man.isc-hmac-fixup.html revision 162933bac8fec492e683b1c09224344e568191e5
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8001ba81cb851b38d86650a2fef5817facffb763johanengelen<tr><th colspan="3" align="center"><span class="application">isc-hmac-fixup</span></th></tr>
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8001ba81cb851b38d86650a2fef5817facffb763johanengelen<p><span class="application">isc-hmac-fixup</span> — fixes HMAC keys generated by older versions of BIND</p>
8001ba81cb851b38d86650a2fef5817facffb763johanengelen<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>
8001ba81cb851b38d86650a2fef5817facffb763johanengelen Versions of BIND 9 up to and including BIND 9.6 had a bug causing
8001ba81cb851b38d86650a2fef5817facffb763johanengelen HMAC-SHA* TSIG keys which were longer than the digest length of the
8001ba81cb851b38d86650a2fef5817facffb763johanengelen hash algorithm (i.e., SHA1 keys longer than 160 bits, SHA256 keys
8001ba81cb851b38d86650a2fef5817facffb763johanengelen longer than 256 bits, etc) to be used incorrectly, generating a
8001ba81cb851b38d86650a2fef5817facffb763johanengelen message authentication code that was incompatible with other DNS
8001ba81cb851b38d86650a2fef5817facffb763johanengelen implementations.
8001ba81cb851b38d86650a2fef5817facffb763johanengelen This bug has been fixed in BIND 9.7. However, the fix may
8001ba81cb851b38d86650a2fef5817facffb763johanengelen cause incompatibility between older and newer versions of
8001ba81cb851b38d86650a2fef5817facffb763johanengelen BIND, when using long keys. <span><strong class="command">isc-hmac-fixup</strong></span>
8001ba81cb851b38d86650a2fef5817facffb763johanengelen modifies those keys to restore compatibility.
8001ba81cb851b38d86650a2fef5817facffb763johanengelen To modify a key, run <span><strong class="command">isc-hmac-fixup</strong></span> and
8001ba81cb851b38d86650a2fef5817facffb763johanengelen specify the key's algorithm and secret on the command line. If the
8001ba81cb851b38d86650a2fef5817facffb763johanengelen secret is longer than the digest length of the algorithm (64 bytes
8001ba81cb851b38d86650a2fef5817facffb763johanengelen for SHA1 through SHA256, or 128 bytes for SHA384 and SHA512), then a
8001ba81cb851b38d86650a2fef5817facffb763johanengelen new secret will be generated consisting of a hash digest of the old
8001ba81cb851b38d86650a2fef5817facffb763johanengelen secret. (If the secret did not require conversion, then it will be
8001ba81cb851b38d86650a2fef5817facffb763johanengelen printed without modification.)
8001ba81cb851b38d86650a2fef5817facffb763johanengelen<a name="id2661481"></a><h2>SECURITY CONSIDERATIONS</h2>
8001ba81cb851b38d86650a2fef5817facffb763johanengelen Secrets that have been converted by <span><strong class="command">isc-hmac-fixup</strong></span>
8001ba81cb851b38d86650a2fef5817facffb763johanengelen are shortened, but as this is how the HMAC protocol works in
8001ba81cb851b38d86650a2fef5817facffb763johanengelen operation anyway, it does not affect security. RFC 2104 notes,
8001ba81cb851b38d86650a2fef5817facffb763johanengelen "Keys longer than [the digest length] are acceptable but the
8001ba81cb851b38d86650a2fef5817facffb763johanengelen extra length would not significantly increase the function
8001ba81cb851b38d86650a2fef5817facffb763johanengelen <em class="citetitle">BIND 9 Administrator Reference Manual</em>,
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