navigatron, 1 year ago

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 :)