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)