Re: [OAUTH-WG] [jose] preventing confusion of one kind of JWT for another in JWT BCP

[Brian Campbell <[e-mail]>]

What other JWTs are there?

All JWTs use JWS and/or JWE. So a JWT is a JOSE JWT by definition. JWT
requires 'crit' processing by virtue of using JWS and JWE for signing and
encryption. The extent to which that processing is actually implemented is
a different and fair question but it's normative requirement per spec and
implementations that don't would be non-compliant.

The byte usage actually is pretty similar depending on the the values used
(admittedly because I chose very compact names/values).  Compare to
secevent, for example,

   "crit":["p"],"p":1
   "typ":"secevent+jwt"


On Thu, Jul 27, 2017 at 3:29 PM, Dick Hardt <[e-mail]> wrote:

> Brian: I did not think that 'crit' processing is required in JWT
> https://tools.ietf.org/html/rfc7519
>
> We have two goals:
>
> Preventing new JWT profiles from being confused with older JWTs, which
> 'typ' solves (as does your proposal of 'crit' and 'p', but requires more
> bytes)
>
> Preventing existing JWT implementations from being confused with new JWT
> profiles. 'crit' can solve that for JOSE JWTs, but not other JWTs.
>
>
>
> On Thu, Jul 27, 2017 at 7:49 PM, Brian Campbell <
> [e-mail]> wrote:
>
>> During the first WG meeting last week
>> <https://datatracker.ietf.org/doc/minutes-99-oauth/> I asked if use of
>> the JOSE "crit" (Critical) Header Parameter had been considered as a
>> recommendation for preventing confusion of one kind of JWT for another.
>> Time was running short in the meeting so there wasn't much discussion and
>> it was requested that I take the question to the list. And so here on the
>> list is that.
>>
>> Section 3.9
>> <https://tools.ietf.org/html/draft-sheffer-oauth-jwt-bcp-01#section-3.9>
>> of the JWT BCP draft now recommends explicit typing using the "typ" JWS/JWE
>> header parameter but does concede that 'the use of explicit typing may not
>> achieve disambiguation from existing kinds of JWTs, as the validation rules
>> for existing kinds JWTs often do not use the "typ" header parameter
>> value.'  And the recommendations for how to use the Type Header
>> Parameter in JWT <https://tools.ietf.org/html/rfc7519#section-5.1>
>> strongly suggest that it's not currently being used for any validation.
>>
>> Alternatively using the JWS/JWE "crit" (Critical) Header Parameter
>> <https://tools.ietf.org/html/rfc7515#section-4.1.11> to signal the
>> type/intent/profile/application of a JWT could achieve disambiguation
>> even in validation of existing kinds of JWTs. The critical header lists
>> other headers which must be understood and processed by the receiver and
>> that the JWS/JWE is invalid if those listed aren't understood. So a new
>> type/profile of JWT that uses the "crit" header would produce JWTs that
>> would be rejected even by existing applications of JWT validation (that
>> actually implement "crit" properly anyway).
>>
>> The JWT BCP could suggest the use of "crit" in conjunction with a
>> profile/application/type specific header. Or it could provide a bit more of
>> a framework like defining a registering a new JOSE header "p" (strawman of
>> p as a very short name for profile) and create a registry for its values. A
>> JWT header using that approach might look like the following where the
>> value 1 is registered as some cool new JWT profile/application. The
>> consumer of such a JWT would have to understand and process the "p" header,
>> which would mean checking that it had the value expected.
>>
>>      {
>>       "alg":"ES256",
>>       "crit":["p"],
>>       "p":1
>>      }
>>
>> A JOSE compliant JWT validator would reject such a JWT even for an OAuth
>> access token or OIDC id_token because the "p" header isn't known or
>> understood but is marked as critical.
>>
>> To me, that seems like an approach to preventing confusion that has more
>> teeth than the "typ" header. Which is why I asked about it last week and am
>> now bringing it to the list.
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
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>
>
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