How to stop SSH from falling back to password?
Solution 1:
If you don't want to globally disable password authentication on your server you can use the -o "PasswordAuthentication no" option on the ssh command line e.g.
ssh -o "PasswordAuthentication no" YourHost
Solution 2:
You can stop password authentication by configuring the ssh daemon. Edit the /etc/ssh/sshd_config file.
#PasswordAuthentication yes
Uncomment and change the above line to "no".
PasswordAuthentication no
Don't forget to restart your ssh daemon!