Further Improvement of a Threshold Proxy Signature Scheme
一个门限代理签名方案的进一步改进*

In 1999,Sun,et al presented a threshold proxy signature,which overcame weaknesses of the schemes proposed by Zhang and Kim,et al,respectively.Recently,Li,et al showed that Sun's scheme cann't resist the public key substitution attack,and proposed an improved scheme.However,their improved scheme is still suffer from the public key substitution attack.Additional,a proxy relationship inversion attack on Li's scheme is proposed,it will provides more information in the design of secure proxy signature scheme.Finally,a further improvement scheme is proposed to eliminate the weaknesses.