The Research Of Chaotic Image Encryption Algorithm Based On Spatial Domain

In recent years, with the high-speed promotion of network bandwidth and performance ability of computer, people are more inclined to share and spread through the network digital images, which brings the enormous convenience to us. But at the same time, it enhances further requirements of the security and secrecy work of image information. Therefore, for many researchers, how to keep information security of the image is becoming a hot topic. The traditional encryption standard techniques are applied directly to image encryption has some disadvantages, and in view of own characteristics of the digital image, the domestic and overseas scholars present many image encryption schemes. In these schemes, the image encryption scheme based on chaotic theory and wavelet transform theory that shows good characteristics of encryption.According to the good characteristics of hyper-chaos sequences and lifting wavelet transform, the safety and efficiency of encryption for digital image are improved greatly. So this encryption effect will be better.On the basis of prior researches, image encryption is studied further by using of hyper-chaos theory and lifting wavelet theory in spatial domain. The achievements can be summarized into the following two aspects:(1) The study of a digital image encryption algorithm based on bit plane scrambling and multiple chaotic systems combination. Firstly, we generate a group of pseudo random integer sequences by using two-dimensional Logistic map and four-dimensional Chen hyper-chaos system with complex dynamic characteristics respectively. Secondly, choosing one group of sequences as parameters and iteration times of generalized Arnold map, the other group of sequences as swapping and scrambling sequences. Then grayscale image is decomposed into bit-plane images, each bit-plane image is shuffled by using generalized Arnold map, swapping and scrambling sequences separately. Finally, the scrambled gray image is reconstructed from those shuffled bit-plane images, which achieves the digital image encryption. By the simulation of Matlab, the experimental results demonstrate that the proposed image encryption algorithm is not only improved the degradation problems of the single chaos mapping, but also effectively improved statistical properties of the known plaintext and the ability of resisting known plaintext and choosing plaintext attacks, and it has a large key space and very sensitivity with respect to the secret key and original image.(2) The study of the hyperchaotic image encryption scheme based on lifting wavelet transforms. Firstly, the image is transformed by using the integer lifting wavelet, we can get the coefficients of low-frequency which are adjusted according to a self-adaptive permutation algorithm. Secondly, according to the pretreated chaotic sequences which are generated by two 2D hyperchaotic systems, we construct dual hybrid feedback. Finally, the image after the wavelet reconstruction is encrypted by dual hybrid feedback systems. The experimental results demonstrate that the encryption scheme can avoid the deficiency which the image after the traditional wavelet transform can not accurately reconstruct as it is. Moreover, it can overcome the deficiency that the confidentiality of single low-dimensional chaotic system is not high, which has better improvement on both the key space and the resistance of various attacks than other schemes, and possesses high security and practicability.