Users attempting to access a device that is utilizing two-factor authentication must pass two different kinds of "tests" before they can view any actual files or gain access otherwise. Perhaps the most common utilization of two-factor authentication is the use of a "possession factor" in combination with a "knowledge factor." In this case, a user would need to
- enter in a pregenerated number, which changes on a set time basis and appears on a physical "token" that the user carries with them (possession factor), and
- enter in a password of the user's choosing (knowledge factor).
Two-factor authentication can also incorporate biometrics, such as fingerprint and retina scans, which may be used in conjunction with another type of factor to form the basis for two-factor authentication.