Hi!
In the DKIM2-Signature header (section 6), we have the rt=
tag-spec like this:
sig-rt-tag = %72 %x74 [FWS] "="
1*( [FWS] "<" local-part "@" domain-name ">" )
For example ...; rt=<[email protected]> <[email protected]>; ...
However, RFC5321 local-part can be a quoted string like this:
<"foo><bar;"@example.com>
In this case,
a) We can't represent such an email address in a tag-value
because of the semicolon. To be honest, in practice I don't
especially care about such email addresses, but in spec
lingo I'd prefer a spec that fits together (i.e. the sig-rt-tag
spec ought to be a subset of tag-spec). At least, the textual
description could clarify this ("mail addresses containing a
semicolon can't be represented in mf= or rt=" or something).
b) My example shows, with the "><" part in the quoted-string
local-part, that a parser for DKIM2-Signature headers can't
operate by first dividing rt= into single addresses in a
simplistic way (search for ">" [FWS] "<" and if found, split
after the ">"). At the same time, there are no commas between
the addresses, so I can't just feed rt= into a parser for
RFC 5322 mailbox-list and afterwards (or on the fly) apply
additional constraints. So a correct rt= parser currently
might have to duplicate code that's in RFC 5321 or RFC 5322
parsers to find the next ">" that's not within a quoted-string.
So the spec might need to be clarified in these respects too.
In addition I found that domain-name isn't a nonterminal at
least in RFC 5321. Perhaps the reference should be to
RFC 5321 "Domain".
Kind regards,
Hannah.
On 12/25/25 02:29, Richard Clayton wrote:
I have put in the changes and clarifications I emailed about earlier.
Should you have nothing to do for a few days other than knock up some
running code I would be very happy to swap emails with you and we can
see if we have both read the spec the same and we can interwork.
-----Original message-----
Subject: I-D Action: draft-clayton-dkim2-spec-05.txt
To: [email protected]
From: [email protected]
Reply-To: [email protected]
Date: Wed, 24 Dec 2025 17:15:45 -0800
Message-ID: <176662534577.1184972.10509632902514714845@dt-datatracker-
5656579b89-p6k4r>
Internet-Draft draft-clayton-dkim2-spec-05.txt is now available.
Title: DomainKeys Identified Mail Signatures v2 (DKIM2)
Authors: Richard Clayton
Wei Chuang
Bron Gondwana
Name: draft-clayton-dkim2-spec-05.txt
Pages: 34
Dates: 2025-12-24
Abstract:
DomainKeys Identified Mail v2 (DKIM2) permits a person, role, or
organization that owns a signing domain to document that it has
handled an email message by associating their domain with the
message. This is achieved by providing a hash value that has been
calculated on the current contents of the message and then applying a
cryptographic signature that covers the hash values and other details
about the transmission of the message. Verification is performed by
querying an entry within the signing domain's DNS space to retrieve
an appropriate public key. As a message is transferred from author
to recipient systems that alter the body or header fields will
provide details of their changes and calculate new hash values.
Further signatures will be added to provide a validatable "chain".
This permits validators to identify the nature of changes made by
intermediaries and apply a reputation to the systems that made
changed. DKIM2 also allows recipients to detect when messages have
been unexpectedly "replayed" and can also ensure that delivery status
notifications are only sent to entities that were involved in the
transmission of a message.
The IETF datatracker status page for this Internet-Draft is:
https://datatracker.ietf.org/doc/draft-clayton-dkim2-spec/
There is also an HTMLized version available at:
https://datatracker.ietf.org/doc/html/draft-clayton-dkim2-spec-05
A diff from the previous version is available at:
https://author-tools.ietf.org/iddiff?url2=draft-clayton-dkim2-spec-05
Internet-Drafts are also available by rsync at:
rsync.ietf.org::internet-drafts
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--
Hannah Stern
Software Developer
Mail Transfer Development
1&1 Mail & Media Development & Technology GmbH | | |
Phone: +49 721 91374-4519
E-Mail: [email protected] | Web: www.mail-and-media.com www.gmx.net
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Geschäftsführer: Alexander Charles, Dr. Michael Hagenau, Thomas Ludwig,
Dr. Verena Patzelt
Member of United Internet
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