# Study on DID Application Methods for Blockchain-Based Traffic Forensic Data
## 2 Materials and Protocols  
A map, which is a part of finding the optimal route for a vehicle and driving, is divided into three types of maps; a navigation map, an ADAS map, and a precision map (LDM: Local Dynamic Map). First, the navigation map that is used on vehicles or cell phones considers traffic conditions and displays the optimal route when a destination is stated. An ADAS map, which is more advanced than the conventional navigation map, assists in making the ride smoother, for it contains information on the curvature and inclination of roads. However, LDM, which is the most essential in autonomous driving, goes beyond the conventional recognition of roads and contains all information about roads such as lanes, centerlines, traffic signals, and guardrails down to an accuracy of within 10 cm. The existing navigation system or an ADAS map is restricted in times of rain or snow, but an LDM contains all the information about roads and can provide the optimal driving conditions without restrictions such as the weather. A CAN (Controller Area Network) is a standard protocol for the communication of numerous electronic control units (ECU). A CAN is widely used in vehicle communication for its universality and efficiency, but issues regarding improvement of its functions and transmission bandwidth have been raised due to the increased number of ECUs installed in a vehicle and the addition of advanced sensors. As such, various protocols such as LIN, FlexyRay, MOST, and CAN-FD were suggested, but none have been able to replace the universality of CAN and are only used for specific parts or OEM [3]. An Automotive Ethernet is also being considered as a new type of vehicle communication network-based technology that accommodates other networks and supports the existing TCP/IP system as well as a wider bandwidth for the increased functionality of CAN. When a so-called Connected Car is connected to a network (e.g., 5G, DSRC etc.) and autonomous driving and connected technology is applied, it is very likely that communication between each ECU and Actuator will be processed by an Automotive Ethernet [3].  
CAN uses the OBD-II port to determine whether vehicle sensors have failed and uses Diagnostic CAN protocol to diagnose a vehicle. An OBD-II port is also used to obtain information from a vehicle's dashcam or navigation system and as an HUD (Head-Up Display) for driver convenience. Only some of the information gathered from sensors defined by IBD-II, such as RPM, vehicle speed, throttle position, information on fuel, and steering, may be used in traffic accident investigations. There are two types of devices that record a vehicle's operation information: An EDR (Event Data Record) and a DTG (Digital Tacho-Graph). Analyzing the data record in an EDR can determine impact velocity, the use of brakes or accelerator, and whether a seatbelt was fastened. A DTG is required by law on commercial vehicles such as taxis, buses, and trucks since 2013 and is proving very useful in traffic accident investigations [4; 5]. Traffic accident analysis using EDR or DTG is more detailed and reliable in analyzing the vehicle that is the subject of a traffic accident compared to the traffic accident analysis method of analyzing damage to a vehicle or skid marks, and has great value as forensic evidence [6]. It is usually difficult to adopt video records used for analyzing traffic accidents as evidence for accident analysis because analyzing whether the driver is at fault, the issue of picture resolution, altering, falsifying, or damaging records are common issues. Digital data generated by various sensors attached to a vehicle is not easy to alter or falsify and are stored in log form, making it valuable as evidence and also making it possible to introduce it to accident investigation or a digital forensics framework. Since there is no framework that applies digital data generated by sensors, however, we would like to propose introducing a framework through case studies of accidents utilizing digital data.