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723f9f463f1922eaef3d24d00cb289e10daa73ffminfrin<tr><th colspan="3" align="center"><span class="application">isc-hmac-fixup</span></th></tr>
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723f9f463f1922eaef3d24d00cb289e10daa73ffminfrin<a name="man.isc-hmac-fixup"></a><div class="titlepage"></div>
d064ff394913fd41d921b1c826f61c7b44931ca1minfrin<p><span class="application">isc-hmac-fixup</span> — fixes HMAC keys generated by older versions of BIND</p>
723f9f463f1922eaef3d24d00cb289e10daa73ffminfrin<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>
723f9f463f1922eaef3d24d00cb289e10daa73ffminfrin Versions of BIND 9 up to and including BIND 9.6 had a bug causing
723f9f463f1922eaef3d24d00cb289e10daa73ffminfrin HMAC-SHA* TSIG keys which were longer than the digest length of the
723f9f463f1922eaef3d24d00cb289e10daa73ffminfrin hash algorithm (i.e., SHA1 keys longer than 160 bits, SHA256 keys
723f9f463f1922eaef3d24d00cb289e10daa73ffminfrin longer than 256 bits, etc) to be used incorrectly, generating a
723f9f463f1922eaef3d24d00cb289e10daa73ffminfrin message authentication code that was incompatible with other DNS
723f9f463f1922eaef3d24d00cb289e10daa73ffminfrin implementations.
723f9f463f1922eaef3d24d00cb289e10daa73ffminfrin This bug has been fixed in BIND 9.7. However, the fix may
723f9f463f1922eaef3d24d00cb289e10daa73ffminfrin cause incompatibility between older and newer versions of
723f9f463f1922eaef3d24d00cb289e10daa73ffminfrin BIND, when using long keys. <span><strong class="command">isc-hmac-fixup</strong></span>
723f9f463f1922eaef3d24d00cb289e10daa73ffminfrin modifies those keys to restore compatibility.
723f9f463f1922eaef3d24d00cb289e10daa73ffminfrin To modify a key, run <span><strong class="command">isc-hmac-fixup</strong></span> and
723f9f463f1922eaef3d24d00cb289e10daa73ffminfrin specify the key's algorithm and secret on the command line. If the
723f9f463f1922eaef3d24d00cb289e10daa73ffminfrin secret is longer than the digest length of the algorithm (64 bytes
723f9f463f1922eaef3d24d00cb289e10daa73ffminfrin for SHA1 through SHA256, or 128 bytes for SHA384 and SHA512), then a
723f9f463f1922eaef3d24d00cb289e10daa73ffminfrin new secret will be generated consisting of a hash digest of the old
723f9f463f1922eaef3d24d00cb289e10daa73ffminfrin secret. (If the secret did not require conversion, then it will be
723f9f463f1922eaef3d24d00cb289e10daa73ffminfrin printed without modification.)
723f9f463f1922eaef3d24d00cb289e10daa73ffminfrin<a name="id2670968"></a><h2>SECURITY CONSIDERATIONS</h2>
723f9f463f1922eaef3d24d00cb289e10daa73ffminfrin Secrets that have been converted by <span><strong class="command">isc-hmac-fixup</strong></span>
723f9f463f1922eaef3d24d00cb289e10daa73ffminfrin are shortened, but as this is how the HMAC protocol works in
723f9f463f1922eaef3d24d00cb289e10daa73ffminfrin operation anyway, it does not affect security. RFC 2104 notes,
723f9f463f1922eaef3d24d00cb289e10daa73ffminfrin "Keys longer than [the digest length] are acceptable but the
723f9f463f1922eaef3d24d00cb289e10daa73ffminfrin extra length would not significantly increase the function
723f9f463f1922eaef3d24d00cb289e10daa73ffminfrin <em class="citetitle">BIND 9 Administrator Reference Manual</em>,
723f9f463f1922eaef3d24d00cb289e10daa73ffminfrin<p><span class="corpauthor">Internet Systems Consortium</span>
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723f9f463f1922eaef3d24d00cb289e10daa73ffminfrin<p style="text-align: center;">BIND 9.11.0pre-alpha</p>