Enhancing User Privacy in Location-Based Services

The ubiquity of cellphones has lead to the introduction of location-based services, which are services tailored to the current location of cellphone users. For example, a cellphone user can retrieve a list of interesting, nearby places, or parents are notified when a child (i.e., her cellphone) leaves a boundary area. Location is a sensitive piece of information, so location-based services raise privacy concerns. In this paper, we identify and address one such concern. Namely, a company providing location-based services will become aware of the location of cellphone users. Therefore, the company can, maybe inadvertently, leak this information to unauthorized entities. We study the question whether it is possible for the company to provide its services without learning the location of cellphone users. We present an architecture that provides this property and show that the architecture is powerful enough to provide various, existing location-based services. Our architecture exploits Trusted Computing and Private Information Retrieval algorithms for implementing location-based services. With the help of Trusted Computing, we ensure that a location-based service operates as expected by a cellphone user and that location information becomes inaccessible to a location-based service upon a compromise of the service. With the help of Private Information Retrieval, we avoid that a company providing a location-based service becomes indirectly aware of the location of cellphone users by observing which of its location-specific information is being accessed. We also discuss an implementation of the proposed approach and alternative design strategies.