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[CFRG] Re: RG Last Call on draft-irtf-cfrg-hybrid-kems-12 and draft-irtf-cfrg-concrete-hybrid-kems-04

Simon Josefsson <simon@josefsson.org> Sun, 12 July 2026 09:06 UTC

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From: Simon Josefsson <simon@josefsson.org>
To: Richard Barnes <rlb@ipv.sx>
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Date: Sun, 12 Jul 2026 11:06:23 +0200
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Subject: [CFRG] Re: RG Last Call on draft-irtf-cfrg-hybrid-kems-12 and draft-irtf-cfrg-concrete-hybrid-kems-04
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Richard Barnes <rlb@ipv.sx> writes:

> 2. "I see no justification for the complication of specifying more than one
> combiner."
>
> Here is the justification: As I said in my message to Simon, there is
> already work using the CG and CK combiners, and the U* combiners are there
> to accommodate those who, like you, do not wish to rely on the C2PRI
> property of the PQ KEM.

Which works are using the CG and CK combiners, beyond ML-KEM +
X25519/NISTPCurves?

It would help understanding if pointers to works using each framework
could be added.  Now readers of the document are left realizing the only
three concrete combiners specified uses a tiny subset of all the generic
parts introduced by the document.  Which makes it unclear why all of the
generalization framework parts are needed at all.

Btw, I wouldn't use the U* combiners since I believe the Chempat
combiner offers better properties.  Which consumers are planning on
using your U* combiners?

/Simon

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