Blockchain Papers

Yonatan Sompolinsky, Yoad Lewenberg, Aviv Zohar

No abstract is available for this record.

Patrick McCorry, Malte Möser, Siamak F. Shahandasti, Feng Hao

No abstract is available for this record.

Tim Ruffing, Pedro Moreno-Sánchez, Aniket Kate

Author(s): Tim Ruffing, Pedro Moreno-Sanchez, Aniket Kate Download: Paper (PDF) Date: 27 Feb 2017 Document Type: Reports Additional Documents: Slides Video Associated Event: NDSS Symposium 2017 Abstract: Starting with Dining Cryptographers networks (DC-nets), several peer-to-peer (P2P) anonymous communication protocols have been proposed. However, despite their strong anonymity guarantees, none of them have been employed in practice so far: Most … Continued

Giuseppe Ateniese, Bernardo Magri, Daniele Venturi, Ewerton R. Andrade

We put forward a new framework that makes it possible to re-write or compress the content of any number of blocks in decentralized services exploiting the blockchain technology. As we argue, there are several reasons to prefer an editable blockchain, spanning from the necessity to remove inappropriate content and the possibility to support applications requiring re-writable storage, to "the right to be forgotten." Our approach generically leverages so-called chameleon hash functions (Krawczyk and Rabin, NDSS '00), which allow determining hash collisions efficiently, given a secret trapdoor information. We detail how to integrate a chameleon hash function in virtually any blockchain-based technology, for both cases where the power of redacting the blockchain content is in the hands of a single trusted entity and where such a capability is distributed among several distrustful parties (as is the case with Bitcoin). We also report on a proof-of-concept implementation of a redactable blockchain, building on top of Nakamoto's Bitcoin core. The prototype only requires minimal changes to the way current client software interprets the information stored in the blockchain and to the current blockchain, block, or transaction structures. Moreover, our experiments show that the overhead imposed by a redactable blockchain is small compared to the case of an immutable one.

S.D. Norberhuis

Peer-to-peer networks are often large, collaborative networks where peers can join openly. The essence of a collaborative, distributed system is that every node performs tasks for other nodes. The peers often help in singular interactions and without direct reciprocity. Malicious peers can abuse and freeride the public goods. The network without countermeasures can fall into a tragedy of the commons where no one helps another and everyone takes advantage of the generosity of peers. Only when the reputation of a peer is publicly available at scale and peers trust this reputation can the network escape the problems of freeriding and attain high utility for all participants. This thesis focuses on designing and implementing the first step of a tamper proof reputation system within Tribler. Tribler is a peer-to-peer BitTorrent system developed at the Delft University of Technology. This first step, made by this thesis, is to create MultiChain, a proof-of-concept bookkeeping system. MultiChain tracks the upload and download amounts of peers to eliminate freeriding. Multi-Chain is cryptographically protected and validated. The bookkeeping system has to be scalable to be publicly available and be able to process enough transactions. The system has to work in an asynchronous network. A new design of a distributed data structure that can be used as a ledger is introduced by this thesis. This first step with MultiChain is already more resilient to tampering than previous work, like BarterCast. BarterCast has no security measures against tampering records. The design of MultiChain is to have a chain of blocks for every peer as a ledger. Peers are participants of a peer-to-peer network. A block contains a transaction between two peers. This block is shared and added to both chains. This makes both chains of the peers intertwined and entangled at a shared block. The proposed design abandons the typical global, full ledger. The protocol of creating these blocks between peers is described. The problems faced by MultiChain in an asynchronous network are explained. The thesis proposes how the design can overcome these problems by only allowing atomic operations to be performed on the chain and to introduce unfinished blocks in the chain. The implementation of the design is tested and experimented with within this thesis to validate it to work correctly. Furthermore, a number of weak points are discussed. These weak points have to be addressed in the future to create a tamper proof reputation system.

