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da2e3ebdc1edfbc5028edf1354e7dd2fa69a7968chin<a name="man.isc-hmac-fixup"></a><div class="titlepage"></div>
da2e3ebdc1edfbc5028edf1354e7dd2fa69a7968chin<p><span class="application">isc-hmac-fixup</span> — fixes HMAC keys generated by older versions of BIND</p>
da2e3ebdc1edfbc5028edf1354e7dd2fa69a7968chin<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>
da2e3ebdc1edfbc5028edf1354e7dd2fa69a7968chin Versions of BIND 9 up to and including BIND 9.6 had a bug causing
da2e3ebdc1edfbc5028edf1354e7dd2fa69a7968chin HMAC-SHA* TSIG keys which were longer than the digest length of the
da2e3ebdc1edfbc5028edf1354e7dd2fa69a7968chin hash algorithm (i.e., SHA1 keys longer than 160 bits, SHA256 keys
da2e3ebdc1edfbc5028edf1354e7dd2fa69a7968chin longer than 256 bits, etc) to be used incorrectly, generating a
da2e3ebdc1edfbc5028edf1354e7dd2fa69a7968chin message authentication code that was incompatible with other DNS
da2e3ebdc1edfbc5028edf1354e7dd2fa69a7968chin implementations.
da2e3ebdc1edfbc5028edf1354e7dd2fa69a7968chin This bug has been fixed in BIND 9.7. However, the fix may
da2e3ebdc1edfbc5028edf1354e7dd2fa69a7968chin cause incompatibility between older and newer versions of
da2e3ebdc1edfbc5028edf1354e7dd2fa69a7968chin BIND, when using long keys. <span class="command"><strong>isc-hmac-fixup</strong></span>
da2e3ebdc1edfbc5028edf1354e7dd2fa69a7968chin modifies those keys to restore compatibility.
da2e3ebdc1edfbc5028edf1354e7dd2fa69a7968chin To modify a key, run <span class="command"><strong>isc-hmac-fixup</strong></span> and
da2e3ebdc1edfbc5028edf1354e7dd2fa69a7968chin specify the key's algorithm and secret on the command line. If the
da2e3ebdc1edfbc5028edf1354e7dd2fa69a7968chin secret is longer than the digest length of the algorithm (64 bytes
da2e3ebdc1edfbc5028edf1354e7dd2fa69a7968chin for SHA1 through SHA256, or 128 bytes for SHA384 and SHA512), then a
da2e3ebdc1edfbc5028edf1354e7dd2fa69a7968chin new secret will be generated consisting of a hash digest of the old
da2e3ebdc1edfbc5028edf1354e7dd2fa69a7968chin secret. (If the secret did not require conversion, then it will be
da2e3ebdc1edfbc5028edf1354e7dd2fa69a7968chin printed without modification.)
da2e3ebdc1edfbc5028edf1354e7dd2fa69a7968chin<a name="id-1.14.34.8"></a><h2>SECURITY CONSIDERATIONS</h2>
da2e3ebdc1edfbc5028edf1354e7dd2fa69a7968chin Secrets that have been converted by <span class="command"><strong>isc-hmac-fixup</strong></span>
da2e3ebdc1edfbc5028edf1354e7dd2fa69a7968chin are shortened, but as this is how the HMAC protocol works in
da2e3ebdc1edfbc5028edf1354e7dd2fa69a7968chin operation anyway, it does not affect security. RFC 2104 notes,
da2e3ebdc1edfbc5028edf1354e7dd2fa69a7968chin "Keys longer than [the digest length] are acceptable but the
da2e3ebdc1edfbc5028edf1354e7dd2fa69a7968chin extra length would not significantly increase the function
da2e3ebdc1edfbc5028edf1354e7dd2fa69a7968chin strength."
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