room with a NAME- or KEY-message respectively.

To send a message a message inside of a room you can use GNUNET_MESSENGER_send_message. If you specify a selected contact as receiver, the message gets encrypted automatically and will be sent as PRIVATE- message instead.

To request a potentially missed message or to get a specific message after its original call of the message-callback, you can use GNUNET_MESSENGER_get_message. Additionally once a message was distributed to application level and the message-callback got called, you can get the contact respresenting a message’s sender respectively with GNUNET_MESSENGER_get_sender. This allows getting name and the public key of any sender currently in use with GNUNET_MESSENGER_contact_get_name and GNUNET_MESSENGER_contact_get_key. It is also possible to iterate through all current members of a room with GNUNET_MESSENGER_iterate_members using a callback.

To leave a room you can use GNUNET_MESSENGER_close_room which will also close the rooms connections once all applications on the same peer have left the room. Leaving a room will also send a LEAVE-message closing a member session on all connected peers before any connection will be closed. Leaving a room is however not required for any application to keep your member session open between multiple sessions of the actual application.

Finally, when an application no longer wants to use CADET, it should call GNUNET_MESSENGER_disconnect. You don’t have to explicitly close the used rooms or leave them.

Here is a little summary to the kinds of messages you can send manually:


MERGE-messages will generally be sent automatically to reduce the amount of parallel chained messages. This is necessary to close a member session for example. You can also send MERGE-messages manually if required to merge two chains of messages.


INVITE-messages can be used to invite other members in a room to a different room, sharing one potential door and the required key to enter the room. This kind of message is typically sent as encrypted PRIVATE-message to selected members because it doesn’t make much sense to invite all members from one room to another considering a rooms key doesn’t specify its usage.


TEXT-messages can be used to send simple text-based messages and should be considered as being in readable form without complex decoding. The text has to end with a NULL-terminator character and should be in UTF-8 encoding for most compatibility.


FILE-messages can be used to share files inside of a room. They do not contain the actual file being shared but its original hash, filename, URI to download the file and a symmetric key to decrypt the downloaded file.

It is recommended to use the FS subsystem and the FILE-messages in combination.


DELETE-messages can be used to delete messages selected with its hash. You can also select any custom delay relative to the time of sending the DELETE-message. Deletion will only be processed on each peer in a room if the sender is authorized.

The only information of a deleted message which being kept will be the chained hashes connecting the message graph for potential traversion. For example the check for completion of a member session requires this information.

Member sessions

A member session is a triple of the room key, the member ID and the public key of the member’s ego. Member sessions allow that a member can change their ID or their ego once at a time without losing the ability to delete old messages or identifying the original sender of a message. On every change of ID or EGO a session will be marked as closed. So every session chain will only contain one open session with the current ID and public key.

If a session is marked as closed the MESSENGER service will check from the first message opening a session to its last one closing the session for completion. If a the service can confirm that there is no message still missing which was sent from the closed member session, it will be marked as completed.

A completed member session is not able to verify any incoming message to ensure forward secrecy preventing others from using old stolen egos.

REST — RESTful GNUnet Web APIs


Define REST

Using the REST subsystem, you can expose REST-based APIs or services. The REST service is designed as a pluggable architecture. To create a new REST endpoint, simply add a library in the form “plugin_rest_*”. The REST service will automatically load all REST plugins on startup.


The REST service can be configured in various ways. The reference config file can be found in src/rest/rest.conf:


The port as well as CORS (cross-origin resource sharing) headers that are supposed to be advertised by the rest service are configurable.

Namespace considerations

The gnunet-rest-service will load all plugins that are installed. As such it is important that the endpoint namespaces do not clash.

For example, plugin X might expose the endpoint “/xxx” while plugin Y exposes endpoint “/xxx/yyy”. This is a problem if plugin X is also supposed to handle a call to “/xxx/yyy”. Currently the REST service will not complain or warn about such clashes, so please make sure that endpoints are unambiguous.

Endpoint documentation

This is WIP. Endpoints should be documented appropriately. Preferably using annotations.

C Tutorial

This tutorials explains how to install GNUnet on a GNU/Linux system and gives an introduction on how GNUnet can be used to develop a Peer-to-Peer application. Detailed installation instructions for various operating systems and a detailed list of all dependencies can be found on our website at and in our Reference Documentation (GNUnet Handbook).

Please read this tutorial carefully since every single step is important, and do not hesitate to contact the GNUnet team if you have any questions or problems! Visit this link in your webbrowser to learn how to contact the GNUnet team:

Introduction to GNUnet Architecture

GNUnet is organized in layers and services. Each service is composed of a main service implementation and a client library for other programs to use the service’s functionality, described by an API. Some services provide an additional command line tool to enable the user to interact with the service.

Very often it is other GNUnet services that will use these APIs to build the higher layers of GNUnet on top of the lower ones. Each layer expands or extends the functionality of the service below (for instance, to build a mesh on top of a DHT).

The main service implementation runs as a standalone process in the Operating System and the client code runs as part of the client program, so crashes of a client do not affect the service process or other clients. The service and the clients communicate via a message protocol to be defined and implemented by the programmer.

First Steps with GNUnet

Configure your peer

First of all we need to configure your peer. Each peer is started with a configuration containing settings for GNUnet itself and its services. This configuration is based on the default configuration shipped with GNUnet and can be modified. The default configuration is located in the $PREFIX/share/gnunet/config.d directory. When starting a peer, you can specify a customized configuration using the the -c command line switch when starting the ARM service and all other services. When using a modified configuration the default values are loaded and only values specified in the configuration file will replace the default values.

Since we want to start additional peers later, we need some modifications from the default configuration. We need to create a separate service home and a file containing our modifications for this peer:

$ mkdir ~/gnunet1/
$ touch peer1.conf

Now add the following lines to peer1.conf to use this directory. For simplified usage we want to prevent the peer to connect to the GNUnet network since this could lead to confusing output. This modifications will replace the default settings:

# Use this directory to store GNUnet data
GNUNET_HOME = ~/gnunet1/
# prevent bootstrapping

Start a peer

Each GNUnet instance (called peer) has an identity (peer ID) based on a cryptographic public private key pair. The peer ID is the printable hash of the public key.

GNUnet services are controlled by a master service, the so called Automatic Restart Manager (ARM). ARM starts, stops and even restarts services automatically or on demand when a client connects. You interact with the ARM service using the gnunet-arm tool. GNUnet can then be started with gnunet-arm -s and stopped with gnunet-arm -e. An additional service not automatically started can be started using gnunet-arm -i <service name> and stopped using gnunet-arm -k <servicename>.

