/mandos/trunk

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<!ENTITY COMMANDNAME "mandos-client">

<!ENTITY TIMESTAMP "2009-01-24">

<!ENTITY % common SYSTEM "../common.ent">

%common;

]>

<refentry xmlns:xi="http://www.w3.org/2001/XInclude">

  <refentryinfo>

    <title>Mandos Manual</title>

    <!-- NWalsh’s docbook scripts use this to generate the footer: -->

    <productname>Mandos</productname>

    <productnumber>&version;</productnumber>

    <date>&TIMESTAMP;</date>

    <authorgroup>

      <author>

	<firstname>Björn</firstname>

	<surname>Påhlsson</surname>

	<address>

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

	</address>

      </author>

      <author>

	<firstname>Teddy</firstname>

	<surname>Hogeborn</surname>

	<address>

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

	</address>

      </author>

    </authorgroup>

    <copyright>

      <year>2008</year>

      <year>2009</year>

      <holder>Teddy Hogeborn</holder>

      <holder>Björn Påhlsson</holder>

    </copyright>

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

  </refentryinfo>

  <refmeta>

    <refentrytitle>&COMMANDNAME;</refentrytitle>

    <manvolnum>8mandos</manvolnum>

  </refmeta>

  <refnamediv>

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

    <refpurpose>

      Client for <application>Mandos</application>

    </refpurpose>

  </refnamediv>

  <refsynopsisdiv>

    <cmdsynopsis>

      <command>&COMMANDNAME;</command>

      <group>

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

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

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

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

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

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

      </group>

      <sbr/>

      <group>

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

	<replaceable>NAME</replaceable></option></arg>

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

	<replaceable>NAME</replaceable></option></arg>

      </group>

      <sbr/>

      <group>

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

	<replaceable>FILE</replaceable></option></arg>

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

	<replaceable>FILE</replaceable></option></arg>

      </group>

      <sbr/>

      <group>

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

	<replaceable>FILE</replaceable></option></arg>

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

	<replaceable>FILE</replaceable></option></arg>

      </group>

      <sbr/>

      <arg>

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

      </arg>

      <sbr/>

      <arg>

	<option>--dh-bits <replaceable>BITS</replaceable></option>

      </arg>

      <sbr/>

      <arg>

	<option>--delay <replaceable>SECONDS</replaceable></option>

      </arg>

      <sbr/>

      <arg>

	<option>--debug</option>

      </arg>

    </cmdsynopsis>

    <cmdsynopsis>

      <command>&COMMANDNAME;</command>

      <group choice="req">

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

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

      </group>

    </cmdsynopsis>

    <cmdsynopsis>

      <command>&COMMANDNAME;</command>

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

    </cmdsynopsis>

    <cmdsynopsis>

      <command>&COMMANDNAME;</command>

      <group choice="req">

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

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

      </group>

    </cmdsynopsis>

  </refsynopsisdiv>

  <refsect1 id="description">

    <title>DESCRIPTION</title>

    <para>

      <command>&COMMANDNAME;</command> is a client program that

      communicates with <citerefentry><refentrytitle

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

      to get a password.  In slightly more detail, this client program

      brings up a network interface, uses the interface’s IPv6

      link-local address to get network connectivity, uses Zeroconf to

      find servers on the local network, and communicates with servers

      using TLS with an OpenPGP key to ensure authenticity and

      confidentiality.  This client program keeps running, trying all

      servers on the network, until it receives a satisfactory reply

      or a TERM signal is received.  If no servers are found, or after

      all servers have been tried, it waits indefinitely for new

      servers to appear.

    </para>

    <para>

      This program is not meant to be run directly; it is really meant

      to run as a plugin of the <application>Mandos</application>

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

      <manvolnum>8mandos</manvolnum></citerefentry>, which runs in the

      initial <acronym>RAM</acronym> disk environment because it is

      specified as a <quote>keyscript</quote> in the <citerefentry>

      <refentrytitle>crypttab</refentrytitle><manvolnum>5</manvolnum>

      </citerefentry> file.

