At 11:24 AM -0500 1/20/97, Amanda Walker wrote:

Please excuse if this is a FAQ.

I'd been operating under the assumption that the Diffie-Hellman patent (4200770) will expire on April 29, 1997 (17 years after the date of issue). Several people have recently told me it doesn't expire until September, evidently confusing the date of issue with the filing date. However, does anyone know of another patent (Hellman-Merkle, perhaps?) that would hve an impact on software that does D-H key exchange? We've got some planned uses of DH; while it doesn't seem cost effective to pay to license DH at this point, that six-month difference is something I need to plan around if necessary.

As a result of the GATT treaty, patent expiration times for some US patents changed. The international standard is 20 years from filing, while old US law was 17 years from issue. On the day which GATT took force for the US (June 8, 1995), all outstanding patents' expiration dates were changed to 20 years from filing or 17 years from issue, whichever is later. This affects some cryptography patents as follows: Here's a summary of some relevant crypto patents: Name Number Filed Issued Expires Diffie-Hellman 4,200,770 Sept. 6, 1977 Apr. 29, 1980 Sept. 6, 1997 Hellman-Merkle 4,218,582 Oct. 6, 1977 Aug. 19, 1980 Oct. 6, 1997 RSA 4,405,829 Dec. 14, 1977 Sept. 20, 1983 Sept. 20, 2000 Data from <http://patents.cnidr.org/patbib_index.html> References: <http://www.lightlink.com/bbm/gatt.html> <http://www.cushman.com/articles/artpat10.htm> - Tim Tim Dierks - timd@consensus.com - www.consensus.com Software Haruspex - Consensus Development Developer of SSL Plus: SSL 3.0 Integration Suite