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.