From: Michael Johnson <mpj@csn.org>
Date: Wed, 29 Sep 93 08:01:51 PDT
To: Mike McNally <m5@vail.tivoli.com>
Subject: Re: Carl Ellison on 'The Death of DES'
In-Reply-To: <9309291229.AA11549@vail.tivoli.com>
Message-ID: <Pine.3.05.9309290818.A2965-b100000@teal.csn.org>
MIME-Version: 1.0
Content-Type: text/plain


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!