Two-Party Quantum Private Comparison with Four-Particle Entangled States

A two-party quantum private comparison (QPC) protocol is constructed with four-particle entangled states, where the third party (TP) is assumed to be semi-honest in the sense that she is allowed to misbehave on her own but cannot conspire with anyone else. The proposed protocol is secure against both the outside attack and the participant attack, and only needs single-particle measurements, neither unitary operations nor quantum entanglement swapping. Without considering the security check process, the qubit efficiency of the proposed protocol attains as high as 25%.