Abstract: The dynamic password user authentication mechanism is an important aspect of the authentication technology development.On the basis of analyzing two protocols，SAS-2 and 2GS，this paper proposes a more secure dynamic password user authentication protocol.The new protocol not only can effectively resist the stolen-verifiers attack in SAS-2 protocol，but also can conquer the refused service attack and realize two-way authentication，which is impossible in 2GS protocol.Thus，it can protect user’s identity and improve network security.

Key words: user authentication, dynamic password, network security, protocol

摘要： 动态口令用户认证机制是当前身份认证技术发展的一个重要方面，在分析了SAS-2和2GS两种动态口令用户认证协议的基础上，提出了一种更安全的动态口令用户认证协议。该协议不仅能有效地抵御SAS-2协议不能抵御盗取验证因子的攻击，而且纠正了2GS协议不能实现双向认证和抵御拒绝服务攻击的缺陷，有效地保护了用户的信息，提高了网络安全。

关键词: 身份认证, 动态口令, 网络安全, 协议