Transaction protocols for self-organizing systems of autonomous entities

Self-organizing systems of autonomous entities have gained wide-spread attention in the research community. The most difficult problem of such systems is that autonomous entities may choose between cooperation and defection in the transactions they participate. In internet based eCommerce, transaction protocols (so-called exchange protocols) are applied for this purpose. Yet, it has been repeatedly conjectured that such protocols are not applicable to self-organizing systems. Distributed reputation systems have been proposed as a means of compensating for such lack of applicability. Still, there is no analysis of the applicability of transaction protocols and their relationship with distributed reputation systems

Optimistic fair exchange

A fair exchange guarantees that a participant only reveals its items (such as signatures, payments, or data) if it receives the expected items in exchange. Efficient fair exchange requires a so-called third party, which is assumed to be correct. Optimistic fair exchange involves this third party only if needed, i.e., if the participants cheat or disagree. In Part I, we prove lower bounds on the message and time complexity of two particular instances of fair exchange in varying models, namely contract signing (fair exchange of two signatures under a contract) and certified mail (fair exchange of data for a receipt). We show that all given bounds are tight by describing provably time- and message-optimal protocols for all considered models and instances. In Part II, we have a closer look at formalizing the security of fair exchange. We introduce a new formal notion of security (including secrecy) for reactive distributed systems. We illustrate this new formalism by a specification of certified mail as an alternative to the traditional specification given in Part I. In Part III, we describe protocols for generic and optimistic fair exchange of arbitrary items. These protocols are embedded into the SEMPER Fair Exchange Layer, which is a central part of the SEMPER Framework for Secure Electronic Commerce.Ein Austausch ist fair, wenn eine Partei die angebotenen Güter, wie zum Beispiel digitale Signaturen, Zahlungen oder Daten, nur abgibt, wenn sie die erwarteten Güter im Tausch erhält. Ohne eine als korrekt angenommene dritte Partei, welche eine mit einem Notar vergleichbare Rolle übernimmt, ist fairer Austausch nicht effizient möglich. Ein fairer Austausch heißt optimistisch, falls diese dritte Partei nur in Problemfällen am Protokoll teilnimmt. In Teil I werden beweisbar zeit- und nachrichtenoptimale Protokolle für die Spezialfälle \u27;elektronische Vertragsunterzeichnung" (fairer Austausch zweier Signaturen; engl. contract signing) und \u27;elektronisches Einschreiben" (fairer Austausch von Daten gegen eine Quittung; engl. certified mail) von fairem Austausch vorgestellt. Teil II beschreibt einen neuen Integritäts- und Geheimhaltungsbegriff für reaktive Systeme. Dieser basiert auf einer Vergleichsrelation \u27;so sicher wie", welche die Sicherheit zweier Systeme vergleicht. Ein verteiltes, reaktives System wird dann als sicher bezeichnet, wenn es so sicher wie ein idealisiertes System (engl. trusted host) für diesen Dienst ist. Mit diesem Formalismus geben wir eine alternative Sicherheitsdefinition von \u27;elektronischem Einschreiben" an, deren Semantik im Gegensatz zu der in Teil I beschriebenen Definition nun unabhängig vom erbrachten Dienst ist. Teil III beschreibt ein Design und optimistische Protokolle für generischen fairen Austausch von zwei beliebigen Gütern und den darauf aufbauenden SEMPER Fair Exchange Layer. Dieser ist ein wesentlicher Baustein des SEMPER Framework for Secure Electronic Commerce

