This series of posts is about security and privacy of vehicular communication (V2X), or Connected Intelligent Transportation Systems (C-ITS). But we first need to discuss the background as a starting point that leads to why security and privacy solutions are defined as such.
Basic services of V2X communication
There are multiple purposes, or use cases, of V2X communication. Among them, the primary purpose is to improve road safety by including the “communication” element in vehicles. Let’s call it basic services. Contrary to this, there are other more advanced use cases that introduce additional value. For the sake of discussion, we focus on basic services and exclude these more advanced, specific use cases, such as remote driving.
Basic services involve two types:
- Cooperative awareness
- Notification/warning of potentially safety-impacting situations
In the first case (cooperative awareness), vehicles share information regarding their kinetic movement and related information, such as:
- Speed
- Direction
- Acceleration
- Position
- And other related meta data (e.g. vehicle type, physical size)
By all vehicles sharing their own information with all other vehicles within the communication range, all vehicles eventually form a mental picture of their surroundings – how many vehicles are present, which direction and how fast they are moving, etc. This is called dynamic map, as this awareness of surroundings changes dynamically.
These information can serve to detect potentially dangerous situation on the road (e.g., imminent collision). In conventional human-driven vehicles, this information can trigger a warning or an alert to the driver by displaying messages on the dashboard, etc. In autonomous driving vehicles (AVs), this information can be input to their navigation decision.
The second case (notification of potentially safety-impacting situations) includes situations that require warning or alerting to vehicles in the area. This includes events such as an emergency vehicle approaching, a vehicle standing on the road side, congestion ahead, etc. To disseminate these warning situations beyond the immediate communication range a single vehicle can reach, vehicles can propagate these messages hop-by-hop.
In the first case, cooperative awareness messages are transmitted periodically to accurately update the reality around vehicles. In the second case, warning or notification messages are aperiodic, i.e., they are transmitted only when a relevant condition occurs.
The “operating environment”
Vehicles move, by definition. This makes communication involving vehicles a rather unique operating environment. Of course, other systems also use wireless communication and involve users’ movement. These include cellular mobile systems (and Wi-Fi to a lesser extent). However, what sets V2X apart from them is that it is a real-time system (RTS) involving road safety. After all, the fundamental purpose of introducing V2X is to use this technology to improve road safety. If it doesn’t attain that goal, there’s no point in doing it.
What it means from security point of view?
From a given vehicle’s point of view, as it moves along the road, it encounters a random number of unknown vehicles, moving in various directions and at various speeds.
The number of vehicles, their directions, and their speed vary, depending on factors such as places, types of the road, time of the day, weather condition, etc. Rush hour on weekdays in a big city would be a very different situation from the rural areas at 3AM on Sunday morning.
Because of this operating environment, the cooperative awareness and notification/warning messages are transmitted in broadcast and in clear. In other words, they are sent to all vehicles without confidential protection (encryption) – [see note 1 below]. Any devices suitable to receive these messages are able to receive, store, and analyze them.
This resulting communication mode (broadcast messages sent in clear) set a constraint on how solutions for security and privacy can be designed in V2X communication.
In the next post, we will go further into details of these solutions.
Note 1: There are schemes to manage encryption in group communication. But, it require dynamically coordinating key distribution and management. In a dynamic topology like vehicles on the road, it is simply not practical to distribute, coordinate, and manage encryption keys.
TY Security Blog 