There’s is already an operating system like that.

https://en.wikipedia.org/wiki/MacOS

https://en.wikipedia.org/wiki/Darwin_(operating_system)

Technically, either side can request that the other generate a key and use that one, and it will cost an additional round trip. But generally in practice, each side generates their own key and tells the other side that it will be using that key.

Yes, those keys are for symmetric encryption, and yes, it’s for performance. It’s way faster to just exchange keys with asymmetric encryption rather than do the whole stream.

Also, I think you meant SSL, not SSH. SSH Uses a different key exchange protocol.

I love cryptography. :)

The CA just signs the certificate. They don’t have access to the private key, and thus can’t decrypt the key exchange.

The key exchange is the only thing decrypted by the private keys. From that point on, everything is encrypted and decrypted by the agreed upon cipher using the exchanged key, which is randomly generated for each session.

Like, decrypt it? None.