Julien Hatin, E. Bertin, Baptiste Hemery, Nour El Madhoun
Blockchain technology has gained increasing attention from research and industry over the recent years. This interest is mainly due to its core property that allows users to perform transactions without a Trusted Third Party (TTP), while offering a transparent and fully protected tracking of these transactions. However, there is a lack of reference models to describe and compare various Blockchain technologies, leading to some confusion between different kinds of solutions. We propose in this paper a reference model aiming to assess and compare different kind of Blockchain-based ecosystems, including Decentralized Applications (DApp).
Zlate Dodevski, Sonja Filiposka, Anastas Mishev, Vladimir Trajkovik
Sensitivity of the health-related data and the focus on compliance and security has traditionally emphasized the need for centralized approach while implementing Electronic Health Records (EHR) systems. These one-institutional architectural designs are leading to fragmented and scattered pieces of valuable data across various data warehouses and silos. Interoperability challenges arise due to the absence of unified data management and exchange mechanisms making the social need for fundamental design changes bigger. The capability of a distributed ledger technology and blockchain to offer immutable, decentralized and cryptographically secured record of transactions throughout a peer-to-peer network can facilitate better collaboration and increased interoperability in the field of health and insurance information exchange processes. The paper examines different approaches and application of blockchain technology and identifies which implementations of components are more suitable and beneficial for the specific eco-system analyzed in the paper. This paper presents alternative way of dealing with information exchange across multiple stakeholders by justifying the use of decentralized approach, distributed access and solution how to comprehensively track and assemble health related data. We propose an architectural design and overview of a specific use case with focus on information exchange processes between health insurance providers and health care organizations, by using blockchain as an underlying technology. The architectural overview and data flows, backed up by sequence diagrams from specific use cases offered in this paper, can serve as a guide to the blockchain technology adoption and initial setup.
Peer-to-peer (p2p) content delivery is promising to provide benefits like cost-saving and scalable peak-demand handling in comparison with conventional content delivery networks (CDNs) and complement the decentralized storage networks such as Filecoin. However, reliable p2p delivery requires proper enforcement of delivery fairness, i.e., the deliverers should be rewarded according to their in-time delivery. Unfortunately, most existing studies on delivery fairness are based on non-cooperative game-theoretic assumptions that are arguably unrealistic in the ad-hoc p2p setting. We for the first time put forth the expressive yet still minimalist securities for p2p content delivery, and give two efficient solutions FairDownload and FairStream via the blockchain for p2p downloading and p2p streaming scenarios, respectively. Our designs not only guarantee delivery fairness to ensure deliverers be paid (nearly) proportional to his in-time delivery, but also ensure the content consumers and content providers to be fairly treated. The fairness of each party can be guaranteed when the other two parties collude to arbitrarily misbehave. Moreover, the systems are efficient in the sense of attaining asymptotically optimal on-chain costs and optimal deliverer communication. We implement the protocols to build the prototype systems atop the Ethereum Ropsten network. Extensive experiments done in LAN and WAN settings showcase their high practicality.
As the typical peer-to-peer distributed networks, blockchain systems require each node to copy a complete transaction database, so as to ensure new transactions can by verified independently. In a blockchain system (e.g., bitcoin system), the node does not rely on any central organization, and every node keeps an entire copy of the transaction database. However, this feature determines that the size of blockchain transaction database is growing rapidly. Therefore, with the continuous system operations, the node memory also needs to be expanded to support the system running. Especially in the big data era, the increasing network traffic will lead to faster transaction growth rate. This paper analyzes blockchain transaction databases and proposes a storage optimization scheme. The proposed scheme divides blockchain transaction database into cold zone and hot zone using expiration recognition method based on Least Recently Used (LRU) algorithm. It can achieve storage optimization by moving unspent transaction outputs outside the in-memory transaction databases. We present the theoretical analysis on the optimization method to validate the effectiveness. Extensive experiments show our proposed method outperforms the current mechanism for the blockchain transaction databases.
Blockchain and general purpose distributed ledgers are foundational technologies which bring significant innovation in the infrastructures and other underpinnings of our socio-economic systems. These P2P technologies are able to securely diffuse information within and across networks, without need for trustees or central authorities to enforce consensus. In this contribution, we propose a minimalistic stochastic model to understand the dynamics of blockchain-based consensus. By leveraging on random-walk theory, we model block propagation delay on different network topologies and provide a classification of blockchain systems in terms of two emergent properties. Firstly, we identify two performing regimes: a functional regime corresponding to an optimal system function; and a non-functional regime characterised by a congested or branched state of sub-optimal blockchains. Secondly, we discover a phase transition during the emergence of consensus and numerically investigate the corresponding critical point. Our results provide important insights into the consensus mechanism and sub-optimal states in decentralised systems.
