Semiassisted Signal Authentication for Galileo: Proof of Concept and Results

Abstract

A <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">semi-assisted</i> GNSS authentication concept is proposed, with two main advantages. Firstly, it can be implemented in a GNSS without modifications to the signal plan, provided that the GNSS can transmit an encrypted signal and an open signal with unpredictable and verifiable bits regularly. Secondly, it can work in a receiver for up to several days without any assistance or the possession of a private key, at the expense of some authentication latency. In this concept, parts of the encrypted signal to be transmitted in the future are re-encrypted, published, and downloaded in the receiver. Some seconds after transmission, the satellite openly broadcasts the decryption key, and the receiver performs the a-posteriori correlation with the encrypted signal. The concept is particularized for the Galileo system as Galileo ACAS (Assisted Commercial Authentication Service), based on OSNMA in E1B for the decryption keys and E6C for the encrypted signal. An end-to-end procedure for measurement authentication is proposed and tested, showing its viability.