# Protecting Hybrid ITS Networks: A Comprehensive Security Approach
###### Abstract
Figure 1: Sybil attack where the attacker claims his existence at multiple locations. Figure 2: Accident where cooperation between soft-mobility users and the G5 network would be beneficial. To address previous issues, this work develops a proof-of-concept approach that introduces security guarantees within a C-ITS ecosystem while accommodating soft-mobility users and legacy vehicles. Additionally, this research intends to evaluate and compare the security protocols proposed in the literature using real equipment. Emphasis is also given to assessing how the security protocols affect performance. Lastly, this study measures the performance cost of incorporating soft-mobility users and legacy vehicles within a realistic testing environment. To accomplish these goals, this work builds and assesses a system that employs a security protocol in a C-ITS environment while operating within a hybrid network, combining intelligent transport systems operating in 5.9 GHz (ITS-G5) and cellular technologies. Thus, the proposed approach integrates G5-connected ITS stations and soft-mobility users connected through their smartphones via cellular networks, such as the fifth- and sixth-generation (5G and 6G) [11; 12]. Two security protocols, DLAPP [13] and MFSPV [14], were implemented using hardware equipment--OBUs, roadside units (RSUs) and smartphones. An application was developed for each of these computing environments. These applications allow sending and receiving/verifying protected messages using a protocol. Viewing through a high-level model, the proposed approach and subsequent experimental environment are embedded in the context of edge computing (EC) and fog computing (FC) paradigms [15]. Devices, such as smartphones, OBUs found in vehicles and RSUs along the road infrastructure, act as communication devices [16] that operate at the edge of the hybrid network. They process data in their local applications, providing low latency and faster response [17]. Lastly, computational, transmission and end-to-end latency were used to assess the system's performance. Our primary contributions are:  
* Development and assessment of a novel approach that employs a security protocol in a C-ITS hybrid environment by combining ITS-G5 and radio-mobile networks;
* Extend the literature by going beyond the traditional focus on connected vehicles to include soft mobility users and legacy vehicles in C-ITS;
* Assessing the effectiveness of security protocols (DLAPP [13] and MFSPV [14]), thus bridging the gap between theory/simulation and real-world implementations;
* Enrichment of the literature's information regarding the implementation of security protocols in real ITS equipment (OBUs and RSUs). This paper is organised as follows. First, Section 2 reviews the existing concepts and research related to this problem, including the implemented security protocols. Section 3 presents the proposed approach and its development. Section 4 analyses and reports the conducted experimental evaluation. Finally, Section 5 concludes the document by summarising the developed work, main remarks and possible future work.