Deening Information Flow

In the past, several deenitions of information ow based upon process algebras have been presented. Unfortunately, these appear to have all been either too weak|failing to identify certain subtle forms of information ow|or too strong|indicating information ow when there is none. In this paper, we produce a deenition that aims to overcome these shortcomings. We base our deenition 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 deenition of information ow then is that the behaviour of one agent can have no innu-ence upon another agent's view of the system. We are able to verify that this deenition of information ow satisses certain desirable properties.