Once you have started your peer, you can use many other GNUnet commands to interact with it. For example, you can run:

$ gnunet-peerinfo -s

to obtain the public key of your peer.

You should see an output containing the peer ID similar to:


Monitor a peer

In this section, we will monitor the behaviour of our peer’s DHT service with respect to a specific key. First we will start GNUnet and then start the DHT service and use the DHT monitor tool to monitor the PUT and GET commands we issue ussing the gnunet-dht-put and gnunet-dht-get commands. Using the “monitor” line given below, you can observe the behavior of your own peer’s DHT with respect to the specified KEY:

# start gnunet with all default services:
$ gnunet-arm -c ~/peer1.conf -s
# start DHT service:
$ gnunet-arm -c ~/peer1.conf -i dht
$ cd ~/gnunet/src/dht;
$ ./gnunet-dht-monitor -c ~/peer1.conf -k KEY

Now open a separate terminal and change again to the gnunet/src/dht directory:

$ cd ~/gnunet/src/dht
# put VALUE under KEY in the DHT:
$ ./gnunet-dht-put -c ~/peer1.conf -k KEY -d VALUE
# get key KEY from the DHT:
$ ./gnunet/src/dht/gnunet-dht-get -c ~/peer1.conf -k KEY
# print statistics about current GNUnet state:
$ gnunet-statistics -c ~/peer1.conf
# print statistics about DHT service:
$ gnunet-statistics -c ~/peer1.conf -s dht

Starting Two Peers by Hand

This section describes how to start two peers on the same machine by hand. The process is rather painful, but the description is somewhat instructive. In practice, you might prefer the automated method (see Starting Peers Using the Testbed Service).

Setup a second peer

We will now start a second peer on your machine. For the second peer, you will need to manually create a modified configuration file to avoid conflicts with ports and directories. A peers configuration file is by default located in ~/.gnunet/gnunet.conf. This file is typically very short or even empty as only the differences to the defaults need to be specified. The defaults are located in many files in the $PREFIX/share/gnunet/config.d directory.

To configure the second peer, use the files $PREFIX/share/gnunet/config.d as a template for your main configuration file:

$ cat $PREFIX/share/gnunet/config.d/*.conf > peer2.conf

Now you have to edit peer2.conf and change:

  • Every (uncommented) value for “PORT” (add 10000) in any section (the option may be commented out if PORT is prefixed by "#", in this case, UNIX domain sockets are used and the PORT option does not need to be touched)
  • Every value for “UNIXPATH” in any section (e.g. by adding a "-p2" suffix)

to a fresh, unique value. Make sure that the PORT numbers stay below 65536. From now on, whenever you interact with the second peer, you need to specify -c peer2.conf as an additional command line argument.

Now, generate the 2nd peer’s private key:

$ gnunet-peerinfo -s -c peer2.conf

This may take a while, generate entropy using your keyboard or mouse as needed. Also, make sure the output is different from the gnunet-peerinfo output for the first peer (otherwise you made an error in the configuration).

Start the second peer and connect the peers

Then, you can start a second peer using:

$ gnunet-arm -c peer2.conf -s
$ gnunet-arm -c peer2.conf -i dht
$ ~/gnunet/src/dht/gnunet-dht-put -c peer2.conf -k KEY -d VALUE
$ ~/gnunet/src/dht/gnunet-dht-get -c peer2.conf -k KEY

If you want the two peers to connect, you have multiple options:

  • UDP neighbour discovery (automatic)
  • Setup a bootstrap server
  • Connect manually

To setup peer 1 as bootstrapping server change the configuration of the first one to be a hostlist server by adding the following lines to peer1.conf to enable bootstrapping server:


Then change peer2.conf and replace the “SERVERS” line in the “[hostlist]” section with “http://localhost:8080/“. Restart both peers using:

# stop first peer
$ gnunet-arm -c peer1.conf -e
# start first peer
$ gnunet-arm -c peer1.conf -s
# start second peer
$ gnunet-arm -c peer2.conf -s

Note that if you start your peers without changing these settings, they will use the “global” hostlist servers of the GNUnet P2P network and likely connect to those peers. At that point, debugging might become tricky as you’re going to be connected to many more peers and would likely observe traffic and behaviors that are not explicitly controlled by you.

How to connect manually

If you want to use the peerinfo tool to connect your peers, you should:

  • Set IMMEDIATE_START = NO in section hostlist (to not connect to the global GNUnet)
  • Start both peers running gnunet-arm -c peer1.conf -s and gnunet-arm -c peer2.conf -s
  • Get HELLO message of the first peer running gnunet-peerinfo -c peer1.conf -g
  • Give the output to the second peer by running gnunet-peerinfo -c peer2.conf -p '<output>'

Check that they are connected using gnunet-core -c peer1.conf, which should give you the other peer’s peer identity:

$ gnunet-core -c peer1.conf
Peer `9TVUCS8P5A7ILLBGO6 [...shortened...] 1KNBJ4NGCHP3JPVULDG'

Starting Peers Using the Testbed Service

GNUnet’s testbed service is used for testing scenarios where a number of peers are to be started. The testbed can manage peers on a single host or on multiple hosts in a distributed fashion. On a single affordable computer, it should be possible to run around tens of peers without drastically increasing the load on the system.

The testbed service can be access through its API include/gnunet\_testbed\_service.h. The API provides many routines for managing a group of peers. It also provides a helper function GNUNET\_TESTBED\_test\_run() to quickly setup a minimalistic testing environment on a single host.

This function takes a configuration file which will be used as a template configuration for the peers. The testbed takes care of modifying relevant options in the peers’ configuration such as SERVICEHOME, PORT, UNIXPATH to unique values so that peers run without running into conflicts. It also checks and assigns the ports in configurations only if they are free.

Additionally, the testbed service also reads its options from the same configuration file. Various available options and details about them can be found in the testbed default configuration file src/testbed/testbed.conf.

