Improving Secure Code Estimation-Replay Attacks and their Detection on GNSS Signals

The secure code estimation and replay (SCER) attack was introduced in [1] as a threat for all the schemes that use cryptographic protection of the GNSS signal. There, three possible attack schemes were considered and a detection technique was proposed that assumes the particular strategy employed by the attacker is known to the receiver. The detection technique is based upon the likelihood ratio test (LRT) principle, but some simplifications were introduced, that reduce its computational burden. In this work, we improve on the results in that seminal work, both on the attack and the defense side, by: 1. generalizing the SCER attacks considered in [1] to a wider class and finding the optimal attack within that class, depending on the system parameters; 2. showing that the actual LRT detection scheme performs significantly better than its modification proposed in [1]; 3. formulating the generalized LRT (GLRT) detection scheme, which does not need knowledge of the attack strategy within this class, and deriving its performance.