Blockchain Papers

Goutam Paul, Pratik Sarkar, Sarbajit Mukherjee

No abstract is available for this record.

Anton Badev, Matthew Chen

This paper provides the necessary technical background to understand basic Bitcoin operations and documents a set of empirical regularities related to Bitcoin usage. We present the micro-structure of the Bitcoin transaction process and highlight the use of cryptography for the purposes of transaction security and distributed maintenance of a ledger. Using publicly available transaction-level data, we examine patterns of general usage together with usage by Satoshi Dice, the largest online gambling service using Bitcoin as the method of payment. Our analysis suggests that less than 50 percent of all bitcoins in circulation are used in transactions. About half of these transactions involve less than U.S.$100 equivalent, and for the period for which we have data for Satoshi Dice, most of these small-value transactions were related to the online gambling service. Relatively less frequent large value transactions drive the average transaction value to levels above U.S.$40,00 0 equivalent value, and are not likely to involve payments for goods and services. Bitcoin exchange rates exhibit somewhat complicated dynamics. In the past 24 months, the USD-BTC exchange rate increased more than 50-fold. The daily variance of the USD-BTC exchange rate remained remarkably stable for this same period, once the variance calculations account for the changing exchange rate level. We also document that the exchange rates between bitcoin and other major currencies are not well aligned. We interpret this as lack of depth of the exchange markets and as costly exchange rather than as unexploited arbitrage opportunities. Finally, we examine the economic incentives for the participants in the distributed implementation of the Bitcoin scheme.

Arthur Gervais, Srđjan Čapkun, Ghassan Karame, Damian Gruber

Lightweight Bitcoin clients are gaining increasing adoption among Bitcoin users, owing to their reduced resource and bandwidth consumption. These clients support a simplified payment verification (SPV) mode as they are only required to download and verify a part of the block chain---thus supporting the usage of Bitcoin on constrained devices, such as smartphones. SPV clients rely on Bloom filters to receive transactions that are relevant to their local wallet. These filters embed all the Bitcoin addresses used by the SPV clients, and are outsourced to more powerful Bitcoin nodes which then only forward to those clients transactions relevant to their outsourced Bloom filters.
\n
\nIn this paper, we explore the privacy of existing SPV clients. We show analytically and empirically that the reliance on Bloom filters within existing SPV clients leaks considerable information about the addresses of Bitcoin users. Our results show that an SPV client who uses a modest number of Bitcoin addresses (e.g., < 20) risks revealing almost all of his addresses. We also show that this information leakage is further exacerbated when users restart their SPV clients and/or when the adversary has access to more than one Bloom filter pertaining to the same SPV client. Motivated by these findings, we propose an efficient countermeasure to enhance the privacy of users which rely on SPV clients; our proposal can be directly integrated within existing SPV client implementations.

Joan Antoni Donet Donet, Cristina Pérez‐Solà, Jordi Herrera‐Joancomartí

No abstract is available for this record.

Karl James O'Dwyer, David Malone

Bitcoin is a digital cryptocurrency that has generated considerable public interest, including both booms in value and busts of exchanges dealing in Bitcoins. One of the fundamental concepts of Bitcoin is that work, called mining, must be done in checking all monetary transactions, which in turn creates Bitcoins as a reward. In this paper we look at the energy consumption of Bitcoin mining. We consider if and when Bitcoin mining has been profitable compared to the energy cost of performing the mining, and conclude that specialist hardware is usually required to make Bitcoin mining profitable. We also show that the power currently used for Bitcoin mining is comparable to Ireland's electricity consumption.

Craig Warmke

Many want to know what bitcoin is and how it works. But bitcoin is as complex as it is controversial, and relatively few have the technical background to understand it. In this paper, I offer an accessible on-ramp for understanding bitcoin in the form of a model. My model reveals both what bitcoin is and how it works. More specifically, it reveals that bitcoin is a fictional substance in a massively coauthored story on a network that automates and distributes jobs normally entrusted to centralized publishing institutions. My model therefore falsifies a popular view according to which each bitcoin is a chunk of code.

