On 6/19/2020 3:13 PM, Brandon Long wrote:
There were several attempts to come up with alternative signing
schemes that would
allow messages to pass through mailing lists and still be verified as
"untampered" with,
and we were unable to come up with such a thing.
Perhaps we could have constrained ourselves to a 80 or 90% solution,
and that would have been
sufficient and a better solution than From header rewriting. Everyone
has their opinion on the must
haves for mailing list message modification, and it becomes quickly
intractable.
There's a chance that it is possible to specify a small range of
modifications and arrange a style of signing that could survive them.
So for originating and mediating sites that conform to that range, a
'preserved' original authentication might be possible.
However...
I don't remember enough detail from the original dmarc discussions, so I
don't remember how much of this was discussed, but I vaguely think it
was covered.
Anyhow, there is a long track record of difficulties getting mailing
list systems and operators to adopt external standards, and it isn't
clear (to me) that the small range would be useful enough. These risk
factors do not encourage pursuing the complexities and costs of a global
standard.
That leaves just a staged trust model, establishing a basis of
accountability (and reputation) for the mediator sequence. Hence, ARC.
d/
--
Dave Crocker
Brandenburg InternetWorking
bbiw.net
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