Re: [auth48] [irsg] AUTH48: RFC-to-be 9496 <draft-irtf-cfrg-ristretto255-decaf448-08> for your review

[Jack Grigg <[e-mail]>]

Hi all,

I have completed my final review and suggested changes. Daira Emma Hopwood
also kindly took a look and gave suggestions, some of which I have
incorporated. All of the RFC Editor's questions have been addressed.

The XML file with changes applied is attached. The diff of changes can be
viewed here:

https://github.com/cfrg/draft-irtf-cfrg-ristretto255/compare/rfc-editor-changes...str4d-final-review

Summary of the changes (which is also visible as the list of commits at the
above URL):

   - Revert removal of formatting during editorial changes.
   - Tweaks to make the entire document consistent with editorial changes.
   - Consistent formatting and section headers for ristretto255 and
   decaf448.
   - [Q1] Add keywords.
   - [Q3] Reword "Discrete Log Hardness".
   - [Q4] Clarify the sentence about benefits of Edwards curves.
   - Clarify that not handling abstraction mismatch is not a protocol tweak.
   - Add reference for Ed25519 validation criteria imprecision.
   - Reword last sentence of "Curve25519" caution to remove "its".
   - [Q5] Update references to RFC 9380 encoding functions.
   - [Q6] Replace "its" with the "canonical generator" it refers to.
   - Clarify that `u/v` quantities are (non-)square in the field.
   - Replace `a == b` with `CT_EQ(a, b)`, and clarify that the equivalent
   byte comparison would also be done in constant time.
   - [Q7] Clarify "reflect" in "API Considerations".
   - [Q8] Replace "allowed operations" with clearer wording.
   - [Q10] Alter test vector whitespace to fit within the 69-character
   margin.
   - [Q11] Move notes into `<aside>` elements.
   - Use fixed-width rendering in a few more places (`IS_NEGATIVE()` and
   `l`).
   - Render non-code exponents as superscript in HTML.
   - Use an en-dash for Diffie–Hellman.
   - Miscellaneous minor editorial cleanups.
   - Update Daira Emma's name.

Note that the above changes, and the attached XML file, are relative to
this commit in which I reproduced the RFC Editor's XML changes in our
Markdown source:

https://github.com/cfrg/draft-irtf-cfrg-ristretto255/commit/92e813635f39dd95f1877f8af25e066daaa94d50

There are slight formatting differences in the resulting generated XML in
that commit (due to the mmark generator), but there should be no semantic
differences between the generated XML as of this commit and the RFC
Editor's provided XML, except for these few points:

   - mmark does not support including the <!DOCTYPE rfc [...]> element at
   the top of the file; I had to prepend that manually to the attached XML
   file.
      - Is this something that all RFCs going forward will include in their
      XML? If so, I can open an issue with mmark to prepend it.
   - mmark requires a full date for an RFC, not just a year and month; I
   picked October 14 (being the day this thread began). I presume this will be
   updated for the final publication.
   - mmark does not allow inserting &nbsp; into a contact's fullname field
   (doing so breaks the <contact> element generation). I saw that the RFC
   Editor had added this after the S. in Riad S. Wahby's name; was this
   intentional? I have left it out of the attached XML file; please re-add it
   if it is critically necessary.

Cheers,
Jack

On Sat, Oct 28, 2023 at 12:30 AM Colin Perkins <[e-mail]> wrote:

