> If NSA and only NSA can crack a particular system, they probably wouldn't mind using it for their own secrets.
How do you think they could assess that they, and only they will ever be able to exploit a particular cryptographic vulnerability at any time over the next few decades?
They can’t, they would be well aware of that, and they are extremely risk averse.
> And anyway why is there any reason to believe they really do use the system they say they use?
Because these systems exist widely throughout government today.
https://www.nsa.gov/Resources/Commercial-Solutions-for-Class...
https://www.disa.mil/-/media/files/disa/fact-sheets/dmcc-s-f...