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a0d34d3982507f513a9d800082481e9faeb9a943Timo Sirainen<a name="man.isc-hmac-fixup"></a><div class="titlepage"></div>
a0d34d3982507f513a9d800082481e9faeb9a943Timo Sirainen<p><span class="application">isc-hmac-fixup</span> — fixes HMAC keys generated by older versions of BIND</p>
287ba82a8da3eaa473b5735d4eeac2fb4c5d8117Timo 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>
a0d34d3982507f513a9d800082481e9faeb9a943Timo Sirainen Versions of BIND 9 up to and including BIND 9.6 had a bug causing
a0d34d3982507f513a9d800082481e9faeb9a943Timo Sirainen HMAC-SHA* TSIG keys which were longer than the digest length of the
a0d34d3982507f513a9d800082481e9faeb9a943Timo Sirainen hash algorithm (i.e., SHA1 keys longer than 160 bits, SHA256 keys
a0d34d3982507f513a9d800082481e9faeb9a943Timo Sirainen longer than 256 bits, etc) to be used incorrectly, generating a
a0d34d3982507f513a9d800082481e9faeb9a943Timo Sirainen message authentication code that was incompatible with other DNS
a0d34d3982507f513a9d800082481e9faeb9a943Timo Sirainen implementations.
a0d34d3982507f513a9d800082481e9faeb9a943Timo Sirainen This bug has been fixed in BIND 9.7. However, the fix may
287ba82a8da3eaa473b5735d4eeac2fb4c5d8117Timo Sirainen cause incompatibility between older and newer versions of
a0d34d3982507f513a9d800082481e9faeb9a943Timo Sirainen BIND, when using long keys. <span><strong class="command">isc-hmac-fixup</strong></span>
287ba82a8da3eaa473b5735d4eeac2fb4c5d8117Timo Sirainen modifies those keys to restore compatibility.
287ba82a8da3eaa473b5735d4eeac2fb4c5d8117Timo Sirainen To modify a key, run <span><strong class="command">isc-hmac-fixup</strong></span> and
287ba82a8da3eaa473b5735d4eeac2fb4c5d8117Timo Sirainen specify the key's algorithm and secret on the command line. If the
a0d34d3982507f513a9d800082481e9faeb9a943Timo Sirainen secret is longer than the digest length of the algorithm (64 bytes
a0d34d3982507f513a9d800082481e9faeb9a943Timo Sirainen for SHA1 through SHA256, or 128 bytes for SHA384 and SHA512), then a
a0d34d3982507f513a9d800082481e9faeb9a943Timo Sirainen new secret will be generated consisting of a hash digest of the old
a0d34d3982507f513a9d800082481e9faeb9a943Timo Sirainen secret. (If the secret did not require conversion, then it will be
287ba82a8da3eaa473b5735d4eeac2fb4c5d8117Timo Sirainen printed without modification.)
a0d34d3982507f513a9d800082481e9faeb9a943Timo Sirainen<a name="id2659826"></a><h2>SECURITY CONSIDERATIONS</h2>
a0d34d3982507f513a9d800082481e9faeb9a943Timo Sirainen Secrets that have been converted by <span><strong class="command">isc-hmac-fixup</strong></span>
287ba82a8da3eaa473b5735d4eeac2fb4c5d8117Timo Sirainen are shortened, but as this is how the HMAC protocol works in
a0d34d3982507f513a9d800082481e9faeb9a943Timo Sirainen operation anyway, it does not affect security. RFC 2104 notes,
a0d34d3982507f513a9d800082481e9faeb9a943Timo Sirainen "Keys longer than [the digest length] are acceptable but the
a0d34d3982507f513a9d800082481e9faeb9a943Timo Sirainen extra length would not significantly increase the function
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