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

Background: The double random phase encoding techniques have received considerable attention from researchers in recent years because of its advantages of parallel and high speed processing capability. Meanwhile, the security of cryptosystem is also one of the major concerns. Methods : We experimentally demonstrated the ciphertext redundancy vulnerability of the coherent double random encryption system (DRPE). Based on the statistical ergodicity of speckles and the consistency of the power spectral density (ESD), we have proved that the most plaintext information can be retrieved from partial ciphertext alone. Results: In this paper, the simulation and experiment result were performed to verify whether the algorithm is effectiveness. The ciphertext redundancy of the DRPE system is analyzed from the results of ciphertext occlusion test. There is a risk of plaintext leakage of this scheme, as long as the average ESD can be estimated from the sub-images. The results will help to open up deeper understanding of limitation of current optical security techniques. Conclusions: The DRPE system has potential redundancy risk. Even one-time-pad manner is not secured in DRPE system. This vulnerability allows a cryptanalyst to estimate the plaintext information with only a half or less ciphertext.