Taking TLS protocol for example, strand space model and theory extended are used to find an attack. In order to avoid the kind of attack, a piece of strategy to be paid attention to is put forward when cryptographic protocols are designed.

• 以TLS协议为例，利用扩展的串空间模型与理论分析，发现了一个攻击，为了避免此类攻击的发生，提出了设计密码协议时应注意的事项。