The mechanism of peers randomly choosing logical neighbors without any knowledge about underlying physical topology can cause a delay overhead in information propagation which makes the system vulnerable to double spend attacks. This paper introduces a proximity-aware extensions to the current Bitcoin protocol, named Master Node Based Clustering (MNBC). The ultimate purpose of the proposed protocol is to improve the information propagation delay in the Bitcoin network.
The number of Internet of Things devices is growing dramatically, generating a huge amount of data which is becoming a valuable asset for data analysts. This trend culminates towards the creation of an IoT data marketplace, where streams of data from heterogeneous sources are sent in real time to various data consumers and are metered for monetization purposes. Publish/subscribe systems, such as Message Queuing Telemetry Transport (MQTT), are a promising solution to act as a transport layer for real-time data streams in a decoupled and large scale manner. However, pub/sub systems lack two key properties for an IoT data marketplace: (1) it does not provide any monetization logic; (2) it assumes that the pub/sub brokers are trusted entities, which is not the case in a decentralized or federated marketplace setting. In this paper, we address these issues using a reliable and transparent monetization system based on Distributed Ledger Technology (DLT) and smart contracts. We propose three monetization solutions and demonstrate the trade-off between the overhead of tracking IoT data on a blockchain vs. the accuracy of the monetization for data producers and consumers. In particular, we provide a Bloom filter-based solution for efficient verification of data exchange. We implement our system using Ethereum and Solidity and evaluate with respect to contract gas cost.
Blockchain is a public distributed ledger, which has the characteristics of decentralization and anonymization, which leads to the frequent occurrence of money laundering and theft. Taking Bitcoin as an example, traders can have multiple addresses, and these addresses have nothing to do with their identities in real life, their identities are difficult to identify, and it is difficult to track the flow of transaction funds on the blockchain. This paper proposes a transaction tracking system that can effectively and accurately track the source and destination of a certain amount of funds on the blockchain, which is superior to existing Bitcoin transaction tracking methods and has a substantial reference value.
Distributed networks have been widely studied in literature. However, the blockchain paradigm has inspired to revisit some of the results under a different point of view. In this paper, we analyze the "classic" spam protection problem applied to the IOTA Tangle, a distributed ledger technology which addresses Bitcoin's (monetary and energy) efficiency issues through the absence of mining pools. However, the lack of miners makes the network vulnerable to denial of service attacks. We propose an anti spam mechanism based on the solution of a cryptographic puzzle: When a node wants to generate a new transaction, it dynamically adapts the difficulty of the puzzle depending on its target throughput and on its reputation score. Specifically, the adaptive difficulty property guarantees that any node, even with low hashing power, can achieve similar throughput for a given reputation. In the paper, we prove this claim both analytically and through simulations, and we show that fairness between low- and high-power nodes is indeed reached.
It is a well-known fact that innovative e-learning concepts have pushed IT technologies to new levels of development or, reciprocally, innovative or even disrupting technologies have opened new possibilities for elearning. There are many examples of IT technologies that contributed to new or improved learning paradigms and styles, such as social networks, mobile devices, augmented and virtual reality, MOOCs and distributed computing. Recently, several research works discuss how the blockchain concepts and technologies can be applied not only in cryptocurrency, but also on elearning and educational processes with an essential impact, e.g. de-centralization of resources, open learning, tokenization of elearning, authenticity and security of information and resources. The current research paper will address how blockchain can be utilized with microservice based architectures, based on similarities, to support the most modern trends in education, such as open learning communities. In the first part of the paper, the main concepts and mechanisms behind the blockchain technologies are reviewed and explained in comparison with concepts and characteristics of microservices, considered a similar architectural pattern. Blockchain relies on the existing algorithms (such as cryptography) and distributed computing to bring new concepts such as ledgers and smart contracts. Likewise, microservices have roots on Service-Oriented Architecture (SOA) and Application Programming Interfaces (API). Microservices represent a new arhitectural pattern, to change the traditional way of software development resulting in "application monoliths" to a true modularization by means of composition of standalone software components (microservices), having well-defined functionality, securely exposed to other microservices or applications. In the second part, a software architecture leveraging blockchain smart contract and microservices to support open learning communities, unique identity, secure storage and retrieval of resources will be proposed and described.
