xShare: supporting impromptu sharing of mobile phones

Loaded with personal data, e.g. photos, contacts, and call history, mobile phones are truly personal devices. Yet it is often necessary or desirable to share our phones with others. This is especially true as mobile phones are integrating features conventionally provided by other dedicated devices, from MP3 players to games consoles. Unfortunately, when we lend our phones to others, we give away complete access because existing phones assume a single user and provide little protection for private data and applications. In this work, we present xShare, a protection solution to address this problem. xShare allows phone owners to rapidly specify what they want to share and place the phone into a restricted mode where only the data and applications intended for sharing can be accessed.

We first present findings from two motivational user studies based on which we provide the design requirements of xShare. We then present the design of xShare based on file-level access control. We describe the implementation of xShare on Windows Mobile and report a comprehensive usability evaluation of the implementation, including mea-surements and user studies. The evaluation demonstrates that our xShare implementation has negligible overhead for interactive phone usage, is extremely favored by mobile users, and provides robust protection against attacks by experienced Windows Mobile users and developers.