Irni Eliana Khairuddin, Corina Sas, Sarah Clinch, Nigel Davies
This paper presents an exploratory study focusing on user experience with Bitcoin technology. We describe interviews with 9 Bitcoin users and report findings related to users' motivations for buying and using bitcoins. Our initial findings capture three main motivations such as Bitcoin's predicted role in a monetary revolution, users' increased empowerment, and their perception of a real value of Bitcoin currency. We conclude with reflections on the value of these findings for HCI researchers.
In January 3, 2009, Satoshi Nakamoto gave rise to the "Bitcoin Block Chain" creating the first block of the chain hashing on his computers central processing unit (CPU). Since then, the hash calculations to mine Bitcoin have been getting more and more complex, and consequently the mining hardware evolved to adapt to this increasing difficulty. Three generations of mining hardware have followed the CPU's generation. They are GPU's, FPGA's and ASIC's generations. This work presents an agent based artificial market model of the Bitcoin mining process and of the Bitcoin transactions. The goal of this work is to model the economy of the mining process, starting from GPU's generation, the first with economic significance. The model reproduces some "stylized facts" found in real time price series and some core aspects of the mining business. In particular, the computational experiments performed are able to reproduce the unit root property, the fat tail phenomenon and the volatility clustering of Bitcoin price series. In addition, under proper assumptions, they are able to reproduce the price peak at the end of November 2013, its next fall in April 2014, the generation of Bitcoins, the hashing capability, the power consumption, and the mining hardware and electrical energy expenses of the Bitcoin network.
Bitcoin was recently introduced as a peer-to-peer electronic currency in order to facilitate transactions outside the traditional financial system. The core of Bitcoin, the Blockchain, is the history of the transactions in the system maintained by all nodes as a distributed shared register. New blocks in the Blockchain contain the last transactions in the system and are added by nodes (miners) after a block mining process that consists in solving a resource consuming proof-of-work (cryptographic puzzle). The reward is a motivation for mining process but also could be an incentive for attacks such as selfish mining. In this paper we propose a solution for one of the major problems in Bitcoin : selfish mining or block withholding attack. This attack is conducted by adversarial or selfish nodes in order to either earn undue rewards or waste the computational power of honest nodes. Contrary to recent solutions, our solution, ZeroBlock, prevents block withholding using a technique free of forgeable timestamps. Moreover, we show that our solution is also compliant with nodes churn.
Cryptocurrencies that are based on Proof-of-Work (PoW) often rely on special purpose hardware to perform so-called mining operations that secure the system, with miners receiving freshly minted tokens as a reward for their work. A notable example of such a cryptocurrency is Bitcoin, which is primarily mined using application specific integrated circuit (ASIC) based machines. Due to the supposed profitability of cryptocurrency mining, such hardware has been in great demand in recent years, in-spite of high associated costs like electricity. In this work, we show that because mining rewards are given in the mined cryptocurrency, while expenses are usually paid in some fiat currency such as the United States Dollar (USD), cryptocurrency mining is in fact a bundle of financial options. When exercised, each option converts electricity to tokens. We provide a method of pricing mining hardware based on this insight, and prove that any other price creates arbitrage. Our method shows that contrary to the popular belief that mining hardware is worth less if the cryptocurrency is highly volatile, the opposite effect is true: volatility increases value. Thus, if a coin's volatility decreases, some miners may leave, affecting security. We compare the prices produced by our method to prices obtained from popular tools currently used by miners and show that the latter only consider the expected returns from mining, while neglecting to account for the inherent risk in mining, which is due to the high exchange-rate volatility of cryptocurrencies. Finally, we show that the returns made from mining can be imitated by trading in bonds and coins, and create such imitating investment portfolios. Historically, realized revenues of these portfolios have outperformed mining, showing that indeed hardware is mispriced.
