John Young asks: Smith stated: "A cipher is Unconditionally Secure (US) if no matter how much ciphertext is intercepted, there is not enough information in the ciphertext to determine the plaintext uniquely." No examples for this strength were given, and it was not clear from Smith's presentation whether there is such a cipher or the category was only provided as a theoretical premise. Question: is there a cipher that is Unconditionally Secure? Yes. A one-time pad based cipher has precisely this property. They are also, however, unpleasant to use. Keep in mind that as soon as you use anything but a perfectly random keystream that is only employed once, it is no longer a one-time pad. "Pseudo" one time pads are not even remotely unconditionally secure. At best they are simply stream ciphers of ordinary security. Frequently, "pseudo" one time pad schemes are totally worthless. -- Perry E. Metzger [EMAIL PROTECTED] -- Quality NetBSD CDs, Support & Service. http://www.wasabisystems.com/