Operating Modes and Performance Evaluation of Galileo Assisted Commercial Authentication Service

The European Global Navigation Satellite System (GNSS), Galileo, is currently leading the development of new services focused on the authentication of the position to mitigate the vulnerabilities of common receivers. It has recently incorporated the Open Service Navigation Message Authentication (OSNMA) in its E1-B signal, which allows to authenticate the navigation data symbols, but it is also working in the encryption of the spreading codes to provide increased security and robustness against malicious attacks like spoofing ones. This last technique will be provided in the forthcoming Commercial Authentication Service (CAS) operating in the E6-C signal. Currently, an 'assisted' mode is being defined, known as Assisted Commercial Authentication Service (ACAS), which aims to authenticate the ranging signal without the need of storing any secret key at the receiver. This paper reviews the key aspects of this service and its implementation issues and analyses the different operating modes that arise from this implementation, identifying the possible threats to face off.