# Protecting Hybrid ITS Networks: A Comprehensive Security Approach
###### Abstract  
Cooperative intelligent transport systems (C-ITS) continue to be developed to enhance transportation safety and sustainability. However, the communication of vehicle-to-everything (V2X) systems is inherently open, leading to vulnerabilities that attackers can exploit. This represents a threat to all road users, as security failures can lead to privacy violations or even fatalities. Moreover, a high fatality rate is correlated with soft-mobility road users. Therefore, when developing C-ITS systems, it is important to broaden the focus beyond connected vehicles to include soft-mobility users and legacy vehicles. This work presents a new approach developed in the context of emerging hybrid networks, combining intelligent transport systems operating in 5.9 GHz (ITS-G5) and radio-mobile cellular technologies. Two protocols were implemented and evaluated to introduce security guarantees (such as privacy and integrity) in communications within the developed C-ITS hybrid environment. As a result, this work securely integrates G5-connected ITS stations and soft-mobility users through a smartphone application via cellular networks. Commercial equipment was used for this goal, including on-board and roadside units. Computational, transmission and end-to-end latency were used to assess the system's performance. Implemented protocols introduce an additional 11% end-to-end latency in hybrid communications. Moreover, workflows employing hybrid communications impose, on average, an extra 28.29 ms of end-to-end latency. The proposal shows promise, as it reaches end-to-end times below the latency requirements imposed in most C-ITS use cases. C-ITS; ITS-G5; cellular network; hybrid network; security; privacy; integrity; V2X +
Footnote †: journal: _Future Internet_  
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Despite the potential benefits, C-ITS/V2X communications are inherently open. This openness creates vulnerabilities [6] that attackers can exploit, representing a significant threat to all road users, as security failures can lead to privacy violations or even fatalities. These security and privacy challenges must be addressed to ensure that road safety is not compromised [7]. According to [PERSON] et al. [8], \"Security plays a crucial role in cooperative applications because a security breach can easily lead to human casualties\". Moreover, C-ITS relies heavily on communication between vehicles that have the necessary equipment installed[PERSON] This issue is also raised by [PERSON] et al. [9], where it is referred that, although in the European Norm (EN) 302 665 (V1.1.1) [10], the European Telecommunications Standards Institute (ETSI) has defined handheld devices as one of the types of ITS stations, subsequent ETSI specifications have mainly focused on a vehicle-centric view. In this regard, a high fatality rate is correlated with soft-mobility road users [1]. Therefore, in the development of C-ITS-based systems, it is essential to broaden the perspective beyond connected vehicles, also considering the needs of soft-mobility users (e.g., cyclists) and legacy vehicles that do not have the required equipment--the on-board units (OBUs). To illustrate these issues, some possible scenarios are described. An attacker could perform a Sybil attack, as illustrated in Figure 1, where he claims the existence of non-existing vehicles at multiple locations [7], creating confusion and disrupting communication. This could lead to inaccurate traffic information (e.g., fake congestion), which can cause misinformed decision-making by drivers. The situation depicted in Figure 2 exemplifies why it is beneficial to include soft-mobility users and legacy vehicles in the C-ITS ecosystem. In this scenario, an accident occurred, and vehicles (legacy and G5-connected) were approaching. The lack of information about the situation makes it unpredictable and unsafe. The cyclist and the pedestrians present could securely notify ITS central systems. Information about this event could then be disseminated to connected vehicles.