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Re: draft-ietf-ipsec-ah-md5-00.txt
The draft says:
2. Calculation
The 128-bit digest is calculated as described in [RFC-1321]. The
specification of MD5 includes a portable 'C' programming language
description of the MD5 algorithm.
The "b-bit message" shall consist of the 128-bit secret
authentication key concatenated with (followed by) the entire IP
datagram. All IP headers and payloads that are present MUST be
included in the computation, with header fields whose value varies in
transit (such as Hop Count) being assumed to contain zeros for the
purpose of the authentication calculation. Also, the Authentication
Data field of the Authentication Header is considered to contain all
zeros.
Ron Rivest has stated that a shared secret at the front of a message is not
sufficient for authentication. I thought that I remembered this being
discussed ath the San Jose IETF. Further, I thought that we agreed that we
would solve this weakness by puting the shared secret before and after the
data payload.
Does anyone else remember this? I seem to remember the discussion causing
a tanget about "prepend" not being a word.
Russ
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