Arthur Gervais, Ghassan Karame, Vedran Čapkun, Srđjan Čapkun

Bitcoin has achieved large-scale acceptance and popularity by promising its users a fully
\ndecentralized and low-cost virtual currency system. However, recent incidents and observations
\nare revealing the true limits of decentralization in the Bitcoin system. In this article, we
\nshow that the vital operations and decisions that Bitcoin is currently undertaking are not
\ndecentralized. More specifically, we show that a limited set of entities currently control the
\nservices, decision making, mining, and the incident resolution processes in Bitcoin. We also
\nshow that third-party entities can unilaterally decide to “devalue” any specific set of Bitcoin
\naddresses pertaining to any entity participating in the system. Finally, we explore possible
\navenues to enhance the decentralization in the Bitcoin system.

Jeremy Clark, Aleksander Essex

Abstract. In the standard definition of a commitment scheme, the sender commits to a message and immediately sends the commitment to the recipient interested in it. However the sender may not always know at the time of commitment who will become interested in verifying it. Further, when the interested party does emerge, it could be critical to establish when the commitment was made. Employing a proof of work protocol at commitment time will later allow anyone to “carbon date ” when the commitment was made, approximately, without trusting any external parties. We present CommitCoin, an instantiation of this approach that harnesses the existing processing power of the Bitcoin peer-to-peer network; a network used to mint and trade digital cash. 1 Introductory Remarks Consider the scenario where Alice makes an important discovery. It is important to her that she receives recognition for her breakthrough, however she would also like to keep it a secret until she can establish a suitable infrastructure for monetizing it. By forgoing publication of her discovery, she risks Bob independently making the same discovery and publicizing it as his own. Folklore suggests that Alice might mail herself a copy of her discovery and leave the letter sealed, with the postal service’s timestamp intact, for a later resolution time. If Bob later claims the same discovery, the

Federica Mandreoli, Riccardo Martoglia, Wilma Penzo, Simona Sassatelli · 5 authors

No abstract is available for this record.

Ying Qiao, Shah Asaduzzaman, Gregor von Bochmann

This chapter presents a clustered peer-to-peer system as a resource organization structure for web-service hosting platforms. Where service quality, such as response time and service availability, are provided with assurance. The peer-to-peer organization allows integration of autonomous resources into a single platform in a scalable manner. In clustered peer-to-peer systems, nodes are organized into clusters based on some proximity metric, and a distributed hash table overlay is created among the clusters. This organization enables lightweight techniques for load balancing among different clusters, which is found to be essential for providing response time guarantees. Service availability is provided by replicating a service instance in multiple nodes in a cluster. A decentralized load balancing technique called diffusive load balancing is presented in the context of clustered peer-to-peer systems and evaluated for effectiveness and performance.

Deng Li, Hui Liu, Athanasios V. Vasilakos

The term Autonomic Communication (AC) refers to self-managing systems which are capable of supporting self-configuration, self-healing and self-optimization. However, information reflection and collection, lack of centralized control, non-cooperation and so on are just some of the challenges within AC systems. Since many self-* properties (e.g. selfconfiguration, self-optimization, self-healing, and self-protecting) are achieved by a group of autonomous entities that coordinate in a peer-to-peer (P2P) fashion, it has opened the door to migrating research techniques from P2P systems. P2P’s meaning can be better understood with a set of key characteristics similar to AC: Decentralized organization, Self-organizing nature (i.e. adaptability), Resource sharing and aggregation, and Fault-tolerance. However, not all P2P systems are compatible with AC. Unstructured systems are designed more specifically than structured systems for the heterogeneous Internet environment, where the nodes’ persistence and availability are not guaranteed. Motivated by the challenges in AC and based on comprehensive analysis of popular P2P applications, three correlative standards for evaluating the compatibility of a P2P system with AC are presented in this chapter. According to these standards, a novel Efficient, Scalable and Robust (ESR) P2P overlay is proposed. Differing from current structured and unstructured, or meshed and tree-like P2P overlay, the ESR is a whole new three dimensional structure to improve the efficiency of routing, while information exchanges take in immediate neighbors with local information to make the system scalable and fault-tolerant. Furthermore, rather than a complex game theory or incentive mechanism, asimple but effective punish mechanism has been presented based on a new ID structure which can guarantee the continuity of each node’s record in order to discourage negative behavior on an autonomous environment as AC.

