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Re: [Cfrg] Critique of AES-GCM-SIV

Aaron Zauner <azet@azet.org> Fri, 17 February 2017 14:23 UTC

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From: Aaron Zauner <azet@azet.org>
In-Reply-To: <20170217125255.GA16732@gmail.com>
Date: Fri, 17 Feb 2017 16:23:16 +0200
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References: <20170217000247.GB23785@gmail.com> <CAPqF7e2xFVqbw0cCi4468_Ag+Lp4QuXPMaR2cNsU4m_F7hFppQ@mail.gmail.com> <20170217125255.GA16732@gmail.com>
To: Marko Kreen <markokr@gmail.com>
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Cc: CFRG <cfrg@irtf.org>
Subject: Re: [Cfrg] Critique of AES-GCM-SIV
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> On 17 Feb 2017, at 14:52, Marko Kreen <markokr@gmail.com> wrote:
> 
> On Fri, Feb 17, 2017 at 11:00:56AM +0100, Daniel Bleichenbacher wrote:
>> On Fri, Feb 17, 2017 at 1:02 AM, Marko Kreen <markokr@gmail.com> wrote:
>>> I have reviewed the AES-GCM-SIV proposal (draft 3).  And while there
>>> are parts I like - overall direction to higher security and
>>> getting rid of GCM bitflipping - current design feels "ugly".
>>> (That's a cryptographic term.)
> 
>> I actually don't know what "ugly" means as a cryptographic term.
> 
> Well, it was supposed to be a joke...
> 
>> My guess would something like difficult to formally analyze.
> 
> But I think we are mostly on same page.  My main complaint was that
> if it's nonce-misuse-resistant mode, then why does nonce misuse
> have such a big effect on behaviour: on one case message is protected
> by fresh key and counter, on other case only fresh counter.

Quick comment: This came up in an earlier thread on that topic already, I've also brought it up last spring. I think for this I-D in it's current form "nonce misuse resistant" might not be the best term (too strong, many people assume you can do what you want with the nonce with such a construction -- which certainly isn't the case for AES-GCM-SIV as proposed here). "nonce-misuse tolerant" came up and other suggestions. I haven't seen an update yet.

Aaron

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