[jose] Re: Do you need the JWP JSON Serialization?

[Orie Steele <[e-mail]>]

That's fair : )

Let's replace "suspicion" with "I would have argued for a different design".

In JOSE, ~ is just used as a placeholder for "missing unprotected header".

You still need to validate that the correct mutable data was included, and
that no "unexpected mutable data" was included.

That's a "verifier policy over mutable data".

In the context of SD-JWT that means checking disclosures, matching their
hash to the kbt and making sure the kbt is signed by the cnf.

That is very similar to the kind of unprotected header processing that COSE
supports, see:

https://www.rfc-editor.org/rfc/rfc9338.html#section-2

Sure maybe it's less obvious that jwt (cnf) -> disclosures -> hash -> kbt
signed by cnf is a kind of counter signature.

But it is a second signature, over a specific set of disclosures that is
grouped together with the first signature, which are verified together.

https://datatracker.ietf.org/doc/html/draft-ietf-oauth-selective-disclosure-jwt-10#section-9.1

"""
Unprotected headers other than disclosures are not covered by the digest,
and therefore, as usual, are not protected against tampering.
"""

This is similar to how values in unprotected headers in COSE are not
protected, unless there is some "verification process" such as checking a
counter signature, or merkle tree inclusion proof.

Isn't JWP meant to replace SD-JWT in some cases that require stronger
unlinkability?

IIRC SD-JWT and OAUTH had good reasons to define a JSON Serialization, and
if it's used, those users should be able to switch to JWP or CWP in the
future.

OS





On Thu, Aug 8, 2024 at 12:33 PM Brian Campbell <[e-mail]>
wrote:

>
>
> On Thu, Aug 8, 2024 at 11:27 AM Orie Steele <[e-mail]>
> wrote:
>  <snip>
>
>>
>> If JWTs had unprotected headers, I suspect SD-JWT would have used them
>> for the mutable part (disclosures).
>>
>
> That suspicion is entirely incorrect.
>
> <snip>
>
>
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-- 


ORIE STEELE
Chief Technology Officer
www.transmute.industries

<https://transmute.industries>