Re: [dmarc-ietf] Alternative draft text for draft-ietf-dmarc-arc-protocol

[Brandon Long <[e-mail]>]

On Tue, May 9, 2017 at 3:56 PM, Gene Shuman <[e-mail]> wrote:

> I've taken a look at the proposed draft and have a few notes as well.
>
> 4.  The currently specified limits on i= are not included MUST >10, SHOULD
> > 50, etc
>
> 5.1 - In the current draft, it's mandated that AMS must use relaxed header
> canonicalization, but that's missing from the proposed draft
>

I think that 5.1.2 in the current draft is wrong, it's overridden by 5.1.2.1.2.
We started out only allowing relaxed, but then added back support for c= in
a later draft.

Brandon

5.2 - I'm a bit confused by the comment noting the importance of i=2.  What
> is it that you're intending there?
>
> 5.3.1 - typo:  one of three possible values: -> one of *four* possible
> values
>
> 7.2 - It may be worth elaborating more on the possible ways in which
> cv=invalid can arise, if not here, maybe somewhere else
>
> 7.4 - In general I prefer this to the psuedo code in the current draft,
> but I think it could still use a bit of work.  In particular, sections C-H
> are exactly describing how to validate a DKIM signature and seems somewhat
> unnecessary. Is there any particular reason you decided to include this, as
> opposed to just relying on the DKIM spec for this?
>
> 7.5 - typo: no -> all
>
> In general though, I agree with Brandon, the proposed draft definitely
> makes some things clearer, which I think is a step in the right direction.
>
> =Gene
>
>
> On Tue, May 9, 2017 at 2:04 PM, Brandon Long <[e-mail]> wrote:
>
>> In 5.1 defining the AMS, you say that it should cover DKIM-Signature and
>> AuthRes headers.  In particular, AuthRes headers are expected to be removed
>> by ADMDs, especially if the message transits the same ADMD multiple times.
>> Also, the information in the AuthRes header is superseded by the ArcAuthRes
>> header.  Including it means an arbitrary AMS breakage for something pretty
>> minor, so I would recommend to not include it.
>>
>> Our implementation explicitly blacklists that header.
>>
>> I know some mailing lists also strip the DKIM-Signature header, but since
>> they are likely to break the AMS anyways, that's less important.  I'm not
>> sure what the benefit is to including it, but it seems harmless.  In
>> particular, if the DKIM-Signature still passes, then the ARC isn't adding
>> that much, and removing the DKIM-Signature header doesn't mean all that
>> much either since it's validity was already assessed and that assessment
>> included in the AAR.  We don't blacklist the DKIM-Signature method in our
>> implementation, but I don't understand the advisement.
>>
>> You also talk about "responsibility".  I'm not sure that's how I would
>> describe it.  An ARC hop is documenting that a message passed through it,
>> and that it evaluated the authentication of the message.  The only
>> responsibility of a hop is to correctly validate the SPF/DKIM/ARC
>> information, there is no ownership implied over the message itself.
>>
>> With AMS, you can answer the question: which ADMD is the last ADMD to
>> have modified the message.  I guess in that sense, the last modifier is
>> "responsible" for the current state of the message... but that kind of
>> means that the AMS of previous hops allows them to disown responsibility
>> for the current state of the message...
>>
>> 5.2 - should we point out that there should be only one of these per
>> hop?  The openspf/dkim/dmarc implementations tend to add separate AuthRes
>> headers for each evaluation, but ARC requires those to be a single instance.
>>
>> 5.3.1 - none as defined as "arrives at an MTA from an MSA", perhaps my
>> understanding of those terms is slightly odd, but I would think that an MSA
>> usually uses an MTA to actually send the message, and it isn't that
>> "sending" MTA that's the first hop, it should be the first "receiving"
>> MTA.  I mean, that's usually the point at which the DKIM signature is
>> applied, and the SPF would be "from" there, not based on the location of
>> the MUA.
>>
>> There are some missing pieces here, corresponding to the current draft
>> sections 5.4 (alternate signing algorithms), 6.4.3 (arc email
>> authentication method for AuthRes), 6.4.5 for dmarc xml.  I see that the
>> arc is included in your IANA section, not sure if the call out outside of
>> the definition is necessary or not.
>>
>> Overall, I think your draft makes some things clearer, and some things in
>> the original are clearer.  It's worth looking into either combining or
>> choosing.
>>
>>
>> Brandon
>>
>> On Thu, May 4, 2017 at 12:56 AM, Murray S. Kucherawy <[e-mail]
>> > wrote:
>>
>>> Colleagues,
>>>
>>> As I progress (slowly, alas) toward completing my sample implementation
>>> of OpenARC, I've found myself taking a lot of notes about the current
>>> draft.  This has helped me make progress; in some cases it became things I
>>> posted to the list, and in others it was just to help or confirm my
>>> understanding of the protocol.
>>>
>>> I have developed this enough to become a fairly comprehensive
>>> alternative text to the current draft.  I find the layout of this version
>>> to flow better for my own purposes, and in a few places I've tried to
>>> clarify some of the material by rewriting chunks of it.  None of this is
>>> meant to assert that the current draft is deficient; I've just found it to
>>> be a helpful exercise for me.
>>>
>>> I offer it here to the WG as a contribution; the WG of course is free to
>>> use some, all, or none of it as it wishes.
>>>
>>> http://blackops.org/~msk/draft-kucherawy-dmarc-arc-base.txt
>>>
>>> If it would be more helpful to post this as an I-D, please let me know.
>>>
>>> -MSK
>>>
>>> _______________________________________________
>>> dmarc mailing list
>>> [e-mail]
>>> https://www.ietf.org/mailman/listinfo/dmarc
>>>
>>>
>>
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