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

On Tue, Nov 24, 2015 at 10:10 PM, Mike Jones
<Michael.Jones@microsoft.com> 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 [mailto:kathleen.moriarty.ietf@gmail.com]
> Sent: Tuesday, November 24, 2015 6:41 PM
> To: Mike Jones <Michael.Jones@microsoft.com>
> Cc: oauth@ietf.org
> 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 <Michael.Jones@microsoft.com> wrote:
>> Thanks for your review comments, Kathleen.  Responses are inline below...
>>
>>> -----Original Message-----
>>> From: OAuth [mailto:oauth-bounces@ietf.org] On Behalf Of Kathleen
>>> Moriarty
>>> Sent: Tuesday, November 24, 2015 9:44 AM
>>> To: oauth@ietf.org
>>> 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
>>> OAuth@ietf.org
>>> https://www.ietf.org/mailman/listinfo/oauth
>>
>>                                 Thanks again,
>>                                 -- Mike
>>
>
>
>
> --
>
> Best regards,
> Kathleen

-- 

Best regards,
Kathleen