I am running a SSH server and I am still using simple password authentication. Everywhere I read about security I am advised to use Public-Key Authentication. But I don't get the advantages. Using them is, in my eyes, either insecure or a lot of handy work.
Of course, if someone tries to brute-force the login into my SSH server Public-Key is a lot stronger than any password. But aside from that, it's totally insecure.
The advisors mostly argue that you don't have to remember a password. How insecure is that? So if someone hacks into my computer, he doesn't just get my computer, but my server too? If I am using SSH from various different clients, I have to store the public keys one every one of them, which multiplies the possibility that they fall into the false hands. I could save them on a usb-stick which I carry with me, but it can be lost and the finder has access to my server.
Possibly I am better served with Two-Factor Authentication.
Is there any argument I am missing? What is the best way for me?
Best Answer
This is potentially true anyway with keyloggers: as soon as you log into your server from the compromised computer, they get the password.
But there are 3 advantages to keys:
1) Cacheable authentication. Enter your passphrase once, carry out multiple ssh commands. This is very useful if you're using something that uses ssh as a transport, like scp, rsync or git.
2) Scaleable authentication. Enter your passphrase once, log into multiple machines. The more machines you have, the more useful this is. If you have 100 machines, what do you do? You can't use the same password (unless it's a clone farm), and you can't remember that many. So you'd have to use a password manager, and you're back to single point of compromise. Effectively the key passphrase is your password manager.
2b) It scales in the other way if you have multiple admins using the same systems, because you can revoke keys from user A without having to tell B,C,D,E,F... that the password has changed.
(This can also be done with individual accounts and sudo, but then you have to provision those accounts somehow)
3) Automation and partial delegation. You can set up SSH to run a particular command when a key connects. This enables an automated process on system A to do something on system B without having full passwordless trust between the two.
(It's a replacement for rlogin/rsh, which was hilariously insecure)
Edit: another advantage to public keys rather than passwords is the common scenario where the server is compromised through a vulnerability. In this case, logging in with a password compromises the password immediately. Logging in with a key does not! I would say this is more common than the admin's originating desktop getting compromised.