Location anonymity in continuous location-based services

• Authors: Toby Xu;Ying Cai
• Venue: Proceedings of the 15th annual ACM international symposium on Advances in geographic information systems
• Year: 2007

A major concern for large-scale deployment of location-based services (LBSs) is the potential abuse of their client location data, which may imply sensitive personal information. Location privacy protection is challenging because a location itself may reveal a subject's identity. To support location anonymity, existing research reduces location resolution by ensuring each location reported to a service provider is a cloaking area that contains at least K mobile nodes. This strategy is effective when each location update can be considered as an independent event. In this paper, we investigate location anonymity in the context of continuous LBSs, which require frequent location updates from service users. Knowing that a user is inside a cloaking area constrains its position in the next cloaking area. Thus, simply ensuring each cloaking area contains at least K users does not give a user K-anonymity protection. We propose to measure the anonymity degree of a cloaking area using entropy, which takes into account not only the number of the entities inside, but also their anonymity probability distribution. To find a cloaking area that can provide a given level of anonymity protection and is also as small as possible, we present a novel technique with a polynomial time complexity. The effectiveness of our techniques is studied under various conditions using location data synthetically generated using real road maps and traffic volume data. The results show that our techniques can indeed protect user anonymity at a desired level, and at the same time, minimize the size of each cloaking area, allowing users to receive high quality services.