[ietf-dkim] chained signatures, was l= summary

[Charles Lindsey]

On Wed, 03 Jun 2009 14:58:06 +0100, John Levine <johnl at iecc.com> wrote:

> The most common use of A-R will likely involve a secure channel
> between the place where it's applied and the place where it's
> interpreted, e.g., it's applied at a border MTA and it's interpreted
> in a downstream MTA or MUA within the same network.  In that case, you
> don't need a signature.

Agreed, but that is not the situation of concern.
>
> If you imagine that there are strangers elsewhere in the world who
> would be impressed by your opinion of a message you were forwarding,
> you might want to sign it, but as I've noted before, if you're
> forwarding it and mutating it enough that recipients wouldn't use an
> incoming signature (i.e., you're a mailing list) you'd best take care
> to send and sign only mail that recipients are likely to want.

A competent mailing list admin would reject all messages from dubious  
sources. But it would be foolish to assume that all such admins are as  
competent as we would wish. So the mere fact that they (re)sign messages  
does not prove their origin, except insofar as you are prepared to have  
confidence in their competence.

If they try to bolster your confidence in them by offering an A-R header  
to show their diligence in eliminating dubious messages, then that is well  
and good, but if they are unwilling to put their signature where their  
mouth is, then why should I be impressed? I don't see why you would choose  
to regard me, as a member of your mailing list, as some "stranger  
elsewhere in the world".

-- 
Charles H. Lindsey ---------At Home, doing my own thing------------------------
Tel: +44 161 436 6131                       
   Web: http://www.cs.man.ac.uk/~chl
Email: chl at clerew.man.ac.uk      Snail: 5 Clerewood Ave, CHEADLE, SK8 3JU, U.K.
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