Re: [COSE] Stephen Farrell's Discuss on draft-ietf-cose-msg-20: (with DISCUSS and COMMENT)

[Stephen Farrell <[e-mail]>]

Hiya,

On 26/10/16 16:06, Justin Richer wrote:
> Hi Stephen,
> 
> Sorry for the delay on answering #2 and #6 below. After researching
> the list archives and issue tracker, neither Kepeng nor I can find
> discussion on either issue. If there is such discussion in the
> archives, we would appreciate the working group members pointing us
> all to it.
> 
> But as such, these both seem to be items that were added to the spec
> by the editor without controversy or contention from the working
> group. Therefore, it does appear to reflect consensus as there were
> no objections raised. We both think that the items are OK as is, but
> we’d like to give the working group a couple days to respond
> otherwise if that’s not the case for anyone.

Thanks for checking. If the WG don't say they'd like a change
within a couple of days, I'll clear the discuss. (Please do
ping me though, I may forget;-)

Cheers,
S.


> 
> Thank you,
> 
> — Justin & Kepeng, as COSE chairs
> 
> 
>> On Oct 19, 2016, at 8:59 AM, Justin Richer <[e-mail]>
>> wrote:
>> 
>> Hi Stephen,
>> 
>> The consensus of the working group after Yokohama was to make the
>> CDDL non-normative and still use it as a description/example
>> format.
>> 
>> https://www.ietf.org/mail-archive/web/cose/current/msg00802.html
>> <https://www.ietf.org/mail-archive/web/cose/current/msg00802.html>
>> 
>> I believe the current draft reflects that state. Yes, CDDL syntax
>> is peppered throughout the document as illustration, but it’s the
>> English text that’s normative.
>> 
>> One point that was discussed was that if the draft did not use
>> CDDL, then another description language would likely need to be
>> made up to make human-readable examples in the text. The group felt
>> that it was better to use an existing (even if
>> unfinished/unofficial) description format but remove the normative
>> dependency.
>> 
>> — Justin, as chair.
>> 
>>> On Oct 16, 2016, at 3:41 PM, Stephen Farrell
>>> <[e-mail] <mailto:[e-mail]>>
>>> wrote:
>>> 
>>> 
>>> Hiya,
>>> 
>>> Dear cose-chairs - there is stuff in this discuss for you to
>>> deal with. (Just putting that there in case you're not delving
>>> down into the body of the mails:-)
>>> 
>>> On 16/10/16 22:50, Jim Schaad wrote:
>>>> I think we dealt with all of the comments.  I cannot help you
>>>> with getting chair response.
>>>> 
>>>> See below for my one issue.
>>>> 
>>>> Jim
>>>> 
>>>> 
>>>>> -----Original Message----- From: Stephen Farrell
>>>>> [mailto:[e-mail]
>>>>> <mailto:[e-mail]>] Sent: Sunday, October 16,
>>>>> 2016 1:57 PM To: The IESG <[e-mail]
>>>>> <mailto:[e-mail]>> Cc: [e-mail]
>>>>> <mailto:[e-mail]>; Goeran Selander 
>>>>> <[e-mail]
>>>>> <mailto:[e-mail]>>; [e-mail]
>>>>> <mailto:[e-mail]>; [e-mail]
>>>>> <mailto:[e-mail]>; [e-mail]
>>>>> <mailto:[e-mail]> Subject: Stephen Farrell's Discuss on
>>>>> draft-ietf-cose-msg-20: (with DISCUSS and COMMENT)
>>>>> 
>>>>> Stephen Farrell has entered the following ballot position
>>>>> for draft-ietf-cose-msg-20: Discuss
>>>>> 
>>>>> When responding, please keep the subject line intact and
>>>>> reply to all email addresses included in the To and CC lines.
>>>>> (Feel free to cut this introductory paragraph, however.)
>>>>> 
>>>>> 
>>>>> Please refer to
>>>>> https://www.ietf.org/iesg/statement/discuss-criteria.html
>>>>> <https://www.ietf.org/iesg/statement/discuss-criteria.html> 
>>>>> for more information about IESG DISCUSS and COMMENT
>>>>> positions.
>>>>> 
>>>>> 
>>>>> The document, along with other ballot positions, can be found
>>>>> here: https://datatracker.ietf.org/doc/draft-ietf-cose-msg/
>>>>> <https://datatracker.ietf.org/doc/draft-ietf-cose-msg/>
>>>>> 
>>>>> 
>>>>> 
>>>>> ----------------------------------------------------------------------
>>>>>
>>>>> 
DISCUSS:
>>>>> ----------------------------------------------------------------------
>>>>>
>>>>>
>>>>>
>>>>> 
Thanks for the updates in -20. I think we've only the following points
left. Note
>>>>> that 2 of those are questions to the WG chairs and not to
>>>>> Jim.
>>>>> 
>>>>> (1.1) table 2: As-is the value type column seems to me to 
>>>>> make CDDL normative. I don't see the natural language
>>>>> version that you said would be normative.
>>>>> 
>>>>> Can you help me see that the changes there are such that CDDL
>>>>> is ok as informative? I'm not sure but as I read it there is
