Stateful Protocol Composition (Extended Version)

We prove a parallel compositionality result for protocols with a shared mutable state, i.e., stateful protocols. For protocols satisfying certain compositionality conditions our result shows that analyzing the component protocols in isolation is sufficient to prove security of the more complex composition. Our main contribution is an extension of the compositionality paradigm to stateful protocols where participants main- tain shared databases. We also support declassification of shared secrets. As a final contribution we prove the core of our result in Isabelle/HOL, providing a strong correctness guarantee of our proofs.