Χρήστος Δουλκερίδης

As data generation becomes increasingly inherently distributed, either due to usergenerated (multimedia) content or because of application-specific needs (sensor networks, data streams, etc.), traditional centralized architectures fail to address the new challenges of contemporary data management.A promising solution for the design and deployment of global-scale applications is the exploitation of the peer-to-peer (P2P) paradigm.P2P has emerged as a powerful model for organizing and searching large data repositories distributed over autonomous independent sources.The main topic and contribution of this thesis is the unsupervised organization of content into Semantic Overlay Networks (SONs), in a decentralized and distributed manner, and subsequently a variety of techniques for efficient searching and query processing in unstructured P2P systems.SONs have been proposed in the relevant research literature, as a way to organize peers into thematic groups, thereby enabling query routing to specific peer groups in a deliberate way, instead of blind forwarding.In particular, this work focuses on unstructured P2P networks that preserve peer autonomy.A novel protocol for unsupervised, distributed and decentralized SON construction is proposed, named DESENT [35,38], which employs distributed clustering of peer contents, respecting the requirements imposed by the distributed nature of the environment [138].Exploiting the generated SONs, we propose efficient routing strategies for answering similarity search queries [37,39].The approach is applied and tested in a distributed IR setting, aiming to address some of the limitations of P2P IR/web search.Towards this goal, a distributed dimensionality reduction algorithm is proposed [96], in order to reduce the high-dimensional feature space and improve clustering quality.Assuming a super-peer architecture we propose an approach called SIMPEER [43] that efficiently supports similarity search over data distributed over a large set of peers.We show how range queries and nearest neighbor queries can be processed.We also explore how to support non-traditional queries (such as top-k [141] and skylines [139]) that involve ranking.Furthermore, by relaxing the restriction of completely unsupervised environment and assuming a semi-supervised context, a novel technique for P2P summary caching of hierarchical information is presented, exploiting either predefined taxonomies [104] or XML schema information [36,40], which is applied in mobile P2P context-aware environments to improve query routing [45,44].6.4 Measurements from using different number of querying peers, given as the fraction of peers in the network. . . . . . . . . . . . . . . . .6.5 Measurements from using different skew (represented by increasing values of a) in the query distributions. . . . . . . . . . . . . . . . . .6.6 Measurements for different network

Zheng Hu

While the pervasiveness of wireless technology has provided a major impetus to mobile services,challenges the mobility of mobile services much.The characteristics of personal environments:heterogeneity,short distance between devices,and group mobility,are analyzed,and a decentralized directory storage method is proposed based on them for the autonomous organization of devices.It provides proper group mobility support and saves bandwidth,so that,improves the stability of system in personal environments.

Gisik Kwon, K. Selçuk Candan

Fundamental challenges in designing environments with media-rich ambient services involves not only the development of appropriate sensing technologies, but as importantly, the implementation of a distributed media processing system which can process, integrate, and leverage the sensed data in real time to provide the various services. In recent years, a great deal of progress has been made in media service workflow processing systems. In most existing solutions, however, the workflow nodes, which operate on the data, are selected out of a centrally assigned candidate pool. These candidate organizations cause either extensive resource provisioning or poor-quality operator mapping between logical workflow nodes and the available physical resources nodes. Consequently, instantiating a media processing workflow to the underlying hardware before the workflow execution begins does not lends itself to adaptive and autonomous operation of the workflow, scalable to resources and demand.In this paper, we propose a novel decentralized multimedia workflow processing system, DANS, in which operators defined in workflows are mapped into (distributed) physical nodes through Distributed Hash Table (DHT)-based overlay substrate in a purely decentralized and adaptive manner. The redundancy in the system, in terms of availability of multiple nodes able to perform the same task, enables the system to scale with demand. Furthermore, physical workflow nodes (operator instances) are able to locate and select the next filter or fusion operator instance autonomously, while ensuring the correct execution of the workflow.

Omar Khadeer Hussain, Elizabeth Chang, Farookh Khadeer Hussain, Tharam S. Dillon

Risk is present in almost every activity. Alternately speaking, almost every activity may have some undesired outcomes which the person doing the activity hopes that they do not occur when it undertakes that particular activity. The quantification of those undesired outcomes can be termed as Risk. Risk is associated with Trust, Security and Privacy. Risk is also associated with transactions, businesses, information systems, environments, networks, partnerships, etc. Generally speaking, Risk signifies the likelihood of financial loss, human casualties, business destruction and environmental damages. It is important to define Risk according to the context of the transaction in order to understand and analyse it better. In the literature Risk has been defined and discussed in areas such as security, health, finance, environment and social life, but there is no systematic study of Risk in decentralized communications, which involves e-business, computer networks and service oriented environments. Hence in this paper, a particular attention is given to define and analyse Risk in the area of Peer-to-Peer business communications, where Risk is every individual and organization?s concern. Also in this paper we develop a risk indicator scale and develop a methodology by which the Riskiness of the peer can be rated according to its behaviour in an interaction. Risk indicator gives an early warning to the party involved and helps avoid disasters.

