Research On Chaotic Image Encryption Technology Based On Control Word

Chaos phenomena is a pseudorandom course that appears in confirmed nonlinear dynamical system. It meets the requirements of the confusion and diffusion principles of cryptograph because of its course irregularity, sensitivity to the initial variables and the its range ergodicity. The study on the theory and design method of chaotic cryptographic technique will provide new clues and directions for cryptograph.Firstly, the relationships between chaotic theory and cryptograph is discussed and a comprehensive survey about the commonly used clues in designing chaotic cryptograph are given. And then the cause and essence of the degradation of the dynamic properties under finite precision are discussed. The methods for solving this problem are analyzed. On this basis, an improved method using the chaotic perturbation model is proposed and the control word is designed to enhance the randomicity and time-variation of the disturbance. And the unilateral directivity of Hash function is used to improve the security of the disturbance. The randomicity of chaotic sequence is introduced to Hash function to exert its virtue of resisting strong collision and weaken the correlations among the disturbances in different rounds. The capability of encryption sequence, which is generated through the control word, is analyzed for correlation, run-length and balance. The result indicates that the sequence has good randomicity. And then the image is reordered by combining Logistic chaotic mapping and Josephus traversing. The correlation between neighboring pixels is depressed by the diffusion of the pixels' positions. Furthermore, the values of pixels are confused by the chaotic image encryption method based on control word. And the image entropy is increased. At last, the encryption result is evaluated with entropy, the percentage of fixed points and the gray disorder degree. The results indicate that the encryption method can adequately disorder the statistics characteristics of the image.A chaotic image encryption method based on control word is designed to improve the chaotic perturbation model and solve the finite precision problem in chaotic encryption. Pseudo-random sequence with good randomicity can be generated. And this method can fully disorder the information of the image and conceal the features of original image. It is an effective encryption. method.