Distributed ledgers are a new type of database technology that allows open access to data stored across distributed, decentralised, publicly maintained infrastructures. Current implementations of the such ledgers expect competition between participants, are often energy hungry, poor in maintaining the natural structure of data and suffer from scalability constraints. The aim of my research work is to develop a distributed ledger-based middleware for data modelling and collection on household energy generation and use, while addressing scalability and energy inefficiency concerns of the ledger for this particular application domain. The energy data collected and made available through this middleware will be used for digital energy service delivery (e.g., automated peer to peer energy trading, topological estimations, etc.). The middleware also provides a platform for a consumer focused digital energy service delivery, as well as service model evaluation. The model evaluation will enable the prospective service users to evaluate the suitability of the given service for their needs before making a decision of service subscription.
Roberta Galici, Laura Ordile, Michele Marchesi, Andrea Pinna · 5 authors
We present a novel strategy, based on the Extract, Transform and Load (ETL) process, to collect data from a blockchain, elaborate and make it available for further analysis. The study aims to satisfy the need for increasingly efficient data extraction strategies and effective representation methods for blockchain data. For this reason, we conceived a system to make scalable the process of blockchain data extraction and clustering, and to provide a SQL database which preserves the distinction between transaction and addresses. The proposed system satisfies the need to cluster addresses in entities, and the need to store the extracted data in a conventional database, making possible the data analysis by querying the database. In general, ETL processes allow the automation of the operation of data selection, data collection and data conditioning from a data warehouse, and produce output data in the best format for subsequent processing or for business. We focus on the Bitcoin blockchain transactions, which we organized in a relational database to distinguish between the input section and the output section of each transaction. We describe the implementation of address clustering algorithms specific for the Bitcoin blockchain and the process to collect and transform data and to load them in the database. To balance the input data rate with the elaboration time, we manage blockchain data according to the lambda architecture. To evaluate our process, we first analyzed the performances in terms of scalability, and then we checked its usability by analyzing loaded data. Finally, we present the results of a toy analysis, which provides some findings about blockchain data, focusing on a comparison between the statistics of the last year of transactions, and previous results of historical blockchain data found in the literature. The ETL process we realized to analyze blockchain data is proven to be able to perform a reliable and scalable data acquisition process, whose result makes stored data available for further analysis and business.
Abstract The inability to scale is one of the most concerning problems looming in blockchain systems, where every node has to store all contents of the ledger database locally, leading to centralization and higher operation costs. In this paper, we propose a model named virtual block group (VBG), which aims at addressing the node storage scalability problem. Adopting the VBG model, each node only needs to store part of block data and saves the VBG storage index to distributed hash table by taking block data as a resource, thus improving the query efficiency of block data. With the incentive mechanism of block data storage, and the storage verification and audit mechanism of block data, the security and reliability of block data storage can be ensured. The analysis and calculation show that this model saves hard drive storage space of the node to a greater extent with a shorter time of requesting block data, in the premise of ensuring secure and reliable block data. Compared to other technologies such as sharding, our model does not change the consensus mechanism or the network topology and retains the reliability and security of the original blockchain system.
We consider two different continuous-time Markov chain models recently studied in Göbel et al.[8 Göbel, J.; Keeler, H. P.; Krzesinski, A. E.; Taylor, P. G. Bitcoin blockchain dynamics: The selfish-mine strategy in the presence of propagation delay. Perform. Eval. 2016, 104, 23–41. DOI: 10.1016/j.peva.2016.07.001.[Crossref], [Web of Science ®] , [Google Scholar]], which were created to model the interactions between a small pool of miners, and a larger collection of miners, within the Bitcoin network. The first model we discuss represents the case where all miners behave honestly and follow the Bitcoin protocol, while the second model represents the case where the smaller pool of miners use the Selfish Mining strategy of Eyal and Sirer[3 Eyal, I.; Sirer, E. G. Majority is not enough: Bitcoin mining is vulnerable. In Financial Cryptography and Data Security; Springer, Berlin, 2013; 436–454. [Google Scholar]]. We give a new derivation of the stationary distribution of the process in the honest mining case and further build on the results of Göbel et al.[8 Göbel, J.; Keeler, H. P.; Krzesinski, A. E.; Taylor, P. G. Bitcoin blockchain dynamics: The selfish-mine strategy in the presence of propagation delay. Perform. Eval. 2016, 104, 23–41. DOI: 10.1016/j.peva.2016.07.001.[Crossref], [Web of Science ®] , [Google Scholar]] by showing that the normalizing constant can be expressed in closed-form. We also use similar techniques to derive expressions for the Laplace transforms of the transition functions. We then illustrate how these techniques yield similar expressions for the stationary distribution of the process when the smaller pool implements Selfish Mining: the Laplace transforms of the transition functions can be calculated as well. Lastly, we briefly explain how our methods can be extended to more general models of a similar type.
