Cryptographic Approaches for Privacy Preservation in Location-Based Services: A Survey

Introduction

In the era of mobile and wireless communication technologies, recent advances in remote sensing and positioning technologies have altered the ways in which people communicate and interact with their environment. In the not-so-far future, Location-Based Services (LBS) that take into account the location information of a user, are expected to be available anywhere and anytime. Such services will be highly personalized and accessible even by resource-constrained mobile devices. A classification of the most popular services includes: a) point-of-interest or “pull” services where a user sporadically queries an LBS provider to receive a nearby point of interest (Konidala et al., 2005; Candebat et al., 2005; Hengartner, 2006; Solanas & Balleste, 2007; Kohlweiss et al., 2007;Ghinita et al., 2008; Solanas & Balleste, 2008; Hengartner, 2008; Olumofin et al., 2009; Ardagna et al., 2009; Ghinita et al., 2009); b) people-locator services, where a watcher asks the LBS provider for the location of a target (Hauser & Kabatnik, 2001; Rodden et al., 2002; Bessler & Jorns, 2005; Jorns et al., 2005, 2007; Zhong et al., 2007; Sun et al., 2009); c) notification-based or “push”' services, where location-based alerts or notifications are sent to a user (Zhu et al., 2003; Kolsch et al., 2005).

A typical scenario involves a user with a handheld device connecting through a mobile communication network to an external third party that provides an LBS service over the Internet. As with many aspects of ubiquitous computing, there is an inherent trade-off between access control and user privacy in LBS applications (Hauser & Kabatnik, 2001; Langheinrich, 2001; Rodden et al., 2002; Duckham & Kulik, 2006; Ardagna et al., 2007). On one hand the system typically needs to be protected from unauthorized access and misuse. On the other hand mobile users require the protection of their context information (e.g., location and/or identity information) against privacy adversaries (e.g., big-brother type threats, user profiling, unsolicited advertising) (Hauser & Kabatnik, 2001; Gruteser & Grunwald, 2003; Duckham & Kulik, 2006; Ardagna & Cremonini, 2009). The privacy issue is amplified by the requirement in modern telematics and location-aware applications for real-time, continuous location updates and accurate location information (e.g., traffic monitoring, asset tracking, location-based advertising, location-based payments, routing directions) (Gruteser & Liu, 2004; Kulik, 2009; Ghinita, 2009).

Recent research highlights the importance of cryptography in privacy preservation for LBSs, and presents solutions that attempt to support the (apparently) mutually exclusive requirements for access control and context privacy, while at the same time adopting conservative assumptions in order to reduce or completely remove the need for trust on system entities (e.g., the LBS provider, the network operator, or even the peer nodes). While a number of recent survey papers (Ardagna et al., 2007; Solanas et al., 2008; Ardagna & Cremonini, 2009; Kulik, 2009) cover aspects of access control and privacy, to the best of our knowledge there has been no thorough survey of the use of cryptographic techniques for privacy-preservation in LBS services.