Security Analysis of a Proxy Blind Signature and Its Improved Scheme

The security of Zheng et al.´s ID-based proxy blind signature scheme from bilinear pairings is analyzed, it is found that their scheme does not possess the blindness property. A dishonest proxy signer can relate the formation process of the proxy blind signature to the unblind signature for the message by gathering the corresponding message of signing protocol, and then he can trace the message holder. An improved scheme is proposed by multiplying the reverse of the blind factor to the blind message. Experimental results show that the new scheme can effectively overcome the disadvantage of the original scheme and resist the signer´s malicious tracking. Furthermore, it can satisfy all the required properties of a proxy blind signature and performs better in security and practicability which can be used to build more secure system.