Range Authentication of Galileo E1 / E5a Signals Using the ACAS Method on a GNSS Hardware Receiver

This paper addresses the growing need for resilient Global Navigation Satellite System (GNSS) receivers against jamming and spoofing threats. We present the implementation of an Assisted Commercial Authentication Service (ACAS) method for range authentication of Galileo signals using the GOOSE v2 receiver. The ACAS service ensures signal integrity by publishing encrypted Pseudo Random Noise (PRN) code snippets, enabling signal authentication through post processing. Our implementation captures snapshots of incoming signals and computes their pseudoranges, allowing for real-time comparison with GNSS system data. Through a series of experiments, including dynamic spoofing scenarios and a 24-hour open-sky test, we demonstrate that the ACAS method can effectively authenticate E1 and E5a signals, achieving a success rate of approximately 99.99%. The results indicate that the first authenticated fix can be achieved within 50 seconds from a cold start and within 5 seconds from a hot start. This is 3 times faster than an authenticated PVT based on message authentication, e.g. OSNMA. These findings underscore the effectiveness of ACAS in enhancing GNSS receiver security and reliability.