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[km-fs-pcs] Re: No ciphersuite negotiation in MLS-TLS with 2-party profile

Konrad Kohbrok <konrad.kohbrok@datashrine.de> Tue, 30 June 2026 07:14 UTC

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From: Konrad Kohbrok <konrad.kohbrok@datashrine.de>
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Date: Tue, 30 Jun 2026 09:14:21 +0200
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To: Gaëtan Wattiau <gaetan.wattiau=40proton.me@dmarc.ietf.org>
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Subject: [km-fs-pcs] Re: No ciphersuite negotiation in MLS-TLS with 2-party profile
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Hi Gaëtan,

Thanks for pointing those out! I expect that we’ll spec out more details around the handshake after the BoF in Vienna. There are multiple ways to solve these problems and I think we should have a discussion in the working group (once it exists) on where we want the protocol to go.

Cheers,
Konrad


> On 25. Jun 2026, at 15:37, Gaëtan Wattiau <gaetan.wattiau=40proton.me@dmarc.ietf.org> wrote:
> 
> The 2-party profile or MLS-TLS drafts don't support ciphersuite negotiation.
> 
> The only mention of it is in §3:
> 
> > The responder inspects the KeyPackage and checks whether it supports
> > the offered ciphersuite and whether the initiator has sufficient
> > capabilities to support the connection.
> Problems:
>     • It doesn't define an error path if the ciphersuite isn't supported by the server.
>     • It doesn't offer any indication of what to do when there is an error.
>     • It doesn't define any efficient negotiation system.
> 
> Best,
> 
> Gaëtan Wattiau
> 
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