Ported from http://code.google.com/p/google-authenticator/ You can use the Google Authenticator app from here http://www.google.com/support/accounts/bin/answer.py?hl=en&answer=1066447 to generate One Time Passwords/Tokens and check them with this little PHP app (Of course, you can also create them with this). There are many real world applications for that, but noone implemented it yet. See example.php for how to use it. There's a little web app showing how it works in web/, please make users.dat writeable for the webserver, doesn't really work otherwise (it can't save the secret). Try to login with chregu/foobar. What's missing in the example: *** * Prevent replay attacks. One token should only be used once * Show QR Code only when providing password again (or not at all) * Regenrate secret