Smart contracts are dependent on oracle systems for their adoption and usability. We perform an empirical study of oracle systems' usage trends and adoption metrics to provide better insight into the health of the smart contract ecosystem. We collect ChainLink usage data on the Ethereum network using a modified Ethereum client and running a full node. We analyze the collected data and present our findings and insights surrounding the usage trends, adoption metrics, oracle pricing and service quality associated with ChainLink on the Ethereum network.
Achieving the equilibrium between scalability, sustainability and security has prevailed as the ideal solution for decentralized blockchain applications over the last years. Several approaches have been proposed being Ethereum a solid proposal among them. Ethereum is on the path of a major protocol improvement called Ethereum 2.0 (Eth2), implementing Sharding and introducing the Proof-of-Stake (PoS). As the change of consensus mechanism is a delicate matter, this improvement will be achieved through different phases, the first of which is the implementation of the Beacon Chain. The implementation of the latest has been stated with the recent launch of the Eth2 main net. In this work, we introduce an Eth2 network monitor tool, called Armiarma, used to generate a complete analysis of the p2p network of the Eth2 main net. In this paper, we present some of the results of what this Eth2 network monitor can achieve.
Achieving the equilibrium between scalability, sustainability, and security while keeping decentralization has prevailed as the target solution for decentralized blockchain applications over the last years. Several approaches have been proposed by multiple blockchain teams to achieve it, Ethereum being among them. Ethereum is on the path of a major protocol improvement called Ethereum 2.0 (Eth2), implementing Sharding and introducing the Proof-of-Stake (PoS). As the change of consensus mechanism is a delicate matter, this improvement will be achieved through different phases, the first of which is the implementation of the Beacon Chain. As Ethereum1, Eth2 relies on a decentralized peer-to-peer (p2p) network for the message distribution. Up to date, we estimate that there are around 5.000 nodes in the Eth2 main net geographically distributed. However, the topology of this one still prevails unknown. In this paper, we present the results obtained from the analysis we performed on the Eth2 p2p network. Describing the topology of the network, as possible hazards that this one implies.
Blockchain technology has enabled the keeping of a decentralized, tamper-proof, immutable, and ordered ledger of transactional events. Efforts to leverage such a ledger may be challenging when data storage requirements exceed most blockchain protocols' current capacities. Storing large amounts of decentralized data while maintaining system efficiency is the challenge that we target. This paper proposes using the IPFS distributed hash table (DHT) technology to store information immutably and in a decentralized manner to mitigate the high cost of storage. A storage system involving blockchain and other storage systems in concert should be based on immutable data and allow removal of data from malicious users in the DHT. Efficiency is improved by decreasing the overall processing time in the blockchain with the help of DHT technology and introducing an agreement service that communicate with the blockchain via a RESTful API. We demonstrate the applicability of the proposed method and conclude that the combination of IPFS and blockchain provides efficient cryptographic storage, immutable history and overall better efficiency in a decentralized manner.
Services computing can offer a high-level abstraction to support diverse applications via encapsulating various computing infrastructures. Though services computing has greatly boosted the productivity of developers, it is faced with three main challenges: privacy and security risks, information silo, and pricing mechanisms and incentives. The recent advances of blockchain bring opportunities to address the challenges of services computing due to its build-in encryption as well as digital signature schemes, decentralization feature, and intrinsic incentive mechanisms. In this paper, we present a survey to investigate the integration of blockchain with services computing. The integration of blockchain with services computing mainly exhibits merits in two aspects: i) blockchain can potentially address key challenges of services computing and ii) services computing can also promote blockchain development. In particular, we categorize the current literature of services computing based on blockchain into five types: services creation, services discovery, services recommendation, services composition, and services arbitration. Moreover, we generalize Blockchain as a Service (BaaS) architecture and summarize the representative BaaS platforms. In addition, we also outline open issues of blockchain-based services computing and BaaS.
Jonas Theis, Luigi Vigneri, Lin Wang, Animesh Trivedi
Permissionless distributed ledger technologies (DLTs) utilize an underlying peer-to-peer network to disseminate transactions. These types of networks have been shown to be highly heterogeneous. However, current DLTs fail to consider this heterogeneity which can render low-end nodes to be unable to participate in consensus.
Ensuring the integrity of executable binaries is of vital importance to systems that run and depend on them. Additionally, supply-chain attacks and security related bugs demonstrate that binaries, once deployed, may need to be revoked and replaced with updated versions.
