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 -

 - This Source Code Form is subject to the terms of the Mozilla Public

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<refentry xmlns="http://docbook.org/ns/docbook" version="5.0" xml:id="man.isc-hmac-fixup">

  <info>

    <date>2013-04-28</date>

  </info>

  <refentryinfo>

    <corpname>ISC</corpname>

    <corpauthor>Internet Systems Consortium, Inc.</corpauthor>

  </refentryinfo>

  <refmeta>

    <refentrytitle><application>isc-hmac-fixup</application></refentrytitle>

    <manvolnum>8</manvolnum>

    <refmiscinfo>BIND9</refmiscinfo>

  </refmeta>

  <refnamediv>

    <refname><application>isc-hmac-fixup</application></refname>

    <refpurpose>fixes HMAC keys generated by older versions of BIND</refpurpose>

  </refnamediv>

  <docinfo>

    <copyright>

      <year>2010</year>

      <year>2013</year>

      <year>2014</year>

      <year>2015</year>

      <year>2016</year>

      <year>2017</year>

      <year>2018</year>

      <year>2019</year>

      <year>2020</year>

      <holder>Internet Systems Consortium, Inc. ("ISC")</holder>

    </copyright>

  </docinfo>

  <refsynopsisdiv>

    <cmdsynopsis sepchar=" ">

      <command>isc-hmac-fixup</command>

      <arg choice="req" rep="norepeat"><replaceable class="parameter">algorithm</replaceable></arg>

      <arg choice="req" rep="norepeat"><replaceable class="parameter">secret</replaceable></arg>

    </cmdsynopsis>

  </refsynopsisdiv>

  <refsection><info><title>DESCRIPTION</title></info>

    <para>

      Versions of BIND 9 up to and including BIND 9.6 had a bug causing

      HMAC-SHA* TSIG keys which were longer than the digest length of the

      hash algorithm (i.e., SHA1 keys longer than 160 bits, SHA256 keys

      longer than 256 bits, etc) to be used incorrectly, generating a

      message authentication code that was incompatible with other DNS

      implementations.

    </para>

    <para>

      This bug was fixed in BIND 9.7.  However, the fix may

      cause incompatibility between older and newer versions of

      BIND, when using long keys.  <command>isc-hmac-fixup</command>

      modifies those keys to restore compatibility.

    </para>

    <para>

      To modify a key, run <command>isc-hmac-fixup</command> and

      specify the key's algorithm and secret on the command line.  If the

      secret is longer than the digest length of the algorithm (64 bytes

      for SHA1 through SHA256, or 128 bytes for SHA384 and SHA512), then a

      new secret will be generated consisting of a hash digest of the old

      secret.  (If the secret did not require conversion, then it will be

      printed without modification.)

    </para>

  </refsection>

  <refsection><info><title>SECURITY CONSIDERATIONS</title></info>

    <para>

      Secrets that have been converted by <command>isc-hmac-fixup</command>

      are shortened, but as this is how the HMAC protocol works in

      operation anyway, it does not affect security.  RFC 2104 notes,

      "Keys longer than [the digest length] are acceptable but the

      extra length would not significantly increase the function

      strength."

    </para>

  </refsection>

  <refsection><info><title>SEE ALSO</title></info>

    <para>

      <citetitle>BIND 9 Administrator Reference Manual</citetitle>,

      <citetitle>RFC 2104</citetitle>.

    </para>

  </refsection>

</refentry>