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19186ef88e80c31204e53a6b401bfea359f9cdeblfrost<a name="man.isc-hmac-fixup"></a><div class="titlepage"></div>
19186ef88e80c31204e53a6b401bfea359f9cdeblfrost<p><span class="application">isc-hmac-fixup</span> — fixes HMAC keys generated by older versions of BIND</p>
a883820d466d0ef5d6ce4d894cf0e1e7f362b344neil_a_wilson<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>
5bb010f0aa6a136889dcf0565922f2fda56761fcmatthew_swift Versions of BIND 9 up to and including BIND 9.6 had a bug causing
5bb010f0aa6a136889dcf0565922f2fda56761fcmatthew_swift HMAC-SHA* TSIG keys which were longer than the digest length of the
5bb010f0aa6a136889dcf0565922f2fda56761fcmatthew_swift hash algorithm (i.e., SHA1 keys longer than 160 bits, SHA256 keys
5bb010f0aa6a136889dcf0565922f2fda56761fcmatthew_swift longer than 256 bits, etc) to be used incorrectly, generating a
5bb010f0aa6a136889dcf0565922f2fda56761fcmatthew_swift message authentication code that was incompatible with other DNS
5bb010f0aa6a136889dcf0565922f2fda56761fcmatthew_swift implementations.
d8ef9e002980c16b5a67b868ed54807fe9f514f6matthew_swift This bug has been fixed in BIND 9.7. However, the fix may
a883820d466d0ef5d6ce4d894cf0e1e7f362b344neil_a_wilson cause incompatibility between older and newer versions of
3ceb1ba801fc1445bacce610f70246b526706df7rhaggard BIND, when using long keys. <span><strong class="command">isc-hmac-fixup</strong></span>
3ceb1ba801fc1445bacce610f70246b526706df7rhaggard modifies those keys to restore compatibility.
3ceb1ba801fc1445bacce610f70246b526706df7rhaggard To modify a key, run <span><strong class="command">isc-hmac-fixup</strong></span> and
3ceb1ba801fc1445bacce610f70246b526706df7rhaggard specify the key's algorithm and secret on the command line. If the
3ceb1ba801fc1445bacce610f70246b526706df7rhaggard secret is longer than the digest length of the algorithm (64 bytes
3ceb1ba801fc1445bacce610f70246b526706df7rhaggard for SHA1 through SHA256, or 128 bytes for SHA384 and SHA512), then a
3ceb1ba801fc1445bacce610f70246b526706df7rhaggard new secret will be generated consisting of a hash digest of the old
d8ef9e002980c16b5a67b868ed54807fe9f514f6matthew_swift secret. (If the secret did not require conversion, then it will be
d8ef9e002980c16b5a67b868ed54807fe9f514f6matthew_swift printed without modification.)
d8ef9e002980c16b5a67b868ed54807fe9f514f6matthew_swift<a name="id2669795"></a><h2>SECURITY CONSIDERATIONS</h2>
a883820d466d0ef5d6ce4d894cf0e1e7f362b344neil_a_wilson Secrets that have been converted by <span><strong class="command">isc-hmac-fixup</strong></span>
3ceb1ba801fc1445bacce610f70246b526706df7rhaggard are shortened, but as this is how the HMAC protocol works in
a883820d466d0ef5d6ce4d894cf0e1e7f362b344neil_a_wilson operation anyway, it does not affect security. RFC 2104 notes,
a883820d466d0ef5d6ce4d894cf0e1e7f362b344neil_a_wilson "Keys longer than [the digest length] are acceptable but the
a883820d466d0ef5d6ce4d894cf0e1e7f362b344neil_a_wilson extra length would not significantly increase the function
3ceb1ba801fc1445bacce610f70246b526706df7rhaggard <em class="citetitle">BIND 9 Administrator Reference Manual</em>,
23af008cf63421c9afb5b63b643481319e8a8322matthew_swift<p><span class="corpauthor">Internet Systems Consortium</span>
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