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Re: Human I&A, IPsec, and their non-relationship
Ran Atkinson says:
> I am glad we agree that application I&A is outside the scope of this
> effort.
(:-)
> I disagree that per-userid-keying is not useful.
> One widely used example is the problem of mutually suspicious users
> (Alice, Bob) on some host X where none of those users has special
> privileges (in UNIX terms, none of them are root). In such a case
> when per-userid-keying is not provided, then user Alice can create
> arbitrary plaintext/ciphertext pairs between its host and another host
> Y in order to assist in Alice's cryptanalysis to determine what data
> Bob is sending to someone on host Y that Bob does not want Alice to
> know about.
So what? A trivial case of chosen plaintext attack? What's the big
deal about it? Aren't you going to require your algorithms be at
least chosen-plaintext-attack secure?
Also, in addition to that, not-brain-dead hosts would probably
update the keys before the amount of traffic encrypted by them
allows anything bad to happen.
> Using a separate key per userid will entirely preclude that attack
> strategy.
Again, this is only to secure host-to-host communications. It's
more than likely, that security-cautious higher levels will have
their *own* authentication and protection. For surely no sane
application is going to trust user A from host B just because
IP layer says so?
> That does not make per-userid-keying useless even for the low
> assurance implementations. Contrariwise it means that the separation
> between users that is provided by the network has similar assurance
> characteristics to the separation between users provided by the
> operating system.
But... If I can break it at system/host level, I don't need to bother
with the network level at all. And if I can't break it on host level,
then it's VERY UNLIKELY I'd be able to get anything from network...No?
> I am not suggesting per-userid-keying primarily for use in
> application-layer I&A and I am not suggesting any particular approach
> to application-layer I&A.
Yes. But still, what are the goals/reasons for supporting
per-application SAIDs/keys? If only preventing chosen
plaintext attacks, I'd say - who cares.
--
Regards,
Uri uri@watson.ibm.com N2RIU
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<Disclamer>
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