full-disclosure - Re: code release: cryptographic attack tool

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Message-Id: <00C71B3D-8731-4A5D-9EBE-9E248691C4EB@gmail.com>
Date: Fri, 12 Jan 2007 14:13:49 -0800
From: Andrew Farmer <andfarm@...il.com>
To: Slythers Bro <slythers@...il.com>
Cc: full-disclosure@...ts.grok.org.uk, "Dave No,
	not that one Korn" <davek_throwaway@...mail.com>
Subject: Re: code release: cryptographic attack tool

On 12 Jan 07, at 08:05, Slythers Bro wrote:
> hi,
> sorry but i know nothing about the real physical "quantic theory"
> i'am not a physician
> i just know there are 3 states : 0 ,1 and unknow
<...>

This approach won't work for anything beyond the most trivial  
cryptographic computations: attempting to reverse MD5 through basic  
logic like this will "stall" as soon as you come to an operation  
where both operands are unknown. In MD5, this will occur at the stage  
where the message is added to word A in the 64th round. By the time  
you get to the end of the 60th round, all bits will be "unknown".

Any attack on a cryptosystem (such as MD5) of this form will need to  
take into account complex correlations between bits. To carry your  
quantum-physics analogy a bit further, you need to be able to keep  
track of "entanglement" between bits. However, the storage necessary  
to carry out such an attack on a large system like MD5 may very well  
be large enough as to be completely infeasible (i.e, above 2^48 bits).

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