On a Debian Sid system, install the following :
apt-get install libpam-google-authenticator
Edit /etc/ssh/sshd_config and set :
ChallengeResponseAuthentication yes
Restart the service :
service ssh restart
Now run :
google-authenticator
Scan the barcode from the Google Authenticator app on your mobile device.
Edit /etc/pam.d/sshd and add at the very beginning of the file :
auth required pam_google_authenticator.so
Now test a SSH connection. You should be prompted by a cool “Verification code :”
Then by the regular password prompt.