一种代理签名方案的分析与改进

在一个指定接收者的签名方案中，只有指定的接收人才能验证签名的有效性。2004年，Dai提出了一个指定接收人的代理签名方案。通过对Dai方案进行安全性分析，发现由于存在一个悬孤因子，它是不安全的，不能抵抗内部伪造攻击。所以，该签名方案不符合数字签名所必须满足的不可伪造性和不可否认性原则。针对此方案的缺陷，进行了伪造性攻击，并提出了两种改进的方案，改进后的方案满足了代理签名的安全性要求。

Analysis and Improvement of A Proxy Signature Scheme

In a designated receiver signature scheme, only the designated receiver could verify the signature. In 2004, a designated receiver proxy signature scheme is proposed by Dai. The security of Dai-scheme is analyzed. The analysis shows that Dai-scheme is insecure to the forgery attack. Because of a hanging isolated factor, Dai-scheme could not meet the needs of digital signature, such as nonforgeability and nondeniability. To avoid these attacks, the old scheme is modified and two improved schemes are given. The improved schemes could satisfy the required security properties of the oroxv signature.