Phase Retrieval Algorithm For Image Encryption Based On

As a most important expression form of information in the multimedia message, digital image has the advantages of image, intuition and vividness. Especially after the problems in the large amount of image data storage and transmission being solved, it has become the mainstream of information expression nowadays and even in the following times. While the related image encryption technology has also become an important research subject in the field of information security.In recent years, because the optical information processing system can provide more degrees of freedom, such as phase, amplitude, direction of polarization, wavelength and so on, and has a high processing speed and degree of parallelism, image encryption based on the optical information processing technology has received substantial attention among scholars home and abroad.Optical image encryption technique based on phase retrieval algorithm is an effective means of image encryption. The method has been developing rapidly since its appearance and has been paid close attention by researchers. Phase retrieval algorithm technology has widespread applications, strong versatility, and require equipments with low condition. With the increasing development and popularization of computer technology, the iteration process will be more rapid and convenient. And the phase retrieval algorithms and techniques will have greater development space. So the discussion and research on image encryption technology based on phase retrieval algorithm is of great significance.In this paper, the application of phase retrieval algorithm in image encryption is firstly expounded. The iterative Fourier transform algorithm (GS algorithm),one of phase retrieval algorithm, and the GS algorithm in the Fresnel domain are discussed and simulated by computer. Then an improved GS algorithm based on interference algorithm is proposed on this basis.In order to improve the security of digital image encryption, the interference GS algorithm is combined with the bit-plane information sharing in this article. The original image is firstly decomposed into three parts, then converted into three phase information through the algorithm encryption processing respectively, next,3phase information is stored in one phase by mutual modulation principle, so as to realize the single image hierarchical encryption. Next, in order to achieve larger capacity of encryption, the image encryption algorithm based on intervention that proposed in recent years is combined with phase recovery algorithm. First convert an image into phase information using the phase recovery algorithm, then construct a complex function about the phase and the amplitude of another image, next, use the image encryption algorithm based on interference to encrypt the complex function which consists of two image information to the two phases, and thus realize the double image encryption.Another larger capacity encryption method proposed in this paper is implemented on the basis of the cascade iteration two-phase recovery algorithm in the Fresnel domain. Through iteration dual phase recovery algorithm, multiple images are encrypted sequentially to two cascaded phase to achieve the classification encryption of multiple images according to their security levels. The higher security level, the more phases are required while in decryption. That is, encrypting the image with the highest security classification require all phases. Moreover, the phase’s cascade sequence plays the role of an additional key in the process of the image decryption at all levels.