  Previous work on misbehavior detection and trust management for
Vehicle-to-Everything (V2X) communication security is effective in identifying
falsified and malicious V2X data. Each vehicle in a given region can be a
witness to report on the misbehavior of other nearby vehicles, which will then
be added to a "blacklist." However, there may not exist enough witness vehicles
that are willing to opt-in in the early stage of connected-vehicle deployment.
In this paper, we propose a "whitelisting" approach to V2X security, titled
Proof-of-Travel (POT), which leverages the support of roadside infrastructure.
Our goal is to transform the power of cryptography techniques embedded within
Vehicle-to-Infrastructure (V2I) protocols into game-theoretic mechanisms to
incentivize connected-vehicle data sharing and validate data trustworthiness
simultaneously.
  The key idea is to determine the reputation of and the contribution made by a
vehicle based on its distance traveled and the information it shared through
V2I channels. In particular, the total vehicle miles traveled for a vehicle
must be testified by digital signatures signed by each infrastructure component
along the path of its movement. While building a chain of proofs of spatial
movement creates burdens for malicious vehicles, acquiring proofs does not
result in extra costs for normal vehicles, which naturally want to move from
the origin to the destination. The POT protocol is used to enhance the security
of previous voting-based data validation algorithms for V2I crowdsensing
applications. For the POT-enhanced voting, we prove that all vehicles choosing
to cheat are not a pure Nash equilibrium using game-theoretic analysis.
Simulation results suggest that the POT-enhanced voting is more robust to
malicious data.
