Separable Reversible Data Hiding in Encrypted Image Against Ciphertext-Only Attack

To improve the security and reversibility,a reversible data hiding in encrypted image capable of ciphertext-only attack(COA)is proposed.The image owner segments the original image into a number of non-overlapping blocks and the encrypted image is generated by combining block scrambling and the designed XOR encryption which three MSBs and five LSBs of pixels in the block are encrypted respectively with different key stream.And then the data hider uses the pixel fluctuation value and lossless compression to gain extra space and embeds the additional information into pixels by bit flipping.To achieve full reversibility,the fluctuation value of the pixels is recorded in marked image.At last,the receiver extracts the embedded data correctly and recovery original image.The proposed algorithm was evaluated on uncompressed color image database.Experimental results show that the correct rate of stream cipher obtained by COA on encrypted image sets of 20,50,70,100 is about 50%,which can effectively resist COA.Compared with three similar algorithms,the embedding capacity is improved respectively by 145.69%,148.21%and 240.85%,and the quality of decrypted image is improved about 5 dB.