Privacy-Preserving Location-based Services for Mobile Users in Wireless Networks

Mobility is key to personal freedom. With the increasing availability of mobile devices, many providers begin to offer location-based services. Although these services greatly enrich our mobility experiences, with them also comes the privacy concerns, as a location-based service provider now can continuously track the location of a user. This tracking may allow unauthorized access and cause serious consequences. Although a few solutions have been proposed to address the privacy concerns in various aspects, there has not been any comprehensive study of the problem; furthermore, most of the existing solutions require that a user trust a third party such as a location server. In this paper, we investigate privacy-preserving locationbased services for the three components involved in providing location-based services: the location-based service component, the localization component, and the communications component. The focus of our study is on the location-based service component, but we also take the other two components into consideration. We identify two major types of location-based services and present novel designs to implement them without using a trusted server. Specifically, we first identify the general locationnotification service, whose goal is to transfer location information of users to authorized entities. We design a security protocol to implement the service without trusting the location server. Thus our design uses the efficiency of a location server but does not suffer from associated privacy issues. Next, we investigate the design of an even more challenging location-based service: a location service whose goal is not transfering user location information but computing an outcome that is a function of user locations. We use dating service as an example and illustrate that an efficient protocol can be built such that no extra information about user locations is revealed during the service. For the localization component, we present an impossibility result and propose a privacy preserving localization technique based on directed signals. For the communications component, we propose an anonymous communication protocol. Our extensive evaluations show that our protocols have low overheads and are suitable for Sheng Zhong is supported in part by NSF grant ANI-0207399. Yang Richard Yang is supported in part by NSF grants ANI-0207399 and ANI-0238038. personal mobile devices.