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1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen<a name="man.isc-hmac-fixup"></a><div class="titlepage"></div>
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen<p><span class="application">isc-hmac-fixup</span> — fixes HMAC keys generated by older versions of BIND</p>
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen<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>
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen Versions of BIND 9 up to and including BIND 9.6 had a bug causing
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen HMAC-SHA* TSIG keys which were longer than the digest length of the
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen hash algorithm (i.e., SHA1 keys longer than 160 bits, SHA256 keys
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen longer than 256 bits, etc) to be used incorrectly, generating a
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen message authentication code that was incompatible with other DNS
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen implementations.
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen This bug has been fixed in BIND 9.7. However, the fix may
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen cause incompatibility between older and newer versions of
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen BIND, when using long keys. <span><strong class="command">isc-hmac-fixup</strong></span>
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen modifies those keys to restore compatibility.
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen To modify a key, run <span><strong class="command">isc-hmac-fixup</strong></span> and
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen specify the key's algorithm and secret on the command line. If the
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen secret is longer than the digest length of the algorithm (64 bytes
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen for SHA1 through SHA256, or 128 bytes for SHA384 and SHA512), then a
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen new secret will be generated consisting of a hash digest of the old
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen secret. (If the secret did not require conversion, then it will be
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen printed without modification.)
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen<a name="id2671789"></a><h2>SECURITY CONSIDERATIONS</h2>
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen Secrets that have been converted by <span><strong class="command">isc-hmac-fixup</strong></span>
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen are shortened, but as this is how the HMAC protocol works in
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen operation anyway, it does not affect security. RFC 2104 notes,
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen "Keys longer than [the digest length] are acceptable but the
1ac7c8e9040e0d0b7e9f849e45b94bfe919595a9Timo Sirainen extra length would not significantly increase the function
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