New important emerging business paradigms, such as ldquoservice virtualizationrdquo can be made easy and convenient by the use of P2P systems. In these paradigms, often the owners of the services are different (and independent) from the owners of the resources used to offer such services. In comparison to centralized servers, P2P systems can conveniently offer higher availability and more bandwidth as they harness the computing and network resources of thousands of hosts in a decentralized fashion. Despite these useful features and their success in the research community, P2P systems are still not very popular in the business world. The main reason for such a skepticism is their lack of proper security. In this paper, we address this issue ...