A Study Of Color Image Encryption Algorithm Based On Chaos Theory

With the rapid development of information technology, Multi-media information has become an indispensable part in people’s daily life. At the same time, it also brought serious problems of information security. As an important part of the multi-media information, digital images have a strong information redundancy and high pixel correlation characteristics. Digital images have a wide range of applications in satellite images, military facilities, remote medical diagnosis images, crime scene photos, and other fields. Therefore digital image in the process of storage and transport security guarantees become an important research topic. And conventional encryption algorithm does not apply to image encryption. As we known, chaos system is extremely sensitive to the initial value, and is able to generate abundant random sequence. The properties of chaos make chaos system suitable to the two significant principles of encryption, which are confusion and diffusion. Thus researchers combine chaos and cryptography, and come up with a theory of chaotic cryptography. For this reason, digital image encryption technology combined with chaotic cryptography can construct high efficiency and secure encryption design.To begin with, research background and research status have been briefly introduced. And then, this article described the basis of chaos theory and cryptography. Afterwards, the article simulated and analyzed several typical chaos systems, and focused on analyzing the connection between chaos and cryptography and the advantages of chaos used in cryptography. Image encryption algorithms in existence were summarized in advance. Besides, the guiding principles for image encryption based on chaos were proposed.In this thesis, two encryption schemes were proposed using the structure of permutation-diffusion for the problem of color image encryption based on chaos. The two schemes are a color image encryption algorithm based on coupled chaotic maps and a self-adaptive color image encryption algorithm based on chaos. The first scheme proposed a new permutation method using chaotic sequence to select the sort. Pseudo-random arrays and reversible integer matrixes are generated by coupled chaotic maps, and the matrix multiplication and exclusive OR operations are used in diffusion part. In the second algorithm, the base components of the three-color are permutated by Chen’s system and in diffusion part, the scheme uses self-adaptive encryption algorithm to complete the encryption.Finally, dozens of experiments have been done to certificate the security of two proposed algorithms.Through the results of key space analysis, key sensitivity analysis, adjacent pixels correlation analysis, statistical characteristics analysis and differential attack analysis, the two encryption schemes can resist these kinds of attacks and have safety and reliability. In summary, the study of the subject of color image encryption algorithm based on chaos has important theoretical and practical significance.