Process Algebra and Information Flow

Peter Ryan

Abstract:
Defining and controlling information flows through a system is the fundamental issue in information security. Making precise the notion of information flow, and in particular the absence of information flow, is a remarkably subtle question, especially in the presence of non-determinism. Many formalisations have been proposed, inspired by the seminal ideas of Goguen and Meseguer with their notion of non-interference, and the information security community has yet to reach a consensus as to the "correct" definition.

In this talk we show that casting the problem in a process algebraic framework sheds light on many of the sources of controversy. In particular we argue that non-interference reduces to characterizing the equivalence of processes, itself a difficult and controversial problem in theoretical computer science. Viewing non-interference in this way also clarifies other questions such as that of compositionality.

We also discuss the role of bi-simulation in information security and argue that it corresponds to the notion of "unwinding" as developed in the security literature. Finally we discuss some generalisations to handle richer information flow policies and to deal with the problem of characterising secrecy in the presence of encrypted channels.

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Marieke Huisman
Last modified: Thu Nov 9 16:10:51 MET 2000