Abstract: With the development of spatial positioning and wireless communication technology, location based services have been promoted greatly. Users can get services by sending their position information to LI3S server. But in this manner, it is inevitable to disclosure users' locations. With witnessed concerning on privacy preservation of individuals, it becomes pressing to provide location based query services without compromising users' location privacy. Most of existing solutions adopt a framework of trusted third parties(TTPs) to serve as intermediary between user clients and LBS server. These solutions suffer from the following issues; (1) Trusted third party is difficult to find, (2)TTP is inclined to be the system's bottleneck. Hence, it results in poor query efficiency and scalabihty. This paper proposed a TTP-free based method that submits coordinates accumulation instead of the user's real location. The client submits the query with coordinate accumulation of his location to the server. Special coordinate accumulation based query process is devised at the server side,which can generate candidate answers including the just query result. Further,an effective pruning strategy is applied to improve communication cost and workload at both client and server sides. Theoretical analysis and experimental results demonstrate that our method can solve the problems mentioned earlier effectively.

Key words: Privacy preserving, Coordinates accumulation, Location privacy, Location based service