Re: [dmarc-ietf] Genart last call review of draft-ietf-dmarc-psd-08

"Murray S. Kucherawy" <> Thu, 09 April 2020 20:36 UTC

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From: "Murray S. Kucherawy" <>
Date: Thu, 9 Apr 2020 13:35:45 -0700
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To: Todd Herr <>
Cc: Dale Worley <>, General Area Review Team <>, dmarc <>
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Subject: Re: [dmarc-ietf] Genart last call review of draft-ietf-dmarc-psd-08
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(Reducing Ccs)

That seems like it paints a much clearer picture, which is what Dale was
after.  A great start!

On Thu, Apr 9, 2020 at 12:54 PM Todd Herr <> wrote:

> Having reviewed the comments, I'm wondering if perhaps the following draft
> rewrite of the Abstract section might be a first step to address many of
> the points raised?
> *AbstractDMARC (Domain-based Message Authentication, Reporting, and
> Conformance) is a scalable mechanism by which a mail-originating
> organization can express domain-level policies and preferences for message
> validation, disposition, and reporting, that a mail-receiving organization
> can use to improve mail handling.  *
> *The original design of DMARC applies only to domains that are registered
> with a domain name registrar (called “Organizational Domains” in RFC 7489)
> and nodes in the tree below Organizational Domains. Organizational Domains
> are themselves nodes in the tree below domain names reserved for
> registration, with the latter commonly referred to as “Top Level Domains”
> (TLDs) (e.g., ‘.com’, ‘ <>’, etc.), although in this
> document they will be referred to as Public Suffix Domains (PSDs).*
> *Since its deployment in 2015, use of DMARC has shown a clear need for the
> ability to express policy for PSDs. This document describes an extension to
> DMARC to enable DMARC functionality for PSDs.*
> *RFC 7489 describes an algorithm for a mail-receiving organization to use
> in determining the Organizational Domain of an inbound mail message, and
> this algorithm recommends the use of a “public suffix list” (PSL), with the
> most common one maintained by the Mozilla Foundation and made public at
> < <>>. Use of such a PSL by
> a mail-receiving organization will be required in order to discover and
> apply any DMARC policy declared by a PSD.*
> *This document also seeks to address implementations that consider a
> domain on a public Suffix list to be ineligible for DMARC*
> On Sun, Apr 5, 2020 at 9:11 PM Dale Worley via Datatracker <
>> wrote:
>> Reviewer: Dale Worley
>> Review result: Ready with Issues
>> I am the assigned Gen-ART reviewer for this draft.  The General Area
>> Review Team (Gen-ART) reviews all IETF documents being processed by
>> the IESG for the IETF Chair.  Please treat these comments just like
>> any other last call comments.
>> For more information, please see the FAQ at
>> <>.
>> Document:  review-draft-ietf-dmarc-psd-08
>> Reviewer:  Dale R. Worley
>> Review Date:  2020-04-05
>> IETF LC End Date:  2020-04-08
>> IESG Telechat date:  not known
>> * Summary:
>>        This draft is on the right track but has open issues, described
>>        in the review.
>> * Major issues:
>> The privacy concerns described in section 4 are written as if there is
>> no certainty that the mechanisms described in the document properly
>> mitigate them.  So the document appears to be incomplete.  OTOH, since
>> this is an Experimental RFC, such mitigation isn't necessary if there
>> is commitment to do so later.  In that case, the section should
>> explicitly state that these are open issues and that there is an
>> intention of revising the document to mitigate them.
>> The text suggests that a mail receiver(?) that does DMARC processing
>> has knowledge of all PSDs.  This seems a priori unlikely and even
>> impossible to implement.  So this ought to be either explained at the
>> appropriate place or resolved technically.
