After reading this scary blog entry about domain hijacking I’ve been a bit concerned about brute forcing of credentials and have been turning on the two-factor authentication facilities that folks like Google provide for my gmail and personal domains.
I’ve just found out about Duo Security, a service that allows you to add two-factor authentication to your SSH server, Juniper VPN and even Wordpress blogs. Their service is free for up to 10 users and they start charging when you pass that threshold.
Read on to find out how to set it up.
I set it up this evening on my Joyent SmartMachine, but the procedure should translate to pretty much any other unix system–Solaris is slightly more involved because it doesn’t ship with OpenSSH.
The first thing to do is to set up an integration; the Duo Security site has the details on this. An integration is basically an authentication domain; you set one up for a service and then you can associate users with it.
With that done (it’s only a few clicks and a text message) you can set things up on your server; there is a tarball to download from github that contains the sources to a PAM module and an alternative “login” program that call back to the two-factor service.
Copy the tarball up to your server and build it:
% scp duo_unix-1.6.tar.gz myserver: % ssh myserver % tar xzf duo_unix-1.6.tar.gz % cd duo_unix-1.6 % ./configure % make % sudo make install
This builds out-of-the-box.
The next thing you need is to provision OpenSSH. This is not the default for Solaris, so we need to obtain and install it via other means. On the Joyent SmartMachine system, we can simply install it from the pkgsrc provided by Joyent:
% sudo pkgin install openssh
Now the slightly tricky part; we want to configure this and make sure it works before we replace the system ssh service with it. We’re going to run it on an alternate port to test it.
Edit the config file:
% sudo vi /opt/local/etc/ssh/sshd_config
and add the following lines:
Port 8080 ForceCommand /usr/local/sbin/login_duo
Now start it up:
% sudo /opt/local/share/examples/rc.d/sshd start
Don’t try and login yet; we need to configure the /etc/duo/login_duo.conf file to match the settings for your integration. Go to the dashboard on the Duo site and call up the details for your integration; you need to transfer the ikey, skey and host settings to your config file:
% sudo vim /etc/duo/login_duo.conf
The default looks like this; fill in the blanks:
[duo] ; Duo integration key ikey = ; Duo secret key skey = ; Duo API host host = api-eval.duosecurity.com ; Send command for Duo Push authentication ;pushinfo = yes
Now fix the ownership and permissions:
% sudo chown sshd /etc/duo/login_duo.conf % sudo chmod 600 /etc/duo/login_duo.conf
And test that the authentication works:
% login_duo echo YOU ROCK Please enroll at https://api-XYZ.duosecurity.com/portal?XYZ
Go to the URL and enroll yourself as a user. This is a straight-forward multi-step process; you register yourself and your cell phone and have the option of completing this via text message or the smartphone apps (iPhone, Android and others that I didn’t care about).
When your enrollment is complete, try it again; you’ll have to confirm the login via your phone:
% login_duo echo YOU ROCK Duo login for wez 1. Duo Push to XXX-XXX-9390 2. Phone call to XXX-XXX-9390 3. SMS passcodes to XXX-XXX-9390 Passcode or option (1-3): 1 Pushed a login request to your phone... Success. Logging you in... YOU ROCK
Now back to SSH; test our OpenSSH server, again, you need to confirm the login via your phone:
% ssh -p8080 myserver Duo login for wez 1. Duo Push to XXX-XXX-9390 2. Phone call to XXX-XXX-9390 3. SMS passcodes to XXX-XXX-9390 Passcode or option (1-3): 1 Pushed a login request to your phone... Success. Logging you in... myserver %
You should land in a shell on the server.
If all is good, you can switch the system to use your OpenSSH server. Make sure you have a couple of SSH sessions open to the system before you start this bit; if you mess up, you may not have an SSH server running, and you’ll need to contact Joyent for help:
% sudo ln -s /opt/local/share/examples/rc.d/sshd \ /etc/rc.d/sshd % sudo svcadm disable ssh
At this point, you are no longer running the regular ssh server, but have OpenSSH running on an alternate port. We configured it to run on startup by creating that symlink, but we need to switch it to the regular port; fix that by editing the config file:
% sudo vi /opt/local/etc/ssh/sshd_config
And change the Port line:
Now to restart our ssh server:
% sudo /etc/rc.d/sshd stop % sudo /etc/rc.d/sshd start
And then verify the login; you will probably need to fix your known_hosts file to reflect that OpenSSH generated a new server key for you–advanced users can probably copy the system key.
% ssh myserver Duo login for wez ....
And voila, we’re all done; now no one can log in to the system without confirming it through a secondary channel, making it that much more difficult for your account credentials to be stolen or guessed and exploited.
Additional exercises for the reader are to reboot to make sure that ssh comes up after a reboot, and to look at setting up an SMF manifest rather than a legacy init script.