Or more specifically, I'm interested in how broad PKP thinks they are. I understand that they claim all public-key systems, but am I correct that that claim is based entirely on the Diffie-Hellman patent expiring in April, 1997? Is Shamir's three-pass protocol as presented on page 376 in applied cryptography covered? If you you used his protocol with the RSA-like symetric algorithm suggested, is it covered under the RSA patent? Would an elliptic analog of this be secure? Are there other cryptographically secure communtative symetric ciphers that could be used in Shamir's three pass protocol? Being able to use this without infringing on any patents would effectively obviate the need for public key cryptography outside of authentication. What about probabilistic encryption using a BBS generator? Does RSADSI claim that because it too depends on the computational hardness of factoring? Thanks in advance, Jason W. Solinsky