Corina Sas, Irni Eliana Khairuddin

Bitcoin is a crypto-currency which differs in several ways from the traditional use of money. It does not require an individual name but digital wallet IDs, which makes it more private. Bitcoin technology currently lacks protection with respect to monetary transfers, and its structure is not endorsed by the governments. Yet, understanding the concept of trust is fundamental to Bitcoin technology and digital currency economy. This paper offers a review of relevant work on cryptocurrency and trust in HCI, and critically examines its value in understanding the issues of trust in Bitcoin technology. Several limitations of the current theories and models of trust are identified, and a research framework is proposed to explore the specific trust challenges raised by the Bitcoin technology.

Richard Dennis, Gareth Owen

This paper presents the first generalized reputation system that can be applied to multiple networks that is based on the blockchain. We first discuss current reputation systems, conducting a critical analysis of their current security vulnerabilities, before looking at how new blockchain based technologies are used. We propose an innovative new reputation system that is based on blockchain technologies which aims to solve many unanswered questions in today's current generation reputation systems. We then consider the limitations of such a system, before using simulations and analyses to demonstrate methods of overcoming these limitations. We conclude by suggesting areas for future studies, and summarizing our findings.

Rafael Pass, Abhi Shelat

Electronic financial transactions in the US, even those enabled by Bitcoin, have relatively high transaction costs. As a result, it becomes infeasible to make micropayments, i.e. payments that are pennies or fractions of a penny. In order to circumvent the cost of recording all transactions, Wheeler (1996) and Rivest (1997) suggested the notion of a probabilistic payment, that is, one implements payments that have expected value on the order of micro pennies by running an appropriately biased lottery for a larger payment. While there have been quite a few proposed solutions to such lottery-based micropayment schemes, all these solutions rely on a trusted third party to coordinate the transactions; furthermore, to implement these systems in today's economy would require a a global change to how either banks or electronic payment companies (e.g., Visa and Mastercard) handle transactions.

Andrew Miller, Ahmed E. Kosba, Jonathan Katz, Elaine Shi

An implicit goal of Bitcoin's reward structure is to diffuse network influence over a diverse, decentralized population of individual participants. Indeed, Bitcoin's security claims rely on no single entity wielding a sufficiently large portion of the network's overall computational power. Unfortunately, rather than participating independently, most Bitcoin miners join coalitions called mining pools in which a central pool administrator largely directs the pool's activity, leading to a consolidation of power. Recently, the largest mining pool has accounted for more than half of network's total mining capacity. Relatedly, "hosted mining" service providers offer their clients the benefit of economies-of-scale, tempting them away from independent participation. We argue that the prevalence of mining coalitions is due to a limitation of the Bitcoin proof-of-work puzzle -- specifically, that it affords an effective mechanism for enforcing cooperation in a coalition. We present several definitions and constructions for "nonoutsourceable" puzzles that thwart such enforcement mechanisms, thereby deterring coalitions. We also provide an implementation and benchmark results for our schemes to show they are practical.

Kai Chain, Yao-Ren Wen

It doesn't matter whether its coin, banknotes or even gold the usual currency in circulation in our communities. But have we ever thought of using virtual currency in the real world, with a higher value to that of gold. Bitcoin have caused waves across the globe, it is believed to be the most valuable currency in the future. This article describes the sensation caused by the global virtual currency Bitcoin, the rise resulting in principle and practical instruction on how to get Bitcoin currently in use.

Krzysztof Rzaḑca, Anwitaman Datta, Gunnar Kreitz, Sonja Buchegger

In a decentralized storage system, agents replicate each other’s data to increase availability. Compared to organizationally centralized solutions, such as cloud storage, a decentralized storage system requires less trust in the provider and may result in smaller monetary costs. Our system is based on reciprocal storage contracts that allow the agents to adopt to changes in their replication partners’ availability (by dropping inefficient contracts and forming new contracts with other partners). The data availability provided by the system is a function of the participating agents’ availability. However, a straightforward system in which agents’ matching is decentralized uses the given agent availability inefficiently. As agents are autonomous, the highly available agents form cliques replicating data between each other, which makes the system too hostile for the weakly available newcomers. In contrast, a centralized, equitable matching is not incentive compatible: it does not reward users for keeping their software running. We solve this dilemma by a mixed solution: an “adoption” mechanism in which highly available agents donate some replication space, which in turn is used to help the worst-off agents. We show that the adoption motivates agents to increase their availability (is incentive-compatible), but also that it is sufficient for acceptable data availability for weakly-available agents.

