O Bitcoin e um sistema de pagamento totalmente digital independente de uma entidade centralizadora como bancos ou governos. O projeto foi criado e publicado em 2008 atraves da Internet. Entretanto apenas em 2009 a rede tornou-se operacional. O Bitcoin e um protocolo de codigo aberto e uma rede ponto a ponto de participantes que e responsavel pelo funcionamento do sistema. Seguranca criptografica, ausencia de taxas e de custos de instalacao sao fatores que convenceram varias empresas do mundo a adota-lo como alternativa de pagamento. Apesar dos trabalhos acerca da moeda digital, pouco ainda se sabe sobre sua topologia e caracteristicas, principalmente pela otica de ciencia de redes. Nesse sentido, o presente trabalho apresenta o estudo da dinamicidade de suas principais variaveis no seu funcionamento diario. No decorrer do trabalho sao apresentadas duas formas de extracao de dados da rede Bitcoin para futuras analises.
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.
Steve Huckle, Rituparna Bhattacharya, Martin White, Natalia Beloff
This paper explores how the Internet of Things and blockchain technology can benefit shared economy applications. The focus of this research is understanding how blockchain can be exploited to create decentralised, shared economy applications that allow people to monetise, securely, their things to create more wealth. Shared economy applications such as Airbnb and Uber are well-known applications, but there are many other opportunities to share in the digital economy. With the recent interest in the Internet of Things and blockchain, the opportunity exists to create a myriad of sharing applications, e.g. peer-to-peer automatic payment mechanisms, foreign exchange platforms, digital rights management and cultural heritage to name but a few. While many types of shared economy scenarios are proliferating, few of them, so far, leverage the Internet of Things and blockchain as technologies to build distributed applications. This paper discusses how we might make use of the Internet of Things and blockchains to create secure shared economy distributed applications. Presented are examples of such distributed applications in the context of an Internet of Things architecture using blockchain technology.
Ittay Eyal, Adem Efe Gencer, Emin Gün Sirer, Robbert van Renesse
Cryptocurrencies, based on and led by Bitcoin, have shown promise as infrastructure for pseudonymous online payments, cheap remittance, trustless digital asset exchange, and smart contracts. However, Bitcoin-derived blockchain protocols have inherent scalability limits that trade-off between throughput and latency and withhold the realization of this potential. This paper presents Bitcoin-NG, a new blockchain protocol designed to scale. Based on Bitcoin's blockchain protocol, Bitcoin-NG is Byzantine fault tolerant, is robust to extreme churn, and shares the same trust model obviating qualitative changes to the ecosystem. In addition to Bitcoin-NG, we introduce several novel metrics of interest in quantifying the security and efficiency of Bitcoin-like blockchain protocols. We implement Bitcoin-NG and perform large-scale experiments at 15% the size of the operational Bitcoin system, using unchanged clients of both protocols. These experiments demonstrate that Bitcoin-NG scales optimally, with bandwidth limited only by the capacity of the individual nodes and latency limited only by the propagation time of the network.
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.
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.
Despite a high volatility and the recent fall in price, more and more merchants and consumers adopt Bitcoin. The virtual currency might be standing at its critical point to reach the early majority of adopters. This paper examines whether an application called ChangeTip has the potential to catalyze the breakthrough of Bitcoin. We assume a strong linkage between the diffusion of ChangeTip and Bitcoin so that we can directly deduce the impact of this application on Bitcoin. Results from a conducted online survey of 210 potential early adopters indicate that the diffusion of ChangeTip has the potential to advance the diffusion of Bitcoin to mainstream markets. We found that performance expectancy is the key driver for the intention to recommend ChangeTip. Also, effort expectancy, social influence and facilitating conditions are important factors for recommending ChangeTip. Concerning the intention to use ChangeTip in the future, performance expectancy and social influence are the main drivers. Furthermore, facilitating conditions are important for using ChangeTip. In addition, an analysis of the non-user of Bitcoin and ChangeTip was conducted. Theoretical and practical implications of these results are discussed.
Bitcoin is widely represented in the popular press, but far less so in serious academic inquiry. Researchers have analyzed Bitcoin from various discipline-specific perspectives using their own sets of theories and jargon. Yet cross-disciplinary research has been muddled by the inaccurate interpretation of terminology across fields of research. This results in polarized assessments. In an effort to examine the Bitcoin phenomenon in a more holistic and multidisciplinary manner, this paper compares Bitcoin with another innovative technology – the World Wide Web – as first envisioned by Tim Berners-Lee. By exploring the early development of the World Wide Web, we seek to compare and contrast its development with that of Bitcoin and blockchain technology. The goal of this study is to show similarities and differences in their historic development, in order to identify key success factors related to the adoption of these technologies. Through identification of these factors we seek to guide both academics and practitioners towards fruitful avenues of research and development.
