/mandos/release : revision 152

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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 VERSION "1.0">

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<!ENTITY COMMANDNAME "password-request">

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<!ENTITY TIMESTAMP "2008-09-03">

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]>

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<title>Mandos Manual</title>

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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@fukt.bsnet.se</email>

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</address>

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</author>

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<firstname>Teddy</firstname>

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<surname>Hogeborn</surname>

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<email>teddy@fukt.bsnet.se</email>

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</address>

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</author>

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</authorgroup>

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<holder>Teddy Hogeborn</holder>

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<holder>Björn Påhlsson</holder>

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</copyright>

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<xi:include href="../legalnotice.xml"/>

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</refentryinfo>

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<refentrytitle>&COMMANDNAME;</refentrytitle>

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<manvolnum>8mandos</manvolnum>

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</refmeta>

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<refname><command>&COMMANDNAME;</command></refname>

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Client for mandos

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</refpurpose>

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</refnamediv>

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<command>&COMMANDNAME;</command>

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<group>

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<arg choice="plain"><option>--connect

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<replaceable>IPADDR</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>IPADDR</replaceable><literal>:</literal

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><replaceable>PORT</replaceable></option></arg>

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</group>

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<sbr/>

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<group>

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<arg choice="plain"><option>--interface

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<arg choice="plain"><option>-i

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</group>

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<sbr/>

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<group>

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<arg choice="plain"><option>--pubkey

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<arg choice="plain"><option>-p

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</group>

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<sbr/>

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<group>

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<arg choice="plain"><option>--seckey

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<arg choice="plain"><option>-s

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</group>

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<sbr/>

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<arg>

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<option>--priority <replaceable>STRING</replaceable></option>

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</arg>

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<sbr/>

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<arg>

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</arg>

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<sbr/>

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<arg>

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<option>--debug</option>

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</arg>

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</cmdsynopsis>

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<command>&COMMANDNAME;</command>

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</group>

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</cmdsynopsis>

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<command>&COMMANDNAME;</command>

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<arg choice="plain"><option>--usage</option></arg>

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</cmdsynopsis>

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<command>&COMMANDNAME;</command>

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<arg choice="plain"><option>--version</option></arg>

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</group>

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</cmdsynopsis>

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</refsynopsisdiv>

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<title>DESCRIPTION</title>

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<para>

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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. It uses IPv6 link-local addresses to get

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network connectivity, Zeroconf to find servers, and TLS with an

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OpenPGP key to ensure authenticity and confidentiality. It

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keeps running, trying all servers on the network, until it

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receives a satisfactory reply or a TERM signal is recieved.

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</para>

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<para>

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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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</para>

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</refsect1>

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<title>PURPOSE</title>

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<para>

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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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</para>

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</refsect1>

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<title>OPTIONS</title>

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<para>

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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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directly.

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</para>

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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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<term><option>-c

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<replaceable>ADDRESS</replaceable><literal>:</literal

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><replaceable>PORT</replaceable></option></term>

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<para>

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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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</para>

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<para>

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This option is normally only useful for testing and

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debugging.

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</para>

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</listitem>

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</varlistentry>

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<term><option>--interface=

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<term><option>-i

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<para>

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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 it

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<quote><literal>eth0</literal></quote>.

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</para>

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<para>

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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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given.

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</para>

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</listitem>

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</varlistentry>

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<term><option>--pubkey=<replaceable

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>FILE</replaceable></option></term>

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<term><option>-p

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<para>

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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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></quote>.

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</para>

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</listitem>

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</varlistentry>

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<term><option>--seckey=<replaceable

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>FILE</replaceable></option></term>

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<term><option>-s

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<para>

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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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></quote>.

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</para>

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</listitem>

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</varlistentry>

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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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</listitem>

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</varlistentry>

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<term><option>--dh-bits=<replaceable

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>BITS</replaceable></option></term>

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<para>

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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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</para>

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</listitem>

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</varlistentry>

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<term><option>--debug</option></term>

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<para>

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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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</para>

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<para>

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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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output.

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</para>

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</listitem>

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</varlistentry>

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<para>

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Gives a help message about options and their meanings.

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</para>

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</listitem>

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</varlistentry>

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<term><option>--usage</option></term>

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<para>

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Gives a short usage message.

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</para>

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</listitem>

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</varlistentry>

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<term><option>--version</option></term>

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<para>

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Prints the program version.

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</para>

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</listitem>

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</varlistentry>

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</variablelist>

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</refsect1>

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<title>OVERVIEW</title>

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<xi:include href="../overview.xml"/>

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<para>

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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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</para>

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<para>

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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 (<citerefentry>

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<refentrytitle>password-prompt</refentrytitle>

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<manvolnum>8mandos</manvolnum></citerefentry>) does that, which

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will be run in parallell to this one by the plugin runner.

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</para>

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</refsect1>

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<title>EXIT STATUS</title>

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<para>

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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 new

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<application>Mandos</application> servers as they appear, trying

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to get a decryptable password.

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</para>

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</refsect1>

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<title>ENVIRONMENT</title>

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<para>

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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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</citerefentry>.

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</para>

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</refsect1>

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<title>FILES</title>

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<term><filename>/conf/conf.d/mandos/pubkey.txt</filename

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></term>

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<term><filename>/conf/conf.d/mandos/seckey.txt</filename

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></term>

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<para>

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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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</para>

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</listitem>

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</varlistentry>

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</variablelist>

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</refsect1>

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<title>EXAMPLE</title>

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<para>

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Note that normally, command line options will not be given

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directly, but via options for the Mandos <citerefentry

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><refentrytitle>plugin-runner</refentrytitle>

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<manvolnum>8mandos</manvolnum></citerefentry>.

