Modern airliners are rather complicated feats of engineering. Innumerable safety-critical components are connected with tens of miles of wiring, complex digital buses, and dozens (perhaps hundreds) of computers. But, as hackers, we know that any computer can be hacked and, of course, aircraft avionics are no different.
Modern aircraft typically use the ARINC 429 protocol. This differs from many protocols we see where multiple transmitters are allowed. ARINC 429 has a single transmission source. This makes a transmission-override attack hypothetically difficult, as an attacker was thought to need to physically replace a legitimate transmitter (like a flight management computer), a rather daunting task. However, the ARINC 429 transmitters sit behind a pair of 37.5 ohm resistors, so by transmitting on the same line, an attack device can simply override the legitimate transmitter’s power.