    </para>

  </refsect1>

  <refsect1 id="purpose">

    <title>PURPOSE</title>

    <para>

      The purpose of this is to enable <emphasis>remote and unattended

      rebooting</emphasis> of client host computer with an

      <emphasis>encrypted root file system</emphasis>.  See <xref

      linkend="overview"/> for details.

    </para>

  </refsect1>

  <refsect1 id="options">

    <title>OPTIONS</title>

    <para>

      This program is commonly not invoked from the command line; it

      is normally started by the <application>Mandos</application>

      plugin runner, see <citerefentry><refentrytitle

      >plugin-runner</refentrytitle><manvolnum>8mandos</manvolnum>

      </citerefentry>.  Any command line options this program accepts

      are therefore normally provided by the plugin runner, and not

      directly.

    </para>

    <variablelist>

      <varlistentry>

	<term><option>--connect=<replaceable

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

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

	<term><option>-c

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

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

	<listitem>

	  <para>

	    Do not use Zeroconf to locate servers.  Connect directly

	    to only one specified <application>Mandos</application>

	    server.  Note that an IPv6 address has colon characters in

	    it, so the <emphasis>last</emphasis> colon character is

	    assumed to separate the address from the port number.

	  </para>

	  <para>

	    This option is normally only useful for testing and

	    debugging.

	  </para>

	</listitem>

      </varlistentry>

      <varlistentry>

	<term><option>--interface=

	<replaceable>NAME</replaceable></option></term>

	<term><option>-i

	<replaceable>NAME</replaceable></option></term>

	<listitem>

	  <para>

	    Network interface that will be brought up and scanned for

	    Mandos servers to connect to.  The default it

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

	  </para>

	  <para>

	    If the <option>--connect</option> option is used, this

	    specifies the interface to use to connect to the address

	    given.

	  </para>

	  <para>

	    Note that since this program will normally run in the

	    initial RAM disk environment, the interface must be an

	    interface which exists at that stage.  Thus, the interface

	    can not be a pseudo-interface such as <quote>br0</quote>

	    or <quote>tun0</quote>; such interfaces will not exist

	    until much later in the boot process, and can not be used

	    by this program.

	  </para>

	</listitem>

      </varlistentry>

      <varlistentry>

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

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

	<term><option>-p

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

	<listitem>

	  <para>

	    OpenPGP public key file name.  The default name is

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

	    ></quote>.

	  </para>

	</listitem>

      </varlistentry>

      <varlistentry>

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

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

	<term><option>-s

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

	<listitem>

	  <para>

	    OpenPGP secret key file name.  The default name is

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

	    ></quote>.

	  </para>

	</listitem>

      </varlistentry>

      <varlistentry>

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

	>STRING</replaceable></option></term>

	<listitem>

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

		      xpointer="priority"/>

	</listitem>

      </varlistentry>

      <varlistentry>

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

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

	<listitem>

	  <para>

	    Sets the number of bits to use for the prime number in the

	    TLS Diffie-Hellman key exchange.  Default is 1024.

	  </para>

	</listitem>

      </varlistentry>

      <varlistentry>

	<term><option>--delay=<replaceable

	>SECONDS</replaceable></option></term>

	<listitem>

	  <para>

	    After bringing the network interface up, the program waits

	    for the interface to arrive in a <quote>running</quote>

	    state before proceeding.  During this time, the kernel log

	    level will be lowered to reduce clutter on the system

	    console, alleviating any other plugins which might be

	    using the system console.  This option sets the upper

	    limit of seconds to wait.  The default is 2.5 seconds.

	  </para>

	</listitem>

      </varlistentry>

      <varlistentry>

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

	<listitem>

	  <para>

	    Enable debug mode.  This will enable a lot of output to

	    standard error about what the program is doing.  The

	    program will still perform all other functions normally.

	  </para>

	  <para>

	    It will also enable debug mode in the Avahi and GnuTLS

	    libraries, making them print large amounts of debugging

	    output.

	  </para>

	</listitem>

      </varlistentry>

      <varlistentry>

	<term><option>--help</option></term>

	<term><option>-?</option></term>

	<listitem>

	  <para>

	    Gives a help message about options and their meanings.

