Provided by: mandos-client_1.7.1-2build1_i386 bug

NAME

       mandos-client - Client for Mandos

SYNOPSIS

       mandos-client [--connect ADDRESS:PORT | -c ADDRESS:PORT]
                     [--interface NAME[,NAME...] | -i NAME[,NAME...]...]
                     [--pubkey FILE | -p FILE]
                     [--seckey FILE | -s FILE]
                     [--priority STRING]
                     [--dh-bits BITS]
                     [--dh-params FILE]
                     [--delay SECONDS]
                     [--retry SECONDS]
                     [--network-hook-dir DIR]
                     [--debug]

       mandos-client {--help | -?}

       mandos-client --usage

       mandos-client {--version | -V}

DESCRIPTION

       mandos-client is a client program that communicates with mandos(8) to
       get a password. In slightly more detail, this client program brings up
       network interfaces, uses the interfaces’ IPv6 link-local addresses to
       get network connectivity, uses Zeroconf to find servers on the local
       network, and communicates with servers using TLS with an OpenPGP key to
       ensure authenticity and confidentiality. This client program keeps
       running, trying all servers on the network, until it receives a
       satisfactory reply or a TERM signal. After all servers have been tried,
       all servers are periodically retried. If no servers are found it will
       wait indefinitely for new servers to appear.

       The network interfaces are selected like this: If any interfaces are
       specified using the --interface option, those interface are used.
       Otherwise, mandos-client will use all interfaces that are not loopback
       interfaces, are not point-to-point interfaces, are capable of
       broadcasting and do not have the NOARP flag (see netdevice(7)). (If the
       --connect option is used, point-to-point interfaces and non-broadcast
       interfaces are accepted.) If any used interfaces are not up and
       running, they are first taken up (and later taken down again on program
       exit).

       Before network interfaces are selected, all “network hooks” are run;
       see the section called “NETWORK HOOKS”.

       This program is not meant to be run directly; it is really meant to run
       as a plugin of the Mandos plugin-runner(8mandos), which runs in the
       initial RAM disk environment because it is specified as a “keyscript”
       in the crypttab(5) file.

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:PORT
           Do 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.

           Normally, Zeroconf would be used to locate Mandos servers, in which
           case this option would only be used when testing and debugging.

       --interface=NAME[,NAME...], -i NAME[,NAME...]
           Comma separated list of network interfaces that will be brought up
           and scanned for Mandos servers to connect to. The default is the
           empty string, which will automatically use all appropriate
           interfaces.

           If the --connect option is used, and exactly one interface name is
           specified (except “none”), 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 normally 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 make mandos-client only
           bring up interfaces specified before this string. 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:!RSA :+SIGN-DSA-SHA256”. See
           gnutls_priority_init(3) for the syntax.  Warning: changing this may
           make the TLS handshake fail, making server-client communication
           impossible. Changing this option may also make the network traffic
           decryptable by an attacker.

       --dh-bits=BITS
           Sets the number of bits to use for the prime number in the TLS
           Diffie-Hellman key exchange. The default value is selected
           automatically based on the OpenPGP key. Note that if the
           --dh-params option is used, the values from that file will be used
           instead.

       --dh-params=FILE
           Specifies a PEM-encoded PKCS#3 file to read the parameters needed
           by the TLS Diffie-Hellman key exchange from. If this option is not
           given, or if the file for some reason could not be used, the
           parameters will be generated on startup, which will take some time
           and processing power. Those using servers running under time, power
           or processor constraints may want to generate such a file in
           advance and use this option.

       --delay=SECONDS
           After bringing a 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

       MANDOSPLUGINHELPERDIR
           This environment variable will be assumed to contain the directory
           containing any helper executables. The use and nature of these
           helper executables, if any, is purposefully not documented.

       This program does not use any other 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:

       start
           This 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 requirements.

       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 interfaces, as specified to mandos-client by the
           --interface option, combined to one string and separated by commas.
           If this is set, and does not contain 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.txt
           OpenPGP 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 interfaces can be
       automatically determined:

       mandos-client

       Search for Mandos servers (and connect to them) using one specific
       interface:

       mandos-client --interface eth1

       Run in debug mode, and use a custom key:

       mandos-client --debug --pubkey keydir/pubkey.txt --seckey
       keydir/seckey.txt

       Run in debug mode, with a custom key, and do not use Zeroconf to locate
       a server; connect directly to the IPv6 link-local address
       “fe80::aede:48ff:fe71:f6f2”, port 4711, using interface eth2:

       mandos-client --debug --pubkey keydir/pubkey.txt --seckey
       keydir/seckey.txt --connect fe80::aede:48ff:fe71:f6f2:4711 --interface
       eth2

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, like SSH server key fingerprints, and unlike
       unencrypted ICMP echo (“ping”) replies.

       Note: This makes it completely insecure to have Mandos clients which
       dual-boot to another operating system which is not trusted to keep the
       initial RAM disk image confidential.

SEE ALSO

       intro(8mandos), cryptsetup(8), crypttab(5), mandos(8), password-
       prompt(8mandos), plugin-runner(8mandos)

       Zeroconf[1]
           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
               This client uses IPv6 link-local addresses, which are
               immediately usable since a link-local addresses is
               automatically assigned to a network interface when it is
               brought up.

       RFC 4346: The Transport Layer Security (TLS) Protocol Version 1.1
           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 © 2008-2015 Teddy Hogeborn, Björn Påhlsson

       This manual page is free software: you can redistribute it and/or
       modify it under the terms of the GNU General Public License as
       published by the Free Software Foundation, either version 3 of the
       License, or (at your option) any later version.

       This manual page is distributed in the hope that it will be useful, but
       WITHOUT ANY WARRANTY; without even the implied warranty of
       MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
       General Public License for more details.

       You should have received a copy of the GNU General Public License along
       with this program. If not, see http://www.gnu.org/licenses/.

NOTES

        1. Zeroconf
           http://www.zeroconf.org/

        2. Avahi
           http://www.avahi.org/

        3. GnuTLS
           http://www.gnu.org/software/gnutls/

        4. GPGME
           http://www.gnupg.org/related_software/gpgme/