When do patents expire on Rabin's public key scheme?

When do patents expire on Rabin's public key scheme?

RSA claims that the Diffie Helman patent, which expires on the 29th of
April, 1997, covers all public key cryptography.

ElGamal and Rabin are unpatented.

Schmeier says that ElGamal will be free of patent restrictions after that,
but he says nothing about Rabin.

Rabin's encryption and signatures take up the same amout of space as RSA
signatures, and encryption, but ElGamal takes up twice the space, thus Rabin
seems preferable to ElGamal.
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On Sat, 27 Jan 1996, James A. Donald wrote:

> When do patents expire on Rabin's public key scheme?
> 
> RSA claims that the Diffie Helman patent, which expires on the 29th of
> April, 1997, covers all public key cryptography.
> 

Actually, I think that the Merkle Hellman patent is the one considered to
cover all public key cryptography.  RSADSI claims that Diffie Hellman also
includes ElGamal, but Cylink now owns the Diffie Hellman patent and I don't
know if they consider it to also cover ElGamal.

> ElGamal and Rabin are unpatented.
> 
> Schmeier says that ElGamal will be free of patent restrictions after that,
> but he says nothing about Rabin.

In _Applied Cryptography_, there is no mention of any patents covering Rabin.
Elliptic curve public key encryption schemes are not covered by any public
key cryptography schemes, so it is possible that Rabin is also not covered
under any patents.

- --Mark

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