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dea636af4d1902a081ee891f1b19ee2f8729d759Pavel Březina <span class="application">isc-hmac-fixup</span>
dea636af4d1902a081ee891f1b19ee2f8729d759Pavel Březina — fixes HMAC keys generated by older versions of BIND
dea636af4d1902a081ee891f1b19ee2f8729d759Pavel Březina {<em class="replaceable"><code>algorithm</code></em>}
dea636af4d1902a081ee891f1b19ee2f8729d759Pavel Březina {<em class="replaceable"><code>secret</code></em>}
dea636af4d1902a081ee891f1b19ee2f8729d759Pavel Březina<a name="id-1.14.30.7"></a><h2>DESCRIPTION</h2>
dea636af4d1902a081ee891f1b19ee2f8729d759Pavel Březina Versions of BIND 9 up to and including BIND 9.6 had a bug causing
dea636af4d1902a081ee891f1b19ee2f8729d759Pavel Březina HMAC-SHA* TSIG keys which were longer than the digest length of the
dea636af4d1902a081ee891f1b19ee2f8729d759Pavel Březina hash algorithm (i.e., SHA1 keys longer than 160 bits, SHA256 keys
dea636af4d1902a081ee891f1b19ee2f8729d759Pavel Březina longer than 256 bits, etc) to be used incorrectly, generating a
dea636af4d1902a081ee891f1b19ee2f8729d759Pavel Březina message authentication code that was incompatible with other DNS
dea636af4d1902a081ee891f1b19ee2f8729d759Pavel Březina implementations.
dea636af4d1902a081ee891f1b19ee2f8729d759Pavel Březina This bug has been fixed in BIND 9.7. However, the fix may
dea636af4d1902a081ee891f1b19ee2f8729d759Pavel Březina cause incompatibility between older and newer versions of
dea636af4d1902a081ee891f1b19ee2f8729d759Pavel Březina BIND, when using long keys. <span class="command"><strong>isc-hmac-fixup</strong></span>
dea636af4d1902a081ee891f1b19ee2f8729d759Pavel Březina modifies those keys to restore compatibility.
dea636af4d1902a081ee891f1b19ee2f8729d759Pavel Březina To modify a key, run <span class="command"><strong>isc-hmac-fixup</strong></span> and
dea636af4d1902a081ee891f1b19ee2f8729d759Pavel Březina specify the key's algorithm and secret on the command line. If the
dea636af4d1902a081ee891f1b19ee2f8729d759Pavel Březina secret is longer than the digest length of the algorithm (64 bytes
dea636af4d1902a081ee891f1b19ee2f8729d759Pavel Březina for SHA1 through SHA256, or 128 bytes for SHA384 and SHA512), then a
dea636af4d1902a081ee891f1b19ee2f8729d759Pavel Březina new secret will be generated consisting of a hash digest of the old
dea636af4d1902a081ee891f1b19ee2f8729d759Pavel Březina secret. (If the secret did not require conversion, then it will be
dea636af4d1902a081ee891f1b19ee2f8729d759Pavel Březina printed without modification.)
dea636af4d1902a081ee891f1b19ee2f8729d759Pavel Březina<a name="id-1.14.30.8"></a><h2>SECURITY CONSIDERATIONS</h2>
dea636af4d1902a081ee891f1b19ee2f8729d759Pavel Březina Secrets that have been converted by <span class="command"><strong>isc-hmac-fixup</strong></span>
dea636af4d1902a081ee891f1b19ee2f8729d759Pavel Březina are shortened, but as this is how the HMAC protocol works in
dea636af4d1902a081ee891f1b19ee2f8729d759Pavel Březina operation anyway, it does not affect security. RFC 2104 notes,
dea636af4d1902a081ee891f1b19ee2f8729d759Pavel Březina "Keys longer than [the digest length] are acceptable but the
dea636af4d1902a081ee891f1b19ee2f8729d759Pavel Březina extra length would not significantly increase the function
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dea636af4d1902a081ee891f1b19ee2f8729d759Pavel Březina<p xmlns:db="http://docbook.org/ns/docbook" style="text-align: center;">BIND 9.11.0pre-alpha</p>