Hardening

Note: This page is still work in progress, so don't use for production (yet).

SSH

/etc/ssh/sshd_config

AuthenticationMethods publickey
ReKeyLimit 1G 10m
AllowAgentForwarding no

A few remarks:

• Disallowing root login doesn't bring any security advantages if you're only allowing secure AuthenticationMethods anyhow. It can even decrease overall security, because if forces you to use sudo, which could be replaced with a malicious (keylogging or command injecting) shell alias within the context of the unprivileged user account you're using sudo from.
• Compared to PasswordAuthentication no, AuthenticationMethods publickey has the advantage of being more easy to check during blackbox security scans, without even requiring a user account on the machine to be scanned. A potential downside is that it will also prevent some 2FA login methods like TOTP from working.