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Re: [TLS] PQC key exchange sizes

Martin Thomson <mt@lowentropy.net> Tue, 26 July 2022 15:31 UTC

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Date: Tue, 26 Jul 2022 11:31:06 -0400
From: Martin Thomson <mt@lowentropy.net>
To: tls@ietf.org
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Subject: Re: [TLS] PQC key exchange sizes
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On Tue, Jul 26, 2022, at 11:21, Stephen Farrell wrote:
> Be interested in how that'd change the CH if ECH is used too.
> I guess the answer mightn't make us happy;-)

PQ HPKE would not fit, but the Kyber-512 numbers mean that we should be OK for ECH if we stuck with classical security.  For obvious reasons, that might not be OK though.

If we wanted a PQ HPKE (or a Hybrid KEM) then ECH would blow out the size so that we would end up with multiple packets for the CH.  That would be basically unworkable from a performance perspective.

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