Identity-Based Proxy Re-encryption Based on SM9

Proxy re-encryption, as a cryptographic primitive, allows an untrusted proxy to transform a ciphertext encrypted with the data owner’s public key to a ciphertext encrypted with the authorized user’s public key, without any knowledge of the underlying plaintext, which achieves the sharing of ciphertext data. As an identity-based cryptosystem, SM9 has been adopted as a Chinese national standard and an ISO/IEC international standard. However, the SM9 encryption algorithm can only achieve the function of data encryption without considering the ciphertext transformation. In this paper, based on SM9, we first propose an identity-based proxy re-encryption scheme (termed IBPRE-I). IBPRE-I has the same user secret key as SM9, so it can be effectively integrated with SM9-based systems. Security proof indicates that IBPRE-I achieves the ciphertext indistinguishability against selective identity and chosen plaintext attack, and the secret key leakage resistance against collusion attack in the random oracle model. Then, by extending the IBPRE-I scheme, we present our second scheme IBPRE-II to achieve the security under chosen ciphertext attack. Finally, the performance is evaluated and the results show that the proposed schemes are practical.