Reversible data hiding in Paillier cryptosystem

In this paper, reversible image data hiding in the Paillier cryptosystem is investigated. To transmit additional data in homomorphic encryption domain, two algorithms are proposed for different application scenarios. By exploiting the additive homomorphism, high-capacity data hiding can be accomplished with the first algorithm by conducting value expansion on the encrypted pixel values. But the hidden data can only be extracted after image decryption (i.e., in plain-text domain). With the second algorithm, both of data embedding and extraction can be performed in the encryption domain by exploiting the self-blinding property, while the corresponding plain-text values are unchanged. Compared with the reversible data hiding algorithms designed for encryption with a cipher stream, the proposed ones are more applicable in cloud computing without degrading the security level. Thus the additional data can be losslessly transmitted in the different applications of Paillier cryptosystem.