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5a4557e8de2951a2796676b5ec4b6a90caa5be14Mark Andrews - Copyright (C) 2004-2015 Internet Systems Consortium, Inc. ("ISC")
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5a4557e8de2951a2796676b5ec4b6a90caa5be14Mark Andrews<a name="man.isc-hmac-fixup"></a><div class="titlepage"></div>
7911e6f9de303bca5a3d8b34f4330c8f7cecffaeTinderbox User<p><span class="application">isc-hmac-fixup</span> — fixes HMAC keys generated by older versions of BIND</p>
7911e6f9de303bca5a3d8b34f4330c8f7cecffaeTinderbox User<div class="cmdsynopsis"><p><code class="command">isc-hmac-fixup</code> {<em class="replaceable"><code>algorithm</code></em>} {<em class="replaceable"><code>secret</code></em>}</p></div>
7911e6f9de303bca5a3d8b34f4330c8f7cecffaeTinderbox User Versions of BIND 9 up to and including BIND 9.6 had a bug causing
7911e6f9de303bca5a3d8b34f4330c8f7cecffaeTinderbox User HMAC-SHA* TSIG keys which were longer than the digest length of the
7911e6f9de303bca5a3d8b34f4330c8f7cecffaeTinderbox User hash algorithm (i.e., SHA1 keys longer than 160 bits, SHA256 keys
7911e6f9de303bca5a3d8b34f4330c8f7cecffaeTinderbox User longer than 256 bits, etc) to be used incorrectly, generating a
7911e6f9de303bca5a3d8b34f4330c8f7cecffaeTinderbox User message authentication code that was incompatible with other DNS
7911e6f9de303bca5a3d8b34f4330c8f7cecffaeTinderbox User implementations.
7911e6f9de303bca5a3d8b34f4330c8f7cecffaeTinderbox User This bug has been fixed in BIND 9.7. However, the fix may
7911e6f9de303bca5a3d8b34f4330c8f7cecffaeTinderbox User cause incompatibility between older and newer versions of
7911e6f9de303bca5a3d8b34f4330c8f7cecffaeTinderbox User BIND, when using long keys. <span><strong class="command">isc-hmac-fixup</strong></span>
7911e6f9de303bca5a3d8b34f4330c8f7cecffaeTinderbox User modifies those keys to restore compatibility.
7911e6f9de303bca5a3d8b34f4330c8f7cecffaeTinderbox User To modify a key, run <span><strong class="command">isc-hmac-fixup</strong></span> and
7911e6f9de303bca5a3d8b34f4330c8f7cecffaeTinderbox User specify the key's algorithm and secret on the command line. If the
7911e6f9de303bca5a3d8b34f4330c8f7cecffaeTinderbox User secret is longer than the digest length of the algorithm (64 bytes
7911e6f9de303bca5a3d8b34f4330c8f7cecffaeTinderbox User for SHA1 through SHA256, or 128 bytes for SHA384 and SHA512), then a
7911e6f9de303bca5a3d8b34f4330c8f7cecffaeTinderbox User new secret will be generated consisting of a hash digest of the old
7911e6f9de303bca5a3d8b34f4330c8f7cecffaeTinderbox User secret. (If the secret did not require conversion, then it will be
7911e6f9de303bca5a3d8b34f4330c8f7cecffaeTinderbox User printed without modification.)
7911e6f9de303bca5a3d8b34f4330c8f7cecffaeTinderbox User<a name="id2671345"></a><h2>SECURITY CONSIDERATIONS</h2>
7911e6f9de303bca5a3d8b34f4330c8f7cecffaeTinderbox User Secrets that have been converted by <span><strong class="command">isc-hmac-fixup</strong></span>
7911e6f9de303bca5a3d8b34f4330c8f7cecffaeTinderbox User are shortened, but as this is how the HMAC protocol works in
7911e6f9de303bca5a3d8b34f4330c8f7cecffaeTinderbox User operation anyway, it does not affect security. RFC 2104 notes,
7911e6f9de303bca5a3d8b34f4330c8f7cecffaeTinderbox User "Keys longer than [the digest length] are acceptable but the
7911e6f9de303bca5a3d8b34f4330c8f7cecffaeTinderbox User extra length would not significantly increase the function
7911e6f9de303bca5a3d8b34f4330c8f7cecffaeTinderbox User <em class="citetitle">BIND 9 Administrator Reference Manual</em>,
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5a4557e8de2951a2796676b5ec4b6a90caa5be14Mark Andrews<p style="text-align: center;">BIND 9.11.0pre-alpha</p>