This paper investigates the semiotics of Bitcoin, an electronic cash system that uses decentralized networking to enable irreversible payments. For enthusiasts, Bitcoin provides an alternative to currencies and payment systems that are seen to threaten users' privacy, limit personal liberty, and undermine the value of money through state and corporate oversight. Bitcoin's promise lies in its apparent capacity to resolve these concerns not through regulatory institutions or interpersonal trust, but through its cryptographic protocols. We characterize this semiotics as a âpractical materialismâ and suggest it replays debates about privacy, labor, and value.
Bid validity proof and verification is an efficiency bottleneck and privacy drawback in homomorphic eâauction. The existing bid validity proof technique is inefficient and only achieves honestâverifier zero knowledge (ZK). In this study, an efficient proof and verification technique is proposed to guarantee bid validity in homomorphic eâauction. The new proof technique is mainly based on hash function operations and only needs a very small number of costly public key cryptographic operations. Moreover, it can handle untrusted verifiers and achieve perfect ZK. As a result, efficiency and privacy of homomorphic eâauction applications are significantly improved. To the best of authorsâ knowledge, it proof technique is the first to handle untrusted verifiers in eâauction applications.
Bitcoin (BTC), the much in-the-news and up-for-government-discussion cryptocurrency favored by Deep Web drug markets, libertarians, anarchists and would-be assassins everywhere, has been on a tear recently, and as of yesterday has hit an all-time high (albeit briefly) of more than USD $900 mark. Itâs not hard to findâin fact itâs difficult to avoidâcyberlibertarians of all...
The main objective of this diploma thesis is to introduce the history and origin of digital currency Bitcoin and how this project works specifically from the perspective of IT. The thesis contains detailed instructions for the process of implementation Bitcoin payments to the company. This diploma thesis describes the possibilities of abuse and security. Further compares advantages and disadvantages with the classical exchange resources. How is it possible to get this currency, use and how it developed its rate against other world currencies. The thesis also mentions similar cryptocurrencies.
A virtual currency can be defined as a type of unregulated, digital money, which is issued and usually controlled by its developers, and used and accepted among the members of a specific virtual community. The recent developments in widely spread internet and data mining activities, highlighted the issue of accepting and using virtual currencies for different purposes, including, buying commodities or services, saving, as well as converting into real currencies, such as US dollars, euro or other currencies. One of the most controversial and the most advanced virtual currency scheme to date is the one so-called Bitcoin, designed and implemented by the Japanese programmer Satoshi Nakamoto in 2009. Although the use of Bitcoin might have positive impact on financial innovation and the provision of additional payment alternatives to consumers, it also might increase the risks in financial payments, exchange rates of real currencies, as well as increase the possibility of money laundering, using them for illegal deeds. Therefore , the purpose of this paper to clarify the main characteristic of Bitcoin, and analyze its positive aspects as well as the threats that may occur to the modern world economy , in case the usage of this money , significantly increases .
In January 2009 the Japanese software-designer SATOSHI NAKAMOTO invented a virtual currency named Bitcoin and released software for managing transactions in the new money.It consists solely of bits and bytes, but we cannot see it as a coin or banknote on the market.There is no cover in terms of gold or stocks, for example -in fact, nothing but the source code of the software which consists of thirty-one thousand lines of code.NAKAMOTO wanted to create a currency immune to potentially predatory bankers and politicians and so the currency and the mechanism to acquire Bitcoin were controlled entirely by software.The payment system is completely decentralised and so contains no central organisation which monitors transactions.Many people use this new currency to pay for services or products on the Internet, since it is no less safe than traditional payment systems.In this paper I will first introduce the basic parameters and functions of the alternative currency, and will deal especially with security and privacy issues relating to the virtual money.After that I will examine the value of Bitcoin on the online market, especially answering questions such as how we can acquire it.After this the legal background will be presented and suggestions made for its possible regulation, whilst its likely role in criminal behaviour is suggested.The paper was written in order to stimulate interest in this special, new currency, its working mechanisms, advantages and possible dangers, and because it represents a unique paradigm-shift, not simply in cyberspace, but in real-world payment systems also.
Aron talks about the virtual currency--Bitcoin. It is a currency founded by revolutionaries that went on to become the worlds dominant payment method. Once little more than the play thing of online libertarians and crypto-anarchists, many Bitcoin advocates are now seeking regulatory and financial legitimacy as an ecosystem of companies springs up to support the currency. In March, the US government sought to actively regulate Bitcoin by requiring companies classified as money transmitters to register with the Financial Crimes Enforcement Network (FinCEN), Mt. Gox, the largest Bitcoin exchange, was founded in 2010 but only registered last month, following the seizure of its accounts in May by the Department of Homeland Security.