Martin Martinez, Arvin Hekmati, Bhaskar Krishnamachari, Seokgu Yun
We present a novel “Proof of Social Contact” approach to Sybil control that utilizes the analysis of digitally signed information about digitally signed pairwise encounters between mobile devices that are logged in a distributed ledger. To illustrate the approach, we show examples of analysis using binary classification techniques under two different adversary detection models, and evaluate them using a real-world mobile device encounter trace. We discuss a number of open problems and future directions that could be pursued by researchers in the field to realize and improve such a system and build on top of it.
Yuechen Tao, Bo Li, Jingjie Jiang, Hok Chu Ng · 6 authors
Current blockchain systems suffer from a number of inherent drawbacks in its scalability, latency, and processing throughput. By enabling parallel confirmations of transactions, sharding has been proposed to mitigate these drawbacks, which usually requires frequent communication among miners through a separate consensus protocol.In this paper, we propose, analyze, and implement a new distributed and dynamic sharding system to substantially improve the throughput of blockchain systems based on smart contracts, while requiring minimum cross-shard communication. Our key observation is that transactions sent by users who only participate in a single smart contract can be validated and confirmed independently without causing double spending. Therefore, the natural formation of a shard is to surround one smart contract to start with. The complication lies in the different sizes of shards being formed, in which a small shard with few transactions tends to generate a large number of empty blocks resulting in a waste of mining power, while a large shard adversely affects parallel confirmations. To overcome this problem, we propose an inter-shard merging algorithm with incentives to encourage small shards to merge with one another and form a larger shard, an intra-shard transaction selection mechanism to encourage miners to select different subsets of transactions for validation, as well as a parameter unification method to further improve these two algorithms to reduce the communication cost and improve system reliability.We analyze our proposed algorithms using the game theoretic approach, and prove that they converge to a Nash Equilibrium. We also present a security analysis on our sharding design, and prove that it resists adversaries who occupy at most 33% of the computation power. We have implemented our designs on go-Ethereum 1.8.0 and evaluated their performance using both real-world blockchain transactions and large-scale simulations. Our results show that throughput has been improved by 7.2×, and the number of empty blocks has been reduced by 90%.
Bitcoin (BTC) is a type of cryptocurrency that supports transaction/payment of virtual money between BTC users without the presence of a central authority or any third party like bank. It uses some cryptographic techniques namely public- and private-keys, digital signature and cryptographic-hash functions, and they are used for making secure transactions and maintaining distributed public ledger called blockchain. In BTC system, each transaction signed by sender is broadcasted over the P2P (Peer-to-Peer) Bitcoin network and a set of such transactions collected over a period is hashed together with the previous block/other values to form a block known as candidate block, where the first block known as genesis-block was created independently. Before a candidate block to be the part of existing blockchain (chaining of blocks), a computation-intensive hard problem needs to be solved. A number of miners try to solve it and a winner earns some BTCs as inspiration. The miners have high computing and hardware resources, and they play key roles in BTC for blockchain formation. This paper mainly analyses the underlying cryptographic techniques, identifies some weaknesses and proposes their enhancements. For these, two modifications of BTC are suggested ― (i) All BTC users must use digital certificates for their authentication and (ii) Winning miner must give signature on the compressed data of a block for authentication of public blocks/blockchain.