Optimistic fair exchange

A fair exchange guarantees that a participant only reveals its items (such as signatures, payments, or data) if it receives the expected items in exchange. Efficient fair exchange requires a so-called third party, which is assumed to be correct. Optimistic fair exchange involves this third party only if needed, i.e., if the participants cheat or disagree. In Part I, we prove lower bounds on the message and time complexity of two particular instances of fair exchange in varying models, namely contract signing (fair exchange of two signatures under a contract) and certified mail (fair exchange of data for a receipt). We show that all given bounds are tight by describing provably time- and message-optimal protocols for all considered models and instances. In Part II, we have a closer look at formalizing the security of fair exchange. We introduce a new formal notion of security (including secrecy) for reactive distributed systems. We illustrate this new formalism by a specification of certified mail as an alternative to the traditional specification given in Part I. In Part III, we describe protocols for generic and optimistic fair exchange of arbitrary items. These protocols are embedded into the SEMPER Fair Exchange Layer, which is a central part of the SEMPER Framework for Secure Electronic Commerce.Ein Austausch ist fair, wenn eine Partei die angebotenen Güter, wie zum Beispiel digitale Signaturen, Zahlungen oder Daten, nur abgibt, wenn sie die erwarteten Güter im Tausch erhält. Ohne eine als korrekt angenommene dritte Partei, welche eine mit einem Notar vergleichbare Rolle übernimmt, ist fairer Austausch nicht effizient möglich. Ein fairer Austausch heißt optimistisch, falls diese dritte Partei nur in Problemfällen am Protokoll teilnimmt. In Teil I werden beweisbar zeit- und nachrichtenoptimale Protokolle für die Spezialfälle ';elektronische Vertragsunterzeichnung" (fairer Austausch zweier Signaturen; engl. contract signing) und ';elektronisches Einschreiben" (fairer Austausch von Daten gegen eine Quittung; engl. certified mail) von fairem Austausch vorgestellt. Teil II beschreibt einen neuen Integritäts- und Geheimhaltungsbegriff für reaktive Systeme. Dieser basiert auf einer Vergleichsrelation ';so sicher wie", welche die Sicherheit zweier Systeme vergleicht. Ein verteiltes, reaktives System wird dann als sicher bezeichnet, wenn es so sicher wie ein idealisiertes System (engl. trusted host) für diesen Dienst ist. Mit diesem Formalismus geben wir eine alternative Sicherheitsdefinition von ';elektronischem Einschreiben" an, deren Semantik im Gegensatz zu der in Teil I beschriebenen Definition nun unabhängig vom erbrachten Dienst ist. Teil III beschreibt ein Design und optimistische Protokolle für generischen fairen Austausch von zwei beliebigen Gütern und den darauf aufbauenden SEMPER Fair Exchange Layer. Dieser ist ein wesentlicher Baustein des SEMPER Framework for Secure Electronic Commerce

Optimistic Fair Exchange based on Publicly Verifiable Secret Sharing

In this paper we propose an optimistic two-party fair exchange protocol which does not rely on a centralized trusted third party. Instead, the fairness of the protocol relies on the honesty of part of the neighbor participants. This new concept, which is based on a generic verifiable secret sharing scheme, is particularly relevant in networks where centralized authority can neither be used on-line nor off-line

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

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

Fair Exchange with Guardian Angels

In this paper we propose a new probabilistic Fair Exchange Protocol which requires no central Trusted Third Party. Instead, it relies on a virtually distributed and decentralized Trusted Third Party which is formalized as a Guardian Angel: a kind of Observer e.g. a tamper proof security device. We thus introduce a network model with Pirates and Guardian Angels which is well suited for Ad Hoc networks. In this setting we reduce the Fair Exchange Problem to a Synchronization Problem in which honest parties need to eventually decide whether or not a protocol succeeded in a synchronous way through a hostile network which does not guaranty that sent messages will be eventually received. This problem can be of independent interest in order to add reliability of protocol termination in secure channels

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 implementation of extensible middleware for non-repudiable interactions

PhD ThesisNon-repudiation is an aspect of security that is concerned with the creation of irrefutable audits of an interaction. Ensuring the audit is irrefutable and verifiable by a third party is not a trivial task. A lot of supporting infrastructure is required which adds large expense to the interaction. This infrastructure comprises, (i) a non-repudiation aware run-time environment, (ii) several purpose built trusted services and (iii) an appropriate non-repudiation protocol. This thesis presents design and implementation of such an infrastructure. The runtime environment makes use of several trusted services to achieve external verification of the audit trail. Non-repudiation is achieved by executing fair non-repudiation protocols. The Fairness property of the non-repudiation protocol allows a participant to protect their own interests by preventing any party from gaining an advantage by misbehaviour. The infrastructure has two novel aspects; extensibility and support for automated implementation of protocols. Extensibility is achieved by implementing the infrastructure in middleware and by presenting a large variety of non-repudiable business interaction patterns to the application (a non-repudiable interaction pattern is a higher level protocol composed from one or more non-repudiation protocols). The middleware is highly configurable allowing new non-repudiation protocols and interaction patterns to be easily added, without disrupting the application. This thesis presents a rigorous mechanism for automated implementation of non-repudiation protocols. This ensures that the protocol being executed is that which was intended and verified by the protocol designer. A family of non-repudiation protocols are taken and inspected. This inspection allows a set of generic finite state machines to be produced. These finite state machines can be used to maintain protocol state and manage the sending and receiving of appropriate protocol messages. A concrete implementation of the run-time environment and the protocol generation techniques is presented. This implementation is based on industry supported Web service standards and services.EPSRC, The Hewlett Packard Arjuna La