Xu Wang, Yang Ji, Xiaosheng Tang, Yinong Li · 5 authors

Our objective is to build a distributed terminal system to provide smart, context-aware, rich-experienced applications upon personal environment networking technologies, such as WLAN, IEEE 802.15.3 series, ZigBee, Bluetooth, etc. For the proliferation of smart devices with autonomous applications, the users can get much more service experiences than before. While smart devices facilitate human operation, the coordination of devices through networks may provide applications proactively by gathering much more service context, which indicates the emergence of the pervasive computing age. Hence, we proposed the distributed terminal system for the cooperating of smart devices. In this paper, we analyzed the organization architecture of universal service terminal (UST), the distributed terminal system proposed by us before. In UST project, we have abstracted and encapsulated the capabilities of devices as servers for remote invocation by applications, moreover, the framework functionalities have been introduced for the organization of the distributed system. Though the architecture of UST has been validated feasible in a demonstration, the centralized control mechanisms in the heterogeneous environment are inefficient and unreliable. Thus, we propose an evolved scheme by introducing decentralized mechanisms in this paper. The devices around the user are organized in an overlay peer-to-peer network, and some powerful nodes of them provide the decentralized mechanisms for resource management, service discovery, etc

Georgia Koloniari, Evaggelia Pitoura

No abstract is available for this record.

Wanzong Peng, Tongliang Lu, Wenju Peng, Zhongpan Wang

File sharing, being the foundation of the Internet, has traditionally relied on a centralized service architecture resulting in significant maintenance costs. Moreover, due to the lack of an effective file management system, instances of sensitive information going out of control and loss of confidentiality in file sharing have occurred frequently. In order to address the difficulty of tamper detection and the lack of supervision in the entire process of file transfer in the current Internet environment, this paper designs a blockchain-based system architecture for secure sharing of electronic documents. An efficient blockchain model is used in our framework, and with the help of distributed storage system and asymmetric encryption technology, file sharing can be controlled, reliable and traceable in the transfer process. Referring to existing consensus mechanisms, e.g., Delegated Proof of Stake (DPoS) and Practical Byzantine Fault Tolerance (PBFT), we propose a new consensus for efficient and secure file sharing. Our experimental results show that our framework can maintain a higher throughput than existing schemes.

Khaled Ragab, T. Ono, N. Kaji, K. Mori

The headway towards the outstanding future can be realized with the productive cooperation among peoples and organizations. Inspired from the spirit of cooperation in the rapidly social changing communities, we propose an autonomous decentralized community (ADC) concept. It is a group of autonomous members, whereas each member has his own objectives, complies with the community obligations and cooperates with the others for achieving his own objectives. ADC system has to meet the heterogeneous and continuously changing requirements of the community service utilization and provision. It requires support for real-time communication among community members. Therefore, we propose an autonomous decentralized community communication technique. It satisfies the fairness by granted an equal opportunity among the community members. Moreover, it approves the scalability of the system regardless with the number of the community members.

Yili Gong, Fangpeng Dong, Wei Li, Zhiwei Xu

Grids enable users to share and access large collections and various types of resources in wide areas, and how to locate resources in such dynamic, heterogeneous and autonomous distributed environments is a key and challenging issue. In this paper, a three-level decentralized and dynamic VEGA Infrastructure for Resource Discovery (VIRD) is proposed. In this architecture, every Border Grid Resource Name Server (BGRNS) or Grid Resource Name Server (GRNS)has its own local policies, governing information organization, management and searching. Changes in resource information are propagated dynamically among GRNS servers according to a link-statelike algorithm. A client can query its designated GRNS either recursively or iteratively. Optimizing techniques, such as shortcut, are adopted to make the dynamic framework more flexible and efficient. A simulator called SimVIRD is developed to verify the proposed architecture and algorithms.Experiment results indicate that this architecture could deliver good scalability and performance for grid resource discovery.