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Re: [Cfrg] ChaCha20

Yoav Nir <ynir.ietf@gmail.com> Fri, 08 August 2014 21:38 UTC

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From: Yoav Nir <ynir.ietf@gmail.com>
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Date: Sat, 09 Aug 2014 00:38:27 +0300
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References: <CACsn0cmUg1A1wxgOuubfPNg2XJGVq6BNFkARkv_eCSYqvqWRCA@mail.gmail.com> <20140808133614.GA24182@LK-Perkele-VII>
To: Ilari Liusvaara <ilari.liusvaara@elisanet.fi>
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Subject: Re: [Cfrg] ChaCha20
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On Aug 8, 2014, at 4:36 PM, Ilari Liusvaara <ilari.liusvaara@elisanet.fi> wrote:

> On Thu, Aug 07, 2014 at 06:23:05PM -0700, Watson Ladd wrote:
>> Dear all,
>> In the past 6 years only one cryptanalysis result has been published
>> against ChaCha, and that was against a variant before the final
>> version was announced. While Salsa20 was an eStream finalist, ChaCha
>> wasn't.
>> 
>> I'd like to see some more cryptanalytic attention on ChaCha: in
>> particular are the differentials from "Latin Dances" still valid for
>> the published version of ChaCha? What are the best differential
>> characteristics? And can we figure this out quickly?
> 
> Trying to find paper about "Latin Dances", I ran into these:
> 
> https://eprint.iacr.org/2007/472
> https://eprint.iacr.org/2012/065
> 
> Both seem to analyze final version of Chacha, and seemingly make
> worse job than on Salsa (e.g. the first "breaks" Salsa8, but not
> Chacha8).

Thanks, Ilari

The second of those is not (yet) referenced in the draft. I will add this to the next revision.

Yoav

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