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To: Rodney Thayer <rodney@sabletech.com> cc: cryptography@c2.net Date: Thu, 31 Jul 1997 11:01:23 -0400 From: Steven Bellovin <smb@research.att.com> I gather DES was originally patented (by IBM?). Now some people are looking at CAST, which is apparently patented but being freely shared by Entrust. Does anyone know where there are references to the DES patent, and/or discussion of it's being released for use without a fee? You're quite right -- IBM did indeed patent DES, but made it freely available. The latter was, if nothing else, a NIST-imposed condition -- they were only going to give their blessing to a freely-available cipher. I'm not certain of the patent number -- a quick rummage through my files shows two candidates, 3,958,081 and 3,962,539, and I don't feel like wading through them to see if either is it. What I'm looking for is documentation to show CAST is freely usable, and as a comparison I am wondering what was done to make DES freely usable. What IBM did was to publish a note in the official Patent and Trademark Office Gazette that gave everyone a royalty-free, non-exclusive license to use DES. Technically, there was a catch -- as I read it (in conjunction with a patent lawyer), DES was only free *if* you used one of the four official modes of operation! As far as I know, they never tried to enforce that... Anyway -- given the legal situation (that NIST required that the standard cipher be free to all comers), IBM needed a nice, formal, legal mechanism to make this grant irrevocable. The Gazette publication was used. Any patent lawyer can show you how to find the statement I'm referring to.
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