>> * Minor issues:
>> The document has the (common) editorial problem that it is written by
>> people who are deeply familiar with the subject, and it's difficult to
>> read if one doesn't share that familiarity.  This is particularly
>> significant because DMARC is an e-mail facility that (ideally) will
>> affect all e-mail that is sent, so the target audience really should
>> be anyone who has a basic understanding of e-mail.  Three particular
>> elements of this are:
>> - It would be very helpful if the Introduction could state, in a few
>>   sentences, the purpose and operation of DMARC, thus informing the
>>   reader of the framework whose deficiencies this document attempts to
>>   address.  In particular, one shouldn't have to read the DMARC RFCs
>>   to be able to read this document and understand its general import.
>> - The "experiment" appendixes are unclear about what the experiments
>>   actually are:  what questions they are to answer, what actions will
>>   be taken, how the results will be evaluated.  Starting each appendix
>>   with an overview paragraph would be helpful.
>> - Forward references should be minimized so that a reader can
>>   understand the document in one pass.
>> As a derivative of the first of these elements, the terminology used
>> for the properties of domain names is not clearly defined.  In
>> particular, where does a registration "occur"?  The only term for
>> which I think the general audience possesses an unambiguous definition
>> is "the registered domain name", e.g.  Now I *think* its PSD
>> is ".org", but it might be "", and I don't know whether the
>> registration of "occurs" at or .org.  Further points
>> I didn't understand are pointed out in the review of the
>> Abstract and Introduction.
>> * Nits/editorial comments:
>> Abstract
>> I'm having quite a bit of difficulty figuring out exactly what the
>> Abstract means.  I'm sure that the working group clearly understands
>> what is meant, but the writing is just loose enough that I can't fix
>> the meaning.  To raise the immediate questions:
>>    DMARC (Domain-based Message Authentication, Reporting, and
>>    Conformance) is a scalable mechanism by which a mail-originating
>>    organization can express domain-level policies and preferences for
>>    message validation, disposition, and reporting, that a mail-receiving
>>    organization can use to improve mail handling.
>> This sentence is quite good, as it introduces what DMARC is all about.
>>    The design of DMARC
>>    presumes that domain names represent either nodes in the tree below
>>    which registrations occur, or nodes where registrations have
>>    occurred; it does not permit a domain name to have both of these
>>    properties simultaneously.
>> You want to make clear here that "registration" means "domain name
>> ownership registration" (which is what section 2.2 says).  Otherwise
>> it leaves open that there is some sort of DMARC registration that you
>> might intend, until the reader gets to section 2.2.
>> There's an ambiguity regarding "where" a registration happens.  E.g.,
>> does the registration of "" "occur at" "" or "occur
>> at" "org"?  It's possible that this could be simplified/disambiguated
>> by not using this term, but instead phrasing this in terms of domain
>> names that "are registered", and the allowed relationships between
>> them.
>> And it appears certain that there are DNS nodes where registrations
>> are only done *above* that node, e.g. "", which
>> this sentence (if taken literally) says is not permitted by DMARC.  Is
>> the property you want to declare "one node where registrations are
>> done cannot exist below another node where registrations are done"?
>> Or perhaps domain names like "" are of no interest
>> to DMARC because DMARC is never applied to messages for which that is
>> the relevant address?
>>    Since its deployment in 2015, use of
>>    DMARC has shown a clear need for the ability to express policy for
>>    these domains as well.
>> This sentence doesn't make it clear what "these domains" refers to.
>>    Domains at which registrations can occur are referred to as Public
>>    Suffix Domains (PSDs).  This document describes an extension to DMARC
>>    to enable DMARC functionality for PSDs.
>> It would probably be clearer to use "domain name ownership
>> registrations" again here.
>> This sentence suggests that the registration of "" "occurs at"
>> "org" and so "org" is a PSD.
>>    This document also seeks to address implementations that consider a
>>    domain on a public Suffix list to be ineligible for DMARC
>>    enforcement.
>> This suggests that implementations believe that they know of all PSDs,
>> so they can "consider them ineligible for DMARC enforcement".  But
>> it's hard to imagine that that they can know that they know of all
>> PSDs.
