Chaotic Image Encryption Algorithm Research

With the rapid development of Internet Technology, the applications of multimedia become more and more popular. Digital image plays an important role in the field of Multimedia information and the digital image can transmit visual expression and abundant information. The Internet is an open platform. The transmission of digital images over the network is vulnerable to be stolen and tampered. As Internet security issues become more prominent, in order to protect the security of digital image transmission in the network, the most direct and effective way is to encrypt digital images.This thesis is divided into three parts:The first part researches the related theories, including Chaos Theory, Cryptography Theory, the image encryption scrambling algorithm and diffusion algorithm, evaluation on the standards about chaotic image encryption security, common chaotic encryption algorithm. This part focuses on image encryption algorithm based on Transformation Domain, image encryption algorithm based on the diffusion of image pixel values, chaotic image encryption algorithm based on DNA coding and chaotic image encryption algorithm based on Fractional Fourier transform, and gives part of the algorithm matlab simulation.The second part proposes chaotic image encryption share algorithm based on Wavelet Transform and the Chinese Remainder Theorem(CRT). On the basis of the existing chaotic image encryption algorithm and image sharing technology, it proposed chaotic image encryption based on Wavelet Transform and Sharing Algorithm of CRT. The algorithm will undergo Logistic chaotic proliferation of encryption to the original image, second wavelet decomposition, extract low-frequency coefficients of wavelet decomposition and scramble the coefficients of the low-frequency by Chebyshev chaotic system, process low-frequency coefficients and high frequency coefficients by wavelet reconstruction getting the encrypted image reconstructed, share encrypted image of wavelet reconstruction based on CRT-Sharing Technology, and get the final encrypted sub-images. The combination algorithms based on wavelet transform, chaos spreading and scrambling encryption technology and sharing technology can improve greatly the security of the encrypted image. To carry out the proposed algorithm matlab simulation experiments, and analyze the relation of adjacent pixels according to the experimental results, the results showed that key sensitivity of the proposed algorithm is strong, correlation between adjacent pixels is small and security is relatively high.The third part proposes chaotic image encryption based on Contourlet(CT) transform. CT transform is proposed on the basis of Curvelet transforms, CT transform in image processing minutiae(texture and outline) is better than the wavelet transform. The encryption principle of chaotic image encryption algorithm based on CT transform is through the original image CT transform and chaotic encryption alternately to realize image encryption. This thesis researches the steps on the algorithm implementation, the matlab algorithm simulation, and analysis on the relation of adjacent pixels according to the experimental results. The results showed that key space of the proposed algorithm is relatively large and key sensitivity is strong, so the proposed algorithm can be effective to fight against a variety of attacks.