By default, Debian 8 has now killed your ability to log into root via SSH directly. This was done for security reasons.
But don’t forget… this is linux. You know you can fix that. And if you want to, here’s how to do it.
Login and su into root. Edit this file:
Scroll down for a bit and you’ll see a line that says
Put a # and a space in front of this line like so:
# PermitRootLogin without-password
now rewrite it on a new line like this:
Now save the file and restart the SSH server.
Ta da! Now SSH into it directly as root. Congrats! Your old insecure ways of doing things have returned. Enjoy.