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<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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"http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [
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<!ENTITY COMMANDNAME "mandos-client">
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<!ENTITY TIMESTAMP "2011-11-27">
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<!ENTITY % common SYSTEM "../common.ent">
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<refentry xmlns:xi="http://www.w3.org/2001/XInclude">
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<title>Mandos Manual</title>
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<!-- NWalsh’s docbook scripts use this to generate the footer: -->
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<productname>Mandos</productname>
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<productnumber>&version;</productnumber>
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<date>&TIMESTAMP;</date>
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<firstname>Björn</firstname>
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<surname>Påhlsson</surname>
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<email>belorn@recompile.se</email>
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<firstname>Teddy</firstname>
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<surname>Hogeborn</surname>
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<email>teddy@recompile.se</email>
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<holder>Teddy Hogeborn</holder>
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<holder>Björn Påhlsson</holder>
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<xi:include href="../legalnotice.xml"/>
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<refentrytitle>&COMMANDNAME;</refentrytitle>
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<manvolnum>8mandos</manvolnum>
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<refname><command>&COMMANDNAME;</command></refname>
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Client for <application>Mandos</application>
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<command>&COMMANDNAME;</command>
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<arg choice="plain"><option>--connect
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<replaceable>ADDRESS</replaceable><literal>:</literal
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><replaceable>PORT</replaceable></option></arg>
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<arg choice="plain"><option>-c
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<replaceable>ADDRESS</replaceable><literal>:</literal
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><replaceable>PORT</replaceable></option></arg>
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<arg choice="plain"><option>--interface
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<replaceable>NAME</replaceable></option></arg>
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<arg choice="plain"><option>-i
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<replaceable>NAME</replaceable></option></arg>
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<arg choice="plain"><option>--pubkey
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<replaceable>FILE</replaceable></option></arg>
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<arg choice="plain"><option>-p
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<replaceable>FILE</replaceable></option></arg>
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<arg choice="plain"><option>--seckey
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<replaceable>FILE</replaceable></option></arg>
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<arg choice="plain"><option>-s
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<replaceable>FILE</replaceable></option></arg>
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<option>--priority <replaceable>STRING</replaceable></option>
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<option>--dh-bits <replaceable>BITS</replaceable></option>
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<option>--delay <replaceable>SECONDS</replaceable></option>
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<option>--retry <replaceable>SECONDS</replaceable></option>
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<option>--network-hook-dir
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<replaceable>DIR</replaceable></option>
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<option>--debug</option>
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<command>&COMMANDNAME;</command>
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<arg choice="plain"><option>--help</option></arg>
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<arg choice="plain"><option>-?</option></arg>
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<command>&COMMANDNAME;</command>
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<arg choice="plain"><option>--usage</option></arg>
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<command>&COMMANDNAME;</command>
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<arg choice="plain"><option>--version</option></arg>
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<arg choice="plain"><option>-V</option></arg>
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<refsect1 id="description">
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<title>DESCRIPTION</title>
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<command>&COMMANDNAME;</command> is a client program that
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communicates with <citerefentry><refentrytitle
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>mandos</refentrytitle><manvolnum>8</manvolnum></citerefentry>
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to get a password. In slightly more detail, this client program
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brings up a network interface, uses the interface’s IPv6
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link-local address to get network connectivity, uses Zeroconf to
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find servers on the local network, and communicates with servers
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using TLS with an OpenPGP key to ensure authenticity and
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confidentiality. This client program keeps running, trying all
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servers on the network, until it receives a satisfactory reply
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or a TERM signal. After all servers have been tried, all
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servers are periodically retried. If no servers are found it
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will wait indefinitely for new servers to appear.
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The network interface is selected like this: If an interface is
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specified using the <option>--interface</option> option, that
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interface is used. Otherwise, <command>&COMMANDNAME;</command>
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will choose any interface that is up and running and is not a
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loopback interface, is not a point-to-point interface, is
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capable of broadcasting and does not have the NOARP flag (see
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<citerefentry><refentrytitle>netdevice</refentrytitle>
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<manvolnum>7</manvolnum></citerefentry>). (If the
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<option>--connect</option> option is used, point-to-point
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interfaces and non-broadcast interfaces are accepted.) If no
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acceptable interfaces are found, re-run the check but without
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the <quote>up and running</quote> requirement, and manually take
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the selected interface up (and later take it down on program
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Before a network interface is selected, all <quote>network
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hooks</quote> are run; see <xref linkend="network-hooks"/>.