With the testbed API, a sample test case can be structured as follows:

#include <unistd.h>
#include <gnunet/platform.h>
#include <gnunet/gnunet_util_lib.h>
#include <gnunet/gnunet_testbed_service.h>
#include <gnunet/gnunet_dht_service.h>
#define NUM_PEERS 20
static struct GNUNET_TESTBED_Operation *dht_op;
static struct GNUNET_DHT_Handle *dht_handle;
struct MyContext

int ht_len; } ctxt; static int result; static void shutdown_task (void *cls) {
if (NULL != dht_op)
GNUNET_TESTBED_operation_done (dht_op);
dht_op = NULL;
dht_handle = NULL;
result = GNUNET_OK; } static void service_connect_comp (void *cls,
struct GNUNET_TESTBED_Operation *op,
void *ca_result,
const char *emsg) {
GNUNET_assert (op == dht_op);
dht_handle = ca_result;
// Do work here...
GNUNET_SCHEDULER_shutdown (); } static void * dht_ca (void *cls, const struct GNUNET_CONFIGURATION_Handle *cfg) {
struct MyContext *ctxt = cls;
dht_handle = GNUNET_DHT_connect (cfg, ctxt->ht_len);
return dht_handle; } static void dht_da (void *cls, void *op_result) {
struct MyContext *ctxt = cls;
GNUNET_DHT_disconnect ((struct GNUNET_DHT_Handle *) op_result);
dht_handle = NULL; } static void test_master (void *cls,
struct GNUNET_TESTBED_RunHandle *h,
unsigned int num_peers,
struct GNUNET_TESTBED_Peer **peers,
unsigned int links_succeeded,
unsigned int links_failed) {
ctxt.ht_len = 10;
dht_op = GNUNET_TESTBED_service_connect
(NULL, peers[0], "dht",
&service_connect_comp, NULL,
&dht_ca, &dht_da, &ctxt);
GNUNET_SCHEDULER_add_shutdown (&shutdown_task, NULL); } int main (int argc, char **argv) {
int ret;
ret = GNUNET_TESTBED_test_run
("awesome-test", "template.conf",
NULL, NULL, &test_master, NULL);
if ( (GNUNET_OK != ret) || (GNUNET_OK != result) )
return 1;
return 0; }

The source code for the above listing can be found at or in the doc/ folder of your repository check-out. After installing GNUnet, the above source code can be compiled as:

$ export CPPFLAGS="-I/path/to/gnunet/headers"
$ export LDFLAGS="-L/path/to/gnunet/libraries"
$ gcc $CPPFLAGS $LDFLAGS -o testbed-test testbed_test.c \

-lgnunettestbed -lgnunetdht -lgnunetutil # Generate (empty) configuration $ touch template.conf # run it (press CTRL-C to stop) $ ./testbed-test

The CPPFLAGS and LDFLAGS are necessary if GNUnet is installed into a different directory other than /usr/local.

All of testbed API’s peer management functions treat management actions as operations and return operation handles. It is expected that the operations begin immediately, but they may get delayed (to balance out load on the system). The program using the API then has to take care of marking the operation as “done” so that its associated resources can be freed immediately and other waiting operations can be executed. Operations will be canceled if they are marked as “done” before their completion.

An operation is treated as completed when it succeeds or fails. Completion of an operation is either conveyed as events through controller event callback or through respective operation completion callbacks. In functions which support completion notification through both controller event callback and operation completion callback, first the controller event callback will be called. If the operation is not marked as done in that callback or if the callback is given as NULL when creating the operation, the operation completion callback will be called. The API documentation shows which event are to be expected in the controller event notifications. It also documents any exceptional behaviour.

Once the peers are started, test cases often need to connect some of the peers’ services. Normally, opening a connect to a peer’s service requires the peer’s configuration. While using testbed, the testbed automatically generates per-peer configuration. Accessing those configurations directly through file system is discouraged as their locations are dynamically created and will be different among various runs of testbed. To make access to these configurations easy, testbed API provides the function GNUNET\_TESTBED\_service\_connect(). This function fetches the configuration of a given peer and calls the Connect Adapter. In the example code, it is the dht\_ca. A connect adapter is expected to open the connection to the needed service by using the provided configuration and return the created service connection handle. Successful connection to the needed service is signaled through service\_connect\_comp\_cb.

A dual to connect adapter is the Disconnect Adapter. This callback is called after the connect adapter has been called when the operation from GNUNET\_TESTBED\_service\_connect() is marked as “done”. It has to disconnect from the service with the provided service handle (op\_result).

Exercise: Find out how many peers you can run on your system.

Exercise: Find out how to create a 2D torus topology by changing the options in the configuration file. See section “The GNUnet Reference Documentation” in The GNUnet Reference Documentation, then use the DHT API to store and retrieve values in the network.

Developing Applications


To develop a new peer-to-peer application or to extend GNUnet we provide a template build system for writing GNUnet extensions in C. It can be obtained as follows:

$ git clone
$ cd gnunet-ext/
$ ./bootstrap
$ ./configure --prefix=$PREFIX --with-gnunet=$PREFIX
$ make
$ make install
$ make check

The GNUnet ext template includes examples and a working buildsystem for a new GNUnet service. A common GNUnet service consists of the following parts which will be discussed in detail in the remainder of this document. The functionality of a GNUnet service is implemented in:

  • the GNUnet service (gnunet-ext/src/ext/gnunet-service-ext.c)
  • the client API (gnunet-ext/src/ext/ext_api.c)
  • the client application using the service API (gnunet-ext/src/ext/gnunet-ext.c)

The interfaces for these entities are defined in:

  • client API interface (gnunet-ext/src/ext/ext.h)
  • the service interface (gnunet-ext/src/include/gnunet_service_SERVICE.h)
  • the P2P protocol (gnunet-ext/src/include/gnunet_protocols_ext.h)

In addition the ext systems provides:

  • a test testing the API (gnunet-ext/src/ext/test_ext_api.c)
  • a configuration template for the service (gnunet-ext/src/ext/

Adapting the Template

The first step for writing any extension with a new service is to ensure that the file contains entries for the UNIXPATH, PORT and BINARY for the service in a section named after the service.

If you want to adapt the template rename the to match your services name, you have to modify the AC\_OUTPUT section in in the gnunet-ext root.

