Fair Exchange in Strand Spaces

Many cryptographic protocols are intended to coordinate state changes among principals. Exchange protocols coordinate delivery of new values to the participants, e.g. additions to the set of values they possess. An exchange protocol is fair if it ensures that delivery of new values is balanced: If one participant obtains a new possession via the protocol, then all other participants will, too. Fair exchange requires progress assumptions, unlike some other protocol properties. The strand space model is a framework for design and verification of cryptographic protocols. A strand is a local behavior of a single principal in a single session of a protocol. A bundle is a partially ordered global execution built from protocol strands and adversary activities. The strand space model needs two additions for fair exchange protocols. First, we regard the state as a multiset of facts, and we allow strands to cause changes in this state via multiset rewriting. Second, progress assumptions stipulate that some channels are resilient-and guaranteed to deliver messages-and some principals are assumed not to stop at certain critical steps. This method leads to proofs of correctness that cleanly separate protocol properties, such as authentication and confidentiality, from invariants governing state evolution. G. Wang's recent fair exchange protocol illustrates the approach

On the Relationship between Strand Spaces and Multi-Agent Systems

Strand spaces are a popular framework for the analysis of security protocols. Strand spaces have some similarities to a formalism used successfully to model protocols for distributed systems, namely multi-agent systems. We explore the exact relationship between these two frameworks here. It turns out that a key difference is the handling of agents, which are unspecified in strand spaces and explicit in multi-agent systems. We provide a family of translations from strand spaces to multi-agent systems parameterized by the choice of agents in the strand space. We also show that not every multi-agent system of interest can be expressed as a strand space. This reveals a lack of expressiveness in the strand-space framework that can be characterized by our translation. To highlight this lack of expressiveness, we show one simple way in which strand spaces can be extended to model more systems.Comment: A preliminary version of this paper appears in the Proceedings of the 8th ACM Conference on Computer and Communications Security,200

Formal Analysis of Fairness for Optimistic Multiparty Contract Signing Protocol

Optimistic multiparty contract signing (OMPCS) protocols are proposed for exchanging multiparty digital signatures in a contract. Compared with general two-party exchanging protocols, such protocols are more complicated, because the number of protocol messages and states increases considerably when signatories increase. Moreover, fairness property in such protocols requires protection from each signatory rather than from an external hostile agent. It thus presents a challenge for formal verification. In our analysis, we employ and combine the strength of extended modeling language CSP# and linear temporal logic (LTL) to verify the fairness of OMPCS protocols. Furthermore, for solving or mitigating the state space explosion problem, we set a state reduction algorithm which can decrease the redundant states properly and reduce the time and space complexity greatly. Finally, this paper illustrates the feasibility of our approach by analyzing the GM and CKS protocols, and several fairness flaws have been found in certain computation times

DRM and Privacy

Interrogating the relationship between copyright enforcement and privacy raises deeper questions about the nature of privacy and what counts, or ought to count, as privacy invasion in the age of networked digital technologies. This Article begins, in Part II, by identifying the privacy interests that individuals enjoy in their intellectual activities and exploring the different ways in which certain implementations of DRM technologies may threaten those interests. Part III considers the appropriate scope of legal protection for privacy in the context of DRM, and argues that both the common law of privacy and an expanded conception of consumer protection law have roles to play in protecting the privacy of information users. As Parts II and III demonstrate, consideration of how the theory and law of privacy should respond to the development and implementation of DRM technologies also raises the reverse question: How should the development and implementation of DRM technologies respond to privacy theory and law? As artifacts designed to regulate user behavior, DRM technologies already embody value choices. Might privacy itself become one of the values embodied in DRM design? Part IV argues that with some conceptual and procedural adjustments, DRM technologies and related standard-setting processes could be harnessed to preserve and protect privacy

Attacking Fair-Exchange Protocols

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Applying Bourdieu to socio-technical systems: The importance of affordances for social translucence in building 'capital' and status to eBay's success

This paper introduces the work of Sociologist Pierre Bourdieu and his concepts of ‘the field’ and ‘capital’ in relation to eBay. This paper considers eBay to be a socio-technical system with its own set of social norms, rules and competition over ‘capital’. eBay is used as a case study of the importance of using a Bourdieuean approach to create successful socio-technical systems.Using a two-year qualitative study of eBay users as empirical illustration, this paper argues that a large part of eBay’s success is in the social and cultural affordances for social translucence and navigation of eBay’s website - in supporting the Bourdieuean competition over capital and status. This exploration has implications for wider socio-technical systems design which this paper will discuss - in particular, the importance of creating socially translucent and navigable systems, informed by Bourdieu’s theoretical insights, which support competition for ‘capital’ and status

Keeping Fairness Alive : Design and formal verification of optimistic fair exchange protocols

Fokkink, W.J. [Promotor]Pol, J.C. van de [Promotor

Abordando fatores humanos no projeto de soluções criptográficas : dois estudos de caso em validação de itens e autenticação

