It’s not a legal right to endanger others so a tailgating protocol isn’t on the face bad. It’d definitely need to be carefully executed though.
Edit-I doubt anyone would be able to make a zero trust network like that incorporate control components. It’d probably be like “I’m going 100 mph with no governor active.” The receiver chooses what to do.
Regulate security measures eg signed messaging where only manufacturers can get certificates? Maybe combine it with license plate so it's traceable to a person?
So the attack will then be to hook into the car's on-board computer and tell it to send the falsified message with a fake plate number, and let the existing cryptographic code handle the signing. Alternatively, dump a legit cert once (e.g. by detailed examination of one on-board computer), then put that into the malicious hardware that sends falsified messages.
This is "the DRM problem", but in reverse. There is no way to give an end user a device that can send cryptographically-protected messages while also guaranteeing that they can't generate messages other than the ones the manufacturer wants them to send. One can make it very, very hard to do so, like with TPM/trusted enclave hardware, but when the potential consequences are people dying in car crashes, and the motivation to send false messages is so high[1], it's just an awful idea, because it will absolutely be misused, and people will die as a result.
Vehicle-to-vehicle communication makes this even worse. At least with a tower intermediary, there would be some sort of forensic evidence stored outside of the vehicles involved.
[1] The ability to manipulate traffic in order to get to one's destination faster would be a huge selling point for a lot of people.
There is also no way to stop someone throwing rocks at passing cars. People will die as a result. The deterrents in both cases will be the same: humanity, liability and law enforcement.
Most of the people who will use malicious signals won't set out to actually hurt other people. They'll just use them to make tailgaters' cars brake quickly, or manipulate traffic in some way that benefits them, like the people in the late 80s or early 90s who figured out that putting strobe lights on their car roofs would let them make some city signals turn green for them. There are far, far more people who would be interested in that sort of thing than would be interested in the electronic equivalent of throwing rocks.
It's the unintended consequences that will generally kill people, like causing a multi-car pileup because the tailgater whose car was forced to brake was being tailgated themselves.
There will be very little way to enforce laws against that kind of activity, because there won't really be any forensic evidence at all.
There is no good way to do this. Even assuming a 100% flawless implementation of a "trusted enclave", people will just buy an ECU from a scrapped car, hook it up to a device that simulates the right sensor input to generate certain vehicle-to-vehicle communications, and stick it in the trunk of their actual car.
That's one of the nice things about 5G. It's an evolution of all the prior mobile protocols that have identity and security baked in from the start. That's what SIM cards are for and why mobile cloning died out.
With 5G and IPv6 you don't really much app-layer security, with the right APIs to give you access to the mobile layer security. The telcos already have the infrastructure to do ID verification on a mass scale and hand out SIMs tied to real world people, or real world manufacturing companies.
The “sharp breaking” message needs to be signed with a key that is tied to the license plate of the car. I.e. the authority that issues license plates also signs the public key whose private key is needed to sign these types of messages.
The more difficult question is how to know whether the car that sends out the message is on the same road as you, and not e.g. on the opposite direction of a highway.
Ensure signals are sent with identifying information (which license plate sent it), and you get 20 years in prison for falsifying the signal or sending it incorrectly, plus whatever manslaughter/murder charges come on top of that.
Seems like the only information you can trust from other cars is "someone broadcast something". You don't know if the message is accurate or even from a car.