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Date: Sun, 8 Aug 2010 04:04:27 +0400
From: Solar Designer <solar@...nwall.com>
To: john-users@...ts.openwall.com
Subject: Re: DES bit slice VS standard

On Sat, Aug 07, 2010 at 07:05:06PM -0400, kenshin himura wrote:
> do you have any pointer regarding the use of JR to exhaust the key space of
> DES (simple plain old ECB DES) ??

No.  JtR does not support "simple plain old ECB DES" (although this is
not too hard to implement), nor does it focus on exhaustive searches.

> that is I'm trying to implement something using CUDA.
> Do I have any advantage to use Bitsliced implementation over the statndard
> one?

Definitely.

> The situation is like this :
> Given:  Cipher text . the first bytes of the plaintext (or at least what
> they should look like)
> unkonwn:  Key (of course :)) and plain text
> 
> The idea is to decrypt the first (and only the first block) and may times as
> needed (in parallel : CUDA) extract first bytes and compare if intresting
> store it.

Well, this is quite possible, but you need to consider how many false
positives you'll get and whether you'll be able to deal with those.
(Depends on what you know about the plaintext.)

Also, consider whether the key is likely totally arbitrary or maybe
user-chosen or generated with some algorithm.

> As I understand the Bitslice is good for multiple enc/dec on diffrent blocks
> using the same key

No, that's not true.  Both data blocks and keys can be different.

Alexander

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