On the Security of a RSA-based Certificateless Signature Scheme

The certificatless cryptography has been studied widely since it could eliminate the need of certificates in the Public Key Infrastructure and solve the inherent key escrow problem in the identity-based cryptography. Recently, Zhang et al.’s proposed the first RSA-based certificateless signature scheme and demonstrated that their scheme is provably secure in the random oracle model. In this paper, we will show that Zhang et al.’s scheme is insecure against a type I adversary who can replace users’ public keys. The analysis shows Zhang et al.’s scheme is not secure for practical applications.