Abstract. A new family of protocols, based on communication over human-based side channels, permit secure pairing or group formation in ways that no party has to prove its name. These protocols are particularly suitable for authentication on mobile phones where PKI or trusted third party solutions are not practical to cover all scenarios. Rather, individuals are able to hook up devices in their possession to others that they can identify by context. By using one of these Human-Interactive Security Protocols (HISPs), we present a new design of mobile payment system to improve on the security of existing solutions, while providing a reliable and ubiquitous foundation for mobile security in general. 1

My research philosophy revolves around the belief that successful systems research has to demonstrate two things: 1) a novel and interesting approach to an important research problem, and 2) usability. I strongly believe that for a system to be successful, it has to be usable by the target audience. On the other hand, a highly usable system that doesn’t advance the state of the art in any way is not particularly interesting from a research perspective either. My research style is strongly systems-oriented with a large emphasis on hands-on system implementation. A real implementation is crucial, in my opinion, for testing complicated distributed systems as the complexity inherent in these systems is incredibly hard to capture by simulation studies alone. A real implementation is also vital in validating the usability of the system. In addition, the software artifacts from such implementations are important contributions that drive future research and even product development in the area. I am also a strong proponent of collaborative research. Modern systems are so complicated that it is impossible for one person to have all the answers to every problem encountered. As such, I tend to work with about 2-4 other people, each with slightly different skills and backgrounds, to tackle a large systems problem. This multi-disciplinary approach is very apparent in all my research undertakings. I describe some of these undertakings along with avenues of future research in the next few sections. My research revolves around the theme of mobility. Around this theme, I have built clusters of research. In particular, I have research thrusts in the areas of Applications for Mobility, Understanding

NFC (Near Field Communication) e pagamentos móveis são duas áreas que se tornaram muito populares ultimamente, ambas duplicaram o seu índice de volume de pesquisas medido pelo Google Trends no último ano. NFC é uma tecnologia de comunicação sem fios já disponível em alguns telemóveis, sendo que mais estão anunciados para breve, e os pagamentos móveis são um serviço cuja utilização se espera que cresça a um ritmo bastante acelerado nos próximos anos. Este crescimento já foi previsto antes, e as expectativas saíram goradas, mas pensa-se que a NFC seja a tecnologia que vai trazer os pagamentos móveis às massas. Esta tese foca-se nestas duas áreas e em como a NFC pode ser útil num protocolo para executar pagamentos móveis nos dias de hoje. Para isto, um novo protocolo chamado mTrocos é apresentado. Este possui várias características desejáveis tais como anonimato, alta segurança, boa usabilidade, a não dependência de bancos ou instituições financeiras tradicionais, o suporte para micro-pagamentos e não requer nenhum hardware especial. O seu desenho é baseado no conceito de dinheiro digital e em protocolos de estabelecimento de chaves ad-hoc. Estes últimos são úteis visto que a NFC é um meio sem fios que não oferece nenhuma