Subject: [NNTP] Comments on draft-...-authinfo-03

From: clive at demon.net (Clive D.W. Feather)
Date: Mon Oct 4 03:02:41 2004

Charles Lindsey said:
>> Only if it knows the exact length of the string. Okay, it can make a
>> separate connection to the server to see, but it's starting to get a bit
>> threadbare as a threat.
> But surely the attacker will wait till he has seen the server's attempt. I
> am assuming that this "man in the middle" is receiving packets from the
> server and normally passing them on to the client unchanged. When he sees
> "AUTHINFO SASL:WEAK,MEDIUM,STRONG", he drops it on the floor and inserts
> "AUTHINFO SASL:WEAK FOOBAR GZNORT" in its place.

As I understand it, this "man in the middle" doesn't have the ability to
delete packets, merely to inject them faster than the server does (so that
the server's are rejected as duplicates).

If he can delete and replace packets (or, equivalently, modify their
contents in flow) he can run two separate conversations and watch the
plaintext; there's no need for this fuss.

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