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This program is not meant to be run directly; it is really meant
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to run as a plugin of the <application>Mandos</application>
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<citerefentry><refentrytitle>plugin-runner</refentrytitle>
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<manvolnum>8mandos</manvolnum></citerefentry>, which runs in the
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initial <acronym>RAM</acronym> disk environment because it is
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specified as a <quote>keyscript</quote> in the <citerefentry>
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<refentrytitle>crypttab</refentrytitle><manvolnum>5</manvolnum>
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</citerefentry> file.
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<refsect1 id="purpose">
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<title>PURPOSE</title>
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The purpose of this is to enable <emphasis>remote and unattended
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rebooting</emphasis> of client host computer with an
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<emphasis>encrypted root file system</emphasis>. See <xref
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linkend="overview"/> for details.
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<refsect1 id="options">
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<title>OPTIONS</title>
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This program is commonly not invoked from the command line; it
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is normally started by the <application>Mandos</application>
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plugin runner, see <citerefentry><refentrytitle
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>plugin-runner</refentrytitle><manvolnum>8mandos</manvolnum>
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</citerefentry>. Any command line options this program accepts
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are therefore normally provided by the plugin runner, and not
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<term><option>--connect=<replaceable
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>ADDRESS</replaceable><literal>:</literal><replaceable
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>PORT</replaceable></option></term>
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<replaceable>ADDRESS</replaceable><literal>:</literal
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><replaceable>PORT</replaceable></option></term>
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Do not use Zeroconf to locate servers. Connect directly
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to only one specified <application>Mandos</application>
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server. Note that an IPv6 address has colon characters in
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it, so the <emphasis>last</emphasis> colon character is
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assumed to separate the address from the port number.
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This option is normally only useful for testing and
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<term><option>--interface=<replaceable
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>NAME</replaceable></option></term>
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<replaceable>NAME</replaceable></option></term>
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Network interface that will be brought up and scanned for
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Mandos servers to connect to. The default is the empty
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string, which will automatically choose an appropriate
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If the <option>--connect</option> option is used, this
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specifies the interface to use to connect to the address
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Note that since this program will normally run in the
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initial RAM disk environment, the interface must be an
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interface which exists at that stage. Thus, the interface
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can not be a pseudo-interface such as <quote>br0</quote>
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or <quote>tun0</quote>; such interfaces will not exist
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until much later in the boot process, and can not be used
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by this program, unless created by a <quote>network
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hook</quote> — see <xref linkend="network-hooks"/>.
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<replaceable>NAME</replaceable> can be the string
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<quote><literal>none</literal></quote>; this will not use
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any specific interface, and will not bring up an interface
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on startup. This is not recommended, and only meant for
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<term><option>--pubkey=<replaceable
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>FILE</replaceable></option></term>
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<replaceable>FILE</replaceable></option></term>
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OpenPGP public key file name. The default name is
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<quote><filename>/conf/conf.d/mandos/pubkey.txt</filename
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<term><option>--seckey=<replaceable
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>FILE</replaceable></option></term>
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<replaceable>FILE</replaceable></option></term>
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OpenPGP secret key file name. The default name is
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<quote><filename>/conf/conf.d/mandos/seckey.txt</filename
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<term><option>--priority=<replaceable
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>STRING</replaceable></option></term>
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<xi:include href="../mandos-options.xml"
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xpointer="priority"/>
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<term><option>--dh-bits=<replaceable
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>BITS</replaceable></option></term>
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Sets the number of bits to use for the prime number in the
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TLS Diffie-Hellman key exchange. Default is 1024.
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<term><option>--delay=<replaceable
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>SECONDS</replaceable></option></term>
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After bringing the network interface up, the program waits
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for the interface to arrive in a <quote>running</quote>
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state before proceeding. During this time, the kernel log
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level will be lowered to reduce clutter on the system
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console, alleviating any other plugins which might be
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using the system console. This option sets the upper
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limit of seconds to wait. The default is 2.5 seconds.
