With this authentication plugin you may selectively choose which Joomla users will require a Yubikey device to log into Joomla!.
Two-factor authentication is achieved by requiring a Yubikey-enabled user to first input their Joomla! password and then adding their Yubikey one-time-password to the end of that forming a single password consisting of the user's Joomla! password and their Yubikey one-time-password concatenated to the end of that. The username/password screens of Joomla! remain the same.
You can read more about the Yubikey one-time-password authentication device from the Yubico homepage at: http://www.yubico.com
The only improvement I can think of would be to allow a more advanced login - instead of having to enter my password into the front end - use the OTP as the authenticating factor.
Otherwise, a good increase in security as far as I am concerned.
Got the API Key from the API generator.
Assigned Yubikey ID to a registered user.
The authentication key (dongle) works good on both Vista and XP platforms. Both platforms recognized and installed the necessary drivers automatically.
Entered username and password+yubikey trigger button on the dongle (do not click the login button on the login form afterwards) simply wait for it to login for you, otherwise you get an "Invalid Token". If you do click the login button and you get the error, simply click on th back button on the web browser.
Couldn't get it to work with Community Builder login form. So I simply activated both Joomla Login Form and CB Login. CB Login module I placed in Registered mode. So it wouldn't display in Public area. Also works with Creative Design popup login form as well.
So far so good. Tested it on four different web sites.