On March 16, 2013, Cyprus announced that it would accept a bailout that required imposing a one-time levy on bank deposits. It has been argued that, by making traditional deposit accounts seem less secure, the bailout announcement prompted some to consider â or reconsider â using the cryptocurrency bitcoin. Relying on rank data for a subset of apps, existing studies maintain that interest in bitcoin increased following the announcement, especially in countries with troubled banks. We argue that (1) focusing on a subset of apps does not allow one to distinguish a general increase in the demand for bitcoin apps from a substitution between bitcoin apps and (2) changes in rank data are a poor predictor of changes in the number of downloads. In order to address these concerns, we collect rank data for all fifteen bitcoin apps available at the time and use an established technique to estimate an index of downloads for each country considered. We find that, while downloads of bitcoin apps increased following the announcement, the observed effect was not especially pronounced in countries thought to have had troubled banking systems at the time.
Arthur Gervais, Hubert Ritzdorf, Ghassan Karame, SrÄjan Äapkun
Given the increasing adoption of Bitcoin, the number of transactions and the block sizes within the system are only expected to increase. To sustain its correct operation in spite of its ever-increasing use, Bitcoin implements a number of necessary optimizations and scalability measures. These measures limit the amount of information broadcast in the system to the minimum necessary. In this paper, we show that current scalability measures adopted by Bitcoin come at odds with the security of the system. More specifically, we show that an adversary can exploit these measures in order to effectively delay the propagation of transactions and blocks to specific nodes for a considerable amount of time---without causing a network partitioning in the system. Notice that this attack alters the information received by Bitcoin nodes, and modifies their views of the ledger state. Namely, we show that this allows the adversary to considerably increase its mining advantage in the network, and to double-spend transactions in spite of the current countermeasures adopted by Bitcoin. Based on our results, we propose a number of countermeasures in order to enhance the security of Bitcoin without deteriorating its scalability.
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Blockchain Technology Applications and Security
Advanced Steganography and Watermarking Techniques
Feroz Ahmad Ahmad, Prashant Kumar, Gulshan Shrivastava, Med Salim Bouhlel
ON 12 JANUARY 2009 a pseudonymous entity signed a transaction that instructed a distributed network to transfer a small amount of digital currency to Hal Finney, one ofthe key figures of the cypherpunk movement. After a few minutes, the transaction was recorded on a distributed public ledger, permanently updating the balance ofbothparties. This transactionâ the first Bitcoin transactionâmarked the beginning of a new era of decentralized payment systems, ushering in a variety of financial Services that do not depend on any centralized clearinghouse or other financial middleman. Bitcoin is regarded by many as a powerful technological innovation that could disrupt many sectors, in the realm of finance and beyond. But the underlying technology on which the network operates, the Bitcoin blockchain can do much more than that. Just as the internet did in the early-1990s, blockchain technology carries with it a whole new range of promises concerning how decentralization can support and promote individual freedoms and autonomy. Blockchain proponents believe that Bitcoin and other cryptocurrency platforms will revolutionize mechanisms of value exchange in the same way that the internet transformed information sharing, by providing a platform for people to exchange digital resources, in a secure and decentralized manner without the need to rely on any intermediary or trusted authority. But this revolutionary potential also carries with it serious implications for censorship, intellectual property, and the regulated flow of information. A blockchain is a decentralized database of transactions maintained by a distributed network of computers, which all contribute to the verification and the validation of transactions. Once accepted, these transactions are recorded inside a âblockâ of transactions, which incorporates a reference to previous blocks. This creates a long chain of blocksâa âblockchainââthat stores the history of all transactions in a chronological order. Every block contains information about a particular set of transactions, a reference to the preceding block in the blockchain, and the answer to a complex mathematical puzzle that is used to validate the data associated with that block. A copy of the blockchain is stored on every computer in the network, making it virtually impossible for anyone unilaterally to modify the data stored on this decentralized database: if anyone tries to modify any transaction the fraud will be immediately detected by all other network participants.
