Research On Image Encryption Algorithm Based On Qi Hyperchaos

Nowadays, network and communication technology develops rapidly.In the network world, multimedia has become the main way in the process of information exchange due to the characteristics of the rich content and easy understanding. Digital image has many advantages of multimedia, so it brings human many conveniences. While at the same time it brings an opportunity to illegal attacker. Image information theft caused a lot of damage.So the image encrypted has become a particularly important question.Chaos theory has attracted the attention of the experts and scholars in various fields in recent years, especially in the field of chaotic cryptography, large numbers of chaos systems have been applied to encryption. The Logistic chaos, Lorenz chaos and Henon chaotic are low-dimensional systems. It is well known that chaotic sequence in the low-dimensional mapping was generated by simple iteration with the minority initial values and parameters. It's not safe enough to apply them into encryption field. So when choosing a chaos system, high-dimensional hyperchaos system is more and more popular with people due to the more complex dynamic behavior, more initial values and parameters.Firstly, this thesis introduces the basic chaos theory and several typical chaos and hyperchaos systems, especially the hyperchaos Qi system. Secondly, considering the degradation phenomenon after digital chaotic sequence, a new method of chaotic binary sequences are presented. It improved the distribution uniformity and randomness in chaotic sequence. Thirdly, image steganographic techniques, bit plane decomposition and Contourlet transform were used to transform the image in space domain and frequency domain. Besides MD5 value of the original images was used to control the chaos initial value in encryption every time to enhance the sensitivity of the sequence. The thesis presented two image encryption algorithms based on Qi hyperchaos. Finally, after a lot of simulation experiments, the simulation results and security analysis show that the algorithms proposed in this thesis have the characteristics of high security, ciphertext uniform distribution, strong resistance to the attack.