Specific attack and security enhancement to optical image cryptosystem based on two random masks and interference

In this paper, we evaluate the security of an amplitude-phase retrieval attack free encryption scheme based on two random masks and interference. In the proposed cryptosystem, two phase-only masks (POMs) are generated from two random images using interference technique. The POMs are then used as encryption keys in a phase-truncated Fourier transform (PTFT) based encryption scheme. Compared to traditional PTFT-based cryptosystem, the security of the encryption scheme is improved by integrating the interference technique. Consequently, the scheme is immune to some attacks. We proposed a specific attack based on a phase retrieval algorithm with median filtering to break the cryptosystem. Numerical simulation results show that the cryptosystem is vulnerable to the proposed attack. Moreover, based on the proposed attack and the existing cryptosystem, full phase encoding technique is added to the previous cryptosystem to enhance the security.