The problem with this is that public-key encryption is slooooow. I never thought of having a fixed key for each user; even the STU-III ignition keys get reloaded every so often.

The slow part is the RSA encryption. The conversation doesn't need to be encrypted with RSA, mabe IDEA or something else. All you really need to do is create a session key for each side once with RSA then you are done (similar to PGP). 2 -- C --