A hybrid attack on ‘double images encryption method with resistance against the specific attack based on an asymmetric algorithm’

A hybrid attack method, which is based on an iteration process and the decisive role of phase in the propagation process of light, is proposed to break the double image encryption system based on a nonlinear algorithm. The whole attack process contains three steps. First, an approximate value of the encoded image is achieved by using the phase retrieval algorithm when the encryption key, placed in the Fourier spectrum plane, and the ciphertext are used as the two constraints. Then, an approximate value of the joint power spectrum (JPS) is obtained based on the result of the first step. Finally, two approximate values of the original images are obtained by the use of the approximate value of the JPS and other two encryption keys. The simulation results show that the hybrid attack is valid and the cryptosystem is vulnerable to this attack.