A double random phase encoding-based asymmetric cryptosystem using QZ modulation

In the existing cryptosystems such as double random phase encoding (DRPE)-based, the input image is usually modulated with the random phase mask (RPM) by multiplication. Based on the existing DRPE cryptosystems, in this paper, we propose a novel asymmetric cryptosystem based on the QZ modulation. We introduce the QZ algorithm to modulate the plain image and the random phase mask for the first time. In our cryptosystem, we take the input image and RPM as two inputs of the QZ algorithm. The outputs of the QZ algorithm include four parts: two upper quasitriangular matrices and two unitary matrices. Then the upper quasitriangular matrice corresponding to the plain image is encoded in the optical transform domain to obtain the cipher image. Meanwhile, the two unitary matrices are regarded as private keys only for decryption. Therefore, our QZ-based cryptosystem is asymmetric. Furthermore, the two RPMs are not required in the whole decryption process. The numerical results have shown the feasibility, security, and superiority of our cryptosystem. The proposed QZ-based modulation method can be applied to any other optical cryptosystem, and the encryption for color normal or medical images.