>>>>> still no natural language statement that a "counter
>>>>> signature" is one (or more) COSE_Signature values.
>>>> 
>>>> In section 1.3 the following text was added:
>>>> 
>>>> Two syntaxes from CDDL appear in this document as shorthand.
>>>> These are:
>>>> 
>>>> FOO / BAR - indicates that either FOO or BAR can appear here [+
>>>> FOO] - indicates that the type FOO appears one or more times in
>>>> an array
>>>> 
>>>> The value from the table is:
>>>> 
>>>> COSE_Signature / [+ COSE_Signature ]
>>>> 
>>>> Section 4.1 contains the text:
>>>> 
>>>> The CBOR object that carries the signature and information
>>>> about the signature is called the COSE_Signature structure.
>>>> 
>>>>> From that I think that all of the needed normative text is
>>>>> present.
>>> 
>>> Yeah, I get that. But then I think you've embedded some CDDL
>>> notation at least as normative. (I mean the constructs you
>>> describe with FOO/BAR above.)
>>> 
>>> While I do start to feel pedantry-panic that I'm saying it, if
>>> really treating CDDL as informative, I think you ought say in
>>> text that one or more COSE_Signature fields need to be in a
>>> counter signature.
>>> 
>>> But I'm gonna clear that anyway as the whole CDDL is not 
>>> normative thing is really pretence IMO and there's no point in me
>>> joining in with that further.
>>> 
>>> That means that clearing this discuss is now solely down to the
>>> chairs saying they're happy that Jim's positions do reflect wG
>>> consensus.
>>> 
>>> Cheers, S.
>>> 
>>> 
>>> 
>>> 
>>>> 
>>>>> 
>>>>> (2) 3.1, alg: so you're disallowing a setup where the kid 
>>>>> alone identifies the key and algorithm to the recipient? That
>>>>> is used in some IETF protocols (OSPF iirc) so rhat's a pity,
>>>>> and will in those (maybe less common) cases consume a few
>>>>> bytes that could otherwise be saved.  I think, but am not 
>>>>> sure, that the WG already discussed this, but if not, maybe 
>>>>> worth a thought? (Or even a 2nd thought:-) And appendix A.1 
>>>>> is really puzzling - as it provides instructions for how to 
>>>>> not follow a MUST in the body of the document.
>>>>> 
>>>>> I think we left the mail thread on this with you saying "Best
>>>>> to ask the chairs if they agree that this is WG consensus,"
>>>>> as you're an admitteddly strong partisan on this topic.
>>>>> 
>>>>> So, COSE chairs - what's your take? (If you say this is ok
>>>>> with the WG, I'll clear.)
>>>>> 
>>>>> (6) section 10: why MUST the kty values be present always? 
>>>>> That seems unnecessary in some contexts and I don't get a 
>>>>> security reason why it's needed e.g. if there's an alg id 
>>>>> somewhere - can you explain? I can see folks omitting this 
>>>>> leading to interop problems for not useful reasons. (Same 
>>>>> comment applies in other cases where kty is a MUST, e.g. 
>>>>> 12.1.2, 12.2.1.)
>>>>> 
>>>>> I think this is the similar to discuss point (2) above.
>>>>> 
>>>>> So again, COSE chairs, can you confirm that this design does
>>>>> reflect WG consensus and isn't just a thorough and good
>>>>> editor getting his way? (If you say this is ok with the WG,
>>>>> I'll clear.)
>>>>> 
>>>>> 
>>>>> ----------------------------------------------------------------------
>>>>>
>>>>> 
COMMENT:
>>>>> ----------------------------------------------------------------------
>>>>>
>>>>>
>>>>>
>>>>> 
OLD COMMENTS BELOW, I DIDN'T CHECK THEM. Happy to chat more about 'em
>>>>> if that's useful.
>>>>> 
>>>>> - 1.4: the 2nd last paragraph is unclear to me. Probably just
>>>>> needs re-phrasing.
>>>>> 
>>>>> - 1.5: I'd add a reference to RFC5116.
>>>>> 
>>>>> - 3.1, crit: The statement that security libraries or
>>>>> application code can handle this is odd - isn't that an API
>>>>> requirement? (I'm not objecting, but it's odd.)
>>>>> 
>>>>> - 3.1, "content type" is the space there intended?  If so,
>>>>> maybe add quotes or a comma or something to disambiguate the
>>>>> name and descriptive text? Same for other multi-word names
>>>>> here.
>>>>> 
>>>>> - 3.1, "all the keys may need to be checked" - really?  Or do
>>>>> you mean all the keys associated with this kid?
>>>>> 
>>>>> - 3.1, IV/Partial IV - I think it's an error to define this
>>>>> here. What if some algorithm can't use that kind of
>>>>> (0|partial)^IV but needs something else instead? Shouldn't
>>>>> all mechanism for handling IVs be defined by the
>>>>> algorithm/mode? (This isn't a discuss because I can't think
