Quantum secure privacy-preserving array equality comparison protocol

This paper presents a quantum protocol for the secure privacy-preserving equality comparison of private arrays. The design overcomes the scalability limitations of conventional quantum private comparison schemes, which are typically restricted to single integers. In the proposed approach, each array element is encoded into the amplitude of a single-photon state. Participants then encrypt the received states via local rotation operations with privately chosen random angles. A circular transmission mode is employed, whereby the encrypted states are sequentially exchanged among all parties, including a semi-honest third party. The TP performs single-particle measurements to determine the equality of the arrays and broadcasts the result simultaneously to ensure fairness. The protocol's functionality and practicality were validated through quantum circuit simulations on the IBM Qiskit platform. Security analysis confirms its robustness against both external eavesdropping attacks and internal privacy threats from honest-but-curious participants. By utilizing single-photon encoding, rotation-based encryption, and single-particle measurement, the protocol achieves enhanced scalability and practical feasibility for multi-element comparisons, advancing beyond the scope of existing single-integer comparison schemes.