Research On The Secure Chaos-based Image Encryption Algorithm

With the rapid development of multimedia and network technologies, the storage and transmitting of the confidential digital image through network has been paid much attention. Image encryption is different from text encryption due to the intrinsic properties of images such as bulky data capacity, high redundancy and strong correlation among image pixels. Therefore, the conventional cryptographic algorithm such as DES may not be a good candidate. Chaotic maps have many desirable properties such as pseudo-randomness, ergodicity, high sensitivity to initial conditions, and these properties have tight link with the two principles of the cryptography that is confusion and diffusion. Consequently, the chaos-based encryption has suggested a new and efficient way to deal with the intractable problem of fast and highly secure image encryption.The multiple chaos-based image encryption technologies have been studied in this dissertation. To begin with, the research developments of the digital image encryption, the basic knowledge of chaos and cryptography, and the relationship between chaos and cryptography are given. Then, the knowledge about chaos-based image encryption is introduced and two image encryption algorithms are proposed. The chaos-based image encryption algorithm with external key is achieved by the pixel position permutation and pixel value scrambling for two rounds with the external keys, which are generated by the Chebyshev map. In the second chaos-based image encryption algorithm, the improved Cat map is used for pixels permutation. Some keys generated by plaintext, together with the given keys control the parameters of the Logistic chaotic map to generate chaotic sequences, which are used to substitute grey values of pixels of image. Subsequently, security analysis has been made for the proposed algorithms from the aspects of key space, key sensitivity, plaintext sensitivity, and statistical property. Simulation results and analysis show that the proposed two cryptosystems have good encryption performance and can resist brute-force attack, statistical attack, known-plaintext attack, chosen-plaintext attack and differential attack in some extent. Comparing with the first cryptosystem, the second one is considered as a better one in encryption efficiency and diffusion property.At last, the research work is concluded comprehensively in the paper, and the further research direction of the chaos-based image encryption is given.