Security enhancement of double random phase encryption with a hidden key against ciphertext only attack

In this paper, we propose a security enhanced double random phase encoding (DRPE) encryption system against common ciphertext only attacks (COA). We point out one common weakness of COA schemes that the cracked plaintext image is usually in wrong circularly shifting positions and flipping status. Regarding to this weakness, an extra security layer (either optical or digital) cascaded with the DRPE system is constructed using a hidden key in our work. Simulation results demonstrate that our proposed system has significantly better security strength against COA than conventional DRPE system.