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Secret speech transmission using a high order sliding mode observer

This paper proposes a chaos-based communication scheme which transmits a secret speech signal. To recover the states of the transmitter and the unknown message, the receiver uses a high order sliding mode observer. Its input is one of the states of the transmitter. The control parameters of the observer constitute the secret key of the transmission. The main aspect in which the present work differs from already known algorithms using sliding-mode observers to recover secret messages embedded in the dynamics of chaotic systems is the nature of the hidden information it applies to. To the knowledge of the authors, no work has yet applied this type of reconstruction method — sliding mode estimators, to recover secret speech signals, but only text and image, included in the evolution of chaotic systems. Numerical simulations are used to find the appropriate parameters for the designed encryption and deciphering. Efficiency and future improvement methods are discussed.