SPOIL: Practical location privacy for location based services

This paper presents SPOIL (Shifted POI List), a new method to achieve location privacy for map services on smartphones. Using SPOIL, users can query routes from POI (Point of Interests) A to POI B, while not revealing the locations of A and B to the map server. Different from previous works, SPOIL is transparent to existing map services, assume no trusted third party, and more efficient for smartphones. The basic idea is simple: the client (i.e., smartphone) shifts user-intended POIs to some neighboring POIs instead, and query the map server using the shifted POIs. By carefully selecting places for shifting, we ensure: (1) privacy: on observing the route query, it is difficult for an adversary to identify the user-intended endpoints. (2) usability: the returned route is very similar to the intended one, thus giving useful directions for the user; To make SPOIL efficient for smartphones, we let clients retrieve candidate places for shifting from an additional server, instead of storing all the places and computing nearest ones locally. We implement SPOIL as an Android application, and evaluate it with real query traces. Experimental results show that SPOIL strikes a good balance among privacy, usability and efficiency.