> Hi,
>
> RFC 5743 section 2.1 requires those statements in the abstract and
> introduction, separately to the boilerplate.
> Colin
>
> On 27 Oct 2023, at 11:58, Jack Grigg wrote:
>
> Thanks Colin.
>
> Relatedly, I note that the consensus attribute's boilerplate text is
> duplicative of the last paragraph of the Introduction. The latter was added
> in February in response to your review (as well as an earlier request to
> add IRTF required statements). Is it still necessary now that the Status of
> This Memo section has the consensus boilerplate, or could that paragraph be
> removed?
>
> For comparison, I note that the last paragraph of the Introduction to RFC
> 9380 is equal to the first sentence of our final Introduction paragraph,
> i.e. it omits the second sentence.
>
> Jack
>
> On Thu, Oct 26, 2023 at 8:33 PM Colin Perkins <[e-mail]> wrote:
>
>> Hi,
>>
>> The consensus attribute does have meaning for the IRTF stream and selects
>> between two different versions of the boilerplate.
>>
>> https://www.rfc-editor.org/styleguide/headers-and-boilerplate/
>>
>> Colin
>>
>>
>> On 26 Oct 2023, at 4:22, Jack Grigg wrote:
>>
>> Hi,
>>
>> On Tue, Oct 24, 2023 at 10:22 AM Sandy Ginoza <[e-mail]> wrote:
>>
>>> Hi Authors,
>>>
>>> Jack, thank you for your reply - please send along comments and updates
>>> from your review once complete.
>>>
>>
>> Apologies for the delay on this; I got COVID for the first time a few
>> weeks ago, and my "next week" was entirely too optimistic about how quickly
>> I'd recover. I'm about half-way through my final review, and will hopefully
>> complete it in the next few days.
>>
>> Part of my review process involved porting the RFC Editor changes to our
>> reference Markdown source code, and regenerating the XML from that with
>> mmark. I have found a few differences between what the RFC Editor
>> provided and what mmark generates; some of them are just formatting (or
>> generation of empty blocks), and some of them look like bugs or
>> unimplemented features in mmark (for which I am opening issues). There
>> is one point I am unclear on however, that I would like to clarify.
>>
>> The RFC Editor changed the document stream metadata from IETF to IRTF,
>> and also added the attribute consensus = "true". mmark only adds the
>> consensus attribute for documents in the IETF stream
>> <https://github.com/mmarkdown/mmark/blob/3d25d9375c96315e75624f8f5b9d814d870e35fe/render/xml/title.go#L46-L52>.
>> RFC 7991 doesn't say
>> <https://datatracker.ietf.org/doc/html/rfc7991#section-2.45.2> whether
>> the consensus attribute is stream-dependent, and points to RFC 7841,
>> which in an appendix
>> <https://datatracker.ietf.org/doc/html/rfc7841#appendix-A.2.2> appears
>> to indicate that consensus language can be present for IRFT stream
>> documents. Is it intended that the consensus attribute be used with IRTF
>> stream documents (i.e. is this a bug in mmark)?
>>
>>
>>>
>>> Authors, please review the document and let us know if any updates are
>>> needed.
>>>
>>
>> Once my review is complete, I will reply here with both the generated
>> XML, and links to the GitHub repo with diffs of all formats.
>>
>> Cheers,
>> Jack
>>
>>
>>>
>>> Thank you,
>>> RFC Editor/sg
>>>
>>> > On Oct 13, 2023, at 10:36 PM, Jack Grigg <[e-mail]> wrote:
>>> >
>>> > Hi all,
>>> >
>>> > Thank you RFC Editor/sg/ap for your work! I will perform my final
>>> review next week, but in the interim I can respond to some of the questions.
>>> >
>>> > For clarity, this email is NOT suggesting any immediate changes to the
>>> text (I will make my own suggestions after my review).
>>> >
>>> > On Sat, Oct 14, 2023 at 12:47 PM <[e-mail]> wrote:
>>> > Authors,
>>> >
>>> > While reviewing this document during AUTH48, please resolve (as
>>> necessary) the following questions, which are also in the XML file.
>>> >
>>> > 1) <!-- [rfced] Please insert any keywords (beyond those that appear
>>> in the title) for use on https://www.rfc-editor.org/search. -->
>>> >
>>> >
>>> > 2) <!-- [rfced] Please ensure that the guidelines listed in Section
