> You can have perfectly encrypted communication that no one can eavesdrop on (not even theoretically). Not exactly. Quantum "cryptography" assures you that on

> You can have perfectly encrypted communication that no one can eavesdrop on (not even theoretically). Not exactly. Quantum "cryptography" assures you that only one party received the data, but not who that other party is. There is no authentication. To prevent a man in the middle attack, you have to use a conventional message authentication code, and the system as a whole is no stronger than the MAC algorithm.