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!
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
Seeing as other answers are either links, or wall of texts, I'll try to keep it short and approachable:
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Encryption, asymmetrical or symmetrical, relies on private keys being private. Once those keys are compromised, the encryption also is (read on).
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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.
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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).
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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.
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The architecture is also essential. Client-Server encryption has entirely different use cases than Client-Client encryption (EE2E).
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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.
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Asymetrical encryption solves this, here is my attempt to do an ELI5:
Adam want's to send a chat message to Ben, but want to do it securely, so they use a special program on their computers.
When the Adam's program first reaches out to Ben's computer, it asks for an unlocked padlock, this is a padlock that can only be unlocked by Ben's program.
Adam's program takes the padlock and crafts a new special series of padlocks that only Adam's program can unlock, which it put's in a box and locks it with Ben's padlock.
The box is sent to Ben's program, the program unlocks the box and creates it's own special series of padlocks that only Ben's program can unlock, put them in a box and locks it with Adam's padlocks.
The box is then sent to Adam's program, and is unlocked.
This now means that Adam's program can put messages to Ben in a box, lock the box with one of Ben's special padlocks and send it on it's way knowing that only Ben can unlock the box and read the message.
Likewise, Ben can also send messages in boxes locked with Adam's padlocks and know that only Adam can unlock them and read the message.
Added to this is the fact that messages from Ben can be verified as having used the special padlocks Adam sent to Ben, as else Adam's special key wouldn't fit the padlocks given to Ben.
In reality the padlocks are keys to lock a message, and the above text describe a secure key exchange.
