Authentification
From Blue-IT.org Wiki
Yubikey
SSH
Generally: only use key based authentification with your ssh-webserver login!
vim /etc/ssh/sshd_config
[...] PermitRootLogin without-password StrictModes yes RSAAuthentication yes PubkeyAuthentication yes IgnoreRhosts yes RhostsRSAAuthentication no HostbasedAuthentication no PermitEmptyPasswords no ChallengeResponseAuthentication no PasswordAuthentication no # <<<< !!!! X11Forwarding no UseLogin no UsePAM no <<<< !!!!