On the security of block scrambling-based ETC systems against jigsaw puzzle solver attacks

This paper is among the first to adapt automatic jigsaw puzzle solvers, which are methods of assembling jigsaw puzzles, to the field of information security. Block-based scrambling encryption schemes, which have been mainly proposed for Encryption-then-Compression (ETC) systems, have enough key spaces for protecting brute-force attacks. However, each block in encrypted images has almost the same correlation as that of original images. Therefore, it is required to consider the security from different viewpoints from number theory-based encryption methods with provable security such as RSA and DES. In this paper, existing jigsaw puzzle solvers are first reviewed in terms of attacking strategies on encrypted images. Then, a new jigsaw puzzle solver is proposed to extend some limitations of the conventional ones. In the experiments, the jigsaw puzzle solvers are applied to encrypted images to consider the security conditions of the encryption schemes.