Reasoning about Concurrency for Security Tunnels

There has been excellent progress on languages for rigorously describing key exchange protocols and techniques for proving that the network security tunnels they establish preserve confidentiality and integrity. New problems arise in describing and analyzing establishment protocols and tunnels when they are used as building blocks to achieve high-level security goals for network administrative domains. We introduce a language called the tunnel calculus and associated analysis techniques that can address functional problems arising in the concurrent establishment of tunnels. In particular, we use the tunnel calculus to explain and resolve cases where interleavings of establishment messages can lead to deadlock. Deadlock can be avoided by making unwelcome security compromises, but we prove that it can be eliminated systematically without such compromises using a concept of session to relate tunnels. Our main results are noninterference and progress theorems familiar to the concurrency community, but not previously applied to tunnel establishment protocols.