Thesis (doctoral)--Universistät Basel, 2007. / Includes bibliographical references (p. 229-247) and index.

Orientador: Ricardo Dahab / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Computação / Made available in DSpace on 2018-08-16T21:50:46Z (GMT). No. of bitstreams: 1 Castro_RafaelDantasde_M.pdf: 1379597 bytes, checksum: 3b065d6b67c5440dc00b0e4663d170d3 (MD5) Previous issue date: 2009 / Resumo: Nesta tese é apresentada uma visão do campo de Assinaturas de Chave Pública sem Certificados (CL-PKC), resultado final de pesquisa empreendida durante o mestrado do autor na Universidade Estadual de Campinas. A abordagem aqui contida tem como principal base a Segurança Demonstrável; analisamos os modelos de segurança de CL-PKC, os esquemas já propostos na literatura, e suas demonstrações de segurança. Contribuímos também alguns novos resultados para a área, especificamente: o estudo da aplicabilidade do Lema da Bifurcação 'a esquemas de CL-PKC (§ 4.3.3); o algumas pequenas otimizações a esquemas seguros (§ 4.4.1); o demonstração de segurança para um esquema cuja segurança ainda era um problema em aberto (§ 4.4.2); o explicação de falhas em demonstrações de segurança de alguns esquemas (§ 4.4.4, § 4.4.5, § 4.4.7); o um ataque desconhecido a um esquema anteriormente suposto seguro (§ 4.4.4); o proposta de um modelo de segurança para agregação de assinaturas no modelo CLPKC (§ 5.4); o proposta de um novo esquema de assinaturas CL-PKC que permite agregação, assim como sua prova de segurança (§ 5.2) / Abstract: In this thesis is presented a broad view of the field of Certificateless Public Key Signatures (CL-PKC), final result of the research undertaken by the author during his masters at the Campinas State University. Our approach is strongly based on the ideas behind Provable Security; we analyze the security models for CL-PKC, all schemes available in the literature, and their security proofs. We also contribute a few novel results, namely: o applicability of the Forking Lemma in the CL-PKC paradigm (§ 4.3.3); o small optimizations to secure schemes (§ 4.4.1); o security proof for a scheme whose security was an open problem (§ 4.4.2); o investigation of the problems in the security proofs of a few schemes (§ 4.4.4, § 4.4.5, § 4.4.7); o an attack on a scheme previously thought to be secure (§ 4.4.4); o proposal of a security model for aggregation of signatures in the CL-PKC paradigm (§ 5.4); o proposal of a new scheme for Certificateless Signatures that allows aggregation, along with its security proof (§ 5.2) / Mestrado / Sistemas de Computação / Mestre em Ciência da Computação

La recherche sur les bases de données chiffrées vise à rendre efficace une tâche apparemment simple : déléguer le stockage de données à un serveur qui ne serait pas de confiance, tout en conservant des fonctionnalités de recherche. Avec le développement des services de stockage dans le Cloud, destinés aussi bien aux entreprises qu'aux individus, la mise au point de solutions efficaces à ce problème est essentielle pour permettre leur déploiement à large échelle. Le principal problème de la recherche sur bases de données chiffrées est qu'un schéma avec une sécurité ''parfaite'' implique un surcoût en termes de calcul et de communication qui serait inacceptable pour des fournisseurs de services sur le Cloud ou pour les utilisateurs - tout du moins avec les technologies actuelles. Cette thèse propose et étudie de nouvelles notions de sécurité et de nouvelles constructions de bases de données chiffrées permettant des recherches efficaces et sûres. En particulier, nous considérons la confidentialité persistante et la confidentialité future de ces bases de données, ce que ces notions impliquent en termes de sécurité et d'efficacité, et comment les réaliser. Ensuite, nous montrons comment protéger les utilisateurs de bases de données chiffrées contre des attaques actives de la part du serveur hébergeant la base, et que ces protections ont un coût inévitable. Enfin, nous étudions les attaques existantes contre ces bases de données chiffrées et comment les éviter. / Searchable encryption aims at making efficient a seemingly easy task: outsourcing the storage of a database to an untrusted server, while keeping search features. With the development of Cloud storage services, for both private individuals and businesses, efficiency of searchable encryption became crucial: inefficient constructions would not be deployed on a large scale because they would not be usable. The key problem with searchable encryption is that any construction achieving ''perfect security'' induces a computational or a communicational overhead that is unacceptable for the providers or for the users --- at least with current techniques and by today's standards. This thesis proposes and studies new security notions and new constructions of searchable encryption, aiming at making it more efficient and more secure. In particular, we start by considering the forward and backward privacy of searchable encryption schemes, what it implies in terms of security and efficiency, and how we can realize them. Then, we show how to protect an encrypted database user against active attacks by the Cloud provider, and that such protections have an inherent efficiency cost. Finally, we take a look at existing attacks against searchable encryption, and explain how we might thwart them.

