Ciphertext-only attacks on the double random phase encryption based on redundancy vulnerability

The double random phase encoding techniques have received considerable attention from researchers in recent years because of their advantages of parallel and high-speed processing capability. Meanwhile, the security of the cryptosystem is also one of the major concerns. We experimentally showed the ciphertext redundancy vulnerability of the coherent double random phase encryption (DRPE) system. Based on the statistical ergodicity of speckles and the consistency of the energy spectral density (ESD), we have proved that the method can retrieve the most plaintext information from partial ciphertext alone. We performed the simulation and experimental results to verify whether the algorithm is effective. The ciphertext redundancy of the DRPE system is analyzed from the results of the ciphertext occlusion test. There is a risk of plaintext leakage in this scheme, as long as the average ESD can be estimated from the sub-images. The results will further our understanding of the limitation of current optical security techniques. The DRPE system has potential redundancy risk. This vulnerability allows a cryptanalyst to estimate the plaintext information with only a half or less ciphertext.