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secnet(8) System Manager's Manual secnet(8)

NAME

secnet - VPN router daemon

SYNOPSIS

secnet [OPTIONS]

DESCRIPTION

secnet allows virtual private networks to be constructed spanning multiple separate sites.

OPTIONS

Enable extra diagnostics.
Suppress warnings.
Display usage message.
Display version string.
Don't go into background. The default behaviour is to become a daemon during startup.
Suppress error messages.
Enable debug messages.
Specify configuration file. The default is /etc/secnet/secnet.conf.
Check configuration and exit.
Configuration file key defining active sites. The default is sites.

CAPABILITY NEGOTIATION

Sites negotiate with each other during key exchange in order to determine which cryptographic algorithms and other features – termed capabilities – they each support. Capabilities are assigned small integer numbers. In many cases, capability numbers can be assigned in the configuration file, as described below; but secnet's default assignments will often be satisfactory.

Capability numbers between 0 and 7 inclusive are reserved for local use: secnet will never make use of them without explicit configuration. This may be useful to migrate from one set of parameters for a particular cryptographic algorithm to different, incompatible, parameters for the same algorithm. Other capability numbers are assigned by default by various kinds of closures. See the descriptions below for details.

It is essential that a capability number mean the same thing to each of a pair of peers. It's possible to configure a site so that it uses different capability numbers for the same feature when it communicates with different peer sites, but this is likely to be more confusing than useful.

CONFIGURATION FILE

Overview

The default configuration file is /etc/secnet/secnet.conf. This can be overridden with the --config option.

The configuration file defines a dictionary (a mapping from keys to values) of configuration information for secnet. It is recursive in nature, i.e. values may themselves include dictionaries. Any node in the nested structure thus defined can be identified by a path, which is the sequence of keys necessary to reach it from the root, separated by "/" characters. See Paths below for how this is used.

Furthermore, when a key is looked up in a dictionary, if it cannot be found, it is sought in the parent dictionary, and so on back to the root. For instance, each site must contain the resolver key, but in a typical configuration there is no value in having different resolvers for each site. Therefore resolver is defined at the root and thus automatically incorporated into all sites.

Whitespace

Whitespace, including newlines, is ignored except to the extent that it bounds other symbols.

Comment begin with "#" and continues to the end of the line. Comments are ignored.

Inclusion

A file may be recursively included into the configuration file using a line of the form:

include PATH

This is handled at a higher level than the main parser and so precludes the possibility of using the string include for any other purpose.

Assignments

The configuration file contains one or more assigments. Each assignment is written:

key [=] list;

i.e. the equals sign is optional. The semicolon is mandatory in all contexts.

Keys start with a letter or "_" and continue with any numbers of letters, digits, "_" and "-".

Each key is a list of one or more values, separated by commas. Possible values types are boolean, string, number, dictionary, path and closure evaluation.

Strings

Strings are contained within "double quotes". There is (currently) no escape syntax and no way to include quotes inside strings.

Example:



        filename "/var/log/secnet";

Numbers

Numbers are encoded in decimal and do not include a sign. Numbers must lie in the range 0 to 4294967295.

Example:



        mtu 1400;

Dictionaries

Dictionaries consist of one or more assignments, in the same syntax as given above, enclosed in "{" and "}".

Example:



        system {


                userid "secnet";


                pidfile "/var/run/secnet.pid";


        };

Paths

Paths allow a key already defined in the configuration to be aliased.

Paths consist of a sequence of keys separated by "/". If the path starts with a "/" then it is an absolute path and the search starts at the root of the configuration. Otherwise it is a relative path and starts in the containing dictionary or in any of its parents, down to and including the root. If there is more than one match, the one furthest from the root "wins".

The value of a path is the list assigned to the key it refers to. Lists are flattened; for example if a key is defined as a list of two paths, and each of those refers to a list of two integers, the original key is therefore defined to be a list of four integers, not a list consisting of two lists.