>>> 2.1 of RFC 5743
>>> > have been adhered to in this document.  See
>>> > https://www.rfc-editor.org/rfc/rfc5743.html#section-2.1.
>>> > -->
>>> >
>>> >
>>> > 3) <!-- [rfced] Please consider including a reference for "Discrete
>>> Log Hardness".
>>> > We do not see this phrase in RFCs and we did not find directly
>>> matching hits via
>>> > our general searches.  Is this the same as the "hardness of the
>>> discrete logarithm
>>> > problem"?
>>> >
>>> > Original:
>>> >    This means the group has a cofactor
>>> >    of 1, and all elements are equivalent from the perspective of
>>> >    Discrete Log Hardness.
>>> > -->
>>> >
>>> >
>>> > I think that "Discrete Log Hardness" and "hardness of the discrete
>>> logarithm problem" could be used interchangeably here.
>>> >
>>> >
>>> > 4) <!-- [rfced] We have updated the following for readability.  Please
>>> review to
>>> > ensure we have not altered the meaning.
>>> >
>>> > Original:
>>> >    Edwards curves provide a number of implementation benefits for
>>> >    cryptography, such as complete addition formulas with no exceptional
>>> >    points and formulas among the fastest known for curve operations.
>>> >
>>> > Current:
>>> >    Edwards curves provide a number of implementation benefits for
>>> >    cryptography, such as complete addition formulas with no exceptional
>>> >    points and formulas known to be among the fastest for curve
>>> >    operations.
>>> > -->
>>> >
>>> >
>>> > 5) <!-- [rfced] Is "hash_to_curve" considered an algorithm? RFC 9380
>>> refers to
>>> > it as an encoding function.
>>> >
>>> > Original:
>>> >    In some contexts this property would be a weakness, but it is
>>> >    important in some contexts: in particular, it means that a
>>> >    combination of a cryptographic hash function and the element
>>> >    derivation function is suitable for use in algorithms such as
>>> >    hash_to_curve [draft-irtf-cfrg-hash-to-curve-16].
>>> > -->
>>> >
>>> >
>>> > A "hash-to-curve algorithm" is something we would have referred to,
>>> yes. This specific reference should be adjusted however, because the
>>> now-published RFC 9380 specifically constrains the definition of
>>> hash_to_curve, and in Appendix B defines hash_to_ristretto255 with the same
>>> security properties and interface (and similarly for decaf448 in Appendix
>>> C). I'll think about a suggestion during my review.
>>> >
>>> > Relatedly, I notice that RFC 9380 refers to an old version of this
>>> RFC-to-be. Once RFC 9496 is published, I presume that RFC 9380's reference
>>> will be fixed? Their reference link is the one that implementers will be
>>> following more (our reference here is effectively an informational
>>> backlink).
>>> >
>>> >
>>> > 6) <!-- [rfced] To what does "its" refer in the last sentence?
>>> >
>>> > Original (the paragraph is provided for context):
>>> >    Since ristretto255 is a prime-order group, every element except the
>>> >    identity is a generator, but for interoperability a canonical
>>> >    generator is selected, which can be internally represented by the
>>> >    Curve25519 basepoint, enabling reuse of existing precomputation for
>>> >    scalar multiplication.  This is its encoding as produced by the
>>> >    function specified in Section 4.3.2:
>>> > -->
>>> >
>>> >
>>> > "its" in the last sentence refers to "a canonical generator" in the
>>> previous sentence.
>>> >
>>> >
>>> > 7) <!-- [rfced] May we change "reflect" to "note" here?
>>> >
>>> > Original:
>>> >    Implementations SHOULD reflect that: the
>>> >    type representing an element of the group SHOULD be opaque to the
>>> >    caller, meaning they do not expose the underlying curve point or
>>> >    field elements.
>>> >
>>> > Suggested:
>>> >    Implementations SHOULD note that the
>>> >    type representing an element of the group SHOULD be opaque to the
>>> >    caller, meaning they do not expose the underlying curve point or
>>> >    field elements.
>>> > -->
>>> >
>>> >
>>> > I don't think so, assuming that "note" is meant in the sense "to take
