Generate keys; private key id_rsa is for client, public key id_rsa.pub is for server.
ssh-keygen -t rsa
Append public key to the authorized_keys.
cat /path/to/id_rsa.pub >> ~/.ssh/authorized_keys
chmod 600 ~/.ssh/authorized_keys
rm /path/to/id_rsa.pub
Backup /etc/ssh/sshd_config.
sudo cp /etc/ssh/sshd_config /etc/ssh/sshd_config.ORIGINAL
Update /etc/ssh/sshd_config.
Protocol 2
AllowUsers user1 user2
PermitRootLogin no
PasswordAuthentication no
LoginGraceTime 60
MaxStartups 2
PermitEmptyPasswords no
Restart service.
sudo service ssh restart
View access log.
cat /var/log/auth.log | grep sshd
Connect to server.
ssh -i /path/to/id_rsa <user>@<host>
Update ~/.ssh/config file to use alias.
Host <alias>
HostName <host>
User <user>
IdentityFile /path/to/id_rsa
Connect.
ssh <alias>