Jean-Marc Seigneur, Sophie Pusterla, Xavier Socquet-Clerc
Relational capital for companies has been theorized and modeled in the past, but so far, no real Web application has tried to bring its value to light, especially concerning the real estate application domain. In this paper, we present the results of our surveys on how the types of relations who have contributed to a product impact price premium and what real estate agencies think about real estate relational value, especially as implemented on our Web marketplace connected to Facebook social network and NEO public blockchain for products certifications transparency.
Summary Topology discovery is a prerequisite when investigating the network properties; with the enormous number of Bitcoin users and performance issues, it becomes critical to analyse the network in a fashion that makes it possible to detect all Bitcoin's nodes and understand their behaviour. In massive, dynamic, and distributed peer‐to‐peer (P2P) networks like Bitcoin, where thousands of updates occur per second, it is hard to obtain an accurate topology representing the structure of the network as a graph with nodes and links by using the traditional local measurement approaches based on batches, offline data, or on the discovery of the topology around a small set of nodes and then combine them to discover an approximate network topology. All of which present some limitation when applying them on blockchain‐based networks. In this paper, we propose a topology discovery system that performs a real‐time data collection and analysis for Bitcoin P2P links, which assembles incoming nodes information for deeper graph analysis processing. The topology discovery system allows us to gain knowledge on the Bitcoin network size, the network stability in terms of reachable, churn, and well‐connected nodes, as well as some data regarding the effects of some countries' Internet infrastructure on Bitcoin traffic.
Scalability has been a bottleneck for major blockchains such as Bitcoin and Ethereum. Despite the significantly improved scalability claimed by several high-profile blockchain projects, there has been little effort to understand how their transactional throughput is being used. In this paper, we examine recent network traffic of three major high-scalability blockchains---EOSIO, Tezos and XRP Ledger (XRPL)---over a period of seven months. Our analysis reveals that only a small fraction of the transactions are used for value transfer purposes. In particular, 96% of the transactions on EOSIO were triggered by the airdrop of a currently valueless token; on Tezos, 76% of throughput was used for maintaining consensus; and over 94% of transactions on XRPL carried no economic value. We also identify a persisting airdrop on EOSIO as a DoS attack and detect a two-month-long spam attack on XRPL. The paper explores the different designs of the three blockchains and sheds light on how they could shape user behavior.
Distributed Ledger Technologies are one of the pillars of future technologies, prognozing to have a great impact to many aspects of our lives, including social, economic, juristic, security and many others. Bitcoin is still the most popular blockchain currency, but the opportunities to use Distribute Ledger Technologies are much more wide, outperforming financial applications as most known and popular. Besides blockchains, there are also other architectures of Distributed Ledger Technologies. This paper observes and analyses one technology as a very strong alternative to blockchains: hashgraphs, which are promising to outperform blockchains, but also tangles. Basis of their architecture and functionality will be explained and directions and prognosis of the further development will be given. The main paper contribution is a comparison of a hashgraph technology to its concurrent architectures, i.e. blockchains and tangles, considering different segments and different properties that define a quality of Distributed Ledgers.
Saeideh G. Motlagh, Jelena Mišić, Vojislav B. Mišić
The aim of this work is to evaluate the impact of node churn -nodes leaving and rejoining the network- on the Bitcoin network. We provide a comprehensive analytical model for the churning process. We use a Continuous Time Markov Chain (CTMC) to describe the behavior of a node, and then apply the results to model the changes in connectivity and the impact on network performance. We analyze the time needed to resynchronize a node upon rejoining the network and find that sleep times of the order of hours require synchronization times limited by a minute. We estimate the impact of sleep and synchronization time on overall network connectivity and block/transaction distribution time. Our results show that networks with less than 4000 nodes are sensitive to churn. This occurs due to opposing impact of decrease in network size (and diameter) due to sleep time and increase of communication load per node. However, the impact of churn on network with more than 4000 nodes is noticeable but small enough to make a large Bitcoin network fairly resilient to churn.