Writing a Client Application

When writing any client application (for example, a command-line tool), the basic structure is to start with the GNUNET\_PROGRAM\_run function. This function will parse command-line options, setup the scheduler and then invoke the run function (with the remaining non-option arguments) and a handle to the parsed configuration (and the configuration file name that was used, which is typically not needed):

#include <gnunet/platform.h>
#include <gnunet/gnunet_util_lib.h>
static int ret;
static void
run (void *cls,

char *const *args,
const char *cfgfile,
const struct GNUNET_CONFIGURATION_Handle *cfg) {
// main code here
ret = 0; } int main (int argc, char *const *argv) {
struct GNUNET_GETOPT_CommandLineOption options[] = {
return (GNUNET_OK ==
gettext_noop ("binary description text"),
options, &run, NULL)) ? ret : 1; }

Handling command-line options

Options can then be added easily by adding global variables and expanding the options array. For example, the following would add a string-option and a binary flag (defaulting to NULL and GNUNET\_NO respectively):

static char *string_option;
static int a_flag;
// ...

struct GNUNET_GETOPT_CommandLineOption options[] = {
GNUNET_GETOPT_option_string ('s', "name", "SOMESTRING",
gettext_noop ("text describing the string_option NAME"),
GNUNET_GETOPT_option_flag ('f', "flag",
gettext_noop ("text describing the flag option"),
string_option = NULL;
a_flag = GNUNET_SYSERR; // ...

Issues such as displaying some helpful text describing options using the --help argument and error handling are taken care of when using this approach. Other GNUNET\_GETOPT\_-functions can be used to obtain integer value options, increment counters, etc. You can even write custom option parsers for special circumstances not covered by the available handlers. To check if an argument was specified by the user you initialize the variable with a specific value (e.g. NULL for a string and GNUNET_SYSERR for a integer) and check after parsing happened if the values were modified.

Inside the run method, the program would perform the application-specific logic, which typically involves initializing and using some client library to interact with the service. The client library is supposed to implement the IPC whereas the service provides more persistent P2P functions.

Exercise: Add a few command-line options and print them inside of run. What happens if the user gives invalid arguments?

Writing a Client Library

The first and most important step in writing a client library is to decide on an API for the library. Typical API calls include connecting to the service, performing application-specific requests and cleaning up. Many examples for such service APIs can be found in the gnunet/src/include/gnunet\_*\_service.h files.

Then, a client-service protocol needs to be designed. This typically involves defining various message formats in a header that will be included by both the service and the client library (but is otherwise not shared and hence located within the service’s directory and not installed by make install). Each message must start with a struct GNUNET\_MessageHeader and must be shorter than 64k. By convention, all fields in IPC (and P2P) messages must be in big-endian format (and thus should be read using ntohl and similar functions and written using htonl and similar functions). Unique message types must be defined for each message struct in the gnunet\_protocols.h header (or an extension-specific include file).

Connecting to the Service

Before a client library can implement the application-specific protocol with the service, a connection must be created:

struct GNUNET_MQ_MessageHandlers handlers[] = {

// ...
GNUNET_MQ_handler_end () }; struct GNUNET_MQ_Handle *mq; mq = GNUNET_CLIENT_connect (cfg,

As a result a GNUNET\_MQ\_Handle is returned which can to used henceforth to transmit messages to the service. The complete MQ API can be found in gnunet\_mq\_lib.h. The handlers array in the example above is incomplete. Here is where you will define which messages you expect to receive from the service, and which functions handle them. The error\_cb is a function that is to be called whenever there are errors communicating with the service.

Sending messages

In GNUnet, messages are always sent beginning with a struct GNUNET\_MessageHeader in big endian format. This header defines the size and the type of the message, the payload follows after this header.

struct GNUNET_MessageHeader

uint16_t size GNUNET_PACKED;
uint16_t type GNUNET_PACKED; };

Existing message types are defined in gnunet\_protocols.h. A common way to create a message is with an envelope:

struct GNUNET_MQ_Envelope *env;
struct GNUNET_MessageHeader *msg;
env = GNUNET_MQ_msg_extra (msg, payload_size, GNUNET_MY_MESSAGE_TYPE);
GNUNET_memcpy (&msg[1],

payload_size); // Send message via message queue 'mq' GNUNET_mq_send (mq, env);

Exercise: Define a message struct that includes a 32-bit unsigned integer in addition to the standard GNUnet MessageHeader. Add a C struct and define a fresh protocol number for your message. Protocol numbers in gnunet-ext are defined in gnunet-ext/src/include/gnunet_protocols_ext.h

Exercise: Find out how you can determine the number of messages in a message queue.

Exercise: Find out how you can determine when a message you have queued was actually transmitted.

Exercise: Define a helper function to transmit a 32-bit unsigned integer (as payload) to a service using some given client handle.

Receiving Replies from the Service

Clients can receive messages from the service using the handlers specified in the handlers array we specified when connecting to the service. Entries in the the array are usually created using one of two macros, depending on whether the message is fixed size or variable size. Variable size messages are managed using two callbacks, one to check that the message is well-formed, the other to actually process the message. Fixed size messages are fully checked by the MQ-logic, and thus only need to provide the handler to process the message. Note that the prefixes check\_ and handle\_ are mandatory.

static void
handle_fix (void *cls, const struct MyMessage *msg)

// process 'msg' } static int check_var (void *cls, const struct MyVarMessage *msg) {
// check 'msg' is well-formed
return GNUNET_OK; } static void handle_var (void *cls, const struct MyVarMessage *msg) {
// process 'msg' } struct GNUNET_MQ_MessageHandler handlers[] = {
GNUNET_MQ_hd_fixed_size (fix,
struct MyMessage,
GNUNET_MQ_hd_fixed_size (var,
struct MyVarMessage,
GNUNET_MQ_handler_end () };

Exercise: Expand your helper function to receive a response message (for example, containing just the struct GNUnet MessageHeader without any payload). Upon receiving the service’s response, you should call a callback provided to your helper function’s API.

Exercise: Figure out where you can pass values to the closures (cls).

Writing a user interface

Given a client library, all it takes to access a service now is to combine calls to the client library with parsing command-line options.

Exercise: Call your client API from your run() method in your client application to send a request to the service. For example, send a 32-bit integer value based on a number given at the command-line to the service.

Writing a Service

Before you can test the client you’ve written so far, you’ll need to also implement the corresponding service.

Code Placement

New services are placed in their own subdirectory under gnunet/src. This subdirectory should contain the API implementation file SERVICE\_api.c, the description of the client-service protocol SERVICE.h and P2P protocol SERVICE\_protocol.h, the implementation of the service itself gnunet-service-SERVICE.h and several files for tests, including test code and configuration files.

Starting a Service

The key API definition for creating a service is the GNUNET\_SERVICE\_MAIN macro:


GNUNET_MQ_hd_fixed_size (...),
GNUNET_MQ_hd_var_size (...),
GNUNET_MQ_handler_end ());

In addition to the service name and flags, the macro takes three functions, typically called run, client\_connect\_cb and client\_disconnect\_cb as well as an array of message handlers that will be called for incoming messages from clients.

