Reversible data hiding scheme in encrypted images based on homomorphic encryption and pixel value ordering

With the growing demands of cloud computing and privacy protection, reversible data hiding in encrypted images (RDHEI) has been gradually developed. This paper proposes a RDHEI scheme based on reserving room before encryption (RRBE). The scheme is divided into three types of users: image owner, data hider and receiver. First, the image owner preprocesses the image using a median-prediction-based pixel value ordering algorithm (M-PVO), and then encrypts the image using the Paillier homomorphic cryptosystem, and the data hider performs two stages of data embedding on the encrypted image. According to the key held by the receiver, the data embedded in different stages can be extracted and the original image can be recovered lossless. The experimental results show that the embedding rate of the first stage is about 0.7 bpp, and the embedding rate of the second stage can reach 12 bpp. Compared with other schemes, the proposed scheme has better image quality at the same embedding rate.