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  • Committer: Teddy Hogeborn
  • Date: 2015-03-10 18:03:38 UTC
  • Revision ID: teddy@recompile.se-20150310180338-pcxw6r2qmw9k6br9
Add ":!RSA" to GnuTLS priority string, to disallow non-DHE kx.

If Mandos was somehow made to use a non-ephemeral Diffie-Hellman key
exchange algorithm in the TLS handshake, any saved network traffic
could then be decrypted later if the Mandos client key was obtained.
By default, Mandos uses ephemeral DH key exchanges which does not have
this problem, but a non-ephemeral key exchange algorithm was still
enabled by default.  The simplest solution is to simply turn that off,
which ensures that Mandos will always use ephemeral DH key exchanges.

There is a "PFS" priority string specifier, but we can't use it because:

1. Security-wise, it is a mix between "NORMAL" and "SECURE128" - it
   enables a lot more algorithms than "SECURE256".

2. It is only available since GnuTLS 3.2.4.

Thanks to Andreas Fischer <af@bantuX.org> for reporting this issue.

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mandos-keygen.xml
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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        "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [
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<!ENTITY COMMANDNAME "mandos-keygen">
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<!ENTITY TIMESTAMP "2011-08-08">
 
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<!ENTITY TIMESTAMP "2014-06-22">
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<!ENTITY % common SYSTEM "common.ent">
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%common;
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]>
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        <firstname>Björn</firstname>
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        <surname>Påhlsson</surname>
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        <address>
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          <email>belorn@fukt.bsnet.se</email>
 
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          <email>belorn@recompile.se</email>
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        </address>
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      </author>
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      <author>
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        <firstname>Teddy</firstname>
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        <surname>Hogeborn</surname>
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        <address>
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          <email>teddy@fukt.bsnet.se</email>
 
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          <email>teddy@recompile.se</email>
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        </address>
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      </author>
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    </authorgroup>
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      <year>2008</year>
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      <year>2009</year>
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      <year>2011</year>
 
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      <year>2012</year>
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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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        <replaceable>TIME</replaceable></option></arg>
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      </group>
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      <sbr/>
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      <arg><option>--force</option></arg>
 
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      <group>
 
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        <arg choice="plain"><option>--force</option></arg>
 
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        <arg choice="plain"><option>-f</option></arg>
 
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      </group>
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    </cmdsynopsis>
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    <cmdsynopsis>
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      <command>&COMMANDNAME;</command>
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        <arg choice="plain"><option>-n
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        <replaceable>NAME</replaceable></option></arg>
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      </group>
 
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      <group>
 
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        <arg choice="plain"><option>--no-ssh</option></arg>
 
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        <arg choice="plain"><option>-S</option></arg>
 
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      </group>
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    </cmdsynopsis>
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    <cmdsynopsis>
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      <command>&COMMANDNAME;</command>
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        <listitem>
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          <para>
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            Target directory for key files.  Default is
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            <filename>/etc/mandos</filename>.
 
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            <filename class="directory">/etc/mandos</filename>.
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          </para>
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        </listitem>
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      </varlistentry>
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        <replaceable>TYPE</replaceable></option></term>
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        <listitem>
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          <para>
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            Key type.  Default is <quote>DSA</quote>.
 
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            Key type.  Default is <quote>RSA</quote>.
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          </para>
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        </listitem>
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      </varlistentry>
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        <replaceable>BITS</replaceable></option></term>
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        <listitem>
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          <para>
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            Key length in bits.  Default is 2048.
 
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            Key length in bits.  Default is 4096.
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          </para>
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        </listitem>
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      </varlistentry>
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        <replaceable>KEYTYPE</replaceable></option></term>
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        <listitem>
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          <para>
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            Subkey type.  Default is <quote>ELG-E</quote> (Elgamal
 
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            Subkey type.  Default is <quote>RSA</quote> (Elgamal
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            encryption-only).
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          </para>
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        </listitem>
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        <replaceable>BITS</replaceable></option></term>
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        <listitem>
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          <para>
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            Subkey length in bits.  Default is 2048.
 
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            Subkey length in bits.  Default is 4096.
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          </para>
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        </listitem>
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      </varlistentry>
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        <replaceable>TEXT</replaceable></option></term>
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        <listitem>
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          <para>
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            Comment field for key.  The default value is
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            <quote><literal>Mandos client key</literal></quote>.
 
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            Comment field for key.  Default is empty.
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          </para>
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        </listitem>
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      </varlistentry>
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          </para>
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        </listitem>
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      </varlistentry>
 
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      <varlistentry>
 
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        <term><option>--no-ssh</option></term>
 
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        <term><option>-S</option></term>
 
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        <listitem>
 
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          <para>
 
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            When <option>--password</option> or
 
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            <option>--passfile</option> is given, this option will
 
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            prevent <command>&COMMANDNAME;</command> from calling
 
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            <command>ssh-keyscan</command> to get an SSH fingerprint
 
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            for this host and, if successful, output suitable config
 
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            options to use this fingerprint as a
 
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            <option>checker</option> option in the output.  This is
 
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            otherwise the default behavior.
 
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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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        </listitem>
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      </varlistentry>
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      <varlistentry>
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        <term><filename>/tmp</filename></term>
 
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        <term><filename class="directory">/tmp</filename></term>
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        <listitem>
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          <para>
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            Temporary files will be written here if
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    </informalexample>
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    <informalexample>
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      <para>
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        Prompt for a password, encrypt it with the key in
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        <filename>/etc/mandos</filename> and output a section suitable
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        for <filename>clients.conf</filename>.
 
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        Prompt for a password, encrypt it with the key in <filename
 
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        class="directory">/etc/mandos</filename> and output a section
 
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        suitable for <filename>clients.conf</filename>.
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      </para>
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      <para>
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        <userinput>&COMMANDNAME; --password</userinput>
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      <citerefentry><refentrytitle>mandos</refentrytitle>
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      <manvolnum>8</manvolnum></citerefentry>,
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      <citerefentry><refentrytitle>mandos-client</refentrytitle>
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      <manvolnum>8mandos</manvolnum></citerefentry>
 
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      <manvolnum>8mandos</manvolnum></citerefentry>,
 
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      <citerefentry><refentrytitle>ssh-keyscan</refentrytitle>
 
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      <manvolnum>1</manvolnum></citerefentry>
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    </para>
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  </refsect1>
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