There is unlikely any non-state actors[1] that has the ability to transmit signals to L2 . Just receiving signals even now (only 2 out of 30 days to l2) the OP used a 6 meter dish. Most of interplanetary mission signals are handled by the DSN.
Any sort of encryption will add both b/w requirements and compute requirements . The CPU/network budgets on such missions are very very limited. Every bit and cycle counts.
Finally standard encryption libraries, algorithms et al, are not likely suitable . I am no expert, but I have not read of any modern algorithms with very low network overhead + compute requirements designed for these kind of use cases, that is also secure from brute force or other attacks.
Mission risk is also a factor, even handshake failures can jeopardize the mission. It is one thing a website did not load because of TLS negotiation failures and $10 B mission overshot its orbit because handshake failures on the encryption layer.
[1] Threats from state actors for science missions is different category of concern, harder to quantify and with not much history of actual attacks. Collateral risks like from the ASAT Russian test to ISS, or in dual use missions would perhaps not apply here .Usually science teams collaborate well even if there is lot of tension in political sphere.
OP was talking about digital signatures and a hobbyist taking command of the spacecraft. In other words authentication.
You said that was unnecessary and too taxing on constrained hardware. That is incorrect. Authentication is both necessary and not excessively taxing, when both considering the risk to the spacecraft's operation or even not considering it, since, as you said yourself, authentication schemes can be reasonably lightweight.
"Not out of the realm of possibility in satellites"
What are you talking about? Of course it isn't! Authentication to satellites is recommended and implemented all the time, for obvious reasons. You think they risk a multi million dollar investment to save some clock cycles? How many commandeered satellites do you read about daily? Do you have sources to back up any of this?
I'd imagine the specs are rated and hardened for radiation first, as seen on all previous NASA satellite and probe missions before getting into the weeds of overhead and encryption.
There is unlikely any non-state actors[1] that has the ability to transmit signals to L2 . Just receiving signals even now (only 2 out of 30 days to l2) the OP used a 6 meter dish. Most of interplanetary mission signals are handled by the DSN.
Any sort of encryption will add both b/w requirements and compute requirements . The CPU/network budgets on such missions are very very limited. Every bit and cycle counts.
Finally standard encryption libraries, algorithms et al, are not likely suitable . I am no expert, but I have not read of any modern algorithms with very low network overhead + compute requirements designed for these kind of use cases, that is also secure from brute force or other attacks.
Mission risk is also a factor, even handshake failures can jeopardize the mission. It is one thing a website did not load because of TLS negotiation failures and $10 B mission overshot its orbit because handshake failures on the encryption layer.
[1] Threats from state actors for science missions is different category of concern, harder to quantify and with not much history of actual attacks. Collateral risks like from the ASAT Russian test to ISS, or in dual use missions would perhaps not apply here .Usually science teams collaborate well even if there is lot of tension in political sphere.