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Re: [openpgp] draft-ietf-openpgp-pqc ECC-based KEMs vs RFC 9180 DHKEM

Aron Wussler <aron@wussler.it> Mon, 19 February 2024 09:27 UTC

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Date: Mon, 19 Feb 2024 09:26:44 +0000
To: Simon Josefsson <simon=40josefsson.org@dmarc.ietf.org>
From: Aron Wussler <aron@wussler.it>
Cc: openpgp@ietf.org
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Subject: Re: [openpgp] draft-ietf-openpgp-pqc ECC-based KEMs vs RFC 9180 DHKEM
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Hi Simon,

The logic in the draft is similar to the one existing in the crypto-refresh [1, 2], just using SHA-3 instead of HKDF.
We chose plain SHA3 over HKDF with SHA2 because it's shared with the key combiner.

It's still a provisional choice, and feedback is welcome! I just sent on Saturday the thread on Signatures, and will soon follow up with KDF and key combination.

Cheers,
Aron

[1] https://www.ietf.org/archive/id/draft-ietf-openpgp-crypto-refresh-13.html#section-5.1.6
[2] https://www.ietf.org/archive/id/draft-ietf-openpgp-crypto-refresh-13.html#section-5.1.7


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Aron Wussler
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On Saturday, 17 February 2024 at 16:10, Simon Josefsson <simon=40josefsson.org@dmarc.ietf.org> wrote:

> Hi
>
> I am reading about OpenPGP's ECC-to-KEM transform here:
>
> https://www.ietf.org/archive/id/draft-ietf-openpgp-pqc-00.html#name-ecc-based-kems
>
> There are similarities to HPKE's DHKEM:
>
> https://www.rfc-editor.org/rfc/rfc9180.html#name-dh-based-kem-dhkem
> https://www.rfc-editor.org/rfc/rfc9180.html#name-algorithm-identifiers
>
> Why doesn't draft-ietf-openpgp-pqc use DHKEM?
>
> /Simon
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