Cryptanalysis of Reversible Data Hiding in Encrypted Images Based on the VQ Attack

Reversible data hiding in encrypted images (RDHEI) is commonly used for privacy protection in images stored on cloud storage. Currently, block permutation and co-modulation (BPCM) encryption is commonly utilized in most existing RDHEI schemes to generate encrypted images. In this paper, we analyze the vulnerabilities of RDHEI based on BPCM encryption and then propose a cryptanalysis method based on the vector quantization (VQ) attack. Unlike the existing cryptanalysis method, our method does not require the help of a plaintext image instead of adopting the symmetric property between the original cover image and the encrypted cover image. To obtain the pixel-changing pattern of a block before and after co-modulation, the concept of a pixel difference block (PDB) is first defined. Then, the VQ technique is used to estimate the content of the ciphertext block. Finally, we propose a sequence recovery method to help obtain the final recovered image based on the premise that the generator is compromised. The experimental results demonstrate that when the block size is 4 x 4, our proposed cryptanalysis method can decrypt the contents of the ciphertext image well. The average similarity can exceed 75% when comparing the edge information of the estimated image and the original image. It is concluded from our study that the BPCM encryption algorithm is not robust enough.