Analysis of the Chimera Time-Binding Scheme for Authenticating GPS L1C

The Chimera scheme was proposed in [1] for protecting the GPS L1C signal by inserting random markers at the chip level in the spreading code. Rather than being uniformly distributed, the markers’ positions are set by picking one pattern out of m=256 in a predetermined, publicly known lookup table, possibly for efficiency reasons. This work analyzes the Chimera scheme, focusing on the lookup table to evaluate whether this structure affects the security of the system. In particular, we compare it with an ideal uniform distribution of the markers in terms of their robustness against guessing and collision attacks. We then proceed analyzing other possible attack strategies, calculating or lower bounding their success probabilities, and finally validate the result through comparisons with Monte Carlo simulations.