Adequate user authentication is a persistent problem, particularly with handheld devices such as Personal Digital Assistants (PDAs), which tend to be highly personal and at the fringes of an organization's influence. Yet, these devices are being used increasingly in corporate settings where they pose a security risk, not only by containing sensitive information, but also by providing the means to access such information over wireless network interfaces. User authentication is the first line of defense for a lost or stolen PDA. However, motivating users to enable simple PIN or password mechanisms and periodically update their authentication information is a constant struggle. This paper describes a general-purpose mechanism for authenticating a user to a PDA using a visual login technique called Picture Password. The underlying rationale is that image recall is an easy and natural way for users to authenticate, removing a serious barrier to compliance with organizational policy. Features of Picture Password include style dependent image selection, password reuse, and embedded salting, which overcome a number of problems with knowledge-based authentication for handheld devices. Though designed specifically for handheld devices, Picture Password is also suitable for notebooks, workstations, and other computational devices.
