A Vehicular Ad hoc NETwork (VANET) is a self-organized network formed by connected vehicles, which allows the exchange of useful traffic information in a timely manner. In such a context, evaluating the reliability of transmissions is vital. Trust can be used to promote such healthy collaboration. In fact, trust enables collaborating vehicles to counter uncertainty and suspicion by establishing trustworthy relationships. The main contribution of this paper is the proposition of a trust-based security scheme for message exchange in a VANET called TSME. Because of VANET characteristics, including dynamicity and high speed, we first proposed a VANET Grouping Algorithm (VGA); a suitable clustering algorithm organizing the network into groups with elected Group-Heads. Second, built on the VGA, we defined our trust management scheme dealing with vehicles’ reputations. Finally, we proposed a formal specification of the scheme using an inference system, and conducted a formal validation to assess its completeness and soundness rather than conducting simulations where some potentially rare conflicting or malfunctioning situations might not be detected. Soundness was proven by showing that there were no conflicts in our scheme, and completeness was established by assessing that all potential situations could be handled. The results obtained showed that our scheme for evaluating the veracity of exchanged messages is formally sound and complete.

车辆自组织网络（VANET）是由联网车辆形成的自组织网络，可以及时交换有用的交通信息。在这种情况下，评估传输的可靠性至关重要。信任可以用来促进这种健康的合作。事实上，信任使协作工具能够通过建立值得信赖的关系来应对不确定性和怀疑。本文的主要贡献是提出了一种基于信任的安全方案，用于 VANET 中的消息交换，称为 TSME。由于VANET的动态性和高速性等特点，我们首先提出了VANET分组算法（VGA）；合适的聚类算法将网络组织成具有选举组头的组。其次，在 VGA 的基础上，我们定义了处理车辆声誉的信任管理方案。最后，我们使用推理系统提出了该方案的正式规范，并进行了正式验证以评估其完整性和健全性，而不是进行可能无法检测到一些潜在罕见冲突或故障情况的模拟。通过证明我们的方案中不存在冲突来证明稳健性，通过评估可以处理所有潜在情况来确定完整性。获得的结果表明，我们评估交换消息准确性的方案在形式上是合理且完整的。