Re: [ietf-dkim] Comments on draft-ietf-dkim-rfc4871bis-04

[Dave CROCKER <[e-mail]>]

Jim,

I found that I got seriously bogged down on some parts of your note, as you and 
everyone else will surely see.  I am glad to try to set up a phone call to get a 
better channel for discussing this.  Beyond the obvious timezone challenges, 
this week, I've got quite a bit of flexibility in time and am glad to find a 
slot where I can call you.

Also, everyone else is hereby invited to jump in and straighten me out.

That said, here's where I got in responding:


On 3/28/2011 11:27 PM, Jim Fenton wrote:
>> 1. "authors and their organizations" could be misinterpreted to mean that the
>> conjunction defines a single identity.
>
> But the current text says "...examples include the author, ..." so that
> misinterpretation exists there as well. I'd be fine with just "authors'
> organizations".

How is the "examples" list a misinterpretation?

The list was crafted carefully to draw some distinctions that can be 
significant. Your wording loses the distinction between author and author's 
organization.

I think the distinction is worth maintaining.

Just to be clear:  A domain name is capable of being author-specific.  I 
recognize that it's not typical, but the construct of 'author' is so fundamental 
in this game, it's worth acknowledging that it is (still) permitted.


>> 3. One form of assessment service -- of which the late Goodmail was an example
>> -- can give a priori assessment and then indicate tghe assessment by providing
>> the signature to the message before it is sent. That is, the authoring
>> organization passes the message to the assessment service and the assessment
>> service hands back the signature to be included in the message. (The details
>> can vary, of course, but this describes the basic model.) Hence the signature
>> is somewhat akin to a capability token. [I thought I had explained this
>> processing option a number of times over the years, specifically citing the
>> Goodmail example.]
>
> That's a specific example of an ISP along the handling path.

Goodmail was not an ISP and it was not along the path.


      .................  Goodmail  ..............
      .                                         .
      V                                         V
   Client -> Mail -> Transfer -> Service -> Receiver -> Recipient

Goodmail interacted with the creator of the document and, separately, with the 
receiving mail service, as an adjunct "back office" service.  To repeat: /It was 
not in the direct handling path./

DKIM supports that mode of operation quite nicely and it is a particularly 
powerful operational mode, so it is worth keeping that "configuration" in mind 
explicitly.  Given how persistent this confusion seems to be it might even be 
worth more language, though I'm not coming up with a suggestion, offhand.


> The potential for
> misinterpretation of this is greater than the benefit of explaining this
> potential usage scenario, especially since "assessment" has a very specific
> definition in the DKIM context.

I think we've just seen a good example that indeed it is easily misunderstood. 
That begs explicit reference, not potentially confusing conflation.


>>> Section 2.9, Common ABNF tokens: Two new tokens are defined based on
>>> field-name and dkim-quoted-printable. But where are field-name and
>>> dkim-quoted-printable defined?
>>
>> field-name is defined in Section 2.10
>>
>> DKIM-Quoted-Printable is defined in Section 2.11
>
> Would it be beneficial to rearrange the sections to avoid the forward reference?

Sounds like moving the current 2.9 to be after the current 2.11 will solve your 
concern.


>>> 6.3 paragraph 5 has changed "signing identity" to SDID. The signing identity
>>> really corresponds to the AUID.
>>
>> That has not been correct for any version of rfc4871bis. The term Signing
>> Identity has no normative value and is now only used in the introductory text.
>>
>> Also note that the Update removed any meaningful semantics for AUID:
>>
>> The AUID comprises a domain name and an optional
>> <Local-part>. The domain name is the same as that used for the
>> SDID or is a sub-domain of it. For DKIM processing, the domain
>> name portion of the AUID has only basic domain name semantics; any
>> possible owner-specific semantics are outside the scope of DKIM.
>>
>> In fact, the AUID is not part of DKIM's formal output. So the formal
>> specification cannot then direct it be supplied to the assessment engine.
>
> Nevertheless, suppose a message with From address <[e-mail]>
> was properly signed with i=marketing.example.com and d=example.com. What the

Your example has d= using a 'parent' domain, not a sub-domain.  Your following 
discussion refers to aspects of the spec that concern sub-domains and I am not 
understanding how the example is relevant to it. Yes, I see that i= has a 
subdomain but, again, I don't see how that relates to your comments.

With obvious trepidation, I am going to raise a concern:  On reviewing the text, 
I find, under the Section 3.5 text for i= includes:

      "The Signer MAY choose to use the same namespace for its AUIDs as its 
users' email addresses or MAY choose other means of representing its users. 
However, the signer SHOULD use the same AUID for each message intended to be 
evaluated as being within the same sphere of responsibility, if it wishes to 
offer receivers the option of using the AUID as a stable identifier that is 
finer grained than the SDID."

I suggest that the first sentence change MAY to "might" in order to make it 
non-normative.

I further suggest removing the second sentence "However...".  It is giving 
(normative) usage guidance for something that it has already made out of scope.


> text is telling us is that the mail system SHOULD take pains to ensure that
> example.com is visible to the user. This is counter to all of the text in the

The closest I can come to what you describe in Section 6.3 is:

      "If the SDID is not the same as the address in the From: header field, the 
mail system SHOULD take pains to ensure that the actual SDID is clear to the 
reader."

As always, anything DKIM says in the space of human factors varies between 
problematic and bad.  "clear to the reader" nicely falls within that range. I 
know something about user interface design and don't know how to satisfy this 
guidance, or what it's supposed benefit is.

Offhand, it appears to reflect the original misunderstanding that DKIM 
"validates" the message.

That said, I don't understand how making the SDID clear to the 'reader' is 
relevant to your concern about AUID.


> DKIM specification that permits keys for a subdomain to be managed in a parent

In what way is any of this counter (per your above assertion)?


> domain. If these is consensus to eliminate signing for subdomains, there is a

You've jumped to a specific conclusion that implies a significant, unstated 
logic sequence and I'm not yet understanding the premise, never mind the rest.

Please clarify.


> lot of other stuff that needs to be removed from the spec, including the i= tag
> itself, the "s" flag in the key record, the text in section 3.9, and the
> security consideration in section 8.13.
>
> The Update removed semantics associated with the local part of the AUID, and not
> the domain-part.

Whereas I think it made changes to the semantics for the entire value.

Please point to the current version's specification of AUID "semantics".


> If there is not consensus to remove subdomain signing, the wording described
> here makes it meaningless. This goes to the heart of why I have been arguing
> that the output of DKIM should be the AUID (or its default value, which is the
> SDID), and not the SDID itself.

I am not understanding how this language affects the use of AUID at all.

d/
-- 

   Dave Crocker
   Brandenburg InternetWorking
   bbiw.net
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