Open access
42 source records
Blockchain Technology Applications and Security
Advanced Steganography and Watermarking Techniques
Bitcoin is the first and most popular decentralized cryptocurrency to date. In this work, we extract and analyze the core of the Bitcoin protocol, which we term the Bitcoin backbone , and prove three of its fundamental properties which we call Common Prefix , Chain Quality, and Chain Growth in the static setting where the number of players remains fixed. Our proofs hinge on appropriate and novel assumptions on the âhashing powerâ of the protocol participants and their interplay with the protocol parameters and the time needed for reliable message passing between honest parties in terms of computational steps. A takeaway from our analysis is that, all else being equal, the protocolâs provable tolerance in terms of the number of adversarial parties (or, equivalently, their âhashing powerâ in our model) decreases as the duration of a message passing round increases. Next, we propose and analyze applications that can be built âon topâ of the backbone protocol, specifically focusing on Byzantine agreement (BA) and on the notion of a public transaction ledger. Regarding BA, we observe that a proposal due to Nakamoto falls short of solving it, and present a simple alternative which works assuming that the adversaryâs hashing power is bounded by 1/3. The public transaction ledger captures the essence of Bitcoinâs operation as a cryptocurrency, in the sense that it guarantees the liveness and persistence of committed transactions. Based on this notion, we describe and analyze the Bitcoin system as well as a more elaborate BA protocol and we prove them secure assuming the adversaryâs hashing power is strictly less than 1/2. Instrumental to this latter result is a technique we call 2-for-1 proof-of-work (PoW) that has proven to be useful in the design of other PoW-based protocols.
La versione italiana di questo documento è disponibile al seguente link: http://ssrn.com/abstract=2731132 The core technology of Bitcoin, the blockchain, has recently emerged as a disruptive innovation with a wide range of applications, potentially able to redesign our interactions in business, politics and society at large. Although scholarly interest in this subject is growing, a comprehensive analysis of blockchain applications from a political perspective is severely lacking to date. This paper aims to fill this gap and it discusses the key points of blockchain-based decentralized governance, which challenges to varying degrees the traditional mechanisms of State authority, citizenship and democracy. In particular, the paper verifies to which extent blockchain and decentralized platforms can be considered as hyper-political tools, capable to manage social interactions on large scale and dismiss traditional central authorities. The analysis highlights risks related to a dominant position of private powers in distributed ecosystems, which may lead to a general disempowerment of citizens and to the emergence of a stateless global society. While technological utopians urge the demise of any centralized institution, this paper advocates the role of the State as a necessary central point of coordination in society, showing that decentralization through algorithm-based consensus is an organizational theory, not a stand-alone political theory.
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.
Magnus Skjegstad, Anil Madhavapeddy, Jon Crowcroft
Devices connected to the Internet today have a wide range of local communication channels available, such as wireless Wifi, Bluetooth or NFC, as well as wired backhaul. In densely populated areas it is possible to create heterogeneous, multihop communication paths using a combination of these technologies, and often transmit data with lower latency than via a wired Internet connection. However, the potential for sharing meshed wireless radios in this way has never been realised due to the lack of economic incentives to do so on the part of individual nodes. In this paper, we explore how virtual currencies such as Bitcoin might be used to provide an end-to-end incentive scheme to convince forwarding nodes that it is profitable to send packets on via the lowest latency mechanism available. Clients inject a small amount of money to transmit a datagram, and forwarding engines compete to solve a time-locked puzzle that can be claimed by the node that delivers the result in the lowest latency. This approach naturally extends congestion control techniques to a surge pricing model when available bandwidth is low. We conclude by discussing several latency-sensitive applications that would benefit for this, such as video streaming and local augmented reality systems.