Waleed W. Smari, Antonio Montero Navarro, William K. McQuay

During the past two decades, we have seen rising interest in computer-supported collaboration and, with the advent of the Web 2.0 and semantic technologies, increased importance for collaborative work. Worldwide, people expect unlimited access to information within and across cultures. Social networking continues to expand and impact collaboration approaches at the personal and enterprise levels. As a result, the computer-supported collaboration research community has turned its attention to the study of human social behavior from records such as blogs, wikis, social media, and social networking sites 1. The desire for mobile and pervasive connectivity is pushing expansion of an ever growing wired and wireless high speed backbone that globally combines computing, sensing, and communication technologies. Annually, new classes of mobile devices are added to the traditional desktop, laptop, tablet, and smartphones. However, computer-based collaboration encompasses complex hardware and software issues that have been in the focus of the research community for a long time 2. In 1981, Johnson-Lenz coined the term groupware as ‘intentional group processes plus software to support them’ 3. By 1988, the term computer-supported cooperative work was defined as ‘a scientific discipline guiding the design and development of groupware in a meticulous and appropriate way’ 4. Computer-supported cooperative work (CSCW) is a multidisciplinary discipline that encompasses technical, human, and social factors that can vary its implementations depending on the context, culture, organization, and country that apply it 5. As collaborative/cooperative applications evolved, important challenges also arose for developers 6. As a result, significant on-going research works address topics such as collaboration systems infrastructure, human systems, collaboration work and processes, and unique domain-specific issues. The field of infrastructure is one of the most active areas in computer-supported collaboration, with research focused on underlying technologies such as cloud computing, big data, service-oriented architectures, smart networks, and grids. Advanced infrastructure technologies offer a vision of resources (networks, computational servers, storage, search engines, collaboration tools and applications, etc.) as a service, with greater ease to collaborate while lowering cost. The Internet of Things (IoT) captures the growing importance of sensor swarms and collaborative devices that are often attached to one's smartphone or tablet. At the same time, there are new complementary challenges for privacy and security as we attempt to understand how to handle trust in complex systems and how to measure trustworthiness in human-to-human, human-to-machine, and machine-to-machine collaborations. The field of human systems focuses on the human component in collaboration such as coordination and cooperation mechanisms, cultural and psychological aspects, natural languages, human-machine interaction and interfaces, human centric aspects of trust and trustworthiness, cognitive engineering, and user-centered design. The field of collaboration work and processes focuses on aspects that traditionally relate to management and business but gradually have been considered by the software engineering area, such as virtual and remote project coordination, distributed team management, workflows, coordination, distributed and virtual organizations, and distributed design and development. Finally, the domains where computer-based collaboration can be applied continue to grow and are almost endless. Social media, knowledge management, e-learning, financial systems, simulation environments, decision making, design and engineering, logistics, e-business, telemedicine, public health, and emergency and disaster response are some examples of these domains. The annual International Conference on Collaboration Technologies and Systems, held since 1999, comes in the mid of these exciting developments. The conference has also produced special journal issues in recent years and this is one of them. This special issue contains eleven papers representing recent advances in the areas of the infrastructure, operation, evaluation, and application of collaboration systems. These papers were carefully selected from the 2012 International Conference on Collaboration Technologies and Systems (CTS 2012), which was held at the Westin Westminster Hotel, Denver, Colorado, USA, on 21–25 May, 2012 7 and the 2013 International Conference on Collaboration Technologies and Systems (CTS 2013), which was held at the Sheraton San Diego Hotel & Marina, San Diego, California, USA, on 20–24 May, 2013 8. Selected papers from the conference were invited for extended submission based on the conference technical program committee and the track organizers recommendations. In addition and in order to provide a wider overview of the current research in collaboration related topics, an open Call for Papers was publicly announced and distributed. In response, additional papers were received with a total of eighteen papers submitted for consideration. The complete set of submissions went through three rigorous review cycles, with three to six reviews per paper per cycle. Upon the conclusion of the review process, the eleven submissions that received the highest review ratings were accepted for publication in this special issue. The papers published in this special issue can be classified under three groups: collaborative system design methodologies, security and trust, and collaborative applications. The selected papers in each of these groups are briefly introduced in this section. There are six manuscripts that fall under this category, which covers a wide range of issues, approaches, and solutions. Drabble 9 presents an overview of the Cassandra Analysis and Planning System (CAPS) collaborative design tool kit, which provides designers