See: http://en.wikipedia.org/wiki/HOTP http://en.wikipedia.org/wiki/HOTP and http://en.wikipedia.org/wiki/Time-based_One-time_Password_Algorithm http://en.wikip

See: http://en.wikipedia.org/wiki/HOTP http://en.wikipedia.org/wiki/HOTP and http://en.wikipedia.org/wiki/Time-based_One-time_Password_Algorithm http://en.wikipedia.org/wiki/Time-based_One-time_Password_Al... You can download the Google Authenticator app. These algorithms are known. You can implement it yourself if you wanted to.