CDR: RE: Re: Permutations in DES

[Trei, Peter]

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 at cyberspace.org]
> Reply To: 	juzam
> Sent: 	Wednesday, September 06, 2000 5:30 PM
> To: 	cypherpunks at 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
> 
> --
> foo=====================
>    rim vilgalys
>