phc-discussions - Re: [PHC] Security concern for Catena

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Message-ID: <52CAC898.9010407@uni-weimar.de>
Date: Mon, 06 Jan 2014 16:15:36 +0100
From: Christian Forler <christian.forler@...-weimar.de>
To: discussions@...sword-hashing.net
Subject: Re: [PHC] Security concern for Catena

On 06.01.2014 12:54, Bill Cox wrote:
> I don't think my attack works with Catena 2, does it?

To a certain degree. :-)

The benefit decrees in a drastic way when you use Catena-2 instead of
Catena-1. It becomes even worse with Catena-3 and so on and so forth.

> I hope not, because I just switched NoelKDF to use something very
> similar to Catena 2 to eliminate timing attacks.  If Catena 2 has a
> weakness, I would appreciate hearing about it.

Catena-\lambda, and especially Catena-2, is *NOT*
sequential-memory-hard. So you do always benefit from multiple cores.
For c cores you can theoretically speed up the performance to a factor
of O(c^(1/\lambda+1)). So, for c=1,000,000  you can speedup the
computation of Catena-2 by a factor of 100.

I'm mot sure if this is either acceptable or not. What do you think?

Best regards,
Christian

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