## 3 Related Work
This shows us that even current security concepts are often not fully developed and cannot offer complete protection. [PERSON] et al. discuss fundamental problems related to car security [72]. The results of their research show that the computing power of a car is very limited and that this can lead to problems when using strong cryptography within certain protocols. In addition, they conclude that car manufacturers must validate the software running on an ECU embedded within a vehicle and test it periodically to guarantee its integrity. An entire vehicle can become vulnerable if bugs remain in the vehicle system. These effects are of course reflected in the severity of the respective bug. If a security flaw is exploited, it can require anywhere from several months to years for a patch to be installed for all of the specific cars that were already on the road. This implies that it is an extremely important task to prevent malicious code from entering the vehicle in the first place. [PERSON] et al. [73] examine architecture and threats that are prevalent in modern vehicles. They discovered that the gateways built into the automotive network require the use of powerful firewalls. In addition to this, they stated that the firewall implemented in the gateways also needs to possess rules that control access based on the security relevance of the particular network. While filtering approaches or firewall concepts for networks inside the vehicle do exist and are not completely unknown, the range of available research is very limited, especially compared to works on inter-vehicle networks. Even less information is available about existing solutions for cars being deployed. For example, NXP describes the need to protect the car's networked devices from unwanted outside traffic by a gateway for 'filtering inbound and outbound network traffic based on rules, disallowing data transfers from unauthorized sources'. NXP further states that a more fine-granular approach '[...] may include context-aware filtering' [74]. But, often, the exact mechanisms and the security functions used in real vehicles are not published. Another manufacturer's solution is the 'Central Gateway' for central in-vehicle communication from Bosch, which lists a firewall and an Intrusion Detection System on its product page [75]. However, neither the info PDFs nor the actual page provides more precise details. Even when we specifically asked the responsible department, we were unable to obtain any further information about the security features mentioned. In 2016, the company Karamba Security [76] released a security architecture that acts as a gateway between a car's access points and critical networks/modules. Karamba calls it ECU Endpoint Security. Dropper Detection and Malware Prevention. To define factory policies, the developers had the idea of having a system embedded directly in the firmware. This is to prevent malicious code from infiltrating the system. Each ECU specifies its own policy and generates a so-called whitelist of permitted program binaries, processes, scripts and benign network activity. In academic literature, [PERSON] et al. present this as a distributed approach for a firewall system in automotive networks [77]. Their system is focused on allowing only authorised packets to reach an internal device using a Hybrid Security System (HSS) that uses many individual firewalls located in front of each module and at each electronic unit. The inspiration for our study comes from a paper [PERSON] et al. [39], where the authors propose a fine-grained filtering mechanism on the CAN-BUS in a vehicle, exploiting a man-in-the-middle vulnerability incorporating a firewall inside the dongle (see Figure 6). According to the analysis results from [39], the proposed approach allows a fine-grained and extensible filtering approach for all protocols within the OBD.