A vehicle-to-vehicle communications system that employs a challenge/response based process to ensure that information received from a vehicle is reliable. The subject vehicle transmits a challenge question to the suspect vehicle to determine whether the suspect vehicle is a reliable source of information. The process increases a number of tokens in a token bucket for the suspect vehicle if the response to the challenge question is correct, and decreases the number of tokens in the token bucket for the suspect vehicle if the response to the challenge question is incorrect. The subject vehicle accepts a message from the suspect vehicle if the number of tokens in the bucket for the suspect vehicle is greater than a predetermined upper threshold, and discards the message from the suspect vehicle if the number of tokens in the bucket for the suspect vehicle is less than a predetermined lower threshold.