I'm nervous asking, but a little curious what kind of equipment someone would need to give it different instructions. Does it use 1970s encryption? How big would your radio need to be?
Voyagers are sent commands using the DSN, which is in high demand: https://arstechnica.com/space/2023/08/nasas-artemis-i-missio...
They need big radios (the biggest!) because the signal strength coming back from the probes these days are very weak, only one-tenth of a billion-trillionth of a watt.
GPS operates at a negative SNR. That also uses code division multiple access to allow multiple transmitters to operate on the same frequency and the signals do not interfere.
Imagine you're watching a trail of animal footprints in the snow, but the snow has covered parts of the trail (noise), so some prints are unclear. You're trying to figure out exactly which path the animal took. The Viterbi algorithm is like a detective method for doing just that, but instead of animal tracks, it's used for decoding messages or signals that got partially scrambled during transmission.
I use it with ham radio, where the software I use sends signals well under the noise floor (-23db) that can still get across call signs, signal reports, and maybe a thank you. The naked ear would not hear a thing at the low end of received signal.
That would actually be fine, because you can do encryption in software. So you wouldn't need to keep any physical artifacts from the 1970s around.
That said, only America, China, Europe, India, Japan and Russia have deep space networks and none of them have anything to gain from investing the resources into trying to harm Voyager. Even with weak encryption it's likely difficult to collect enough samples to be able to break it and even once it's broken you still need to figure out a valid set of commands to send to achive your goal.
I wouldn't jump to that conclusion. Some things encrypted now are intended to be secure for 50 years.
You mention a one-time pad in another comment. In theory they could have sacrificed a bunch of tape space to store a pad for commands.
Maybe it's not fully contemporaneous with Voyager but the claim that 70s encryption is insufficient doesn't stand up to scrutiny
I don't think Voyager would be very vulnerable to an adaptive chosen ciphertext attack regardless. But you don't need the 70s maths to be wrong, you only need the engineering to have a flaw.
The RSA paper recommends 200 digit keys, which is somewhat under 700 bits. Would even that size run acceptably on an 8 kiloword 0.1MIPS machine? (I couldn't quickly find an actual opcode listing, so I can't say exactly how fast it multiplies, but it's probably not great.)
(And I'm not counting "the idea" of 3DES when even that was after voyager already launched and it wasn't properly set up until 1981. Also 3DES has enough weaknesses that I wouldn't trust it to be uncrackable today.)
It’s doubtful that there’s enough processing or memory headroom for any decent encryption.
You’d have to not only add decryption routines, a key (even 128 bits is a lot!), and that’s another point of failure.
As we know one of the memory modules already corrupted, so if encryption was implemented, chances are the Voyager would be a brick now.
Maybe they use a one-time pad. :) I'm only half joking (imagining the person who has spent the last 40+ years on Voyager with a book). Why not? How much memory and cpu would be required?