Xuan Luo, Zehua Wang, Wei Cai, Xiuhua Li · 5 authors
Traditional centralized token exchange (CEX) has been suffering from hacking due to the centralized management of users’ tokens. In contrast, decentralized token exchange (DEX) maintains users’ assets by smart contracts in a decentralized manner, but introduces additional overhead in terms of gas fee and transaction confirmation latency. Hybrid decentralized token exchange (HEX) has been proposed to combine the benefits of CEX and DEX. However, existing HEX is criticized for two issues. First, trading transactions are time-consuming and expensive for frequent token traders. Second, excessive simultaneous transactions might cause the pending transaction congestion in the Ethereum network. In this paper, we propose a payment channel based HEX, which extends existing solutions by adding a new payment channel layer to benefit frequent traders and alleviate the pending transaction congestion. Besides, we propose the very first gas-price vs. transaction-confirmation-latency function to guide Ethereum transaction issuers to choose an optimal gas price that minimizes the overall cost. Extensive simulations are conducted to compare the cost in the proposed HEX with that in the conventional HEX. The results demonstrate the effectiveness of our proposed mechanism in terms of reducing gas fees and transaction confirmation latency for frequent traders as well as the pending transaction congestion in Ethereum.
Florian Adamsky, Daniel Kaiser, Michael Steglich, Thomas Engel
Distributed Hash Table (DHT) protocols, such as Kademlia, provide a decentralized key-value lookup which is nowadays integrated into a wide variety of applications, such as Ethereum, InterPlanetary File System (IPFS), and BitTorrent. However, many security issues in DHT protocols have not been solved yet. DHT networks are typically evaluated using mathematical models or simulations, often abstracting away from artefacts that can be relevant for security and/or performance. Experiments capturing these artefacts are typically run with too few nodes.
The major challenges of operating data-intensive of Distributed Ledger Technology (DLT) are (1) to reach consensus on the main chain as a set of validators cast public votes to decide on which blocks to finalize and (2) scalability on how to increase the number of chains which will be running in parallel. In this paper, we introduce a new proximal algorithm that scales DLT in a large-scale Internet of Things (IoT) devices network. We discuss how the algorithm benefits the integrating DLT in IoT by using edge computing technology, taking the scalability and heterogeneous capability of IoT devices into consideration. IoT devices are clustered dynamically into groups based on proximity context information. A cluster head is used to bridge the IoT devices with the DLT network where a smart contract is deployed. In this way, the security of the IoT is improved and the scalability and latency are solved. We elaborate on our mechanism and discuss issues that should be considered and implemented when using the proposed algorithm, we even show how it behaves with varying parameters like latency or when clustering.
The Bitcoin P2P network is at the core of all communications between clients. The reachable part of this network has been explored and analyzed by numerous studies. Unreachable nodes, however, are, in most part, overlooked. Nonetheless, they are a relevant part of the network and play an essential role in the propagation of messages. In this paper, we focus on transaction propagation and show that increasing the participation of unreachable nodes can potentially improve the robustness and efficiency of the network. In order to do that, we propose a few changes to the network protocol. Additionally, we design a novel transaction propagation protocol that explicitly involves unreachable nodes to provide better protection against deanonymization attacks. Our solutions are simple to implement and can effectively bring immediate benefits to the Bitcoin network.
The Bitcoin P2P network is at the core of all communications between clients.\nThe reachable part of this network has been explored and analyzed by numerous\nstudies. Unreachable nodes, however, are, in most part, overlooked.\nNonetheless, they are a relevant part of the network and play an essential role\nin the propagation of messages. In this paper, we focus on transaction\npropagation and show that increasing the participation of unreachable nodes can\npotentially improve the robustness and efficiency of the network. In order to\ndo that, we propose a few changes to the network protocol. Additionally, we\ndesign a novel transaction propagation protocol that explicitly involves\nunreachable nodes to provide better protection against deanonymization attacks.\nOur solutions are simple to implement and can effectively bring immediate\nbenefits to the Bitcoin network.\n
Bryan Wolff, Diego Fernandes Gonçalves Martins, Marco Aurélio Amaral Henriques
A blockchain é um sistema de registro seguro e distribuído que necessita de um mecanismo de consenso capaz de definir quais novos blocos são inseridos à cadeia, a medida que são produzidos pelos participantes da rede. A análise da evolução de uma blockchain controlada por um novo mecanismo de consenso pode ser complexa. Para simplificar tal análise, este artigo apresenta o desenvolvimento de uma nova ferramenta para monitoramento da evolução dinâmica de uma blockchain. É apresentada em detalhes a arquitetura da mesma e sua integração com o protocolo Probabilistic Proof-of-Stake (PPoS).
