man.isc-hmac-fixup.html revision c60ee6edf129596fa04db86c6865d75b5a412598
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3dec9fcdd56adf1b4a563137b4915c8f2d83b881qs<p><span class="application">isc-hmac-fixup</span> — fixes HMAC keys generated by older versions of BIND</p>
3dec9fcdd56adf1b4a563137b4915c8f2d83b881qs<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>
3dec9fcdd56adf1b4a563137b4915c8f2d83b881qs Versions of BIND 9 up to and including BIND 9.6 had a bug causing
3dec9fcdd56adf1b4a563137b4915c8f2d83b881qs HMAC-SHA* TSIG keys which were longer than the digest length of the
3dec9fcdd56adf1b4a563137b4915c8f2d83b881qs hash algorithm (i.e., SHA1 keys longer than 160 bits, SHA256 keys
3dec9fcdd56adf1b4a563137b4915c8f2d83b881qs longer than 256 bits, etc) to be used incorrectly, generating a
3dec9fcdd56adf1b4a563137b4915c8f2d83b881qs message authentication code that was incompatible with other DNS
3dec9fcdd56adf1b4a563137b4915c8f2d83b881qs implementations.
3dec9fcdd56adf1b4a563137b4915c8f2d83b881qs This bug has been fixed in BIND 9.7. However, the fix may
3dec9fcdd56adf1b4a563137b4915c8f2d83b881qs cause incompatibility between older and newer versions of
3dec9fcdd56adf1b4a563137b4915c8f2d83b881qs BIND, when using long keys. <span><strong class="command">isc-hmac-fixup</strong></span>
3dec9fcdd56adf1b4a563137b4915c8f2d83b881qs modifies those keys to restore compatibility.
3dec9fcdd56adf1b4a563137b4915c8f2d83b881qs To modify a key, run <span><strong class="command">isc-hmac-fixup</strong></span> and
3dec9fcdd56adf1b4a563137b4915c8f2d83b881qs specify the key's algorithm and secret on the command line. If the
3dec9fcdd56adf1b4a563137b4915c8f2d83b881qs secret is longer than the digest length of the algorithm (64 bytes
3dec9fcdd56adf1b4a563137b4915c8f2d83b881qs for SHA1 through SHA256, or 128 bytes for SHA384 and SHA512), then a
3dec9fcdd56adf1b4a563137b4915c8f2d83b881qs new secret will be generated consisting of a hash digest of the old
3dec9fcdd56adf1b4a563137b4915c8f2d83b881qs secret. (If the secret did not require conversion, then it will be
3dec9fcdd56adf1b4a563137b4915c8f2d83b881qs printed without modification.)
3dec9fcdd56adf1b4a563137b4915c8f2d83b881qs Secrets that have been converted by <span><strong class="command">isc-hmac-fixup</strong></span>
3dec9fcdd56adf1b4a563137b4915c8f2d83b881qs are shortened, but as this is how the HMAC protocol works in
3dec9fcdd56adf1b4a563137b4915c8f2d83b881qs operation anyway, it does not affect security. RFC 2104 notes,
3dec9fcdd56adf1b4a563137b4915c8f2d83b881qs "Keys longer than [the digest length] are acceptable but the
3dec9fcdd56adf1b4a563137b4915c8f2d83b881qs extra length would not significantly increase the function
3dec9fcdd56adf1b4a563137b4915c8f2d83b881qs strength."
3dec9fcdd56adf1b4a563137b4915c8f2d83b881qs <em class="citetitle">BIND 9 Administrator Reference Manual</em>,
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