	  </para>

	</listitem>

      </varlistentry>

      <varlistentry>

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

	<listitem>

	  <para>

	    Gives a short usage message.

	  </para>

	</listitem>

      </varlistentry>

      <varlistentry>

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

	<term><option>-V</option></term>

	<listitem>

	  <para>

	    Prints the program version.

	  </para>

	</listitem>

      </varlistentry>

    </variablelist>

  </refsect1>

  <refsect1 id="overview">

    <title>OVERVIEW</title>

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

    <para>

      This program is the client part.  It is a plugin started by

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

      <manvolnum>8mandos</manvolnum></citerefentry> which will run in

      an initial <acronym>RAM</acronym> disk environment.

    </para>

    <para>

      This program could, theoretically, be used as a keyscript in

      <filename>/etc/crypttab</filename>, but it would then be

      impossible to enter a password for the encrypted root disk at

      the console, since this program does not read from the console

      at all.  This is why a separate plugin runner (<citerefentry>

      <refentrytitle>plugin-runner</refentrytitle>

      <manvolnum>8mandos</manvolnum></citerefentry>) is used to run

      both this program and others in in parallel,

      <emphasis>one</emphasis> of which will prompt for passwords on

      the system console.

    </para>

  </refsect1>

  <refsect1 id="exit_status">

    <title>EXIT STATUS</title>

    <para>

      This program will exit with a successful (zero) exit status if a

      server could be found and the password received from it could be

      successfully decrypted and output on standard output.  The

      program will exit with a non-zero exit status only if a critical

      error occurs.  Otherwise, it will forever connect to new

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

      to get a decryptable password and print it.

    </para>

  </refsect1>

  <refsect1 id="environment">

    <title>ENVIRONMENT</title>

    <para>

      This program does not use any environment variables, not even

      the ones provided by <citerefentry><refentrytitle

      >cryptsetup</refentrytitle><manvolnum>8</manvolnum>

    </citerefentry>.

    </para>

  </refsect1>

  <refsect1 id="files">

    <title>FILES</title>

    <variablelist>

      <varlistentry>

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

	></term>

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

	></term>

	<listitem>

	  <para>

	    OpenPGP public and private key files, in <quote>ASCII

	    Armor</quote> format.  These are the default file names,

	    they can be changed with the <option>--pubkey</option> and

	    <option>--seckey</option> options.

	  </para>

	</listitem>

      </varlistentry>

    </variablelist>

  </refsect1>

<!--   <refsect1 id="bugs"> -->

<!--     <title>BUGS</title> -->

<!--     <para> -->

<!--     </para> -->

<!--   </refsect1> -->

  <refsect1 id="example">

    <title>EXAMPLE</title>

    <para>

      Note that normally, command line options will not be given

      directly, but via options for the Mandos <citerefentry

      ><refentrytitle>plugin-runner</refentrytitle>

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

    </para>

    <informalexample>

      <para>

	Normal invocation needs no options, if the network interface

	is <quote>eth0</quote>:

      </para>

      <para>

	<userinput>&COMMANDNAME;</userinput>

      </para>

    </informalexample>

    <informalexample>

      <para>

	Search for Mandos servers (and connect to them) using another

	interface:

      </para>

      <para>

	<!-- do not wrap this line -->

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

      </para>

    </informalexample>

    <informalexample>

      <para>

	Run in debug mode, and use a custom key:

      </para>

      <para>

<!-- do not wrap this line -->

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

      </para>

    </informalexample>

    <informalexample>

      <para>

	Run in debug mode, with a custom key, and do not use Zeroconf

	to locate a server; connect directly to the IPv6 address

	<quote><systemitem class="ipaddress"

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

	port 4711, using interface eth2:

      </para>

      <para>

<!-- do not wrap this line -->

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

      </para>

    </informalexample>

  </refsect1>

  <refsect1 id="security">

    <title>SECURITY</title>

    <para>

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

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

      bringing up the network interface.

