table of contents
MANDOS-CLIENT(8mandos) | Mandos Manual | MANDOS-CLIENT(8mandos) |
NAME¶
mandos-client - Client for MandosSYNOPSIS¶
mandos-client
[ --connect ADDRESS:PORT |
-c ADDRESS:PORT]
[ --interface NAME |
-i NAME]
[ --pubkey FILE | -p FILE]
[ --seckey FILE | -s FILE]
[ --priority STRING]
[ --dh-bits BITS]
[ --delay SECONDS]
[ --retry SECONDS]
[ --network-hook-dir DIR]
[ --debug]
mandos-client
{ --help | -?}
mandos-client
--usage
mandos-client
{ --version | -V}
DESCRIPTION¶
PURPOSE¶
The purpose of this is to enable remote and unattended rebooting of client host computer with an encrypted root file system. See the section called “OVERVIEW” for details.OPTIONS¶
This program is commonly not invoked from the command line; it is normally started by the Mandos plugin runner, see plugin-runner(8mandos). Any command line options this program accepts are therefore normally provided by the plugin runner, and not directly. --connect=ADDRESS:PORT, -c ADDRESS:PORTDo not use Zeroconf to locate servers. Connect
directly to only one specified Mandos server. Note that an IPv6 address has
colon characters in it, so the last colon character is assumed to
separate the address from the port number.
This option is normally only useful for testing and debugging.
--interface=NAME, -i NAME
Network interface that will be brought up and
scanned for Mandos servers to connect to. The default is the empty string,
which will automatically choose an appropriate interface.
If the --connect option is used, this specifies the interface to use to
connect to the address given.
Note that since this program will normally run in the initial RAM disk
environment, the interface must be an interface which exists at that stage.
Thus, the interface can not be a pseudo-interface such as “br0” or
“tun0”; such interfaces will not exist until much later in the
boot process, and can not be used by this program, unless created by a
“network hook” — see the section called “NETWORK
HOOKS”.
NAME can be the string “none”; this will not use any specific
interface, and will not bring up an interface on startup. This is not
recommended, and only meant for advanced users.
--pubkey=FILE, -p FILE
OpenPGP public key file name. The default name
is “/conf/conf.d/mandos/pubkey.txt”.
--seckey=FILE, -s FILE
OpenPGP secret key file name. The default name
is “/conf/conf.d/mandos/seckey.txt”.
--priority=STRING
GnuTLS priority string for the TLS handshake.
The default is “SECURE256:!CTYPE-X.509:+CTYPE-OPENPGP”. See
gnutls_priority_init(3) for the syntax. Warning: changing this
may make the TLS handshake fail, making server-client communication
impossible.
--dh-bits=BITS
Sets the number of bits to use for the prime
number in the TLS Diffie-Hellman key exchange. Default is 1024.
--delay=SECONDS
After bringing the network interface up, the
program waits for the interface to arrive in a “running” state
before proceeding. During this time, the kernel log level will be lowered to
reduce clutter on the system console, alleviating any other plugins which
might be using the system console. This option sets the upper limit of seconds
to wait. The default is 2.5 seconds.
--retry=SECONDS
All Mandos servers are tried repeatedly until
a password is received. This value specifies, in seconds, how long between
each successive try for the same server. The default is 10
seconds.
--network-hook-dir=DIR
Network hook directory. The default directory
is “/lib/mandos/network-hooks.d”.
--debug
Enable debug mode. This will enable a lot of
output to standard error about what the program is doing. The program will
still perform all other functions normally.
It will also enable debug mode in the Avahi and GnuTLS libraries, making them
print large amounts of debugging output.
--help, -?
Gives a help message about options and their
meanings.
--usage
Gives a short usage message.
--version, -V
Prints the program version.
OVERVIEW¶
This is part of the Mandos system for allowing computers to have encrypted root file systems and at the same time be capable of remote and/or unattended reboots. The computers run a small client program in the initial RAM disk environment which will communicate with a server over a network. All network communication is encrypted using TLS. The clients are identified by the server using an OpenPGP key; each client has one unique to it. The server sends the clients an encrypted password. The encrypted password is decrypted by the clients using the same OpenPGP key, and the password is then used to unlock the root file system, whereupon the computers can continue booting normally. This program is the client part. It is a plugin started by plugin-runner(8mandos) which will run in an initial RAM disk environment. This program could, theoretically, be used as a keyscript in /etc/crypttab, but it would then be impossible to enter a password for the encrypted root disk at the console, since this program does not read from the console at all. This is why a separate plugin runner ( plugin-runner(8mandos)) is used to run both this program and others in in parallel, one of which ( password-prompt(8mandos)) will prompt for passwords on the system console.EXIT STATUS¶
This program will exit with a successful (zero) exit status if a server could be found and the password received from it could be successfully decrypted and output on standard output. The program will exit with a non-zero exit status only if a critical error occurs. Otherwise, it will forever connect to any discovered Mandos servers, trying to get a decryptable password and print it.ENVIRONMENT¶
This program does not use any environment variables, not even the ones provided by cryptsetup(8).NETWORK HOOKS¶
If a network interface like a bridge or tunnel is required to find a Mandos server, this requires the interface to be up and running before mandos-client starts looking for Mandos servers. This can be accomplished by creating a “network hook” program, and placing it in a special directory. Before the network is used (and again before program exit), any runnable programs found in the network hook directory are run with the argument “start” or “stop”. This should bring up or down, respectively, any network interface which mandos-client should use.REQUIREMENTS¶
A network hook must be an executable file, and its name must consist entirely of upper and lower case letters, digits, underscores, periods, and hyphens. A network hook will receive one argument, which can be one of the following: startThis should make the network hook create (if
necessary) and bring up a network interface.
stop
This should make the network hook take down a
network interface, and delete it if it did not exist previously.
files
This should make the network hook print,
one file per line, all the files needed for it to run. (These files
will be copied into the initial RAM filesystem.) Typical use is for a network
hook which is a shell script to print its needed binaries.
