Σκοπός της παρούσας διπλωματικής εργασίας είναι η εξέταση της τεχνολογίας που κρύβεται πίσω από τα κρυπτονομίσματα. Η τεχνολογία αυτή είναι το Blockchain και συγκεκριμένα το Blockchain Ethereum, το οποίο είναι μια δημόσια αποκεντρωμένη και κατανεμημένη πλατφόρμα που επιτρέπει σε οποιονδήποτε να δημιουργεί και να χρησιμοποιεί αποκεντρωμένες εφαρμογές που λειτουργούν με αυτή την τεχνολογία. Η καινοτομία της τεχνολογίας Blockchain δίνει λύση στο ζήτημα που αφορά την συγχρονισμένη καταγραφή δεδομένων σε ένα κατανεμημένο δίκτυο από ανεξάρτητους και άγνωστους μεταξύ τους κόμβους (υπολογιστές), συμφωνώντας ότι τα δεδομένα που αποθηκεύονται κάθε φορά είναι ακριβώς τα ίδια. Όλοι οι υπολογιστές που συμμετέχουν σε ένα δίκτυο Blockchain έχουν ακριβώς τα ίδια δεδομένα χωρίς να μπορούν να τα αλλάξουν ή να τα παραμετροποιήσουν, ενώ η ασφάλεια αυτών των δεδομένων επιτυγχάνεται μέσω της κρυπτογραφίας. \nΧρησιμοποιώντας λοιπόν την τεχνολογία Ethereum Blockchain, επιχειρήθηκε η δημιουργία μιας αποκεντρωμένης κατανεμημένης εφαρμογής σε συνεργασία με την εταιρία Intelen Inc. Συγκεκριμένα, έγινε χρήση της τεχνολογίας Blockchain για να επιτευχθεί επικοινωνία μεταξύ έξυπνων οικιακών μπαταριών χωρίς να απαιτείται η παρέμβαση οποιασδήποτε κεντρικής αρχής. Με άλλα λόγια δημιουργήθηκε σχετική εφαρμογή όπου οι έξυπνες μπαταρίες είναι σε θέση να χρησιμοποιήσουν το προσωπικό τους ηλεκτρονικό πορτοφόλι για να ανταλλάζουν κρυπτονομίσματα και πληροφορίες χωρίς την παρέμβαση από τρίτα άτομα.
Online portals include an increasing amount of user feedback in form of ratings and reviews. Recent research highlighted the importance of this feedback and confirmed that positive feedback improves product sales figures and thus its success. However, online portals' operators act as central authorities throughout the overall review process. In the worst case, operators can exclude users from submitting reviews, modify existing reviews, and introduce fake reviews by fictional consumers. This paper presents ReviewChain, a decentralized review approach. Our approach avoids central authorities by using blockchain technologies, decentralized apps and storage. Thereby, we enable users to submit and retrieve untampered reviews. We highlight the implementation challenges encountered when realizing our approach on the public Ethereum blockchain. For each implementation challange, we discuss possible design alternatives and their trade-offs regarding costs, security, and trustworthiness. Finally, we analyze which design decision should be chosen to support specific trade-offs and present resulting combinations of decentralized blockchain technologies, also with conventional centralized technologies.
Initial Coin Offerings (ICO) are public offers of new cryptocurrencies in exchange of existing ones, aimed to finance projects in the blockchain development arena. In the last 8 months of 2017, the total amount gathered by ICOs exceeded 4 billion US$, and overcame the venture capital funnelled toward high tech initiatives in the same period. A high percentage of ICOS is managed through Smart Contracts running on Ethereum blockchain, and in particular to ERC-20 Token Standard Contract. In this work we examine 1388 ICOs, published on December 31, 2017 on icobench.com Web site, gathering information relevant to the assessment of their quality and software development management, including data on their development teams. We also study, at the same date, the financial data of 450 ICO tokens available on coinmarketcap.com Web site, among which 355 tokens are managed on Ethereum blochain. We define success criteria for the ICOs, based on the funds actually gathered, and on the behavior of the price of the related tokens, finding the factors that most likely influence the ICO success likeliness.