>>> notice of". The SHOULD applies as-written to implementations, not
>>> implementers. An implementation reflects what its implementer has noted.
>>> >
>>> > I will consider during my review whether in context "Implementations
>>> SHOULD reflect" or "Implementers SHOULD note" makes more sense.
>>> >
>>> >
>>> > 8) <!--[rfced] May we clarify "allowed operations" as follows?
>>> >
>>> > Original:
>>> >    The decoding
>>> >    function always returns a valid internal representation, or an
>>> error,
>>> >    and allowed operations on valid internal representations return
>>> valid
>>> >    internal representations.
>>> >
>>> > Perhaps:
>>> >    The decoding
>>> >    function always returns a valid internal representation, or an
>>> error,
>>> >    and operations that are allowed on valid internal representations
>>> return valid
>>> >    internal representations.
>>> > -->
>>> >
>>> >
>>> > 9) <!-- [rfced] FYI, we have alphabetized the references. Please let
>>> us know
>>> > of any objections.
>>> > -->
>>> >
>>> >
>>> > 10) <!-- [rfced] The sourcecode in Appendices A.1, A.2, and A.3 extend
>>> > beyond the 69-character margin.  Please let us know how the lines may
>>> > be broken.
>>> > -->
>>> >
>>> >
>>> > As these are not actual source code with established parsing rules,
>>> breaking the lines must be done carefully to ensure that adjacent test
>>> vectors are correctly separated. I'll make a suggestion to this effect in
>>> my review.
>>> >
>>> >
>>> > 11) <!-- [rfced] Please review whether any of the notes in this
>>> document
>>> > should be in the <aside> element. It is defined as "a container for
>>> > content that is semantically less important or tangential to the
>>> > content that surrounds it" (
>>> https://authors.ietf.org/en/rfcxml-vocabulary#aside).
>>> > -->
>>> >
>>> >
>>> > 12) <!-- [rfced] Please review the "Inclusive Language" portion of the
>>> online
>>> > Style Guide <
>>> https://www.rfc-editor.org/styleguide/part2/#inclusive_language>
>>> > and let us know if any changes are needed.
>>> >
>>> > For example, please consider whether "whitespace" should be updated.
>>> > -->
>>> >
>>> >
>>> > "Whitespace" here means any character that represents horizontal or
>>> vertical space in typography (
>>> https://en.wikipedia.org/wiki/Whitespace_character). To my knowledge
>>> there are no "positive or less harmful" connotations associated with this
>>> term (unlike other historic terms of art in computer science), and I don't
>>> know of another term that denotes the same set. But really all we need here
>>> is a concise way to say "if you're copy-pasting these hex strings into your
>>> code, any spaces, tabs, newlines, or whatever else the rendered version of
>>> this RFC happens to put into those gaps can be ignored and must be removed,
>>> and the position of them is irrelevant".
>>> >
>>> > Cheers,
>>> > Jack
>>> >
>>> >
>>> > Thank you.
>>> >
>>> > RFC Editor/sg/ap
>>> >
>>> >
>>> > On Oct 13, 2023, at 4:46 PM, [e-mail] wrote:
>>> >
>>> > *****IMPORTANT*****
>>> >
>>> > Updated 2023/10/13
>>> >
>>> > RFC Author(s):
>>> > --------------
>>> >
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>>> >
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>>> >
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>>> >    https://www.rfc-editor.org/authors/rfc9496-rfcdiff.html (side by
>>> side)
>>> >
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>>> >
>>> >
>>> > Tracking progress
>>> > -----------------
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>>> >    https://www.rfc-editor.org/auth48/rfc9496
>>> >
>>> > Please let us know if you have any questions.
>>> >
>>> > Thank you for your cooperation,
>>> >
>>> > RFC Editor
>>> >
>>> > --------------------------------------
>>> > RFC9496 (draft-irtf-cfrg-ristretto255-decaf448-08)
>>> >
>>> > Title            : The ristretto255 and decaf448 Groups
>>> > Author(s)        : H. Valence, J. Grigg, M. Hamburg, I. Lovecruft, G.
>>> Tankersley, F. Valsorda
>>> > WG Chair(s)      :
>>> > Area Director(s) :
>>> >
>>> >
>>>
>>>