Research On Key Technologies Of Virtual Optical Image Encryption Based On Chaos

Recently, with the rapid development of communication and computer technologies, digitalinformation is being applied widely in all fields of the society. Therefore, people urgently need safe,reliable and efficient information security technology. With the natural advantages, such as largecapacity, high-speed, parallel and multi-dimensional, the optical information security technologyhas become a hot research field of information security. Digital image, with intuition, vividness andimaginable performance, has become one of the most important expression forms of information.So, the study of image encryption based on optical methods is of profound theoretical and practicalsignificance.This dissertation focuses on analysis of some typical optical encryption cryptosystems.Meanwhile, based on chaos theory and characteristic, several new image cryptosystems areproposed. The main achievements in this dissertation are as follows:(1) In view of the safety of virtual optical imaging system, an improved encryption algorithm isproposed based on chaos. In the proposed algorithm, chaotic system is introduced to generate therandom mask, and suggestions on choice of chaos and pretreatment method of chaoticpseudo-random sequences are proposed in detail. Security of the encryption system is improvedtake the advantage of special characteristics of chaotic system, such as nonlinearity,pseudo-randomness and high sensitivity to initial values. Further, in the digital environment,weighting factor is introduced at the interference process of original image and random phasemask, so as to improve the complexity of the system. Theoretical analysis and simulation resultsdemonstrate that the safety level of the encryption system combined with chaos was enhancedeffectively.(2) To solve the insensitive issue of plaintext, a security enhancement encryption algorithm ofvirtual optical imaging based on chaos is proposed. With initial value sensitivity of chaotic systems,correlating keys with plaintext are designed to improve the sensitivity of plaintext. Numericalexperiments are simulated on both gray level images and binary images to verify the effectivenessof the algorithm. Security analysis shows that the proposed algorithm is effective on resistingstatistical attacks, brute-force attacks, known plaintext and chosen plaintext attacks. Theexperimental results demonstrate that in the suggested system the security strength is enhanced.(3) Aiming at the safety of double random phase encoding system in the Fresnel domain, an improved encryption algorithm is proposed. There are many improvements in the algorithm, such asthe phase encoding in advance, the secondary encryption based on the amplitude-phase substitutionof complex value image after the double random phase encoding module and the generation of threerandom masks. These improvements make the pixel value distribution of encrypted image moreuniform and the algorithm more sensitive to the keys. Simulation is conducted on statistical analysis,correlation analysis and key sensitivity. The experimental results show that the improved algorithmhas higher security.(4) For the problems of cross-talk and low system capacity in some existing multi-imageencryption algorithms, a novel algorithm is proposed based on wavelete transform and doublerandom phase encoding. The proposed method achieves of compromise of system capacity andreconstruction quality. The idea of generating random phase masks with chaotic maps increases thesensitivity of keys while decreasing the key volume. Finally, numerical experiments show that theproposed method is effective on multiple-image encryption, extremely sensitive to keys and robust.