Multi-user Privacy Cooperation Game by Leveraging Users’ Service Flexibility

In location-based services (LBSs), it is promising for multiple users to cache and share their Point-of-Interest (PoI) information with each other to reduce overall query frequency and preserve location privacy. Yet most studies on multi-user privacy preservation overlook the opportunity of leveraging service flexibility, where many users are flexible and may add obfuscation to individual LBS query. This paper is the first to study how multiple users cooperate to query with obfuscation against the adversary’s optimal inference attack, by leveraging their mutual service flexibility. Unlike the literature, even if a user already finds the shared PoI information useful, we prove it beneficial for him to further query with obfuscated location to confuse the adversary. To save the computational complexity of the max-min adversarial game problem and derive the closed-form solution, we also propose a binary approximate solution, which is proved to guarantee good privacy performance for an average user. Perhaps surprisingly, the user with greater service flexibility should choose to query the LBS with less misreported location, to maximally confuse the adversary. Finally, we numerically compare our optimal and approximate solutions with the existing approaches to show our effective privacy improvement.