I wonder what kind of useful info they actually get from monitoring network cables these days? source and destination IP address?
That's a big part of it, but it's also worth noting that intelligence agencies collect encrypted data as well because it might be possible to break the encryption in the future.
They can likely decrypt the majority of traffic. Google, Facebook and all other American companies will have handed over their SSL certs so all content can be intercepted and read.
Same for any servers using cloudflare. Those servers are literally sending all traffic directly to the US.
exactly
and also now.. not all encryption is equal
indeed
Yes, they are mapping human networks because humans are the weakest link in any security. Once you know who's talking with whom, when, where, and how frequently, you can essentially get anything you need by finding the weakest links and exploiting them.
There's an old exercise that shows you dont even have to exploit them. Just knowing the metadata can tell you a loooot.
What old exercise? Reading about cryptography and network stuff involves wading through a lot of weird blog posts and github and mastodon discussions for me. There has got be a better way.
It's kinda funny because 90% of the traffic is just going to be people connecting to whatever online service with known public IPs. But I guess that tells you what household is using what online service. Maybe which businesses are doing network communication with what other businesses i.e. they have some kind of data integration, etc.
Plus you can (sometimes) easily correlate an IP address with an online advertising ID...
Another interesting thing to know would be how detailed the routing table information different countries and intelligence agencies have. You can easily use a service that can tell you where you are located based on your IP address, but it's usually limited to city, state/province, or country. I wonder if for example, the US has the routing tables for specific Chinese neighborhoods or specific houses or apartments.
Meanwhile, the US reportedly responded with: "Nuh uh! 
is spying on you!"
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