Security Analysis Of JPEG Image Encryption Based On DCT Coefficients Shuffling And Decomposing

Technological progress has promoted the rapid development of information technology,image has become one of the most important information storage and transmission because of its easy acquisition and informative content.When transmitted via open networks,images may be accessed by unauthorized users.Image encryption can effectively protect image content and privacy information.In practical,images are usually compressed before storage and transmission for efficiency.JPEG standard is widely used in image compression because of its good compression performance and visual effect.On this basis,scholars have proposed many JPEG image encryption algorithms.In order to retain the excellent compression performance of JPEG image coding,an effective JPEG image encryption algorithm should not only ensure the security of the encryption algorithm,but also keep the compression ratio in an acceptable range.In order to improve the encryption algorithms,it is necessary to perform cryptanalysis for existing encryption algorithms.In this paper,the traditional JPEG image encryption algorithms are introduced,and analyzes that the traditional intra-block encryption has the defect of not changing the number of non-zero coefficients in the block.The security problem of a novel JPEG image encryption algorithm is analyzed.By theoretical analysis and experimental simulation,the Mosaic image of original plain-text image can be recovered without key.The conclusion of the cryptanalysis is that slight change of the number of non-zero quantization DCT(Discrete Cosine Transform)coefficients does not affect the basic visual information of the image.The influence of number of non-zero coefficients to the image content reorganization is explored.Based on this exploration,an evaluation of JPEG image encryption scheme is proposed.The novel encryption performance evaluation constructs a two-dimensional deviation matrix by the difference of the number of non-zero coefficients between plain-text and cipher-text image in the corresponding position block of DCT domain.And the ratio between the elements in the matrix and the maximum number of non-zero coefficients in DCT domain of plain-text image is calculated.The normalized result obtained by dividing the sum of the ratios by the size of the image to describe the deviation between plain-text image and cipher-text image.The evaluation value of this method effectively reflects the relationship between the number of non-zero coefficients and the encryption effect.