Persistent Stochastic Non-Interference

TL;DR

This paper introduces Persistent Stochastic Non-Interference (PSNI), a security property for stochastic processes modeled in PEPA, ensuring that observable steady-state behaviors are unaffected by high-level interactions.

Contribution

It defines PSNI within PEPA, providing two characterization methods: a bisimulation-like check and unwinding conditions, advancing formal security analysis of stochastic systems.

Findings

PSNI guarantees independence of observable states from high-level interactions.

Two characterization methods for PSNI: bisimulation and unwinding conditions.

Ensures steady-state probabilities are unaffected by high-level actions.

Abstract

In this paper we present an information flow security property for stochastic, cooperating, processes expressed as terms of the Performance Evaluation Process Algebra (PEPA). We introduce the notion of Persistent Stochastic Non-Interference (PSNI) based on the idea that every state reachable by a process satisfies a basic Stochastic Non-Interference (SNI) property. The structural operational semantics of PEPA allows us to give two characterizations of PSNI: the first involves a single bisimulation-like equivalence check, while the second is formulated in terms of unwinding conditions. The observation equivalence at the base of our definition relies on the notion of lumpability and ensures that, for a secure process P, the steady state probability of observing the system being in a specific state P' is independent from its possible high level interactions.