Research On Security Analysis Of JPEG Image Encryption Algorithm

The continuous development and progress of the Internet and mobile terminals promote the wide application of multimedia information.Digital images have become one of the most common carriers for data storage and transmission in commercial,military and medical fields due to its intuitive content and abundant information.In practical applications,in order to save network bandwidth and storage space,digital images often need to be compressed to reduce redundant information.At present,Joint Photographic Experts Group(JPEG)has become the most popular encoding format because of its high compression ratio,strong compatibility and convenient storage among many image compression standards issued by the International Standards Organization(ISO).JPEG images carrying important information need to be encrypted to ensure their confidentiality during transmission.Therefore,the research on the encryption schemes of JPEG images has become a current popular direction.The ideal JPEG image encryption schemes should not only maintain high compression rate and good format compatibility,but also be secure against all kinds of cryptanalysis methods.Cryptanalysis aims to discover the JPEG image encryption schemes’ security vulnerabilities and evaluate their security performance,so as to help cryptdesigners improve them and promote the development of JPEG image encryption technology.Therefore,cryptanalysis of JPEG image encryption schemes is of paramount importance.This theseis analyzed the security of two JPEG image encryption algorithms proposed in recent years and gave corresponding attack schemes.And the security defects in the mainstream JPEG image encryption schemes in recent years were analyzed and summarized with the corresponding improvement suggestions.The work achievements of this thesis mainly include the following three parts:(1)The security of a content-adaptive joint image compression and encryption algorithm designed by Li et al was analyzed.The algorithm didn’t change the image feature information related to the key embedding,and the relative positions of the key embedding were the same for images with the same feature information,so the adaptive key couldn’t be transmitted safely.Based on the above defects,the attacker could use the selected plaintext attack to decrypt the equivalent working-key embedded in the plaintext image.Theoretical analysis and simulation results results prove the effectiveness and correctness of the attack scheme.(2)The security of an encryption-then-compression systems for grayscale-based JPEG images encryption algorithm designed by Chuman et al was analyzed.Several security flaws of the underline algorithm were identified.Firstly,the random working-key sequences used in the encryption process were generated by the initial keys and independent from the plaintext images,which may cause the key stream to be reused for different images.Secondly,the scrambling and substitution operations of the algorithm were too simple to achieve ideal diffusion and confusion effect.Therefore,the plaintext image could be deciphered by recovering the equivalent working-key of each iteration round with chosen-plaintext attack.Theoretical analysis and simulation results show the effectiveness and correctness of the proposed cryptanalysis scheme.(3)The security vulnerabilities existing in the current high-security JPEG image encryption scheme were analyzed and summarized,and some feasible improvement suggestions were put forward.The final part analyzed and summarized the common security defects in the current mainstream JPEG image encryption schemes,and proposed some improvement suggestions.