disclaimer: I’m just asking to get understanding of the theory behind network traffic encryption, I know this doesn’t happen irl most likely.
Let’s take https connection for example. I like watching revolutionary things on youtube and do not wish for authorities to know what I am watching, we accept here for the sake of showcase that google won’t sell my watch history if asked (LMAO what am I even saying?).
So if I’m not mistaken since youtube has https implemented, our communication is encrypted, the keys are shared only between me and youtube. But when Youtube shares the key with me/my client the first time, is that also encrypted? Wouldn’t the same question keep getting answered until there is something unencrypted? I know this is a bit too much unlikely, but if ISP automated the process of gathering keys and decrypting web traffic for a certain site with them for all users, would that work for them?
I’m taking https here as an example, while I have the same question for like VPN.
Other comments here do a great job pointing to DH key exchange; I’d like to try explaining it with the paint analogy.
You and Youtube need to agree on a “color of paint” (encryption key) without ever sending it over the network.
You and Youtube agree on a common “yellow” in the clear, and you each pick a secret color. Youtube mixes yellow and their secret and sends it to you. This is okay, because un-mixing paint (factoring large prime numbers) is really hard. You add your secret to the mixture, and now you have yellow+Youtube’s secret+your secret.
You mix yellow and your secret and send it to youtube. Youtube adds their secret; now they’ve got yellow+Youtube’s secret+your secret. You both have the final color!
An eavesdropper can’t reconstruct this - everything sent over the network had yellow mixed in, and un-mixing paint can be really hard. Maybe you can guess that green minus yellow is probably blue, but you can’t get close enough to decrypt anything. And what if it’s brown? Is that blue + orange, or is it red + green?
Cryptographers have worked very hard to make the communications secure. I would be more worried about the other end ratting you out - using a relay / proxy / vpn that you trust is a good idea :)