Image Encryption Based On Optical Transform And Chaotic Random Phase Encoding

How to protect the images from illegally tampering,coping and spreading has become an important issue in our today's world.Image encryption has become one of the hot areas of research for information security.Among numerous technologies for image encryption,optical techniques have attracted more and more attention due to their inherent advantages of high computation speed,high parallelism in applications,and so on.In this dissertation,some optical image encryption methods are proposed based on chaotic random phase encoding and optical transforms.The main works include the following aspects:(1)We compare and analyze the performance of several optical encryption systems based on the double random phase encoding,including the Fourier transform(FT)based system,the fractional Fourier transform(FrFT)based system,the Fresnel transform(FrT)based system,the Gyrator transform(GT)based system and the linear canonical transform(LCT)based system.In addition,we compare and analyze the performance of several chaotic maps when they are used to generate the random phase masks in FT-based encryption system.These chaotic maps mainly include the Logistic map,the Chebyshev map,the ICMIC map,the Tent map,the Ushiki map,the Standard map,the Lozi map and the Henon map.(2)We propose an image encryption system in fractional Fourier transform field based on the spherical wave and the chaotic single random phase encoding.In the proposed encryption system,the single random phase mask is generated by the Ushiki map.The initial values and control parameters of the Ushiki map can replace the single random phase mask to serve as the main secret keys during the encryption and decryption processes.Thus the management and transmission of the secret keys are more convenient.In addition,the orders of fractional Fourier transform and parameters of spherical wave can also serve as the additional keys which can enlarge the key space and improve the security of the system.The proposed encryption system is simple because the system contains only one random phase mask.(3)We propose an image encryption system in linear canonical transform field based on the Fresnel transform and the chaotic double random phase encoding.In the proposed encryption system,the random phase masks are generated by Standard map.The initial values and control parameters of the Standard map can replace the random phase masks to act as the main secret keys which facilitate the management and transmission of secret keys.For the linear canonical transform encryption system based on double random phase encoding,the first random phase mask placed on the input plane cannot serve as the secret key during the decryption process when the input image is an amplitude-only map.In the proposed encryption system,the introduction of the Fresnel transform can make the first random phase mask also act as the secret key which can enlarge the system's key space.In addition,three parameters of the linear canonical transform and parameters of the Fresnel transform can act as the additional keys which also enlarge the key space.Simulation results demonstrate the security and feasibility of the proposed encryption system.