ssh

Hello, I have been running ssh for some time time now however I have been using password authentication. I would now like to use RSA too. I need help on how this is done. As well I would like to have my set up such thatboth RSA and password authentication have to work before someone can login. This is simply because I provide ftp and if such a password is sniffed then it can be used to start an ssh session. However if I use RSA authentication as well then there would be another line of defence against sniffed passwords.