Subject: [dmarc-ietf] Benjamin Kaduk's Discuss on draft-ietf-dmarc-eaiauth-05: (with DISCUSS and COMMENT)

From: Benjamin Kaduk via Datatracker <[email-masked]>
Date: Thu, 11 Apr 2019 10:56:18 -0700

Benjamin Kaduk has entered the following ballot position for
draft-ietf-dmarc-eaiauth-05: Discuss

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DISCUSS:
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Thanks for this document; it's good to improve the clarity and precision
of how various pieces of the ecosystem interact.  That said, I do have an
issue that needs to be addressed prior to publication:

We need to properly document the consequences of causing the %{s} and
%{l} macros to never match when the local-part contains non-ASCII characters.
I understand that they are quite rare in practice, and this rarity justifies not
going to great lengths to provide a technical solution, but that doesn't mean
that we can silently ignore the issues.

[discussion of specificity of Updates  removed, as the discussion happened]

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COMMENT:
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Section 3

   In headers in EAI mail messages, domain names that were restricted to
   ASCII can now be U-labels, and mailbox local parts can be UTF-8.

nit: "can now" implies some previous baseline state, but that reference
for comparison is not especially clear just from context.

Section 5

I'm having a hard time following this paragraph:

   Section 3.5 of [RFC6376] states that IDNs in the d=, i=, and s= tags
   of a DKIM-Signature header MUST be encoded as A-labels.  This rule is
   relaxed only for internationalized messages headers [RFC6532] so IDNs
   SHOULD be represented as U-labels but MAY be A-labels.  This provides
   improved consistency with other headers.  The set of allowable
   characters in the local-part of an i= tag is extended as described in
   [RFC6532].  When computing or verifying the hash in a DKIM signature
   as described in section 3.7, the hash MUST use the domain name in the
   format it occurs in the header.

Is "this rule is relaxed" a new policy as of this document?  RFC 6532
does not mention an "i=" tag anywhere, so I feel like we may need
greater detail on what behavior from 6532 we're pulling in.  (Are we
just intending to add the UTF8-non-ascii block as valid ABNF for the RHS
of the "i=" tag?)

Is there any risk that an intermediary will reencode the domain name and
cause the signature validation to fail?

Section 6

   Section 6.6.1 specifies, somewhat imprecisely, how IDNs in the
   RFC5322.From address domain are to be handled.  [...]

A bare "Section 6.6.1" normally refers to the current document, so
repeating RFC 7489 is probably in order.

(Same for the other Section references in this section.)

Section 8

(Depending on how the first DISCUSS point is resolved, we may be adding
some new threats that need to be covered.)