Study Of Digital Image Nonlinear Encryption Algorithms

With the rapid development of multimedia technology, the acquisition of digital image is easier. The application of digital image seeped into people's living, entertainment, work, study and so on, besides, the importance of it has gotten more and more attentions from the nation, the government, the industry and scientists as well as individuals. As the global popularity of INTERNET and wireless network, the sharing and transmission of digital image online become more fast, with which, however, people have to remain vigilant when faced with the rich information of these images, because kinds of unauthorized theft, data tampering, data deletion and virus attack to image information cause a big trouble on the use and transmission of digital image. Therefore, that how to ensure the information security of digital image becomes the hotspot in the research of image processing. This paper focuses on digital image nonlinear encryption technology and the improvement of two existing types of encryption algorithm.This paper will briefly introduce the definition of nonlinear systems and the main study object. It then will focus on the definition of chaotic systems, the basic characteristics as well as the criteria and guidelines of the study, which offers the basic knowledge for necessary nonlinear systems, especially chaotic systems in later.Then the thesis reviews the general theory and technology of digital image encryption. From the Ancient Chinese secret writing technique to the modern cryptography and password system structure, it compares the advantages and disadvantages of group password system and sequence password system, besides, it makes a brief summarize to the five aspects of password analysis. At the same time, this thesis makes a brief commentary on the common principles of digital image encryption technology and does an introduction to the requirements of measuring digital image encryption technology's performance. About the key point of this paper——nonlinear digital image encryption technology, it lists some common nonlinear digital image encryption algorithm, preparing for the later improvement and analysis of the relevant algorithms. Based on the cryptanalysis of the discrete skew tent map's encryption system that proposed by Masuda and Aihara, this paper give a spread and replacement of discrete tent map image encryption algorithm about key pair. Through experimental tests show that the encryption algorithm is simple, effective and fast, has some practical value.This paper also detailed describes the chaotic character of Arnold map, extends Arnold map to the high dimensional case. Because the image scrambling encryption security relies on matrix transformation cycles, the paper discusses T-matrix transformation cycle in depth, then put forward two types of matrix transformation based image encryption algorithm. Focus on the second image encryption algorithm feasibility analysis, statistical analysis and difference analysis, the results show that the image encryption system has high security, with some prospect.