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



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

SYNOPSIS
       isc-hmac-fixup {algorithm} {secret}

DESCRIPTION
       Versions of BIND 9 up to and including BIND 9.6 had a bug causing HMAC-SHA* TSIG keys which were longer than
       the digest length of the hash algorithm (i.e., SHA1 keys longer than 160 bits, SHA256 keys longer than 256
       bits, etc) to be used incorrectly, generating a message authentication code that was incompatible with other
       DNS implementations.

       This bug has been fixed in BIND 9.7. However, the fix may cause incompatibility between older and newer
       versions of BIND, when using long keys.  isc-hmac-fixup modifies those keys to restore compatibility.

       To modify a key, run isc-hmac-fixup and specify the key's algorithm and secret on the command line. If the
       secret is longer than the digest length of the algorithm (64 bytes for SHA1 through SHA256, or 128 bytes for
       SHA384 and SHA512), then a new secret will be generated consisting of a hash digest of the old secret. (If the
       secret did not require conversion, then it will be printed without modification.)

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

SEE ALSO
       BIND 9 Administrator Reference Manual, RFC 2104.

AUTHOR
       Internet Systems Consortium

COPYRIGHT
       Copyright (C) 2010 Internet Systems Consortium, Inc. ("ISC")



BIND9                           January 5, 2010              ISC-HMAC-FIXUP(1)