The Research Of Digital Image Compression And Encryption Technology Based On Chaos

As a kind of important information medium,digital images are widely used on the Internet in recent years.Some digital images which involve confidential information need to be encrypted to prevent information leakage.At the same time,given that the digital image has the feature of large data volume,compression processing is required when we use them Since the encryption operation destroys the redundancy characteristics of the image data,it is difficult to obtain a high compression ratio when compressing the encrypted image.If the image is compressed first and then encrypted,it will take a lot of time and it is difficult to meet the requirements of real-time performance.Based on this background,this thesis studies the image compression and encryption technology,and proposes two joint algorithms of compression and encryption,so that compression and encryption can be completed at the same time,and the algorithm has good compression performance and high security.The specific research contents are as follows:(1)Based on the Logistic chaotic system,an image encryption algorithm combined with JPEG compression is designed.The algorithm combines the encryption operation with the compression operation,and can complete the image encryption while compressing the image.Firstly,the algorithm scrambles the RGB components of the image sub-blocks in the spatial domain to achieve color component recombination,and then scrambles the quantized DC coefficients and AC coefficients.After the scrambling is completed,the symbol bits of each coefficient are randomly modified.The entire encryption process is controlled by the Logistic chaotic system.Theoretical analysis and simulation experiments showed that the algorithm has good encryption effect,large key space and strong key sensitivity.At the same time,the encryption operation has little effect on the compression algorithm,and the encrypted image still has a high compression ratio.(2)An self-adaptive compression encryption algorithm is proposed.The idea of self-adaptive encryption technology is introduced into compression and encryption algorithm,and improved the security of the algorithm.Firstly,the algorithm uses the key stream generated by Logistic chaotic system to self-adaptively scramble the quantized DC coefficients.Secondly,we use Chen's hyper-chaotic system to self-adaptively substitute DC coefficients and modify the sign of AC coefficients.The whole process of encryption is highly correlated with plaintext information,that enhanced the plaintext sensitivity of the algorithm,and the algorithm can resist effectively known plaintext attacks and selective plaintext attacks.The simulation results showed that the algorithm has good encryption effect and compression performance,which can fully meet the performance requirements of image compression and encryption.