Optical multiple-image encryption based on the chaotic structured phase masks under the illumination of a vortex beam...

A novel multiple-image encryption scheme using the nonlinear iterative phase retrieval algorithm in the gyrator transform domain under the illumination of an optical vortex beam is proposed. In order to increase the randomness, the chaotic structured phase mask based on the logistic map, Fresnel zone plate and radial Hilbert mask is proposed. With the help of two chaotic phase masks, each plain image is encoded into two phase-only masks that are considered as the private keys by using the iterative phase retrieval process in the gyrator domain. Then, the second keys of all plain images are modulated into the ciphertext, which has the stationary white noise distribution. Due to the use of the chaotic structured phase masks, the problem of axis alignment in the optical setup can easily be solved. Two private keys are directly relative to the plain images, which makes that the scheme has high resistance against various potential attacks. Moreover, the use of the vortex beam that can integrates more system parameters as the additional keys into one phase mask can improve the security level of the cryptosystem, which makes the key space enlarged widely. Simulation results are given to verify the feasibility and robustness of the proposed encryption scheme.