Abstract:

The security of two provable secure proxy signature schemes based on Waters in the standard mode, which are proposed by Ji et al. and Yu et al. recently,is analyzed,and the two drawbacks of the two schemes are pointed out: delegation forgeability exists so that anyone may disguise as the original signer to issue valid proxy delegation warrants to the proxy signer, and proxy signature forgeability exists so that anyone can forge the signature of the proxy signer without knowing the private key of the proxy signer.An improved proxy signature scheme that can overcome the drawbacks is proposed,and its correctness,efficiency and security are analyzed in detail. The analysis shows that the improved scheme has the same length of signature and almost the same execution efficiency in comparison to the two original schemes,but has higher security.

Key words: proxy signature;identity-based cryptography;security analysis;unforgeability