>> An additional point, and I'm not sure how valuable this is, would be
>> to clarify "I'm holding an e-mail message in my hands.  What do I do
>> next?", that is, What address in the message is the domain whose DMARC
>> information is applied to the message?  And what indeed does DMARC
>> processing do to a message?  For most of the sentences of the
>> Abstract, this is not important, but it leaves the effect of the last
>> sentence unclear, as "DMARC is not enforced on messages whose *sender*
>> is in a PSD" is quite a bit different from "DMARC is not enforced on
>> messages whose *recipient* is in a PSD".  (Section 3.3 suggests that
>> the address in the From header of the message is the one that is used
>> for DMARC processing.)
>> It's unclear what exactly is the contents of a "public suffix list".
>> Naively, it appears that it is the list of domain names under which
>> names can be registered, but the text uses the term in the plural, so
>> there must be some additional structure.
>> Also, it seems there are some significant privacy matters addressed by
>> this document, and it's probably worth adding a sentence to notify the
>> reader of that.
>> 1.  Introduction
>> A number of the questions about the Abstract apply to the Introduction
>> as well.  But generally, since e-mail is a subject that every reader
>> has a basic knowledge of, it would be useful to write the introduction
>> so that one did not have to have a knowledge of the DMARC architecture
>> to understand the introduction.
>>    "gov.example" publishes the following DMARC record:
>>    "v=DMARC1; p=reject;"
>>    at
>> Even better would be this aid to people who don't already know DMARC
>> implementation:
>>    "gov.example" publishes the following DMARC DNS record:
>>  TXT \
>>         "v=DMARC1; p=reject;"
>> --
>>    the non-existent organizational domain of
>> I suspect you mean "" here.
>>    This document provides a simple extension to DMARC [RFC7489] to
>>    allow [...]
>> This sentence lists 4 important items, each of which is fairly long,
>> which together are the summary of the whole document, so it might be
>> useful to break this into a bullet-list.
>> 2.  Terminology and Definitions
>>    In many cases the public portion of the DNS tree is [...]
>> What does "the public portion" mean?  I'm guessing it means "the names
>> not available for private registration", but you should be unambiguous
>> here.
>>    They are not available for private
>>    registration.  In many cases the public portion of the DNS tree is
>>    more than one level deep.
>> It seems like these two sentences are redundant and the flow of the
>> paragraph would be better if they were removed. ... Actually once they
>> are removed, it reveals that the next two sentences largely duplicate
>> the first two sentences of the paragraph.
>>    2.3.  Longest PSD
>>    The longest PSD is the Organizational Domain with one label removed.
>>    2.4.  Organizational Domain
>>    The term Organizational Domains is defined in DMARC [RFC7489]
>>    Section 3.2.
>> 2.4 should be moved ahead of 2.3 to avoid a forward-reference.  But it
>> would be really helpful if the definition of Organizational Domain was
>> either summarized here or completely copied from RFC7489.  In
>> particular, if Organizational Domain is not the same as registered
>> domain name, that should be flagged.
>>    2.5.  Public Suffix Operator (PSO)
>>    A Public Suffix Operator manages operations within its PSD.
>> Better to explicitly define the possession relationship explicitly:
>>    A Public Suffix Operator is an organization which manages
>>    operations within a PSD, particularly the DNS records published for
>>    names at and under that domain name.
>> --
>>    2.6.  PSO Controlled Domain Names
>>    PSO Controlled Domain Names are names in the DNS that are managed by
>>    a PSO and are not available for use as Organizational Domains.
>>    Depending on PSD policy, these will have one (e.g., ".com") or more
>>    (e.g., "") name components.
>> The second sentence is odd; is it useful?  Is it just to say "PSO
>> Controlled Domain Names may have one or more components."?
>>    3.1.  General Updates
>>    References to "Domain Owners" also apply to PSOs.
>> This change really ought to be localized to a specific textual change
>> somewhere in RFC 7489, in the say way that the other changes are
>> specific amendments to the DMARC algorithm.
>>    3.2.  Section 6.3 General Record Format
>> These section titles are difficult to read.  At first I thought there
>> was some typographical problem.  But you could clarify this as "3.2.
