Subject: [dmarc-ietf] ARC: Syntax for ARC-Authentication Results header

From: Steven M Jones <[email-masked]>
Date: Thu, 29 Sep 2016 16:55:03 -0700

I've noticed that one ARC implementation in development does *not* use a
semi-colon delimiter after the prefixed "i=N" sequence tag in the
ARC-Authentication-Results: header, but does use it in the other two.
This is probably just a bug, but it prompted me to check the spec.

In section 5 of the current draft ARC spec, I couldn't find any mention
one way or another about this delimiter. (And there's no ABNF, for
whatever that's worth.) However if you check the examples in the
appendix, I think every example has this delimiter in all three ARC
headers, in each set of ARC headers for "multi-hop" examples.

The use of the semi-colon is a little different under RFC7601
(Authentication-Results:), in that the semicolon separates "clauses" or
"phrases" as opposed to the tag/value pairs within each clause. (And the
authserv-id generally isn't a tag/value pair.)  But I don't see any
problem with the ARC "i=N" sequence tag/value being treated as a
separate pre-pended clause, so long as it properly references RFC7601 in
the spec.

Any thoughts on this? Any other areas that need to be tightened up in
the ARC draft spec??

Thanks,
--Steve.

-- 
Steven M Jones
DMARC.org

e: [email-masked], [email-masked]

---

From: Kurt Andersen <[email-masked]>
Date: Thu, 29 Sep 2016 21:33:34 -0700

> This is probably just a bug, but it prompted me to check the spec.

<elided>

> . . . I don't see any
> <https://www.ietf.org/mailman/listinfo/dmarc>

In the ARC draft spec, as illustrated by the examples, I was considering
the prepended i=N to be a clause in itself and thus delimited with a
semi-colon. I agree that the description in the I-D for ARC does not
clearly state that and the ABNF for the A-R header in 7601 attaches the
semi-colon to the trailing clause, as the header gets built up. In the case
of ARC's usage, we are building by pre-pending rather than tacking on the
end. I can clarify the syntax in the ARC I-D (along with a couple of other
minor edit points that were previously raised).

If anyone thinks that's a bad idea, please let me know. Steve, thanks for
getting this discrepancy highlighted.

--Kurt Andersen