The birth of Bitcoin brings new concept to the currency issuance and circulation.Its characteristics of decentralization and full electronization challenge the current currency system.Theoretically,Bitcoin possesses all the attributes that the currency has,and it will become real legal currency in circulation as long as legal permission.The use of Bitcoin in circulation now will suffer legal issues such as lack of legal status and credit,difficulty in evidence collection and remedy,jurisdiction conflict and so on.The problems mentioned above could only be fundamentally solved if the authority accelerated legislation,established a uniform dispute settlement mechanism,speeded up the establishment of credit system,and enhanced supervision.
Bachelor's thesis is focused on digital currency Bitcoin, mainly on Bitcoin transactions and their attributes like speed, fees and safety. Main goals of this thesis are three, analysis of bitcoin buying possibilities in Czech Republic, comparison of Bitcoin transactions with common payment methods like bank transfers, credit card payment or PayPal, and analysis of number of merchants accepting bitcoin in time and discovery of trend from these data. This thesis is divided into theoretical and practical part. In theoretical part there are described basics of cryptography, which are necessary for understanding Bitcoin, and in depth description how Bitcoin works. Practical part is focused on fulfilment of described goals, besides that thesis is also addressing Bitcoin clients and comparison between most popular ones. Contribution of this bachelor's thesis is analysis of bitcoin buying possibilities in Czech Republic, comparing Bitcoin transactions with transactions of standard payment methods in terms of fees and time, and analysis of trend in number of merchants accepting bitcoin as one of the payment method.
Bitcoin is a new kind of money, which means a digital currency which can be used for commercial purposes. Over time, the trade has evolved from barter to the use of the precious metals as money, then to the coins with intrinsic value and to the symbol coins and later to the use of the electronic money, reaching at present to a virtual currency, created and used through the internet network. Bitcoin promises to its users getting high returns under conditions of low risk arising from transactions carried out instantly, without intermediary bank and almost no fees. At this moment, Bitcoin is still an experimental new currency, but in the future it can offer an alternative to previous costly systems and it can increase online business access to developing countries.
Bachelor's thesis is focused on digital currency Bitcoin, mainly on Bitcoin transactions and their attributes like speed, fees and safety. Main goals of this thesis are three, analysis of bitcoin buying possibilities in Czech Republic, comparison of Bitcoin transactions with common payment methods like bank transfers, credit card payment or PayPal, and analysis of number of merchants accepting bitcoin in time and discovery of trend from these data. This thesis is divided into theoretical and practical part. In theoretical part there are described basics of cryptography, which are necessary for understanding Bitcoin, and in depth description how Bitcoin works. Practical part is focused on fulfilment of described goals, besides that thesis is also addressing Bitcoin clients and comparison between most popular ones. Contribution of this bachelor's thesis is analysis of bitcoin buying possibilities in Czech Republic, comparing Bitcoin transactions with transactions of standard payment methods in terms of fees and time, and analysis of trend in number of merchants accepting bitcoin as one of the payment method.
This bachelor's thesis focuses on the digital currency called Bitcoin. The theoretical part discusses the concept of money (its history, issuance, the gold standard, etc.) as well as central banking and local currencies. It also tackles the concept of Bitcoin itself, the way it functions, its advantages and disadvantages and its issuance (so-called mining). The practical part discusses whether or not it is possible to profit through bitcoin mining, by speculating on its relative value to the (US) dollar and if it is possible for Bitcoin to replace traditional payment systems and currencies in the future (or at least prove itself to be a potent competitor).
Lately,Canard et al.(CANARD S,JAMBERT A.Untraceability and profiling are not mutually exclusive [C]// TrustBus 2010:Proceedings of the 7th International Conference on Trust,Privacy and Security in Digital Business,LNCS 6264.Berlin:Springer-Verlag,2010:117-128) introduced the notion of multi-service subscription and proposed several instantiations.Unfortunately,their systems only satisfied a weaker variant of anonymity called revocable-anonymity and they were not fit for services.To this end,a revised multi-service subscription system was put forward to extending Canard et al's system.The new system achieved pay-per-use subscriptions by incorporating the anonymous payment system raised by Liu et al.(LIU J K,AU M H,SUSILO W,et al.Enhancing location privacy for electric vehicles(at the right time).[2012-08-01].http://eprint.iacr.org/2012/342).To allow users to prove in zero-knowledge that their account balance is enough for making a payment for the required access,it also utilized the Peng-Bao range proof for small ranges.Furthermore,it was constructed on several 4-round perfect zero-knowledge proofs of knowledge,which were obtained by applying a technique by Cramer et al.to the underlying Sigma-protocols.Compared with typical systems in the literature,the new solution gains advantages in terms of security.Concretely,it can be proved secure in the standard model.Moreover,it matches the strongest level of three crucial security notions,such as inseparability for spendable tokens,anonymity for users,and zero-knowledge for underlying proof systems.