Initial Coin Offerings (ICO) are public offers of new cryptocurrencies in\nexchange of existing ones, aimed to finance projects in the blockchain\ndevelopment arena. In the last 8 months of 2017, the total amount gathered by\nICOs exceeded 4 billion US$, and overcame the venture capital funnelled toward\nhigh tech initiatives in the same period. A high percentage of ICOS is managed\nthrough Smart Contracts running on Ethereum blockchain, and in particular to\nERC-20 Token Standard Contract. In this work we examine 1388 ICOs, published on\nDecember 31, 2017 on icobench.com Web site, gathering information relevant to\nthe assessment of their quality and software development management, including\ndata on their development teams. We also study, at the same date, the financial\ndata of 450 ICO tokens available on coinmarketcap.com Web site, among which 355\ntokens are managed on Ethereum blochain. We define success criteria for the\nICOs, based on the funds actually gathered, and on the behavior of the price of\nthe related tokens, finding the factors that most likely influence the ICO\nsuccess likeliness.\n
We design and implement the first private and anonymous decentralized crowdsourcing system ZebraLancer, and overcome two fundamental challenges of decentralizing crowdsourcing, i.e., data leakage and identity breach. First, our outsource-then-prove methodology resolves the tension between the blockchain transparency and the data confidentiality to guarantee the basic utilities/fairness requirements of data crowdsourcing, thus ensuring: (i) a requester will not pay more than what data deserve, according to a policy announced when her task is published via the blockchain; (ii) each worker indeed gets a payment based on the policy, if he submits data to the blockchain; (iii) the above properties are realized not only without a central arbiter, but also without leaking the data to the open blockchain. Second, the transparency of blockchain allows one to infer private information about workers and requesters through their participation history. Simply enabling anonymity is seemingly attempting but will allow malicious workers to submit multiple times to reap rewards. ZebraLancer also overcomes this problem by allowing anonymous requests/submissions without sacrificing accountability. The idea behind is a subtle linkability: if a worker submits twice to a task, anyone can link the submissions, or else he stays anonymous and unlinkable across tasks. To realize this delicate linkability, we put forward a novel cryptographic concept, i.e., the common-prefix-linkable anonymous authentication. We remark the new anonymous authentication scheme might be of independent interest. Finally, we implement our protocol for a common image annotation task and deploy it in a test net of Ethereum. The experiment results show the applicability of our protocol atop the existing real-world blockchain.
Leopoldo Catania, Stefano Grassi, Francesco Ravazzolo
This paper studies the predictability of cryptocurrencies time series. We compare several alternative univariate and multivariate models in point and density forecasting of four of the most capitalized series: Bitcoin, Litecoin, Ripple and Ethereum. We apply a set of crypto–predictors and rely on Dynamic Model Averaging to combine a large set of univariate Dynamic Linear Models and several multivariate Vector Autoregressive models with different forms of time variation. We find statistical significant improvements in point forecasting when using combinations of univariate models and in density forecasting when relying on selection of multivariate models.
Mareena Fernandes, Saloni Khanna, Leandra Monteiro, Anu Thomas · 5 authors
Advancement in technological developments introduced virtual currency exchange methods viz Bitcoin, Litecoin, Ethereum and so on which are evolving rapidly. Cryptocurrencies were introduced to eliminate financial intermediaries leading to direct peer-to-peer transactions. With the spread of the global Coronavirus pandemic, the relationship between Bitcoin and the equity market has expanded. Cryptocurrencies are highly volatile but can also prove to be good investments. Cryptocurrency, being a novel technique for transaction systems, has led to a lot of confusion among investors and any rumours or news on social media has been claimed to significantly affect the prices of cryptocurrencies. The huge percentage increase/decrease in Bitcoin's price over a short period of time is an intriguing phenomenon that cannot be foreseen. For a long time, bitcoin price prediction has been a hot topic of study.In this paper, we discuss the implementation and results of the Deep Learning Bitcoin Price Prediction Model and prepare a strategy to maximize gains for investors. The paper covers to framework with a set of deep learning models, analysis methods with a fixed set of factors to predict daily Bitcoin prices and design-integration of price prediction of different cryptocurrencies using RNN (Recurrent Neural Network), LSTM (Long Short-Term Memory) and GRU (Gated recurrent units). The idea of incorporating Public Sentiment in the prediction of the hikes and falls of the Bitcoin market from Social Media platforms like Reddit and Twitter leading to meaningful predicted results. This prediction can bring confidence to the common man to invest with lesser risk and more profit. Also, this can enable the digital new-age currency to become a primary method of transaction.
