"perfect secrecy" . "Information-theoretically secure" . "information-theoretic cryptography" . "Information-theoretic security" . "unconditionally secure" . . . "Physical Layer Encryption" . . . "physical layer encryption" . "Information-theoretic security" . "information-theoretically secure" . "statistical security" . "unbreakable in theory" . "Information theoretic security" . . "information-theoretic security" . . "information theoretically secure" . "MIMO wiretap channel" . .