A Revocable Certificateless Aggregate Signature Scheme with Enhanced Security

In certificateless public key cryptosystem, a tough problem is how to revoke a user when the user's private key is compromised or expired. So the revocable certificateless schemes come into being. Certificateless aggregate signature (CLAS) is an efficient way to verify a large amount of signatures from different users simultaneously. However, none of CLAS schemes considers the user revocation currently. In this paper, we firstly demonstrate that an efficient certificateless aggregate signature (abbreviated to ECLAS) scheme proposed by Kang et al. is vulnerable to forged signature attack from the type II adversary by a concrete example, although they claimed that their scheme is existentially unforgeable against the adaptively chosen-message attacks. Furthermore, based on the ECLAS scheme and the revocable idea, we proposed a revocable certificateless aggregate signature scheme, which was proved to be existentially unforgeable against adaptive chosen-messages attacks under the hardness assumption of computational Diffie-Hellman problem. As far as we know, this is the first revocable CLAS scheme. Finally, numerical analyses and performance comparisons show our scheme saves computational cost, communication bandwidth and storage space than some related schemes.