The blockchain paradigm provides a mechanism for content dissemination and distributed consensus on Peer-to-Peer (P2P) networks. While this paradigm has been widely adopted in industry, it has not been carefully analyzed in terms of its network scaling with respect to the number of peers. Applications for blockchain systems, such as cryptocurrencies and IoT, require this form of network scaling. In this paper, we propose a new stochastic network model for a blockchain system. We identify a structural property called \emph{one-endedness}, which we show to be desirable in any blockchain system as it is directly related to distributed consensus among the peers. We show that the stochastic stability of the network is sufficient for the one-endedness of a blockchain. We further establish that our model belongs to a class of network models, called monotone separable models. This allows us to establish upper and lower bounds on the stability region. The bounds on stability depend on the connectivity of the P2P network through its conductance and allow us to analyze the scalability of blockchain systems on large P2P networks. We verify our theoretical insights using both synthetic data and real data from the Bitcoin network.
As eBook readers have expanded on the market, various online eBook markets have arisen as well. Currently, the online eBook market consists of at least publishers and online platform providers and authors, and these actors inevitably incur intermediate costs between them. In this paper, we introduce a blockchain-based eBook market system that enables self-published eBook trading and direct payments from readers to authors without any trusted party; because authors publish themselves and readers purchase directly from authors, neither actor incurs any intermediate costs. However, because of this trustless environment, the validity, ownership and intellectual property of digital contents cannot be verified and protected, and the safety of purchase transactions cannot be ensured. To address these shortcomings, we propose a secure and reliable eBook transaction system that satisfies the following security requirements: (1) verification of the ownership of each eBook, (2) confidentiality of eBook contents, (3) authorization of a right to read a book, (4) authentication of a legitimate purchaser, (5) verification of the validity and integrity of eBook contents, (6) safety of direct purchase transactions, and (7) preventing eBook piracy and illegal distribution. We provide practical cryptographic protocols for the proposed system and analyze the security and simulated performance of the proposed schemes.
Open access
Blockchain Technology Applications and Security
Advanced Steganography and Watermarking Techniques
Suyash Gupta, Sajjad Rahnama, Jelle Hellings, Mohammad Sadoghi
Recent developments in blockchain technology have inspired innovative new designs in resilient distributed and database systems. At their core, these blockchain applications typically use Byzantine fault-tolerant consensus protocols to maintain a common state across all replicas, even if some replicas are faulty or malicious. Unfortunately, existing consensus protocols are not designed to deal with geo-scale deployments in which many replicas spread across a geographically large area participate in consensus. To address this, we present the Geo-Scale Byzantine FaultTolerant consensus protocol (GeoBFT). GeoBFT is designed for excellent scalability by using a topological-aware grouping of replicas in local clusters, by introducing parallelization of consensus at the local level, and by minimizing communication between clusters. To validate our vision of high-performance geo-scale resilient distributed systems, we implement GeoBFT in our efficient ResilientDB permissioned blockchain fabric. We show that GeoBFT is not only sound and provides great scalability, but also outperforms state-of-the-art consensus protocols by a factor of six in geo-scale deployments.
Saeideh G. Motlagh, Jelena Mišić, Vojislav B. Mišić
In this work, we present an analytical model for the churning process in Bitcoin network. We model the churning process for ordinary (non-gateway) nodes with homogeneous sleep time using Continuous Time Markov Chain. Within performance results, we present mean synchronization time needed when nodes come back from sleep and block distribution time in presence of churning nodes. Our results indicate that sleep times of the order of several hours require synchronization times in the order of a minute. Also, a large number of churning nodes can significantly affect the distribution power of the Bitcoin network.
We present eclipse attacks on Ethereum nodes that exploit the peer-to-peer network used for neighbor discovery. Our attacks can be launched using only two hosts, each with a single IP address. Our eclipse attacker monopolizes all of the victim’s incoming and outgoing connections, thus isolating the victim from the rest of its peers in the network. The attacker can then filter the victim’s view of the blockchain, or co-opt the victim’s computing power as part of more sophisticated attacks. We argue that these eclipse-attack vulnerabilities result from Ethereum’s adoption of the Kademlia peer-to-peer protocol, and present countermeasures that both harden the network against eclipse attacks and cause it to behave differently from the traditional Kademlia protocol. Several of our countermeasures have been incorporated in the Ethereum geth 1.8 client released on February 14, 2018.