Co-utile P2P Anonymous Keyword Search

Web search engines have become an essential tool to find online resources. However, their use can reveal very detailed information about the interests of their users. In this chapter, we detail co-utile protocols for exchanging queries between users in an anonymous way. Specifically, by exchanging queries with other users, the query profile associated to each user is masked and approximates the average group interests. However, the query exchange protocol has a cost. To thwart free-riders (who take advantage of the protocol to mask their profile but are reluctant to help others) we employ a co-utile reputation management system. The theoretical analysis is complemented with empirical results obtained from an implementation in a simulated multi-agent environment, which illustrates how co-utility can make cooperation self-enforcing and improve the agents' welfare.