A separable reversible data hiding scheme for encrypted JPEG bitstreams

In this paper, we construct a separable reversible data hiding scheme for encrypted JPEG bitstreams. Our proposed scheme is constructed via a reserving-room-before-encryption manner, that is, the original JPEG bitstream is modified with small distortion so that the content owner can reserve enough space for future data embedding and then the modified JPEG bitstream is encrypted. To do that, our key observation is that the least significant bits of the two-bit appended values in the JPEG bitstream is a biased bitstream. Thus we design a new lossless compression algorithm for biased bitstreams with better compression ratio than the binary arithmetic coding method to fulfill the above task for pre-reserving space. With this room-reserving technique, the encrypted JPEG bitstream can be generated and the data embedding in this encrypted bitstream can be done easily by the data hider. Finally, the receiver is able to extract the embedded data and recovers the original JPEG bitstream independently.