Digital currencies represent a new method for exchange and investment that differs strongly from any other fiat money seen throughout history. A digital currency makes it possible to perform all financial transactions without the intervention of a third party to act as an arbiter of verification; payments can be made between two people with degrees of anonymity, across continents, at any denomination, and without any transaction fees going to a central authority. The most successful example of this is Bitcoin, introduced in 2008, which has experienced a recent boom of popularity, media attention, and investment. With this surge of attention, we became interested in finding out how people both inside and outside the Bitcoin community perceive Bitcoin -- what do they think of it, how do they feel, and how knowledgeable they are. Towards this end, we conducted the first interview study (N = 20) with participants to discuss Bitcoin and other related financial topics. Some of our major findings include: not understanding how Bitcoin works is not a barrier for entry, although non-user participants claim it would be for them and that user participants are in a state of cognitive dissonance concerning the role of governments in the system. Our findings, overall, contribute to knowledge concerning Bitcoin and attitudes towards digital currencies in general.
PGP is built upon a Distributed Web of Trust in which the trustworthiness of a user is established by others who can vouch through a digital signature for that particular identity. Preventing its wholesale adoption are a number of inherent weaknesses to include (but not limited to) the following: 1) Trust Relationships are built on a subjective honor system, 2) Only first degree relationships can be fully trusted, 3) Levels of trust are difficult to quantify with actual values, and 4) Issues with the Web of Trust itself (Certification and Endorsement). Although the security that PGP provides is proven to be reliable, it has largely failed to garner large scale adoption. In this paper, we propose several novel contributions to address the aforementioned issues with PGP and associated Web of Trust. To address the subjectivity of the Web of Trust, we provide a new certificate format based on Bitcoin which allows a user to verify a PGP certificate using Bitcoin identity-verification transactions - forming first degree trust relationships that are tied to actual values (i.e., number of Bitcoins transferred during transaction). Secondly, we present the design of a novel Distributed PGP key server that leverages the Bitcoin transaction blockchain to store and retrieve Bitcoin-Based PGP certificates. Lastly, we provide a web prototype application that demonstrates several of these capabilities in an actual environment.
Bitcoin is a decentralized P2P digital currency in which coins are generated by a distributed set of miners and transaction are broadcasted via a peer-to-peer network. While Bitcoin provides some level of anonymity (or rather pseudonymity) by encouraging the users to have any number of random-looking Bitcoin addresses, recent research shows that this level of anonymity is rather low. This encourages users to connect to the Bitcoin network through anonymizers like Tor and motivates development of default Tor functionality for popular mobile SPV clients. In this paper we show that combining Tor and Bitcoin creates an attack vector for the deterministic and stealthy man-in-the-middle attacks. A low-resource attacker can gain full control of information flows between all users who chose to use Bitcoin over Tor. In particular the attacker can link together user's transactions regardless of pseudonyms used, control which Bitcoin blocks and transactions are relayed to the user and can \ delay or discard user's transactions and blocks. In collusion with a powerful miner double-spending attacks become possible and a totally virtual Bitcoin reality can be created for such set of users. Moreover, we show how an attacker can fingerprint users and then recognize them and learn their IP address when they decide to connect to the Bitcoin network directly.
Saramago, Rodrigo Q., Meling, Hein, Jehl, Leander N.
A certification system is responsible for issuing digital credentials, which attest claims about a subject, e.g., an academic diploma. Such credentials are valuable for individuals and society, and widespread adoption requires a trusted certification system. Trust can be gained by being transparent when issuing and verifying digital credentials. However, there is a fundamental tradeoff between privacy and transparency. For instance, admitting a student to an academic program must preserve the student’s privacy, i.e., the student’s grades must not be revealed to unauthorized parties. At the same time, other applicants may demand transparency to ensure fairness in the admission process. Thus, building a certification system with the right balance between privacy and transparency is challenging. This paper proposes a novel design for a certification system that provides sufficient transparency and preserves privacy through selective disclosure of claims such that authorized parties can verify them. Moreover, unauthorized parties can also verify the correctness of the certification process without compromising privacy. We achieve this using an incremental Merkle tree of cryptographic commitments to users' credentials. The commitments are added to the tree based on verifying zero-knowledge issuance proofs. Users store credentials off-chain and can prove the ownership and authenticity of credentials without revealing their commitments. Further, our approach enables users to prove statements about the credential’s claims in zero-knowledge. Our design offers a cost-efficient solution, reducing the amount of linkable on-chain data by up to 79% per credential compared to prior work, while maintaining transparency.
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.
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.
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
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.
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.