Comment on Quantum Cryptography - Which is More Important, Signal Security, Information Security or Communication Reliability

Signal security aims to prevent the adversary from copying communication signals—so it is with quantum cryptography. Information security focuses on preventing the adversary from knowing plaintext or cheating users—so it is with classical cryptography. Communication reliability means that the intended receiver can recover the right communication signals sent by the sender. In this note, we stress that in the presence of an adversary quantum cryptography can do nothing except for detecting the presence, because the intrusion of adversary has to disturb communication signals so that the intended receiver can not recover the right signals. But classical cryptography works well in the presence of eavesdropping although it cannot detect it. We also remark that in the past decades the functionality of quantum cryptography to detect eavesdropping has been overstated. The plan to build a large quantum photonic network is infeasible.