Efficient Zero-Knowledge Proofs and their Applications

A zero-knowledge proof is a fundamental cryptographic primitive that enables the verification of statements without revealing unnecessary information. Zero-knowledge proofs are a key component of many cryptographic protocols and, often, one of their main efficiency bottlenecks. In recent years there have been great advances in improving the efficiency of zero-knowledge proofs, bring them closer to wide deployability. In this thesis we make another step towards the construction of computationally-efficient zero-knowledge proofs. Specifically, we construct efficient zero-knowledge proofs for the satisfiability of arithmetic circuits for which the computational cost of the prover is only a constant factor more expensive than direct evaluation of the circuit. We also construct efficient zero-knowledge proofs to check the correct execution of (Tiny)RAM programs. In this case the computational cost for the prover is a superconstant factor larger than executing the program directly. Our proofs also support efficient verification and small proof sizes. For security, they rely on symmetric primitives and could potentially withstand attacks from quantum computers. On a different research direction, we look at group signatures, a fundamental primitive which relies on zero-knowledge proofs. A group signature enables users to sign anonymously on behalf of a group of users. In case of dispute a Manager can identify the author of a signature and potentially banish the user from the group. In this thesis we address the fundamental question of defining the security of fully dynamic group signatures, for which the users can join and leave at any time. Differently from other restricted settings, this case has been largely overlooked in the past. Our security model is general, does not implicitly assume existing design paradigms and captures the security of existing models for more restricted settings

Formal Aspects in Security and Trust

his book constitutes the thoroughly refereed post-proceedings of the Third International Workshop on Formal Aspects in Security and Trust, FAST 2005, held in Newcastle upon Tyne, UK in July 2005. The 17 revised papers presented together with the extended abstract of 1 invited paper were carefully reviewed and selected from 37 submissions. The papers focus on formal aspects in security and trust policy models, security protocol design and analysis, formal models of trust and reputation, logics for security and trust, distributed trust management systems, trust-based reasoning, digital assets protection, data protection, privacy and ID issues, information flow analysis, language-based security, security and trust aspects in ubiquitous computing, validation/analysis tools, web service security/trust/privacy, GRID security, security risk assessment, and case studies

Application of service composition mechanisms to Future Networks architectures and Smart Grids

Aquesta tesi gira entorn de la hipòtesi de la metodologia i mecanismes de composició de serveis i com es poden aplicar a diferents camps d'aplicació per a orquestrar de manera eficient comunicacions i processos flexibles i sensibles al context. Més concretament, se centra en dos camps d'aplicació: la distribució eficient i sensible al context de contingut multimèdia i els serveis d'una xarxa elèctrica intel·ligent. En aquest últim camp es centra en la gestió de la infraestructura, cap a la definició d'una Software Defined Utility (SDU), que proposa una nova manera de gestionar la Smart Grid amb un enfocament basat en programari, que permeti un funcionament molt més flexible de la infraestructura de xarxa elèctrica. Per tant, revisa el context, els requisits i els reptes, així com els enfocaments de la composició de serveis per a aquests camps. Fa especial èmfasi en la combinació de la composició de serveis amb arquitectures Future Network (FN), presentant una proposta de FN orientada a serveis per crear comunicacions adaptades i sota demanda. També es presenten metodologies i mecanismes de composició de serveis per operar sobre aquesta arquitectura, i posteriorment, es proposa el seu ús (en conjunció o no amb l'arquitectura FN) en els dos camps d'estudi. Finalment, es presenta la investigació i desenvolupament realitzat en l'àmbit de les xarxes intel·ligents, proposant diverses parts de la infraestructura SDU amb exemples d'aplicació de composició de serveis per dissenyar seguretat dinàmica i flexible o l'orquestració i gestió de serveis i recursos dins la infraestructura de l'empresa elèctrica.Esta tesis gira en torno a la hipótesis de la metodología y mecanismos de composición de servicios y cómo se pueden aplicar a diferentes campos de aplicación para orquestar de manera eficiente comunicaciones y procesos flexibles y sensibles al contexto. Más concretamente, se centra en dos campos de aplicación: la distribución eficiente y sensible al contexto de contenido multimedia y los servicios de una red eléctrica inteligente. En este último campo se centra en la gestión de la infraestructura, hacia la definición de una Software Defined Utility (SDU), que propone una nueva forma de gestionar la Smart Grid con un enfoque basado en software, que permita un funcionamiento mucho más flexible de la infraestructura de red eléctrica. Por lo tanto, revisa el contexto, los requisitos y los retos, así como los enfoques de la composición de servicios para estos campos. Hace especial hincapié en la combinación de la composición de servicios con arquitecturas Future Network (FN), presentando una propuesta de FN orientada a servicios para crear comunicaciones adaptadas y bajo demanda. También se presentan metodologías y mecanismos de composición de servicios para operar sobre esta arquitectura, y posteriormente, se propone su uso (en conjunción o no con la arquitectura FN) en los dos campos de estudio. Por último, se presenta la investigación y desarrollo realizado en el ámbito de las redes inteligentes, proponiendo varias partes de la infraestructura SDU con ejemplos de aplicación de composición de servicios para diseñar seguridad dinámica y flexible o la orquestación y gestión de servicios y recursos dentro de la infraestructura de la empresa eléctrica.This thesis revolves around the hypothesis the service composition methodology and mechanisms and how they can be applied to different fields of application in order to efficiently orchestrate flexible and context-aware communications and processes. More concretely, it focuses on two fields of application that are the context-aware media distribution and smart grid services and infrastructure management, towards a definition of a Software-Defined Utility (SDU), which proposes a new way of managing the Smart Grid following a software-based approach that enable a much more flexible operation of the power infrastructure. Hence, it reviews the context, requirements and challenges of these fields, as well as the service composition approaches. It makes special emphasis on the combination of service composition with Future Network (FN) architectures, presenting a service-oriented FN proposal for creating context-aware on-demand communication services. Service composition methodology and mechanisms are also presented in order to operate over this architecture, and afterwards, proposed for their usage (in conjunction or not with the FN architecture) in the deployment of context-aware media distribution and Smart Grids. Finally, the research and development done in the field of Smart Grids is depicted, proposing several parts of the SDU infrastructure, with examples of service composition application for designing dynamic and flexible security for smart metering or the orchestration and management of services and data resources within the utility infrastructure