Re: [TLS] 0-RTT in DTLS 1.3

Hanno Becker <Hanno.Becker@arm.com> Mon, 24 May 2021 05:02 UTC

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From: Hanno Becker <Hanno.Becker@arm.com>
To: Martin Thomson <mt@lowentropy.net>, "tls@ietf.org" <tls@ietf.org>
Thread-Topic: [TLS] 0-RTT in DTLS 1.3
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Date: Mon, 24 May 2021 05:01:49 +0000
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Archived-At: <https://mailarchive.ietf.org/arch/msg/tls/VGRWSSlBUkGKMw6OMyKFbiRT3q4>
Subject: Re: [TLS] 0-RTT in DTLS 1.3
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Hi,

> It's not necessarily the case that you would end up with an insecure protocol in this case.

One should rather ask: Is it necessarily the case that you would still end up with a secure protocol, and if so, why.

I don't see an attack either, but I think the binding of epochs to keys is fundamental
to DTLS, and if there's danger of violating it, this may well be worth pointing out.

For example, is it obvious enough that there cannot be any risk to early data confidentiality if a non-conforming
client sends two batches of 0-RTT after its first and second ClientHello, both with epoch 1 but with different keys?
Unless this can be ruled out easily, I think it would be worth adding an explicit reminder and/or entry in the
"Implementation pitfalls" section.

Cheers,
Hanno
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