A secure location verification method for ADS-B

At the heart of the NextGen Air Traffic Control System, there is the ADS-B (Automatic Dependent Surveillance - Broadcast) that provides aircraft location data. Despite its importance, ADS-B has been developed without consideration of security risks and is subject to various types of attacks. Although a number of techniques have been proposed to protect ADS-B, there are many challenges remaining for applying them to real world. We have developed a practical method that can reject virtually all spoofed ADS-B messages by monitoring the radio propagation time between senders and receivers. To measure the actual propagation time, it uses a small timestamp value; hence we call it ADS-B with Timestamp (ADS-BT). ADS-BT monitors the discrepancy between the time of flight based on the timestamp values and the time of flight based on the location data. In spoofed ADS-B messages, the discrepancy between them diverges over time, which allows us to identify spoofed ADS-B messages accurately. Our study shows a 99% detection rate within a few seconds and 100% rate within 25 seconds, with 0% false positive ratio. ADS-BT does not require any special hardware or 3^rd party stations to collaborate. It does not require synchronized clocks or cryptographic processing. In this paper, we describe how the time discrepancies are measured, how the timestamps are implemented and used, and how the spoofed message frames are rejected passively and actively. We then demonstrate its performance through simulation study under various attack scenarios. If ADS-BT is adopted in the NextGen ATC, the security risk for the ADS-B can be substantially reduced.