The growth of Internet has extended the scope of software applications, leading to network-based architectures. The main characteristic of these architectures is that they restrict the communication between remote components to message passing. Service-oriented computing is a solution to organise the exchange of messages in a network-based architecture, by using services as primitive components. Thus, each component can be a client, a server or both. Since a service-oriented application typically spans a number of different organizations, its executions is subject to stringent security requirements. That is the reason why the partners involved generally define a contract at the global level in order to enforce some security policy. From the contract, each partner deduces by projection a specification of the security functionalities that it must locally implement. Of course, in order to be useful, all these projections must ensure that the local functionalities effectively collaborate to realize the global contract.