>The big issue, in my mind, is how the ftpd is going to get the key >to unlock the *system's* private key... Do you compile it into the >code? Should ftpd ask for it when it comes up? Since active interception is not nearly so easy as passive listening, it would be appropriate to use a Diffie-Hellman key exchange in this situation. This protocol has no persistent private keys, so the issue of keeping a private key around securely is not an issue. But you still have to type a password to a command that itself could have been compromised. (Not that D-H wouldn't be a tremendous help, of course.) All of the hand-held authenticators I'm familiar with require that the host -- or a dedicated, trusted, security server -- keep a secret key per user. That's not a great idea. Bellcore's S/Key doesn't, but I don't know of any hardware devices that implement it. Another possibility would be hand-held digital signature boxes that could sign a random challenge from the host.