A Privacy-Preserving Protocol for Proximity-Based Services in Social Networks

A number of real-life social networks provide the users with proximity-based services. This feature exposes to seri-ous privacy threats, because it could allow massive tracking from an honest-but-curious provider. Whilst proximity-based services have been deeply studied in the literature in a general setting, no solution (to the best of our knowledge) has been provided to the problem of delivering privacy-preserving proximity-based services entirely within existing social networks. The problem is not trivial, because a social network provider can play as a global passive adversary, monitoring the flow of all the messages exchanged in the network. Therefore, to allow proximity testing between Alice and Bob not requiring that they reveal their position to the social network provider is not enough. Indeed, even the fact that proximity testing is performed between Alice and Bob (independently of the result) is a serious privacy leakage. In this paper, we provide a solution preventing also this privacy leak, giving thus a concrete way to implement privacy-preserving proximity-based services in social networks.