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

[Seth Blank <[e-mail]>]

Looping back about this.

Currently openarc only supports relaxed canonicalization for the ARC
Message Signature.

On closer inspection, https://tools.ietf.org/html/
draft-ietf-dmarc-arc-protocol-03#section-5.1.2 and https://tools.ietf.org/
html/draft-ietf-dmarc-arc-protocol-03#section-5.1.2.1.2 do *not* appear to
be in direct contradiction of each other.

5.1.2 states that AMS header canonicalization must be relaxed, and
5.1.2.1.2 says that AMS body canonicalization must respect the c= value.

Is this what was intended (AMS headers=relaxed, body=[c value]), and should
be included in the proposed draft? Or should the entire AMS (headers and
body) respect the c value and both specs be updated?

Seth

On Wed, May 10, 2017 at 12:34 AM, Brandon Long <[e-mail]> wrote:

>
>
> 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
>>>>
>>>> _______________________________________________
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>>>> [e-mail]
>>>> https://www.ietf.org/mailman/listinfo/dmarc
>>>>
>>>>
>>>
>>> _______________________________________________
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>>>
>>>
>>
>
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