Bitcoin is a potentially disruptive new crypto-currency based on a decentralized opensource protocol which is gradually gaining popularity. Perhaps the most important question that will affect Bitcoinâs success, is whether or not it will be able to scale to support the high volume of transactions required from a global currency system. We investigate the restrictions on the rate of transaction processing in Bitcoin as a function of both the bandwidth available to nodes and the network delay, both of which lower the efficiency of Bitcoinâs transaction processing. The security analysis done by Bitcoinâs creator Satoshi Nakamoto [12] assumes that block propagation delays are negligible compared to the time between blocksâan assumption that does not hold when the protocol is required to process transactions at high rates. We improve upon the original analysis and remove this assumption. Using our results, we are able to give bounds on the number of transactions per second the protocol can handle securely. Building on previously published measurements by Decker and Wattenhofer [5], we show these bounds are currently more restrictive by an order of magnitude than the bandwidth needed to stream all transactions. We additionally show how currently planned improvements to the protocol, namely the use of transaction hashes in blocks (instead of complete transaction records), will dramatically alleviate these restrictions. Finally, we present an easily implementable modification to the way Bitcoin constructs its main data structure, the blockchain, that immensely improves security from attackers, especially when the network operates at high rates. This improvement allows for further increases in the number of transactions processed per second. We show that with our proposed modification, significant speedups can be gained in confirmation time of transactions as well. The block generation rate can be securely increased to more than one block per second â a 600 fold speedup compared to todayâs rate, while still allowing the network to processes many transactions per second.
Cloud computing is a model for enabling convenient, on-demand network access to a shared pool of configurable computing resources (e.g., network, servers, storage, applications and services) that can be rapidly provisioned and released with minimal management effort or service provider interaction. During the last a few years, data security and integrity in cloud computing has emerged as a significantly important research area that has attracted increasing attention from both industry and academia. The virtual environment of cloud computing allows users to access computing power that exceeds what is contained within their own physical worlds. To enter this virtual environment, cloud users must transfer data throughout the cloud. Typically, cloud users know neither the exact location of their data nor the other sources of the data collectively stored with theirs. Consequently, several data security and integrity concerns have arisen, including key management, access control, searchable encryption techniques, remote integrity checks and proof of ownership in the cloud.\nThe first aspect of the work presented in this thesis is tree-based key management in cloud computing. Data encryption before outsourcing to the cloud is a common way to protect data privacy. Thus, key management is a challenging issue in cloud computing. It is the ability to correctly assign, monitor and secure keys which defines the level of operational security provided by any encryption implementation. The fundamental idea of this work is to design a secure and flexible key management mechanism for the outsourced data in cloud computing. In this thesis, an innovative tree-based key management scheme is proposed. The outsourced database remains private and secure, while some selected data and key nodes are shared with other parties in the cloud. Flexibility of key management is achieved and the security is proved in the standard model.\nThe second aspect of the work presented in this thesis is fine-grained access control. In order to secure the outsourced data in the cloud, designing efficient and secure access control is a challenging issue. Unlike traditional access control in which the data users and storage servers are in the same trust domain, access control techniques are very different in cloud computing, as the cloud servers are not trusted by most cloud users. The key idea of this work is to attribute sets-based access control. This thesis points out that any access policy can be defined as a logical expression formula over different attribute sets. Logical expression indicates what kind of user is allowed to access the data. A fine-grained and efficient access control is proposed, based on logical expression.\nThe third aspect of the work presented in this thesis is efficient searchable encryption techniques in cloud computing. Because the data is usually encrypted before being outsourced to the cloud, searching the encrypted data in cloud computing has recently gained attention and led to the development of efficient searchable encryption techniques. The fundamental idea of this work is to reduce the search cost on encrypted data. In this thesis, a practical keyword searching mechanism is proposed. The solution is very simple. It enables efficient multi-user keyword searches and hides the private information in the search queries. The security is proved in the standard model.\nThe fourth aspect of the work presented in this thesis is public remote data integrity checks. As the clients store important data in remote cloud storage without a local copy, it is important to check the remote data integrity. Design of efficient remote integrity check protocols without downloading the data is a challenging issue in cloud computing. The key idea of this work is a public remote integrity check based on zero-knowledge proof. In this thesis, an innovative public remote integrity check scheme (PRIC) is proposed. No information of either the verified data or the homomorphic tags is leaked. In addition, the experiment result shows that PRIC is efficient, especially when the data size is large or the integrity check is frequent. The security of PRIC is proved in the random oracle model.\nThe last aspect of the work presented in this thesis is proof of multiparty ownership for encrypted data in the cloud. There are many applications of ownership sharing by different users and the design of the proof protocols of joint ownership is a challenging issue. Meanwhile, the design of proof-of-ownership mechanisms for encrypted data is even more difficult. This is because encryption of the same file by different users with random keys results in different ciphertexts, and the cloud server cannot store the same hash root value for ownership verification. In this thesis, a proof of multiparty ownership solution (PMOW) with encrypted data is proposed. Every user can prove that he/she holds the plaintext of the encrypted file when the server stores one ciphertext only. In addition, a PMOW system is constructed. The security of PMOW is proved in the ideal cipher model.\nThe major contribution of this thesis is innovative and improved approaches to secure data in cloud computing. Using these approaches developed, a trustworthy cloud environment can be achieved.
