Abstract: To solve the problems of message integrality protection and dictionary attack of password in SAKI private key issuing protocol，a new improved SAKI private key issuing protocol is presented.New protocol solves the problems of juggle message attack and dictionary attack via extending entropy of password.At the same time，it uses the master key to protect the password，prevents attacker from imitating user to get private key when the password is leaked.The security of new protocol improves remarkably.Protocol’s security is based on computational Diffie-Hellman and bilinear Diffie-Hellman assumption.

Key words: private key issuing, protocol, password, Separable and Anonymous Identity-based Key Issuing（SAKI）

摘要： 为了解决SAKI私钥分发协议中报文的完整性保护和对口令的字典攻击问题，给出了一个改进的SAKI私钥分发协议，通过对口令信息熵的扩展，解决了篡改报文攻击和对口令的字典攻击；同时针对口令组泄露引起的安全隐患，改进的协议由系统主密钥加强对口令的保护，防止了口令组泄露时攻击者冒充用户申请私钥，改进的协议安全性能显著提高。该协议利用椭圆曲线上的双线性映射构造，其安全性基于Diffie-Hellman和Bilinear Diffie-Hellman计算问题的困难性假设。

关键词: 私钥分发, 协议, 口令, 可分离匿名的私钥分发（SAKI）