I am still not entirely clear on how they are able to extract the key (does the victim computer need to process the provided encrypted payload? So if the victim never does that, they can't steal the key?), but it's still a fascinating read.
if ( password = "hunter2" ):
return True
Attacks like the author are performing are a lot more complicated and use tricks like coercing the victim into signing distinctive plaintexts, but the example also works for more complex systems like ECDSA where people can derive the signing key by just knowing how long it took.
Instead of going to the effort of making the function run in a constant time, might adding a small random delay before it returns also mitigate against this type of attack?
Noise technically mitigates, but it's like covering your unlocked safe with a cardboard box.
That being the case, there are a lot of systems where that is easy to achieve. If you have GPG in your mail client, it will decrypt anything anybody sends you.
Another thing to keep in mind is that attacks always get better, they never get worse. So today's chosen ciphertext attack is tomorrow's zero-knowledge attack.
In general, it is like many other side channel attacks, where you can use the data to put constraints on the search space for a brute force attack.