man.isc-hmac-fixup.html revision 4f9cb7bd58e2c0a7407fee3758ea265aee329ac6
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cb2846ded4de1abbb5934b92132baf826f1babfebnicholes<a name="man.isc-hmac-fixup"></a><div class="titlepage"></div>
cb2846ded4de1abbb5934b92132baf826f1babfebnicholes<p><span class="application">isc-hmac-fixup</span> — fixes HMAC keys generated by older versions of BIND</p>
cb2846ded4de1abbb5934b92132baf826f1babfebnicholes<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>
cb2846ded4de1abbb5934b92132baf826f1babfebnicholes Versions of BIND 9 up to and including BIND 9.6 had a bug causing
cb2846ded4de1abbb5934b92132baf826f1babfebnicholes HMAC-SHA* TSIG keys which were longer than the digest length of the
cb2846ded4de1abbb5934b92132baf826f1babfebnicholes hash algorithm (i.e., SHA1 keys longer than 160 bits, SHA256 keys
cb2846ded4de1abbb5934b92132baf826f1babfebnicholes longer than 256 bits, etc) to be used incorrectly, generating a
cb2846ded4de1abbb5934b92132baf826f1babfebnicholes message authentication code that was incompatible with other DNS
cb2846ded4de1abbb5934b92132baf826f1babfebnicholes implementations.
cb2846ded4de1abbb5934b92132baf826f1babfebnicholes This bug has been fixed in BIND 9.7. However, the fix may
cb2846ded4de1abbb5934b92132baf826f1babfebnicholes cause incompatibility between older and newer versions of
cb2846ded4de1abbb5934b92132baf826f1babfebnicholes BIND, when using long keys. <span><strong class="command">isc-hmac-fixup</strong></span>
cb2846ded4de1abbb5934b92132baf826f1babfebnicholes modifies those keys to restore compatibility.
cb2846ded4de1abbb5934b92132baf826f1babfebnicholes To modify a key, run <span><strong class="command">isc-hmac-fixup</strong></span> and
cb2846ded4de1abbb5934b92132baf826f1babfebnicholes specify the key's algorithm and secret on the command line. If the
cb2846ded4de1abbb5934b92132baf826f1babfebnicholes secret is longer than the digest length of the algorithm (64 bytes
cb2846ded4de1abbb5934b92132baf826f1babfebnicholes for SHA1 through SHA256, or 128 bytes for SHA384 and SHA512), then a
cb2846ded4de1abbb5934b92132baf826f1babfebnicholes new secret will be generated consisting of a hash digest of the old
cb2846ded4de1abbb5934b92132baf826f1babfebnicholes secret. (If the secret did not require conversion, then it will be
cb2846ded4de1abbb5934b92132baf826f1babfebnicholes printed without modification.)
cb2846ded4de1abbb5934b92132baf826f1babfebnicholes<a name="id2659206"></a><h2>SECURITY CONSIDERATIONS</h2>
cb2846ded4de1abbb5934b92132baf826f1babfebnicholes Secrets that have been converted by <span><strong class="command">isc-hmac-fixup</strong></span>
cb2846ded4de1abbb5934b92132baf826f1babfebnicholes are shortened, but as this is how the HMAC protocol works in
cb2846ded4de1abbb5934b92132baf826f1babfebnicholes operation anyway, it does not affect security. RFC 2104 notes,
cb2846ded4de1abbb5934b92132baf826f1babfebnicholes "Keys longer than [the digest length] are acceptable but the
cb2846ded4de1abbb5934b92132baf826f1babfebnicholes extra length would not significantly increase the function
cb2846ded4de1abbb5934b92132baf826f1babfebnicholes <em class="citetitle">BIND 9 Administrator Reference Manual</em>,
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