Research On The Algorithm Of Optical Chaotic Encryption Based On Phase-shifting Digital Holography And Image Scrambling

As a new encryption method, optical encryption gradually becomes a research hotspot by virtueof its high speed, inherent parallelism, multi-dimensional, high-capacity and other advantages.The thesis firstly summarizes the information security, including cryptography and informationhiding technique, and analyzes the characteristics of optical encryption system. After expoundingthe theoretical basis of the optical encryption, it introduces several kinds of typical opticalencryption algorithm. By simulation with MATLAB platform, it confirms that replacing randomphase mask with random amplitude mask and replacing Fourier transform with Fresnel transformcan not only damage the linearity of the system but also promote the key space, so as to enhance thesecurity of the system. Moreover, it also verifies that image preprocessing with the pixel scramblingbased on logistic map and pure phase encoding method can enhance the security and anti-noiserobustness of the encryption system.This thesis proposes an algorithm of optical chaotic encryption based on phase-shifting digitalholography and image scrambling. The encryption algorithm is an improvement based on thecoding system which is put forward by Tajahuerce. The basic structure of the encryption system is aMach-Zender interferometer. The to-be encrypted image is firstly preprocessed and then disturbedby random amplitude mask and random phase mask combining with double Fresnel diffractiontransforms. Four holograms resulted from the interference of object wave in one arm and referencewave in the other arm through phase delay plates are scrambles randomly.It uses the PSNR(Peak Signal to Noise Ratio) and IF(Image Fidelity) to evaluate theperformance of the proposed algorithm. The simulation results prove its validity, security androbustness. The proposed algorithm has a huge key space and the ability to resist violent attacks.Moreover, the sensitivity of each key is improved on the basis of the original scheme. All of theseenhance the security of the encryption system. Experimental results show that the encryption systemhas strong robustness in signal interference and signal loss.