If you really want to run a masternode although you aren't too much into the security stuff (which I advise against!) then you at least might wanna use 2-FA for your SSH access.
Here's a fool-proof (well, there's always a greater fool!) tutorial on how to do that on Ubuntu.
http://www.howtogeek.com/121650/how-to-secure-ssh-with-google-authenticators-two-factor-authentication/edit: btw, the Android Google Authenticator isn't open source anymore! You can download "OTP Authenticator" which is a fork of the last Google Authenticator version that was open source. There's the binaries on the play store, the source is hosted on sourceforge iirc.
tried this, but apparently it doesn't work together with pubkey authentification

pubkey Auth just skips the 2FA. Does anyone know how to get this working together?
got it kind of working. If you have pubkeys auth already enabled and follow this simple guide posted by hartvercoint and add "AuthenticationMethods publickey,keyboard-interactive" to the sshd_config you need the pubkey then the password and then the 2FA code

Super secure!
But I kind of want to eliminate the password and just have pubkey and 2FA

If Anyone knows how. Shoot it!