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?
No encryption; security through expensivity. A major developed nation would be the only candidate with enough resources to build something to communicate with Voyager. But to what end?
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.
I thought you were being handwave-y about the signal being returned because that's an obscenely small amount of power, but you're right. Hardware that is probably 50 years old at this stage, in the cold of (interstellar)space, and we're still able to talk to it despite the signal after its long journey back being ~0.000000000000000001w.
Essentially averaging. To put it simply, noise is random while the signal is not. So if you average 2x the noise reduces but sqrt(2) but the signal remains. Keep doing that and you have the signal appear out of the noise.
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.
This is fascinating. It sounds like viterbi builds probabilities from known data, is that right? Is it essentially looking at the faint signal now and comparing it to data from when the signal was stronger and extrapolating?
That’s how I understand it. I think it uses knowledge of the state changes, what they should be like, and selects the most likely one from a table of options. Based on what it knows about the signal, it guessed whether it’s more likely to be a or b.
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.
I think OP's concern was more around that it's likely easy to break any encryption that was used in the 1970s so someone could send the spacecraft malicious commands.
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.
We have much better chances of designing a cryptography system today that can survive 50 years of math, and with computers a billion times faster we can make the encryption O((1.something)^billion) times harder to brute force. Nothing in the 70s was capable of resisting today's attacks.
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.
Encryption in the 70s resists today's attacks just fine. DES was weakened on purpose (short key length, but the idea for 3DES dates from 1978). In the asymmetric realm you still can't break a full length RSA key.
Maybe it's not fully contemporaneous with Voyager but the claim that 70s encryption is insufficient doesn't stand up to scrutiny
It's not the full length RSA key that's the worry, though, it's the structure around it that Bleichenbacher finds clever ways of poking holes in.
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.
Is today's engineering different? One could argue that we have 50 years more of experience with the engineering (though the components have changed too, requiring newish engineering), and I would guess that we invest more resources in such things these days.
What was "full length" at the time, even if they got RSA implemented immediately after the paper was announced?
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.)
What's a symmetric cipher from the 70s that we can't brute force today?
(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.
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?
Comments
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?
No encryption; security through expensivity. A major developed nation would be the only candidate with enough resources to build something to communicate with Voyager. But to what end?
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.
I thought you were being handwave-y about the signal being returned because that's an obscenely small amount of power, but you're right. Hardware that is probably 50 years old at this stage, in the cold of (interstellar)space, and we're still able to talk to it despite the signal after its long journey back being ~0.000000000000000001w.
I still havent figured out how people decide signals under the noise floor
Essentially averaging. To put it simply, noise is random while the signal is not. So if you average 2x the noise reduces but sqrt(2) but the signal remains. Keep doing that and you have the signal appear out of the noise.
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.
Look up viterbi algorithm.
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.
This is fascinating. It sounds like viterbi builds probabilities from known data, is that right? Is it essentially looking at the faint signal now and comparing it to data from when the signal was stronger and extrapolating?
That’s how I understand it. I think it uses knowledge of the state changes, what they should be like, and selects the most likely one from a table of options. Based on what it knows about the signal, it guessed whether it’s more likely to be a or b.
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.
I need a Jupyter notebook example!
A lot of the signal processioning/decoding gear is cryogenic. Maybe everything to the ADC?
Applied radio astronomy with a transmit component.
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.
I think OP's concern was more around that it's likely easy to break any encryption that was used in the 1970s so someone could send the spacecraft malicious commands.
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.
We have much better chances of designing a cryptography system today that can survive 50 years of math, and with computers a billion times faster we can make the encryption O((1.something)^billion) times harder to brute force. Nothing in the 70s was capable of resisting today's attacks.
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.
Encryption in the 70s resists today's attacks just fine. DES was weakened on purpose (short key length, but the idea for 3DES dates from 1978). In the asymmetric realm you still can't break a full length RSA key.
Maybe it's not fully contemporaneous with Voyager but the claim that 70s encryption is insufficient doesn't stand up to scrutiny
It's not the full length RSA key that's the worry, though, it's the structure around it that Bleichenbacher finds clever ways of poking holes in.
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.
Is today's engineering different? One could argue that we have 50 years more of experience with the engineering (though the components have changed too, requiring newish engineering), and I would guess that we invest more resources in such things these days.
What was "full length" at the time, even if they got RSA implemented immediately after the paper was announced?
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.)
Why would you use public key encryption here in the first place? Just use a symmetric cipher.
What's a symmetric cipher from the 70s that we can't brute force today?
(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.)
Theoretically but probably not practically.
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?
OP might be concerned it's bogus untested crypto from the bleeding edge 70s. not tested crypto from the 40s to 60s we use safely on everything today.