with the capabilities to identify the direct effects of their own decisions and their indirect effects on the designs of others. The CAPS provides capabilities for reasoning with both quantitative and qualitative constraints and employs two dependency reasoning engines—one handles quantitative values and the other controls qualitative ones. CAPS supports a dynamic design process which identifies the most important design decisions, alerts the impacted designers, and supports a mitigation process to deal with any issues. The paper describes the CAPS architecture and an initial evaluation against a large collaborative task involving the design of a helicopter's electrical, hydraulic, structural, and mechanical systems. Tanaka et al. 10 study the effects real-time avatars had on distant communications when the avatars served as a substitute for videos in distributed environments. The paper discusses two experiments involving videos, photos, or avatars to supplement voice communications. In the first experiment, the subjects watched a conversation partner's video, avatar, photo, or nothing when speaking to the distant partner. The trials were made separately to observe the effects of motion and appearance on the frequency of pauses and speed of speaking. In the second experiment, the researchers compared avatar chat and a tele-operated robot conferencing to find how a physical embodiment influenced the degree of smoothness of speech. Traditionally, in distributed collaborative systems, video connections have been considered unimportant to effective distant communication. Dorn and Taylor 11 investigate the adaptability of the collaboration structure based on an analysis framework consisting of aspects such as behavior, asynchrony, state, and execution. They discuss seven distinctively different collaboration patterns in terms of those aspects. These collaboration patterns and resulting insights into their inherent adaptability may guide design decisions and trade-off analyses for the development of collaborative environments. The collaboration pattern construct is an extension of design pattern concepts and mechanisms from the software architecture domain. The success of software architecture description languages 20 led the authors to investigate a modeling approach for collaboration topologies and the development of a human Architecture Description Language (hADL) for specifying adaptation authority or flexibility conditions. In Davoust et al. 12, the authors define, classify, and characterize distributed wikis. They have identified three classes of distributed wiki systems, each using a different collaboration model and distribution scheme: highly available wikis, decentralized social wikis, and federated wikis. They have classified existing distributed wikis according to these classes and detail their underlying complexities and social and technical motivations. Davoust et al. 13 address the challenge that existing wiki systems, such as Wikipedia, depend on a centralized authority and cannot easily accommodate multiple points of view. The authors present P2Pedia, a social peer-to-peer wiki system, where users have their own local repository and can collaborate by creating, discovering, editing, and sharing pages with their peers but without synchronizing them. Multiple versions of each page can thus coexist on each repository and across the network, which allows for multiple points of view. Browsing or searching the wiki can yield multiple page versions. The authors describe an experimental study where the system was deployed for academic writing exercises, and the results are analyzed to demonstrate this collaboration approach. Missikoff et al. 14 present an end-to-end framework based on an open, collaborative approach for developing and maintaining business domain ontologies. While modern virtual enterprises require the definition of a common, agreed to, and shared conceptual basis that is captured in a reference ontology, no single methodology has been recognized as the primary solution for building ontologies. The authors propose a method for building domain ontologies, which is capable of integrating in one single software framework the features of cooperative participation, shared agreement, multilevels of formalism, and reuse of knowledge. The authors' methodology is characterized by a social participation approach that allows a community of practice, including knowledge engineers, domain experts, and ontology stakeholders to cooperate to produce conceptual models and reach consensus on their suitability while providing formal encoding into a computational ontology. Security and privacy issues in collaboration environments continue to be a major concern. We have three manuscripts that address some of the contemporary concerns. In Aldini et al. 15, the authors have proposed a collaborative framework for checking Android applications for malware by generating probabilistic behavior contracts. Repackaged Android applications are based on genuine applications, but they can include some hidden malwares to access private data or user credit information. The proposed framework performs analysis of the app's behavior at run-time from a contract that is built dynamically from monitoring real world usage. The contract specifies the set of legal actions that can be performed by an application. In the proposed framework, application contracts are generated dynamically by a central server that merges execution traces that are collected and shared continuously by collaborative users executing the application. Because the contract is built by monitoring real user behaviors, it is possible to detect misbehaviors that may not be noticed through static analysis alone. Kong et al. 16 present a technique for indoor location of mobile devices using Bluetooth wireless signal strength. The proposed method treats locations as fuzzy sets and fuzzifies the signal strength to define set membership. Membership values are