Impact and purpose of IP/FP in DES

[David Honig]

At 09:42 PM 4/24/01 +0200, Martin Olsson wrote:
>
>"The initial permutation and the corresponding final permutation do not
>affect the security of DES. (As near as anyone can tell, its primary
>purpose is to make it easier to load plaintext and ciphertext data into a
>DES chip in byte sized pieces. Remember that DES predates 16-bit or 32-bit
>microprocessor busses.) ... many software implementations of DES leave out
>both the initial and the final permutations. ... While the new algorithm is
>no less secure than DES, it does not follow the DES standard and should not
>be called DES."
>
></quote>
>
>First; I do not exactly understand what Mr.Schneier means. How can it be
>easier to transfer 8-bits of data into a chip if one first rearranges the
>bits? 

In software, this is a necessary chore for being compliant with the Standard.
However, cryptographically, it does nothing.

Hint: In hardware, its free.

dh




 






  







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