🚀 go-pugleaf

In article <6681@tuegate.tue.nl> bartjan@blade.stack.urc.tue.nl (Bartjan Wattel) writes:
>Hi,
>
>I'm currently working on a project which involves the design of a DES cryto-
>chip. When reading some papers on this subject, it appeared to me that there
>is a great need for enlarging the number of bits used in the cipher key. I read
>about an implementation of the DES with a cipher key of 768 bits in the paper
>of T.Kropf, J.Fr"ossl, W.Beller and T.Giesler: A hardware implementation of a
>modified DES-algorithm, in North-Holland Micorprocessing and Microprogramming
>30, 1990.
>
>Questions:
>
>  1)  Does anybody know the reason(s) for the number of circular left shifts
>      which are performed on the cipher key each iteration in the original
>      DES algorithm ?

They are designed to mix up the key.  As to the actual reason that particular
number was chosen...that is shrouded in mystery.

>  2)  Does anybody know of other modifications concerning the key size ?

There have been many.  None of them are any good.  Biham and Shamir showed
that DES with independent subkeys (the 768-bit key variant you mentnion) is no
more secure than DES.  Something else called GDES was also shown to be no more
secure than DES.  The security of DES seems pretty much limited to a 56-bit
key.

>  3)  Do modifications exist which have been published or proposed by the
>      NBS, or do other (de facto) standard modifications exist ?

No.

By the way, I knew about the DES-with-independent-subkeys variant, but I did
not have a reference for it.  Could you please E-Mail me with the complete
citation for the article you mentioned in your post.  A physical copy of the
article in my mailbox would be even better.

Thanks,
Bruce

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