Re: [Cfrg] AES GCM SIV analysis

Andy Lutomirski <luto@amacapital.net> Tue, 31 January 2017 03:55 UTC

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From: Andy Lutomirski <luto@amacapital.net>
Date: Mon, 30 Jan 2017 19:55:34 -0800
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To: Adam Langley <agl@imperialviolet.org>
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Subject: Re: [Cfrg] AES GCM SIV analysis
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On Fri, Jan 27, 2017 at 12:21 PM, Adam Langley <agl@imperialviolet.org> wrote:
> On Thu, Jan 26, 2017 at 6:26 PM, Dan Harkins <dharkins@lounge.org> wrote:
>>   But that is the definition used in the seminal work on the matter, [1].
>> If you want to have a different notion concerning a lesser restriction on
>> nonce reuse then you should use a different term.
>
> That paper formalises an advantage that an attacker might have over an
> ideal scheme. In the same way that block ciphers aren't ideal PRFs,
> nonce-misuse-resistant schemes aren't hitting that ideal either. RFC
> 5297 doesn't hit it, at minimum because it'll run out of counter-space
> after enough messages. AES-GCM-SIV isn't hitting it either.
>
> But that doesn't mean that they aren't practically useful.
>
> I'm not sure what an ideal NMR AEAD would look like, but it's probably
> quite different to both RFC 5297 and AES-GCM-SIV and probably looks
> like a wide-block construction. If someone can point at something they
> think does hit it, that would be interesting to me at least. (Although
> perhaps it's well trodden ground for those who are more familiar with
> the literature than I.)

AEZ looks promising to me:

http://web.cs.ucdavis.edu/~rogaway/aez/

--Andy