[ElectRabbit]

Galileo offers optional cryptographic signatures for their positioning data.

It's a solved problem and free for use.

https://www.gsc-europa.eu/sites/default/files/sites/all/file...

[michaelt]

Sadly this doesn’t solve the problem.

Spoofers simply receive the signed signal and re-broadcast it with a tiny delay. Signatures still intact.

[brohee]

If you ever received unspoofed data, and have a somewhat accurate local clock (rubidium is fairly cheap), you can detect the spoofing.