## 4 The Design of the QKD-Secured V2I System
The University of Warwick campus is integrated into the Midlands Future Mobility (MFM) testbed. MFM has 200+ miles of public roads available for vehicle trials and is part of the UK's strategic connected and automated mobility (CAM) physical development and testing infrastructure. The QKD-secured V2I testing took place on the V2I-enabled  
Figure 4: There are a pair of FSO-QKD optical assemblies: (**A**) Each transmitter and receiver optical unit is mounted onto a tripod. (**B**) The optical transmitter is located on the roof of a building and is aimed at the optical receiver. (**C**) Likewise, the optical receiver is located on the roof of another building, up to 300 metres from the optical transmitter. Images from the AirQKD partner, the Fraunhofer Centre for Applied Photonics. Warwick campus, utilising the KMM and QKD management layers via the Angoka zero-trust authentication protocol (ZAP) security software. WMG worked closely with its AirQKD partner, Angoka, to integrate the security technology into the V2I campus testbed. The equipment and intellectual property (IP) provided by Angoka played an important role in the execution of the AirQKD demonstration. The ZAP IP developed within AirQKD is able to use QKD-generated keys as the base keys for the security process. It ensures authentication of devices within the V2I process and secures communication between OBUs, RSUs, and the infrastructure. The ZAP protocol follows the zero-trust architecture (ZTA) principles of always authenticating devices, verifying requests, and providing minimal access to essential resources [38]. A secure source of OTP keys aids the implementation of ZTA-based systems. The University of Warwick's V2I infrastructure features both fixed and weatherproof mobile DSRC installations, supported by WMG's Catapult Open Innovation Vehicle Platform; see Figure 5. The WMG vehicle is equipped with a variety of systems for vehicular communications and autonomous driving research. The DSRC equipment used in the testbed is from a company called Cohda. The Cohda MK5 RSUs are mounted on the testbed's fixed and mobile installations, and Cohda MK5 OBUs are used in testbed vehicles. The Cohda RSU and OBU units communicate via the IEEE 802.11p wireless standard. They are Linux-based-embedded computers with a software development kit (SDK). This allows for custom applications to be loaded and executed. The V2I infrastructure includes cameras that are used to identify fixed and mobile traffic and hazards. The systems supporting the V2I infrastructure are able to perform image processing for collective perception and generate CPM data streams. The vehicle platform is fitted with similar capabilities. The CPMs generated from the infrastructure and vehicle cameras can be shared throughout the system to enable route planning, obstacle avoidance, and traffic safety research applications. The Cohda RSUs and OBUs are configured with a modified operating system that implements the Angoka ZAP protocol [37]. An Angoka device authentication unit (DAU) is installed onto the Cohda units. The DAU is connected to the universal serial ports (USBs) of Cohda OBUs/RSUs. The DAU is based on a physical unclonable function (PUF), providing a unique fingerprint for any device; it is used as part of the Angoka ZAP process:  
1. The Angoka gateway requests keys from OLC's KMM software. 2. To safeguard against the FSO-QKD's inability to provide keys (due to optical link issues or system failure), a process called _key amplification_, which is similar to _key  
Figure 5: The University of Warwick campus is used as a testbed for V2X and vehicle research and has (**A**) fixed V2I equipment and RSUs, (**B**) mobile V2I equipment and RSUs, and (**C**) research vehicles equipped with V2I equipment, vision systems, and OBUs. The images (by the authors) are of WMG V2I equipment. stretching_, [39] is used (where a small secret is used to create a longer securer key). The secured keys are stored in the Angoka gateway's key management system (KMS). 3.