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three more changes to HMAC-MD5-96 & HMAC-SHA1-96 spec




After receiving comments from Bart Preneel and Hugo Krawczyk
and having an e-mail discussion with Hugo over the weekend,
the following changes have been made.

1).  Change "no known cryptographic attacks" to no practical
     cryptographic attacks.

2).  Move paragraph 6 in section 3 to paragraph 2 of section 5
     which is a followup discussion on the "no practical" part
     from above.

3).  Replace the last paragraph in section 3 with (taken almost
     directly from [RFC-2104]):

     [RFC-2104] makes the following recommendation with regard to
     rekeying.  Current attacks do not indicate a specific recommended
     frequency for key changes as these attacks are practically infeasible.
     However, periodic key refreshment is a fundamental security practice
     that helps against potential weaknesses of the function and keys,
     reduces the information avaliable to a cryptanalyst, and limits
     the damage of an exposed key.

The new drafts should be online in the next couple days.

Rob G.
rob.glenn@nist.gov