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<term><option>--retry=<replaceable
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>SECONDS</replaceable></option></term>
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All Mandos servers are tried repeatedly until a password
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is received. This value specifies, in seconds, how long
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between each successive try <emphasis>for the same
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server</emphasis>. The default is 10 seconds.
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<term><option>--network-hook-dir=<replaceable
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>DIR</replaceable></option></term>
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Network hook directory. The default directory is
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<quote><filename class="directory"
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>/lib/mandos/network-hooks.d</filename></quote>.
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<term><option>--debug</option></term>
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Enable debug mode. This will enable a lot of output to
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standard error about what the program is doing. The
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program will still perform all other functions normally.
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It will also enable debug mode in the Avahi and GnuTLS
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libraries, making them print large amounts of debugging
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<term><option>--help</option></term>
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<term><option>-?</option></term>
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Gives a help message about options and their meanings.
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<term><option>--usage</option></term>
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Gives a short usage message.
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<term><option>--version</option></term>
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<term><option>-V</option></term>
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Prints the program version.
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<refsect1 id="overview">
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<title>OVERVIEW</title>
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<xi:include href="../overview.xml"/>
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This program is the client part. It is a plugin started by
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<citerefentry><refentrytitle>plugin-runner</refentrytitle>
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<manvolnum>8mandos</manvolnum></citerefentry> which will run in
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an initial <acronym>RAM</acronym> disk environment.
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This program could, theoretically, be used as a keyscript in
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<filename>/etc/crypttab</filename>, but it would then be
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impossible to enter a password for the encrypted root disk at
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the console, since this program does not read from the console
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at all. This is why a separate plugin runner (<citerefentry>
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<refentrytitle>plugin-runner</refentrytitle>
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<manvolnum>8mandos</manvolnum></citerefentry>) is used to run
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both this program and others in in parallel,
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<emphasis>one</emphasis> of which (<citerefentry>
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<refentrytitle>password-prompt</refentrytitle>
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<manvolnum>8mandos</manvolnum></citerefentry>) will prompt for
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passwords on the system console.
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<refsect1 id="exit_status">
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<title>EXIT STATUS</title>
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This program will exit with a successful (zero) exit status if a
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server could be found and the password received from it could be
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successfully decrypted and output on standard output. The
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program will exit with a non-zero exit status only if a critical
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error occurs. Otherwise, it will forever connect to any
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discovered <application>Mandos</application> servers, trying to
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get a decryptable password and print it.
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<refsect1 id="environment">
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<title>ENVIRONMENT</title>
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This program does not use any environment variables, not even
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the ones provided by <citerefentry><refentrytitle
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>cryptsetup</refentrytitle><manvolnum>8</manvolnum>
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<refsect1 id="network-hooks">
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<title>NETWORK HOOKS</title>
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If a network interface like a bridge or tunnel is required to
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find a Mandos server, this requires the interface to be up and
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running before <command>&COMMANDNAME;</command> starts looking
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for Mandos servers. This can be accomplished by creating a
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<quote>network hook</quote> program, and placing it in a special
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Before the network is used (and again before program exit), any
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runnable programs found in the network hook directory are run
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with the argument <quote><literal>start</literal></quote> or
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<quote><literal>stop</literal></quote>. This should bring up or
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down, respectively, any network interface which
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<command>&COMMANDNAME;</command> should use.
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<refsect2 id="hook-requirements">
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<title>REQUIREMENTS</title>
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A network hook must be an executable file, and its name must
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consist entirely of upper and lower case letters, digits,
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underscores, periods, and hyphens.
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A network hook will receive one argument, which can be one of
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<term><literal>start</literal></term>
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This should make the network hook create (if necessary)
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and bring up a network interface.
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<term><literal>stop</literal></term>
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This should make the network hook take down a network
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interface, and delete it if it did not exist previously.
