Unconditionally Secure Revocable Storage: Tight Bounds, Optimal Construction, and Robustness

Data stored in cloud storage sometimes requires long-term security due to its sensitivity (e.g., genome data), and therefore, it also requires flexible access control for handling entities who can use the data. Broadcast encryption can partially provide such flexibility by specifying privileged receivers so that only they can decrypt a ciphertext. However, once privileged receivers are specified, they can be no longer dynamically added and/or removed. In this paper, we propose a new type of broadcast encryption which provides long-term security and appropriate access control, which we call unconditionally secure revocable-storage broadcast encryption (RS-BE). In RS-BE, privileged receivers of a ciphertext can be dynamically updated without revealing any information on the underlying plaintext. Specifically, we define a model and security of RS-BE, derive tight lower bounds on sizes of secret keys required for secure RS-BE, and propose a construction of RS-BE which meets all of these bounds. Our lower bounds can be applied to traditional broadcast encryption. Furthermore, to detect an improper update, we consider security against modification attacks to a ciphertext, and present a concrete construction secure against this type of attacks

Key management for wireless sensor network security

Wireless Sensor Networks (WSNs) have attracted great attention not only in industry but also in academia due to their enormous application potential and unique security challenges. A typical sensor network can be seen as a combination of a number of low-cost sensor nodes which have very limited computation and communication capability, memory space, and energy supply. The nodes are self-organized into a network to sense or monitor surrounding information in an unattended environment, while the self-organization property makes the networks vulnerable to various attacks.Many cryptographic mechanisms that solve network security problems rely directly on secure and efficient key management making key management a fundamental research topic in the field of WSNs security. Although key management for WSNs has been studied over the last years, the majority of the literature has focused on some assumed vulnerabilities along with corresponding countermeasures. Specific application, which is an important factor in determining the feasibility of the scheme, has been overlooked to a large extent in the existing literature.This thesis is an effort to develop a key management framework and specific schemes for WSNs by which different types of keys can be established and also can be distributed in a self-healing manner; explicit/ implicit authentication can be integrated according to the security requirements of expected applications. The proposed solutions would provide reliable and robust security infrastructure for facilitating secure communications in WSNs.There are five main parts in the thesis. In Part I, we begin with an introduction to the research background, problems definition and overview of existing solutions. From Part II to Part IV, we propose specific solutions, including purely Symmetric Key Cryptography based solutions, purely Public Key Cryptography based solutions, and a hybrid solution. While there is always a trade-off between security and performance, analysis and experimental results prove that each proposed solution can achieve the expected security aims with acceptable overheads for some specific applications. Finally, we recapitulate the main contribution of our work and identify future research directions in Part V

Cryptographic Key Management in Delay Tolerant Networks (DTNs): A survey

Since their appearance at the dawn of the second millennium, Delay or Disruption Tolerant Networks (DTNs) have gradually evolved, spurring the development of a variety of methods and protocols for making them more secure and resilient. In this context, perhaps, the most challenging problem to deal with is that of cryptographic key management. To the best of our knowledge, the work at hand is the first to survey the relevant literature and classify the various so far proposed key management approaches in such a restricted and harsh environment. Towards this goal, we have grouped the surveyed key management methods into three major categories depending on whether the particular method copes with a) security initialization, b) key establishment, and c) key revocation. We have attempted to provide a concise but fairly complete evaluation of the proposed up-to-date methods in a generalized way with the aim of offering a central reference point for future research

Cryptographic Key Management in Delay Tolerant Networks (DTNs): A survey

Since their appearance at the dawn of the second millennium, Delay or Disruption Tolerant Networks (DTNs) have gradually evolved, spurring the development of a variety of methods and protocols for making them more secure and resilient. In this context, perhaps, the most challenging problem to deal with is that of cryptographic key management. To the best of our knowledge, the work at hand is the first to survey the relevant literature and classify the various so far proposed key management approaches in such a restricted and harsh environment. Towards this goal, we have grouped the surveyed key management methods into three major categories depending on whether the particular method copes with a) security initialization, b) key establishment, and c) key revocation. We have attempted to provide a concise but fairly complete evaluation of the proposed up-to-date methods in a generalized way with the aim of offering a central reference point for future research