Orientador: Antonio Vidiella Barranco / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin / Made available in DSpace on 2018-08-18T11:59:35Z (GMT). No. of bitstreams: 1 Souza_DouglasDelgadode_M.pdf: 7468816 bytes, checksum: aba803ba35bfdb89aa8428cc3b6862d3 (MD5) Previous issue date: 2011 / Resumo: Neste trabalho, introduzimos um protocolo para a distribuição quântica de chaves (QKD) que faz uso de três estados comprimidos da luz: dois estados de bit, utilizados para a transmissão de informação, e um estado de Isca, utilizado para a detecção de espionagem. Seu desenvolvimento teve como base o protocolo de P. Horak (H04) para estados comprimidos, que por sua vez consiste de uma generalização do protocolo de R. Namiki e T. Hirano (NH03) para estados coerentes. Analisamos sua segurança considerando dois tipos de ataques: ataque por medida simultânea das quadraturas e ataque por troca do canal por canal superior. Para esta análise utilizamos uma descrição em termos da função de Wigner, obtendo a partir dela distribuições de probabilidade conjuntas e marginais. Da distribuição para os estados de Isca definimos uma Medida da Espionagem M, e discutimos sua utilidade para o cálculo da taxa de informação vazada para Eva em cada ataque. Por fim, para o ataque por troca do canal, analisamos o efeito da introdução de um limiar de pós-seleção sobre as informações de Bob e Eva, demonstrando que maiores distâncias de transmissão (menores transmissividades) podem ser suportadas pelo protocolo com o aumento deste parâmetro, ao custo de menores taxas de aceitação de bits / Abstract: In this work, we introduce a new protocol for Quantum Key Distribution which makes use of three squeezed coherent states of light: two bit states, used for transmission of information, and a Decoy state, used for eavesdropping detection. Its development was based on the protocol for squeezed coherent states suggested by P. Horak [39], which in turn consists of a generalization of the protocol by R. Namiki and T. Hirano [38] for coherent states. We analyze its security by considering two kinds of attack: simultaneous quadrature measurement attack and superior channel attack. For this analysis we use a description in terms of the Wigner function, obtaining from it some joint and marginal probability distributions. From the distribution for the Decoy states we define an Eavesdropping Measure M, and discuss its usefulness in calculating the rate of information leaked to Eve in each attack. Finally, for the superior channel attack, we analyze the influence of a post-selection threshold over the Bob and Eve information, showing that, by raising this parameter, larger transmission distances (smaller transmittivities) can be handled by the protocol at the expense of lower bit acceptance rates / Mestrado / Física Geral / Mestre em Física

The aim of this work is to describe current opportunities of in-browser encryption and focus on usage of new emerging standard Web Cryptography API. By using these new technologies we going to design and implements software library enabling authorized access to web pages or their part by cryptography.

