SSH on Debian: Allow public key access only – no passwords
cd /etc/ssh
cp sshd_config sshd_config.orig
nano sshd_config

Make sure the following three lines are set to “no”. They may be in various locations throughout the file:

PermitRootLogin		no
PasswordAuthentication	no
UsePAM			no

Then restart the service:

/etc/init.d/ssh restart

I learned this at http://www.howtoforge.com/set-up-ssh-with-public-key-authentication-debian-etch