Abstract: The optimistic e-commerce protocol is made up of multiple sub-protocols，and is significantly different from traditional authentication protocol.The main purpose of the e-commerce protocol is to realize fair exchange between both buyers and sellers who are assumed to be dishonest.That is，it is necessary for those buyers and sellers to prevent the internal attack.Based on the deep analysis of each attribute in fair exchange protocols，the authentication attribute of item is defined.The fairness that should be met by e-commerce protocols is defined，and an extended SVO logic syntax which takes an optimistic e-commerce protocol as an object is proposed to demonstrate the fairness analysis method.The security vulnerabilities and improvement suggestions of the e-commerce protocol are also discussed.

摘要： 乐观电子商务协议通常具有复杂结构，由多个子协议组合而成，与传统认证协议具有显著不同。电子商务协议最主要目的是实现买卖双方的公平交换，同时假定交换双方都可能是不诚实的，需要考虑来自协议合法实体的内部攻击。文章在深入分析公平交换协议各项属性的基础上，定义了电子项的认证属性，对SVO逻辑进行了扩展，使用SVO逻辑语法定义了电子商务协议应满足的公平性。文章以一种真实的电子商务协议为对象，演示了基于SVO逻辑的电子商务协议公平性分析方法，并指出该协议存在安全缺陷，提出改进意见。