Orientador: Ricardo DahabTese (doutorado) - Universidade Estadual de Campinas, Instituto de ComputaçãoResumo: O projeto de soluções criptográficas seguras a partir de uma perspectiva puramente teórica não é suficiente para garantir seu sucesso em cenários realistas. Diversas vezes, as premissas sob as quais estas soluções são propostas não poderiam estar mais longe das necessidades do mundo real. Um aspecto frequentemente esquecido, que pode influenciar em como a solução se sai ao ser integrada, é a forma como o usuário final interage com ela (i.e., fatores humanos). Neste trabalho, estudamos este problema através da análise de dois cenários de aplicação bem conhecidos da pesquisa em Segurança da Informação: O comércio eletrônico de itens digitais e Internet banking. Protocolos de trocas justas tem sido amplamente estudados, mas continuam não sendo implementados na maioria das transações de comércio eletrônico disponíveis. Para diversos tipos de itens digitais (e-goods), o modelo de negócios atual para comércio eletrônico falha em garantir justiça aos clientes. A validação de itens é um passo crítico em trocas justas, e recebeu pouca atenção dos pesquisadores. Nós acreditamos que estes problemas devam ser abordados de forma integrada, para que os protocolos de trocas justas possam ser efetivamente implementados no mercado. De forma geral, acreditamos também que isso seja um reflexo de paradigmas de projeto orientado a sistemas para soluções de segurança, que são centrados em dados em vez de usuários, o que resulta em métodos e técnicas que frequentemente desconsideram os requisitos de usuários. Contextualizamos como, ao subestimar as sutilezas do problema da validação de itens, o modelo atual para compra e venda de itens digitais falha em garantir sucesso, na perspectiva dos compradores, para as transações ¿ sendo, portanto, injusto por definição. Também introduzimos o conceito de Degradação Reversível, um método que inerentemente inclui o passo de validação de itens em transações de compra e venda com a finalidade de mitigar os problemas apresentados. Como prova-de-conceito, produzimos uma implementação de Degradação Reversível baseada em códigos corretores de erros sistemáticos (SECCs), destinada a conteúdo multimídia. Este método é também o subproduto de uma tentativa de incluir os requisitos do usuário no processo de construção de métodos criptográficos, uma abordagem que, em seguida, evoluímos para o denominado projeto de protocolos orientado a itens. De uma perspectiva semelhante, também propomos um método inovador para a autenticação de usuários e de transações para cenários de Internet Banking. O método proposto, baseado em Criptografia Visual, leva em conta tanto requisitos técnicos quanto de usuário, e cabe como um componente seguro ¿ e intuitivo ¿ para cenários práticos de autenticação de transaçõesAbstract: Designing secure cryptographic solutions from a purely theoretical perspective is not enough to guarantee their success in a realistic scenario. Many times, the assumptions under which these solutions are designed could not be further from real-world necessities. One particular, often-overlooked aspect that may impact how the solution performs after deployment is how the final user interacts with it (i.e., human factors). In this work, we take a deeper look into this issue by analyzing two well known application scenarios from Information Security research: The electronic commerce of digital items and Internet banking. Fair exchange protocols have been widely studied, but are still not implemented on most e-commerce transactions available. For several types of digital items (e-goods), the current e-commerce business model fails to provide fairness to customers. A critical step in fair exchange is item validation, which still lacks proper attention from researchers. We believe this issue should be addressed in a comprehensive and integrated fashion before fair exchange protocols can be effectively deployed in the marketplace. More generally, we also believe this to be the consequence of ongoing system-oriented security solution design paradigms that are data-centered, as opposed to user-centered, thus leading to methods and techniques that often disregard users¿ requirements. We contextualize how, by overlooking the subtleties of the item validation problem, the current model for buying and selling digital items fails to provide guarantees of a successful transaction outcome to customers, thus being unfair by design. We also introduce the concept of Reversible Degradation, a method for enhancing buy-sell transactions concerning digital items that inherently includes the item validation step in the purchase protocol in order to tackle the discussed problems. As a proof-of-concept, we produce a deliverable instantiation of Reversible Degradation based on systematic error correction codes (SECCs), suitable for multimedia content. This method is also the byproduct of an attempt to include users¿ requirements into the cryptographic method construction process, an approach that we further develop into a so-called item-aware protocol design. From a similar perspective, we also propose a novel method for user and transaction authentication for Internet Banking scenarios. The proposed method, which uses Visual Cryptography, takes both technical and user requirements into account, and is suitable as a secure ¿ yet intuitive ¿ component for practical transaction authentication scenariosDoutoradoCiência da ComputaçãoDoutor em Ciência da Computaçã

Design and Evaluate a Fair Exchange Protocol Based on Online Trusted Third Party (TTP)

One of the most crucial factors that e-commerce protocols should address is a fair exchange. In this research, an advanced method of cryptography coupled with the pay per use technique is used. A new electronic commerce protocol for the exchange of commodities is introduced. The proposed new protocol guarantees both features while addressing the main drawbacks associated with other related protocols. The new suggested e-commerce protocol is composed of two stages: pre-exchange and exchange stages. When the suggested new protocol is analysed with scrupulous protocol analysis, it attains fair exchange and a secure method of payment. The suggested new e-commerce protocol is more efficient than other related existing protocols. In this research “protocol prototype” and “model checking” is used for the purpose of authentication. The protocol prototype verifies that the suggested new protocol is executable when it's used in a real context. By experimental designs, this research shows the length of asymmetric keys as the biggest element that affects the efficiency of the protocol. When model-checking is applied in this protocol, the outcome indicates that the suggested protocol achieves the required features of fairness. Protocol extensions give those involved in the protocol the capacity to be resilient to failure. By using three methods of authentication, this research confirms that the new proposed protocol is well formulated. The work reported in this thesis first study the existing fair exchange protocols that solve the fairness problem. Then, propose more efficient protocol to solve the fairness problem. The original idea in this thesis is to reduce the communication overheads, risks and solve the bottleneck problems in the protocols that involve an online TTP