International Journal of Scientific Engineering and Technology ISSN : 2277-1581 Volume No. 6, Issue No. 8, PP : 313-317 1 Aug. 2017 DOI : 10.5958/2277-1581.2017.00044.4 Page 313 Hyperchaos to Secure Communications According to Synchronization by a High Gain Observer S.N. Lagmiri, M. Amghar, N. Sbiti Information and Production System ,Mohammadia School Engineering University Mohammed V Rabat - MOROCCO najoua.lagmiri@gmail.com, amghar@emi.ac.ma, sbiti@emi.ac.ma Abstract - The purpose of this article is to secure the information message using a new six order continuous hyperchaotic system that we have developed. After studying and verifying the hyperchaotic behavior and stability of this system, a chaotic masking scheme is applied to secure the information between a transmitter and a receiver. The results of the simulations confirm the high performance of the observer designed for this high order system and the proposed method leads to an almost perfect restoration of the original signal. Keyword: 7D sixorder hyperchaotic system, Equilibrium point,Lyapunov exponent,High gain observer, Chaotic masking scheme. I. INTRODUCTION Over the past few years, chaos has been increasingly used to secure communications. Compared to other methods, the additive encryption method has advantages such as good security, high dynamic storage capacity and low power, which considerably improves the security and reliability of the transmission of information. When the signal from the chaotic system is used as an encrypted signal, the message can be decrypted and attacked easily. However, the characteristics of the hyperchaotic system are more complex. Thus, for greater safety, the use of the hyperchaotic signal presents a wider application perspective [1-4]. In [5-6], we give the four dimensional system, the six dimensional system and their construction circuits, which is the basis of the construction of the hyperchaotic system of superior dimension. The objective of this article is to secure communications by using a new 7D hyperchaotic system and based on the theory of high gain observers. In this approach, once the drive system is given, the response system can be selected as an observer and the control signal must be selected so that the drive system verifies certain conditions. II. RESEARCH METHOD Consider the hyperchaotic system described by the dynamic: ݔ = ݔܣ+ (ݔ) (1) Where ݔ∈  is the state of the system, A is the n×nmatrix of the system parameters and:   →  is the nonlinear part of the system. We consider the system (1) as the drive system. As the response system, we consider the following hyperchaotic system described by the dynamic: ݕ = ݕܤ+ ݕ + ܭ() (2) Where ݕ∈  the state of the system, B is the n×nmatrix of the system parameters and :   →  is the nonlinear part of the system and  is the gain of the response system. In the nonlinear feedback control approach, we design an observer, which synchronizes the states of the drive system (1) and the response system (2) for all initial conditions (ݔ(0), ݕ(0)) ∈  . If we define the synchronization error as: e = y – x (3) Thus, the synchronization problem is essentially to find a controller  so as to stabilize the error  for all initial conditions (0) ∈  . In our case  is a high gain observer. III. HIGH GAIN OBSERVER DESIGN The problem of observer design naturally arises in a system approach, as soon as one needs unmeasured internal information from external measurements. As we know, it is almost impossible to measure all the elements of the state vector in practice (e.g., the unknown state variables, fault signals, etc). State observers are able to provide a continuous estimation of some signals which are not measured by hardware sensors. They need a mathematical model of the process and hardware measurements of some other signals. An observer is a dynamic system whose input includes the control u and the output y and whose output is an estimate of the state vector ݔ as it’s shown in figure1. Fig1: Principle of the observer We consider a general representation of the hyperchaotic system as follow:  ݔ = (ݔ) ݕ= ݔܥ (4) Where: