Is this true for Signal too? I thought it wasn’t.
Signal does indeed use an architecture (at least for chats with contacts, or optionally everyone when you enable the "sealed sender" option that makes you a bit more prone to receiving spam) where Signal doesn't know who's sending a given message from a given IP address, and only which account it's destined for.
But any entity in position to globally correlate traffic flows into and out of Signal's servers can just make correlations like "whenever Alice, as identified by her phone's IP, sends traffic to Signal, Bob seems to be getting a push notification from Apple or Google, and then his phone connects to Signal, so I think they're talking".
Also, Signal relies on AWS, which could also perform such an attack it seems.
The Internet Is Broken: https://secushare.org/broken-internet
The Hitchhiker’s Guide to Online Anonymity: https://anonymousplanet.org/guide.html
Pointers to more resources: https://discuss.grapheneos.org/d/15005-books-or-sources-on-p...
It is, because you cannot use Signal without giving them your mobile phone number, and from that point onward they (and anyone they might be sharing data with) know the who/what/when, and more. My gut feeling, notwithstanding any apologist and their weak arguments, is that the design choice is exactly about the who/what/when because it's mandatory despite being entirely unnecessary from a technical perspective.