Asymmetric optical cryptosystem based on modulus decomposition in Fresnel domain

We propose a scheme of attacking the pure phase asymmetric optical cryptosystem based on equal modulus decomposition (EMD) method. The cryptosystem is proven to be vulnerable to our modified iterative algorithm, even though the applying of phase encoding can reduce the constrain conditions. Furthermore, since that the improvement of system space asymmetry and key variety is an effective way to further enhance the security, we have proposed an asymmetric cryptosystem based on modulus decomposition in Fresnel domain. Compared with traditional asymmetric cryptosystem in Fourier domain, the combination with Fresnel transform cannot only simplify the system, but also improve the space asymmetry and introduce the geometric parameters as security keys. Numerical simulations are performed to demonstrate the feasibility and security of the proposed cryptosystem. In addition, several exemplary schemes for security-enhanced asymmetric cryptosystems are presented, which may bring profound illumination to many deeper researches in asymmetric optical cryptosystem.