I am a big fan of RPi and I allowed one of my RPis (I have 3) to be accessible from the Internet via SSH. But, I was stressed because somebody might do a DoS on my device with the intent to hack into it and this way would prevent me to access it.
So, wanting to secure it, I researched a bit how to enable two-factor authentication for SSH. I don’t want expensive SMS services, actually I don’t want to pay anything at all.
I found some great tutorials on the net, and here is my take on how to enable this great service via Google’s open-source Authenticator.
Here are all the details about how to do this:
http://sorinmustaca.com/2013/04/09/enab ... pberry-pi/