S/KEY是基于一次性口令技术开发的身份认证系统。在深入分析S/KEY协议的过程及其安全性的基础上,主要针对其不能抵抗小数攻击的缺陷,设计了S/KEY协议的改进方案,通过引用椭圆曲线密钥交换算法,完成了会话密钥的协商,保证了会话密钥的新鲜性,实现了通信双方的双向认证,分析表明改进后的协议进一步增强了S/KEY身份认证系统的安全性。 S / KEY is based on one-time password technology developed authentication system. On the basis of deeply analyzing the process and security of S / KEY protocol, an improved scheme of S / KEY protocol is designed mainly for the defects that it can not resist the fractional attack. Through the reference to the elliptic curve key exchange algorithm, the session secret Key negotiation ensures the freshness of the session key and realizes two-way authentication between the two parties. The analysis shows that the improved protocol further enhances the security of the S / KEY authentication system.