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Re: [TLS] WGLC for draft-ietf-tls-tls13-cert-with-extern-psk

Geoff Keating <geoffk@geoffk.org> Fri, 31 May 2019 21:31 UTC

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From: Geoff Keating <geoffk@geoffk.org>
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Date: Fri, 31 May 2019 14:31:44 -0700
Cc: Russ Housley <housley@vigilsec.com>, IETF TLS <tls@ietf.org>
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To: Hugo Krawczyk <hugo@ee.technion.ac.il>
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Subject: Re: [TLS] WGLC for draft-ietf-tls-tls13-cert-with-extern-psk
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> On 21 May 2019, at 2:08 pm, Hugo Krawczyk <hugo@ee.technion.ac.il> wrote:
> 
> A clarification on the text suggest below by Russ.
> 
> The way I see it, the external PSK as used in draft-ietf-tls-tls13-cert-with-extern-psk is not intended as a means of authentication but as a way of regaining forward secrecy in case the (EC)DHE mechanism is ever broken (e.g., by cryptanalysis or by a quantum computer).

It’s a bit problematic if the expected use of the draft is with quantum-resistant certificates, because TLS doesn’t support those yet.

If that’s the intent, shouldn’t the draft say something like "The server MUST choose a quantum-resistant algorithm when considering those listed in signature_algorithms_cert and/or signature_algorithms.  The client MUST supply at least one quantum-resistant algorithm in signature_algorithms, and in signature_algorithms_cert if present.”  ?  But that makes it unimplementable until such an algorithm is specified...

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