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]
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