/mandos/trunk

<!ENTITY COMMANDNAME "mandos-client">

<!ENTITY TIMESTAMP "2019-02-09">

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

%common;

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

    <productnumber>&version;</productnumber>

          <email>belorn@recompile.se</email>

          <email>teddy@recompile.se</email>

      <year>2009</year>

      <year>2010</year>

      <year>2011</year>

      <year>2012</year>

      <year>2013</year>

      <year>2014</year>

      <year>2015</year>

      <year>2016</year>

      <year>2017</year>

      <year>2018</year>

  

      Client for <application>Mandos</application>

  

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

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

      <group rep='repeat'>

        <replaceable>NAME</replaceable><arg rep='repeat'

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

        <arg choice="plain"><option>-i <replaceable>NAME</replaceable

        ><arg rep='repeat'>,<replaceable>NAME</replaceable></arg

        ></option></arg>

      <group>

        <arg choice="plain"><option>--tls-privkey

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

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

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

      </group>

      <sbr/>

      <group>

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

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

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

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

      </group>

      <sbr/>

        <option>--dh-params <replaceable>FILE</replaceable></option>

      </arg>

      <sbr/>

      <arg>

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

      </arg>

      <sbr/>

      <arg>

        <option>--retry <replaceable>SECONDS</replaceable></option>

      </arg>

      <sbr/>

      <arg>

        <option>--network-hook-dir

        <replaceable>DIR</replaceable></option>

      </arg>

      <sbr/>

      <arg>

  

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

      brings up network interfaces, uses the interfaces’ IPv6

      link-local addresses to get network connectivity, uses Zeroconf

      to find servers on the local network, and communicates with

      servers using TLS with a raw public key to ensure authenticity

      and confidentiality.  This client program keeps running, trying

      all servers on the network, until it receives a satisfactory

      reply or a TERM signal.  After all servers have been tried, all

      servers are periodically retried.  If no servers are found it

      will wait indefinitely for new servers to appear.

    </para>

    <para>

      The network interfaces are selected like this: If any interfaces

      are specified using the <option>--interface</option> option,

      those interface are used.  Otherwise,

      <command>&COMMANDNAME;</command> will use all interfaces that

      are not loopback interfaces, are not point-to-point interfaces,

      are capable of broadcasting and do not have the NOARP flag (see

      <citerefentry><refentrytitle>netdevice</refentrytitle>

      <manvolnum>7</manvolnum></citerefentry>).  (If the

      <option>--connect</option> option is used, point-to-point

      interfaces and non-broadcast interfaces are accepted.)  If any

      used interfaces are not up and running, they are first taken up

      (and later taken down again on program exit).

    </para>

    <para>

      Before network interfaces are selected, all <quote>network

      hooks</quote> are run; see <xref linkend="network-hooks"/>.

            Normally, Zeroconf would be used to locate Mandos servers,

            in which case this option would only be used when testing

            and debugging.

        <term><option>--interface=<replaceable

        >NAME</replaceable><arg rep='repeat'>,<replaceable

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

        <replaceable>NAME</replaceable><arg rep='repeat'>,<replaceable

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

            Comma separated list of network interfaces that will be

            brought up and scanned for Mandos servers to connect to.

            The default is the empty string, which will automatically

            use all appropriate interfaces.

          </para>

          <para>

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

            exactly one interface name is specified (except

            <quote><literal>none</literal></quote>), 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 normally 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, unless created by a

            <quote>network hook</quote> — see <xref

            linkend="network-hooks"/>.

          </para>

          <para>

            <replaceable>NAME</replaceable> can be the string

            <quote><literal>none</literal></quote>; this will make

            <command>&COMMANDNAME;</command> only bring up interfaces

            specified <emphasis>before</emphasis> this string.  This

            is not recommended, and only meant for advanced users.

            OpenPGP public key file name.  The default name is

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

            ></quote>.

      

            OpenPGP secret key file name.  The default name is

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

            ></quote>.

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

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

        <term><option>-T

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

        <listitem>

          <para>

            TLS raw public key file name.  The default name is

            <quote><filename>/conf/conf.d/mandos/tls-pubkey.pem</filename

            ></quote>.

          </para>

        </listitem>

      </varlistentry>

 

      <varlistentry>

        <term><option>--tls-privkey=<replaceable

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

        <term><option>-t

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

        <listitem>

          <para>

            TLS secret key file name.  The default name is

            <quote><filename>/conf/conf.d/mandos/tls-privkey.pem</filename

            ></quote>.

          </para>

        </listitem>

      </varlistentry>

 

      <varlistentry>

      

            TLS Diffie-Hellman key exchange.  The default value is

            selected automatically based on the GnuTLS security

            profile set in its priority string.  Note that if the

            <option>--dh-params</option> option is used, the values

            from that file will be used instead.

          </para>

        </listitem>

      </varlistentry>

      

      <varlistentry>

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

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

        <listitem>

          <para>

            Specifies a PEM-encoded PKCS#3 file to read the parameters

            needed by the TLS Diffie-Hellman key exchange from.  If

            this option is not given, or if the file for some reason

            could not be used, the parameters will be generated on

            startup, which will take some time and processing power.