Bitcoin is a rising digital currency and exemplifies the grow- ing need for systematically gathering and analyzing pub- lic transaction data sets such as the blockchain. However, the blockchain in its raw form is just a large ledger listing transfers of currency units between alphanumeric character strings, without revealing contextually relevant real-world information. In this demo, we present GraphSense, which is a solution that applies a graph-centric perspective on digital currency transactions. It allows users to explore transactions and follow the money ow, facilitates analytics by semantically enriching the transaction graph, supports path and graph pattern search, and guides analysts to anomalous data points. To deal with the growing volume and velocity of transaction data, we implemented our solution on a horizontally scalable data processing and analytics infrastructure. Given the ongoing digital transformation in financial services and technologies, we believe that our approach contributes to development of analytics solutions for digital currency ecosystems, which is relevant in fields such as financial analytics, law enforcement, or scientific research
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
Bit coin, as the foundation for a secure electronic payment system, has drawn broad interests from researchers in recent years. In this paper, we analyze a comprehensive Bit coin transaction dataset and investigate the interrelationship between the flow of Bit coin transactions and its price movement. Using network theory, we examine a few complexity measures of the Bit coin transaction flow networks, and we model the joint dynamic relationship between these complexity measures and Bit coin market variables such as return and volatility. We find that a particular complexity measure of the Bit coin transaction network flow is significantly correlated with the Bit coin market return and volatility. More specifically we document that the residual diversity or freedom of Bit coin network flow scaled by the total system throughput can significantly improve the predictability of Bit coin market return and volatility.
Christian Decker, Jochen Seidel, Roger Wattenhofer
The Bitcoin system only provides eventual consistency. For everyday life, the time to confirm a Bitcoin transaction is prohibitively slow. In this paper we propose a new system, built on the Bitcoin blockchain, which enables strong consistency. Our system, PeerCensus, acts as a certification authority, manages peer identities in a peer-to-peer network, and ultimately enhances Bitcoin and similar systems with strong consistency. Our extensive analysis shows that PeerCensus is in a secure state with high probability. We also show how Discoin, a Bitcoin variant that decouples block creation and transaction confirmation, can be built on top of PeerCensus, enabling real-time payments. Unlike Bitcoin, once transactions in Discoin are committed, they stay committed.
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.
Andrew Miller, Ari Juels, Elaine Shi, Bryan Parno · 5 authors
Bit coin is widely regarded as the first broadly successful e-cash system. An oft-cited concern, though, is that mining Bit coins wastes computational resources. Indeed, Bit coin's underlying mining mechanism, which we call a scratch-off puzzle (SOP), involves continuously attempting to solve computational puzzles that have no intrinsic utility. We propose a modification to Bit coin that repurposes its mining resources to achieve a more broadly useful goal: distributed storage of archival data. We call our new scheme Perm coin. Unlike Bit coin and its proposed alternatives, Perm coin requires clients to invest not just computational resources, but also storage. Our scheme involves an alternative scratch-off puzzle for Bit coin based on Proofs-of-Retrievability (PORs). Successfully minting money with this SOP requires local, random access to a copy of a file. Given the competition among mining clients in Bit coin, this modified SOP gives rise to highly decentralized file storage, thus reducing the overall waste of Bit coin. Using a model of rational economic agents we show that our modified SOP preserves the essential properties of the original Bit coin puzzle. We also provide parameterizations and calculations based on realistic hardware constraints to demonstrate the practicality of Perm coin as a whole.
Bitcoin has become increasingly important in recent years. The exchange rate raised from $14 in January 2013 up to $240 in April 2013 and even $900 in early 2014. In this paper, we present novel insights about Bitcoin's peer-to-peer (P2P) network with a special focus on its distribution among distinct autonomous systems. We traversed Bitcoin's P2P network in a protocol-compliant manner and collected information about the network size, the number of clients, and the network distribution among autonomous systems. Our findings lead to conclusions about the resilience of the Bitcoin ecosystem, the unambiguousness of the blockchain in use, and the propagation and verification of transaction blocks.
Bitcoin is a digital currency which is based on P2P network and open source software. It is avirtual currency without any control by any centralized organization. New Bitcoins are issuedby lots of specified algorithms. The whole Bitcoin network utilizes the distributed database toverify and record all the transactions through the nodes in the P2P network in which thedouble spending is prevented. No person or organization is able to control Bitcoin based on adecentralized P2P network and algorithm. The cryptographic functions of Bitcoin are designedto allow only the real Bitcoin owner to pay and transfer, and ensure the anonymity andmarketability.The purpose of this thesis is to analyze the security architecture and services for the Bitcoin system and describe of all the features and infrastructures of the whole Bitcoin network. A whole establishment demo including wallet client, mining server with GUI and mining client is implemented. Further improvement will be suggested and recommended for the system