CDR: Re: Permutations in DES

[Kevin Elliott]

At 17:30 -0400 9/6/00, juzam wrote:
>according to applied cryptography, these permutaions do not effect the
>security of the algorithm, but i'm not sure about the purpose.

As I recall the basic purpose was to make it slow in software meaning 
that software cracking apps were/are at a severe disadvantage vs. 
hardware implementations.  It would be interesting to see how much 
longer that extended DES's effective lifetime.   I would consider the 
initial permutations to be in the same category as Blowfish's (and 
derivative algorithm's) time consuming key expansion phase- a neat 
"trick" that does not improve theoretical security but significantly 
increases the difficulty of real world attacks.
-- 

Kevin "The Cubbie" Elliott 
<mailto:kelliott at mac.com>                             ICQ#23758827
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