Defeating Satellite Spoofing with Galileo’s Encryption

What happened

The Galileo ground station pre-selects signal spreading codes, which it then encrypts with a regularly-changing secret key and publishes. Considering how important it is for everything from navigation to keeping clocks in sync, satellite navigation systems are surprisingly vulnerable to a variety of attacks, ranging from simple jamming to more sophisticated spoofing attacks.

Galileo’s Signal Authentication System (SAS) aims to fix this. A receiver which anticipates needing a verified signal can then download these encrypted codes ahead of time and store them.

Galileo satellites then transmit on the E6-C pilot signal, and the receiver records the signal. After transmitting a message block, it then transmits the decryption key on a separate signal, which the receiver operates with to recover the spreading codes.