Location Privacy via Geo-Indistinguishability

In this paper we report on the ongoing research of our team Comète on location privacy. In particular, we focus on the problem of protecting the privacy of the user when dealing with location-based services. The starting point of our approach is the principle of geo-indistinguishability, a formal notion of privacy that protects the user's exact location, while allowing approximate information --- typically needed to obtain a certain desired service --- to be released. Then, we discuss the problem that raise in the case of traces, when the user makes consecutive uses of the location based system, while moving along a path: since the points of a trace are correlated, a simple repetition of the mechanism would cause a rapid decrease of the level of privacy. We then show a method to limit such degradation, based on the idea of predicting a point from previously reported points, instead of generating a new noisy point. Finally, we discuss a method to make our mechanism more flexible over space: we start from the observation that space is not uniform from the point of view of location hiding, and we propose an approach to adapt the level of privacy to each zone.