Paper 2026/1706

Comment on ‘Quantum public key encryption scheme with four states key’

Abstract

Liu et al. (2022 Phys. Scr. 97 045102) propose a quantum public key encryption scheme in which a qubit message is encrypted by a controlled-NOT gate driven by a four-state public key, followed by measurement of the message register, and claim information-theoretic security. I show that the encryption map reduces exactly to \( |M\rangle \mapsto R_{\theta}X^{m}|M\rangle \), where the outcome \(m\) is published. \(R_{\theta}\) is diagonal and the ciphertext reproduces the computational-basis distribution \((|\alpha|^2,|\beta|^2)\) of the plaintext, while the plaintexts \(|0\rangle\) and \(|1\rangle\) are perfectly distinguishable. The claim of information-theoretic security is therefore invalid.