Carl Ellison on 'The Death of DES'
Michael Johnson
mpj at csn.org
Wed Sep 29 08:01:51 PDT 1993
On Wed, 29 Sep 1993, Mike McNally wrote:
> > Carl Ellison says:
> > > 3. in between DES operations, mix bytes up as with tran (posted on
> > > sci.crypt occasionally, avbl from me by mail or on ripem.msu.edu)
> > > -- spreading bytes out within a huge block, further hiding any
> > > known text
> Can someone comment on the efficacy of this technique when used in
> conjunction with encryption modes other than ECB, and/or with the
> simple XOR "pre-scramble" technique? I agree that it "couldn't hurt",
> security-wise, but of course it does introduce a (slight) processing
> overhead. If it introduces no real additional security, I don't see
> the point. (Enlighten me!)
>
> (This for some reason reminds me of the way little kids tie shoes;
> they sometimes make enormous knots which, ultimately, are weaker than
> a simple bow.)
One integrated large block cipher is much more secure than this kind of
combination of ciphers, unless you repeat them in enough rounds to make a
compound product cipher out of it. In other words, des | tran really
isn't much stronger than des, but des|tran|des|tran|des|tran|des|tran...
could be quite strong (not to mention slow).
Mike Johnson
Long live the U. S. Constitution!
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