Abstract: A proxy signature allows an original signer to delegate his/her signing capability to a proxy signer
so that the proxy signer can sign messages on behalf of the original signer. Wang et al. proposed a digital blind
proxy signature scheme in 2003. That scheme has the properties that the original signer can not identify the proxy
signer through a proxy signature and the proxy signer can blindly sign a message，but when it’s necessary,the
anonymity can be revoked by a proxy signature management center. In this paper we will point out some of
the security °aws of their scheme by presenting an e®ective attack.One can forge a e®ective proxy signature，so
the signature veri¯er will accept the proxy signature,but the management center can’t identify the proxy signer
through the signature.

Key words: blind proxy signature, anonymity-revoking, cryptanalysis