Cooperative vehicle platooning significantly improves highway safety, fuel efficiency, and traffic flow. In this model, a set of vehicles move in line formation and coordinate acceleration, braking, and steering using a combination of physical sensing and vehicle-to-vehicle (V2V) messaging. The authenticity and integrity of the V2V messages are paramount to safety. For this reason, recent V2V and V2X standards support the integration of a PKI. However, a PKI cannot bind a vehicle's digital identity to the vehicle's physical state (location, velocity, etc.). As a result, a vehicle with valid cryptographic credentials can impact platoons from a remote location. In this paper, we seek to provide the missing link between the physical and the digital world in the context of vehicle platooning. We propose a new access control protocol we call Proof-of-Following (PoF) that verifies the following distance between a candidate and a verifier. The main idea is to draw security from the common, but constantly changing environment experienced by the closely traveling vehicles. We use the large-scale fading effect of ambient RF signals as a common source of randomness to construct a {\em PoF} primitive. The correlation of large-scale fading is an ideal candidate for the mobile outdoor environment because it exponentially decays with distance and time. We evaluate our PoF protocol on an experimental platoon of two vehicles in freeway, highway, and urban driving conditions. We demonstrate that the PoF withstands both the pre-recording and following attacks with overwhelming probability.

翻译：协作式车辆编队行驶可显著提升公路安全、燃油效率和交通流。在此模型中，一组车辆以队列形式行驶，通过物理传感与车对车（V2V）消息的组合来协调加速、制动和转向。V2V消息的真实性和完整性对安全至关重要。为此，最新的V2V和V2X标准支持集成公钥基础设施（PKI）。然而，PKI无法将车辆的数字化身份与其物理状态（位置、速度等）绑定。因此，持有有效加密凭证的车辆可从远程位置影响队列。本文旨在填补车辆编队场景中物理世界与数字世界之间的缺失环节。我们提出一种名为“跟随证明”（PoF）的新型访问控制协议，用于验证候选车辆与验证车辆之间的跟车距离。核心思想是借助紧密跟随车辆所共享的常见但持续变化的环境来获取安全性。我们利用环境射频信号的大尺度衰落效应作为公共随机源，构建PoF原语。大尺度衰落的相关性随距离和时间呈指数衰减，是移动户外环境的理想候选方案。我们在高速公路、城市快速路及城市道路条件下对两车实验队列评估了PoF协议。实验表明，PoF能以压倒性概率抵御预录制攻击和跟随攻击。