Technology

Huh what do you propose then, go back to the 1960s and ensure they are only using VOR and DME ground equipment. There isn't a check sum to check on GPS/GNSS it just a bunch of satellites broadcasting what they think is the correct time. If you jam those and replace them with signals close enough but wrong values you can trick the math that's used inside the GPS/GNSS receiver that computes the the position (and velocity), and it looks like this signal can be introduced slow enough to trick the receiver in real-world applications. One trick to protect yourself is to ensure the signals you receive are from the direction you expect but we aren't going to attach directional antennas on every face of a civilian aircraft, to ensure the strongest signal is from the top of the plane and not the bottom. Essentially civil navigation equipment isn't supposed to be messed with and if it is authorities are supposed to go over and arrest and fine the idiots doing things over the radio they shouldnt. When the bad guy is a government well yea I guess that plan doesn't work and governing bodies such as ICAO should impose penalties like no commerical aircraft from companies from those countries are not allowed elsewhere.