Optimizing Pseudonym Updation for Anonymity in VANETS

A vehicle can be tracked through its locatable transmission. The broadcast by a source contains its current identity and also allows estimation of its location by a receiver. This possibility of mapping between the physical entity and the estimated location through the communication broadcast is a threat to privacy. The changes in the location due to motion and the alteration in the temporal identifiers diminish the correlation between location and physical entity. However, such a mapping can still be recognized when an actively communicating node in relative isolation is observed for a sufficient interval of time. This paper addresses the challenges in providing anonymity to a moving vehicle that continually switches identifiers. As a vehicle moves on a road, its neighbors change in accordance to its relative speed with neighboring vehicles. This change in the nature and size of the neighborhood, i.e. the entropy, the degree of the anonymity of a vehicle. It is shown that the effective entropy reduces drastically due to change in the neighbors and transmissions by vehicles. The work studies the possibility that a node may retain its anonymity by switching identities in the vicinity of other vehicles to decorrelate its location and identity relation. A heuristic that allows a vehicle to switch its identity at a time and place where the potential of anonymity preservation can be maximized by increasing the entropy is proposed. The performance of the proposed heuristic is evaluated in a highway environment with vehicle mobility and dynamic vehicle population. Simulation results indicate that updating pseudonyms in accordance to the heuristic maximizes the entropy and through it, the anonymity of a vehicle.