[ietf-dkim] Conflicts between -ssp-requirements and -ssp

[Graham Murray]

"Charles Lindsey" <chl at clerew.man.ac.uk> writes:

> The scenario you need to consider is where A asserts a policy of "I
> sign everything", and sends a correctly signed message to some mailing
> list B.
>
> B can (and should) check that the signature is good, and is consistent
> with A's policy, etc. But then B add his standard mailing list
> boilerplate  "NOTE WELL ..." thus breaking A's signature. He then
> signs the message  again (as a 3rd party).
>
> Now the ultimate recipients see A's signature (no longer good), plus
> A's policy. So the message is on the face of it "suspicious". So what
> is the  recipient supposed to do? He is a member of the list, and is
> happy to  trust the list maintainer, and can check the 2nd
> signature. But he is  still receiving conflicting advice.
>
> The only real solution to this problem is for B to add an
> Authentication-Results header (see the Mail-Vet-Discuss mailing list),
> and  to incluide that header in is own signature. Maybe that is
> veering off  topic for this list, but at least there should be a
> pointer to that sort  of possibility.

If A had used 'l=' and assuming the boilerplate is added to end of the
message and that B does not change the headers (eg to add [listname] at
the start of Subject:) then A's and B's signatures should both
validate.