Re: [OAUTH-WG] AD review of draft-ietf-oauth-proof-of-possession

Mike Jones <> Thu, 26 November 2015 06:59 UTC

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From: Mike Jones <>
To: Kathleen Moriarty <>, John Bradley <>
Thread-Topic: [OAUTH-WG] AD review of draft-ietf-oauth-proof-of-possession
Date: Thu, 26 Nov 2015 06:59:31 +0000
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Subject: Re: [OAUTH-WG] AD review of draft-ietf-oauth-proof-of-possession
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I hadn't seen this part of the thread until now.  (I thought it was part of the voluminous thread on the PoP architecture document.)

The "may accept JWT containing “cnf” elements" language sounds like it's giving applications permission to do this.  Is that the intent of the language you proposed, or were you intending something different, John?

Also, can you expand on the "pseudo audience" idea?  In what way might a proof-of-possession be confused with an audience?

				-- Mike

-----Original Message-----
From: Kathleen Moriarty [] 
Sent: Wednesday, November 25, 2015 2:13 PM
To: John Bradley <>
Cc: Mike Jones <>;
Subject: Re: [OAUTH-WG] AD review of draft-ietf-oauth-proof-of-possession

Thanks, John!

On Wed, Nov 25, 2015 at 4:41 PM, John Bradley <> wrote:
> I prefer the new wording.
> However the last part could be clearer.
>>  use be implemented by recipients.
> Or perhaps the blunter “Recipients only understanding bearer tokens may accept JWT containing “cnf” elements if all the other required claims are valid.  It is important for security to audience restrict tokens using the JWT “aud claim.  The “cnf” claim MUST NOT be used as a pseudo audience restriction.”

More explicit text like this is is more helpful in my opinion.

