Location-proof system based on secure multi-party computations

Location-based services are quite popular. Their variety and their numerous users show it clearly. However, these applications rely on the persons’ honesty to use their real location. If they are motivated to lie about their position, they can do so. A location-proof system allows a prover to obtain proofs from nearby witnesses, for being at a given location at a given time. Such a proof can be used to convince a verifier later on. Many solutions have been designed in the last decade, but none protects perfectly the privacy of their participants. Indeed, provers and witnesses may want to keep their identity and location private. In this paper, a solution is presented in which a malicious adversary, acting as a prover, cannot cheat on his position. It relies on multi-party computations and group-signature schemes to protect the private information of both the prover and the witnesses against any semi-honest participant. Additionally, this paper gives a new secure multi-party maximum computation protocol requiring O(n log(n)) computations and communications, which greatly improves the previously known solutions having O(n²) complexities. Although it is designed for our location-proof system, it can be applied to any scenario in which a small information leakage is acceptable.