A portable device includes a touch screen that includes a display screen and that generates touch screen data in response to a user's interaction with the touch screen. A processor executes a security application for authenticating the user to the portable device that provides first display data to the touch screen for displaying a security prompt on the display screen. Touch screen data is received from the touch screen in response to the user's interaction with the touch screen and is processed to determine when an authentication shape is recognized as being indicated by the touch screen data. The user is authenticated to the portable device when the authentication shape is recognized as being indicated by the touch screen data.