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:
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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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SSL/TLS, the “S” in HTTPS, and other network encryption protocols such as SSH, use a technique called a Diffie-Hellman key exchange. This is a mode of cryptography where each side generates two keys: a public half and a private half. Anything encrypted with the public half is only decryptable by the associated private half (and vice versa).
You and Youtube only ever exchange the public halves of your respective key pairs. If someone snoops on the key exchange all they can do is insert spoofed messages, not decrypt real ones.
Moreover, the keypairs are generated on the fly for each new session rather than reused. This means that even a future compromise of youtube won’t unlock old sessions. This is a concept called forward secrecy.
Message spoofing is prevented by digital signatures. These also use the Diffie-Hellman principle of pairs of public/private keys, but use separate longer-term key pairs than those used with encryption. The public half of youtube’s signing key, as presented by the server when you connect to it, has to be digitally signed by a well-known public authority whose public signing key was shipped with your web browser.
this is very detailed answer thank you. however I face an ambiguity regarding this:
This is a mode of cryptography where each side generates two keys: a public half and a private half. Anything encrypted with the public half is only decryptable by the associated private half (and vice versa).
How can this private half be something that I know, Youtube knows but impossible for the snooper to our communication to know??
