Proof of Work systems are used in cryptocurrencies to obtain consensus in distributed peer-to-peer systems that share no trust. Miners of cryptocurrency compete by engaging in the Proof of Work to solve a cryptographic challenge. The first to successfully provide a solution to the challenge wins by minting new currency. The process of mining also simultaneously prevents double-spending through the creation of an append-only distributed database known as the blockchain. The most widely adopted Proof of Work is the Hashcash scheme and the most widely deployed miners are ASIC-based. Despite the popularity of Hashcash, two issues are commonly identified its use. Firstly, the high energy consumption of the scheme is perceived as wasteful because the solutions found provide no useful output, and secondly, the computational complexity class of the scheme is not formally known. Based on these deficiencies, we propose a novel Proof of Work system which achieves the following goals:
In recent years, the increasing concerns around the centralized cloud web services (e.g. privacy, governance, surveillance, security) have triggered the emergence of new distributed technologies, such as IPFS or the Blockchain. These innovations have tackled technical challenges that were unresolved until their appearance. Existing models of peer-to-peer systems need a revision to cover the spectrum of potential systems that can be now implemented as peer-to-peer systems. This work presents a framework to build these systems. It uses an agent-oriented approach in an open environment where agents have only partial information of the system data. The proposal covers data access, data discovery and data trust in peer-to-peer systems where different actors may interact. Moreover, the framework proposes a distributed architecture for these open systems, and provides guidelines to decide in which cases Blockchain technology may be required, or when other technologies may be sufficient.
Florian Wessling, Christopher Ehmke, Marc Hesenius, Volker Gruhn
Adding blockchain technology to existing systems instead of building them from the ground up poses several challenges. It is difficult to find out which attributes of blockchains are important for a given use case (e.g. immutable, trustless, anonymous) and to decide which elements of an architecture should employ blockchain technologies. Current approaches generally only give a hint on whether blockchain technology makes sense for a given use case or not. This paper proposes a more fine-grained approach to decide which elements of an application architecture could benefit from the use of blockchain technology. We illustrate the first outline of our approach which identifies participants, their trust relations and interactions to derive a hybrid architecture (i.e., an architecture embedding blockchain technology in existing software systems or creating new systems using blockchain only in certain parts).
Even though blockchain is mostly popular for its cryptocurrency, smart contracts have become a very prominent blockchain application. Smart contracts are like classes that can be called by client applications outside the blockchain. Therefore it is possible to develop blockchain-oriented software (BOS) that implements part of the business logic in the blockchain by using smart contracts. Currently, there is no design standard to model BOS. Since modeling is an important part of designing a software, developers may struggle to plan their BOS. In this paper, we show three complementary modeling approaches based on well-known software engineering models and apply them to a BOS example. Our goal is to start the discussion on specialized blockchain modeling notations.
Santiago Bragagnolo, Henrique Rocha, Marcus Denker, Sté́phane Ducasse
Blockchains store a massive amount of heterogeneous data which will only grow in time. When searching for data on the Ethereum platform, one is required to either access the records (blocks) directly by using a unique identifier, or sequentially search several records to find the desired information. Therefore, we propose the Ethereum Query Language (EQL), a query language that allows users to retrieve information from the blockchain by writing SQL-like queries. The queries provide a rich syntax to specify data elements to search information scattered through several records. We claim that EQL makes it easier to search, acquire, format, and present information from the blockchain.
We review the so called selfish mining strategy in the Bitcoin network and compare its profitability to honest mining.We build a rigorous profitability model for repetition games. The time analysis of the attack has been ignored in the previous literature based on a Markov model,but is critical. Using martingale's techniques and Doob Stopping Time Theorem we compute the expected duration of attack cycles. We discover a remarkable property of the bitcoin network: no strategy is more profitable than the honest strategy before a difficulty adjustment. So selfish mining can only become profitable afterwards, thus it is an attack on the difficulty adjustment algorithm. We propose an improvement of Bitcoin protocol making it immune to selfish mining attacks. We also study miner's attraction to selfish mining pools. We calculate the expected duration time before profit for the selfish miner, a computation that is out of reach by the previous Markov models.
In this work, we present a low-latency partition tolerant distributed ledger using a novel directed acyclic graph (DAG) structure. By forcing information to be published at specific deterministic locations, we avoid complex consensus algorithms and eliminate confirmation periods. We implement our DAG over a fully decentralized overlay network, leveraging BitTorrent concepts for peer-to-peer (P2P) rendezvous and block propagation. We compute overall expected latency using Erd¨os-R´enyi random graph models and present initial proof-of-concept software. The resulting work will allow anyone to create fully decentralized services (records, databases, etc.) resistant to attack, manipulation, and censorship.
