Design Drivers, Solutions and Robustness Assessment of Navigation Message Authentication for the Galileo Open Service

As part of its duties concerning Galileo Services & Exploitation, the European Commission is studying services to be offered by Galileo to the GNSS community in the next few years. A service that could be provided without modifying the payload of the current Galileo satellites is the authentication of the navigation information. The Galileo data authentication service would contribute to improving worldwide GNSS security and make Galileo more attractive to user communities. In order to design and compare different solutions, a conceptual framework including performance indicators is presented. Based on standard navigation performance analysis metrics, the higher-level performance indicators considered in the authentication framework are Availability, Accuracy, Time to First Authenticated Fix and Robustness. Other lower level indicators traced to the above will be defined as well. It is justified why Authentication Error Rate (AER) and Time Between Authentications (TBA) arise as the main indicators. Indicators related to robustness against replay attacks and signal unpredictability, as Maximum Predictable Time (MPT) or Unpredictable Symbol Ratio (USR) will be presented as well. Secondly, this paper presents contributions to the state-of-the-art of standard symmetric, asymmetric and hybrid (symmetric and asymmetric) authentication approaches for satellite navigation. Implementations of cross-authentication among satellites are discussed, and some schemes based on a Timed Efficient Stream Loss-tolerant Authentication (TESLA) protocol are presented. The paper then presents and characterizes one Navigation Message Authentication (NMA) solution for the Galileo E1B Open Service signal. Finally, some conclusions and further work are proposed.