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 © 2010, 2013 Internet Systems Consortium, Inc. ("ISC")