Novel Sketch Attack For Inter-block Shuffle Encryption

Multimedia is an information carrier that cannot be lacked in the Internet world today.Digital image is a very important multimedia information in the fields of military,medical and economic.Without the safe and effective protection of these sensitive information,it will bring significant losses to individuals or countries,so image encryption technology has become a key technology to protect digital image security.In practical applications,it is often necessary to compress an image to reduce the burden of a large amount of image data for transmission,storage,and encryption.The good compression performance of JPEG images makes it the most widely used compressed image.Therefore,the encryption method for JPEG images has emerged.The ideal JPEG image encryption scheme not only has a fast processing speed in the process of encryption and decryption,but also can withstand the common attack methods while maintaining the compression ratio,such as statistical attacks and chosen-plain-text attacks,etc.Therefore,the task of cryptographic analysis that promotes encryption methods has become indispensable.Finding vulnerabilities and defects in existing algorithms can improve the development of JPEG image encryption methods.Based on the analysis of cryptography,this paper studies the security of JPEG image encryption algorithm from the perspectives of "attack" and "defense".The main contents of this article are as follows:(1)In-depth analysis and classification of several traditional JPEG image-based encryption algorithms.(2)A new attack method is proposed,which combines the Chosen Plain-Text Attack and Non-Zero Count Attack to break the image encrypted by the Inter-block Shuffle algorithm.Through theoretical analysis and simulation experiments,it is proved that the proposed new attack method(CPT&NZCA)can crack any image encryption algorithm that does not change the number of non-zero coefficients in 8×8 blocks without knowing the details and keys of the encryption algorithm.The resulting plain-text sketch of the cipher-text image is finally obtained.(3)Based on the proposed new attack method(CPT&NZCA),an improved attack scheme(Fast Attack,FA)is proposed,which can significantly improve the attack speed by appropriately designing auxiliary images.