My understanding is that the initial permutation, (which essentially writes the 64 bits of key in a 8 x 8 block by column and row, then reads it out by row and column) was included to simplify early DES chip hardware. It has no impact on the security of the algorithm. If you know what you are doing, it does not effect key agility in software implementations. Peter Trei

---------- From: juzam[SMTP:juzam@cyberspace.org] Reply To: juzam Sent: Wednesday, September 06, 2000 5:30 PM To: cypherpunks@einstein.ssz.com Subject: CDR: Re: Permutations in DES

according to applied cryptography, these permutaions do not effect the security of the algorithm, but i'm not sure about the purpose.

Augusto Jun Devegili wrote:

...

Hi all,

I was just wondering... In DES, there's an Initial Permutation (IP) on the plaintext, then 16 rounds, and then the inverse permutation (IP^-1) of the result to produce the ciphertext.

How effective are these permutations? Do they really add diffusion to the algorithm, considering that they don't depend on the key?

Someone told me that they are necessary to provide reversibility to DES. Is this correct?

Thanks in advance, Best Regards,

Devegili

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