It is not necessary to print any non-executable files already in the network
hook directory, these will be copied implicitly if they otherwise satisfy the
name requirement.
modules
This should make the network hook print, on
separate lines, all the kernel modules needed for it to run. (These
modules will be copied into the initial RAM filesystem.) For instance, a
tunnel interface needs the “tun” module.
The network hook will be provided with a number of environment variables:
MANDOSNETHOOKDIR
The network hook directory, specified to
mandos-client by the --network-hook-dir option. Note: this
should always be used by the network hook to refer to itself or any
files in the hook directory it may require.
DEVICE
The network interface, as specified to
mandos-client by the --interface option. If this is not the
interface a hook will bring up, there is no reason for a hook to
continue.
MODE
This will be the same as the first argument;
i.e. “start”, “stop”, “files”, or
“modules”.
VERBOSITY
This will be the “1” if the
--debug option is passed to mandos-client, otherwise
“0”.
DELAY
This will be the same as the --delay
option passed to mandos-client. Is only set if MODE is
“start” or “stop”.
CONNECT
This will be the same as the --connect
option passed to mandos-client. Is only set if --connect is
passed and MODE is “start” or “stop”.
A hook may not read from standard input, and should be restrictive in printing
to standard output or standard error unless VERBOSITY is
“1”.
FILES¶
/conf/conf.d/mandos/pubkey.txt, /conf/conf.d/mandos/seckey.txtOpenPGP public and private key files, in
“ASCII Armor” format. These are the default file names, they can
be changed with the --pubkey and --seckey options.
/lib/mandos/network-hooks.d
Directory where network hooks are located.
Change this with the --network-hook-dir option. See the section called
“NETWORK HOOKS”.
EXAMPLE¶
Note that normally, command line options will not be given directly, but via options for the Mandos plugin-runner(8mandos). Normal invocation needs no options, if the network interface can be automatically determined:SECURITY¶
This program is set-uid to root, but will switch back to the original (and presumably non-privileged) user and group after bringing up the network interface. To use this program for its intended purpose (see the section called “PURPOSE”), the password for the root file system will have to be given out to be stored in a server computer, after having been encrypted using an OpenPGP key. This encrypted data which will be stored in a server can only be decrypted by the OpenPGP key, and the data will only be given out to those clients who can prove they actually have that key. This key, however, is stored unencrypted on the client side in its initial RAM disk image file system. This is normally readable by all, but this is normally fixed during installation of this program; file permissions are set so that no-one is able to read that file. The only remaining weak point is that someone with physical access to the client hard drive might turn off the client computer, read the OpenPGP keys directly from the hard drive, and communicate with the server. To safeguard against this, the server is supposed to notice the client disappearing and stop giving out the encrypted data. Therefore, it is important to set the timeout and checker interval values tightly on the server. See mandos(8). It will also help if the checker program on the server is configured to request something from the client which can not be spoofed by someone else on the network, unlike unencrypted ICMP echo (“ping”) replies.SEE ALSO¶
Zeroconf is the network protocol standard used
for finding Mandos servers on the local network.
Avahi[2]
Avahi is the library this program calls to
find Zeroconf services.
GnuTLS[3]
GnuTLS is the library this client uses to
implement TLS for communicating securely with the server, and at the same time
send the public OpenPGP key to the server.
GPGME[4]
GPGME is the library used to decrypt the
OpenPGP data sent by the server.
RFC 4291: IP Version 6 Addressing Architecture
Section 2.2: Text Representation of Addresses
Section 2.5.5.2: IPv4-Mapped IPv6 Address
Section 2.5.6, Link-Local IPv6 Unicast Addresses
RFC 4346: The Transport Layer Security (TLS) Protocol Version 1.1
This client uses IPv6 link-local addresses,
which are immediately usable since a link-local addresses is automatically
assigned to a network interfaces when it is brought up.
TLS 1.1 is the protocol implemented by
GnuTLS.
RFC 4880: OpenPGP Message Format
The data received from the server is binary
encrypted OpenPGP data.
RFC 5081: Using OpenPGP Keys for Transport Layer Security
This is implemented by GnuTLS and used by this
program so that OpenPGP keys can be used.
COPYRIGHT¶
Copyright © 2008-2009, 2012 Teddy Hogeborn, Björn PåhlssonNOTES¶
- 1.
- Zeroconf
- 2.
- Avahi
- 3.
- GnuTLS
- 4.
- GPGME
2012-05-27 | Mandos 1.5.5 |