The choice of optical system is critical for the security of double random phase encryption systems

The linear canonical transform (LCT) is used in modeling a coherent light field propagation through first-order optical systems. Recently, a generic optical system, known as the Quadratic Phase Encoding System (QPES), for encrypting a two-dimensional (2D) image has been reported. In such systems, two random phase keys and the individual LCT parameters (, , ) serve as secret keys of the cryptosystem. It is important that such encryption systems also satisfies some dynamic security properties. In this work, we therefore examine such systems using two cryptographic evaluation methods, the avalanche effect and bit independence criterion, which indicate the degree of security of the cryptographic algorithms using QPES. We compared our simulation results with the conventional Fourier and the Fresnel transform based DRPE systems. The results show that the LCT based DRPE has an excellent avalanche and bit independence characteristics compared to the conventional Fourier and Fresnel based encryption systems.Keywords: Quadratic Phase Encoding system, linear canonical transform, Double Random Phase Encryption, Avalanche effect and bit independence criterion.