I recall seeing a story in the past about how the NSA planted a misleadingly weak encryption library.

https://golem.ph.utexas.edu/category/2014/10/new_evidence_of...

If the encryption used is flawed, they could see whatever they want.

> what can they actually see if the traffic is encrypted?

They can see who is talking to who, and when:

* https://en.wikipedia.org/wiki/Traffic_analysis

Source, destination, message length, etc. Lots of interesting meta data to play with.

Considering they do intercept, as widely documented, question is how do they see if traffic is encrypted?

And at 250tb passing by every second

Nobody knows. Probably not.

But Snowden showed us that a lot of it is scooped up and warehoused. Maybe they can see your traffic in a decade or two?

Forget encryption every second so much data passes through at a time can they even isolate particular data let alone encrypted data. Can they process all that data in real time if not how are they storing it to process later. This is just 1 cable from 1 company there are now dozens of cables of different companies.