The Galileo Signal Authentication System works by pre-publishing encrypted spreading codes; the satellite transmits on E6-C, the receiver records the whole block, and only afterwards does the satellite broadcast the decryption key. So an adversary can't know the spreading code in advance and can't forge a correlated spoof — the best they can do is blanket noise. It's a time-delayed disclosure scheme, not the naive "encrypt everything" approach, and importantly the keys go out publicly: this isn't a military-only service. The result: at Jammertest in Andøya, Norway, ESA held a stable lock on their receiver using five Galileo satellites while under active spoofing. That's the first cryptographically-verified position fix demonstrated in the field, not a lab claim. Commenters correctly note it does nothing against jamming or meaconing — denial of service remains fully available to the attacker. Authentication buys you integrity, not availability. In principle the design ports to GPS and other GNSS, though GPS's existing anti-spoof modes (P(Y), M-Code) are keyed military-only, so the civilian signal stays bare until someone in Colorado decides otherwise. Open question: what's the receiver storage and latency cost of pre-downloading encrypted codes ahead of needing a verified fix? The source doesn't say.