The past decade has witnessed the rapid evolution in blockchain technologies, which has attracted tremendous interests from both the research communities and the industry. The blockchain network was originated in the Internet finical sector as a decentralized, immutable ledger system for transactional data ordering. Nowadays, it is envisioned as a powerful backbone/framework for decentralized data processing and data-driven self-organization in flat, open-access networks. In particular, the plausible characteristics of decentralization, immutability and self-organization are primarily owing to the unique decentralized consensus mechanisms introduced by blockchain networks. This survey is motivated by the lack of a comprehensive literature review on the development of decentralized consensus mechanisms in blockchain networks. In this survey, we provide a systematic vision of the organization of blockchain networks. By emphasizing the unique characteristics of incentivized consensus in blockchain networks, our in-depth review of the state-of-the-art consensus protocols is focused on both the perspective of distributed consensus system design and the perspective of incentive mechanism design. From a game-theoretic point of view, we also provide a thorough review on the strategy adoption for self-organization by the individual nodes in the blockchain backbone networks. Consequently, we provide a comprehensive survey on the emerging applications of the blockchain networks in a wide range of areas. We highlight our special interest in how the consensus mechanisms impact these applications. Finally, we discuss several open issues in the protocol design for blockchain consensus and the related potential research directions.
Doriane Perard, Jérôme Lacan, Yann Bachy, Jonathan Detchart
The concept of a decentralized ledger usually implies that each node of a blockchain network stores the entire blockchain. However, in the case of popular blockchains, which each weigh several hundreds of GB, the large amount of data to be stored can incite new or low-capacity nodes to run lightweight clients. Such nodes do not participate to the global storage effort and can result in a centralization of the blockchain by very few nodes, which is contrary to the basic concepts of a blockchain. To avoid this problem, we propose new low storage nodes that store a reduced amount of data generated from the blockchain by using erasure codes. The properties of this technique ensure that any block of the chain can be easily rebuild from a small number of such nodes. This system should encourage low storage nodes to contribute to the storage of the blockchain and to maintain decentralization despite of a globally increasing size of the blockchain. This system paves the way to new types of blockchains which would only be managed by low capacity nodes.
Distributed Ledger Technology (DLT) is probably going, in the near future, to disrupt B2B and B2C interactions even more than the advent of the World Wide Web, thanks to the transfer of trust from personal and commercial relationships to computing algorithms. However, a less commonly perceived property of DLT is that of enabler of decentralized computing. In this paper, we explore the use of DLT to innovate Industrial Cyber-Physical Systems.
Eleftherios Kokoris-Kogias, Philipp Jovanovic, Linus Gasser, Nicolas Gailly · 6 authors
Designing a secure permissionless distributed ledger (blockchain) that performs on par with centralized payment processors, such as Visa, is a challenging task. Most existing distributed ledgers are unable to scale-out, i.e., to grow their total processing capacity with the number of validators; and those that do, compromise security or decentralization. We present OmniLedger, a novel scale-out distributed ledger that preserves longterm security under permissionless operation. It ensures security and correctness by using a bias-resistant public-randomness protocol for choosing large, statistically representative shards that process transactions, and by introducing an efficient cross-shard commit protocol that atomically handles transactions affecting multiple shards. OmniLedger also optimizes performance via parallel intra-shard transaction processing, ledger pruning via collectively-signed state blocks, and low-latency "trust-but-verify" validation for low-value transactions. An evaluation of our experimental prototype shows that OmniLedger's throughput scales linearly in the number of active validators, supporting Visa-level workloads and beyond, while confirming typical transactions in under two seconds.
Bitcoins and Blockchain technologies are attracting the attention of different scientific communities. In addition, their widespread industrial applications and the continuous introduction of cryptocurrencies are also stimulating the attention of the public opinion. The underlying structure of these technologies constitutes one of their core concepts. In particular, they are based on peer-to-peer networks. Accordingly, all nodes lie at the same level, so that there is no place for privileged actors as, for instance, banking institutions in classical financial networks. In this work, we perform a preliminary investigation on two kinds of network, i.e. the Bitcoin network and the Bitcoin Cash network. Notably, we analyze their global structure and we try to evaluate if they are provided with a small-world behavior. Results suggest that the principle known as 'fittest-gets-richer', combined with a continuous increasing of connections, might constitute the mechanism leading these networks to reach their current structure. Moreover, further observations open the way to new investigations into this direction.
