Coupling chaotic system based on unit transform and its applications in image encryption

•A novel chaotic system named as UT-CCS is proposed to generate new chaotic maps with excellent performance. A feasible way on how to select UTFs in UT-CCS to generate preferable chaotic maps is discussed.•A new chaos-based pseudo-random number generator (CBPRNG) with good randomness is proposed.•A novel digital image encryption algorithm based on CBPRNG is designed and tested. Chaotic maps are very important for establishing chaos-based image encryption systems. This paper introduces a coupling chaotic system based on a certain unit transform, which can combine any two 1D chaotic maps to generate a new one with better performance in cryptography applications. The chaotic behavior analysis has verified this coupling system’s effectiveness and progress. In particular, we give a specific strategy about selecting an appropriate unit transform function to enhance the chaotic behaviors of generated maps. Besides, a new chaos-based pseudo-random number generator, shorted as CBPRNG, is designed to improve the randomness of chaotic sequences. Moreover, based on CBPRNG, a novel digital image encryption algorithm is introduced, where we design a two-way multi-round transformation network to encrypt the higher bits and lower bits of input images separately. Simulation results and security analysis indicate that the proposed image encryption scheme is competitive with some existing methods.