Re: Crypto cannot mitigate replay?
Absolutely! I agree it would be a stupendous and expensive task, which is why you will probably see ILS gradually replaced as a standard, but not for decades after any potential decision to do so. Unless people deliberately start crashing aircraft using combined ILS/GNSS spoofing. In that case, industry will drag it's feet, and it will take decades.
At least on the US what I see is some thinking that we can possibly eschew large, expensive airport systems for dependent broadcasts from the aircrafts' own nav systems. As in, ultimately replace primary and secondary radar with ADSB.
I think that's idiotic from a perspective of denial of service through ADSB jam/spoof, GNSS jam/spoof, ASAT attacks, truck bombs into GNSS ground stations, etc. But it's cheaper! Must be better!
At some point we might realize that a secure off board source of precision nav might be nice for landing. Given the need is decades out, the process should probably start now.