Chaotic Signals and Their Use in Secure Communications

Abstract

This chapter introduces nonlinear dynamical systems known as chaotic systems and describes their suitability for application to secure communications. A nonlinear or chaotic signal is characterised by its high sensitivity to parameter and initial condition perturbations, the random like nature and broadband spectrum [1]. From a nonlinear dynamical perspective, chaotic motion is a motion which possesses at least one positive Lyapunov exponent. Furthermore, for a given set of parameters and initial conditions chaotic motion is highly deterministic. Among other applications, these properties make chaotic systems suitable for the application in secure communications [2-9]. One of the main reasons for the increased security of communication provided by the chaotic signals is their broadband nature. In many cases the broadband nature of a chaotic system allows for the effective spectral cover up of the message by the chaotic carrier. In addition, the high sensitivity of chaotic signals to parameter and initial condition perturbations often can act as the encryption keys. In this chapter, the distinguishing features of chaotic systems are first presented and some approaches, used to identify chaotic behavior, are introduced. Furthermore, the approaches and the suitability of chaotic systems to the implementation within secure communication systems are examined. Finally, some of the noise reduction techniques, used to filter chaotic communication systems, are introduced.