Reduction of Dynamical Degradation in Chaotic Image Encryption System by Coupling Multiple Chaotic Maps and Perturbation

Secure multimedia communication presents new challenges that are difficult to handle by using the currently adopted encryption methods. Chaotic encryption is a new direction of cryptography. It uses chaotic system properties such as sensitivity to initial condition and loss of information. In order to reach higher performance, these methods take advantage of the more and more complex behavior of chaos. Since digital computers deal with finite precision, when chaos is realized in digital computers, generation of pure random numbers (true chaotic sequence) is almost impossible. In this paper, real numbers have been generated from a chaotic map and are then converted into 8 bit and 32 bit numbers to accomplish image encryption and decryption. It is reported that encryption security becomes system specific and if an 8 bit encryption system is designed with increased security level and minimised dynamical degradation, the algorithm will get a wide area of application (e.g. 8 bit systems). The proposed 8 bit algorithm uses two tent maps to enhance the security level. It is also shown that the new algorithm increases the cryptanalytic complexity to the known plaintext attack. A comparison in terms of some well defined metrics is also done.