On the security of a certificateless signature scheme

Certificateless public key cryptography (CLPKC) eliminates certificate management in traditional public key infrastructure and solves the problem of the key escrow in identity-based cryptography. Certificateless signature is one of the most important primitives in CLPKC. Many certificateless signature (CLS) schemes have been proposed these years. For a CLS scheme to be secure, it should be resistant to the attacks of both Type I Adversary and Type II Adversary. In this paper, we give cryptanalysis to a recently proposed certificateless signature scheme. We show it is insecure against a Type II adversary who models a malicious-but-passive key generation center (KGC). An attack is described which reveals that a Type II adversary can successfully forge a certificateless signature of any signer upon obtaining two valid signatures of that signer.