An asymmetric color-image cryptosystem based on spiral phase transformation and equal modulus decomposition

In this paper, we propose an asymmetric color-image cryptosystem based on spiral phase transform (SPT) and equal modulus decomposition (EMD). The original image is divided into three-channel components of R, G and B firstly. Then we encrypt these components by two random phase mask (RPMs) modulations, two spiral phase transformations, and an equal modulus decomposition. Finally, we obtain four encryption keys which are RPM1, RPM2, an EMD's angle and the order q of the SPT, and produce two private keys (PKs) which are PK1 and PK2. The proposed method has enhanced the key sensitivity of the order q with 100 times, while it maintains the advantages of simple structure, high speed and less data amount. The proposed method is highly robust to iteration attack and other attacks. Numerical simulation results show the effectiveness and feasibility of the proposed cryptosystem.