A minimal version of the three central service functions would look like this:

static void
run (void *cls,

const struct GNUNET_CONFIGURATION_Handle *c,
struct GNUNET_SERVICE_Handle *service) { } static void * client_connect_cb (void *cls,
struct GNUNET_SERVICE_Client *c,
struct GNUNET_MQ_Handle *mq) {
return c; } static void client_disconnect_cb (void *cls,
struct GNUNET_SERVICE_Client *c,
void *internal_cls) {
GNUNET_assert (c == internal_cls); }

Exercise: Write a stub service that processes no messages at all in your code. Create a default configuration for it, integrate it with the build system and start the service from gnunet-service-arm using gnunet-arm -i NAME.

Exercise: Figure out how to set the closure (cls) for handlers of a service.

Exercise: Figure out how to send messages from the service back to the client.

Each handler function in the service must eventually (possibly in some asynchronous continuation) call GNUNET\_SERVICE\_client\_continue(). Only after this call additional messages from the same client may be processed. This way, the service can throttle processing messages from the same client.

Exercise: Change the service to “handle” the message from your client (for now, by printing a message). What happens if you forget to call GNUNET\_SERVICE\_client\_continue()?

Interacting directly with other Peers using the CORE Service

FIXME: This section still needs to be updated to the latest API!

One of the most important services in GNUnet is the CORE service managing connections between peers and handling encryption between peers.

One of the first things any service that extends the P2P protocol typically does is connect to the CORE service using:

#include <gnunet/gnunet_core_service.h>
struct GNUNET_CORE_Handle *
GNUNET_CORE_connect (const struct GNUNET_CONFIGURATION_Handle *cfg,

void *cls,
GNUNET_CORE_StartupCallback init,
GNUNET_CORE_ConnectEventHandler connects,
GNUNET_CORE_DisconnectEventHandler disconnects,
const struct GNUNET_MQ_MessageHandler *handlers);

New P2P connections

Before any traffic with a different peer can be exchanged, the peer must be known to the service. This is notified by the CORE connects callback, which communicates the identity of the new peer to the service:

void *
connects (void *cls,

const struct GNUNET_PeerIdentity *peer,
struct GNUNET_MQ_Handle *mq) {
return mq; }

Note that whatever you return from connects is given as the cls argument to the message handlers for messages from the respective peer.

Exercise: Create a service that connects to the CORE. Then start (and connect) two peers and print a message once your connect callback is invoked.

Receiving P2P Messages

To receive messages from CORE, you pass the desired handlers to the GNUNET\_CORE\_connect() function, just as we showed for services.

It is your responsibility to process messages fast enough or to implement flow control. If an application does not process CORE messages fast enough, CORE will randomly drop messages to not keep a very long queue in memory.

Exercise: Start one peer with a new service that has a message handler and start a second peer that only has your “old” service without message handlers. Which “connect” handlers are invoked when the two peers are connected? Why?

Sending P2P Messages

You can transmit messages to other peers using the mq you were given during the connect callback. Note that the mq automatically is released upon disconnect and that you must not use it afterwards.

It is your responsibility to not over-fill the message queue, GNUnet will send the messages roughly in the order given as soon as possible.

Exercise: Write a service that upon connect sends messages as fast as possible to the other peer (the other peer should run a service that “processes” those messages). How fast is the transmission? Count using the STATISTICS service on both ends. Are messages lost? How can you transmit messages faster? What happens if you stop the peer that is receiving your messages?

End of P2P connections

If a message handler returns GNUNET\_SYSERR, the remote peer shuts down or there is an unrecoverable network disconnection, CORE notifies the service that the peer disconnected. After this notification no more messages will be received from the peer and the service is no longer allowed to send messages to the peer. The disconnect callback looks like the following:

disconnects (void *cls,

const struct GNUNET_PeerIdentity * peer) {
/* Remove peer's identity from known peers */
/* Make sure no messages are sent to peer from now on */ }

Exercise: Fix your service to handle peer disconnects.

Storing peer-specific data using the PEERSTORE service

GNUnet’s PEERSTORE service offers a persistorage for arbitrary peer-specific data. Other GNUnet services can use the PEERSTORE to store, retrieve and monitor data records. Each data record stored with PEERSTORE contains the following fields:

  • subsystem: Name of the subsystem responsible for the record.
  • peerid: Identity of the peer this record is related to.
  • key: a key string identifying the record.
  • value: binary record value.
  • expiry: record expiry date.

The first step is to start a connection to the PEERSTORE service:

#include "gnunet_peerstore_service.h"
peerstore_handle = GNUNET_PEERSTORE_connect (cfg);

The service handle peerstore_handle will be needed for all subsequent PEERSTORE operations.

Storing records

To store a new record, use the following function:

struct GNUNET_PEERSTORE_StoreContext *

const char *sub_system,
const struct GNUNET_PeerIdentity *peer,
const char *key,
const void *value,
size_t size,
struct GNUNET_TIME_Absolute expiry,
enum GNUNET_PEERSTORE_StoreOption options,
GNUNET_PEERSTORE_Continuation cont,
void *cont_cls);

The options parameter can either be GNUNET_PEERSTORE_STOREOPTION_MULTIPLE which means that multiple values can be stored under the same key combination (subsystem, peerid, key), or GNUNET_PEERSTORE_STOREOPTION_REPLACE which means that PEERSTORE will replace any existing values under the given key combination (subsystem, peerid, key) with the new given value.

The continuation function cont will be called after the store request is successfully sent to the PEERSTORE service. This does not guarantee that the record is successfully stored, only that it was received by the service.

The GNUNET_PEERSTORE_store function returns a handle to the store operation. This handle can be used to cancel the store operation only before the continuation function is called:

GNUNET_PEERSTORE_store_cancel (struct GNUNET_PEERSTORE_StoreContext


Retrieving records

To retrieve stored records, use the following function:

struct GNUNET_PEERSTORE_IterateContext *

const char *sub_system,
const struct GNUNET_PeerIdentity *peer,
const char *key,
GNUNET_PEERSTORE_Processor callback,
void *callback_cls);

The values of peer and key can be NULL. This allows the iteration over values stored under any of the following key combinations:

  • (subsystem)
  • (subsystem, peerid)
  • (subsystem, key)
  • (subsystem, peerid, key)

The callback function will be called once with each retrieved record and once more with a NULL record to signal the end of results.

