I know a lot of older communications satellites (incl. commercial ones) were just dumb repeaters - receive a signal on one frequency, retransmit it in real time on a different one, don't need to decode it or authenticate anything (although you still need the specialized radio transmitter hardware). This is how Captain Midnight [0] was possible.

I can't imagine modern satellites work the same way.

[0] https://en.wikipedia.org/wiki/Captain_Midnight_broadcast_sig...

"Bent pipe" dumb repeaters are still common for geostationary satellites, AFAIK. Being future-proof against anything except spectrum reallocation (modulation and protocol upgrades can be implemented just by changing equipment on the ground) is valuable for things with long lifespans and high replacement costs.