Couldn't this be solved better by some form of web of trust (WoT)?
Say your car A trusts other cars B, C ... Y to varying degree in a WoT. It meets a brand new car Z that is not yet trusted by any cars A-Y. Car A receives a message from Z, to which it assigns 0 credence points, meaning this data is not taken into account in any decisions. If car A then makes an observation confirming the message, car A now trusts Z by +1 point, and lets other cars know this. (I'm unsure how to make aggregation/distribution of trust work smoothly, but I believe the random mixing of traffic patterns will work in the system's favor.)
So gradually car Z becomes trusted, up to some maximum, e.g. 100. The only worry then is a malicious actor who mostly sends true messages, but that's hard to distinguish from a car with a sometimes faulty sensor. Those problems could be handled the same way, namely aggressively penalising a car for sending incorrect data (e.g. by -30), such that it's quickly distrusted, together with a prominent warning in the failing car when it goes below 0 trust that it needs maintenance (after which trust would be reset to 0). Possibly also increased insurance premium if your car remains with a trust below 0.
Say your car A trusts other cars B, C ... Y to varying degree in a WoT. It meets a brand new car Z that is not yet trusted by any cars A-Y. Car A receives a message from Z, to which it assigns 0 credence points, meaning this data is not taken into account in any decisions. If car A then makes an observation confirming the message, car A now trusts Z by +1 point, and lets other cars know this. (I'm unsure how to make aggregation/distribution of trust work smoothly, but I believe the random mixing of traffic patterns will work in the system's favor.)
So gradually car Z becomes trusted, up to some maximum, e.g. 100. The only worry then is a malicious actor who mostly sends true messages, but that's hard to distinguish from a car with a sometimes faulty sensor. Those problems could be handled the same way, namely aggressively penalising a car for sending incorrect data (e.g. by -30), such that it's quickly distrusted, together with a prominent warning in the failing car when it goes below 0 trust that it needs maintenance (after which trust would be reset to 0). Possibly also increased insurance premium if your car remains with a trust below 0.