Authentication of Galileo GNSS Signal by Superimposed Signature with Artificial Noise

Global navigation satellite systems (GNSS) are widely used in many civil applications to get information on position, velocity and timing (PVT). However, current systems (such as global positioning system (GPS) and Galileo) do not include any feature to authenticate the received signal, therefore leaving open the possibility from an attacker to spoof the GNSS signal and induce a wrong PVT computation at the receiver. In this paper we propose a solution based on the superposition of an authentication message (signature) and artificial noise (AN) on top of the existing navigation signal. Both the authentication message and AN are unpredictable and therefore can not be arbitrarily generated by an attacker. After transmission, through an external public authenticated but asynchronous (thus not useful for PVT) channel, both the authentication message and the AN are revealed, allowing the receiver to check if they were present along the previously received navigation signal. We consider the hypothesis testing problem at the legitimate receiver to decide the authenticity of the message, and we analyze its performance under two attacks: a generation attack in which the attacker does not generate the authentication signal and a replay attack in which a legitimate (including authentication message) signal is replayed by the attacker with a suitable delay in order to induce the desired PVT at the victim. The receiver operating characteristic (ROC) curve is obtained for the hypothesis testing problem under the two attacks.