The xkcd solution should work : https://xkcd.com/538/

I'm surprised that the FSB was actually called upon, Russian SIGINT efforts are directed by the GRU, they inherited the KGB's SIGINT network and personnel, and they are the one heading Russia's terrestrial and space based SIGINT operations and platforms. The FSB is more akin to the FBI+ICE+ATF, MI5 or the Israeli Internal Security Service (Shin-Bet) they are responsible for state and internal security, not intelligence collection on this scale, also so far all the high confidence attributed Russian cyber operations were also attributed to the GRU not the FSB.

Secondary hypothesis: Putin is ex-KGB, he's probably got closer contacts in the FSB than the GRU; easy to tell them to say "yes" to whatever deadline he gives them. Looks good all around.

Putin main KGB career was in the 1st Directorate (Foreign Intelligence Service) in which he served as an FIO, which turned into the SVR when the Russian Federation was established, the SVR and GRU are 2 sides of the same coin. He later did serve as the director of the FSB for a very short period but he's best known for reforming the organization which resulted in major "layoffs" (and being laid off in the intelligence world, especially in pseudo authoritarian regimes rarely ends well), but again this is an odd case, but as some others have mentioned it seems to be a legal framework to compel companies (or individuals) to hand off their keys rather than some technical solution.