Using blockchain technology, it is possible to create contracts that offer a reward in exchange for a trained machine learning model for a particular data set. This would allow users to train machine learning models for a reward in a trustless manner. The smart contract will use the blockchain to automatically validate the solution, so there would be no debate about whether the solution was correct or not. Users who submit the solutions won't have counterparty risk that they won't get paid for their work. Contracts can be created easily by anyone with a dataset, even programmatically by software agents. This creates a market where parties who are good at solving machine learning problems can directly monetize their skillset, and where any organization or software agent that has a problem to solve with AI can solicit solutions from all over the world. This will incentivize the creation of better machine learning models, and make AI more accessible to companies and software agents.
Blockchain-based distributed computing platforms enable the trusted execution\nof computation - defined in the form of smart contracts - without trusted\nagents. Smart contracts are envisioned to have a variety of applications,\nranging from financial to IoT asset tracking. Unfortunately, the development of\nsmart contracts has proven to be extremely error prone. In practice, contracts\nare riddled with security vulnerabilities comprising a critical issue since\nbugs are by design non-fixable and contracts may handle financial assets of\nsignificant value. To facilitate the development of secure smart contracts, we\nhave created the FSolidM framework, which allows developers to define contracts\nas finite state machines (FSMs) with rigorous and clear semantics. FSolidM\nprovides an easy-to-use graphical editor for specifying FSMs, a code generator\nfor creating Ethereum smart contracts, and a set of plugins that developers may\nadd to their FSMs to enhance security and functionality.\n
Reasoning about commutativity between data-structure operations is an important problem with applications including parallelizing compilers, optimistic parallelization and, more recently, Ethereum smart contracts. There have been research results on automatic generation of commutativity conditions, yet we are unaware of any fully automated technique to generate conditions that are both sound and effective. We have designed such a technique, driven by an algorithm that iteratively refines a conservative approximation of the commutativity (and non-commutativity) condition for a pair of methods into an increasingly precise version. The algorithm terminates if/when the entire state space has been considered, and can be aborted at any time to obtain a partial yet sound commutativity condition. We have generalized our work to left-/right-movers and proved relative completeness. We describe aspects of our technique that lead to useful commutativity conditions, including how predicates are selected during refinement and heuristics that impact the output shape of the condition. We have implemented our technique in a prototype open-source tool Servois. Our algorithm produces quantifier-free queries that are dispatched to a back-end SMT solver. We evaluate Servois through two case studies: (i) We synthesize commutativity conditions for a range of data structures including Set, HashTable, Accumulator, Counter, and Stack. (ii) We consider an Ethereum smart contract called BlockKing, and show that Servois can detect serious concurrency-related vulnerabilities and guide developers to construct robust and efficient implementations.
Since 2004, different research was handling the challenges in the centralized voting systems, e-voting protocols and recently the decentralized voting. So electronic voting puts forward some difficulties regarding the voter anonymity, the secure casting of the votes and to prevent the voting process from frauding. The Decentralized property of the technology called "blockchain" could have the solution for many of the challenges in voting research area and brings a new secure mechanism of safe and transparent voting. In this paper, a broad comparison between ongoing voting systems has studied by analyzing their structure and the drawbacks that should consider in future to improve the whole election process from keeping the privacy of the voter, casting a vote with the possibility to check if it was counted correctly to publishing the results. The result of the paper will give a new approach to extend the target of the election from small scale to large scale despite the fact of Ethereum limitation which can cast on the blockchain just five votes per minute. The primary challenge is to find an answer for this question: "How to balance between voter privacy and transparency without breaking the important rule where the voter can proof for a specific candidate that he voted for him in a bribe situation?".
