[ietf-nntp] Re: SASL capability

[Clive D.W. Feather]

Charles Lindsey said:
>> The theory goes something like:
> 
>> Client asks for mechanism list
>> Client picks "Best" mechanism, and authenticates
>> If client now has a protection layer (integrity or encryption), it can ask
>>  for the list of mechanisms again.
>> If there is now a stronger mechanism available, then presumably you've
>>  detected a MITM (note, there may be a weaker mechanism available as well,
>>  but generally the idea is that the list shouldn't change at all).
> 
> That sounds fine if encryption has been negotiated (assuming it cannot be
> broken by the MITM), but if only integrity has been established and the
> MITM is still there, then surely he can continue to report bogus lists of
> extensions? Or are we only trying to make it proof against a passive MITM?

It sounds like, to me, that protecting against a subset of MITM attacks
doesn't justify breaking our paradigm for reporting extensions.

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