Louis, Lester and Pierre: Three Protocols for Location Privacy

Location privacy is of utmost concern for location-based services. It is the property that a person’s location is revealed to other entities, such as a service provider or the person’s friends, only if this release is strictly necessary and authorized by the person. We study how to achieve location privacy for a service that alerts people of nearby friends. Here, location privacy guarantees that users of the service can learn a friend’s location if and only if the friend is actually nearby. We introduce three protocols—Louis, Lester and Pierre—that provide location privacy for such a service. The key advantage of our protocols is that they are distributed and do not require a separate service provider that is aware of people’s locations. The evaluation of our sample implementation demonstrates that the protocols are sufficiently fast to be practical.