This paper presents BoD Shapes, a novel authentication method for smartphones that uses the back of the device for input. We argue that this increases the resistance to shoulder surfing while remaining reasonably fast and easy-to-use. We performed a user study (n = 24) comparing BoD Shapes to PIN authentication, Android grid unlock, and a front version of our system. Testing a front version allowed us to directly compare performance and security measures between front and back authentication. Our results show that BoD Shapes is significantly more secure than the three other approaches. While performance declined, our results show that BoD Shapes can be very fast (up to 1.5 seconds in the user study) and that learning effects have an influence on its performance. This indicates that speed improvements can be expected in long-term use.

Abstract. Large public displays have become a regular conceptual element in many shops and businesses, where they advertise products or highlight upcoming events. In our work, we are interested in exploring how these isolated display solutions can be interconnected to form a single large network of public displays, thus supporting novel forms of sharing access to display real estate. In order to explore the feasibility of this vision, we investigated today's practices surrounding shared notice areas, i.e. places where customers and visitors can put up event posters and classifieds, such as shop windows or notice boards. In particular, we looked at the content posted to such areas, the means for sharing it (i.e., forms of content control), and the reason for providing the shared notice area. Based on two-week long photo logs and a number of in-depth interviews with providers of such notice areas, we provide a systematic assessment of factors that inhibit or promote the shared use of public display space, ultimately leading to a set of concrete design implication for providing future digital versions of such public notice areas in the form of networked public displays.

Despite the proliferation of location-based services on mobile platforms, privacy concerns still refrain many people from using them regularly. Moreover, current location sharing tools often present over-simplistic privacy settings by which users are forced to the binary alternative of sharing everything or nothing. The goal of this research is to build novel privacy-aware tools through which users can share their location more easily and in the way they consider more appropriate. Starting from the study of the sharing functionalities and how people use them, I aim at building a platform for efficiently sharing location, supported by a usable interface through which users can easily understand how sharing works and feel in control of their data. Furthermore, the security mechanisms employed are conceived such that privacy is considered as an integral part of the sharing mechanisms, in a privacy-by-design approach.

We analyze the users' intimacy to investigate the differences in smartphone usage, considering the user's location and number and kind of people physically around the user. With a first user study we (1) validate the intimacy concept, (2) evaluate its correlation to smartphone usage features and (3) we computationally model it. Shorter, more frequent, and less engaging interactions take place when intimacy is lower, while longer, less frequent, and engaging interactions when intimacy is higher. With a second user study, we investigate the intimacy predictability in practice. Location-time features are predictive for the intimacy, and other smartphone-based features can improve the intimacy prediction accuracy.

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