Abstract: A secure automatic dependant surveillance—broadcast system includes: an authenticator including a unique id generator memory storing an authenticator secret key and a transmitter for transmitting the unique id to a responder; a responder including a secure hash algorithm generator combining the received unique id with a responder secret key and a data signal to generate a secure response and a transmitter transmitting the secure response and the data signal to the authenticator; the interrogator also including a receiver receiving the secure response and the data; the authenticator including an secure hash algorithm generator combining the received data and the received secure response and generating an output signal; and a comparator for comparing the output signal with the received secure response and providing an authentication signal based on the comparison.