There was more or less such a thing in an earlier draft ( https://tools.ietf.org/html/draft-ietf-jose-jwk-thumbprint-01#section-4) of what would become RFC 7638: There was some disagreement about it that I don't quite remember the details of and it was pulled out. I think what Justin said did come up as justification for not needing something more explicit. If a thumbprint is used as a kid, then the parties involved need to know that and also know the hash alg. I realize that doesn't really answer the question but is a little background/context.
On Thu, Jul 21, 2016 at 7:00 PM, Nathaniel McCallum <[email protected]> wrote: > Specifically, I'm thinking of the problem of validating a thumbprint. > > The RFC does not define a hash function. Nor does the output format > contain a hash function name. > > So if I hand JWK to an entity, how does that entity validate that the > thumbprint in the kid is actually a valid thumbprint and wasn't > modified? I supose the entity could try all its supported hash > functions; but that seems a little heavy handed. > > The existing kid could be used with contents like: <hash>.<thumbprint> > > Alternatively, RFC 7517 uses the x5t and x5t#S256 variants. This is > precisely why I wondered about a thumbprint specific attribute. > Something like thp and thp#S256 would make this explicit. > > Thoughts? > > On Tue, 2016-07-19 at 12:09 -0400, Nathaniel McCallum wrote: > > Has there been any talk about using a prefix to specify the hash > > algo? > > > > On Tue, 2016-07-19 at 11:24 -0400, Justin Richer wrote: > > > > > > This was discussed on the list a while ago, and the thought was > > > that > > > you could easily use the JWK thumbprint *as* the “kid” value > > > instead > > > of defining a new field for this use case. The header values are > > > protected by the signature in the normal (compact) JWS/JWE formats, > > > and ought to be protected in the JSON representations too for > > > exactly > > > the reasons you’re talking about. > > > > > > — Justin > > > > > > > > > > > > > > > On Jul 19, 2016, at 10:48 AM, Nathaniel McCallum <npmccallum@redh > > > > at > > > > .com> wrote: > > > > > > > > The JWS and JWE specs defined the "kid" header value that can be > > > > used > > > > to identify the key used for signing or encryption. Subsequently, > > > > the > > > > JWK thumbprint method was defined. > > > > > > > > Has anyone put any thought into registering a header value for > > > > JWS > > > > and > > > > JWE headers that indicates the thumbprint of the key used for > > > > signing > > > > or encryption? This would be very helpful for key indexes > > > > especially > > > > when using unprotected headers since the value of "kid" might be > > > > modified. > > > > > > > > _______________________________________________ > > > > jose mailing list > > > > [email protected] > > > > https://www.ietf.org/mailman/listinfo/jose > > > > > > > _______________________________________________ > > jose mailing list > > [email protected] > > https://www.ietf.org/mailman/listinfo/jose > > _______________________________________________ > jose mailing list > [email protected] > https://www.ietf.org/mailman/listinfo/jose >
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