Alberto Sonnino, Mustafa Al-Bassam, Shehar Bano, Sarah Meiklejohn · 5 authors
Coconut is a novel selective disclosure credential scheme supporting distributed threshold issuance, public and private attributes, re-randomization, and multiple unlinkable selective attribute revelations. Coconut integrates with blockchains to ensure confidentiality, authenticity and availability even when a subset of credential issuing authorities are malicious or offline. We implement and evaluate a generic Coconut smart contract library for Chainspace and Ethereum; and present three applications related to anonymous payments, electronic petitions, and distribution of proxies for censorship resistance. Coconut uses short and computationally efficient credentials, and our evaluation shows that most Coconut cryptographic primitives take just a few milliseconds on average, with verification taking the longest time (10 milliseconds).
Smart contracts---stateful executable objects hosted on blockchains like Ethereum---carry billions of dollars worth of coins and cannot be updated once deployed. We present a new systematic characterization of a class of trace vulnerabilities, which result from analyzing multiple invocations of a contract over its lifetime. We focus attention on three example properties of such trace vulnerabilities: finding contracts that either lock funds indefinitely, leak them carelessly to arbitrary users, or can be killed by anyone. We implemented MAIAN, the first tool for precisely specifying and reasoning about trace properties, which employs inter-procedural symbolic analysis and concrete validator for exhibiting real exploits. Our analysis of nearly one million contracts flags 34,200 (2,365 distinct) contracts vulnerable, in 10 seconds per contract. On a subset of3,759 contracts which we sampled for concrete validation and manual analysis, we reproduce real exploits at a true positive rate of 89%, yielding exploits for3,686 contracts. Our tool finds exploits for the infamous Parity bug that indirectly locked 200 million dollars worth in Ether, which previous analyses failed to capture.
Patrick G. Sylim, Fang Liu, Alvin Marcelo, Paul Fontelo
<sec> <title>BACKGROUND</title> Drug counterfeiting is a global problem with significant risks to consumers and the general public. In the Philippines, 30% of inspected drug stores in 2003 were found with substandard/spurious/falsely-labeled/falsified/counterfeit drugs. The economic burden on the population drug expenditures and on governments is high. The Philippine Food and Drug Administration (FDA) encourages the public to check the certificates of product registration and report any instances of counterfeiting. The National Police of Philippines responds to such reports through a special task force. However, no literature on its impact on the distribution of such drugs were found. Blockchain technology is a cryptographic ledger that is allegedly immutable through repeated sequential hashing and fault-tolerant through a consensus algorithm. This project will develop and test a pharmacosurveillance blockchain system that will support information sharing along the official drug distribution network. </sec> <sec> <title>OBJECTIVE</title> This study aims to develop a pharmacosurveillance blockchain system and test its functions in a simulated network. </sec> <sec> <title>METHODS</title> We are developing a Distributed Application (DApp) that will run on smart contracts, employing Swarm as the Distributed File System (DFS). Two instances will be developed: one for Ethereum and another for Hyperledger Fabric. The proof-of-work (PoW) consensus algorithm of Ethereum will be modified into a delegated proof-of-stake (DPoS) or practical Byzantine fault tolerance (PBFT) consensus algorithm as it is scalable and fits the drug supply chain environment. The system will adopt the GS1 pedigree standard and will satisfy the data points in the data standardization guidelines from the US FDA. Simulations will use the following 5 nodes: for FDA, manufacturer, wholesaler, retailer, and the consumer portal. </sec> <sec> <title>RESULTS</title> Development is underway. The design of the system will place FDA in a supervisory data verification role, with each pedigree type–specific data source serving a primary data verification role. The supply chain process will be initiated by the manufacturer, with recursive verification for every transaction. It will allow consumers to scan a code printed on the receipt of their purchases to review the drug distribution history. </sec> <sec> <title>CONCLUSIONS</title> Development and testing will be conducted in a simulated network, and thus, results may differ from actual practice. The project being proposed is disruptive; once tested, the team intends to engage the Philippine FDA to discuss implementation plans and formulate policies to facilitate adoption and sustainability. </sec> <sec> <title>REGISTERED REPORT IDENTIFIER</title> RR1-10.2196/10163 </sec>