It is not possible to refer to a later key using a path.

Example:



        vpn {


          test {


            kakajou vpn-data/test/kakajou/kakajou;


            araminta vpn-data/test/araminta/araminta;


            deodand vpn-data/test/deodand/deodand;


            all-sites kakajou,araminta,deodand;


          };


        };


        all-sites vpn/test/all-sites;

Here, each of vpn/test/kakajou, vpn/test/araminta and vpn/test/deodand are defined as aliases to values defined elsewhere. vpn/tests/all-sites is defined as the list of all three of those values, and all-sites is then defined to be an alias for that.

Booleans

The (single-element) paths false, no and nowise are predefined and refer to a boolean false value. Similarly true, yes and verily point at a boolean true value.

In all six cases, variants with just the first letter capitalized, and with all letters capitalized, are also provided.

Example:



        random randomfile("/dev/urandom",no);

Closure Evaluation

Closure evaluation uses the following syntax:

CLOSURE ( ARGUMENTS )

CLOSURE may be a path referring to a closure, or may itself be a closure evaluation.

ARGUMENTS is a list of zero or more values, separated by commas. As a shortcut, if the arguments consist of a single dictionary, the parentheses may be ommitted:

CLOSURE { ... }

Example:



        sites map(site, vpn/test/all-sites);

When a closure is evaluated it returns a value (a list, much as above) and may also have side effects (which may be immediate or may be deferred to some later phase of execution). A list of built-in closures is given below.

Mandatory Keys

Two keys are mandatory. system must be a dictionary in which the following keys can be looked up:

A log closure; see the logfile documentation below. The destination for log messages. Mandatory.
A string. The userid to run as after dropping privilege. Optional.
A string. The path to write a pidfile. Optional.

sites should be a list of site closures; see the site documentation below. This defines the collection of tunnel endpoints that secnet will communicate with.

Recall the recursive lookup logic described in Overview above: if (for instance) log is defined in the top level dictionary but not in system, it will nevertheless be found when looked up in the latter.

CLOSURES

secnet contains a collection of built-in closures with names (i.e. single-element paths) given below.

Most of them return anonymous closures of various types, which are described contextually.

adns

adns(DICT) => resolver closure

This either be empty or contain the single key config, with a string value giving configuration to supply to ADNS. This might be read from a file using readfile.

A resolver closure is a means of converting hostnames into network addresses.

diffie-hellman

diffie-hellman(MODULUS, GENERATOR[, CHECK]) => dh closure

String. The prime modulus p in hex.
String. The generator g in hex.
Boolean. If true (the default) then check if p is prime.

A dh closure defines a group to be used for key exchange.

logfile

logfile(DICT) => log closure

Valid keys in the DICT argument are:

The path to log to.
A list of strings defining which classes of message to log. The possible message classes are debug-config, debug-phase, debug, info, notice, warning, error, security and fatal.
all-debug is the union of all the debug... classes. default is equivalent to warning, error, security, fatal. verbose is equivalent to info, notice, warning, error, security, fatal. quiet is equivalent to fatal.

A log closure is a means of saving log messages. See also syslog below.

makelist

makelist(DICT) => LIST

Returns the (flattened) list of values from the dictionary, discarding the keys.

map

map(CLOSURE, INPUT...) => LIST

Applies CLOSURE to all its additional input arguments and returns the resulting list.

md5

md5 is a hash closure implementing the MD5 algorithm.

null-netlink(DICT) => netlink closure
null-netlink(DICT) => pure closure

Valid keys in the DICT argument are:

String. The name for the netlink device. The default is null-netlink.
List of strings. The networks on the host side of the netlink device.
List of strings. Networks that may be claimed by remote sites using this netlink device.
String. IP address of this netlink. Incompatible with ptp-address.
String. IP address of the other end of a point-to-point link. Incompatible with secnet-address.
Number. The MTU of the netlink device. The default is 1000.

