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Location based services(LBS) are becoming increasingly important to the success and attractiveness of next generation wireless systems. However, a natural tension arises between the need for user privacy and the flexible use of location information. In this paper we present a framework to support privacy enhanced location based services. We classify the services according to several basic criteria and we propose a hierarchical key distribution method to support these services. The key idea behind the system is to hierarchically encrypt location information under different keys, and distribute the appropriate keys only to group members with the necessary permission. Four methods are proposed to deliver hierarchical location information while maintaining privacy. We propose a key tree rebalancing algorithm to maintain the re-keying performance of the group key management. Furthermore, we present a practical LBS system implementation. Hierarchical location information coding offers flexible location information access which enables a rich set of location based services. Our load tests show such a system is highly practical with good efficiency and scalability.
Date of Publication: March 2009