Encryption Technology, Based On Calculation Of The Optical Image Of The Hologram And The Iterative Fourier Transform Algorithm

With the rapid development of Internet, data encryption, anti-counterfeiting application and information security are becoming more and more important. Compare with the traditional computer and electrical systems, optical technology for information security have received increasing interests in the past decade because of its distinct advantages: (1) Optical systems have an inherent capability for parallel processing, that is, rapid transmission of information. (2) Information can be hidden in any of several freedoms, such as phase, wavelength, spatial frequency or polarization, that is, optical systems have excellent capability for encoding information. Many optical systems have been proposed and used in verification and data encryption. Among those architectures the most attractive one is the so-called double random phase encoding technique proposed by B. Javidi and coworkers in 1995.The aim of this thesis is to give a comprehensive review on the double random phase encoding technique, and then propose and numerically simulate some novel methods and techniques of optical image encryption, which are based on the Iterative Fourier Transform Algorithm (IFTA), binary Fourier transform computer-generated hologram and pixel scrambling technology. The main research work in this thesis includes the following:(1) This thesis reviews the progress of the optical image encryption, and gives a general introduction about optical scalar diffraction, optical Fourier transform, design methods for diffractive optics element and the theory of the Computer Generated Hologram.(2) The Iterative Fourier Transform Algorithm, 4/system, joint transform correlator, and the optical image encryption based on these techniques are introduced in detail, and the computer simulations are given.(3) A new method of optical image encryption with binary Fourier transform computer-generated hologram (CGH) and pixel scrambling technology is presented. Because the encrypted image is a binary image, so it is easy to be fabricated and robust against noise and distortion. Computer simulation and experimental results are given to verify the feasibility of this method and its robustness against occlusion and additional noise.(4) The method of the multiple-random-phase by use of forward iterative phase retrieval algorithm for optical image encryption is described and demonstrated with computer simulation experiments. The convergent speed of the method is significantly increased and the decrypted image is similar to the target image. The errors caused by the quantization of phase masks are decreased with the proposed method. The relationships between the numbers of phase masks and quantized phase levels are also discussed by the results of computer simulation. In addition, with more phase keys, the security and secrecy of image are greatly increased. Computer simulations are demonstrated to verify the proposed method.(5) A novel approach - multiple phase encoding for hierarchical security by use of a 4f optical system and iterative Fourier transform algorithm is presented, which is based on the methodology of virtual optics. Two or more phase masks produced by multiple iterative Fourier transform algorithm are used in this hierarchical security system, in which different target images can be retrieved by use of different numbers of phase masks. In addition to the application of hierarchical data encryption, the system can also provide the verification of the identity of the persons legally wishing to access it. Simulation results indicate that our proposed system is effective and efficient.