If ptp-address is used then the result is a netlink closure. This can be used directly with the link key in the sites closure (see below).

If secnet-address is used then the result is a pure closure. This must be evaluated to yield a netlink closure, using a dictionary argument with the following keys:

String list. networks reachable via this tunnel, in address/bits format.
String list. A list of options:
Allow packets received via this tunnel to be routed down other tunnels (without this option only packets from the host will be routed).
Remove these routes from the host routing table when the link quality is 0.
Number. Default MTU over this link. The default is inherited from the pure closure.
Number. The priority of this link. Higher values beat lower values. The default is 0.

A netlink closure is a virtual IP link, and is supplied to the link key of a site closure.

The netlink created by null-netlink has no connection to the host. See tun and userv-ipif below for more useful alternatives.

randomfile

randomfile(FILENAME[, BLOCKING]) => randomsource closure

String. Path to random device, e.g. /dev/urandom.
Boolean. True if this is a blocking device and false otherwise (the default). Blocking device support is not implemented so this must always be False or absent.

A randomsource closure is a source of random numbers.

readfile

readfile(PATH) => STRING

Read the contents of the file PATH (a string) and return it as a string.

eax-serpent

eax-serpent(DICT) => transform closure

Valid keys in the DICT argument are:

The maximum acceptable difference between the sequence number in a received, decrypted message and the previous one. The default is 10. It may be necessary to increase this is if connectivity is poor.
The length of the message authentication tag. The default is 16, for a 128-bit tag length. It must be no longer than the Serpent blocksize, 16. Must be have the same value at both ends.
Messages are padded to a multiple of this many bytes. This serves to obscure the exact length of messages. The default is 16,
The capability number to use when advertising this transform. The default for serpent-eax is 9.

A transform closure is a reversible means of transforming messages for transmission over a (presumably) insecure network. It is responsible for both confidentiality and integrity.

serpent256-cbc

serpent256-cbc(DICT) => transform closure

This transform is deprecated as its security properties are poor; it should be specified only alongside a better transform such as eax-serpent.

Valid keys in the DICT argument are:

As above. The default for serpent256-cbc is 8.
As above.

Note that this uses a big-endian variant of the Serpent block cipher (which is not compatible with most other Serpent implementations).

rsa-private

rsa-private(PATH[, CHECK]) => sigprivkey closure

String. The path to a file containing an RSA private key in SSH format (version 1). There must be no passphrase.
Boolean. If true (the default) then check that the key is valid.

rsa-public

rsa-public(KEY, MODULUS) => sigpubkey closure

String. The public key exponent (e), in decimal.
String. The modulus (n), in decimal.

sha1

sha1 is a hash closure implementing the SHA-1 algorithm.

site

site(DICT) => site closure

Valid keys in the DICT argument are:

String. The site's name for itself.
String. The name of the site's peer.
A netlink closure.
A comm closure.
A resolver closure.
A randomsource closure.
An sigprivkey closure. The key used to prove our identity to the peer.
String. The DNS name of the peer. Optional, but if it is missing then it will not be possible to initiate new connections to the peer.
Number. The port to contact the peer.
An sigpubkey closure. The key used to verify the peer's identity.
One or more transform closures. Used to protect packets exchanged with the peer. These should all have distinct capab-num values, and the same capab-num value should have the same (or a compatible) meaning at both ends. The list should be in order of preference, most preferred first. (The end which sends MSG1,MSG3 ends up choosing; the ordering at the other end is irrelevant.)
A dh closure. The group to use in key exchange.
The hash function used during setup.
Number. The maximum lifetime of a session key in milliseconds. The default is one hour.
Number. The maximum number of times a key negotiation packet will be transmitted before giving up. The default is 5.
Number. The time between retransmissions of key negotiation packets, in milliseconds. The default is one second.
Number. The time to wait after a failed key setup before making another attempt, in milliseconds. The default is 20s.
Number. The time after which a new session key will be negotiated, if there is traffic on the link, in milliseconds. It must not be greater than the key-lifetime. The default 5 minutes less than the key lifetime, unless the lifetime is less than 10 minutes in which case the default is half the lifetime.
Boolean. If true then attempt to always maintain a live session key. Not implemented.
String list. Types of event to log for this site.
Unexpected key setup packets (including late retransmissions).
Start of attempt to setup a session key.
Failure of attempt to setup a session key, through timeout.
Activation of a new session key.
Deletion of current session key through age.
Anything potentially suspicious.
Steps in the key setup protocol.
Whenever we throw away an outgoing packet.
Every key setup packet we see.
Failure of name resolution, internal errors.
Everything (too much!)

