[ietf-dkim] draft-ietf-dkim-ssp-02.txt Discardable/Exclusive

[Douglas Otis]

On Feb 7, 2008, at 4:54 PM, Eric Allman wrote:
>> The EXCLUSIVE concept can still be covered using DKIM=DISCARDABLE.
>
> Except that DISCARDABLE doesn't prohibit 3PS.  It doesn't even say  
> that messages without any signatures MUST or even SHOULD be  
> discarded.  All it says is how the purported author domain views the  
> messages that it sends out.  The furthest it goes is to say that the  
> purported Author Domain "encourages the recipient(s) to discard it."

Eric,

Agreed.  This changes "strict" (the exclusivity) assertion into  
something that does not express a domain's intentions on exclusivity.   
This assertion simply increases the likelihood of having the domain's  
messages discarded.


You have previously mentioned the motivation was to accommodate high  
profile domains finding themselves victims of phishing attacks.  Using  
the term "discardable" appears to be sending the wrong message.  It  
seems unlikely these high profile domains want their messages silently  
discarded, as this assertion implies.  Discarding of messages does  
several things:

- Destroys evidence of a serious crime

- Reduces delivery integrity for important transactional messages

- Makes resolving compatibility far more problematic

Can you see changing this into terminology that does not attempt to  
suggest a verifier action?  Going out on limb, I'll add a modified  
furthermore statement.  (Frankly, this furthermore statement seems to  
belong in a BCP that happens later.)


Using Hector's term "exclusive"-

exclusive:
All mail from the domain is signed with an intent to avoid
agents that may damage or remove signatures.  Furthermore,
in lieu of a trusted third-party signature, if a message
arrives without a valid Author Signature due to
modification in transit, submission via a path without
access to a signing key, or other reason, the domain
encourages the recipient(s) to reject the message or issue
a DSN when the RFC 2821 MAILFROM domains match.

-Doug