Termination of smart contracts is crucial for any blockchain system's security and consistency, especially for those supporting Turing-complete smart contract languages. Resource-constrained blockchain systems, like Ethereum and Hyperledger Fabric, could prevent smart contracts from terminating properly when the pre-allocated resources are not sufficient. The Zen system utilizes the dependent type system of the programming language F* to prove the termination of smart contracts for all inputs during compilation time. Since the smart contract execution usually depends on the current blockchain state and user inputs, this approach is not always successful. In this work, we propose a lazy approach by statically proving conditional termination and non-termination of a smart contract to determine input conditions under which the contract terminates or not. Prior to the execution of the smart contract, the proof-carrying blockchain system will check that its current state and the contract's input satisfy the termination conditions in order to determine if the contract is qualified (i.e., eventually terminating) to run on the chain.
Younggee Hong, Hyunsoo Kwon, Jihwan Lee, Junbeom Hur
Bitcoin mixing services improve anonymity by breaking the connection between Bitcoin addresses. In the darkweb environment, many illegal trades, such as in drugs or child pornography, avoid their transactions being traced by exploiting mixing services. Therefore, de-mixing algorithms are needed to identify illegal financial flows and to reduce criminal activity. Unfortunately, to the best of our knowledge, few studies on analyzing mixing services and de-anonymizing transactions have been proposed. In this paper, we conduct an in-depth analysis of real-world mixing services, and propose a de-mixing algorithm for Helix, one of the most widely used Bitcoin mixing services. The proposed algorithm de-anonymizes the relationship between the input and output addresses of mixing services by exploiting the static and dynamic parameters of mixing services. Our experiment showed that, we could identify the relationships between the input and output addresses of the Helix mixing service with a 99.14% accuracy rate.
Yandamuri, Sravya, Abraham, Ittai, Nayak, Kartik, Reiter, Michael K.
A smart contract on a blockchain cannot keep a secret because its data is replicated on all nodes in a network. To remedy this problem, it has been suggested to combine blockchains with trusted execution environments (TEEs), such as Intel SGX, for executing applications that demand privacy. Untrusted blockchain nodes cannot get access to the data and computations inside the TEE. This paper first explores some pitfalls that arise from the combination of TEEs with blockchains. Since TEEs are, in principle, stateless they are susceptible to rollback attacks, which should be prevented to maintain privacy for the application. However, in blockchains with non-final consensus protocols, such as the proof-of-work in Ethereum and others, the contract execution must handle rollbacks by design. This implies that TEEs for securing blockchain execution cannot be directly used for such blockchains; this approach works only when the consensus decisions are final. Second, this work introduces an architecture and a prototype for smart-contract execution within Intel SGX technology for Hyperledger Fabric, a prominent platform for enterprise blockchain applications. Our system resolves difficulties posed by the execute-order-validate architecture of Fabric and prevents rollback attacks on TEE-based execution as far as possible. For increasing security, our design encapsulates each application on the blockchain within its own enclave that shields it from the host system. An evaluation shows that the overhead moving execution into SGX is within 10%-20% for a sealed-bid auction application.
Yackolley Amoussou-Guenou, Antonella Del Pozzo, Maria Potop-Butucaru, Sara Tucci-Piergiovanni
Tendermint-core blockchains (e.g. Cosmos) are considered today one of the most viable alternatives for the highly energy consuming proof-of-work blockchains such as Bitcoin and Ethereum. Their particularity is that they aim at offering strong consistency (no forks) in an open system combining two ingredients (i) a set of validators that generate blocks via a variant of Practical Byzantine Fault Tolerant (PBFT) consensus protocol and (ii) a selection strategy that dynamically selects nodes to be validators for the next block via a proof-of-stake mechanism. However,the exact assumptions on the system model under which Tendermint underlying algorithms are correct and the exact properties Tendermint verifies have never been formally analyzed. The contribution of this paper is two-fold. First, while formalizing Tendermint algorithms we precisely characterize the system model and the exact problem solved by Tendermint. We prove that in eventual synchronous systems a modified version of Tendermint solves (i) under additional assumptions, a variant of one-shot consensus for the validation of one single block and (ii) a variant of the repeated consensus problem for multiple blocks. These results hold even if the set of validators is hit by Byzantine failures, provided that for each one-shot consensus instance less than one third of the validators is Byzantine. Our second contribution relates to the fairness of the rewarding mechanism. It is common knowledge that in permisionless blockchain systems the main threat is the tragedy of commons that may yield the system to collapse if the rewarding mechanism is not adequate. Ad minimum the rewarding mechanism must be fair, i.e.distributing the rewards in proportion to the merit of participants. We prove, for the first time in blockchain systems, that in repeated-consensus based blockchains there exists an (eventual) fair rewarding mechanism if and only if the system is (eventual) synchronous. We also show that the original Tendermint rewarding is not fair, however, a modification of the original protocol makes it eventually fair.
