full-disclosure - Comparing Algorithms On The List OfHard-to-brut-force?

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Date: Tue Nov  1 18:55:45 2005
From: andfarm at gmail.com (Andrew Farmer)
Subject: Comparing Algorithms On The List
	OfHard-to-brut-force?

On 01 Nov 05, at 10:11, Brandon Enright wrote:
> Brute forcing an algorithm suggests that you are not attacking a  
> weakness or
> known flaw in the algorithm but rather just running through the  
> keyspace
> trying to recover the plaintext.  In that case, whichever allows  
> you to use
> the most bits is what you want.

Note that the encryption speed of an algorithm is *not* a significant  
factor
in the time taken to brute-force it, except for extremely small  
keyspaces!
Remember that the time taken to brute-force an N-bit algorithm that  
takes K
seconds per encryption is, on average

         N
    K * 2

which increases much more rapidly with N than it does with K. Adding  
even one
more bit will double the average time taken to brute-force an  
algorithm, while
using a slower algorithm will only increase the difficulty marginally.

Also note that anything beyond 256 bits is silly. Brute-forcing a 256- 
bit
algorithm can be shown to be PHYSICALLY impossible, so there's no  
reason to
go anywhere beyond that.
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