1ISC-HMAC-FIXUP(1)                    BIND9                   ISC-HMAC-FIXUP(1)
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NAME

6       isc-hmac-fixup - fixes HMAC keys generated by older versions of BIND
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SYNOPSIS

9       isc-hmac-fixup {algorithm} {secret}
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DESCRIPTION

12       Versions of BIND 9 up to and including BIND 9.6 had a bug causing
13       HMAC-SHA* TSIG keys which were longer than the digest length of the
14       hash algorithm (i.e., SHA1 keys longer than 160 bits, SHA256 keys
15       longer than 256 bits, etc) to be used incorrectly, generating a message
16       authentication code that was incompatible with other DNS
17       implementations.
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19       This bug has been fixed in BIND 9.7. However, the fix may cause
20       incompatibility between older and newer versions of BIND, when using
21       long keys.  isc-hmac-fixup modifies those keys to restore
22       compatibility.
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24       To modify a key, run isc-hmac-fixup and specify the key's algorithm and
25       secret on the command line. If the secret is longer than the digest
26       length of the algorithm (64 bytes for SHA1 through SHA256, or 128 bytes
27       for SHA384 and SHA512), then a new secret will be generated consisting
28       of a hash digest of the old secret. (If the secret did not require
29       conversion, then it will be printed without modification.)
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SECURITY CONSIDERATIONS

32       Secrets that have been converted by isc-hmac-fixup are shortened, but
33       as this is how the HMAC protocol works in operation anyway, it does not
34       affect security. RFC 2104 notes, "Keys longer than [the digest length]
35       are acceptable but the extra length would not significantly increase
36       the function strength."
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SEE ALSO

39       BIND 9 Administrator Reference Manual, RFC 2104.
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AUTHOR

42       Internet Systems Consortium
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45       Copyright © 2010 Internet Systems Consortium, Inc. ("ISC")
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49BIND9                           January 5, 2010              ISC-HMAC-FIXUP(1)
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