From: thad@hammerhead.com (Thaddeus J. Beier)
Date: Mon, 5 Feb 1996 15:24:54 +0800
To: cypherpunks@toad.com (Cypherpunks Mailing List)
Subject: Re: RC2 protected by copyright?
Message-ID: <199602050503.VAA18831@hammerhead.com>
MIME-Version: 1.0
Content-Type: text/plain


Lewis (nee' Futplex) McCarthy writes:

> I think many cryptographers would agree that the S boxes in DES represent
> some pretty weighty ideas indeed, and constitute an intrinsic part of the
> algorithm. Offhand the precise construction of the RC2 permutation table
> doesn't seem to me to be nearly as important to the strength of RC2 as the
> S boxes are to DES' strength. I'm certainly no expert. But I'm a little 
> hesitant to dismiss the specified table as "a bit of text". 

> Do you think the table would be more like an idea if it turned out to be
> determined by pi ?  (not a rhetorical question)

Yes, the table would have been more an idea, and less "just text" if it
was derived from pi (as the comment in the posted code suggests...)

What I was suggesting is a way to get the tremendous protection of
copyright (that is, 75 year term, no filing fees, protected from birth, no
secrecy required) on ciphers. 

Now, this was tried with video games, each Nintendo cartridge had in
it something like "copyright Nintendo", as a way to try to get that
protection, and I believe that they lost in court (if my memory is
correct)

Everyone knows the story of the compositions of the S-Boxes in DES, that
they just happen to contain constants that make it difficult to attack
DES with differential cryptanalysis.  There are almost an infinite number
of S-Boxes that would have that property (probably more that wouldn't).
But if you were going to write a code that would interoperate
with somebody else's DES, there is absolutely no way to do describe it
except to enumerate the S-Boxes, hence perhaps violating the copyright.
You can say "make it resistant to linear and differential cryptanalysis",
and you may get something as good, or better, but it wouldn't interoperate.

thad
-- Thaddeus Beier                     thad@hammerhead.com
   Technology Development                   408) 286-3376
   Hammerhead Productions        http://www.got.net/~thad