Passwords are the most commonly used method to provide secure access to user accounts. However, text and pattern passwords are vulnerable to different attacks, such as shoulder-surfing attacks, guessing attacks, and smudge attacks. To resist these attacks, this article proposes an operational grid (OP-Grid) technique: an implicit graphical authentication scheme having different patterns on every login session. With a one-time login pointer, the user creates his/her password pattern. A legitimate user is authenticated not only through the user-created pattern but also the way the user performs it using finger velocity and stroke time features. OP-Grid is implemented on Android cell phones, samples are gathered from 33 volunteers, and the experimental study is carried out to evaluate its accuracy and usability.