Strongly Unforgeable Revocable Certificateless Signature

Certificateless public-key systems (CL-PKS) were introduced to simultaneously solve the key escrow problem in ID-based public-key systems and eliminate the need of certificates in traditional public-key systems. Since certificates are not required in CL-PKS settings, the existing user revocation mechanisms for traditional public-key systems are no longer suitable for certificateless public-key systems. Indeed, the design of efficient revocation mechanisms for CL-PKS settings is a critical issue. In 2014, Sun et al. proposed the first revocable certificateless signature (RCLS) scheme possessing existential unforgeability by adopting Tseng and Tsai’s revocation mechanism for ID-based public-key systems. However, Sun et al.’s RCLS scheme lacks computation efficiency for both signing and verifying phases. In the article, we propose an efficient RCLS scheme while retaining the merits of Tseng and Tsai’s revocation mechanism. Under the computational Diffie– Hellman assumption, we formally prove that our scheme offers strong unforgeability against adaptive chosen-message attacks in the random oracle model. When compared with Sun et al.’s RCLS scheme, our scheme not only has better performance but also achieves stronger security.