This article presents a new method for managing digital reuse rights of research data, which leverages technologies such as the blockchain and smart contracts. This allows, on one hand, the creation of a permanent record on the agreements between the authors of the data and the reusers, with the possibility of verifying compliance at any time, and on the other hand, a higher level of granularity on defining the conditions of reuse. A practical implementation of such a workflow using the Solidity smart contract language is included, along with a brief analysis over the Ethereum blockchain network.
Valentina Lenarduzzi, Maria Ilaria Lunesu, Michele Marchesi, Roberto Tonelli
We present an application of Blockchain technology and Smart Contracts to the management of Agile projects, using Scrum or Lean-Kanban processes. In our application the duties of the Product Owner for certifying the correctness of the outcomes are delegated to one or more Smart Contracts deployed on the Ethereum Blockchain and written in Solidity. An agreement with the Customer can also allow the Smart Contracts to automatically enable payments, to introduce penalties or grants on the basis of the outcome. Product Owner duties and work can thus be relieved allowing to allocate resources on more profitable and productive tasks. Other possibilities are examined as well.
Over the years, as a response to the increased demand for international clearing of transactions that are conditioned by globalization, it has inevitably led to the expansion of product assortments and, consequently, services. The economy and the finance of this century are characterized by innovation and recognition of new trends and needs for simple and maximum available non-border products. For example, as Google assumed the role of Yahoo, so in the world of finance it was looking for a single practical system to outperform the previous ones. With the emergence of cryptocurrency, we can consider that there has been a new global system without the involvement of mediators and expensive international transactions. The idea was to create an electronic payment system that would be decentralized so that individual entities do their job themselves. The use of cryptocurrency might be able to replace Internet banking and mobile banking to a greater extent. But, it is not yet known which will be the first cryptocurrency found on official financial stock markets, and which will be able to provide the easiest implementation and use today. So far, no cryptocurrency is in any official stock market yet, and the transactions are carried out through private sites. There are over one thousand cryptocurrencies in the world and, depending on the current market situation, and the adequate investment moment in a particular cryptocurrency, it can be gain, but at the same time it can be loss. Cryptocurrency have caused a real financial insanity in recent years. In that period, a handful of people gained great wealth, while others remained without millions of dollars due to unpredictable fall in prices. The basic parameters for deciding when investing in a particular cryptocurrency are numerous and some of them are: the stability of the currency in a certain period, the final number of coins to be released into circulation and their security of storage, the number of users and merchants who have accepted that currency as a means of payment and other. One thing is for sure, that there were a lot of comments and confusion when the cryptocurrency was introduced and when it became very popular. The aim of this paper work is to expand, as much as possible, the knowledge that new innovative changes in the world of finance are inevitable and, if they are good, to be acceptable and useful as soon as possible. The paper work will also show the types of cryptocurrencies, but among them the bitcoin will be distinguished as the most famous cryptocurrency of the world. Among other things, we will see the cryptocurrency market in Serbia, how we can buy bitcoin, types of bitcoin digital wallets and we will give a prognosis of the bitcoin rate by 2020.
Roberto Tonelli, Andrea Pinna, Gavina Baralla, Simona Ibba
We propose a model of software architecture where microservices are implemented by mean of Smart Contracts deployed in a blockchain, discussing similarities among the two paradigms and presenting an example of the implementation of an e-commerce platform.
