Computational Issues in Secure

| Advances in distributed systems and networking technology have made interoperation not only feasible but also increasingly popular. We deene the interoperation of secure systems and its security, and prove complexity and composability results on obtaining optimal and secure interoperation. Most problems are NP-complete even for systems with very simple access control structures, while for a general setting the problem is undecidable. Nevertheless , composability reduces complexity in that secure global interoperation can be obtained incrementally by composing secure local interoperation. We illustrate, through an application in secure database interoperation, how these theoretical results can help system designers in practice.