Hi Jon, Hi Goeran,

Thanks for bringing this issue up.

I had noticed that HPKE defines its own registry and re-using that registry 
would be beneficial. I then thought that the group would not be happy to define 
an extra parameter given that there is already an algorithm registry. This lead 
me to the current design.

I do, however, agree that the cleaner way is to define a new parameter, as you 
suggested, and then re-use the HPKE registry. By doing this we also make sure 
that the two registries do not get out of sync.
So, unless there is an objection I would go head and make the chance to the 
draft.

Ciao
Hannes

From: COSE <[email protected]> On Behalf Of John Mattsson
Sent: Monday, November 8, 2021 5:26 PM
To: [email protected]
Subject: Re: [COSE] HPKE for COSE

Göran Selander [email protected]<mailto:[email protected]> 
wrote:

>We could e.g. define a COSE Header Parameter (say 'hpke-alg'; label 11)
>signifying that this is an HPKE algorithm, in which case e.g. {11 : 17} would
>indicate DHKEM(P-384, HKDF-SHA384).

A new 'hpke-alg' parameter with values from the "HPKE KEM Identifiers" IANA 
registry seems like a very good solution. I think this makes a lot of sense in 
this case. All future HPKE KEMs would then automatically be usable in COSE and 
we would avoid COSE WG work registering new HPKE KEMs.

If COSE adopt this draft, we should discuss if COSE WG sees HPKE as the main 
way to use KEMs in COSE in the future. Note that all the current ECDH-ES 
algorithms are KEMs. A general HPKE mechanism would mean COSE can automatically 
use any HPKE PQC KEMs, but nothing would stop COSE from registering more 
optimized PQC KEMs if needed.

Cheers,
John

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