In the last decade, the number of location-aware mobile devices has mushroomed. Just as location-based services grow fast, they lay out many questions and challenges when it comes to privacy. For example, who owns the location data and for what purpose is the data used? To answer these questions, we need new tools for location privacy. In this paper, we focus on the problem of secure location sharing, where a group of n clients want to collaborate with each other to anonymously share their location data with a location database server and execute queries based on them. To become more realistic, we assume up to a certain fraction of the clients are controlled arbitrarily by an active and computationally unbounded adversary. A relaxed version of this problem has already been studied in the literature assuming either a trusted third party or a weaker adversarial model. We alternatively propose a scalable fully-decentralized protocol for secure location sharing that tolerates up to n/6 statically-chosen malicious clients and does not require any trusted third party. We show that, unlike most other location-based services, our protocol is secure against traffic-analysis attacks. We also show that our protocol requires each client to send a polylogarithmic number of bits and compute a polylogarithmic number of operations (with respect to n) to query a point of interest based on its location.
['Mahdi Zamani', 'Mahnush Movahedi']
Secure location sharing