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.
EDIT: Thank you everybody. I am not a member of this community, but every comment was a golden experience to read!
Seeing as other answers are either links, or wall of texts, I’ll try to keep it short and approachable:
-
Encryption, asymmetrical or symmetrical, relies on private keys being private. Once those keys are compromised, the encryption also is (read on).
-
By default, in the most simplistic form, it doesn’t matter when the content was encrypted, the private key can decrypt it. There are solutions to this problem, making encryption time (or iteration) sensitive.
-
For an attacker with enough means, the private keys can always be exfiltrated, and content can be intercepted, but usually there are much simpler solutions for snooping on encrypted content: the devil is in the (implementation) details (this link is an illustration, and by no means an exhaustive list).
-
Cryptography is always simpler to go around than to break. So never be satisfied with a cryptography only (or protocol only) audit. There are near infinite of ways to neutralize encryption with a single line of code in a client.
-
The architecture is also essential. Client-Server encryption has entirely different use cases than Client-Client encryption (EE2E).
-
And finally, Schneier’s law:
Any person can invent a security system so clever that she or he can’t think of how to break it.
I think no one has mentioned the base for all the cryptographic functions. A mathematical operation which is simple in one direction but very hard in the the other (backwards). The factorisation of large prime numbers is one example.
I’m satisfied with the answers and insights I got so far. But if you may add I’d be happy to know why factorization of prime numbers is so crucial in cryptography. I heard about this a lot before but don’t know anything. I know quite well about Prime number and theorems about them on math, but not their applications
As I understand it, it’s just as they said:
Calculating primes is fairly straightforward so you calculate a few large prime numbers, and do some math to them.
Now you have a strong key that didn’t require a supercomputer to create but taking that final number and turning it back into those original primes is a much more computationally expensive proposition.
In fact, it’s one that’s not viable with current technology.
While we’re talking about asymmetric encryption, can someone explain to me why you can’t decrypt information with the same public key that encrypted it? I understand the analogies (locks on a briefcase, unmixing paint, etc), but I can’t “un-analogize” them to understand what’s actually going on. Encryption keys aren’t physical locks or paint. They’re numbers(?). So why can I encrypt something by multiplying by a known public encryption key, but I can’t decrypt it by dividing by that same known public key?
the government
The secret world government ☝️
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 :)
