Research And Analysis Of Self-adaptive Image Encryption Algorithm Based On Hash

With the rapid development of Internet and continuous improving of computer processing capacity, the security of images has become a crucial issue. In recent years, images are more and more widely used on the Internet. Some images involving individual privacy, commercial confidentiality and national security, should be transmitted secretly. In comparison to the text, the image is characteristic of a huge amount of data, high redundancy and high relationship among pixels. It is both resource and time consuming for image encryption using traditional text encryption algorithms. Therefore, the image encryption has captured more and more attention, and it is of great academic and practical significance to study it.The work of this thesis are listed as follows.First, the basic overview of the cryptography and image encryption is introduced, including cryptosystems, cryptanalysis, the digital representation and the characteristics of image, and the performance indicators as well as encryption technique. Furthermore, the advantages of hash function and DCT-FFT nested algorithm is presented. All the presentations lay a theoretical foundation for the following study.Second, a hash-based image encryption algorithm is introduced in detail, and the advantages and disadvantages of it are analysed. Because the characteristic of diffusion is too poor to resist Chosen Plaintext Attack and Known Plaintext Attack, a feasible attack process is proposed.Next, according to the advantages of self-adaptive algorithm, an improved algorithm based on self-adaptive algorithm is presented. First, the image is divided into two parts. The information of one part is used to encrypt the other part; then, the information of the encrypted part is used to encrypt the plain part. After that, the two encrypted parts are combined together. The improved encryption mode has a good diffusion and it can resist Chosen Plaintext Attack and Known Plaintext Attack. In addition, the classic cat map is adopted to enhance the confusion effect.Finally, the results of simulation experiments and security analyses indicate that the encryption system combined with self-adaptive algorithm has a large key space, a high sensitivity to the secret key and the plain image, and good diffusion properties. At the same time, it can resist plaintext attacks strongly.