Study On The Methods Of Optical Image Encryption Based On Double Random Phase Encoding

Since the 21 st century, the rapid development and popularization of the Internet and digital communication technology have brought great convenience to people’s life and work. But at the same time, how to ensure the security of network information has also become a issue not to be ignored. As the most common form of expression of information in the Internet, the security of digital image also has attracted widespread attention, and image encryption technology is a key technique to ensure the safety of digital image.Optical image encryption technology, compared with the past computer image encryption technology, has many inherent advantages, such as large capacity, fast encryption speed,multi-channel parallel transmission, multi-key dimension and so on. All these advantages make the method of optical image encryption faster and more efficient.Although the research in the field of optical information security has gained significant progress at home and abroad, it still located in the stage of exploration and experimentation, and we need to carry out a more systematic and in-depth research. In this paper, we systematically study the optical image encryption algorithm which based on the double random phase encoding(DRPE) through theoretical analysis combined with computer simulation, analyze several typical optical image encryption systems deeply,and explore encryption scheme which can simultaneously enhance the security and robustness of cryptosystem.The main contents of this paper include the following four aspects:1. The overview of relevant concepts and basic theory of traditional cryptography is given, and the basic theoretical knowledge related to optical image encryption are introduced, so that we can master the overall basic content of optical image encryption, and lay a theoretical foundation for the study of the optical image encryption system.2. Four typical optical encryption systems are analyzed deeply: DRPE system based on Fourier transform, DRPE system based on Fresnel diffraction, optical encryption system based on the principle of interference and asymmetric optical encryption system based on phase-truncation Fourier transform(PTFT). The encryption and decryption algorithms of each system are elaborated, and the feasibility and security of each system are simulated with particular emphasis through MATLAB simulation software. Meanwhile,the simulation results are analyzed in detail, and improved analysis of the deficiency of these systems is carried out.3. The asymmetric optical encryption system based on PTFT is vulnerable to the special attack based on iterative amplitude phase retrieval(APR) algorithm. To solve this issue, a novel nonlinear optical image encryption system based on phase truncation Fresnel diffraction(PTFD) is proposed in this paper. In this proposed scheme, the two private keys generated by a random amplitude mask(RAM) and the two public keys are used as encryption keys. The nonlinear characteristic of the proposed scheme allows it to resist chosen-ciphertext attack(CCA), chosen-plaintext attack(CPA) and the known-plaintext attack(KPA), and it is impracticable for the attacker to decipher the cryptosystem by iterative APR algorithm due to lack of enough constraints. The encryption and decryption algorithm of the system is analyzed theoretically, and the feasibility and security of this system are verified by computer simulation.4. The quik response(QR) code which has strong capacity of error correction is introduced into the proposed cryptosystem, which makes the system with strong robustness.The plaintext is transformed into a QR code and then the code is encrypted into a real-valued noise-like ciphertext by employing the PTFD-based cryptosystem. The noisy QR code can be retrieved after decryption, and noise-free original plaintext can be restored by scanning the retrieved QR code with corresponding applications in a smartphone or a tablet. Simulation results show that even if the ciphertext is disturbed by noise or part of its information is lost, the initial plaintext image still can be retrieved without any distortion.