Die Digitalisierung erfasst alle Lebens- und Rechtsbereiche, auch das Gesellschaftsrecht. Der Beitrag befasst sich mit den Einflüssen der Digitalisierung auf die verschiedenen Formen der Kommunikation im Gesellschaftsrecht, sei es der virtuellen Gesellschafterversammlung oder des Einsatzes digitaler Medien in den Organen, aber auch gegenüber potentiellen Investoren. Dabei werden die jeweiligen rechtlichen Rahmenbedingungen auch jenseits des Gesellschaftsrechts beleuchtet, etwa medien- oder datenschutzrechtliche Fragen. Die Digitalisierung wirkt sich aber auch auf die Haftung der Organe aus, indem mehr verfügbare Daten und verbesserte Algorithmen dazu führen, dass die Organe die verbesserten Informationen zur Entscheidungsfindung nutzen müssen. Umgekehrt ist IT-Sicherheit heute „Chefsache“ geworden, da durch die Digitalisierung der Wertschöpfungsprozesse Unternehmen bei Ausfall ihrer IT-Systeme in ihrer Existenz bedroht werden können. Ferner ermöglicht die neue Technologie der Blockchain die eindeutige Nachvollziehung von Transaktionen, damit auch von Abstimmungen, bis hin zum Einsatz in der Rechnungslegung. Besondere Fragen werfen neue Investitionsformen unter Einsatz der Blockchain-Technologie auf, etwa die DAO Ethereum. Abschließend wird ein Blick auf die Formen der engen vertraglichen Kooperation bei Industrie 4.0 geworfen.
It is undeniable that artificial intelligence (AI) and blockchain concepts are spreading at a phenomenal rate. Both technologies have distinct degree of technological complexity and multi-dimensional business implications. However, a common misunderstanding about blockchain concept, in particular, is that blockchain is decentralized and is not controlled by anyone. But the underlying development of a blockchain system is still attributed to a cluster of core developers. Take smart contract as an example, it is essentially a collection of codes (or functions) and data (or states) that are programmed and deployed on a blockchain (say, Ethereum) by different human programmers. It is thus, unfortunately, less likely to be free of loopholes and flaws. In this article, through a brief overview about how artificial intelligence could be used to deliver bug-free smart contract so as to achieve the goal of blockchain 2.0, we to emphasize that the blockchain implementation can be assisted or enhanced via various AI techniques. The alliance of AI and blockchain is expected to create numerous possibilities.
This paper investigates a critical access control issue in the Internet of Things (IoT). In particular, we propose a smart contract-based framework, which consists of multiple access control contracts (ACCs), one judge contract (JC), and one register contract (RC), to achieve distributed and trustworthy access control for IoT systems. Each ACC provides one access control method for a subject-object pair, and implements both static access right validation based on predefined policies and dynamic access right validation by checking the behavior of the subject. The JC implements a misbehavior-judging method to facilitate the dynamic validation of the ACCs by receiving misbehavior reports from the ACCs, judging the misbehavior and returning the corresponding penalty. The RC registers the information of the access control and misbehavior-judging methods as well as their smart contracts, and also provides functions (e.g., register, update, and delete) to manage these methods. To demonstrate the application of the framework, we provide a case study in an IoT system with one desktop computer, one laptop and two Raspberry Pi single-board computers, where the ACCs, JC, and RC are implemented based on the Ethereum smart contract platform to achieve the access control.
Roberto Tonelli, G. A. Pierro, Marco Ortu, Giuseppe Destefanis
Smart contracts (SC) are software programs that reside and run over a blockchain. The code can be written in different languages with the common purpose of implementing various kinds of transactions onto the hosting blockchain. They are ruled by the blockchain infrastructure with the intent to automatically implement the typical conditions of traditional contracts. Programs must satisfy context-dependent constraints which are quite different from traditional software code. In particular, since the bytecode is uploaded in the hosting blockchain, the size, computational resources, interaction between different parts of the program are all limited. This is true even if the specific programming languages implement more or less the same constructs as that of traditional languages: there is not the same freedom as in normal software development. The working hypothesis used in this article is that Smart Contract specific constraints should be captured by specific software metrics (that may differ from traditional software metrics). We tested this hypothesis on 85K Smart Contracts written in Solidity and uploaded on the Ethereum blockchain. We analyzed Smart Contracts from two repositories "Etherscan" and "Smart Corpus" and we computed the statistics of a set of software metrics related to Smart Contracts and compared them to the metrics extracted from more traditional software projects. Our results show that generally, Smart Contract metrics have more restricted ranges than the corresponding metrics in traditional software systems. Some of the stylized facts, like power law in the tail of the distribution of some metrics, are only approximate but the lines of code follow a log-normal distribution which reminds us of the same behaviour already found in traditional software systems.
