Optical encryption scheme for multiple color images using complete trinary tree structure

•The proposed encryption scheme can make different color image have different encryption and decryption paths, and can realize an authority management with high security among multiple users.•The proposed encryption scheme possesses high encryption efficiency and high robustness against various attacks.•The proposed encryption scheme can encrypt multiple color images into a real-value cipher image, which can be recorded, stored and transmitted conveniently.•The proposed encryption scheme can be directly applied to encrypt multiple gray images.

We propose an optical encryption scheme for multiple color images based on the complete trinary tree structure. In the proposed encryption scheme, the encryption modules (EMs) are taken as branch nodes, and the color components of plain images are input as leaf nodes. In each EM which consists of phase truncated Fresnel transforms and random amplitude-phase masks, three input images are subsequently encoded into a complex function and finally encrypted to a real-value image. The proposed encryption scheme can encrypt multiple color images into a real-value grayscale cipher image, and make different color images have different encryption and decryption paths. By the proposed encryption scheme, we can realize an authority management with high security among multiple users. In addition, the proposed scheme possesses the advantages such as high robustness against various attacks and high encryption efficiency. Moreover, as the number of plain color images increases, high quality of the decrypted color images can still be maintained. Extensive simulation results have shown the performance of the proposed scheme. The proposed scheme can also be directly extended to encrypt multiple gray images.