  Participatory Sensing is an emerging computing paradigm that enables the
distributed collection of data by self-selected participants. It allows the
increasing number of mobile phone users to share local knowledge acquired by
their sensor-equipped devices, e.g., to monitor temperature, pollution level or
consumer pricing information. While research initiatives and prototypes
proliferate, their real-world impact is often bounded to comprehensive user
participation. If users have no incentive, or feel that their privacy might be
endangered, it is likely that they will not participate. In this article, we
focus on privacy protection in Participatory Sensing and introduce a suitable
privacy-enhanced infrastructure. First, we provide a set of definitions of
privacy requirements for both data producers (i.e., users providing sensed
information) and consumers (i.e., applications accessing the data). Then, we
propose an efficient solution designed for mobile phone users, which incurs
very low overhead. Finally, we discuss a number of open problems and possible
research directions.
