Asymmetric Color Image Cryptosystem Using Detour Cylindrical-Diffraction and Phase Reservation & Truncation

Recently, color image encryption has attracted extensive research interests. However, challenging issues, such as linearity, complex-valued output, and information disclosure, remain. To address these issues, we propose an asymmetric color image cryptosystem by using detour cylindrical-diffraction and phase reservation and truncation (PRT). In this cryptosystem, a complex combination of two color components of a color image is encrypted through a detour cylindrical-diffraction process with double random phase masks, which are located on the input and intermediate surfaces. The diffraction distribution of complex amplitude is separated into phase and amplitude parts using PRT. The phase parts are saved as asymmetric keys, while the two amplitude parts are combined with another color component and saved as ciphertext, respectively. The asymmetric detour cylindrical-diffraction destroys the linearity of the proposed cryptosystem and solves the issue of information disclosure. Meanwhile, the PRT ensures that the cryptosystem is asymmetric and has amplitude-only output, which further destroys the linearity. Therefore, the three issues in color image encryption are resolved. Numerical simulation results validate the effectiveness and flexibility of the proposed cryptosystem.