@golgaloth So those steps -- the way they work is something called "public/private key cryptography". The details aren't important, but it means you can use math and find pairs of numbers, a secret lock and a public key, that let you say,
"This is my private, secret, number.
I can use this number to put a lock on a message so it can only be opened by the matching public key,
and if you open a message like that that you know that only I, who knows my private, secret, number, could have said it."