    </para>

    <para>

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

      linkend="purpose"/>), the password for the root file system will

      have to be given out to be stored in a server computer, after

      having been encrypted using an OpenPGP key.  This encrypted data

      which will be stored in a server can only be decrypted by the

      OpenPGP key, and the data will only be given out to those

      clients who can prove they actually have that key.  This key,

      however, is stored unencrypted on the client side in its initial

      <acronym>RAM</acronym> disk image file system.  This is normally

      readable by all, but this is normally fixed during installation

      of this program; file permissions are set so that no-one is able

      to read that file.

    </para>

    <para>

      The only remaining weak point is that someone with physical

      access to the client hard drive might turn off the client

      computer, read the OpenPGP keys directly from the hard drive,

      and communicate with the server.  To safeguard against this, the

      server is supposed to notice the client disappearing and stop

      giving out the encrypted data.  Therefore, it is important to

      set the timeout and checker interval values tightly on the

      server.  See <citerefentry><refentrytitle

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

    </para>

    <para>

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

      configured to request something from the client which can not be

      spoofed by someone else on the network, unlike unencrypted

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

    </para>

    <para>

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

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

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

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

      confidential.

    </para>

  </refsect1>

  <refsect1 id="see_also">

    <title>SEE ALSO</title>

    <para>

      <citerefentry><refentrytitle>cryptsetup</refentrytitle>

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

      <citerefentry><refentrytitle>crypttab</refentrytitle>

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

      <citerefentry><refentrytitle>mandos</refentrytitle>

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

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

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

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

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

    </para>

    <variablelist>

      <varlistentry>

	<term>

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

	</term>

	<listitem>

	  <para>

	    Zeroconf is the network protocol standard used for finding

	    Mandos servers on the local network.

	  </para>

	</listitem>

      </varlistentry>

      <varlistentry>

	<term>

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

	</term>

      <listitem>

	<para>

	  Avahi is the library this program calls to find Zeroconf

	  services.

	</para>

      </listitem>

      </varlistentry>

      <varlistentry>

	<term>

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

	  >GnuTLS</ulink>

	</term>

      <listitem>

	<para>

	  GnuTLS is the library this client uses to implement TLS for

	  communicating securely with the server, and at the same time

	  send the public OpenPGP key to the server.

	</para>

      </listitem>

      </varlistentry>

      <varlistentry>

	<term>

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

		 >GPGME</ulink>

	</term>

	<listitem>

	  <para>

	    GPGME is the library used to decrypt the OpenPGP data sent

	    by the server.

	  </para>

	</listitem>

      </varlistentry>

      <varlistentry>

	<term>

	  RFC 4291: <citetitle>IP Version 6 Addressing

	  Architecture</citetitle>

	</term>

	<listitem>

	  <variablelist>

	    <varlistentry>

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

	      Addresses</citetitle></term>

	      <listitem><para/></listitem>

	    </varlistentry>

	    <varlistentry>

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

	      Address</citetitle></term>

	      <listitem><para/></listitem>

	    </varlistentry>

	    <varlistentry>

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

	    Addresses</citetitle></term>

	    <listitem>

	      <para>

		This client uses IPv6 link-local addresses, which are

		immediately usable since a link-local addresses is

		automatically assigned to a network interfaces when it

		is brought up.

	      </para>

	    </listitem>

	    </varlistentry>

	  </variablelist>

	</listitem>

      </varlistentry>

      <varlistentry>

	<term>

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

	  Protocol Version 1.1</citetitle>

	</term>

      <listitem>

	<para>

	  TLS 1.1 is the protocol implemented by GnuTLS.

	</para>

      </listitem>

      </varlistentry>

      <varlistentry>

	<term>

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

	</term>

      <listitem>

	<para>

	  The data received from the server is binary encrypted

	  OpenPGP data.

	</para>

      </listitem>

      </varlistentry>

      <varlistentry>

	<term>

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

	  Security</citetitle>

	</term>

      <listitem>

	<para>

	  This is implemented by GnuTLS and used by this program so

	  that OpenPGP keys can be used.

	</para>

      </listitem>

      </varlistentry>

    </variablelist>

  </refsect1>

</refentry>

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