then fused from multiple sources using a rules engine to deduce location values. The principal benefits of this technique include that it requires little or no calibration, can be used with widely available commercial devices, and places more attention on location information such as a room and floor of a building rather than coordinates. In Tang et al. 17, the authors address the need for extensions to the role-based access control model as cloud service providers expand user activities for cross-tenant interaction. Currently, most cloud service providers isolate user activities and data within a single tenant boundary. It is anticipated that this situation will evolve to foster cross-tenant collaboration supported by Authorization as a Service (AaaS). At present, there is no widely accepted model for cross-tenant authorization. The authors have built on an existing informal multi-tenancy authorization system (MTAS) 21, formalized the MTAS model, and proposed extensions for finer-grained cross-tenant trust. They have demonstrated the utility and feasibility of MTAS by means of an example policy specification, developed a prototype system, and conducted experiments on the prototype. The design and development of collaboration applications are important to respond to society's needs and solutions. In this special issue, there are two papers that apply. Lang and Fink 18 address rival machine scheduling of one or more homogeneous machines by autonomous agents. Machine scheduling by itself is computationally complex, and the presence of autonomous agents makes the problem more difficult. Autonomous agents pursue their own goals, act noncooperatively, and might not be willing to reveal information due to privacy concerns. To overcome the conflict of interests and prevent strategic interactions, the authors present a negotiation protocol to facilitate the coordination of noncooperative agents. Pani et al. 19 present the design and evaluation of a patient-centric collaborative tele-rehabilitation framework aimed at supporting a multidisciplinary team in the follow-up of domiciliary patients. The proposed framework builds on the experience of a clinical trial that exploited a novel tele-rehabilitation device not originally intended to support collaborative scenarios. The authors argue that collaborative technology in healthcare represents an important way to improve the quality of the care services and at a reduced cost. The authors conducted semi-structured interviews with a panel of experts to evaluate the proposed approach. Based on the papers submitted to and accepted in this special issue, we can draw some interesting conclusions. Computer-supported collaboration is in the mainstream interest of the research community. It is utilized in the everyday way of work of individuals, communities, and organizations. This usage is identifying subtle problems that have to be solved by researchers and practitioners in academia and industry. Technological, procedural, human, and domain-dependent issues have to be addressed by works such as those presented in this special issue. However, because computer-supported collaboration is being used in vastly different domains, the problems that this use identify are of very diverse nature. As we have seen, the papers published in this special issue address collaborative design, real time avatars, collaboration patterns, distributed wikis, business ontologies, malware detection, location of mobile devices, access control, autonomous agents, and tele-health. We anticipate this trend to continue as these systems and technologies get more pervasive and experience wider usage in numerous sectors and application domains. In some cases, the issues addressed by computer-supported collaboration fall within the focus of interest of other well-established areas of computer science and engineering such as operating systems, software engineering, information systems, or telecommunications,. In other cases, they are more related to organizational and business, sociology, psychology, anthropology, or human factors. If computer-supported collaboration is to be a discipline on its own, the key issues that describe it have to be identified. It is commonly accepted that computer-supported collaboration is not just a narrow and deep computing discipline but, on the contrary, is a broad and multidisciplinary field that cuts across many computing and noncomputing areas. In our opinion, the definition of the discipline of computer-supported collaboration has to be one of the hot topics of the research community in the short term. Thus, the development of the computer-supported collaboration body of knowledge could help to define this discipline. We hope that works like this special issue promote the interest for this discipline and its research topics. The guest editors of this special issue would like to express their deep gratitude to all authors, external reviewers, and Geoffrey Fox for their efforts in making this special issue possible. Moreover, they wish to thank all of the external reviewers who contributed at different levels to this special issue: Marie-Hélène Abel, Gail-Joon Ahn, Mortaza S. Barg, Louise Barkhuus, Sanat K. Bista, Christos Bouras, Mario Cannataro, Kyle Chard, Giuliana Dettori, Schahram Dustdar, Ana María Fernández-Pampillón, Maria Grazia Fugini, Ronald Hartung, Andrea J. Hester, Douglas Hodson, Claudia Ignat, James Joshi, Malik Ahmad Kamran, Kyoung-Yun Kim, Gregorij Kurillo, Tanu Malik, Cristina Manresa, Laurent Moccozet, Pascal Molli, James Myers, Grzegorz J. Nalepa, Mads Nygaard, Francesco Palmieri, Daniel Perry, T.K. Prasad, Wolfgang Prinz, Paolo Renna, Vassil Roussev, Filippo A. Salustri, Liliana P. Santacruz, Antonio Sarasa, José Luis Sierra, Hala Skaf-Molli, Irena Spasic, Anna Squicciarini, Kyle Stewart, Julianne Stiller, Jeffrey Stuckman, Hassan Takabi, Giordano Tamburrelli, Srikumar Venugopal, Bin Wang, Liu Yang, Chee Shin Yeo, Dimitrios Zissis, and Urko Zurutuza.