>> Updates to Section 6.3.  General Record Format".  Similarly for the
>> other subsections of section 3.
>> 3.3.  Section 6.5.  Domain Owner Actions
>>    The mechanism for doing so is one of the
>>    experimental elements of this document.
>> I think that what this means is that the whole document is an
>> experimental "mechanism for doing so".  If so, I think it could be
>> better phrased
>>    This document is an experimental mechanism for doing so.
>> --
>>    3.4.  Section 6.6.1.  Extract Author Domain
>>    [...] when the domain name extracted by the receiver (from the
>>    RFC5322.From) is on the public suffix list used by the receiver.
>> This touches the question above about what a public suffix list is,
>> and how there can be more than one of them.  But without that
>> knowledge, it's hard to see which PSL is "used" by the receiver of the
>> message.
>> Also, it's not clear to me how *this* document creates a capability
>> which applies to domains that are on the PSL.  E.g., if an "np" is
>> defined for ".org", it applies to (that is, affects processing of
>> e-mail from) any "" that doesn't have its own DMARC records.  But
>> I don't see how an "np" tag for ".org" affects processing of messages
>> from "example@org".
>>    3.5.  Section 6.6.3.  Policy Discovery
>>       (discussed in the experiment description
>>       (Appendix A))
>> Given that this text is nominally an update to the text of RFC 7489,
>> you want to disambiguate the binding of "Appendix A":
>>       (discussed in the experiment description
>>       ([this document] Appendix A))
>>    3.6.  Section 7.  DMARC Feedback
>>    See Section 4 of this document for discussion of Privacy
>>    Considerations.
>> Similarly to section 3.5, but also clarifying the scope of "privacy
>> considerations":
>>    See Section 4 of [this document] for discussion of Privacy
>>    Considerations for PSD DMARC.
>>    4.  Privacy Considerations
>>    The Privacy Considerations of [RFC7489] apply to this document.
>> This could be clarified as
>>    Additionally, the Privacy Considerations of [RFC7489] apply to the
>>    mechanisms described by this document.
>> --
>>    Providing feedback reporting to PSOs can, in some cases, create
>>    leakage of information outside of an organization to the PSO.
>> "outside" probably isn't the word you want to use here, as it is
>> easier to read "outside" as giving the original location of
>> "information" than to read "outside" as giving the direction of
>> "leakage".  Perhaps
>>    Providing feedback reporting to PSOs can, in some cases, create
>>    leakage of information out of an organization to the PSO of its
>>    domain name.
>> --
>>    To minimize this potential concern,
>>    PSD DMARC feedback is best limited to Aggregate Reports.  [...]
>>    [...] any Feedback Reporting related to multi-
>>    organizational PSDs ought to be limited to non-existent domains
>>    except in cases where the reporter knows that PSO requires use of
>>    DMARC.
>> I can't see where in the document that these principles are turned
>> into MUST statements that ensure the privacy issues are solved.
>>    The experiment is to evaluate different possible approaches.
>> Calling this an "experiment" suggests that these is an intended series
>> of actions whose result will answer the listed questions.  But there
>> doesn't seem to be any such actions listed.  The description makes it
>> sound like what is intended is continuing discussions in the working
>> group, but that wouldn't be an "experiment".
>> A.2.  Non-Existent Subdomain Policy
>> Similar questions arise for this section.  The second paragraph
>> suggests that the experiment is to see whether the "np" tag is
>> successful.
>>    There are also
>>    suggestions that it would be more generally useful for DMARC.
>> What does "it" refer to?  (Does it mean "this ability"?)
>> Appendix B.  DMARC PSD Registry Examples
>> In this appendix, it appears that the contents of the experiment are
>> clear in the authors' minds, but there is no summary at the top that
>> states what the experimental facilities are and the "big picture" into
>> which they fit.
>> Appendix C.  Implementations
>>    C.1.  Authheaders Module
>> What e-mail MTA is Authheaders an extension for?
>> [END]
>> _______________________________________________
>> dmarc mailing list
> --
> Todd Herr