            Those using servers running under time, power or processor

            constraints may want to generate such a file in advance

            and use this option.

          </para>

        </listitem>

      </varlistentry>

 

      <varlistentry>

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

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

        <listitem>

          <para>

            After bringing a 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>--retry=<replaceable

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

        <listitem>

          <para>

            All Mandos servers are tried repeatedly until a password

            is received.  This value specifies, in seconds, how long

            between each successive try <emphasis>for the same

            server</emphasis>.  The default is 10 seconds.

          </para>

        </listitem>

      </varlistentry>

 

      <varlistentry>

        <term><option>--network-hook-dir=<replaceable

        >DIR</replaceable></option></term>

        <listitem>

          <para>

            Network hook directory.  The default directory is

            <quote><filename class="directory"

            >/lib/mandos/network-hooks.d</filename></quote>.

      

  

      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 (<citerefentry>

      <refentrytitle>password-prompt</refentrytitle>

      <manvolnum>8mandos</manvolnum></citerefentry>) will prompt for

      passwords on the system console.

      error occurs.  Otherwise, it will forever connect to any

      discovered <application>Mandos</application> servers, trying to

      get a decryptable password and print it.

    <variablelist>

      <varlistentry>

        <term><envar>MANDOSPLUGINHELPERDIR</envar></term>

        <listitem>

          <para>

            This environment variable will be assumed to contain the

            directory containing any helper executables.  The use and

            nature of these helper executables, if any, is

            purposefully not documented.

        </para>

        </listitem>

      </varlistentry>

    </variablelist>

      This program does not use any other environment variables, not

      even the ones provided by <citerefentry><refentrytitle

  <refsect1 id="network-hooks">

    <title>NETWORK HOOKS</title>

    <para>

      If a network interface like a bridge or tunnel is required to

      find a Mandos server, this requires the interface to be up and

      running before <command>&COMMANDNAME;</command> starts looking

      for Mandos servers.  This can be accomplished by creating a

      <quote>network hook</quote> program, and placing it in a special

      directory.

    </para>

    <para>

      Before the network is used (and again before program exit), any

      runnable programs found in the network hook directory are run

      with the argument <quote><literal>start</literal></quote> or

      <quote><literal>stop</literal></quote>.  This should bring up or

      down, respectively, any network interface which

      <command>&COMMANDNAME;</command> should use.

    </para>

    <refsect2 id="hook-requirements">

      <title>REQUIREMENTS</title>

      <para>

        A network hook must be an executable file, and its name must

        consist entirely of upper and lower case letters, digits,

        underscores, periods, and hyphens.

      </para>

      <para>

        A network hook will receive one argument, which can be one of

        the following:

      </para>

      <variablelist>

        <varlistentry>

          <term><literal>start</literal></term>

          <listitem>

            <para>

              This should make the network hook create (if necessary)

              and bring up a network interface.

            </para>

          </listitem>

        </varlistentry>

        <varlistentry>

          <term><literal>stop</literal></term>

          <listitem>

            <para>

              This should make the network hook take down a network

              interface, and delete it if it did not exist previously.

            </para>

          </listitem>

        </varlistentry>

        <varlistentry>

          <term><literal>files</literal></term>

          <listitem>

            <para>

              This should make the network hook print, <emphasis>one

              file per line</emphasis>, all the files needed for it to

              run.  (These files will be copied into the initial RAM

              filesystem.)  Typical use is for a network hook which is

              a shell script to print its needed binaries.

            </para>

            <para>

              It is not necessary to print any non-executable files

              already in the network hook directory, these will be

              copied implicitly if they otherwise satisfy the name

              requirements.

            </para>

          </listitem>

        </varlistentry>

        <varlistentry>

          <term><literal>modules</literal></term>

          <listitem>

            <para>

              This should make the network hook print, <emphasis>on

              separate lines</emphasis>, all the kernel modules needed

              for it to run.  (These modules will be copied into the

              initial RAM filesystem.)  For instance, a tunnel

              interface needs the

              <quote><literal>tun</literal></quote> module.

            </para>

          </listitem>

        </varlistentry>

      </variablelist>

      <para>

        The network hook will be provided with a number of environment

        variables:

      </para>

      <variablelist>

        <varlistentry>

          <term><envar>MANDOSNETHOOKDIR</envar></term>

          <listitem>

            <para>

              The network hook directory, specified to

              <command>&COMMANDNAME;</command> by the

              <option>--network-hook-dir</option> option.  Note: this

              should <emphasis>always</emphasis> be used by the

              network hook to refer to itself or any files in the hook

              directory it may require.

            </para>

          </listitem>

        </varlistentry>

        <varlistentry>

          <term><envar>DEVICE</envar></term>

          <listitem>

            <para>

              The network interfaces, as specified to

              <command>&COMMANDNAME;</command> by the

              <option>--interface</option> option, combined to one

              string and separated by commas.  If this is set, and

              does not contain the interface a hook will bring up,

              there is no reason for a hook to continue.

