On Tue, 14 Nov 2006 16:57:28 -0000, Hallam-Baker, Phillip
<pbaker(_at_)verisign(_dot_)com> wrote:
From: ietf-dkim-bounces(_at_)mipassoc(_dot_)org
[mailto:ietf-dkim-bounces(_at_)mipassoc(_dot_)org] On Behalf Of Charles Lindsey
AXIOM-2 denied.
If it finds a satisfactory authentication from a signer with
an apalling reputation, it should be _very_ suspicious.
In fact if the sender has a bad reputation I will not even bother to
verify the signature let alone the policy. I will return to this when
proposing a processing algorithm for my policy mechanism.
The apalling reputations I have in mind are when the signer is a known
spammer who tries to dupe people by providing a valid signature which has
no value. Oddly, in this case, it would have marginally more value if
verification failed.
> 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.
OK: correction no point in distinguishing between states that are
reachable with equal degree of difficulty.
But there may well be value in distinguishing the likelihood of some state
being reached accidentally rather than deliberately. So you might conclude
that C1 was more (or maybe less) likely than C2, according to your
esperience of how well genuine signatures survive on the real net. So if
you are using spamassassin and applying a given score to a missing
signatue (case A) you might apply a different score to a failed signature
(case B) and a different score again to an unacceptable signature (case
D). And the score would in all cases be adjusted according to the SSP
reported by the signer.
--
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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