Subject: Re: [dmarc-ietf] Response to a claim in draft-crocker-dmarc-author-00 security considerations
From: Dave Crocker <[email-masked]>
To: Alessandro Vesely <[email-masked]>, [email-masked]
Date: Sun, 26 Jul 2020 04:32:59 -0700
List-Id: "Domain-based Message Authentication, Reporting, and Compliance \(DMARC\)" <dmarc.ietf.org>

On 7/20/2020 1:44 AM, Alessandro Vesely wrote:
> On Sun 19/Jul/2020 20:33:46 +0200 Dave Crocker wrote:
>> The essential point that needs to be made is that standards like this 
>> MUST NOT be cast in terms of what end users will do.  In practical 
>> terms, this work has nothing to do with end users. Really.  Nothing.
>> [...]
>> (*) I've seen one posting here or somewhere else that noted that 
>> letting bad mail through can lead to end-users being deceived. I'll 
>> claim that while true, it is not relevant, since the behavior happens 
>> after DMARC, and the like, are relevant.  That is, DMARC, etc., do 
>> not inform the end-user behavior.
>
> Aren't those two paragraphs self-contradictory?

No.

A specification defines a field of activity.  (A sandbox.) Things 
outside that field are not relevant to the specification, even though 
they might be highly relevant from a larger perspective. There is a 
constant desire to have a specification that involves security-related 
decision-making include the (human) recipient be an actor within the 
scope of the specification. The first paragraph, quoted above, is a 
reminder that we need to resist that desire.

The second paragraph, quoted above, is a reminder about a specific 
example of this, namely about the DMARC specification. It acknowledges 
that, in general, recipients can be deceived, for the specific From: 
field protection that DMARC provides, the recipient is not a relevant actor.

> If DMARC were dependable, maybe users would learn to trust From:. Or 
> maybe not.  Avoiding end user considerations cuts both ways. Yet, we 
> can trust that if we do a well-defined, clear job, then the whole 
> system will work better.

It is expensive and highly risky to create an international standard 
that relies on such a tenuous hope about future behavior, especially in 
the face of consistent empirical evidence that it won't happen.

d/

-- 
Dave Crocker
Brandenburg InternetWorking
bbiw.net