Question on Diffie-Hellman patent

[Amanda Walker <amanda@intercon.com>]

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.


Thanks,

Amanda Walker
Senior Software Engineer
InterCon Systems Corporation