Research On Color Image Encryption Based On 2D-VMD And Hyperchaotic System

As the society has entered into the era of big data,and the processing and computing capability of the computer has been improved greatly,digital image has become the most common and important form of multimedia information because of its large amount of information and intuitiveness.The growth of the amount of information must be accompanied by serious information security threats.In recent years,the researchers use a series of characteristics of chaotic system to achieve digital image encryption.Most of the existing encryption methods are based on the low dimensional chaotic mapping,which results in a small key space,and they only performed in the time domain,the performance of security is limited.In this paper,the image encryption method is regarded as the main line.Firstly the dynamic characteristics of chaotic system are analyzed,then the eight dimensional hyperchaotic system is constructed by signal coupling,finally an encryption method for color images is proposed based on two-dimensional variational mode decomposition(2D-VMD)and hyperchaotic system.On the one hand,on the basis of the existing chaotic systems,two linear coupling terms are added into two identical chaotic systems respectively,and a new high dimensional hyperchaotic system is constructed through compounding the two systems.Through the dissipative analysis,balance points analysis,Lyapunov exponent analysis,the drawings of attractor phase diagram and power spectrum,the dynamic characteristics of the chaotic system are described in detail.The randomness of chaotic sequence generated by hyperchaotic system is tested by SP800-22 suite.The results show that the system is hyperchaotic,its dynamic characteristics is complex,and the chaotic sequences have strong randomness.On the other hand,under the framework of "confusion-diffusion",an encryption method for color image based on 2D-VMD and hyperchaotic system is proposed.Firstly,the plain-image is decomposed into several modes using 2D-VMD,and the chaotic sequences generated by combining the hyperchaotic system with plain-image are regarded as the key sequence of scrambling stage,combining the sub-sequences of the original sequences and then the homogenized sequences are regarded as the key sequence of diffusion stage.Finally,the each mode is encrypted respectively.The experimental results show that the cipher-image sequences can pass the SP800-22 pseudo random test.By testing the histogram,information entropy,key sensitivity,resistance to differential attacks of the cipher-image,the results show that 2D-VMD can reduce the correlation between adjacent pixels of the image to a certain extent,and the method proposed has a larger key space and higher security.