Privacy-preserving greater-than integer comparison without binary decomposition in the malicious model.

Wilko Henecka, Nigel Geoffrey Bean, Matthew Roughan

Tushar Kanti Saha, Takeshi Koshiba

Jun Sakuma, Kobayashi Shigenobu

Florian Bourse, Olivier Sanders, Jacques Traoré

Ali Ataeemh Allami

Secure comparison (SC) is an essential primitive in Secure Multiparty Computation (SMC) and a fundamental building block in Privacy-Preserving Data Analytics (PPDA). Although secure comparison has been studied since the introduction of SMC in the early 80s and many protocols have been proposed, there is still room for improvement, especially providing security against malicious adversaries who form the majority among the participating parties. It is not hard to develop an SC protocol secure against malicious majority based on the current state-of-the-art SPDZ framework. SPDZ is designed to work for arbitrary polynomially-bounded functionalities; it may not provide the most efficient SMC implementation for a specific task, such as SC. In this thesis, we propose a novel and efficient compiler specifically designed to convert most existing SC protocols with semi-honest security into the ones secure against the dishonest majority (malicious majority). We analyze the security of the proposed solutions using the real-ideal paradigm. Moreover, we provide computation and communication complexity analysis. Comparing to the current state-of-the-art SC protocols Rabbit and edaBits, our design offers significant performance gain. The empirical results show that the proposed solution is at least 5 and 10 times more efficient than Rabbit in run-time and communication cost respectively.

Min Hou, Yue Wu, Shibin Zhang

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.