At 6:09 AM -0700 4/21/06, Michael Thomas wrote:
IMO, the problem here saying that MUA's can praticipate in verification is
a large rathole.
"can participate" and "can participate as well as MTAs" are very
different things.
There many structural impediments with them reliably
verifying signatures. For one, many MDA's torture messages in very DKIM
unfriendly ways. Like sucking the attachments into a database and regenerating
the mime on output to the MUA.
If this is true, then wouldn't most MUAs fail to work with OpenPGP
and S/MIME messages? Or are you saying that the MDAs munge the
headers particularly hard? We know that some MUAs are useless with
OpenPGP and S/MIME, but that most work fine.
For a pretty large class of MUA/MDA
mating, it's my understanding that trying to get this to work is pretty much
a fools errand.
Pointers to tables of these bad combinations would be really useful.
On the DKIM side, however, if we define that MUA's can verify at all,
draft-ietf-dkim-base-01.txt very clearly defines that in many places.
we
need to exactly qualify what that MUA is to match the general expectation
we place on MTA's and MDA's: that they are connected and that they are
will verify the message within reasonable transit time, and store
the *results*
of the verification for later use if necessary (ie, it for display
purposes). If
they won't or can't do those things, then they aren't a
DKIM-verification-capable
MUA.
Fully disagree. MUAs can do their best to validate well, and we can
suggest how to do that, but we cannot mandate it.
Thus a DKIM-verification-capable MxA:
1) MUST receive email in a form whose transformations fall within
the acceptable set of
modifications as defined in -base-nn (eg, canon, l=)
How could we measure that, much less enforce it? Some MxAs will work
fine with one set of messages and break with a different set.
2) MUST perform the verification within the "transport window",
typically 7 days.
How could we enforce that with an MUA? Obviously, it would try to
verify immediately on receipt, but an MUA cannot be forced to
download mail when the computer is off. For that matter, an MTA
cannot do it either. You are defining a system, not an MxA.
3) MUST store the results of the verification process if results of
the verification process
will be used for some later process
How would the MxA know that the results would be used by a later
process? Are we going to create a protocol for the later process to
tell the upstream MxAs that they need the verification results? (The
latter question is meant to be humorous....)
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