/mandos/trunk : revision 149

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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 "mandos">

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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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</refmeta>

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

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Gives encrypted passwords to authenticated Mandos clients

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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>--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>--address

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<replaceable>ADDRESS</replaceable></option></arg>

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

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<replaceable>ADDRESS</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>--port

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

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</group>

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<sbr/>

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<arg><option>--priority

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<replaceable>PRIORITY</replaceable></option></arg>

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<sbr/>

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<arg><option>--servicename

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<sbr/>

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<arg><option>--configdir

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<replaceable>DIRECTORY</replaceable></option></arg>

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<sbr/>

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<arg><option>--debug</option></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>--version</option></arg>

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</cmdsynopsis>

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<command>&COMMANDNAME;</command>

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

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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 server daemon which

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handles incoming request for passwords for a pre-defined list of

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client host computers. The Mandos server uses Zeroconf to

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announce itself on the local network, and uses TLS to

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communicate securely with and to authenticate the clients. The

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Mandos server uses IPv6 to allow Mandos clients to use IPv6

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link-local addresses, since the clients will probably not have

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any other addresses configured (see <xref linkend="overview"/>).

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Any authenticated client is then given the stored pre-encrypted

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password for that specific client.

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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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Show a help message and exit

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</para>

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</listitem>

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</varlistentry>

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<term><option>--interface</option>

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<xi:include href="mandos-options.xml" xpointer="interface"/>

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</listitem>

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</varlistentry>

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<term><option>--address

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<replaceable>ADDRESS</replaceable></option></term>

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<term><option>-a

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<replaceable>ADDRESS</replaceable></option></term>

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<xi:include href="mandos-options.xml" xpointer="address"/>

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</listitem>

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</varlistentry>

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<term><option>--port

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<term><option>-p

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<xi:include href="mandos-options.xml" xpointer="port"/>

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</listitem>

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</varlistentry>

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<term><option>--check</option></term>

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<para>

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Run the server’s self-tests. This includes any unit

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tests, etc.

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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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<xi:include href="mandos-options.xml" xpointer="debug"/>

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</listitem>

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</varlistentry>

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<term><option>--priority <replaceable>

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PRIORITY</replaceable></option></term>

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<xi:include href="mandos-options.xml" xpointer="priority"/>

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</listitem>

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</varlistentry>

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<term><option>--servicename

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<xi:include href="mandos-options.xml"

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xpointer="servicename"/>

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</listitem>

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</varlistentry>

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<term><option>--configdir

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<replaceable>DIRECTORY</replaceable></option></term>

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<para>

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Directory to search for configuration files. Default is

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<quote><literal>/etc/mandos</literal></quote>. See

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<citerefentry><refentrytitle>mandos.conf</refentrytitle>

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<refentrytitle>mandos-clients.conf</refentrytitle>

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<manvolnum>5</manvolnum></citerefentry>.

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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 and exit.

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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 server part. It is a normal server program

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and will run in a normal system environment, not in an initial

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<acronym>RAM</acronym> disk environment.

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</para>

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</refsect1>

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<title>NETWORK PROTOCOL</title>

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<para>

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The Mandos server announces itself as a Zeroconf service of type

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<quote><literal>_mandos._tcp</literal></quote>. The Mandos

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client connects to the announced address and port, and sends a

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line of text where the first whitespace-separated field is the

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protocol version, which currently is

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<quote><literal>1</literal></quote>. The client and server then

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start a TLS protocol handshake with a slight quirk: the Mandos

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server program acts as a TLS <quote>client</quote> while the

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connecting Mandos client acts as a TLS <quote>server</quote>.

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The Mandos client must supply an OpenPGP certificate, and the

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fingerprint of this certificate is used by the Mandos server to

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look up (in a list read from <filename>clients.conf</filename>

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at start time) which binary blob to give the client. No other

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authentication or authorization is done by the server.

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</para>

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<table>

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<title>Mandos Protocol (Version 1)</title><tgroup cols="3"><thead>

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<row>

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<entry>Mandos Client</entry>

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<entry>Direction</entry>

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<entry>Mandos Server</entry>

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</row>

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</thead><tbody>

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<row>

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<entry>Connect</entry>

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</row>

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<row>

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</row>

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<row>

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<entry>TLS handshake <emphasis>as TLS <quote>server</quote>

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</emphasis></entry>

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<entry>TLS handshake <emphasis>as TLS <quote>client</quote>

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</emphasis></entry>

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</row>

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<row>

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<entry>OpenPGP public key (part of TLS handshake)</entry>

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</row>

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<row>

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<entry>Binary blob (client will assume OpenPGP data)</entry>

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</row>

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<row>

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<entry>Close</entry>

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</row>

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</tbody></tgroup></table>

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</refsect1>

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<title>CHECKING</title>

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<para>

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The server will, by default, continually check that the clients

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are still up. If a client has not been confirmed as being up

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for some time, the client is assumed to be compromised and is no

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longer eligible to receive the encrypted password. The timeout,

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checker program, and interval between checks can be configured

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both globally and per client; see <citerefentry>

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<refentrytitle>mandos-clients.conf</refentrytitle>

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<manvolnum>5</manvolnum></citerefentry>.

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</para>

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</refsect1>

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<title>LOGGING</title>

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<para>

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The server will send log message with various severity levels to

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<filename>/dev/log</filename>. With the

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<option>--debug</option> option, it will log even more messages,

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and also show them on the console.

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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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The server will exit with a non-zero exit status only when a

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critical error is encountered.

