Preserving privacy for location-based services with continuous queries

Location-based service (LBS) is gaining momentum as GPS-equipped mobile devices become increasingly affordable and popular. One of the potential obstacles faced by LBS is that users may raise concerns about their personal privacy when location data are sent to a distrusted LBS provider. A well-known solution is to render the location data less accurate through spatial or temporal cloaking. However, such a solution has limitations when the LBS is based on location data that either include speed and heading direction, or are sent at a regular time interval. In the former case, by combining consecutive location data including speed, heading direction, and cloaked locations, an adversary can obtain more accurate estimation of the actual location. In the latter case, an adversary can infer additional information when an expected update to the location data is not received because cloaking is not possible. In this thesis, we will first show how privacy protection provided by spatial cloaking can be breached, and proposed a new cloaking method to integrate the speed and direction into the spatial cloaking process. We then propose an auditing system to ensure all the mobile devices can be well protected even when it is impossible to cloak some of them to meet their customized privacy requirements. We evaluate the proposed methods with experiments based on simulated mobile devices using real city maps. The experiments show that our speed and direction cloaking methods can achieve sufficient privacy protection without causing significant decrease in the service quality.;...