On Mon, 13 Nov 2006 21:06:58 -0000, Hallam-Baker, Phillip
<pbaker(_at_)verisign(_dot_)com> wrote:
LEMMA-1: The objective of policy is to allow a verifier to draw
conclusions from the absence of satisfactory authentication
PROOF:
AXIOM-1: The objective of policy is to influence the verifier
AXIOM-2: A verifier only looks at the policy record if
it fails to find satisfactory authentication.
AXIOM-2 denied.
If it finds a satisfactory authentication from a signer with an apalling
reputation, it should be _very_ suspicious.
THEREFORE: LEMMA-1 follows from the axioms.
FALSE
......
C: An acceptable signature is present that failed verification
C1: A genuine signature that failed because the message was modified
C2: A fake signature
D: An unacceptable signature is present that assed verification
D1: A genuine signature
D2: A fake signature added by a party that has compromised the
algorithm
I am not clear what you mean by "acceptable/unacceptable signature".
LEMMA-2: There is no value in distinguishing between any of the cases A,
B, C, D
AXIOM-4: There is no value in distinguishing between states that
can be reached by an attacker.
AXION-4 Denied.
Attackers can easily do bad things before the message is submitted to the
MSA.
It is much harder to attack a message once it has left its originating
MUA. You either need to have accomplices inside the ISP, or to be able to
hack into it, or to have discovered a weakness in its procedures, ... .
This limits the states that attackers can easily be reach, and verifiers
are quite entitled to attribute more suspicion to the easier states.
AXIOM-5: Stastes A2, B2, C2, D2 can be reached by an attacker [by
definition]
THEREFORE: LEMMA-2 follows.
FALSE
--
Charles H. Lindsey ---------At Home, doing my own thing------------------------
Tel: +44 161 436 6131
Web: http://www.cs.man.ac.uk/~chl
Email: chl(_at_)clerew(_dot_)man(_dot_)ac(_dot_)uk Snail: 5 Clerewood Ave, CHEADLE, SK8 3JU, U.K.
PGP: 2C15F1A9 Fingerprint: 73 6D C2 51 93 A0 01 E7 65 E8 64 7E 14 A4 AB A5
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