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

Aaron Zauner <azet@azet.org> Fri, 15 April 2016 17:21 UTC

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From: Aaron Zauner <azet@azet.org>
In-Reply-To: <em070ccf63-3cd3-456a-be17-518f0f50130e@sgueron-mobl3>
Date: Sat, 16 Apr 2016 00:22:05 +0700
Message-Id: <06550747-D138-45A2-B0CB-B3680460C853@azet.org>
References: <em070ccf63-3cd3-456a-be17-518f0f50130e@sgueron-mobl3>
To: "Gueron, Shay" <shay.gueron@gmail.com>
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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 ---- Some clarifications
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Hi,

> On 16 Apr 2016, at 00:04, Gueron, Shay <shay.gueron@gmail.com> wrote:
> 
> Hi -
> 
> Sure, we can add the comment to the next revision.
> 
> (In any case, this follows from the security bounds, but spelling this out in the CFRG document would not hurt)

I think the clearer the wording here, the better the outcome in the understanding of implementers, not all are mathematicians or cryptographers themselves.

> [ About using AES-GCM with a random IV 2^48 times: this violates the guidelines of AES-GCM spec ( http://csrc.nist.gov/publications/nistpubs/800-38D/SP-800-38D.pdf, section 8.3). ]

I am aware of that. Joux provided a comment on the matter during the NIST specification phase: http://csrc.nist.gov/groups/ST/toolkit/BCM/documents/comments/800-38_Series-Drafts/GCM/Joux_comments.pdf (section 3)

The problem here is not the spec itself - it's human error and misunderstanding during implementation phase. I feel nonce-misuse resistant modes should effectively prevent such scenarios in the first place. At least that was my understanding until today.

Aaron

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