Security of Smartphones at the Dawn of their Ubiquitousness

The importance of researching in the field of smartphone security is substantiated in the increasing number of smartphones, which are expected to outnumber common computers in the future. Despite their increasing importance, it is unclear today if mobile malware will play the same role for mobile devices as for common computers today. Therefore, this thesis contributes to defining and structuring the field mobile device security with special concern on smartphones and on the operational side of security, i.e., with mobile malware as the main attacker model. Additionally, it wants to give an understanding of the shifting boundaries of the attack surface in this emerging research field. The first three chapters introduce and structure the research field with the main goal of showing what has to be defended against today. Besides introducing related work they structure mobile device attack vectors with regard to mobile malicious software and they structure the topic of mobile malicious software itself with regard to its portability. The technical contributions of this thesis are in Chapters 5 to 8, classified according to the location of the investigation (on the device, in the network, distributed in device and network). Located in the device is MobileSandbox, a software for dynamic malware analysis. As another device-centric contribution we investigate on the efforts that have to be taken to develop an autonomously spreading smartphone worm. The results of these investigations are used to show that device-centric parts are necessary for smartphone security. Additionally, we propose a novel device-centric security mechanism that aims at reducing the attack surface of mobile devices to mobile malware. The network-centric investigations show the possibilities that a mobile network operator can use in its own mobile network for protecting the mobile devices of its clients. We simulate the effectiveness of different security mechanisms. Finally, the distributed investigations show the feasibility of distributed computation algorithms with security modules. We give prototypic implementations of protocols for secure multiparty computation as a modularized version with failure detector and consensus algorithms, and for fair exchange with guardian angels

Design and implementation of extensible middleware for non-repudiable interactions

Non-repudiation is an aspect of security that is concerned with the creation of irrefutable audits of an interaction. Ensuring the audit is irrefutable and verifiable by a third party is not a trivial task. A lot of supporting infrastructure is required which adds large expense to the interaction. This infrastructure comprises, (i) a non-repudiation aware run-time environment, (ii) several purpose built trusted services and (iii) an appropriate non-repudiation protocol. This thesis presents design and implementation of such an infrastructure. The runtime environment makes use of several trusted services to achieve external verification of the audit trail. Non-repudiation is achieved by executing fair non-repudiation protocols. The Fairness property of the non-repudiation protocol allows a participant to protect their own interests by preventing any party from gaining an advantage by misbehaviour. The infrastructure has two novel aspects; extensibility and support for automated implementation of protocols. Extensibility is achieved by implementing the infrastructure in middleware and by presenting a large variety of non-repudiable business interaction patterns to the application (a non-repudiable interaction pattern is a higher level protocol composed from one or more non-repudiation protocols). The middleware is highly configurable allowing new non-repudiation protocols and interaction patterns to be easily added, without disrupting the application. This thesis presents a rigorous mechanism for automated implementation of non-repudiation protocols. This ensures that the protocol being executed is that which was intended and verified by the protocol designer. A family of non-repudiation protocols are taken and inspected. This inspection allows a set of generic finite state machines to be produced. These finite state machines can be used to maintain protocol state and manage the sending and receiving of appropriate protocol messages. A concrete implementation of the run-time environment and the protocol generation techniques is presented. This implementation is based on industry supported Web service standards and services.EThOS - Electronic Theses Online ServiceEPSRC : Hewlett Packard Arjuna LabGBUnited Kingdo