Analysis And Design Of Image Encryption Algorithms Based On Block Permutation

Digital image is one of the most popular multimedia forms at present.In order to ensure the security of digital image transmission in the network,various encryption algorithms are proposed and analyzed for security.This thesis analyzes the security of two typical image encryption algorithms based on block permutation.By giving a ciphertextonly attack on such algorithms,the security shortcomings of this type of encryption algorithm are revealed.An image encryption algorithm compatible with JPEG compression standard is designed.main tasks as follows:(1)A security analysis was performed on an image encryption algorithm based on block permutation in an Encrypted-Then-Compression(ETC)system.The automatic jigsaw puzzle is linked with the ciphertext-only attack of the ETC system,and the extended automatic jigsaw scheme is applied to the ETC system ciphertext to achieve a high-accuracy jigsaw attack.At the same time,the key space and visual security of the ETC system encryption algorithm are analyzed,and the security performance is seriously overestimated by the designer.(2)A ciphertext-only attack was performed on a Hierarchical Chaotic Image Encryption algorithm(HCIE).The accuracy of sub-block matching for various histogram distances is compared by experiments.Combining the histogram distance matching and the proposed sub-block recombination algorithm,the subblock position relationship of HCIE ciphertext is successfully restored,and the part of plaintext information is reproduced.(3)By improving the encryption algorithm of ETC system,a color image encryption algorithm compatible with JPEG compression standard is designed.And compared with the security and data compression efficiency of the current ETC encryption algorithm.The experimental results show that the algorithm has the advantages of high data compression rate and high encryption and decryption speed under the premise of ensuring good security performance,and it is expected to be applied to various network real-time systems.