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 Guter, wie zum Beispiel digitale Signaturen, Zahlungen oder Daten, nur abgibt, wenn sie die erwarteten Guter im Tausch erhalt. Ohne eine als korrekt angenommene dritte Partei, welche eine mit einem Notar vergleichbare Rolle ubernimmt, ist fairer Austausch nicht effizient moglich. Ein fairer Austausch heist optimistisch, falls diese dritte Partei nur in Problemfallen am Protokoll teilnimmt. In Teil I werden beweisbar zeit- und nachrichtenoptimale Protokolle fur die Spezialfalle ';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 Integritats- und Geheimhaltungsbegriff fur 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) fur 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 unabhangig vom erbrachten Dienst ist. Teil III beschreibt ein Design und optimistische Protokolle fur generischen fairen Austausch von zwei beliebigen Gutern und den darauf aufbauenden SEMPER Fair Exchange Layer. Dieser ist ein wesentlicher Baustein des SEMPER Framework for Secure Electronic Commerce.

/pdf/optimistic-fair-exchange-3kjcurvhpf.pdf

Optimistic fair exchange

SUMMARY: The development of e-commerce technologies in relation to construction management have been improved significantly in the recent years and are perceived as a mainstream to improve productivity and information flow as well as communications However, until now, not much evident research has been conducted to pursue successful applications of e-commerce technologies to the construction supply chain This research aims to understand the current state of e-commerce technologies applications in the construction supply chain and provide recommendations for future improvement Both survey and semi-structured interviews were conducted with the construction supply chain members to obtain sufficient and useful research data The results showed that while everyone agrees on the importance of implementing e-commerce technologies in the construction supply chain, the major barriers lies with the reluctance or inability of the subcontractors/suppliers to adopt the technologies and lack of in-house technical expertise as well as lack of integrated information management systems The results also showed that increased awareness of company’s objectives and more userfriendly, cost-reduced, standardised and integrated e-commerce systems, together with a positive organisational culture on top management supporting continuous IT training and learning and knowledge-sharing are needed in order to promote better use of e-commerce technologies

/pdf/effective-applications-of-e-commerce-technologies-in-bykkfdv0ih.pdf

Effective applications of e-commerce technologies in construction supply chain: current practice and future improvement

This paper reviews the changing nature of construction design and the potential for e‐procurement to respond to these changes. With the emphasis shifting from supply‐driven to demand‐driven product design the trading relationships within the industry must become more complex. This paper hypothesizes an electronic market in design and supply capability to exploit distributed design knowledge within the supply chain. In their current form, e‐commerce and brokering systems are too immature to support such relationships, but many elements of a technical solution are available. However, how they will reshape working practices is uncertain and this poses architectural and human organization problems for information systems (IS) developers. They must anticipate and address changes in working practices across a whole group of industries competing within a complex market place. We postulate a development approach that uses simulation models supported by soft systems methods to explore these process re‐engineering options and human issues. The simulation of new business processes, combined with prototype IS designs, offers a powerful mechanism for evaluating the effects of proposed architectures for “design transactions” in e‐procurement. The open learning that occurs in simulation experiments is also a key element in helping the management of the individual organizations in understanding how to shape their particular contribution to the new collaborative process. A major barrier to enhancing construction industry performance in this way is the defensive nature of existing contracts and lack of trust between parties; we therefore propose the use of COLA process in parallel with the simulation work to engender trust and improved working relationships between the collaborating organizations.

