Actually, the NSA has always been tasked with electronic spying *and* securing US DoD traffic from snooping. It's why they hire the most mathematicians in the world, to crack codes and create difficult to impossible to crack code.
Every bit of crypto kit I had, back when I was in the business of shooting and blowing people up, had NSA crypto keys. We knew that the NSA kept a copy and could listen in if something was amiss and we really didn't care.
We *would* care if the NSA was snooping on Congress, as then, they'd be seen to be attempting to undermine their oversight.
Our keys for network services, such as SSL and our CAC cards came from DISA, rather than the NSA and DISA retained a copy. That came in handy when one's encryption key was expired and replaced, as one could retrieve that key and decrypt old messages.
Now, I can't speak on how the GCHQ does things on Landing Strip One, province of Oceania.