> The way you verify your identity to Let's Encrypt is the same as with other certificate authorities: you don't really. You place a file somewhere on your website, and they access that file over plain HTTP to verify that you own the website. The one attack that signed certificates are meant to prevent is a man-in-the-middle attack. But if someone is able to perform a man-in-the-middle attack against your website, then he can intercept the certificate verification, too. In other words, Let's Encrypt certificates don't stop the one thing they're supposed to stop.
Doesn't ssl handshake require knowing the private key?
Last time I checked it didn't have functions. Has that changed?