On Thu, Apr 2, 2015 at 6:59 AM, Anne Bennett <[email protected]> wrote:

> > As I recall this was considered during the development of DKIM
> originally,
> > exactly for this reason.  We rejected it because we couldn't come up
> with a
> > safe description of what a tag should look like.  If arbitrary text is
> > allowed in there, then one could "tag" a spam URL at the front of a
> > legitimate message's Subject field and the signature would still pass.
>
> Right, but if that tag were explicitly deemed to be excluded
> from the signature, it could be handled differently.  Hmm, but
> if this resulted in (for example) the tag not being displayed,
> then we would have gained nothing in the case of mailing lists.
>

Handled by whom?  If we're talking about telling MUAs "Don't render the
unsigned part of the content the same way as the signed content", then a
bunch of additional complexities begin to appear:

- MUAs now need to know how to do DKIM themselves, so that they know what
parts were signed and what parts were not; alternatively, we need a way to
signal between the DKIM verifier and the MUA what parts are safe to render,
beyond what Authentication-Results already provides

- We're wandering into conversations about how MUAs should interact with
users, which this community typically avoids like a terrible allergy

- Even if the above aren't problems, we're relying on MUAs to adapt to this
change in a relatively short period of time

Here be dragons.

-MSK
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