The complexity and composability of secure interoperation

Advances in distributed systems and networking technology have made interoperation not only feasible but also increasingly popular. We deene the interop-eration 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. Nevertheless, composability reduces complexity in that secure global interoperation can be obtained incrementally by composing secure local in-teroperation. We illustrate, through an application, how these theoretical results can help system designers in practice.