Digital signatures, which take the properties of classical signatures, are used to secure the actual content of documents, which can be modified during transmission over an insecure channel. The problems of security and protection of communicating participants are solved by cryptographic techniques. Identity verification, message integrity, credibility, the ownership of documents, and the secure transmission of information over an unsecured channel, are all dealt with in secure communications - Public Key Infrastructure, which uses digital signatures. Nowadays digital signatures are often used to secure data in communication over an unsecured channel. The aim of the following master’s thesis is to familiarize readers with the necessary technological aspects of digital signatures, as well as their advantages and disadvantages. By the time digital signatures are being used they will have to be improved and modified to be secure against more sophisticated attacks. In this paper, proposals of new efficient digital signature schemes and their comparison with current ones are described. Also are examined their implications for computationally weak devices, or deployment in low speed channel transmission systems. After an explanation of cryptography and a description of its basic subjects, digital signatures are introduced. The first chapter describes the possible formatting and architecture of the digital signature. The second part of this master’s thesis is about current digital signature schemes and their properties. Chapter 3 describes some proposals of new efficient digital signature schemes and their comparison to those currently in use. In the practical part, the implementations (in the environment .NET in C#) of two effective digital signature schemes as part of a client-server application are presented and described (Chapter 4). In the last chapter the comparison and analysis of the implemented signature schemes are provided.

No description available.

Many systems contain sensitive data such as user credentials used for authentication purposes. For large systems, a common approach is to store the data in a configuration file at a trusted third party. However, that would imply a single point of failure if an adversary gains access to the trusted party. In theory this could be solved by encrypting the data but in practice this only moves the problem and does not solve it, since some type of credential data is needed to decrypt the configuration file. A more flexible solution is needed that requires less of human interaction while also providing a higher degree of security. This thesis proposes a complete cryptographical system for solving this problem in a typical enterprise setting with a set of additional implementation requirements by using multi-party computation and Shamir's secret sharing protocol. Additionally, the work combines the mentioned system with a certificateless cryptography based multi-party computation protocol, since certificates usually implies a time-consuming process. The system has been evaluated in terms of security and efficiency with the conclusion that the results look promising. In terms of performance, the bulk of the overhead comes from certificateless cryptography, a constraint for the specific scenario which might not be present in general. The work also provides incentives for developing and further evolving Java libraries for cryptography, especially for multi-party computation and certificateless cryptography. / Många system innehåller känslig data, exempelvis användaruppgifter som används för autentiseringsändamål. För stora system är en vanlig lösning att lagra data i en konfigurationsfil hos en betrodd tredje part. Det skulle emellertid innebära att den svagaste länken är om motståndare får tillgång till den betrodda parten. I teorin kan detta lösas genom att kryptera data men i praktiken flyttar det bara på problemet men löser det inte, eftersom någon typ av autentiseringsdata behövs för att dekryptera konfigurationsfilen. En mer flexibel lösning behövs som kräver mindre mänsklig interaktion samtidigt som det ger en högre grad av säkerhet. Denna avhandling föreslår ett komplett kryptografiskt system för att lösa detta problem i en typisk företagsmiljö med en ytterligare uppsättning implementationskrav genom att använda multipartsberäknande och Shamirs secret sharing protokoll. Dessutom kombinerar arbetet det nämnda systemet med ett certifikatfritt krypteringsbaserat protokoll kombinerat med multipartsberäkningar, eftersom certifikat oftast innebär en tidskrävande process. Systemet har utvärderats med avseende på säkerhet och effektivitet med slutsatsen att det ser lovande ut. När det gäller prestanda kommer huvuddelen av omkostnaden från den certifikatfria kryptografin, en begränsning för det specifika scenariot som kanske inte är närvarande i allmänhet. Arbetet ger också motiv för att vidareutveckla Java-bibliotek för kryptografi, speciellt för multipartsberäknande protokoll och certifikatlös kryptering.

No description available.

No description available.