Contextualizing Alternative Models of Secret Sharing

A secret sharing scheme is a means of distributing information to a set of players such that any authorized subset of players can recover a secret and any unauthorized subset does not learn any information about the secret. In over forty years of research in secret sharing, there has been an emergence of new models and extended capabilities of secret sharing schemes. In this thesis, we study various models of secret sharing and present them in a consistent manner to provide context for each definition. We discuss extended capabilities of secret sharing schemes, including a comparison of methods for updating secrets via local computations on shares and an analysis of approaches to reproducing/repairing shares. We present an analysis of alternative adversarial settings which have been considered in the area of secret sharing. In this work, we present a formalization of a deniability property which is inherent to some classical secret sharing schemes. We provide new, game-based definitions for different notions of verifiability and robustness. By using consistent terminology and similar game-based definitions, we are able to demystify the subtle differences in each notion raised in the literature

A Survey on Routing in Anonymous Communication Protocols

The Internet has undergone dramatic changes in the past 15 years, and now forms a global communication platform that billions of users rely on for their daily activities. While this transformation has brought tremendous benefits to society, it has also created new threats to online privacy, ranging from profiling of users for monetizing personal information to nearly omnipotent governmental surveillance. As a result, public interest in systems for anonymous communication has drastically increased. Several such systems have been proposed in the literature, each of which offers anonymity guarantees in different scenarios and under different assumptions, reflecting the plurality of approaches for how messages can be anonymously routed to their destination. Understanding this space of competing approaches with their different guarantees and assumptions is vital for users to understand the consequences of different design options. In this work, we survey previous research on designing, developing, and deploying systems for anonymous communication. To this end, we provide a taxonomy for clustering all prevalently considered approaches (including Mixnets, DC-nets, onion routing, and DHT-based protocols) with respect to their unique routing characteristics, deployability, and performance. This, in particular, encompasses the topological structure of the underlying network; the routing information that has to be made available to the initiator of the conversation; the underlying communication model; and performance-related indicators such as latency and communication layer. Our taxonomy and comparative assessment provide important insights about the differences between the existing classes of anonymous communication protocols, and it also helps to clarify the relationship between the routing characteristics of these protocols, and their performance and scalability

Relativistic quantum cryptography

In this thesis we explore the benefits of relativistic constraints for cryptography. We first revisit non-communicating models and its applications in the context of interactive proofs and cryptography. We propose bit commitment protocols whose security hinges on communication constraints and investigate its limitations. We explain how some non-communicating models can be justified by special relativity and study the limitations of such models. In particular, we present a framework for analysing security of multiround relativistic protocols. The second part of the thesis is dedicated to analysing specific protocols. We start by considering a recently proposed two-round quantum bit commitment protocol. We propose a fault-tolerant variant of the protocol, present a complete security analysis and report on an experimental implementation performed in collaboration with an experimental group at the University of Geneva. We also propose a new, multiround classical bit commitment protocol and prove its security against classical adversaries. This demonstrates that in the classical world an arbitrarily long commitment can be achieved even if the agents are restricted to occupy a finite region of space. Moreover, the protocol is easy to implement and we report on an experiment performed in collaboration with the Geneva group.Comment: 123 pages, 9 figures, many protocols, a couple of theorems, certainly not enough commas. PhD thesis supervised by Stephanie Wehner at Centre for Quantum Technologies, Singapor

