Paul, I noticed you mentioned that you will be using key rings in your cryptophones, so here's an idea I think would be great for cryptophones. This is a simple solution to the key-exchange problem. Cryptophone users would not need to exchange keys beforehand nor need to store other people's public keys on their cryptophone. - Every cryptophone user has a public and private key pair (like in RSA or PGP) - When a person calls another person, the phones automatically exchange their public keys before the voice conversation begins. Obviously the private keys are never transmitted. With this method, all one needs to initiate a secure telephone conversation is the phone number of whoever you're calling, just like using a regular telephone. I am assuming this is how Clipper/Skipjack phones would do this. I hope your cryptophone software does this as well, since I don't want to or need to keep keyrings full of public keys of everyone I might ever have to call. Thug