US Patent 7650509 Encoding data in a password

A password authentication mechanism is capable of determining whether a password has expired without referring to a database or other information repository. Additional information can be encoded in the password without unduly lengthening the password, so that the additional information can be extracted from the password when the user provides the password for authentication purposes. Thus, the password serves as an information-carrying data item as well as acting as an authentication mechanism. Such a password can be used, for example, to provide time-limited access to a vehicle in response to receipt of timely payment, and to disable the vehicle if payment is not made.