Bitcoins and Blockchain technologies are attracting the attention of different scientific communities. In addition, their widespread industrial applications and the continuous introduction of cryptocurrencies are also stimulating the attention of the public opinion. The underlying structure of these technologies constitutes one of their core concepts. In particular, they are based on peer-to-peer networks. Accordingly, all nodes lie at the same level, so that there is no place for privileged actors as, for instance, banking institutions in classical financial networks. In this work, we perform a preliminary investigation on two kinds of network, i.e. the Bitcoin network and the Bitcoin Cash network. Notably, we analyze their global structure and we try to evaluate if they are provided with a small-world behavior. Results suggest that the principle known as 'fittest-gets-richer', combined with a continuous increasing of connections, might constitute the mechanism leading these networks to reach their current structure. Moreover, further observations open the way to new investigations into this direction.
In this tutorial, I survey some of the private blockchain systems with respect to their architectures in general and their approaches to some specific technical areas. Specifically, I focus on how the functionality of traditional and modern data stores are being utilized or not utilized in the different blockchain systems.
Building blockchain-oriented applications forces developers to rethink the architecture of their software from the ground up. The use of blockchain technology poses multiple challenges as the software is operated in a decentralized, trustless, transparent and tamper-proof environment. When building decentralized apps the developers need to deal with blockchain properties such as decentralization, a certain delay in the execution of function calls of distributed code contracts and particularly need to consider how users interact with their application. We surveyed several existing decentralized apps and examined their architecture to identify multiple reoccurring architectural patterns, each with different implications regarding the trust, user experience and security. As building blockchain-oriented applications is gaining importance, models, tools and methods for blockchain-oriented software engineering have to be developed. This paper gives a first hint towards architectural patterns for blockchain-based applications and motivates why it is important to consider how the user interacts with the decentralized apps.
The current web 2.0 is about connecting people. In which the social media platforms were invented, and the concentration of development was focused on the application layer. There are different approaches to think about web 3.0, some; would say the future is when we have a semantic web others would argue that the future is the virtual web. In this paper, we will talk about another direction to think about the future web called the decentralized web. To enhance the web, we should be concerned with solving the problems that we have and the problems that these platforms have created. The decentralized web is focused on developing protocols and the underlying technologies that are not noticed by end users. This paper gives an overview of the challenges in the current web 2.0. Describes the decentralized web, and what are the technologies that are in development now.
The phenomenal growth of Internet-services has created a vibrant new domain for sharing economy. Millions of users around the world share personal services and possessions with others - often complete strangers. Such sharing schemes also increase the risk of violation of one's informational and physical privacy. Strangers often have to trust each other with their privacy (e.g. a surveillance camera in an Airbnb room). However, very little research has been devoted to investigate privacy in sharing economy. In this paper, we explore the privacy concerns associated with contractual renting or leasing of IoT devices-enabled home. We propose a methodology to eliminate privacy threats from IoT-enabled telematics devices in a smart home via blockchain-based smart contract. For the purpose of illustration, we focus on how we can circumvent the privacy threat from indoor surveillance IP cameras in a smart home-sharing economy.
Alexander Yakubov, Wazen M. Shbair, Anders Wallbom, David Sanda · 5 authors
Public-Key Infrastructure (PKI) is the cornerstone technology that facilitates secure information exchange over the Internet. However, PKI is exposed to risks due to potential failures of Certificate Authorities (CAs) that may be used to issue unauthorized certificates for end-users. Many recent breaches show that if a CA is compromised, the security of the corresponding end-users will be in risk. As an emerging solution, Blockchain technology potentially resolves the problems of traditional PKI systems - in particular, elimination of single point-of-failure and rapid reaction to CAs shortcomings. Blockchain has the ability to store and manage digital certificates within a public and immutable ledger, resulting in a fully traceable history log. In this paper we designed and developed a blockchain-based PKI management framework for issuing, validating and revoking X.509 certificates. Evaluation and experimental results confirm that the proposed framework provides more reliable and robust PKI systems with modest maintenance costs.
Paul Dunphy, Luke Garratt, Fabien A. P. Petitcolas
Distributed Ledger Technology (DLT) has been proposed as a new way to incorporate decentralization into a wide range of digital infrastructures. Applications of DLT to digital identity are increasing in prevalence, with a recent survey reporting that 55% of DLT technologies in development track digital identity. However, while proofs of concept, open source software, and new ideas are readily available, it is still unclear the extent to which DLT can play a role to underpin new forms of digital identity. In this position paper, we situate this fast-moving application domain into the broader challenges faced in digital identity, with the aim to highlight the socio-technical nature of the challenge at hand, and to propose directions for future research.
