Secure and noise-free nonlinear optical cryptosystem based on phase-truncated Fresnel diffraction and QR code

A novel secure and noise-free nonlinear optical cryptosystem based on phase-truncated Fresnel diffraction (PTFD) and QR code is proposed. In this paper, we introduce QR code to resist the noise which contaminates the retrievals of normal optical cryptosystems. The plaintext is transformed into a QR code and then the code is encrypted into a real-valued noise-like ciphertext by employing the PTFD-based cryptosystem. The two private encryption keys (EKs) are generated by the PTFD of a random amplitude mask with the two public keys. In the process of generating the EKs, just the amplitude in the Fresnel and output planes need to be recorded. There are no iterative calculations in the whole encryption and decryption process. Moreover, owing to the nonlinear operation of PTFD and the two generated private EKs, the proposed scheme is supposed to against existing attacks. Numerical simulations are carried out to demonstrate the validity and security of the proposed cryptosystem.