On Tue, Mar 8, 2011 at 3:55 PM, Peter Gutmann
<pgut001(_at_)cs(_dot_)auckland(_dot_)ac(_dot_)nz> wrote:
Martin Rex <mrex(_at_)sap(_dot_)com> writes:
Truncating HMACs and PRFs may have become first popular in the IETF within
IPSEC.
It wasn't any "may have become first popular", there was only room for 96 bits
of MAC data in the IP packet, so MD5 was truncated to that size.
This is an odd claim, since:
(a) RFC 1828 (http://tools.ietf.org/html/rfc1828) originally specified
not HMAC but a keyed MD5 variant
with a 128-bit output.
(b) The document that Martin points to has MACs > 96 bits long.
Can you please point to where in IP there is a limit that requires a
MAC no greater than 96 bits.
-Ekr
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