The Research Of Image Encryption Algorithm Based On Chaos Theory

With the rapid development of media technology and network, more and more digital images have been quickly and conveniently transmitted through the network, which has gradually become the main way for people to obtain information in modern society. At the same time, due to the existence of potential safety hazard, the security of images has gained wide attention. Image encryption is the first way to ensure the safety of image. Image encryption is different from text encryption due to some intrinsic properties of images such as bulky data capacity and high redundancy, which are generally difficult to handle by using traditional techniques such as International Data Encryption Algorithm (IDEA), Advanced Encryption Standard (AES), Data Encryption Standard (DES) and RSA. Chaotic cryptosystems have been studied extensively due to its ergodicity, pseudo-randomness and sensitivity to initial conditions and control parameters, which are similar to confusion and diffusion in cryptography. These properties make chaotic systems a potential choice for constructing cryptosystems especially image encryption.In this thesis, previous work, an image encryption algorithm based on chaos theory is made deep research, and a novel fast mage encryption algorithm based on wavelet transformation is designed. The main research work in this thesis focuses on the following aspects:Cryptanalysis of image encryption schemes using reverse two-dimensional chaotic map and dependent diffusion. Chosen plaintext attacks on these two algorithms are presented and some flaws of these algorithms are pointed out. For Algorithm1, chosen plaintext attack can recover the corresponding parameters instead of secret keys themselves in some cases, and simulation results demonstrate the effectiveness of this attack. The security conditions of Algorithm1against chosen plaintext attack are given. For Algorithm2, chosen plaintext attack shows that Algorithm2cannot be used because of its low security, and then an improved scheme is given out.Design of a novel lightweight image encryption algorithm based on integer wavelet transformation and chaos theory. First, have the integer wavelet transformation (IWT) for a plain image and confuse the coefficient of low frequency by chaotic sequence generated from secret key. After inverse IWT, the pixels of the image are further confused by the same chaotic sequence. To show security level of the algorithm, we analyze key space, sensitivity of secret keys and plain images and confusion and diffusion rate. Simulation results show that the algorithm has good confusion and diffusion and high efficiency.