Perkembangan teknologi informasi dan didukung pula dengan teknologi komputer yang semakin canggih serta adanya jaringan internet yang menciptakan terkoneksinya perangkat-perangkat komputer baik berbentuk personal komputer maupun super komputer sehingga terciptanya aktivitas bisnis dengan teknologi jaringan internet atau disebut electronic commerce (e-commerce). Maka dari sinilah lahir pula mata uang virtual dunia maya (virtual currency) dengan konsep nilai berdasarkan supply dan demand serta mudah, praktis dan efisien dalam melakukan transaksi perdagangan maupun bisnis lainnya. Namun dampak terbesar dalam transaksi online seperti ini diantaranya adalah penipuan, pencurian dan kerugian yang akan dialami pengguna secara tidak wajar. \nBerangkat dari masalah di atas ada beberapa permasalahan yang dirumuskan untuk mengetahui analisis jual-beli bitcoin di dunia maya yaitu meliputi bagaimana analisis undang-undang tentang mata uang terhadap alat tukar bitcoin dan prespektif hukum Islam terhadap jual-beli bitcoin di dunia maya. Penyusun memilih tempat penelitian tersebut di website bitcoin exchanger (www.vip.bitcoin.co.id.) \nDalam menelusuri, menjelaskan dan menyimpulkan objek pembahasan pada skripsi ini. Penyusun menempuh metode jenis penelitian lapangan di dunia maya dengan menggunakan metode observasi partisipasif lengkap dimana peneliti menjadi bagian dalam aktivitas pada sumber data yang diteliti. Untuk mendapatkan informasi secara akurat, aktual dan terpercaya. Penyusun melakukan beberapa metode pengumpulan data yakni menggunakan metode wawancara, observasi dan dokumentasi yang selanjutnya dianalisis menggunakan metode deskriptif kualitatif. \nDari hasil penelitian ini dapat disimpulkan yakni analisis Undang-Undang No 7 Tahun 2011 Tentang Mata uang, bahwa bitcoin yang dijadikan alat tukar dalam pembayaran di Negara Indonesia ini termasuk melanggar undang-undang karena undang-undang sudah mengatur mengenai alat pembayaran yang sah di Indonesia. Penggunaan bitcoin tidak dijadikan sebagai alat tukar atau hanya sebagai komoditas ini tidak dipermasalahkan secara yuridis karena tidak ada peraturan yang mengatur maupun melarang dari OJK atau Bank Indonesia terhadap bitcoin. Akan tetapi terkait resiko seperti kehilangan dan kerugian itu ditanggung sendiri oleh penggunanya sebagaimana siaran pers âPernyataan Bank Indonesia Terkait Bitcoin dan Virtual Currency Lainnyaâ No: 16/ 6 /DKom. Dalam prespektif hukum Islam bitcoin yang dijadikan sebagai alat tukar maupun alat investasi diharamkan. Sebab praktek yang terjadi terdapat unsur gharar dan maisir, serta menghindari kemadharatan yang dapat terjadi pada pengguna.
A main focus in economics research is understanding the time series of prices of goods and assets. While statistical models using only the properties of the time series itself have been successful in many aspects, we expect to gain a better understanding of the phenomena involved if we can model the underlying system of interacting agents. In this article, we consider the history of Bitcoin, a novel digital currency system, for which the complete list of transactions is available for analysis. Using this dataset, we reconstruct the transaction network between users and analyze changes in the structure of the subgraph induced by the most active users. Our approach is based on the unsupervised identification of important features of the time variation of the network. Applying the widely used method of Principal Component Analysis to the matrix constructed from snapshots of the network at different times, we are able to show how structural changes in the network accompany significant changes in the exchange price of bitcoins.
Chain Of A Lifetime: How Blockchain Technology Might Transform Personal Insurance is the outcome of a research project conducted between August and December 2014 which explored how blockchain technology might transform personal insurance and in particular interactions among individuals and insurance companies over time.
Blockchain technology's main innovation is an electronic public transaction record of integrity without central authority. Beside cryptocurrencies and distributed payment systems, blockchain applications could include areas of finance where a central, trusted third party has traditionally been used, trade reporting, depository receipts, escrow accounts or trade finance. Blockchains can contain set of documents, record assets and help to manage interconnected devices. Emerging applications, such as smart contracts and decentralised autonomous organisations, might in future also permit blockchains to act as automated agents.
The report concludes that blockchain technology could transform the way people manage identities and personal information; blur even further the divide between global and local; influence consumer perception of time; drive honesty and transparency; and, influence consumer perceptions of risk that could change the way insurers support mutualisation. The report highlights how, at the time of writing, most insurance companies do not yet seem ready to experiment with blockchain technology. They find it difficult enough to understand Bitcoin or cryptocurrencies. Non-insurers are more likely to be the first to create insurance or insurance-related applications. Blockchain applications in insurance are likely to start with digital identity systems and management of personal data.
De executeur in een nalatenschap met bitcoins en andere âdigitale bezittingenâ In deze bijdrage gaat de auteur op zoek naar wat de verplichtingen zijn die de executeur heeft ten aanzien van de onlinenalatenschap. Moet een executeur actief op zoek naar bitcoins en andere digitale bezittingen? Hoever gaat zijn onderzoeksplicht in een onlinenalatenschap? Ook gaat de auteur kort in op de erfbelasting en digitale bezittingen: de executeur moet ook hier aangifte van doen.
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. With two pools, or any number of identical pools, there exists an equilibrium that constitutes a tragedy of the commons where the pools attack one another and all 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.
