Vulnerability of the security enhanced double random phase-amplitude encryption scheme to point spread function attack

The security enhanced double random phase-amplitude encryption (DRPAE) scheme which has been shown to be resistant to the known plaintext attack, is found susceptible to a simple point spread function (PSF) attack, as in case of the DRPE. Analogy of the DRPAE scheme with the 4-f imaging system is utilized to search for the required PSF, and an a priori knowledge of the amplitude mask is not required. Numerical simulations validate the efficacy of our proposed attack. Existence of the linearity in the DRPAE scheme is also examined.