From: wcs@anchor.ho.att.com (Bill Stewart)
Date: Fri, 23 Oct 92 07:55:30 PDT
To: cypherpunks@toad.com
Subject: Re: Diffie-Hellman
Message-ID: <9210231456.AA20396@anchor.ho.att.com>
MIME-Version: 1.0
Content-Type: text


Unfortunately, Diffie-Hellman *is* patented, and I'm pretty sure Public Key Partners
(closely related to RSA) holds the patent, just as they hold RSA's.
To quote Steve Bellovin: 
	U.S. Patent Number: 4200770
	Title: Cryptographic Apparatus and Method
	Inventors: Hellman, Diffie, Merkle
	Assignee: Stanford University
	Filed: September 6, 1977
	Granted: April 29, 1980
	[Expires: April 28, 1997]
So we're stuck with it being patented until 1997.
Too bad - I was starting to think along the same lines about doing a D-H-based mailer.
It's non-trivial, if you have to worry about active eavesdroppers swapping
mail messages on you, and it's easier to do if there's a trusted Key Distribution
Center, and if you think about all the cases carefully you tend to re-create
either Needham-Schroeder or the Everhart-Osborn Bell Labs patent (~1980++),
but you can certainly do it for the common case that says the Bad Guys are
only listening to your mail and not tampering with it.

			Bill Stewart, wcs@anchor.ho.att.com