I mean the Voyager 1 probe which is currently the human-made object the farthest away from earth. The space program people operating the mission seem to have great control options, they even “moved software from one chip to another” (link) Apart from the probably gigantic and expensive installation needed to receive and/or send messages from/to that far away from home (23 hours of delay?), are there any safety measures to prevent a potentially malicous actor from sending commands to the probe?
I don’t see why they would encrypt it at all. I assume everything is setup to keep power usage to a minimum. I would assume some sort of compacting might be done. Its that type of thing which I would assume would kinda secure it. They don’t use bog standard stuff and if they can use some unique protocol that saves just a bit of energy they are likely to do it. Keep in mind that since like the 90’s a lot of tech stuff has been muscled through rather than maximizing its efficiency. We tend to do efficiency has afterthoughts that effect large swatches like with using video hardware and such.