Support for strong electronic mail security is widely available yet only few communicants appear to make use of these features. Apparently, the operational overhead of security outweighs its perceived benefits. Towards increasing the benefits versus overhead ratio we follow an approach that considers security and usability tradeoffs from the outset. We separate key exchange from binding keys to identities. The best effort key exchange and key maintenance scheme that we devise operates transparently for the user. We also describe complementary visualization and interaction techniques that communicate the security state of sent and received mail to users in a non-intrusive fashion. Structured interviews were conducted with 19 users to assess the usability of the metaphors and the complementary visualizations of the security state. Towards a practical assessment of the overheads of binding keys to identities, we conducted a quantitative analysis of 17 users' anonymized mailbox extracts to determine which security mechanisms would be most appropriate for their communication patterns. We argue that for individual non-commercial users, out-of-band verification of keys could be more economical than building trust in public key certificates issued by third parties

Next generation mobile devices will allow users to share and pass information within anonymous groups of people in an ad hoc manner. This will smooth the path for many kinds of new mobile commerce applications. In this paper we present a mobile commerce application that is part of the iClouds research project. It allows the dissemination of digital advertisements among interested mobile users. To create an incentive, an anonymous bonus point system rewards users who help to carry an advertisement from a merchant to a customer. This work includes a formal description of our bonus point model, a thorough discussion of the security goals, their realization and some first results about crypto-operation runtime behavior on a state-of-the-art PDA.

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The growing share of people using mobile devices, that support wireless peer-to-peer interaction, offers the opportunity to build a ubiquitous infrastructure for electronic word-of-mouth messaging and advertising. This chapter introduces Opportunistic Networks as a layer for one-hop communication that opens up electronic word-of-mouth messaging for mobile devices. The reader will learn about adPASS (short for advertisement passing), a system build on top of Opportunistic Networks for digital advertisement distribution stimulated by an anonymous and tamper-resistant bonus point model. A simulation based on empirical movement patterns indicates the feasibility of our approach. This chapter concludes with a summary and provides an outlook on further research paths starting from our findings.

Taking typical ubiquitous computing settings as a starting point, this chapter motivates the need for security. The reader will learn what makes security challenging and what the risks predominant in ubiquitous computing are. The major part of this chapter is dedicated to the description of sample solutions in order to illustrate the wealth of protection mechanisms. A background in IT security is not required as this chapter is self-contained. A brief introduction to the subject is given as well as an overview of cryptographic tools.