Generate SSH public key authentication

$ ssh-keygen
You can just press enter to create a rsa key pair;
.ssh/id_rsa is your priviate key stays in this machine
.ssh/id_rsa.pub is the public key you need to copy to the remote machine
I would suggest to use a passphrase, which only need to enter once for each OS boot

$ ssh-copy-id username@remote.machine.com
It copies the public key from local machine to a remote machine, and stores it at .ssh/authorized_key file