Subject: [ietf-dkim] Re: Straw poll on x=

From: Mark Delany <[email-masked]>
Date: Wed, 12 Apr 2006 03:45:55 +0000

Remove x=

The tagging mechanism makes it trivial to add new tags. If at some
point in the future, x= is given a precise and purposeful rationale,
that can easily be done as an extension to the base.

Mark.
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From: "Hector Santos" <[email-masked]>
Date: Wed, 12 Apr 2006 01:07:22 -0400

----- Original Message -----
From: "Mark Delany" <[email-masked]>
To: <[email-masked]>
Sent: Tuesday, April 11, 2006 11:45 PM
Subject: [ietf-dkim] Re: Straw poll on x=

> that can easily be done as an extension to the base.

IMO, there is a precise and purposeful rationale.   I  can come up with
atleast a dozen reasons or more why a signer may want to utilize an
expiration concept.

But there all for under a single rationale:

The signer wants the verifier to classify the message as "invalid" at this
time and date.    Its should not be the verifier's concern why the signer
wants expire a signing.  It might not even apply to all outgoing mail.  It
might just be set for certain kinds of high-value transactions.   The
possibilities are end-less.

Also consider, per spec, If the signer doesn't want to define one, he
doesn't have to.  This is the default condition.

However, I agree what isn't precise is the mechanics.   What isn't resolved
is the design question:

      a) It is a transaction expiration concept, or
      b) Message Validity expiration concept?

And this touches base with a more general implementation conflict regarding
dynamic transport verification mode vs. post transport delay verification
mode.

This is fixable with the proposed change to the x= mechanics.

---
Hector

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From: Mark Delany <[email-masked]>
Date: Wed, 12 Apr 2006 06:12:55 +0000

> atleast a dozen reasons or more why a signer may want to utilize an

As you say, and I agree, the benefits flow mostly, if not entirely, to
the signer ... even though earlier discussions mooted benefits to the
verifier.

As I understand it, when x= expires the signer wants verifiers to
treat the mail as unverified - in effect signers get to disclaim
responsibility for that email after a certain point in time.

This seems entirely at odds with DKIM which is about senders taking
responsibility for an email for the benefit of the verifier.

DKIM is not about senders taking responsibility for just 5 seconds or
just 5 minutes or just 5 days. If a mail is signed and sent, a sender
has no right, in my mind, to subsequently disclaim
responsibility. It's their content; they wear the consequences
forever.

In short: x= gives senders wiggle room to expire responsibility - that
seems at odds with our goals.

Mark.