Our paper presents on an information dissemination model for scholars on cryptocurrencies. The objectives are to review the existing information dissemination models, identify known factors influencing information dissemination process, and propose an information dissemination model for scholars on cryptocurrencies. The research questions are on why the epidemic models could be used for understanding cryptocurrencies, what are the known factors influencing the relevant information dissemination model, and how could information spreading model on cryptocurrencies work for scholars. We explored the epidemic models and their influencing factors on cryptocurrencies through a survey of literature. We found that the epidemic model can describe the information spreading for scholars on cryptocurrencies. We have added the activities triggering the S-I-E-R model.
Blockchain is a distributed ledger system based on P2P network and originally used for a crypto currency system. The P2P network of Blockchain is maintained by full nodes which are in charge of verifying all the transactions in the network. However, most Blockchain user nodes do not act as full nodes, because workload of full nodes is quite high for personal mobile devices. Blockchain search queries, such as confirming balance, transaction contents, and transaction histories, from many users go to the full nodes. As a result, search throughput of full nodes would be a new bottleneck of Blockchain system, because the number of full nodes is less than the number of users of Blockchain systems. In this paper, we propose an acceleration method of Blockchain search using GPUs. More specifically, we introduce an array-based Patricia tree structure suitable for GPU processing so that we can make effective use of Blockchain feature that there are no update and delete queries. In the evaluations, the proposed method is compared with an existing GPU-based key-value search and a conventional CPU-based search in terms of the throughput of Blockchain key search. As a result, the throughput of our proposal is 3.4 times higher than that of the existing GPU-based search and 14.1 times higher than that of the CPU search when the number of keys is 80 ×2^20 and the key length is 256-bit in Blockchain search queries.
Mar 1, 2018·2018 Internat2018 International Conference on Computation of Power, Energy, Information and Communication (ICCPEIC)ional conference on computation of power, energy, Information and Communication (ICCPEIC)
Cryptocurrencies have transpired as one of the trending financial software systems. They depend on a secure and consigned ledger data structure; mining being an indispensable part of such systems. Mining reconsiliates records of past transactions to the distributed register known as the Blockchain, that allows users to reach secure, robust and concord for each transaction. Mining also introduces wealth in the form of new units of currency named as “bitcoins”. Cryptocurrencies lack a central delegate or authority to mediate transactions because they were designed as peer to-peer end sub-systems. They rely on miners to validate and scrutinize their transactions. Hence Cryptocurrencies require a strong, secure mining algorithms. In this article we survey, compare and contrast the current mining techniques as used by major Cryptocurrencies. We scrutinize the strengths, weaknesses, and possible threats to mining strategy. Overall, a perspective on how Cryptocurrencies mine the datasets, where they have comparable performance and assurance, and where they have unique threats and strengths are outlined.
Blockchains have revolutionized the storage of data in an immutable, transparent and non-centralized way. However, public blockchain systems like the Bitcoin system face a problem of scalability, primarily due to the significant and growing size of its blockchain. This paper introduces a method, termed block summarization, which reduces blockchain storage overhead for systems having transferable transactions. The proposed method allows resource-restricted light nodes to store a form of the blockchain such that it can validate the transactions independently which ultimately reduce dependency on full nodes. This way, we can achieve a middle ground between Simplified Payment Verification (SPV) nodes which can only verify the membership of a transaction in the blockchain, and full nodes with pruning enabled which can only support pruning provided they have an infrastructure of full nodes. We implemented our algorithm for a custom blockchain using Bitcoin blocks and were able to achieve a compression ratio of 0.54.
In the era of digitalization, crypto-currency has become the talk of the town and Bitcoin is one of it. Bitcoin System is not controlled by any central authority or governed by any management division. Bitcoin is the first digital decentralized currency and its economic growth has encompassed to billions of dollars within a few years. In this paper we present detailed Introduction to the digital currency including the crypto-currency, then we present Bitcoin system in depth with the process of transactions, mining, miners' pooling. As we know that the popularity of Bitcoin is increasing day by day so are the attacks. We present an analysis of major attacks in the Bitcoin system such as eclipse attack, Sybil attack, >51% attack, selfish mining. More importantly, we present how these attacks play an important role for the attackers in order to receive unfair incentives or fraud the honest users. The current researchers are focusing on creating new protocols as defensive measures for the attacks; we also analyze the security of these protocols.