I've been following the thread(s) regarding how to enable 3rd parties where a 
formal relationship doesn't exist and this reinforces my thought that it is 
ultimately easier systemically (even allowing for the arguments that it is 
unfair) for intermediaries to take ownership of messages they (intentionally) 
modify and sign d= as first party signers.

I understand that there is a one-time cost (my own organization incurred this 
cost in changing how we handle mail for our website domains) to changing and I 
understand the reasons expressed by some for not wanting to make such changes 
based on principle, etc. I understand the argument that some are externalizing 
their costs.

Mike

From: dmarc [mailto:[email protected]] On Behalf Of Rolf E. Sonneveld
Sent: Tuesday, April 14, 2015 4:24 PM
To: Murray S. Kucherawy; Scott Kitterman
Cc: [email protected]
Subject: Re: [dmarc-ietf] Updated mandatory tag/conditional signature draft

On 04/14/2015 09:15 PM, Murray S. Kucherawy wrote:
On Tue, Apr 14, 2015 at 8:25 AM, Scott Kitterman 
<[email protected]<mailto:[email protected]>> wrote:
I haven't reviewed his in detail, so I've no opinion.  I was talking about
this proposal.  Not getting fancy with MIME parts would be nice, so if this
one can work, I already like it better than Murray's, but if we have to pile
this onto the stack of nice ideas, then that's probably what I'll look at
next.

The elegance of John's idea is that it's content-agnostic, and is apparently 
backward compatible because v=1 verifiers will not consider the weak signature 
to be valid (unless they're already quite broken).  There's no need to learn to 
parse MIME structure in order to produce a signature.
I think the concerning part is deciding when to add the weak signature.  The 
simplest thing is to always add it along with an "@fs=" signature, but then 
you're basically allowing the forwarding domain to sign any content it wants 
and you'll be approving it too, implicitly.


Remembering to what great lengths the ietf-dkim group went to make sure that 
every bit of a message was covered by the signature (and with the l= 
discussions in mind) I would really be surprised if adding the @fs= for all 
outbound mail would be an acceptable solution for the problem.

/rolf
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