Research On Image Encryption Algorithm Based On Labyrinth Displacement And Chaotic Mapping Equation

Digital image encryption is the core of digital image security which has gotten the wide attention of researchers both at home and abroad. But most of conventional image encryption algorithms are based on permutation and confusion structure, there usually exists some problems such as inefficient permutation, the low coupling degree between permutation and confusion, and difficult to resist known or chosen plaintext attack. In addition, conventional image encryption algorithms, there usually encrypts the whole image or the selected rectangle regions and research about arbitrary irregular non-rectangular region encryption is lagged behind. Therefore, how to improve efficiency of encryption algorithm and how to resist known or chosen plaintext attack, and how to flexibly encrypt the selected arbitrary irregular non-rectangular key region are becoming research problems of vital importance. Conventional maze generation algorithms have a wide applications in fields of artificial intelligence, but applications in information security field is very rare. Maze generation algorithms can efficiently generate permutations in any selected irregular closed connected region. So these methods can encrypt any selected irregular key image region efficiently. Based on this, this paper combines DFS and BFS maze generation algorithms with chaos theory to research the image encryption algorithm. The finished research works are followings:1) To solve problems such as inefficient permutation and difficult to resist known or chosen plaintext attack, an image encryption algorithm based on maze permutation and Logistic mapping was proposed, where Depth First Search(DFS) maze permutation was used to product permutation efficiently. In order to resist known or chosen plaintext attack, the plaintext image Message Digest Algorithm 5(MD5) digest was bound with the user key to generate maze starting coordinates,Logistic chaotic map parameters and initial values which drive Logistic maps to generate random numbers. These random numbers were used to determine maze node probing directions and participate in image confusion to make all encryption stages tight coupled with the plaintext image.2) To solve the problem which conventional image encryption algorithms can’t focus on the encryption of the irregular region which contains main key information in the image, a background and foreground separated image encryption algorithm combined with BFS maze permutation and OCML spatiotemporal chaotic map is proposed. To get the key irregular region of image, the plaintext image is divided into foreground and background regions by using mean-shift algorithm and the corresponding chain codes of foreground region’s contour is extracted by using contour tracing algorithm which is used as the contour key, which can effectively guarantee the irregular region image information security; To enhance the non-rectangle encryption capability, conventional BFS maze generation algorithm is extended to make it permute pixels in irregular foreground region. In order to resist known or chosen plaintext attack, both plaintext image’s and contour key’s SHA-1 values are bound with user key to drive the OCML spatiotemporal chaos mapping to permute image foreground with extend BFS maze permutation algorithm and confuse the whole image pixels, so that the proposed encryption algorithm can guarantee the key irregular region image security and resist known or chosen plaintext attack effectively.