Some Certiticateless Short Signature Schemes of Security Analysis and Simple Improvement

Certificateless signature (CLS) scheme as an important filed of cryptography has a wide range of applications, such as information security, network security and so on. But, in the CLS scheme, the public key of the signer is generated directly by the signer itself without the verification of the trusted third part, so the public key easily is replaced by the malicious users which lead to the forgeability of the signature. In this paper, we show three CLS schemes proposed recently which have high efficient with short signature are not secure and the malicious user can forge a signature by replacing the public key of the signer. In the same, we also present three improved CLS schemes with simple modifying based on the original CLS schemes respectively. We also make a simple security analysis and efficiency analysis on the three improved CLS schemes. The analysis shows that the improved schemes not only can overcome the security problem but also almost have the same efficiency with the original CLS schemes.