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From: tjt@lll-risky.arpa (Tim Tessin)
Newsgroups: sci.crypt,comp.misc
Subject: Re: public key encryption and RSA patent status
Message-ID: <106@lll-risky.arpa>
Date: Fri, 25-Sep-87 18:35:26 EDT
Article-I.D.: lll-risk.106
Posted: Fri Sep 25 18:35:26 1987
Date-Received: Sun, 27-Sep-87 05:47:55 EDT
Reply-To: tjt@lll-tis.arpa (Tim Tessin)
Lines: 89
Keywords: RSA patent
Xref: mnetor sci.crypt:574 comp.misc:1327

In article <615@rocky.STANFORD.EDU> andy@rocky.UUCP (Andy Freeman) writes:
> 
> Since no one has bothered to actually look up the RSA patent to find
> out what is covered, various people on the net have assumed that what
> it covers supports their position.  One possibility is that it is for
> the use of a certain integer function to encrypt digital information.
> Another possibility is that it is for one way to encrypt digital information
> using integer functions with certain properties.  A third possibility is
> that it covers encryption of digital information using integer functions
> with certain properties.  Bob's objection suggests that he thinks that the
> RSA patent is one of the latter two.
> ...
> So Bob, what do you think the RSA patent covers?  What do you think it
> would be legitimate for it to cover?
> 
> Andy Freeman

Ok, here are the facts.  
Disclaimer: my description here of what our lawyers
said may not fully render the legal opinion of the U.S. Government on 
this matter.

First the patent itself:

U.S. Patent # 4,405,829
Title:	   Cryptographic communications system and method
Inventors: Rivest, Shamir, Adleman
Assignee:  Massachusetts Institute of Tech.
Filed:	   Dec. 14, 1977
Granted:   Sep. 20, 1983

40 Claims, 7 Drawing Figures

Abstract:  
  A cryptographic communications system and method.  The system
  includes a communications channel coupled to at least one terminal
  having an encoding device and to at least one terminal having a
  decoding device.  A message-to-be-transferred is enciphered to
  ciphertext at the encoding terminal by first encoding the message as a
  number M in a predetermined set, and then raising that number to a
  first predetermined power (associated with the intended receiver) and
  finally computing the remainder, or residue, C, when the
  exponentiated number is divided by the product of two predetermined
  prime numbers (associated with the intended receiver).  The residue C
  is the ciphertext.  The ciphertext is deciphered to the original
  message at the decoding terminal in a similar manner by raising the
  ciphertext to a second predetermined power (associated with the
  intended receiver), and then computing the residue, M', when the
  exponentiated ciphertext is divided by the product of the two
  predetermined prime numbers associated with the intended receier.  The
  residue M' corresponds to the original encoded message M.


There follows a detailed description of the math and examples are
given.  Then come the claims (which are the actual legal claims to
which infringement protection is given).  The claims basically state
(there are 40 of them) that rendering this algorithm into hardware
or rendering the specific methods to encrypt a message into an
implementation (such as a software package), and combining them with a
communications channel of any kind, is protected.   Note the
significance of the term METHOD.  ANY methodical, repeatable use of
the steps required to encrypt a message using the algorithm is
protected!  This means coding the RSA algorithm and combining it
with a communications channel without an agreement with the RSA
company is an infringment.  Barring any procedural errors MIT and RSA
made in obtaining the patent (a low probability) 
and barring excruciating analysis of the patent to determine just exactly 
how one might implement a crypto-system without infringment, the
legal-eagles say you're screwed.  (This is if you are a commercial
venture.  Exactly what the U.S. Government has as patent rights are
still being determined.  The research was partly funded by
the U.S. Government and it retains some rights.)
Of course, the burden of a patent infringment suit is on RSA.  They
must sue you to gain an infringment judgement.  Do you feel lucky?
You are free to use the math to provide any other product other
than a cryptographic comunications system.  Presumably, you could
use the algorithm to encrypt files stored locally, as long as you didn't
transmit them anywhere and have someone decrypt them (but this is not
a legal opinion).

Hope this clears things up a bit.

(You Government sites, don't touch that dial! More to follow 
when it comes in.)

Tim Tessin - Lawrence Livermore National Laboratory 
Phone: (415) 423-4560 / 422-8971
ARPA:  tjt@lll-tis.ARPA
UUCP:  {ihnp4,dual,sun}!lll-lcc!lll-tis!tjt