Developing distributed design capabilities in the construction supply chain

Mit Electronic Commerce wird i. allg. die automatische Durchführung von Handelstransaktionen über Kommunikationsnetze bezeichnet. Bereits seit den 70 er Jahren wurde nach dieser Definition Electronic Commerce auf der Basis des elektronischen Datenaustausches (EDI) betrieben. Daû Electronic Commerce stark an Prominenz gewonnen hat und droht, als Modebegriff überhöht zu werden, liegt insbesondere an der Vielfalt der Anwendungsmöglichkeiten, die sich heute aus dem Zusammentreffen des Internet, preiswerter Hardund Software sowie preiswerter Kommunikationsverbindungen ergeben hat. Eine weitere wichtige Grundbedingung ist die inzwischen weit gediehene Standardisierung von grundlegenden Kommunikationsprotokollen und Sicherheitsmechanismen, die zur Abwicklung von EC-OnlineTransaktionen erforderlich sind. Dabei spielen heute v. a. (natürlich) das WWW, gängige Zahlungsverfahren sowie allgemein unterstützte Verfahren zur Verschlüsselung, Authentisierung und Vertrauensbildung eine wichtige Rolle. Für das Jahr 2000 erwartet die Europäische Kommission ein EC-Weltmarktvolumen von 200 Milliarden Euro (EITO 1999). Im Durchschnitt erwarten Analysten und Marktforscher für die Jahre 2000 bis 2002 ein Volumen von 154,5 Mrd. USD (OECD 1999). Dies sind Durchschnittswerte, die sich aus den Prognosen von 12 Instituten ergeben. Weiteren Analysen zufolge soll sich der Electronic Commerce in Deutschland von 73 Mio. USD (1996/97) über 9.700 Mio. (2000/01) bis zu 16.090 Mio. in den Jahren 2001/02 entwickeln. Für die EU wird im gleichen Zeitraum folgendes Volumen erwartet: 96 Mio. USD, 44.300 Mio. und 64.360 Mio. Da der elektronische Handel naturgemäû über die Grenzen einzelner Organisationen hinweg geführt wird, geht mit der Realisierung von Electronic-Commerce-Systemen immer auch eine Unterstützung durch entsprechende Kommunikationsund Kooperationsprotokolle einher. Es liegt daher in der Natur der Sache, daû bei einer technologisch orientierten Herangehensweise verteilte Systeme und die in ihrem Umfeld bereits vorhandenen Technologien einen wichtigen Ausgangspunkt für die Realisierung von EC-Systemen bilden. Zielsetzung dieses Artikels ist, das komplexe Feld des Electronic Commerce etwas zu strukturieren und dabei Hinweise auf relevante Standards, Technologien und ihre Anwendungsmöglichkeiten zu geben. Dabei liegt in diesem Beitrag der Schwerpunkt im Bereich der dazu

Electronic Commerce Technologische und organisatorische Grundlagen

Bartering plays a significant role in today's global economy-both between individuals as well as in B2B settings. However, aside from lacking automation, today's bartering solutions and supporting platforms typically neglect the privacy needs of their users. In this paper, we present a novel two-party protocol which addresses these shortcomings. The new protocol automatically determines whether the desired and offered commodities and quantities overlap in such a way that both parties are willing to barter. Throughout the protocol, the commodities and quantities as specified by the parties are kept private. We show that the protocol is privacy-preserving in the semi-honest model. As main building blocks, the new bartering protocol uses a novel privacy-preserving protocol for selecting a random subinterval out of the overlap of two intervals as well as a newly-developed secure protocol for input-symmetric strong conditional oblivious transfer.

A secure two-party bartering protocol using privacy-preserving interval operations

Barter is a scalable, highly-available and efficient electronic commerce system that facilitates digital content trade over an open network. Barter is designed to operate over a large-scale, global and heterogeneous communication network infrastructure. The barter protocols address two vital requirements from an electronic commerce system, neglected from existing systems: scalability and transactional efficiency. barter suggests three basic protocols, offering different levels of trust in the system.

/pdf/barter-a-backbone-architecture-for-trade-of-electronic-1gjjt30pjy.pdf

BARTER: A Backbone Architecture for Trade of Electronic Content

BARTER (a Backbone ARchitecture for Trade of ElectRonic content) is a payment infrastructure that facilitates digital content trade over an open network. BARTER is designed to operate over a large-scale, global and heterogeneous communication network. The BARTER protocols address two vital requirements, neglected from existing electronic commerce systems: scalability and transactional efficiency. These protocols possess strong properties such as delivery atomicity, agreement validation and the ability to resolve several classes of disputes. BARTER's novelty is twofold: First, BARTER servers are not required to perform expensive cryptographic operations such as commitment verification; commitments are cross-verified by the parties themselves, thus reducing the overhead of online transaction processing by orders of magnitude. Consequently, BARTER can serve as an efficient online/offline clearing infrastructure. Second, BARTER integrates scalability considerations into several system components (the authentication subsystem, the account management subsystem, and the maintenance of global data) that are likely to suffer service degradation in a world-wide setting. In addressing these issues, BARTER takes into account the inherent asynchronous, unreliable, insecure and failure-prone environment assumptions. We contend that by employing service distribution, BARTER is expected to scale well, meeting the demands of a world-wide setting, over which it is intended to operate.

Gadi Shamir

Papers

BARTER: A Backbone Architecture for Trade of Electronic Content

A safe and scalable payment infrastructure for trade of electronic content