Re: New Version Notification for draft-kucherawy-mta-malformed-00

On 11/30/10 11:55 AM, Murray S. Kucherawy wrote:
>> On Tuesday, November 30, 2010 11:11 AM, Douglas Otis wrote:
>>
>> DKIM should be repaired to ensure deceptive malformed header fields do
>> not verify as having valid DKIM signatures to prevent the exploits, such
>> as having multiple singleton header fields invalidate signatures.  DKIM
>> should have included checks necessary to disqualify messages likely
>> crafted by malefactors.  These checks may need to grow over time.  The
>> impact of adding checks to DKIM's verification process will not justify
>> new mandates for making message repairs or rejections by SMTP or MUAs.
>> [...]
> I think this is completely off-topic for the work being discussed here, Doug.  The discussion has to do with what MTAs, and perhaps MUAs if that's appropriate, should do with common malformations independent of things like DKIM.
Murray,

Any deviations from standards normally used by malefactors to deceive 
recipients should be rejected!  Unfortunately this draft suggests:

1) Ignore
2) Repair
3) Reject

Ignoring and repairing remains problematic.  IMHO, repair will never be 
required for SMTP or MUA level compliance.  Without format compliance 
being part of trust related verifications, systems claiming enhanced 
levels of trust will not be trustworthy.  Since SMTP does not mandate 
non-compliance be rejected, the only reasonable strategy is to ensure 
mechanisms such as DKIM makes no exploitable assertions when confronting 
malformed messages.

I see this draft as a dubious attempt to suggest SMTP or MUAs should be 
expected to defend enhanced levels of trust based upon mechanisms such 
as DKIM.  This is inherently wrong, as this will result in indeterminate 
message status and untrustworthy systems.

-Doug