Smart contracts gain rapid exposure since the inception of blockchain<br/>technology. Today's smart contracts are coded in non-mainstream<br/>procedural programming languages (e.g. Solidity for Ethereum),<br/>which lifts the requirement to draft enterprise ready smart contract to<br/>both a legal professional and a programmer instead of only the former.<br/>In search for a smart contract language that reduces the threshold to<br/>draft one, this conceptual paper elaborates how business logic can be<br/>converted to executable code for commitment-based smart contracts.<br/>Hereby, a contract is viewed as a set of reciprocal commitments. The<br/>smart contract ensures the automated execution of all or most of these<br/>commitments. In order to leverage its event processing capabilities,<br/>Reaction RuleML has been used to appropriately represent the<br/>elements and working of passive and active rules within a<br/>commitment based smart.
One of the most popular platform based on blockchain technology is Ethereum. Internal activity on this public blockchain is analyzed both from a quantitative and qualitative point of view. In a first part, it is shown that the creation of the Ethereum Alliance consortium has been a game changer in the use of the technology. In a second part, the network robustness against attacks is investigated from a graph point of view, as well as the distribution of internal activity among users. Addresses of great influence were identified, and allowed to formulate conjectures on the current usage of this technology.
Digital banking as an essential service can be hard to access in remote, rural regions where the network connectivity is unavailable or intermittent. The payment operators like Visa and Mastercard often face difficulties reaching these remote, rural areas. Although micro-banking has been made possible by short message service or unstructured supplementary service data messages in some places, their security flaws and session-based nature prevent them from wider adoption. Global-level cryptocurrencies enable low-cost, secure, and pervasive money transferring among distributed peers, but are still limited in their ability to reach people in remote communities. We propose a blockchain-based digital payment scheme that can deliver reliable services on top of unreliable networks in remote regions. We focus on a scenario where a community-run base station provides reliable local network connectivity while intermittently connects to the broader Internet. We take advantage of the distributed verification guarantees of the Blockchain technology for financial transaction verification and leverage smart contracts for secure service management. In the proposed system, payment operators deploy multiple proxy nodes that are intermittently connected to the remote communities where the local blockchain networks, such as Ethereum are composed of miners, vendors, and regular users. Through probabilistic modeling, we devise design parameters for the blockchain network to realize robust operation over the top of the unreliable network. Furthermore, we show that the transaction processing time will not be significantly impacted due to the network unreliability through extensive emulations on a private Ethereum network. Finally, we demonstrate the practical feasibility of the proposed system by developing Near Field Communication (NFC)-enabled payment gateways on Raspberry-Pis, a mobile wallet application and mining nodes on off-the-shelf computers.
Permission-less blockchains can realise trustless trust, albeit at the cost of limiting the complexity of computation tasks. To explain the implications for scalability, we have implemented a trust model for smart contracts, described as agents in an open multi-agent system. Agent intentions are not necessarily known and autonomous agents have to be able to make decisions under risk. The ramifications of these general conditions for scalability are analysed for Ethereum and then generalised to other current and future platforms.
Consensus protocols inherently rely on the notion of leader election, in which one or a subset of participants are temporarily elected to authorize and announce the network's latest state. While leader election is a well studied problem, the rise of distributed ledgers (i.e., blockchains) has led to a new perspective on how to perform large-scale leader elections via solving a computationally difficult puzzle (i.e., proof of work). In this paper, we present Caucus, a large-scale leader election protocol with minimal coordination costs that does not require the computational cost of proof-of-work. We evaluate Caucus in terms of its security, using a new model for blockchain-focused leader election, before testing an implementation of Caucus on an Ethereum private network. Our experiments highlight that one variant of Caucus costs only $0.10 per leader election if deployed on Ethereum.