This study back-tests a marginal cost of production model proposed to value the digital currency Bitcoin. Results from both conventional regression and vector autoregression (VAR) models show that the marginal cost of production plays an important role in explaining Bitcoin prices, challenging recent allegations that Bitcoins are essentially worthless. Even with markets pricing Bitcoin in the thousands of dollars each, the valuation model seems robust. The data show that a price bubble that began in the Fall of 2017 resolved itself in early 2018, converging with the marginal cost model. This suggests that while bubbles may appear in the Bitcoin market, prices will tend to this bound and not collapse to zero.
This study back-tests a marginal cost of production model proposed to value\nthe digital currency bitcoin. Results from both conventional regression and\nvector autoregression (VAR) models show that the marginal cost of production\nplays an important role in explaining bitcoin prices, challenging recent\nallegations that bitcoins are essentially worthless. Even with markets pricing\nbitcoin in the thousands of dollars each, the valuation model seems robust. The\ndata show that a price bubble that began in the Fall of 2017 resolved itself in\nearly 2018, converging with the marginal cost model. This suggests that while\nbubbles may appear in the bitcoin market, prices will tend to this bound and\nnot collapse to zero.\n
We follow existing distributed systems frameworks employing methods from algebraic topology to formally define primitives of blockchain technology. We define the notion of cross chain liquidity, sharding and probability spaces between and within blockchain protocols. We incorporate recent advancements in synthetic homology to show that this topological framework can be implemented within a type system. We use recursion schemes to define kernels admitting smooth manifolds across protocol complexes, leading to the formal definition of a Poincare protocol.
Revisiting analytically the notion of embeddedness and its connections with the concept of trust, this paper shows that contrary to Bitcoin’s premises and promises to be a trust-low or even trust-less currency, trust enters the system at many various levels and with different nuances. Applying a conceptual framework that conceives embeddedness as both the possible source and outcome of trust, it is pointed out that Bitcoin should better be regarded as doubly embedded: in technology and in its peculiar social structure. Due to the existence of computational and cognitive asymmetries within the system, in fact, trust is necessary for the very functioning of this new form of money, as well as for its future prospects.
Xin Sun, Quanlong Wang, Piotr Kulicki, Xishun Zhao
We proposed a framework of quantum-enhanced logic-based blockchain, which improves the efficiency and power of quantum-secured blockchain. The efficiency is improved by using a new quantum honest-success Byzantine agreement protocol to replace the classical Byzantine agreement protocol, while the power is improved by incorporating quantum protection and quantum certificate into the syntax of transactions. Our quantum-secured logic-based blockchain can already be implemented by the current technology. The cryptocurrency created and transferred in our blockchain is called qulogicoin. Incorporating quantum protection and quantum certificates into blockchain makes it possible to use blockchain to overcome the limitations of some quantum cryptographic protocols. As an illustration, we show that a significant shortcoming of cheat-sensitive quantum bit commitment protocols can be overcome with the help of our blockchain and qulogicoin.
Sanal para sistemi bitcoin ve altcoins olarak tanımlanan türevleri mevcut para politikasını ve para sistemlerini değişim ve dönüşüme zorlayacak bir trendin içinde oldukları gözlenmektedir. Genel olarak kripto para olarak tanımlanan bu sistem elektronik ortamda oluşturulabilen ve nakit benzeri bir ödeme aracı sisteminden ibarettir. Bu sistemin mevcut para ve ödeme araçlarına alternatif ve hatta geleneksel para teori ve uygulamalarının yerini alacağı yönünde bir gelişim süreci içinde olması bu sisteme odaklanmayı zorunlu hale getirmektedir. Bu makalede bitcoin ve benzeri kripto paraların yapıları, işlevleri ve mevcut para sistemi içerisindeki yeri ve önemi karşılaştırmalı ve analitik bir analizle değerlendirilmiştir.
