ISC-HMAC-FIXUP(8)                    BIND9                   ISC-HMAC-FIXUP(8)

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

BIND9                           January 5, 2010              ISC-HMAC-FIXUP(8)

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