Preserving users´ privacy for continuous query services in road networks

Mobile devices (e.g., smart phones) and location based services are very popular with today´s users. Due to this popularity, there has been a tremendous increase in use of these services and as a result, leakages of both location and query contents is common. In a case where users are constrained by road network, an attacker can follow users´ trajectory with ease. Most of the current privacy preserving solutions focus on temporal and spatial cloaking based methods to protect users´ location privacy. However, these solutions are vulnerable when subjected to continuous query environments. In this paper, we offer our solution to the problem of preserving privacy of users´ trajectory for continuous LBS queries in road networks. We propose a centralized architecture in form of honest-but-curious model to provide anonymity for users as they use LBS services. To achieve this, we employ mix zone approach and design two algorithms namely; Optimal Mixing Load Sub-graph (OMLS) Algorithm that finds an optimal placement of mix zones and creates three levels of security, and Semantically Based Graph Abstraction (SBGA) Algorithm that uses the three layers of security to achieve greater anonymity strength. We analyze the capability of our algorithms to withstand attacks prone to mix zones and carry out experiments to verify this. The experiments results show that our Algorithms preserves privacy for users based on their privacy condition.