A problem facing healthcare record systems throughout the world is how to share the medical data with more stakeholders for various purposes without sacrificing data privacy and integrity. Blockchain, operating in a state of consensus, is the underpinning technology that maintains the Bitcoin transaction ledger. Blockchain as a promising technology to manage the transactions has been gaining popularity in the domain of healthcare. Blockchain technology has the potential of securely, privately, and comprehensively manage patient health records. In this work, we discuss the latest status of blockchain technology and how it could solve the current issues in healthcare systems. We evaluate the blockchain technology from the multiple perspectives around healthcare data, including privacy, security, control, and storage. We review the current projects and researches of blockchain in the domain of healthcare records and provide the insight into the design and construction of next generations of blockchain-based healthcare systems.
The building of the blockchain is predicted to harken the end of the contemporary sovereign order. Some go further to claim that as a powerful decentering technology, blockchain contests the continued functioning of world capitalism. Are such claims merited? In this paper we consider sovereignty and blockchain technology theoretically, posing possible futures for sovereignty in a blockchain world. These possibilities include various forms of individual, popular, technological, corporate, and techno-totalitarian state sovereignty. We identify seven structural tendencies of blockchain technology and give examples as to how these have manifested in the construction of new forms of sovereignty. We conclude that the future of sovereignty in a blockchain world will be articulated in the conjuncture of social struggle and technological agency and we call for a stronger alliance between technologists and democrats.
This thought-provoking article discusses how the technology that underpins cryptocurrencies can be put to use for transfer pricing purposes. At present, the use of blockchain technology in the field of transfer pricing is at a nascent stage. Its practical use would depend on actual advancement in technology and, more importantly, its acceptability with tax administrations.
Cryptocurrency is constantly increasing in popularity at global level. While it provides advantages such as limited government oversight and low transaction cost for the users, it can cause concern for the state and tax administrations. On the basis of this concern is the fact that cryptocurrency can not easily be placed in the legal categories of the country's legislation. From this point on this study; aims to evaluate the idea of taxation of cryptocurrency from the perspective of Turkish Tax System in the light of different country practices. Findings of work; the economic dimension of the crypto money is that it has a significant tax revenue potential. The results of the study show that cryptocurrency carries a significant tax revenue potential due to the economic size it has.
The emergence of new technologies leads to the reconsideration of business processes identified with older technologies, but many advantages that they promise do not immediately appear. The transfer of the ledgers kept in paper form to the computer environment presents a challenge as a revolution in the field of payments. However, since this change takes place in the form of recording rather than recording the transaction, the processes underlying the transactions remain substantially the same.
In this position paper we discuss the methodological challenges associated with engaging citizens, publics and research participants in speculations around future socio-technical systems. We focus on distributed autonomous organizations and associated smart contracting and distributed ledger technologies as an example of such systems. Drawing on our prior work on Speculative Enactments, we highlight the potential value of speculative approaches to engaging people in the design of DAOs that (i) have clear consequentiality for participants, (ii) illustrate scenarios of the future mundane involving these technologies, and (iii) give opportunities for participants to co-construct speculations. We suggest these as provocative starting points to conducting future participatory and speculative design research on DAOs, and to promote discussion with workshop attendees.
The IRS recently dealt a blow to Bitcoin enthusiasts by ruling that Bitcoin and other similar currencies should be treated as property–and not foreign currency–for income tax purposes. As a result, those who use bitcoins to purchase goods or services must report gain or loss on each transactionn if the bitcoins have changed value between the time they were acquired and spent. Treating Bitcoin as a foreign currency would have permitted individuals to take advantage of the $200 personal-use exemption and required taxpayers to adopt a formulaic system for tracking the basis of commingled bitcoins.The IRS's decision seems correct as a matter of positive law, but laws can always be changed. In this Article I consid4r whether Bitcoin should be treated as a foreign currency for income tax purposes. I conclude that tax authorities should adopt a foreign currency definition that excludes bitcoin and similar currencies because (1) a broad definition ciould create significant administrative and line-drawing problems, and (2) the government has little interest in promoting alternate currencies . Nor should authorities extend the personal-use exemption to virtual currencies. In contrast, authorities should extend the basis rules applicable to foreign currency to virtual currencies to prevent taxpayers from using the basis rules to improperly reduce their tax obligations.