Certificateless Aggregate Signature schemes for Privacy Protection of Security Anlysis and Improvement

Vehicular Ad-Hoc Network (VANET) is an open environment. In VANET, it needs protect some privacy information of the vehicle, such as the real identity of the vehicle, the number of the vehicle. Certificateless aggregate signature (CLAS) scheme can reduce the calculation cost and communication cost due to the aggregation property, which is important part of cryptography. In this paper, we present two CLAS schemes proposed recently and also give a security analysis on the two CLAS schemes. By security analysis on the both CLAS schemes, it finds that the two CLAS schemes can be forged by the malicious enemy by replacing the public key of the user but without knowing the master key of key generation center. At the same time, we also show that second CLAS scheme does not satisfy the tractability property. In other words, the malicious vehicle cannot be traced after it makes some malicious signatures. We also present an improved CLAS schemes based on the original CLAS scheme respectively. By some security analysis and efficiency analysis, it can find that the improved CLAS schemes both not only can overcome the security problem but also are still efficient.