A site closure defines one site to communicate with. secnet expects the (root) key site to be a list of site closures.

sysbuffer

sysbuffer([SIZE[, OPTIONS]]) => buffer closure

Number. The size of the buffer in bytes. This must be between 64 and 131072. The default is 4096.
Dictionary. Optional and presently unused.

A buffer closure is a means of buffering packets to send or that have been received.

syslog

syslog(DICT) => log closure

Valid keys in the DICT argument are:

String. The ident string to pass to openlog(3); this value will appear in each message.
String. The facility to log as. The possible values are authpriv, cron, daemon, kern, local0-7, lpr, mail, news, syslog, user and uucp.

See also logfile above.

tun

tun(DICT) => netlink closure
tun(DICT) => pure closure

Valid keys in the DICT argument are those documented for null-netlink above, plus:

String. The type of TUN interface to use. Possible values are linux, bsd, streams and guess. The default is guess.
String. The path to the TUN/TAP device file. The default is /dev/net/tun for the linux flavour and /dev/tun for the others.
String. The interface to use. The default is to pick one automatically. This cannot be used with the streams flavour.
String. IP address of the host's tunnel interface.

String. The name of the ifconfig command. The default is simply "ifconfig".
String. The name of the route command. The default is simply "route".
String. The syntax expected by the ifconfig command. Possible values are linux, bsd, ioctl, solaris-2.5 and guess. The default is guess.
String. The syntax expected by the ifconfig command. Possible values are linux, bsd, ioctl, solaris-2.5 and guess. The default is guess.
A buffer closure to use for packets transferred from the host to secnet. The buffer size must be at least 60 greater than the MTU.

The ifconfig-type and route-type values determine how those commands are executed. If they are set to ioctl then low-level system calls are used directly instead of invoking the commands.

The netlink created by tun uses the tun device to communicate with the host kernel.

udp

udp(DICT) => comm closure

Valid keys in the DICT argument are:

String. The IP address to bind on. The default is 0.0.0.0, i.e. "any".
Number. The port number to bind to. The default is 0, i.e. the OS will choose one. It is suggested that any given VPN agree a common port number.
A buffer closure. See the sysbuffer closure above.
String. The path to a helper program to bind the socket. Optional.
The program will be invoked with the address and port number as its arguments, and with the socket to bind as file descriptor 0. It should either bind the socket as requested, or exit with nonzero status.

A comm closure is a means of sending and receiving messages via a network. It does not provide confidentiality, reliablity or availability.

userv-ipif

userv-ipif(DICT) => netlink closure
userv-ipif(DICT) => pure closure

Valid keys in the DICT argument are those documented for null-netlink above, plus:

String. IP address of the host's SLIP interface.

String. Where to find userv(1). The default is "userv".
String. The name of the user that owns the service. The default is "root".
String. The name of the service to request. The default is "ipif".
A buffer closure to use for packets transferred from the host to secnet.

The netlink created by userv-ipif invokes the specified userv service with pipes connected to its standard input and output. It uses SLIP to communicate with the host kernel via these pipes.

FILES

/etc/secnet/secnet.conf
Configuration file.

SEE ALSO

userv(1)