CO-PRIVACY has a paradigm-changing vision of double sustainability: on the one hand, privacy preservation is essential to make the information society sustainable just as environment preservation is essential to make the physical world sustainable; on the other hand, privacy preservation itself should be sustainable, and be achieved effortlessly as the result of rational co-operation rather than as an expensive legal requirement.

We introduce the novel concept of coprivacy or co-operative privacy: a protocol is coprivate if the best option for a player to preserve her privacy is to help another player in preserving his privacy. Coprivacy makes an individual's privacy preservation a goal that rationally interests other individuals: it is a matter of helping oneself by helping someone else. We formally define coprivacy in game-theoretic terms, specifically, as pure strategy Nash equilibria. We then extend the concept to: i) general coprivacy, where a helping player's utility (i.e. interest) may include gaining functionality and security in addition to privacy preservation; and ii) mixed coprivacy, where mixed strategies and mixed Nash equilibria are allowed with some restrictions.

The theoretical objective of CO-PRIVACY is to develop the theory of coprivacy, general coprivacy and mixed coprivacy to characterize the classes of problems that can be solved using coprivate protocols, generally coprivate protocols and mixedly coprivate protocols, respectively. Proposing suitable utility functions to reflect the rational interests of players is also an important theoretical challenge.

Practical objectives are to devise coprivate protocols to make privacy sustainable in at least a few hot applications: communication in vehicular ad hoc networks-VANETs (subproject CO-PRIVACY/V-PRIVACY), peer-to-peer private information retrieval (subproject CO-PRIVACY/DBPRIVACY) and controlled content broadcast in on-line social networks (subproject CO-PRIVACY/OSNPRIVACY). For each of those applications, we plan underpinning theoretical work to design new cryptographic protocols allowing gradual privacy that can be traded off against functionality and security. Enabling such a trade-off between players is a precondition to find coprivate protocols.