Hybrid attack free optical cryptosystem based on two random masks and lower upper decomposition with partial pivoting

We propose a novel asymmetric optical image encryption scheme using two random phase masks (RPMs) and lower upper decomposition with partial pivoting (LUDP), in which the encryption process is different from the decryption process and encryption keys are also different from decryption keys. In the proposed algorithm, LUDP is a matrix decomposition operation, which is used to replace the phase-truncated (PT) operation in the encryption path of conventional optical image encryption schemes based on phase-truncated Fourier transform (PTFT). In the proposed decryption process, the original image is completely retrieved by an optical architecture based on the modified 4f system with two private keys generated in the encryption process. Compared to conventional PTFT-based cryptosystems which are vulnerable to special attacks based on the amplitude-phase retrieval technique, our proposed algorithm is immune to the iterative attack and has a higher security level. Numerical simulations are presented to demonstrate the feasibility and robustness of the proposed encryption scheme.