On Sat, 20 Nov 2004, Hallam-Baker, Phillip wrote:
Both authentication mechanisms have shortcommings due to the fact that we
are attempting to retrofit a legacy infrastructure.
Sender-ID:
Can only provide a definitve 'success', 'not success' can be due to
either forgery or a non compliant forwarding server.
You also cannot rely on the "PASS" result from Sender-ID or SPF if the
sender shares their outgoing email infrastructure with any other untrusted
third parties. This is common for senders who use their ISP's outgoing
relays.
SPF and Sender-ID provide extremely weak and very brittle security, with
next to no assurance that the result they return is correct.
Signature:
Can provide a qualified 'success' that is subject to a replay attack
for certain senders.
Why do you think replay of entire messages is a problem?
Or are you concerned with attacks based on the canonicalization algorithm,
which might allow an attacker to add content to a previous message? This
is a message modification attack rather than a replay attack (to use the
terminology in RFC 3552).
Tony.
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