Hi Vladimir,

I kinda got the same question from someone a couple days ago and could
pinpoint a clear normative answer.

We have https://tools.ietf.org/html/rfc7520 that shows ECDH-ES with P-384
and P-256. In not having any normative text around these curves being
allowed or P-521 being disallowed I always assumed all original three are
fair use for ECDH-ES (and its composite KW variants).

We also have https://tools.ietf.org/html/rfc8037 which specifically
mentions X25519 and X448 OKP subtypes to be usable for ECDH-ES (and its
composite KW variants).

Then we have the JOSE registration of EC secp256k1 curve which specifically
mentions that the curve is NOT released for ECDH in that document.

So,

EC P-256
EC P-384
EC P-521
OKP X25519
OKP X448

S pozdravem,
*Filip Skokan*


On Tue, 3 Nov 2020 at 22:40, Vladimir Dzhuvinov <[email protected]>
wrote:

> Today we received the question why the Nimbus JOSE+JWT lib supports the
> EC curves it does for ECDH (P-256, P-384, P-512) and I couldn't find any
> normative text or reference in the JWA spec to explain this.
>
> https://tools.ietf.org/html/rfc7518#section-4.6
>
>
> We also looked at the IANA registry for hints:
>
> https://www.iana.org/assignments/jose/jose.xhtml
>
>
> Contrast this with the JWS ECDSA, where the curves to go with the ESxxx
> algs are specced:
>
> https://tools.ietf.org/html/rfc7518#section-3.4
>
>
> Can someone help here? :)
>
>
> Thanks,
>
> Vladimir
>
> --
> Vladimir Dzhuvinov
>
>
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