It is widely accepted that Ethereum mining is highly centralized.\nNonetheless, centralization has been mostly characterized by exclusively\nlooking at the influence that independent miners or mining pools can have over\nthe network. Moreover, models of mining behavior assume that miners are either\nunrelated or only relate via mining pools under highly structured and\ntransparent agreements. If these assumptions and the predictions they entail\nwere to be completely accurate, there would not be any evidence of on-chain\ntransactions between miners, other than the ones expected from mining pool\npayouts. By looking at on-chain transactions between miners in the Ethereum\nNetwork we find that aside from the payouts from mining pools to small miners,\nthere are also transactions that define relationships between mining pools,\nindependent miners and between independent miners and mining pools.\nFurthermore, by characterizing the topology of the network of miner\ntransactions, we find the emergence of highly connected clusters that control\nsignificant amounts of hashing power and exhibit relationships in the opposite\ndirection of what theoretical models predict. This more nuanced\ncharacterization of mining centralization can help identify network\nvulnerabilities and inform protocol redesigns.\n
Oct 8, 2020·Proceedings of the Twenty-First International Symposium on Theory, Algorithmic Foundations, and Protocol Design for Mobile Networks and Mobile Computing
Navin V. Keizer, Onur Ascigil, Ioannis Psaras, George Pavlou
Traversing NAT's remains a big issue in P2P networks, and many of the previously proposed solutions are incompatible with truly decentralised emerging applications. Such applications need a decentralised NAT traversal solution without trusted centralised servers.
The peer-to-peer (P2P) network of blockchain used to transport its transactions and blocks has a high impact on the efficiency and security of the system. The P2P network topologies of popular blockchains such as Bitcoin and Ethereum, therefore, deserve our highest attention. The current Ethereum blockchain explorers (e.g., Etherscan) focus on the tracking of block and transaction records but omit the characterization of the underlying P2P network. This work presents the Ethereum Network Analyzer (Ethna), a tool that probes and analyzes the P2P network of the Ethereum blockchain. Unlike Bitcoin that adopts an unstructured P2P network, Ethereum relies on the Kademlia DHT to manage its P2P network. Therefore, the existing analytical methods for Bitcoin-like P2P networks are not applicable to Ethereum. Ethna implements a novel method that accurately measures the degrees of Ethereum nodes. Furthermore, it incorporates an algorithm that derives the latency metrics of message propagation in the Ethereum P2P network. We ran Ethna on the Ethereum Mainnet and conducted extensive experiments to analyze the topological features of its P2P network. Our analysis shows that the Ethereum P2P network possesses a certain effect of small-world networks, and the degrees of nodes follow a power-law distribution that characterizes scale-free networks.
Distributed Ledgers (DLs) like Blockchain have become a popular technique to build collective trust in digital records. The rationale is that any agent wishing to append a block to a DL needs to provide proof of holding some property/asset or having performed some costly activity. Thus, “poisoning” a DL with spurious content requires much more effort than poisoning a conventional shared data structure. Based on this idea, DLs are now being deployed as community stores of trusted transaction records, reputation values and even of trustworthy training data for Machine Learning (ML) models. Certainly, when injecting spurious or hostile content in a DL, a rational attacker has to consider whether the damage δ caused by a spurious block B is worth the effort ε needed to append B to the DL; but practical experience has shown that being certain to disrupt a DL-supported application may be a powerful motivator for digital vandalism even when it is costly. In this paper, we put out an alternative idea: Reciprocally Useful Work (RUW), a novel DL update mechanism where any agent wishing to add a block B to the ledger must first perform an activity that will improve the utility for the DL-supported application of some other agent's block B'. We discuss in detail how to apply RUW to DLs storing training data for Machine Learning (ML) models, in order to show that reciprocity can play the role of a direct compensation of the potential disruption, which is measurable in term of the performance of the ML model trained on the DL content.
Since Bitcoin and the blockchain were proposed in 2008, distributed ledger technologies and cryptocurrencies have spanned several areas of research. One of the biggest challenges of the field is how to scale the distributed system to support a higher transaction throughput, keeping a safe, distributed, and permissionless network. This work builds on top of the current blockchain and directed acyclic graph distributed ledger technologies literature and proposes a simple, fast and predictable algorithm to reach network consensus. It builds a model to formalize consensus on a DAG DLT and performs experiments to validate the feasibility of the proposed algorithm.