Research Of Two Image Encryption Algorithms Based On Chaos Theory

In recent years, with the rapid development of communication technology, it becomes more and more frequently to exchange information through network. As a carrier of information exchange, digital image with the image, intuitive, vivid features transmits in network more and more widely, therefore how to ensure safety of image information has become the focus of researches in information security field. But image information has its own features, such as large data, high correlations, which is very different from text information. Traditional encryption algorithms are not suitable for image encryption, while natural links between chaotic systems and cryptography make people naturally put chaotic system into image encryption. Currently, a large number of image encryption algorithms based on chaos theory have been proposed, but some algorithms have been proven to be unsafe. This paper focuses on the analysis of two chaotic image encryption algorithm which are proposed recently, then points out their design flaws, and proposes decipher methods and improvement measures. Main works of this paper are as follows:①Firstly, current research status of chaotic image encryption algorithm are summarized and analyzed; Chaos theory and basic cryptography concepts and knowledge are simply introduced; Natural connection between chaos and cryptography is also pointed out. Then brief introductions for image encryption features and scrambling and diffusion methods used by general image encryption are given. Next, design principles and design steps of chaotic image cryptography system are summarized. Finally, a safety criteria standard for chaotic image encryption algorithm is defined.②This paper analyzes the chaotic image encryption algorithm proposed by Wang Jijun, and points out the design flaw in this encryption algorithm, and has deciphered the original algorithm by using chosen-plaintext attack. Aiming at the defects of the original algorithm, an improved algorithm is put forward, and a safety analysis on this improved algorithm is given.③The chaotic image encryption algorithm proposed by Fu Chong is analyzed, in which transformations of random numbers are controlled by plaintext. Analysis revealed that the design flaws in original algorithm which will cause the cipher system resistless in front of chosen-plaintext attack, and a specific attack method is given. Simultaneously, improvements on resolving shortcomings of the original algorithm have been proposed. Then security analysis on the improved algorithm has been made.