Abstract: As pervasive environments become more commonplace, the privacy of users is placed at an increased risk. The numerous and diverse sensors in these environments can record contextual information about users, leading to users unwittingly leaving ``digital footprints.'' Users must therefore be allowed to control how their digital footprints are reported to third parties. While a significant amount of prior work has focused on location privacy, location is only one specific type of footprint, and we expect most users to be incapable of specifying fine-grained policies for a multitude of footprints. In this paper we present a policy language based on the metaphor of physical walls, and posit that users will find this to be an intuitive way to control access to their digital footprints. For example, users understand the physical privacy implications of conducting a meeting in a room enclosed by physical walls. By allowing users to deploy ``virtual walls,'' they can control the privacy of their digital footprints much in the same way they control their privacy in the physical world. We present a policy framework and model for virtual walls with three levels of transparency that correspond to intuitive levels of privacy. We also describe the results of a user study (N = 23) that indicates that our model is easy to understand and use.
Copyright © 2007 by Springer-Verlag.The copy made available here is the authors' version; for a definitive copy see the publisher's version described above.