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65fea56f17cd614bc8908264df980a62e1931468vboxsync<a name="man.isc-hmac-fixup"></a><div class="titlepage"></div>
65fea56f17cd614bc8908264df980a62e1931468vboxsync<p><span class="application">isc-hmac-fixup</span> — fixes HMAC keys generated by older versions of BIND</p>
65fea56f17cd614bc8908264df980a62e1931468vboxsync<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>
65fea56f17cd614bc8908264df980a62e1931468vboxsync Versions of BIND 9 up to and including BIND 9.6 had a bug causing
65fea56f17cd614bc8908264df980a62e1931468vboxsync HMAC-SHA* TSIG keys which were longer than the digest length of the
65fea56f17cd614bc8908264df980a62e1931468vboxsync hash algorithm (i.e., SHA1 keys longer than 160 bits, SHA256 keys
65fea56f17cd614bc8908264df980a62e1931468vboxsync longer than 256 bits, etc) to be used incorrectly, generating a
65fea56f17cd614bc8908264df980a62e1931468vboxsync message authentication code that was incompatible with other DNS
65fea56f17cd614bc8908264df980a62e1931468vboxsync implementations.
65fea56f17cd614bc8908264df980a62e1931468vboxsync This bug has been fixed in BIND 9.7. However, the fix may
65fea56f17cd614bc8908264df980a62e1931468vboxsync cause incompatibility between older and newer versions of
65fea56f17cd614bc8908264df980a62e1931468vboxsync BIND, when using long keys. <span><strong class="command">isc-hmac-fixup</strong></span>
65fea56f17cd614bc8908264df980a62e1931468vboxsync modifies those keys to restore compatibility.
65fea56f17cd614bc8908264df980a62e1931468vboxsync To modify a key, run <span><strong class="command">isc-hmac-fixup</strong></span> and
65fea56f17cd614bc8908264df980a62e1931468vboxsync specify the key's algorithm and secret on the command line. If the
65fea56f17cd614bc8908264df980a62e1931468vboxsync secret is longer than the digest length of the algorithm (64 bytes
65fea56f17cd614bc8908264df980a62e1931468vboxsync for SHA1 through SHA256, or 128 bytes for SHA384 and SHA512), then a
65fea56f17cd614bc8908264df980a62e1931468vboxsync new secret will be generated consisting of a hash digest of the old
65fea56f17cd614bc8908264df980a62e1931468vboxsync secret. (If the secret did not require conversion, then it will be
65fea56f17cd614bc8908264df980a62e1931468vboxsync printed without modification.)
65fea56f17cd614bc8908264df980a62e1931468vboxsync<a name="id2619307"></a><h2>SECURITY CONSIDERATIONS</h2>
65fea56f17cd614bc8908264df980a62e1931468vboxsync Secrets that have been converted by <span><strong class="command">isc-hmac-fixup</strong></span>
65fea56f17cd614bc8908264df980a62e1931468vboxsync are shortened, but as this is how the HMAC protocol works in
65fea56f17cd614bc8908264df980a62e1931468vboxsync operation anyway, it does not affect security. RFC 2104 notes,
65fea56f17cd614bc8908264df980a62e1931468vboxsync "Keys longer than [the digest length] are acceptable but the
65fea56f17cd614bc8908264df980a62e1931468vboxsync extra length would not significantly increase the function
65fea56f17cd614bc8908264df980a62e1931468vboxsync <em class="citetitle">BIND 9 Administrator Reference Manual</em>,
65fea56f17cd614bc8908264df980a62e1931468vboxsync<p><span class="corpauthor">Internet Systems Consortium</span>