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<term><literal>files</literal></term>
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This should make the network hook print, <emphasis>one
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file per line</emphasis>, all the files needed for it to
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run. (These files will be copied into the initial RAM
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filesystem.) Typical use is for a network hook which is
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a shell script to print its needed binaries.
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It is not necessary to print any non-executable files
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already in the network hook directory, these will be
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copied implicitly if they otherwise satisfy the name
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<term><literal>modules</literal></term>
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This should make the network hook print, <emphasis>on
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separate lines</emphasis>, all the kernel modules needed
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for it to run. (These modules will be copied into the
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initial RAM filesystem.) For instance, a tunnel
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<quote><literal>tun</literal></quote> module.
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The network hook will be provided with a number of environment
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<term><envar>MANDOSNETHOOKDIR</envar></term>
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The network hook directory, specified to
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<command>&COMMANDNAME;</command> by the
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<option>--network-hook-dir</option> option. Note: this
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should <emphasis>always</emphasis> be used by the
541
network hook to refer to itself or any files in the hook
542
directory it may require.
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<term><envar>DEVICE</envar></term>
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The network interface, as specified to
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<command>&COMMANDNAME;</command> by the
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<option>--interface</option> option. If this is not the
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interface a hook will bring up, there is no reason for a
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<term><envar>MODE</envar></term>
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This will be the same as the first argument;
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i.e. <quote><literal>start</literal></quote>,
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<quote><literal>stop</literal></quote>,
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<quote><literal>files</literal></quote>, or
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<quote><literal>modules</literal></quote>.
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<term><envar>VERBOSITY</envar></term>
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This will be the <quote><literal>1</literal></quote> if
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the <option>--debug</option> option is passed to
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<command>&COMMANDNAME;</command>, otherwise
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<quote><literal>0</literal></quote>.
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<term><envar>DELAY</envar></term>
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This will be the same as the <option>--delay</option>
586
option passed to <command>&COMMANDNAME;</command>.
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A hook may not read from standard input, and should be
593
restrictive in printing to standard output or standard error
594
unless <varname>VERBOSITY</varname> is
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<quote><literal>1</literal></quote>.
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<refsect1 id="files">
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<term><filename>/conf/conf.d/mandos/pubkey.txt</filename
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<term><filename>/conf/conf.d/mandos/seckey.txt</filename
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OpenPGP public and private key files, in <quote>ASCII
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Armor</quote> format. These are the default file names,
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they can be changed with the <option>--pubkey</option> and
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<option>--seckey</option> options.
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class="directory">/lib/mandos/network-hooks.d</filename></term>
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Directory where network hooks are located. Change this
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with the <option>--network-hook-dir</option> option. See
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<xref linkend="network-hooks"/>.
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<!-- <refsect1 id="bugs"> -->
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<!-- <title>BUGS</title> -->
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<refsect1 id="example">
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<title>EXAMPLE</title>
640
Note that normally, command line options will not be given
641
directly, but via options for the Mandos <citerefentry
642
><refentrytitle>plugin-runner</refentrytitle>
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<manvolnum>8mandos</manvolnum></citerefentry>.
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Normal invocation needs no options, if the network interface
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is <quote>eth0</quote>:
651
<userinput>&COMMANDNAME;</userinput>
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Search for Mandos servers (and connect to them) using another
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<!-- do not wrap this line -->
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<userinput>&COMMANDNAME; --interface eth1</userinput>
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Run in debug mode, and use a custom key:
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<!-- do not wrap this line -->
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<userinput>&COMMANDNAME; --debug --pubkey keydir/pubkey.txt --seckey keydir/seckey.txt</userinput>
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Run in debug mode, with a custom key, and do not use Zeroconf
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to locate a server; connect directly to the IPv6 link-local
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address <quote><systemitem class="ipaddress"
680
>fe80::aede:48ff:fe71:f6f2</systemitem></quote>, port 4711,
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using interface eth2:
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<!-- do not wrap this line -->
686
<userinput>&COMMANDNAME; --debug --pubkey keydir/pubkey.txt --seckey keydir/seckey.txt --connect fe80::aede:48ff:fe71:f6f2:4711 --interface eth2</userinput>
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<refsect1 id="security">
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<title>SECURITY</title>
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This program is set-uid to root, but will switch back to the
696
original (and presumably non-privileged) user and group after
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bringing up the network interface.
