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Re: [Cfrg] Adopting "AES-GCM-SIV: Nonce Misuse-Resistant Authenticated Encryption" as a CFRG document

Yoav Nir <ynir.ietf@gmail.com> Mon, 28 March 2016 15:23 UTC

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From: Yoav Nir <ynir.ietf@gmail.com>
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Date: Mon, 28 Mar 2016 18:22:50 +0300
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To: "Paterson, Kenny" <Kenny.Paterson@rhul.ac.uk>
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Cc: Yehuda Lindell <Yehuda.Lindell@biu.ac.il>, "cfrg@irtf.org" <cfrg@irtf.org>, Adam Langley <agl@google.com>
Subject: Re: [Cfrg] Adopting "AES-GCM-SIV: Nonce Misuse-Resistant Authenticated Encryption" as a CFRG document
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> On 28 Mar 2016, at 5:34 PM, Paterson, Kenny <Kenny.Paterson@rhul.ac.uk> wrote:
> 
> Dear CFRG,
> 
> Shay, Adam and Yehuda have asked the CFRG chairs whether their draft for
> AES-GCM-SIV can be adopted as a CFRG document. We are minded to do so, but
> first wanted to canvass members of the group for their opinions on taking
> this step.

+1: definitely take this step.

That said, I think the current document is missing a convincing motivation. The security considerations section talks about randomly choosing nonces and limits the number of such nonces that can safely be randomly generated to 2^32. This makes sense, but for most uses (TLS, IPsec, SSH) we can use a non-random nonces (a counter; an LFSR if you want to get fancy; DES-encrypting a counter if you want to get really fancy). I’d be happier if there was an example where a counter is not practical. 

Yoav

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