Marc Solanas, Julio Hernandez-Castro, Debojyoti Dutta
More users and companies make use of cloud services every day. They all expect a perfect performance and any issue to remain transparent to them. This last statement is very challenging to perform. A user's activities in our cloud can affect the overall performance of our servers, having an impact on other resources. We can consider these kind of activities as fraudulent. They can be either illegal activities, such as launching a DDoS attack or just activities which are undesired by the cloud provider, such as Bitcoin mining, which uses substantial power, reduces the life of the hardware and can possibly slow down other user's activities. This article discusses a method to detect such activities by using non-intrusive, privacy-friendly data: billing data. We use OpenStack as an example with data provided by Telemetry, the component in charge of measuring resource usage for billing purposes. Results will be shown proving the efficiency of this method and ways to improve it will be provided as well as its advantages and disadvantages.
Enas Al Kawasmi, Edin ArnautoviÄ, Davor SvetinoviÄ
ABSTRACT This paper presents a systemâofâsystems architecture model for a Decentralized Carbon Emissions Trading Infrastructure (DâCETI) with focus on privacy and system security goals. The structure and behavior are implemented as a solution to the problem of trading carbon emissions anonymously among the trading agents. Privacy and security of the trading agents and their carbon credits are the main requirements behind the architecture of DâCETI. The decentralized structure of multiple systems and distributed behavior are the two main features of DâCETI that distinguish it from the traditional carbon trading schemes and protocols. DâCETI is based on Bitcoin, a peerâtoâpeer digital currency with no central authority, and Open Transactions, a system that simplifies the use of cryptography in financial transactions. The architecture of DâCETI is evaluated and compared with the architecture of five other carbon emissions trading platforms.
We show that the behaviour of Bitcoin has interesting similarities to stock\nand precious metal markets, such as gold and silver. We report that whilst\nLitecoin, the second largest cryptocurrency, closely follows Bitcoin's\nbehaviour, it does not show all the reported properties of Bitcoin. Agreements\nbetween apparently disparate complexity measures have been found, and it is\nshown that statistical, information-theoretic, algorithmic and fractal measures\nhave different but interesting capabilities of clustering families of markets\nby type. The report is particularly interesting because of the range and novel\nuse of some measures of complexity to characterize price behaviour, because of\nthe IRS designation of Bitcoin as an investment property and not a currency,\nand the announcement of the Canadian government's own electronic currency\nMintChip.\n
This paper explores the recent development of digital currenciesâcurrencies which are creatures of the Internet, self-authenticating, and usable worldwide by members of the general public to engage in the same types of direct, one-to-one transactions that daily occur using government-issued currencies. At present, the most developed digital currency measured by market capitalization is Bitcoin, which will be used as a proxy for the general phenomenon. Not surprisingly, as Bitcoinâs circulation and visibility has increased, so have the number of practical and legal issues surrounding its use. Some of these will be explored in this paper, with a view to considering the utility and viability of such currencies for widespread, global use.
Jelle van den Hooff, M. Frans Kaashoek, Nickolai Zeldovich
VerSum allows lightweight clients to outsource expensive computations over large and frequently changing data structures, such as the Bitcoin or Namecoin blockchains, or a Certificate Transparency log. VerSum clients ensure that the output is correct by comparing the outputs from multiple servers. VerSum assumes that at least one server is honest, and crucially, when servers disagree, VerSum uses an efficient conflict resolution protocol to determine which server(s) made a mistake and thus obtain the correct output.
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.
Bitcoin, a virtual currency created in 2009, has resulted in the unlikely pairing of the underworld criminals with the Harvard educated Winklevoss brothers. The online currency can be obtained by âminingâ through solving complex equations, and can be bought and sold on Bitcoin Exchanges. It is primarily utilized for investment in Bitcoin financial products as well as speculating on the value of the currency. It is also used as a method of payment for legal and illegal goods and services. This comment addresses the regulatory issues Bitcoin faces, namely the regulation and taxation of financial products. After providing a fundamental definition of Bitcoin and how it operates, this Comment explores issues stemming from anonymity, price volatility, and use in criminal activity. It then provides an analysis of classifying and regulating Bitcoin as currency and examines how FinCEN and Treasury Regulations issued by the IRS will reduce criminal activity stemming from anonymity. Next, it discusses how SEC and CFTC regulations could stabilize Bitcoinâs volatile market value, and explains why the IRS was incorrect to classify Bitcoin as property. It concludes by addressing the policy implications of classifying Bitcoin as currency under various regulatory laws.