The GNUNET_PEERSTORE_iterate function returns a handle to the iterate operation. This handle can be used to cancel the iterate operation only before the callback function is called with a NULL record.

Monitoring records

PEERSTORE offers the functionality of monitoring for new records stored under a specific key combination (subsystem, peerid, key). To start the monitoring, use the following function:

struct GNUNET_PEERSTORE_WatchContext *

const char *sub_system,
const struct GNUNET_PeerIdentity *peer,
const char *key,
GNUNET_PEERSTORE_Processor callback,
void *callback_cls);

Whenever a new record is stored under the given key combination, the callback function will be called with this new record. This will continue until the connection to the PEERSTORE service is broken or the watch operation is canceled:

GNUNET_PEERSTORE_watch_cancel (struct GNUNET_PEERSTORE_WatchContext


Disconnecting from PEERSTORE

When the connection to the PEERSTORE service is no longer needed, disconnect using the following function:

GNUNET_PEERSTORE_disconnect (struct GNUNET_PEERSTORE_Handle *h,

int sync_first);

If the sync_first flag is set to GNUNET_YES, the API will delay the disconnection until all store requests are received by the PEERSTORE service. Otherwise, it will disconnect immediately.

Using the DHT

The DHT allows to store data so other peers in the P2P network can access it and retrieve data stored by any peers in the network. This section will explain how to use the DHT. Of course, the first thing to do is to connect to the DHT service:

dht_handle = GNUNET_DHT_connect (cfg, parallel_requests);

The second parameter indicates how many requests in parallel to expect. It is not a hard limit, but a good approximation will make the DHT more efficient.

Storing data in the DHT

Since the DHT is a dynamic environment (peers join and leave frequently) the data that we put in the DHT does not stay there indefinitely. It is important to “refresh” the data periodically by simply storing it again, in order to make sure other peers can access it.

The put API call offers a callback to signal that the PUT request has been sent. This does not guarantee that the data is accessible to others peers, or even that is has been stored, only that the service has requested to a neighboring peer the retransmission of the PUT request towards its final destination. Currently there is no feedback about whether or not the data has been successfully stored or where it has been stored. In order to improve the availablilty of the data and to compensate for possible errors, peers leaving and other unfavorable events, just make several PUT requests!

message_sent_cont (void *cls,

const struct GNUNET_SCHEDULER_TaskContext *tc) {
// Request has left local node } struct GNUNET_DHT_PutHandle * GNUNET_DHT_put (struct GNUNET_DHT_Handle *handle,
const struct GNUNET_HashCode *key,
uint32_t desired_replication_level,
enum GNUNET_DHT_RouteOption options,
enum GNUNET_BLOCK_Type type,
size_t size,
const void *data,
struct GNUNET_TIME_Absolute exp,
struct GNUNET_TIME_Relative timeout,
GNUNET_DHT_PutContinuation cont, void *cont_cls)

Exercise: Store a value in the DHT periodically to make sure it is available over time. You might consider using the function GNUNET\_SCHEDULER\_add\_delayed and call GNUNET\_DHT\_put from inside a helper function.

Obtaining data from the DHT

As we saw in the previous example, the DHT works in an asynchronous mode. Each request to the DHT is executed “in the background” and the API calls return immediately. In order to receive results from the DHT, the API provides a callback. Once started, the request runs in the service, the service will try to get as many results as possible (filtering out duplicates) until the timeout expires or we explicitly stop the request. It is possible to give a “forever” timeout with GNUNET\_TIME\_UNIT\_FOREVER\_REL.

If we give a route option GNUNET\_DHT\_RO\_RECORD\_ROUTE the callback will get a list of all the peers the data has travelled, both on the PUT path and on the GET path.

static void
get_result_iterator (void *cls, struct GNUNET_TIME_Absolute expiration,

const struct GNUNET_HashCode *key,
const struct GNUNET_PeerIdentity *get_path,
unsigned int get_path_length,
const struct GNUNET_PeerIdentity *put_path,
unsigned int put_path_length,
enum GNUNET_BLOCK_Type type, size_t size,
const void *data) {
// Optionally:
GNUNET_DHT_get_stop (get_handle); } get_handle =
GNUNET_DHT_get_start (dht_handle,

Exercise: Store a value in the DHT and after a while retrieve it. Show the IDs of all the peers the requests have gone through. In order to convert a peer ID to a string, use the function GNUNET\_i2s. Pay attention to the route option parameters in both calls!

Implementing a block plugin

In order to store data in the DHT, it is necessary to provide a block plugin. The DHT uses the block plugin to ensure that only well-formed requests and replies are transmitted over the network.

The block plugin should be put in a file plugin\_block\_SERVICE.c in the service’s respective directory. The mandatory functions that need to be implemented for a block plugin are described in the following sections.

Validating requests and replies

The evaluate function should validate a reply or a request. It returns a GNUNET\_BLOCK\_EvaluationResult, which is an enumeration. All possible answers are in gnunet\_block\_lib.h. The function will be called with a reply\_block argument of NULL for requests. Note that depending on how evaluate is called, only some of the possible return values are valid. The specific meaning of the xquery argument is application-specific. Applications that do not use an extended query should check that the xquery\_size is zero. The block group is typically used to filter duplicate replies.

static enum GNUNET_BLOCK_EvaluationResult
block_plugin_SERVICE_evaluate (void *cls,

enum GNUNET_BLOCK_Type type,
struct GNUNET_BlockGroup *bg,
const GNUNET_HashCode *query,
const void *xquery,
size_t xquery_size,
const void *reply_block,
size_t reply_block_size) {
// Verify type, block and bg }

Note that it is mandatory to detect duplicate replies in this function and return the respective status code. Duplicate detection is typically done using the Bloom filter block group provided by Failure to do so may cause replies to circle in the network.