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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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To start the configured checker (see <xref

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linkend="checking"/>), the server uses

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<filename>/bin/sh</filename>, which in turn uses

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<varname>PATH</varname> to search for matching commands if

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an absolute path is not given. See <citerefentry>

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</citerefentry>.

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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>FILES</title>

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<para>

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Use the <option>--configdir</option> option to change where

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<command>&COMMANDNAME;</command> looks for its configurations

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files. The default file names are listed here.

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</para>

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<term><filename>/etc/mandos/mandos.conf</filename></term>

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<para>

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Server-global settings. See

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<citerefentry><refentrytitle>mandos.conf</refentrytitle>

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<manvolnum>5</manvolnum></citerefentry> for details.

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</para>

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</listitem>

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</varlistentry>

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<term><filename>/etc/mandos/clients.conf</filename></term>

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<para>

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List of clients and client-specific settings. See

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<citerefentry><refentrytitle>mandos-clients.conf</refentrytitle>

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<manvolnum>5</manvolnum></citerefentry> for details.

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</para>

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</listitem>

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</varlistentry>

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<term><filename>/var/run/mandos/mandos.pid</filename></term>

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<para>

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The file containing the process id of

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<command>&COMMANDNAME;</command>.

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</para>

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</listitem>

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</varlistentry>

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<para>

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The Unix domain socket to where local syslog messages are

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sent.

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</para>

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</listitem>

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</varlistentry>

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<para>

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This is used to start the configured checker command for

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each client. See <citerefentry>

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<refentrytitle>mandos-clients.conf</refentrytitle>

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<manvolnum>5</manvolnum></citerefentry> for details.

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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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<para>

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This server might, on especially fatal errors, emit a Python

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backtrace. This could be considered a feature.

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</para>

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<para>

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Currently, if a client is declared <quote>invalid</quote> due to

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having timed out, the server does not record this fact onto

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permanent storage. This has some security implications, see

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<xref linkend="CLIENTS"/>.

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</para>

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<para>

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There is currently no way of querying the server of the current

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status of clients, other than analyzing its <systemitem

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class="service">syslog</systemitem> output.

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</para>

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<para>

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There is no fine-grained control over logging and debug output.

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</para>

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<para>

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Debug mode is conflated with running in the foreground.

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</para>

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<para>

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The console log messages does not show a timestamp.

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</para>

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<para>

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This server does not check the expire time of clients’ OpenPGP

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keys.

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</para>

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</refsect1>

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<title>EXAMPLE</title>

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<para>

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Normal invocation needs no options:

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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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Run the server in debug mode, read configuration files from

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the <filename>~/mandos</filename> directory, and use the

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Zeroconf service name <quote>Test</quote> to not collide with

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any other official Mandos server on this host:

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</para>

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<para>

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<userinput>&COMMANDNAME; --debug --configdir ~/mandos --servicename Test</userinput>

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</para>

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</informalexample>

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<para>

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Run the server normally, but only listen to one interface and

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only on the link-local address on that interface:

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</para>

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<para>

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<userinput>&COMMANDNAME; --interface eth7 --address fe80::aede:48ff:fe71:f6f2</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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<title>SERVER</title>

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<para>

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Running this <command>&COMMANDNAME;</command> server program

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should not in itself present any security risk to the host

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computer running it. The program does not need any special

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privileges to run, and is designed to run as a non-root user.

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</para>

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</refsect2>

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<title>CLIENTS</title>

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<para>

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The server only gives out its stored data to clients which

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does have the OpenPGP key of the stored fingerprint. This is

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guaranteed by the fact that the client sends its OpenPGP

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public key in the TLS handshake; this ensures it to be

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genuine. The server computes the fingerprint of the key

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itself and looks up the fingerprint in its list of

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clients. The <filename>clients.conf</filename> file (see

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<citerefentry><refentrytitle>mandos-clients.conf</refentrytitle>

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<manvolnum>5</manvolnum></citerefentry>)

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<emphasis>must</emphasis> be made non-readable by anyone

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except the user running the server.

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</para>

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<para>

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As detailed in <xref linkend="checking"/>, the status of all

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client computers will continually be checked and be assumed

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compromised if they are gone for too long.

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</para>

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<para>

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If a client is compromised, its downtime should be duly noted

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by the server which would therefore declare the client

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invalid. But if the server was ever restarted, it would

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re-read its client list from its configuration file and again

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regard all clients therein as valid, and hence eligible to

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receive their passwords. Therefore, be careful when

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restarting servers if it is suspected that a client has, in

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fact, been compromised by parties who may now be running a

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fake Mandos client with the keys from the non-encrypted

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initial <acronym>RAM</acronym> image of the client host. What

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should be done in that case (if restarting the server program

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really is necessary) is to stop the server program, edit the

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configuration file to omit any suspect clients, and restart

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the server program.

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</para>

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<para>

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For more details on client-side security, see

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<citerefentry><refentrytitle>password-request</refentrytitle>

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

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</para>

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</refsect2>

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</refsect1>

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<para>

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<refentrytitle>mandos-clients.conf</refentrytitle>

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<refentrytitle>mandos.conf</refentrytitle>

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<refentrytitle>password-request</refentrytitle>

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

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</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 by clients

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for finding this Mandos server 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 server calls to implement

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Zeroconf service announcements.

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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 server uses to implement TLS for

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communicating securely with the client, and at the same time

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confidently get the client’s public OpenPGP key.

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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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The clients use 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 sent to clients is binary encrypted 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 server 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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