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To use this program for its intended purpose (see <xref
701
linkend="purpose"/>), the password for the root file system will
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have to be given out to be stored in a server computer, after
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having been encrypted using an OpenPGP key. This encrypted data
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which will be stored in a server can only be decrypted by the
705
OpenPGP key, and the data will only be given out to those
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clients who can prove they actually have that key. This key,
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however, is stored unencrypted on the client side in its initial
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<acronym>RAM</acronym> disk image file system. This is normally
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readable by all, but this is normally fixed during installation
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of this program; file permissions are set so that no-one is able
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The only remaining weak point is that someone with physical
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access to the client hard drive might turn off the client
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computer, read the OpenPGP keys directly from the hard drive,
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and communicate with the server. To safeguard against this, the
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server is supposed to notice the client disappearing and stop
719
giving out the encrypted data. Therefore, it is important to
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set the timeout and checker interval values tightly on the
721
server. See <citerefentry><refentrytitle
722
>mandos</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
725
It will also help if the checker program on the server is
726
configured to request something from the client which can not be
727
spoofed by someone else on the network, unlike unencrypted
728
<acronym>ICMP</acronym> echo (<quote>ping</quote>) replies.
731
<emphasis>Note</emphasis>: This makes it completely insecure to
732
have <application >Mandos</application> clients which dual-boot
733
to another operating system which is <emphasis>not</emphasis>
734
trusted to keep the initial <acronym>RAM</acronym> disk image
739
<refsect1 id="see_also">
740
<title>SEE ALSO</title>
742
<citerefentry><refentrytitle>intro</refentrytitle>
743
<manvolnum>8mandos</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>cryptsetup</refentrytitle>
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<manvolnum>8</manvolnum></citerefentry>,
746
<citerefentry><refentrytitle>crypttab</refentrytitle>
747
<manvolnum>5</manvolnum></citerefentry>,
748
<citerefentry><refentrytitle>mandos</refentrytitle>
749
<manvolnum>8</manvolnum></citerefentry>,
750
<citerefentry><refentrytitle>password-prompt</refentrytitle>
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<manvolnum>8mandos</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>plugin-runner</refentrytitle>
753
<manvolnum>8mandos</manvolnum></citerefentry>
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<ulink url="http://www.zeroconf.org/">Zeroconf</ulink>
762
Zeroconf is the network protocol standard used for finding
763
Mandos servers on the local network.
769
<ulink url="http://www.avahi.org/">Avahi</ulink>
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Avahi is the library this program calls to find Zeroconf
780
<ulink url="http://www.gnu.org/software/gnutls/"
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GnuTLS is the library this client uses to implement TLS for
786
communicating securely with the server, and at the same time
787
send the public OpenPGP key to the server.
793
<ulink url="http://www.gnupg.org/related_software/gpgme/"
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GPGME is the library used to decrypt the OpenPGP data sent
805
RFC 4291: <citetitle>IP Version 6 Addressing
806
Architecture</citetitle>
811
<term>Section 2.2: <citetitle>Text Representation of
812
Addresses</citetitle></term>
813
<listitem><para/></listitem>
816
<term>Section 2.5.5.2: <citetitle>IPv4-Mapped IPv6
817
Address</citetitle></term>
818
<listitem><para/></listitem>
821
<term>Section 2.5.6, <citetitle>Link-Local IPv6 Unicast
822
Addresses</citetitle></term>
825
This client uses IPv6 link-local addresses, which are
826
immediately usable since a link-local addresses is
827
automatically assigned to a network interfaces when it
837
RFC 4346: <citetitle>The Transport Layer Security (TLS)
838
Protocol Version 1.1</citetitle>
842
TLS 1.1 is the protocol implemented by GnuTLS.
848
RFC 4880: <citetitle>OpenPGP Message Format</citetitle>
852
The data received from the server is binary encrypted
859
RFC 5081: <citetitle>Using OpenPGP Keys for Transport Layer
864
This is implemented by GnuTLS and used by this program so
865
that OpenPGP keys can be used.
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