I recall reading that the Galileo signals have some built in authentication scheme, e.g. something along the lines of what is mentioned here: https://www.gsa.e

I recall reading that the Galileo signals have some built in authentication scheme, e.g. something along the lines of what is mentioned here: https://www.gsa.europa.eu/newsroom/news/new-funding-opportunity-galileo-open-service-authentication-user-terminal https://www.gsa.europa.eu/newsroom/news/new-funding-opportun... I would have thought that the military level GPS signals might have something similar already.