Authentication of signals

I realize this is a broad topic but since there are so many signalheads here maybe it’s a good place to ask.

Is there anything akin to PKI (public key infrastructure) in the world of signal rx/tx?

Or to state the question simply, are there implementations for authenticating signals that are in use? What are they called?

Why do public broadcasts not use some form of authentication? AFAIK there’s currently no way to know if you’re getting an authentic signal from channel 9 or whether someone near is overpowering channel 9 and sending you their version. i.e. MITM (man in the middle)

Encryption is sort of an authenticating system but there’s nothing to prevent me from encrypting my tx and sending that. (presuming I have the encrypting hardware). But I say sort of only because AFAIK the encryption is just a barrier and not an authentication system.

Yes, at least in terms of authenticating the payload. This is why GSM handsets have a SIM card with a crytographic key locked inside, that is used to authenticate a subscriber to the network. There is no reverse of this in GSM, though, where the network proves its identity to the handset. Which is obviously a major flaw. This has subsequently been addressed in — I think, as I’m not so familiar with it — 3G/UMTS onwards.

Interesting. Well we all now know who/what might benefit from the flaw. I guess there must be other schemes because there are too many use cases I can think of that insist/require/must have authentication. i.e. Driving drones, flying drones, etc.

Another use case to consider. I just read and he notes that the Cubesats are equipped with transcievers. So how do they prevent take over of their satellites? I would expect it might be difficult to intercept the terrestrial-to-satellite comms. But is it impossible? I’d expect that sniffing that traffic would be something some might like to do.