> Looking at the comments, I get the feeling that some people might think that cnf may restrict what endpoints can receive the token (because of the key distribution)  it only allows endpoints that should receive the token to reject ones that come from entities who don’t possess the correct confirmation.
> John B.
>> On Nov 25, 2015, at 12:25 AM, Mike Jones <> wrote:
>> Rather than elaborating, having looked at the text we're discussing again, I'm going to counter-propose that we instead simplify - sticking only to the point that the paragraph is intending to get across.  Would it work for you to simplify the current text:
>>    "A recipient might not understand the cnf claim, in which case it will typically be ignored. Unless this is acceptable behavior, applications that need the proof-of-possession keys communicated with it to be understood and processed must require that the parts of this specification that they use be implemented."
>> to this simpler text?
>>    "A recipient might not understand the cnf claim.  Applications that need the proof-of-possession keys communicated with it to be understood and processed must require that the parts of this specification that they use be implemented."
>> The "must ignore" topic is already addressed in the second paragraph of 3.1 (and with exactly the semantics as the rest of JWT), and so doesn't have to be re-raised here, as it currently is.  Re-raising it is clearly a point of distraction.
>> For what it's worth, I don't remember any DISCUSSes on this topic (although it's possible that your memory is better than mine on this point).
>>                               Best wishes,
>>                               -- Mike
>> -----Original Message-----
>> From: Kathleen Moriarty []
>> Sent: Tuesday, November 24, 2015 7:14 PM
>> To: Mike Jones <>
>> Cc:
>> Subject: Re: [OAUTH-WG] AD review of 
>> draft-ietf-oauth-proof-of-possession
>> On Tue, Nov 24, 2015 at 10:10 PM, Mike Jones <> wrote:
>>> Fair question about the use of "typically".  The reason it's there is that this language in JWT [RFC 7519] Section 4 does permit applications to require that JWTs with not-understood claims be rejected, rather than ignored, even though that's not the default behavior:
>>>   The set of claims that a JWT must contain to be considered valid is
>>>   context dependent and is outside the scope of this specification.
>>>   Specific applications of JWTs will require implementations to
>>>   understand and process some claims in particular ways.  However, in
>>>   the absence of such requirements, all claims that are not understood
>>>   by implementations MUST be ignored.
>>> So when not understood, "cnf" would typically be ignored, but might not be.
>> I find that confusing and am now thinking this came up in a discuss as well during the review for 7519, didn't it?  Can you elaborate int eh security considerations section a bit more, otherwise this text appears to be conflicting and even with what you intend, it's confusing for implementers and will lead to issues with interoperability.
>> Thanks,
>> Kathleen
>>>                                -- Mike
>>> -----Original Message-----
>>> From: Kathleen Moriarty []
>>> Sent: Tuesday, November 24, 2015 6:41 PM
>>> To: Mike Jones <>
>>> Cc:
>>> Subject: Re: [OAUTH-WG] AD review of 
>>> draft-ietf-oauth-proof-of-possession
>>> Hi Mike,
>>> Thanks for the quick turn-around.  Just one more comment on my comments.
>>> On Tue, Nov 24, 2015 at 9:10 PM, Mike Jones <> wrote:
>>>> Thanks for your review comments, Kathleen.  Responses are inline below...
>>>>> -----Original Message-----
>>>>> From: OAuth [] On Behalf Of Kathleen 
>>>>> Moriarty
>>>>> Sent: Tuesday, November 24, 2015 9:44 AM
>>>>> To:
>>>>> Subject: [OAUTH-WG] AD review of
>>>>> draft-ietf-oauth-proof-of-possession
>>>>> Hi,
>>>>> Thank you all for your work on this draft!  I just have a few questions:
>>>>> 1. Security considerations section says:
>>>>> "All of the normal security issues, especially in relationship to
>>>>>   comparing URIs and dealing with unrecognized values, that are
>>>>>   discussed in JWT [JWT] also apply here."
>>>>> I find that to be odd phrasing that would likely be picked up in 
>>>>> subsequent reviews.  Please remove the word "normal" so that all 
>>>>> of the security issues discusses in JWT are included.  Are there 
>>>>> other 'normal considerations in addition to those in JWT that need 
>>>>> to be listed?  The phrasing reads as if that may the case and 
>>>>> would be better to include them all or pointers or change the phrasing.
>>>> You're right.  I removed this awkward wording.
>>>>> 2. Also in the security considerations section,
>>>>>   "A recipient may not understand the newly introduced "cnf" claim and
>>>>>   may consequently treat it as a bearer token."
>>>>> What is the proper handling requirement when an unknown claim is 
>>>>> present?  Section 3.1 says:
>>>>>  "When a recipient receives a "cnf" claim with a
>>>>>   member that it does not understand, it MUST ignore that member."
>>>>> Is this why it is treated as a bearer token rather than being 
>>>>> rejected?  Is this really the action you want to see with cnf?  
>>>>> Why isn't there an error and a resend as a bearer token so that 
>>>>> parties understand (or have an opportunity to understand) that there were issues?
>>>>> Then the following text in the security section says:
>>>>>  "While this is a
>>>>>   legitimate concern, it is outside the scope of this specification,
>>>>>   since demonstration the possession of the key associated with the
>>>>>   "cnf" claim is not covered by this specification. For more 
>>>>> details,
>>>>> How is this outside of the scope of this draft?  cnf is defined in 
>>>>> this draft, so handling should be covered in this draft.  A 
>>>>> pointer to the POP architecture draft is not helpful as it is not 
>>>>> defined there, it's covered int his draft.  Should this text just 
>>>>> be removed and replaced with more explicit handling information int he body of this draft?
>>>> Good catch.  JWT [RFC 7519] Section 4 says that claims that are not understood must be ignored unless otherwise specified by the application.  This allows new claims to be dynamically added without breaking existing applications.  For the same reason, I have incorporated this language about understanding claims from 7519, but having it be about understanding confirmation members.  Ultimately, what features must be implemented are always up to the application, just as with JWT claims.
>>> The new text in Section 3.1 looks good.  I'm not sure why the word "typically" appears int he new text of the security considerations section though after reading the new text in 3.1.  Wouldn't it just be ignored since 3.1 now says:
>>>   "However, in the absence of such requirements,
>>>    all confirmation members that are not understood by implementations
>>>    MUST be ignored."
>>> Thanks,
>>> Kathleen
>>>>> Thanks!
>>>>> --
>>>>> Best regards,
>>>>> Kathleen
>>>>> _______________________________________________
>>>>> OAuth mailing list
>>>>                                Thanks again,
>>>>                                -- Mike
>>> --
>>> Best regards,
>>> Kathleen
>> --
>> Best regards,
>> Kathleen
>> _______________________________________________
>> OAuth mailing list


Best regards,