[ietf-dkim] Email upgrade history

[Dave Crocker]

Michael Thomas wrote:
>>    If we allow multiple algorthims, and not all the
>> algorithms are the the "MUST implement" level, this attack is 
>> feasible. 
...
> At this point, all we have is MUST implements. Considering there is
> no opportunity for negotiation with mail, MAY/SHOULD implement
> algorithms seems like a pretty bad idea altogether. So is this still a real
> problem for DKIM?


It is probably worth making sure that we are all in synch about some 
relatively basic email protocol points:

1. SMTP permits negotiation. That's hop-by-hop, rather than end-to-end, which 
is what I assume you meant.

2. It turns out that there is also a newly-defined capability for negotiation 
between originator and recipient, but it is neither broadly adopted nor useful 
for DKIM-related issues, IMO.

3. Email has been doing upgrades for a long time. New header fields.  MIME. 
HTML.  Text line-wrapping.  And so on.   None of these has used any sort of 
policy publication mechanism.  All have had massive, long-term success.


So,

As much as upgrades might be made easier by being able to query a record 
published by the signer, there is no track-record of requiring such a thing, 
for email or, I believe, any other Internet protocol.  This means that we need 
to be extremely clear about the reason that any such a record is absolutely 
essential.

d/

-- 

   Dave Crocker
   Brandenburg InternetWorking
   bbiw.net