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</para>

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<para>

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Normal invocation needs no options, if the network interface

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is <quote>eth0</quote>:

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</para>

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<para>

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<userinput>&COMMANDNAME;</userinput>

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</para>

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</informalexample>

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<para>

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Search for Mandos servers on another interface:

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</para>

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<para>

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<userinput>&COMMANDNAME; --interface eth1</userinput>

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</para>

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</informalexample>

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<para>

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Run in debug mode, and use a custom key:

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</para>

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<para>

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<userinput>&COMMANDNAME; --debug --pubkey keydir/pubkey.txt --seckey keydir/seckey.txt</userinput>

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</para>

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</informalexample>

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<para>

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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 address

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<quote><systemitem class="ipaddress"

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>2001:db8:f983:bd0b:30de:ae4a:71f2:f672</systemitem></quote>,

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port 4711, using interface eth2:

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</para>

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<para>

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<userinput>&COMMANDNAME; --debug --pubkey keydir/pubkey.txt --seckey keydir/seckey.txt --connect 2001:db8:f983:bd0b:30de:ae4a:71f2:f672:4711 --interface eth2</userinput>

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</para>

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</informalexample>

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</refsect1>

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<title>SECURITY</title>

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<para>

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This program is set-uid to root, but will switch back to the

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original (and presumably non-privileged) user and group after

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bringing up the network interface.

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</para>

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<para>

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To use this program for its intended purpose (see <xref

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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

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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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to read that file.

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</para>

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<para>

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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. The defense against this is

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that the server is supposed to notice the client disappearing

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and will stop giving out the encrypted data. Therefore, it is

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important to set the timeout and checker interval values tightly

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on the server. See <citerefentry><refentrytitle

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>mandos</refentrytitle><manvolnum>8</manvolnum></citerefentry>.

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</para>

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<para>

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It will also help if the checker program on the server is

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configured to request something from the client which can not be

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spoofed by someone else on the network, unlike unencrypted

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<acronym>ICMP</acronym> echo (<quote>ping</quote>) replies.

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</para>

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<para>

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<emphasis>Note</emphasis>: This makes it completely insecure to

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have <application >Mandos</application> clients which dual-boot

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to another operating system which is <emphasis>not</emphasis>

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trusted to keep the initial <acronym>RAM</acronym> disk image

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confidential.

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</para>

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</refsect1>

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<para>

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<citerefentry><refentrytitle>cryptsetup</refentrytitle>

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<manvolnum>8</manvolnum></citerefentry>,

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<citerefentry><refentrytitle>crypttab</refentrytitle>

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<manvolnum>5</manvolnum></citerefentry>,

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<citerefentry><refentrytitle>mandos</refentrytitle>

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<manvolnum>8</manvolnum></citerefentry>,

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<citerefentry><refentrytitle>password-prompt</refentrytitle>

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<manvolnum>8mandos</manvolnum></citerefentry>,

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<citerefentry><refentrytitle>plugin-runner</refentrytitle>

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<manvolnum>8mandos</manvolnum></citerefentry>

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</para>

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<term>

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<ulink url="http://www.zeroconf.org/">Zeroconf</ulink>

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</term>

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<para>

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Zeroconf is the network protocol standard used for finding

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Mandos servers on the local network.

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</para>

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</listitem>

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</varlistentry>

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<term>

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<ulink url="http://www.avahi.org/">Avahi</ulink>

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</term>

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<para>

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Avahi is the library this program calls to find Zeroconf

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services.

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</para>

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</listitem>

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</varlistentry>

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<term>

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<ulink url="http://www.gnu.org/software/gnutls/"

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>GnuTLS</ulink>

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</term>

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<para>

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GnuTLS is the library this client uses to implement TLS for

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communicating securely with the server, and at the same time

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send the public OpenPGP key to the server.

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</para>

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</listitem>

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</varlistentry>

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<term>

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<ulink url="http://www.gnupg.org/related_software/gpgme/"

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>GPGME</ulink>

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</term>

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<para>

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GPGME is the library used to decrypt the OpenPGP data sent

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by the server.

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</para>

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</listitem>

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</varlistentry>

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<term>

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RFC 4291: <citetitle>IP Version 6 Addressing

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Architecture</citetitle>

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</term>

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<term>Section 2.2: <citetitle>Text Representation of

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Addresses</citetitle></term>

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</varlistentry>

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<term>Section 2.5.5.2: <citetitle>IPv4-Mapped IPv6

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Address</citetitle></term>

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</varlistentry>

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<term>Section 2.5.6, <citetitle>Link-Local IPv6 Unicast

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Addresses</citetitle></term>

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<para>

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This client uses IPv6 link-local addresses, which are

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immediately usable since a link-local addresses is

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automatically assigned to a network interfaces when it

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is brought up.

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</para>

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</listitem>

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</varlistentry>

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</variablelist>

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</listitem>

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</varlistentry>

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<term>

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RFC 4346: <citetitle>The Transport Layer Security (TLS)

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Protocol Version 1.1</citetitle>

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</term>

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<para>

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TLS 1.1 is the protocol implemented by GnuTLS.

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</para>

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</listitem>

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</varlistentry>

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<term>

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RFC 4880: <citetitle>OpenPGP Message Format</citetitle>

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</term>

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<para>

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The data received from the server is binary encrypted

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OpenPGP data.

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</para>

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</listitem>

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</varlistentry>

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<term>

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RFC 5081: <citetitle>Using OpenPGP Keys for Transport Layer

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Security</citetitle>

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</term>

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<para>

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This is implemented by GnuTLS and used by this program so

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that OpenPGP keys can be used.

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</para>

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</listitem>

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</varlistentry>

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</variablelist>

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</refsect1>

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</refentry>

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