Rodrigue Carlos Nana Mbinkeu, Bernabé Batchakui

For the past five years, the bitcoin network constantly experience a growth in its size as more communities turn to accept the currency for payment exchanges. Using Flat File and a LevelDB of indices to save blocks on disk, bitcoin users require more memory to save the history of transaction. We focus on issues of memory management and access time in the bitcoin protocol using SQLite DataBase. With all the advantages of SQLite DataBase, it would be efficient if it is fitted in this architecture. The SQLite comes with many flavors one of which is its ability to support sql queries. Thus, instead of parsing indices to search a block from the database, a more powerful query can do the job.

Yoad Lewenberg, Yoram Bachrach, Yonatan Sompolinsky, Aviv Zohar · 5 authors

Bitcoin is an innovative decentralized cryptocurrency whose core security relies on a “proof of work ” procedure, which requires network participants to repeatedly compute hashes on inputs from a large search space. Finding one of the rare inputs that generates an extremely low hash value is consid-ered a successful attempt, allowing miners to approve new transactions and, in return, to collect rewards in bitcoins. This reward allocation, which provides the incentive for miners to participate, is a random process with a large vari-ance. Miners who desire a steady income thus often par-ticipate in mining pools that divide among their members the earned rewards, and reduce this variance. Mining pools are slightly better at coordinating participants due to lower-latency communication, a fact which implies that they man-age to collect slightly higher rewards. We examine dynamics of pooled mining and the rewards that pools manage to collect, and use cooperative game the-oretic tools to analyze how pool members may share these rewards. We show that for some network parameters, es-pecially under high transaction loads, it is difficult or even impossible to distribute rewards in a stable way: some par-ticipants are always incentivized to switch between pools.

Till Neudecker, Philipp Andelfinger, Hannes Hartenstein

We present a simulation model of the Bitcoin peer-to-peer network, a widely deployed distributed electronic currency system. The model enables evaluations of the feasibility and cost of attacks on the Bitcoin network at full scale of 6,000 nodes. The simulation model is based on unmodified code from core segments of the Bitcoin reference implementation used by 99% of nodes. Parametrization of the model is performed based on large-scale measurements of the real-world network. We present preliminary validation results showing a reasonable correspondence of the propagation of messages in the Bitcoin network compared with simulation results. We apply the model to study the feasibility of a partitioning attack on the network and show that the attack is sensitive to the churn of the attacking nodes.

Weihong Wang, Peng Li

Bitcoin is a virtual currency based on the P2P network. Because of decentralization, anonymity, stability and other advantages, Bitcoin develops rapidly. In order to cope with increasingly wide application fields of bitcoin, this research designs bitcoin's payment based on the IC card, which improves its safety and convenience. According to Bitcoin's unique utilization, we've designed and achieved the documental structure of Bitcoin IC card and mutual authentication between PSAM card and IC card. With the combination of IC card private key and user's private key leading to account's private key, it will be safer to private key. Besides using merge-avoidance algorithm when trading improves the security of the account.

