phc-discussions - Re: [PHC] Maximising Pseudo-Entropy versus resistance to Side-Channel Attacks

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Message-ID: <alpine.DEB.2.11.1505060827590.8792@debian>
Date: Wed, 6 May 2015 08:32:30 +0200 (CEST)
From: Stefan.Lucks@...-weimar.de
To: "discussions@...sword-hashing.net" <discussions@...sword-hashing.net>
Subject: Re: [PHC] Maximising Pseudo-Entropy versus resistance to Side-Channel
 Attacks

On Tue, 5 May 2015, Bill Cox wrote:

>       No! Say H2 runs in 1 second allocating 10 MB, while H2, allocating the same 10
>       MB is ten times faster 0.1 second. If the defender is willing to wait 1 second,
>       for either H1 or H2, H1 could then allocate 100 MB.
>
>       cost for H1: 100 sMB (seconds * Megabyte)
>
>       cost for H2: 10 sMb (sconds * Megabyte)
>
>       So the pseudo-entropy for H1 is 3.32 bit larger than the pseudo-entropy for H2,
>       not 6.64.
>
>       Stefan
> 
> 
> Sorry, your math is still wrong.  Mallory gets a 100X benefit.

My math is correct. But I see what you mean. Increasing the memory by a 
factor of ten on the defender's machine, at the same speed, can actually 
increase Malory's costs by more than a factor of ten, depending on 
Mallory's hardware.

Stefan


------  I  love  the  taste  of  Cryptanalysis  in  the morning!  ------
uni-weimar.de/de/medien/professuren/mediensicherheit/people/stefan-lucks
--Stefan.Lucks (at) uni-weimar.de, Bauhaus-Universität Weimar, Germany--