Strand Spaces with Choice via a Process Algebra Semantics

Roles in cryptographic protocols do not always have a linear execution, but may include choice points causing the protocol to continue along different paths. In this paper we address problem of representing strand space model protocols, particularly as it is used Maude-NPA analysis tool. To achieve goal, develop and give formal semantics process algebra for that supports rich taxonomy primitives composing spaces. our taxonomy, deterministic non-deterministic choices are broken down further. Non-deterministic can be either explicit, i.e., one two paths chosen, or implicit, value variable chosen non-deterministically. Likewise, an explicit if-then-else choice, path if predicate satisfied, while other not, implicit execution continues only certain pattern matched. We identified class which includes finite branching some cases infinite branching, paper. provide bisimulation result between expected forwards new original symbolic backwards preserves attack reachability. fully integrated syntax its transformation into strands Maude-NPA. illustrate expressive power naturalness with various examples, show how effectively analysis. This allows users write from now on using syntax, more convenient expressing than specified implicitly, via identical until point.