Design And Analysis Of Fast Encryption Algorithms For Digital Image

With the development of computing and network technology, multimedia data are used more widely. At the same time, the information security for multimedia data becomes increasingly important and cryptography is the primary method to resolve it. Contrast to texts, multimedia contents contain usually huge volume of data, which make their encryption become very slow and power-consuming. This paper focuses on the approaches to improve the speed of encryption based on the characteristics of digital images, under the condition that those approaches satisfy the security requirements. Some of the conclusions of this paper are listed as follows.First, a parallel image encryption model in space domain is proposed. It is well known that cipher block chain mode is widely used in almost all image encryption algorithms, which makes the encryption can not be implemented effectively in parallel computing platform. To fast the encryption, we proposed a parallel image encryption. Two image encryption algorithms are proposed based on this model too.Secondly, two fast image encryption algorithms are proposed based on lossless compression techniques namely quad-tree coding and MH coding. So far, the performances of all known algorithms are checked by qualitative analysis and simulations. In this paper, the encryption algorithm for MH coding is designed so that its performance can be analyzed quantitatively by using information theories.Thirdly, two fast image encryption algorithms are proposed for two most popular loss compression standards GIF and JPEG. Four encryption algorithms are proposed for JPEG standard, covering both confidentiality and degradation mode for image encryption. The performances of JPEG encryption are analyzed quantitatively too. Furthermore, a new cryptanalysis method is proposed based on image processing techniques.Fourthly, a multimedia encryption algorithm based on multiple Huffman table is crypto-analyzed. This well-known algorithm is analyzed by chosen-plaintext attack, known-plaintext attack and ciphertext-only attack respectively in this paper. It has been pointed out that this algorithm is not suitable for practical use.Fifthly, the above results are applied to video encryption, which is of greater value than image encryption. The encryption algorithms for JPEG standard are revised and applied to the encryption of MPEG. The problems and their solutions when encrypting the stream media are also discussed in detail.Finally, the dissertation is concluded. Some problems as well as further work are also given.