RE: pppcn

Bernard Aboba writes:
> >It is for both peers to anticipate each others' sequence
> >and magjic numbers and options, and to send a single burst of LCP,
> >authentication, and IPCP packets.  This solution requires no changes
> >in PPP state machines except for what might be called "pre-loading.
> 
> How is it possible to "anticipate" authentication protocols?  If this were
> true, it would imply that the authentication algorithms were broken since
> they are required to demonstrate pseudo-randomness.

It's actually fairly easy.  All that needs to be done is guarantee
that someone who doesn't know a shared secret cannot predict the
'random' portions of the message.  For example, generate a
cryptographic hash based on a shared secret and the challenge used in
the last session (saved in some local storage), and use that hash as
the challenge string.

Obviously, such a trick is ineffective if the authentication mechanism
is more obtuse than either PAP or CHAP.

-- 
James Carlson, IP Systems Group                <[email protected]>
Sun Microsystems / 1 Network Drive         71.234W   Vox +1 781 442 2084
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