Deriving a key from a reply

The DHT can operate more efficiently if it is possible to derive a key from the value of the corresponding block. The get\_key function is used to obtain the key of a block — for example, by means of hashing. If deriving the key is not possible, the function should simply return GNUNET\_SYSERR (the DHT will still work just fine with such blocks).

static int
block_plugin_SERVICE_get_key (void *cls, enum GNUNET_BLOCK_Type type,

const void *block, size_t block_size,
struct GNUNET_HashCode *key) {
// Store the key in the key argument, return GNUNET_OK on success. }

Initialization of the plugin

The plugin is realized as a shared C library. The library must export an initialization function which should initialize the plugin. The initialization function specifies what block types the plugin cares about and returns a struct with the functions that are to be used for validation and obtaining keys (the ones just defined above).

void *
libgnunet_plugin_block_SERVICE_init (void *cls)

static enum GNUNET_BLOCK_Type types[] =
struct GNUNET_BLOCK_PluginFunctions *api;
api = GNUNET_new (struct GNUNET_BLOCK_PluginFunctions);
api->evaluate = &block_plugin_SERICE_evaluate;
api->get_key = &block_plugin_SERVICE_get_key;
api->types = types;
return api; }

Shutdown of the plugin

Following GNUnet’s general plugin API concept, the plugin must export a second function for cleaning up. It usually does very little.

void *
libgnunet_plugin_block_SERVICE_done (void *cls)

struct GNUNET_TRANSPORT_PluginFunctions *api = cls;
GNUNET_free (api);
return NULL; }

Integration of the plugin with the build system

In order to compile the plugin, the file for the service SERVICE should contain a rule similar to this:

plugindir = $(libdir)/gnunet
plugin_LTLIBRARIES = \ libgnunet_plugin_block_ext_la_SOURCES = \
plugin_block_ext.c libgnunet_plugin_block_ext_la_LIBADD = \
$(prefix)/lib/ \
$(prefix)/lib/ \
$(prefix)/lib/ libgnunet_plugin_block_ext_la_LDFLAGS = \
$(GN_PLUGIN_LDFLAGS) libgnunet_plugin_block_ext_la_DEPENDENCIES = \

Exercise: Write a block plugin that accepts all queries and all replies but prints information about queries and replies when the respective validation hooks are called.

Monitoring the DHT

It is possible to monitor the functioning of the local DHT service. When monitoring the DHT, the service will alert the monitoring program of any events, both started locally or received for routing from another peer. The are three different types of events possible: a GET request, a PUT request or a response (a reply to a GET).

Since the different events have different associated data, the API gets 3 different callbacks (one for each message type) and optional type and key parameters, to allow for filtering of messages. When an event happens, the appropriate callback is called with all the information about the event.

static void
get_callback (void *cls,

enum GNUNET_DHT_RouteOption options,
enum GNUNET_BLOCK_Type type,
uint32_t hop_count,
uint32_t desired_replication_level,
unsigned int path_length,
const struct GNUNET_PeerIdentity *path,
const struct GNUNET_HashCode * key) { } static void get_resp_callback (void *cls,
enum GNUNET_BLOCK_Type type,
const struct GNUNET_PeerIdentity *get_path,
unsigned int get_path_length,
const struct GNUNET_PeerIdentity *put_path,
unsigned int put_path_length,
struct GNUNET_TIME_Absolute exp,
const struct GNUNET_HashCode * key,
const void *data,
size_t size) { } static void put_callback (void *cls,
enum GNUNET_DHT_RouteOption options,
enum GNUNET_BLOCK_Type type,
uint32_t hop_count,
uint32_t desired_replication_level,
unsigned int path_length,
const struct GNUNET_PeerIdentity *path,
struct GNUNET_TIME_Absolute exp,
const struct GNUNET_HashCode * key,
const void *data,
size_t size) { } monitor_handle = GNUNET_DHT_monitor_start (dht_handle,

Debugging with gnunet-arm

Even if services are managed by gnunet-arm, you can start them with gdb or valgrind. For example, you could add the following lines to your configuration file to start the DHT service in a gdb session in a fresh xterm:

PREFIX=xterm -e gdb --args

Alternatively, you can stop a service that was started via ARM and run it manually:

$ gnunet-arm -k dht
$ gdb --args gnunet-service-dht -L DEBUG
$ valgrind gnunet-service-dht -L DEBUG

Assuming other services are well-written, they will automatically re-integrate the restarted service with the peer.

GNUnet provides a powerful logging mechanism providing log levels ERROR, WARNING, INFO and DEBUG. The current log level is configured using the $GNUNET_FORCE_LOG environmental variable. The DEBUG level is only available if --enable-logging=verbose was used when running configure. More details about logging can be found under

You should also probably enable the creation of core files, by setting ulimit, and echo’ing 1 into /proc/sys/kernel/core\_uses\_pid. Then you can investigate the core dumps with gdb, which is often the fastest method to find simple errors.

Exercise: Add a memory leak to your service and obtain a trace pointing to the leak using valgrind while running the service from gnunet-service-arm.

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or any later version published by the Free Software Foundation;
with no Invariant Sections, no Front-Cover Texts, and no Back-Cover
Texts.  A copy of the license is included in the section entitled ``GNU
Free Documentation License''.

If you have Invariant Sections, Front-Cover Texts and Back-Cover Texts, replace the “with…Texts.” line with this:

with the Invariant Sections being list their titles, with
the Front-Cover Texts being list, and with the Back-Cover Texts
being list.

If you have Invariant Sections without Cover Texts, or some other combination of the three, merge those two alternatives to suit the situation.

If your document contains nontrivial examples of program code, we recommend releasing these examples in parallel under your choice of free software license, such as the GNU General Public License, to permit their use in free software.


The code documentation will soon be ported here. Until then you can find it in the old place:


On this page you can find links to our RFC-style technical protocol specifications:

  • LSD0000: Reserved
  • LSD0001: The GNU Name System
  • LSD0002: re:claimID
  • LSD0003: Byzantine Fault Tolerant Set Reconciliation (work-in-progress)
  • LSD0004: The R5N Distributed Hash Table (work-in-progress)


The GNUnet Assigned Numbers Authority (GANA) contains various registries we maintain, for GNUnet other projects that need names and numbers for use in network protocols. If you need to open a new registry, please feel free to contact us at

The registries can be found here:


Barry Leiba wrote on April 4th 2020 that “Neither IANA nor participants in the IETF will have any necessary expertise to evaluate registration requests in the sort of registry described, and no one will be well served by the creation of such a registry at IANA. It would be far better to have a registration process be described in this document involving experts from the industry as reviewers and maintenance of the registrations by an industry organization, rather than by IANA.”

So here we are. As IETF/IANA “lack the necessary expertise to operate a registry” for names and numbers used in network protocols, the GNUnet project is happy to step up.


The GANA database is licensed under the GPL. See COPYING in the Git repository.


Each registry must have a unique name and all associated information lives in a directory under that unique name in the Git repository.

