Securing GNSS signals: a software solution for Galileo signal authentication
- A. Ramírez, A. Chamorro, S. Cancela, D. Calle, GMV
The utilization of GNSS services has become pivotal in various aspects of our daily lives. Whether it is mass-market activities like sports tracking, user guidance, or critical domains such as banking, telecommunication timing, aviation, and automotive solutions, GNSS plays a fundamental role. However, the substantial growth witnessed in the last decade has made GNSS a target for potential attackers.
To enhance future services, the Galileo program is adding a layer of security through the Galileo Assisted Commercial Authentication Service (ACAS). This service complements the Galileo Open Service Navigation Message Authentication (OSNMA) by introducing signal authentication through Commercial Service signals.
In this framework, the ACAS employs a unique approach to protect pseudoranges by incorporating authentication features. These features are implemented at the spreading-code level, utilizing spreading code encryption on the signal to perform Spreading Code Authentication. The service is based on the re-encryption and publication of short-duration spreading sequences from an existing encrypted signal, such as the Galileo E6C signal. The re-encryption process enables the receiver to autonomously retrieve the required sequences without continuous communication with an external server.
This paper details a commercial software solution implementing the ACAS service, designed for integration across a wide array of applications. The software retrieves and decrypts spreading sequences using OSNMA keys transmitted through the Signal-In-Space (SIS). The description on the functionalities is thoroughly described, including FFT-based circular convolution methods for signal acquisition processes, code phase and Doppler computation, pseudorange comparison, and authentic PVT computation.
A comprehensive solution description of the ACAS software solution, highlighting multiple integrations for diverse use cases. Testing in nominal and adverse scenarios, including Signal-In-Space tests, to showcase its real-time operational robustness will be presented. Results are analyzed using key performance indicators, leading to conclusions that assess the software solution's performance, capabilities in real scenarios, and suggestions for further improvements.
