Caracterização de serviços de Internet geo-replicados

Dissertação para obtenção do Grau de Mestre em Engenharia InformáticaCom o aumento da popularidade de serviços distribuídos que recorrem à geo-replicação, a comunidade científica tem efectuado um esforço activo para desenvolver modelos de consistência e esquemas de replicação, que permitam a estas aplicações encontrar um equilíbrio adequado entre desempenho e a exposição da camada de replicação para os utilizadores destas aplicações. No entanto, é pouco claro quais os modelos de consistência que são oferecidos por aplicações reais e extremamente populares, como por exemplo o Facebook ou o Twitter. Nesta tese é proposta uma metodologia e é descrita uma arquitectura que pretende validar um conjunto de propriedades relevantes relativas ao modelo de consistência oferecido por aplicações reais de grande escala. Em particular a nossa abordagem permite verificar violações de propriedades de sessão bem conhecidas, assim como verificar se a causalidade entre os efeitos das operações observados pelos utilizadores é violada. Adicionalmente, a nossa abordagem tenta também inferir a janela de divergência observada pelos clientes. Desta forma consegue-se observar que garantias de consistência são respeitadas por um serviço distribuído sem que seja necessário ter conhecimento sobre o seu funcionamento interno, permitindo construindo melhores modelos de consistência. Esta metodologia serve ainda como uma ferramenta auxiliar no desenvolvimento de um serviço distribuído, permitindo verificar se este oferece o modelo de consistência esperado

Temporal meta-model framework for Enterprise Information Systems (EIS) development

This thesis has developed a Temporal Meta-Model Framework for semi-automated Enterprise System Development, which can help drastically reduce the time and cost to develop, deploy and maintain Enterprise Information Systems throughout their lifecycle. It proposes that the analysis and requirements gathering can also perform the bulk of the design phase, stored and available in a suitable model which would then be capable of automated execution with the availability of a set of specific runtime components

Understanding and Improving Security of the Android Operating System

Successful realization of practical computer security improvements requires an understanding and insight into the system\u27s security architecture, combined with a consideration of end-users\u27 needs as well as the system\u27s design tenets. In the case of Android, a system with an open, modular architecture that emphasizes usability and performance, acquiring this knowledge and insight can be particularly challenging for several reasons. In spite of Android\u27s open source philosophy, the system is extremely large and complex, documentation and reference materials are scarce, and the code base is rapidly evolving with new features and fixes. To make matters worse, the vast majority of Android devices in use do not run the open source code, but rather proprietary versions that have been heavily customized by vendors for product differentiation. Proposing security improvements or making customizations without sufficient insight into the system typically leads to less-practical, less-efficient, or even vulnerable results. Point solutions to specific problems risk leaving other similar problems in the distributed security architecture unsolved. Far-reaching general-purpose approaches may further complicate an already complex system, and force end-users to endure significant performance and usability degradations regardless of their specific security and privacy needs. In the case of vendor customization, uninformed changes can introduce access control inconsistencies and new vulnerabilities. Hence, the lack of methodologies and resources available for gaining insight about Android security is hindering the development of practical security solutions, sound vendor customizations, and end-user awareness of the proprietary devices they are using. Addressing this deficiency is the subject of this dissertation. New approaches for analyzing, evaluating and understanding Android access controls are introduced and used to create an interactive database for use by security researchers as well as system designers and end-user product evaluators. Case studies using the new techniques are described, with results uncovering problems in Android\u27s multiuser framework and vendor-customized System Services. Finally, the new insights are used to develop and implement a novel virtualization-based security architecture that protects sensitive resources while preserving Android\u27s open architecture and expected levels of performance and usability