[ietf-dkim] New DKIM threat analysis draft

[John Levine]

>I have only one real reservation. In section 6.3, discussing the message 
>replay attack, ...
esp. in 2nd paragraph... It is presented as if DKIM 
>cannot be applied against replay since replay is indistinguishable from 
>acceptable acts e.g. forwarding. This is not necessarily true. A 
>legitimate application of DKIM may require senders to indicate specific 
>recipient; this would allow replay prevention, of course in the price of 
>requiring additional support to deal with legitimate forwarding. I'm not 
>suggesting DKIM should be modified to support that, indeed this is not 
>required at DKIM level at all, but I think the text now seems to exclude 
>this usage, and this should be fixed imho.

DKIM doesn't do path authentication by design.  It's not a bug.  

It would be fine to mention that, but it would be a grave mistake to
jump into the forwarding swamp from which no path authentication
scheme has ever emerged.

R's,
John