Each registry must include at least the following files:

  • README[.*]: document describing the purpose of the registry in English
  • POLICY[.*]: registration policy, explaining required fields and the procedure for adding, updating and deleting entries
  • registry.rec: GNU recutils data file with all of the current entries in the registry
  • Makefile: GNU make makefile with a make check target to run the validation logic. Ideally, the registry.rec should be written such that the check target is simply invoking recfix --check registry.rec. Additional targets to convert data.rec to various formats may be defined. In particular, see in the root directory of the Git repository (try --help).


The graphical configuration interface

If you also would like to use gnunet-gtk and gnunet-setup (highly recommended for beginners), do:

Configuring your peer

This chapter will describe the various configuration options in GNUnet.

The easiest way to configure your peer is to use the gnunet-setup tool. gnunet-setup is part of the gnunet-gtk package. You might have to install it separately.

Many of the specific sections from this chapter actually are linked from within gnunet-setup to help you while using the setup tool.

While you can also configure your peer by editing the configuration file by hand, this is not recommended for anyone except for developers as it requires a more in-depth understanding of the configuration files and internal dependencies of GNUnet.

Configuration of the HOSTLIST proxy settings

The hostlist client can be configured to use a proxy to connect to the hostlist server. This functionality can be configured in the configuration file directly or using the gnunet-setup tool.

The hostlist client supports the following proxy types at the moment:

  • HTTP and HTTP 1.0 only proxy
  • SOCKS 4/4a/5/5 with hostname

In addition authentication at the proxy with username and password can be configured.

To configure proxy support for the hostlist client in the gnunet-setup tool, select the "hostlist" tab and select the appropriate proxy type. The hostname or IP address (including port if required) has to be entered in the "Proxy hostname" textbox. If required, enter username and password in the "Proxy username" and "Proxy password" boxes. Be aware that this information will be stored in the configuration in plain text (TODO: Add explanation and generalize the part in Chapter 3.6 about the encrypted home).

Configuration of the HTTP and HTTPS transport plugins

The client parts of the http and https transport plugins can be configured to use a proxy to connect to the hostlist server. This functionality can be configured in the configuration file directly or using the gnunet-setup tool.

Both the HTTP and HTTPS clients support the following proxy types at the moment:

  • HTTP 1.1 proxy
  • SOCKS 4/4a/5/5 with hostname

In addition authentication at the proxy with username and password can be configured.

To configure proxy support for the clients in the gnunet-setup tool, select the "transport" tab and activate the respective plugin. Now you can select the appropriate proxy type. The hostname or IP address (including port if required) has to be entered in the "Proxy hostname" textbox. If required, enter username and password in the "Proxy username" and "Proxy password" boxes. Be aware that these information will be stored in the configuration in plain text.

GTK File-sharing User Interface

This chapter describes first steps for file-sharing with GNUnet. To start, you should launch gnunet-fs-gtk.

As we want to be sure that the network contains the data that we are looking for for testing, we need to begin by publishing a file.


To publish a file, select "File Sharing" in the menu bar just below the "Statistics" icon, and then select "Publish" from the menu.

Afterwards, the following publishing dialog will appear:


In this dialog, select the "Add File" button. This will open a file selection dialog:


Now, you should select a file from your computer to be published on GNUnet. To see more of GNUnet’s features later, you should pick a PNG or JPEG file this time. You can leave all of the other options in the dialog unchanged. Confirm your selection by pressing the "OK" button in the bottom right corner. Now, you will briefly see a "Messages..." dialog pop up, but most likely it will be too short for you to really read anything. That dialog is showing you progress information as GNUnet takes a first look at the selected file(s). For a normal image, this is virtually instant, but if you later import a larger directory you might be interested in the progress dialog and potential errors that might be encountered during processing. After the progress dialog automatically disappears, your file should now appear in the publishing dialog:


Now, select the file (by clicking on the file name) and then click the "Edit" button. This will open the editing dialog:


In this dialog, you can see many details about your file. In the top left area, you can see meta data extracted about the file, such as the original filename, the mimetype and the size of the image. In the top right, you should see a preview for the image (if GNU libextractor was installed correctly with the respective plugins). Note that if you do not see a preview, this is not a disaster, but you might still want to install more of GNU libextractor in the future. In the bottom left, the dialog contains a list of keywords. These are the keywords under which the file will be made available. The initial list will be based on the extracted meta data. Additional publishing options are in the right bottom corner. We will now add an additional keyword to the list of keywords. This is done by entering the keyword above the keyword list between the label "Keyword" and the "Add keyword" button. Enter "test" and select "Add keyword". Note that the keyword will appear at the bottom of the existing keyword list, so you might have to scroll down to see it. Afterwards, push the "OK" button at the bottom right of the dialog.

You should now be back at the "Publish content on GNUnet" dialog. Select "Execute" in the bottom right to close the dialog and publish your file on GNUnet! Afterwards, you should see the main dialog with a new area showing the list of published files (or ongoing publishing operations with progress indicators).


Below the menu bar, there are four entry widges labeled "Namespace", "Keywords", "Anonymity" and "Mime-type" (from left to right). These widgets are used to control searching for files in GNUnet. Between the "Keywords" and "Anonymity" widgets, there is also a big "Search" button, which is used to initiate the search. We will ignore the "Namespace", "Anonymity" and "Mime-type" options in this tutorial, please leave them empty. Instead, simply enter "test" under "Keywords" and press "Search". Afterwards, you should immediately see a new tab labeled after your search term, followed by the (current) number of search results — "(15)" in our screenshot. Note that your results may vary depending on what other users may have shared and how your peer is connected.

You can now select one of the search results. Once you do this, additional information about the result should be displayed on the right. If available, a preview image should appear on the top right. Meta data describing the file will be listed at the bottom right.

Once a file is selected, at the bottom of the search result list a little area for downloading appears.


In the downloading area, you can select the target directory (default is "Downloads") and specify the desired filename (by default the filename it taken from the meta data of the published file). Additionally, you can specify if the download should be anonymous and (for directories) if the download should be recursive. In most cases, you can simply start the download with the "Download!" button.

Once you selected download, the progress of the download will be displayed with the search result. You may need to resize the result list or scroll to the right. The "Status" column shows the current status of the download, and "Progress" how much has been completed. When you close the search tab (by clicking on the "X" button next to the "test" label), ongoing and completed downloads are not aborted but moved to a special "*" tab.

You can remove completed downloads from the "*" tab by clicking the cleanup button next to the "*". You can also abort downloads by right clicking on the respective download and selecting "Abort download" from the menu.

That’s it, you now know the basics for file-sharing with GNUnet!


This will be available here soon. Until then, look here:


GNUnet Project


2022, GNUnet Project

August 15, 2022