Re: Steganography & Cryptography
It is very easy to distinguish an artificial signal from random noise, because the artificial signal has to maintain some sort of timing while random noise is, you know, completely random.
Not always. Asynchronous comms has been a thing for decades, and from memory, has been used by NASA and others to communicate with spacecraft. I think that Voyager uses an async protocol so it didn't have to worry about clock drift. But think early days where serial comms and good'ol RS232/V.24 could manage using just 3 pins, 2, 3, 7 for tx, rx and gnd. Then how quickly we've migrated from HTTP to HTTPS, and the way good encryption should appear random.
The only way we would ever receive anything though is if it is either broadcast directly at us, or with a very wide beam, and even then unless they are powering it with a star they will need to be in our galactic neighborhood for us to receive it with enough SNR.
Some of that can be done by transmitting duplicate packets and relying on the endpoint(s) to do reassembly, with things like sequence numbers and checksums helping. Again something I think Voyager uses. Also one of the reasons I was disinvited from the Interplanetary Internet project for saying stuff like 'the protocols you're using are really neat, why would you want to use TCP/IP?'
But there's also fun science meets SF happening. So rather than using a star to power your transmitter, why not just make the star into a transmitter-
https://en.wikipedia.org/wiki/Pulsar-based_navigation
X-ray pulsar-based navigation and timing (XNAV) or simply pulsar navigation is a navigation technique whereby the periodic X-ray signals emitted from pulsars are used to determine the location of a vehicle, such as a spacecraft in deep space. A vehicle using XNAV would compare received X-ray signals with a database of known pulsar frequencies and locations. Similar to GPS, this comparison would allow the vehicle to calculate its position accurately (±5 km). The advantage of using X-ray signals over radio waves is that X-ray telescopes can be made smaller and lighter. Experimental demonstrations have been reported in 2018
Then hope whoever's done this already is benevolent and doesn't object to us using their nav system. A species that can turn stars into nav beacons or X-ray WiFi APs is probably not to be messed with. Or there's other fun stuff, like quantum entanglement and quantum teleportation. Or maybe my favourite.. Neutrinos. There was a successful experiment a few years back using neutrino comms to transmit through a mountain. Currently we have neutrino observatorys, but those can't provide too much detail about the neutrinos. That's been used in SF though to detect alien signals.
If they are trying to say "we are here" they would presumably try to make it easy for us to understand. There might be no hope of giving us real information though, like the plans for building a machine (or two, for twice the price) to take us somewhere.
That assumes benevolence and some alien civilisation firing off 'Hello other world!'. Not transmitting to their approaching invasion fleet. Or maybe we'll identify and decode a signal and discover it's a friendlier species trying to warn us about the approaching invasion fleet. Or it's telling us to evacuate because construction on the new hyperspace bypass is beginning in a few weeks.
Biting the hand that feeds IT
