Separable Reversible Data Hiding in Encrypted Images Based on Systematic Polar Code and Flag Bit Transmission Channel Model

This paper proposes a novel method of vacatingroom-after-encryption reversible data hiding in encrypted image (VRAE RDHEI), which uses the ideas of channel modeling and channel coding to achieve the enhancement of capacity. The framework of the proposed method maps the processes of data embedding and image recovery to a virtual noisy channel for transmitting special flag bits of image content, and then it uses the systematic polar code to ensure error-free transmission for reversible data hiding. On the data hider side, to reversibly vacate room for secret data, the selected bits of the encrypted image are transformed to flag bits and then encoded to fewer parity bits by systematic polar code. On the receiver side, the secret data can be extracted without error and separate from image recovery. To recover the image, the receiver uses pixel prediction to obtain the noisy flag bits and decodes them to the original flag bits by a special channel knowledge-based decoding algorithm with the parity bits. Then, the original image can be recovered by the flag bits. The experimental results prove that the proposed method outperforms the state-of-the-art VRAE methods.