Novel Multiple-Image Encryption Scheme Based on Coherent Beam Combining and Equal Modulus Decomposition

In our research, we propose a novel asymmetric multiple-image encryption method using a conjugate Dammann grating (CDG), which is based on the coherent beam combining (CBC) principle. The phase generated by the Dammann grating (DG) beam splitting system is processed and added to the image to be encrypted, and then, the ciphertexts and keys are generated by equal modulus decomposition (EMD). Decryption is to combine the beams through the CDG and collect the combined images in the far field. The proposed encryption scheme is flexible and thus extendable. CDG structure parameters, such as one period length of CDG, can be used as encryption key for the increase of the complexity. The Fresnel diffraction distance can also be used as an encryption key. The power of the combined beam is stronger than that of the single beam system, which is convenient for long-distance transmission and also easy to detect. Simulation results show that the proposed method is effective and efficient for asymmetric multiple-image encryption. Sensitivity analysis of CDG alignment has also been performed showing the robustness of the system. The influence of occlusion attack and noise attack on decryption are also discussed, which proves the stability of the system.

A Multi-Image Encryption with Super-Lager-Capacity Based on Spherical Diffraction and Filtering Diffusion

A multi-image encryption with super-large-capacity is proposed by using spherical diffraction and filtering diffusion. In the proposed method, initial images are processed sequentially by filtering diffusion and chaos scrambling. The images are combined into one image using XOR operation. The combined image is encrypted by improved equal modulus decomposition after spherical diffraction. There are three main contributions of the proposed method—(1) resisting phase-retrieval attack due to the asymmetry of spherical diffraction; (2) high flexibility of decrypting images individually; and (3) super-large encryption capacity of the product of image resolution and grayscale level, which is the most significant advantage. The feasibility and effectiveness of the proposed encryption are verified by numerical simulation results.