Time-synchronised nonlinear active controller for secure image communication using nonidentical chaotic systems

This paper proposes a time-synchronised nonlinear active controller designed for synchronisation between nonidentical chaotic systems so that all the error states converge to zero simultaneously, and its Lyapunov stability analysis is given. Two-stage image encryption of a colour image is proposed based on the combination of the chaotic oscillator and diffusion algorithm. The designed diffusion algorithm is applied by shuffling the clockwise rotation of the image pixels. At the transmitter side, the Lorenz chaotic oscillator is used to generate the key for the image encryption process. The proposed controller is used at the receiver side to synchronise the Rössler chaotic oscillators at the receiver side with the Lorenz chaotic oscillator at the transmitter side. After synchronisation, the Rössler chaotic oscillator is used to generate the same key at the receiver side for the image decryption process. The ratio-persistent nature of the proposed controller converges all the error states to zero simultaneously. The fact that the encrypted image is perfectly compatible with the received image within synchronised settling time further demonstrates the effectiveness. Finally, the simulation results verify the effectiveness of the proposed time-synchronised controller through both theoretical and practical verification of picture encryption and decryption procedures.