>>393140
No Such Agency needs its backdoors to be accessible only by them, because they build their backdoors into the chips they issue to the rest of the US government. (No public source for the latter statement.) In the old days, they used centralized key generation, and relied on cryptographic algorithms which are easily broken for most keys to prevent anyone else from generating keys independently; their current approach is to use an obfuscated form of public-key encryption to make key material available to them.
https:// projectbullrun.org/dual-ec/
Clowns In America and Goofy Clowns Hailing the Queen over in the UK have always backdoored things by making them buggy. (See the old OSS sabotage manual on Project Gutenberg.) In hindsight, that's exactly what you would do if you wanted to be able to distribute access to your backdoors to other parties (e.g. MS13).