Cryptographic key distribuition in sensor networks

Orientador: Ricardo DahabTese (doutorado) - Universidade Estadual de Campinas, Instituto de ComputaçãoResumo: Redes de Sensores Sem Fio (RSSFs) são compostas em sua maioria por pequenos nós sensores dotados de recursos extremamente limitados. Estes, por sua vez, se comunicam com o mundo externo através de nós poderosos chamados de sorvedouros ou estações rádio base. RSSFs são empregadas com o objetivo de monitorar regiões, oferecendo dados sobre a área monitorada para o resto do sistema. Tais redes podem ser utilizadas para diferentes aplicações, tais como operações de resgate em áreas de conflito/desastre, espionagem industrial e detecção de exploração ilegal de recursos naturais. Em RSSFs existem aplicações críticas nas quais propriedades de segurança são de vital importância. Segurança, por sua vez, é comumente alavancada através de esquemas de distribuição de chaves. A maioria dos padrões de distribuição de chaves presentes na literatura, todavia, não são apropriados para RSSFs: métodos baseados em esquemas de chave pública convencionais, devido aos seus requisitos de processamento e banda; chaves de grupo, em função das suas vulnerabilidades de segurança; e chaves par-a-par (pairwise), por causa da baixa escalabilidade. Um outro dado é que há uma vasta gama de arquiteturas propostas para RSSFs e que uma mesma técnica de distribuição de chaves pode ser a melhor para uma, mas não para outra, visto que diferentes arquiteturas de rede exibem padrões de comunicação distintos. Em outras palavras, não existe uma panacéia, e mecanismos de distribuição de chaves para RSSFs devem, portanto, levar em consideração as idiossincrasias das arquiteturas para as quais são projetadas. Tudo isso torna extremamente difícil e desafiadora a tarefa de dotar RSSFs de segurança. O objetivo deste trabalho foi propor soluções de distribuição de chaves que, concomitantemente, (i) fossem compatíveis com os recursos dos sensores e (ii) considerassem as particularidades das arquiteturas para as quais são propostas. Como será mostrado ao longo desta tese, iniciamos nosso trabalho com soluções personalizadas para certas arquiteturas de RSSFs e evoluímos para soluções flexíveis em que a segurança é alavancada de forma não interativa - o que é ideal para este tipo de rede. Até onde sabemos, nosso trabalho é pioneiro em soluções de segurança para RSSFs hierárquicas e em distribuição de chaves de forma autenticada e não interativa, usando Criptografia Baseada em Identidade, neste tipo de rede.Abstract: Wireless sensor networks (WSNs) are ad hoc networks comprised mainly of small sensor nodes with limited resources and one or more base stations, which are much more powerful laptop-class nodes that connect the sensor nodes to the rest of the world. WSNs are used for monitoring purposes, providing information about the area being monitored to the rest of the system. Application areas range from battlefield reconnaissance and emergency rescue operations to surveillance and environmental protection. There are also critical WSN applications in which security properties are of paramount importance. Security, in turn, is frequently bootstrapped through key distribution schemes. Most of the key distribution techniques, however, are ill-suited to WSNs: public key based distribution, because of its processing and bandwidth requirements; global keying, because of its security vulnerabilities; complete pairwise keying, because of its memory requirements. It is worth noting, however, that a large number of WSN architectures have been proposed and a key distribution solution that is well suited to one architecture is likely not to be the best for another, as different network architectures exhibit different communication patterns. In other words, there is no panacea and the design of a key distribution scheme must therefore be driven by the peculiarities of the WSN architecture in question. This all makes extremely hard and challenging the objective of securing WSNs. In this work, we aimed at proposing key distribution schemes that are both (i) lightweight and (ii) able to fulfill architecture-specific needs. As it will be shown throughout this thesis, we began our work with customized solutions for certain types of WSNs and then, subsequently, turned our attention to more flexible solutions, where security is bootstrapped in a non-interactive way through the use of Identity-Based Cryptography.DoutoradoTeoria da ComputaçãoDoutor em Ciência da Computaçã