Georg Neugebauer, Lucas Brutschy, Ulrike Meyer, Susanne Wetzel
Abstract. The problem of fair and privacy-preserving ordered set reconciliation arises in a variety of applications like auctions, e-voting, and appointment reconciliation. While several multi-party protocols have been proposed that solve this problem in the semi-honest model, there are no multi-party protocols that are secure in the malicious model so far. In this paper, we close this gap. Our newly proposed protocols are shown to be secure in the malicious model based on a variety of novel non-interactive zero-knowledge-proofs. We describe the implementation of our protocols and evaluate their performance in comparison to protocols solving the problem in the semi-honest case.
Abstract. Verifiably encrypted signatures (VES) are signatures encrypted by a public key of a trusted third party and we can verify their validity without decryption. This paper proposes a new VES scheme which is secure under the decisional linear (DLIN) assumption in the standard model. We also propose new obfuscators for encrypted signatures (ES) and encrypted VES (EVES) which are secure under the DLIN assump-tion. All previous efficient VES schemes in the standard model are either secure under standard assumptions (such as the computational Diffie-Hellman assumption) with large verification (or secret) keys or secure under (non-standard) dynamic q-type assumptions (such as the q-strong Diffie-Hellman extraction assumption) with short verification keys. Our construction is the first efficient VES scheme with short verification (and secret) keys secure under a standard assumption (DLIN). As by-products of our VES scheme, we construct new obfuscators for ES/EVES based on our new VES scheme. They are more efficient than previous obfuscators with respect to the public key size. Previous ob-fuscators for EVES are secure under non-standard assumption and use zero-knowledge (ZK) proof systems and Fiat-Shamir heuristics to obtain non-interactive ZK, i.e., its security is considered in the random oracle model. Thus, our construction also has an advantage with respect to as-sumptions and security models. Our new obfuscator for ES is obtained from our new obfuscator for EVES.
Recently,more and more people are quite attracted to a new digital currency which is called Bitcoin because of its anonymity,non-central authority,limited total amount,low transaction cost and free? convertibility.However,it could cause problems or risk of speculation,cyber crime,the waste of resource,the huge fluctuation in the price and so on.The emergence of Bitcoin is attributed to technical,economic and social factors.So rather than in just one aspect,Bitcoin should be concerned in different aspects,such as research,education and governance.
Abstract. We present a set of new, efficient, universally composable two-party protocols for evaluating reactive arithmetic circuits modulo n, where n is a safe RSA modulus of unknown factorization. Our protocols are based on a homomorphic encryption scheme with message space Zn, zero-knowledge proofs of existence, and a novel âmixed â trapdoor commitment scheme. Our protocols are proven secure against adaptive corruptions (assuming secure erasures) under standard assumptions in the CRS model (without random oracles). Our protocols appear to be the most efficient ones that satisfy these security requirements. In contrast to prior protocols, we provide facilities that allow for the use of our protocols as building blocks of higher-level protocols. An additional contribution of this paper is a universally composable construction of the variant of the Dodis-Yampolskiy oblivious pseudorandom function in a group of order n as originally proposed by Jarecki and Liu.
In this article, we discuss a possible exploit in Bitcoin that arises from the simultaneous adoption of client versions 0.8.1 and 0.8.2 (or 0.8.3) in the network. In version 0.8.2, Bitcoin clients no longer accept transactions with non-strict signature encoding. As we show, this incompatibility with prior client versions can potentially lead to a double-spending attack in a fast payment setting in Bitcoin. The attack can only work when merchants operate on any client version prior to 0.8.2. Our aim is therefore to raise the awareness of merchants to adopt version 0.8.2 (or 0.8.3) if they are willing to accept fast payments [1].