Abstract
Abstract: Over the last decade, opacity of discrete event systems (DES) has become a very fertile field of research. Driven by safety and privacy concerns in network communications and online services, much theoretical work has been conducted in order to design opaque systems. A system is opaque if an external observer in unable to infer a secret about the system behavior. This paper aims to review the most commonly used techniques of opacity validation for deterministic models and opacity quantification for probabilistic ones. Available complexity results are also provided. Finally, we review existing tools for opacity validation and current applications.
Highlights
Online services and network communications have become ubiquitous over the past 30 years
We focus on opacity, which characterizes whether a given ”secret” about a system behavior is hidden or not from an external observer, further called the intruder
The property of K-step strong opacity holds if the system is K-step weakly opaque and there exists a trace of the system which does not cross any secret state over the last K steps
Summary
Online services and network communications have become ubiquitous over the past 30 years. A new problem has arisen in computer science, called Information Flow It characterizes the (possibly illegal and indirect) transmission of secret data from a high level user to a low level one. We focus on opacity, which characterizes whether a given ”secret” about a system behavior is hidden or not from an external observer, further called the intruder. Opacity is a rather recent field of research It was first introduced in 2004 in computer science to analyze cryptographic protocols (Mazare (2004)). It reached the discrete event systems (DES) community with the work of Bryans et al (2005) which investigated opacity in systems modeled as Petri nets.
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