ESP ad AH _should_ be very similar and thus utilize the same features.
Having one use a 32-bit replay counter and the other use a 64-bit one
is silly as Derrell stated. If 64-bit alignment is required, as in
IPv6, then padding should be appended to the end of the header if it
is needed due to the size of the digest algorithm used.
Why was RFC2085 (HMAC-MD5 IP Authentication with Replay Prevention)
released with a 64-bit replay counter if so many of us objected?
Furthermore, why wasn't a generic digest algorithm RFC released
(HMAC-x Authentication) instead? We must standardize the common
elements of our IPSEC protocols. Things like Replay Counter, HMAC,
Digest Algorithms, Cipher Algorithms, generation of Keys from keying
material. All of these common elements should be the same for all
'transforms' and not have to be re-defined/re-invented in every
transform RFC. Can you imagine every cipher algorithm defining a
different way to generate its keys and IV from the keying material?
We should be able to just plug in a new cipher algorithm and a new
digest algorithm without having to re-invent the wheel. Just plug in
their identifiers and go...The common RFCs (ESP, AH, IPSEC-DOI) should
define how to this without having to write a new transform RFC. This
way we do not need to create a new transform RFC for every combination
of parameters. For example, 3DES-Replay-HMAC-SHA1-LZS, has five
parameters; cipher algorithm, replay, keyed function, digest
algorithm, and compression algorithm. With five parameters we can
have quite a lot of transform RFCs.
Cipher Algorithm: None, DES, 3DES, RC5, Blowfish, IDEA
Replay Protection: No Replay, Replay
Keyed Function: None, Keyed, HMAC
Digest Algorithm: None, MD5, SHA1, Tiger
Compression Algorithm: None, LZS, GZIP
6 * 2 * 3 * 4 * 3 = 432 different transform RFC combinations!!!
----------
From: Derrell Piper[SMTP:piper@tgv.com]
Sent: Saturday, February 08, 1997 7:45 PM
To: ipsec@tis.com
Subject: replay field size
There was clear consensus at the ANX IPSEC bakeoff last week to make
the
size of the replay field 32-bits for both AH and ESP. If we _must_
have
alignment for IPv4 IPSEC then the additional bits should be specified
as
alignment. No one wants to do 64-bit math for replay computation.
It's
silly. In my opinion, IPv4 is misaligned for 64-bit hardware anyway
and I
don't see the point of aligning the fields just to keep the protocol
consistent with IPv6.
I don't think this issue needs the Security AD to resolve. I think
we
already have consensus. Let's hear now from anyone who absolutely
must
have 64 bits or else move to revise AH and ESP to reflect consensus.
We
have much more interesting things to argue about.
Derrell