This is an excellent tool to implement 2 factor authentication on your server. Granted you will need your phone close by in order to login but if you have ever used RSA, this will be very familiar to you.
You will need to sign up in order to use this.
Once you sign up, you will receive an email to authenticate against the account. Once this is done, you will need to install the smartphone app. Once this is installed, you will begin receiving updates every 20 seconds with new codes when the app is active.
Once you login to your new Authy account, go to the User Menu (top left) and create a new application. Name the app and it will provide the API key needed for the server install in step 2.
Next you will be asked what you would like to do in case your server cannot connect to API. Select option 1 or 2 at this point. Authy will then be installed and configured. Next, enable the 2 factor authentication by adding the needed user info seen below in step 3. That’s it, the authentication is ready to go. Restart SSH to make sure the new configs take effect.
Here is a video of the install process for Authy
The github code can be found here
To install on the server:
$ curl 'https://raw.github.com/authy/authy-ssh/master/authy-ssh' -o authy-ssh
$ sudo bash authy-ssh install /usr/local/bin
$ sudo /usr/local/bin/authy-ssh enable `whoami` (your-email) (your-country-code) (your-cellphone)
$ authy-ssh test
$ sudo service ssh restart