关键词: 门限代理签名, 基于身份, 原始签名人改变攻击

Abstract: Present a security analysis of the Xu-zhang-feng identity based threshold proxy signature scheme，which can not resist original singer changing attack，at the same time，this scheme can’t withstand conspiracy attack，any [t]（or more） proxy signers can conspire to gain the private keys of other [n-t] proxy signers，and can forge their valid signature.An improved threshold proxy signature scheme is proposed，which can resolve the security problem existing in the Xu-zhang-feng identity based proxy threshold signature scheme.

Key words: threshold proxy signature, identity based, original signer changing attack