            </para>

          </listitem>

        </varlistentry>

        <varlistentry>

          <term><envar>MODE</envar></term>

          <listitem>

            <para>

              This will be the same as the first argument;

              i.e. <quote><literal>start</literal></quote>,

              <quote><literal>stop</literal></quote>,

              <quote><literal>files</literal></quote>, or

              <quote><literal>modules</literal></quote>.

            </para>

          </listitem>

        </varlistentry>

        <varlistentry>

          <term><envar>VERBOSITY</envar></term>

          <listitem>

            <para>

              This will be the <quote><literal>1</literal></quote> if

              the <option>--debug</option> option is passed to

              <command>&COMMANDNAME;</command>, otherwise

              <quote><literal>0</literal></quote>.

            </para>

          </listitem>

        </varlistentry>

        <varlistentry>

          <term><envar>DELAY</envar></term>

          <listitem>

            <para>

              This will be the same as the <option>--delay</option>

              option passed to <command>&COMMANDNAME;</command>.  Is

              only set if <envar>MODE</envar> is

              <quote><literal>start</literal></quote> or

              <quote><literal>stop</literal></quote>.

            </para>

          </listitem>

        </varlistentry>

        <varlistentry>

          <term><envar>CONNECT</envar></term>

          <listitem>

            <para>

              This will be the same as the <option>--connect</option>

              option passed to <command>&COMMANDNAME;</command>.  Is

              only set if <option>--connect</option> is passed and

              <envar>MODE</envar> is

              <quote><literal>start</literal></quote> or

              <quote><literal>stop</literal></quote>.

            </para>

          </listitem>

        </varlistentry>

      </variablelist>

      <para>

        A hook may not read from standard input, and should be

        restrictive in printing to standard output or standard error

        unless <varname>VERBOSITY</varname> is

        <quote><literal>1</literal></quote>.

      </para>

    </refsect2>

  </refsect1>

  

  <refsect1 id="files">

      <varlistentry>

        <term><filename>/conf/conf.d/mandos/tls-pubkey.pem</filename

        ></term>

        <term><filename>/conf/conf.d/mandos/tls-privkey.pem</filename

        ></term>

        <listitem>

          <para>

            Public and private raw key files, in <quote>PEM</quote>

            format.  These are the default file names, they can be

            changed with the <option>--tls-pubkey</option> and

            <option>--tls-privkey</option> options.

          </para>

        </listitem>

      </varlistentry>

      <varlistentry>

        <term><filename

        class="directory">/lib/mandos/network-hooks.d</filename></term>

        <listitem>

          <para>

            Directory where network hooks are located.  Change this

            with the <option>--network-hook-dir</option> option.  See

            <xref linkend="network-hooks"/>.

          </para>

        </listitem>

      </varlistentry>

  <refsect1 id="bugs">

    <title>BUGS</title>

    <xi:include href="../bugs.xml"/>

  </refsect1>

  

        Normal invocation needs no options, if the network interfaces

        can be automatically determined:

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

        specific interface:

        Run in debug mode, and use custom keys:

 

<!-- do not wrap this line -->

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

 

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

        to locate a server; connect directly to the IPv6 link-local

        >fe80::aede:48ff:fe71:f6f2</systemitem></quote>, port 4711,

        using interface eth2:

<userinput>&COMMANDNAME; --debug --pubkey keydir/pubkey.txt --seckey keydir/seckey.txt --tls-pubkey keydir/tls-pubkey.pem --tls-privkey keydir/tls-privkey.pem --connect fe80::aede:48ff:fe71:f6f2:4711 --interface eth2</userinput>

  

      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 and TLS 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, like SSH server key

      fingerprints, and 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.

  

      <citerefentry><refentrytitle>intro</refentrytitle>

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

      <citerefentry><refentrytitle>cryptsetup</refentrytitle>

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

      <citerefentry><refentrytitle>crypttab</refentrytitle>

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

    <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="https://www.gnutls.org/">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 key to the server.

        </para>

      </listitem>

      </varlistentry>

      <varlistentry>

        <term>

          <ulink url="https://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 interface when it

                is brought up.

              </para>

            </listitem>

            </varlistentry>

          </variablelist>

        </listitem>

      </varlistentry>

      <varlistentry>

        <term>

          RFC 5246: <citetitle>The Transport Layer Security (TLS)

          Protocol Version 1.2</citetitle>

        </term>

      <listitem>

        <para>

          TLS 1.2 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 7250: <citetitle>Using Raw Public Keys in Transport

          Layer Security (TLS) and Datagram Transport Layer Security

          (DTLS)</citetitle>

        </term>

      <listitem>

        <para>

          This is implemented by GnuTLS in version 3.6.6 and is, if

          present, used by this program so that raw public keys can be

          used.

        </para>

      </listitem>

      </varlistentry>

      <varlistentry>

        <term>

          RFC 6091: <citetitle>Using OpenPGP Keys for Transport Layer

          Security</citetitle>

        </term>

      <listitem>

        <para>

          This is implemented by GnuTLS before version 3.6.0 and is,

          if present, used by this program so that OpenPGP keys can be

          used.

        </para>

      </listitem>

      </varlistentry>

    </variablelist>