Semantic models for information flow

Abstract

In the past, several definitions of information flow have been presented, based upon process algebras. Unfortunately, all these appear to be either too weak—failing to identify certain subtle forms of information flow or too strong—indicating information flow when there is none. In this paper, we produce a definition that aims to overcome these shortcomings. We base our definition upon an operational model of CSP that reasons about the ways in which nondeterministic choices can be resolved, and so is more discriminating than previous models. Our definition of information flow is then that the behaviour of one agent can have some influence upon another agent's view of the system. This definition gives the expected results on all thought experiments tried to date, and also satisfies certain desirable properties.