On Mon 24/Mar/2025 20:19:29 +0100 Richard Clayton wrote:
In message <b9029423-1b4a-4e82-b8ae-4acbbe810...@tana.it>, Alessandro Vesely
<ves...@tana.it> writes
BTW, is dkim2=fail different from "failing DKIM2 signatures from a 100% DKIM2
mail chain"? I mean, do verifiers always check all the signatures along the
chain or can sometimes check just the last one?
In DKIM2 you need to validate the signature of the entity passing you
the message (the highest numbered header field) because that assures you
that you can give it back to them if you need to...
What does that mean? Should I wait for more information in order to make a
delivery decision?
"Similar to ARC" should mean that all signatures have to be valid.
... you then need to undo all the modifications in other header fields
(if any) but you don't need to check those signatures !
Then you can check the very first signature (if there is more than one
of course) and that tells you if the purported original sender did
indeed sign the message.
Checking the chain of rt= =~ next mf= would be pointless if a man in the middle
could insert fake signatures to make the chain look legit.
Of course, If I trust the signer of the last signature, it would be fine to
check only that. Bat that would be too similar to ARC...
If you want to do forensics you can check more, but that's all that a
receiver is likely to care about.
It ought to be not very hard to check all signatures, reversing the changes.
There needs to be a way to tell what changes are tolerated. For example, I'd
accept a plain text footer of a few lines, but not html inserts that could
completely replace the original content in the end recipient's eyes.
Best
Ale
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