1. In a computer-implemented trust management system, a method for controlling access to a computing resource, the method including; obtaining a request for the computing resource; obtaining a group of certificates, each certificate expressing at least one authorization by at least one principal; identifying a set of principals associated with the certificates; initializing a state associated with each principal; evaluating a certificate as a function of the state associated with one or more of the principals; updating the state of one or more of the principals if the result of said evaluating step indicates that the state of a principal should be changed; and repeating said evaluating and updating steps until a fixpoint is reached or until a predefined principal is found to authorize the request.