this post was submitted on 21 Jan 2024
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Privacy
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this is very detailed answer thank you. however I face an ambiguity regarding this:
How can this private half be something that I know, Youtube knows but impossible for the snooper to our communication to know??
Youtube never knows the private half of your key pair. That never leaves your system.
Anything encrypted with the private half can only be decrypted with the public half, and anything encrypted with the public half can only be decrypted with the private half. These halves are known as the public key and the private key. Each side of the connection generates their own key pairs.
We both generate a set of keys, and exchange the public halves with each other. I then want to send you a message: I first encrypt it using my private key, I then encrypt it again using your public key and send that to you.
In order to read that message, you first decrypt it using your private key. This ensures the message was intended for you and wasn't modified in transit, as you are the only one with access to that private key and only its matching public key could have been used to encrypt that layer.
You then decrypt it a second time using my public key. As I'm the only one with access to my own private key, you can be sure the message was sent by me.
As long as that resulted in a readable message; You've now verified who sent the message, that it was intended for you, and that the contents have not been modified or read in transit.
All this, including the key exchange is handled for you by the https (tls) protocol every time you connect to a website. Each of the messages sent between you and the site are encrypted in this manner.
so you can encrypt a message with my public key but you cannot decrypt it afterward ??
The best way I find to think about it is a padlocked box.
The public key is a box with an open padlock on it. I can give it to anyone. If someone puts a message inside the box they can lock the padlock, but they don't have the key to open it again.
I keep the key private. If someone sends me a locked box that has my padlock on it, only I have the key to open it and read the message.