Marco Mancini

No abstract is available for this record.

Frederik Armknecht, Ghassan Karame, Avikarsha Mandal, Franck Youssef · 5 authors

No abstract is available for this record.

David J. Rolfe, Steve Dittmore

Traditional sports ticket sales have followed a basic model of tickets in exchange for cash or credit. In an evolving and competitive market, sports marketing professionals must adapt and consider alternate forms of ticket sales. This case study follows Julie Lin, the director of ticket sales for a fictional National Hockey League expansion team, the Seattle Salmon. In an effort to align with the strategic vision of being considered a highly innovative sports franchise, Lin is considering accepting Bitcoin, a virtual currency, as a form of payment. Considered a “cryptocurrency,” Bitcoin is awarded through the solving of complex computer riddles, is devoid of a physical form, has no government or regulatory body backing it, and has value based largely on speculation. Bitcoin has found popularity and legitimacy among technology companies and companies considered to be innovative. At the present time, three professional sports accept Bitcoin for the purchase of tickets. This case will follow Lin and her exploration of Bitcoin within her franchise. Readers will consider positive and negative aspects of Bitcoin in a sports ticketing environment, and ultimately present an educated and data-driven recommendation regarding the details of this case.

Imre Szücs, Attila Kiss

The role of Bitcoin -open source virtual peer-to-peer money -in finance has become more important with the increasing acceptance by service providers. Nevertheless several financial institutes and governments explain their revulsion against Bitcoin, due to the unknown financial risks behind it which could have an impact on the global financial world. In this paper we examine the relationship between BTC/USD exchange rate and the network properties of the underlying transactional graph. The main goal of our research is to get a deeper understanding on the behavior of Bitcoin and ground further researches on exploring the financial risk. To characterize the transactional graph network analysis techniques, while to examine the relationship data mining and time series analysis techniques were used.

Joshua Elkington

Bitcoin is a decentralized peer-to-peer payment system that has the potential to disrupt the financial industry. In order for the Bitcoin network to function properly, people within the network need to follow the protocol and contribute computing power. However, selfish strategies can be used to disproportionately increase one’s payoff relative to their computational power. Three approaches are used to analyze selfish mining strategies in the Bitcoin network in order to determine when this strategy will dominate.

Wojciech Nowakowski

No abstract is available for this record.

Ittay Eyal

An open distributed system can be secured by requiring participants to present proof of work and rewarding them for participation. The Bitcoin digital currency introduced this mechanism, which is adopted by almost all contemporary digital currencies and related services. A natural process leads participants of such systems to form pools, where members aggregate their power and share the rewards. Experience with Bitcoin shows that the largest pools are often open, allowing anyone to join. It has long been known that a member can sabotage an open pool by seemingly joining it but never sharing its proofs of work. The pool shares its revenue with the attacker, and so each of its participants earns less. We define and analyze a game where pools use some of their participants to infiltrate other pools and perform such an attack. With any number of pools, no-pool-attacks is not a Nash equilibrium. We study the special cases where either two pools or any number of identical pools play the game and the rest of the participants are uninvolved. In both of these cases there exists an equilibrium that constitutes a “tragedy of the commons” where the participating pools attack one another and earn less than they would have if none had attacked. For two pools, the decision whether or not to attack is the miner’s dilemma, an instance of the iterative prisoner’s dilemma. The game is played daily by the active Bitcoin pools, which apparently choose not to attack. If this balance breaks, the revenue of open pools might diminish, making them unattractive to participants.

Martina E. Greiner, Hui Wang

Trust has always been important in electronic commerce. Prior research in MIS has mainly focused on trust-building mechanisms and insurance against opportunistic behavior. We suggest a “trust-free system” approach, which addresses trust issues by eliminating the need for trust. Using Bitcoin, a decentralized electronic cash system, we illustrate how a system can solve trust issues by becoming “trust-free” through design. We discuss the design features of this approach, and explore research questions for generalizing the design to other information systems. The idea of a trust-free system opens a new way of thinking about trust issues in information systems. We believe that there is an untapped potential for new ideas and research on how to design and evaluate information systems.