中文摘要：

对两个基于多个私钥产生中心的私钥分发协议给出了具体的攻击方法,指出这两个协议都无法抵抗恶意的私钥产生中心的攻击;提出了相应的改进方案,改进方案由用户的秘密参数和私钥产生中心的秘密参数共同生成用户私钥,并且在协议的交互过程中接收方都要验证收到的消息的真实性,从而使恶意的私钥产生中心无法成功得到系统用户的私钥,解决了私钥分发协议存在的用户私钥托管问题;并且对改进方案的安全性和计算复杂度进行了分析.

英文摘要：

The attack methods of two identity-based key issuing protocols are presented, and the conclusion that key generator center can compute secret key of any users is introduced. Two improved schemes are proposed in which the secret key of user is produced by the secret parameters of user and key generator center, and the reality of messages are varified in every step of the potoeols, thereby, key generator center cannot get the secret key of users and the problem of secret key escrow is solved. The safety and computational complexity of improved schemes are analyzed.