>>>>> of a good counter example and there'd be other ways around
>>>>> the problem too probably.)
>>>>> 
>>>>> - 4.1: signingTime is often needed with signatures. Isn't
>>>>> that common enough to want to define a way to do it, as an
>>>>> option?
>>>>> 
>>>>> - 4.1: If I sign with a private key corresponding to a 2047
>>>>> or 2049 bit RSA public key modulus, then is it clear what to
>>>>> put where in the signature bstr? (Yes, that'd be dumb, but I
>>>>> wonder is what to do well enough defined, as I don't think
>>>>> you can rule it out in all cases.) Since you don't include
>>>>> RSA here I guess it's ok to skip this, but maybe you need to
>>>>> say that such issues need to be handled in the definition of
>>>>> signature algs.
>>>>> 
>>>>> - 4.3: "cannot bleed" isn't clear enough maybe, give an
>>>>> example perhaps where the decoder can fail to disambiguate a
>>>>> boundary?
>>>>> 
>>>>> 4.4, last para: I disagree that one must (even lowercase 
>>>>> must) check the signing identity.  That's application
>>>>> behaviour and should be stated here in such concrete terms. 
>>>>> At least s/must also/may also want to/
>>>>> 
>>>>> (Note - the above were comments on -18, but also seem to work
>>>>> based on -19. Subsequent comments are on -19.)
>>>>> 
>>>>> - 7.1: "starting at the same base IV" - are you missing "and
>>>>> incrementing" or something? Otherwise I think this seems
>>>>> unclear.
>>>>> 
>>>>> - 8.2.1: is the phrasing of the 1st para right? would it be
>>>>> better to say that the value of a key for EdDSA MUST NOT be
>>>>> used for ECDH and vice-versa. (Or maybe points instead of 
>>>>> keys?)
>>>>> 
>>>>> - 8.2.1: you need a reference for batch signing. (Or could it
>>>>> be omitted?)
>>>>> 
>>>>> - section 9: I think it'd be good to be clearer about the
>>>>> strength of truncated MAC values. (And I can't recall the
>>>>> right thing to say off the top of my head:-)
>>>>> 
>>>>> - 11: RFC2898 is about to be obsoleted by [1]. I suspect it'd
>>>>> be better to refer to the draft as that should be published
>>>>> soon. (Same for RFC3447 btw.)
>>>>> 
>>>>> [1]
>>>>> https://datatracker.ietf.org/doc/draft-moriarty-pkcs5-v2dot1/
>>>>> <https://datatracker.ietf.org/doc/draft-moriarty-pkcs5-v2dot1/>
>>>>>
>>>>>
>>>>> 
- 12.4: Why "OKP"? And saying there's no "simple way" to do point validation
>>>>> seems fairly opaque, a reference there or explanatory text
>>>>> would be good. (Ah, it's in section 13, maybe shuffle the
>>>>> text or include a pointer.) Octet key pair doesn't seem like
>>>>> that good a name to me btw.
>>>>> 
>>>>> - 12.5: The 1st para seems wrong. (Or at least is unclear to 
>>>>> me.) "Encrypted with <foo> and <bar>" seems ambiguous anyway,
>>>>> does it mean double encryption or two parallel ciphertexts? 
>>>>> (I assume the former.) What's the algebraic thing you're
>>>>> trying to explain?  It'd be good to provide that for such
>>>>> relatively complex operations I think. Is this what you
>>>>> mean?
>>>>> 
>>>>> KW(KDF(DH-shared),CEK)
>>>>> 
>>>>> - Table 22: The EC2 or OKP value is fixed per curve and the
>>>>> cryptographic function being performed so seems unnecessary. 
>>>>> Do you really need it so? Why? (I'm not buying that some
>>>>> future form of ECC might mean this is needed btw - and
>>>>> codepoints aren't expensive here, right? So other forms of
>>>>> ECC can burn codepoints when that's needed and in the 
>>>>> meantime we'd save bytes and complexity.)
>>>>> 
>>>>> - Section 15: Do we have any examples of such a profile?  I
>>>>> think it'd be great if we did and could add an informative
>>>>> reference here (even if that's to an early I- D).
>>>>> 
>>>>> - section 19: I don't get how ECDSA is normative and the cfrg
>>>>> curves are not. Same for RFC6979. Maybe these all could do
>>>>> with checking? (No big deal IMO but maybe worth it.)
>>>>> 
>>>>> - Appendices A.1 (as already noted) and A.2 are a puzzle. Why
>>>>> say in the body of the document to do <foo> and then an
>>>>> appendix that says how to do <not-foo>?
>>>>> 
>>>>> - Appendix C and the implementation status section: Many
>>>>> thanks - great to see that! (I didn't check 'em though:-)
>>>>> 
>>>>> - Thanks also for speedily handling the extensive secdir
>>>>> review.
>>>>> 
>>>>> [2]
>>>>> https://www.ietf.org/mail-archive/web/secdir/current/msg06801.html
>>>>> <https://www.ietf.org/mail-archive/web/secdir/current/msg06801.html>
>