SAT: Security in the air using Tesla

Automated Dependent Surveillance - Broadcast (ADS-B) is an aircraft surveillance technology introduced as part of the US Next-Generation Air Transportation System (NextGen) initiative, in which aircraft broadcast their position based on satellite navigation (e.g. GPS). This information can then be used by other aircraft for traffic awareness and collision avoidance (TCAS), and by ground personnel to provide air traffic control (ATC) services. Unfortunately, ADS-B presents important security problems, since there are no integral mechanisms for message authentication nor message integrity verification. In this paper, we propose SAT, a secure, backward-compatible replacement for ADS-B. SAT uses the TESLA broadcast authentication protocol, a hybrid solution that combines the advantages of symmetric cryptography (low use of bandwidth) with those of asymmetric cryptography (no shared keys). Our proposal adapts the TESLA constructs in order to make it suitable for use in ATC and collision avoidance. In particular, we replace the synchronization mechanism of TESLA with the use of satellite time, thus making the implementation more lightweight. We also use a public key infrastructure based on the air traffic control hierarchy (including national civil aviation authorities and potentially ICAO), in order to allow for SAT to be used not only for aircraft authentication but also for aircraft flight authorization. We implemented the SAT protocol on SDR and performed laboratory experiments in order to measure computation and transmission overheads, and to determine the shortest authentication delay we could achieve. In particular, we explored the trade-off between interval duration and bandwidth use. Finally, we tested our new protocol on SDR.