Location Privacy and Attacker Knowledge: Who Are We Fighting against?

Location privacy research has received wide attention in the past few years owing to the growing popularity of location-based applications, and the skepticism thereof on the collection of location information. A large section of this research is directed towards mechanisms based on location obfuscation. The primary motivation for this engagement comes from the relatively well researched area of database privacy. Researchers in this sibling domain have indicated multiple times that any notion of privacy is incomplete without explicit statements on the capabilities of an attacker. The question we ask in the context of location privacy is whether the attacker we are fighting against exists or not. In this paper, we provide a classification of attacker knowledge, and explore what implication does a certain form of knowledge has on location privacy. We argue that the use of cloaking regions can adversely impact the preservation of privacy in the presence of approximate location knowledge, and demonstrate how perturbation based mechanisms can instead be useful.