Since the introduction of the first cryptocurrency, Bitcoin, in 2008, the gain in popularity of distributed ledger technologies (DLTs) has led to an increasing demand and, consequently, a larger number of network participants in general. Scaling blockchain-based solutions to cope with several thousand transactions per second or with a growing number of nodes has always been a desirable goal for most developers. Enabling these performance metrics can lead to further acceptance of DLTs and even faster systems in general. With the introduction of directed acyclic graphs (DAGs) as the underlying data structure to store the transactions within the distributed ledger, major performance gains have been achieved. In this article, we review the most prominent directed acyclic graph platforms and evaluate their key performance indicators in terms of transaction throughput and network latency. The evaluation aims to show whether the theoretically improved scalability of DAGs also applies in practice. For this, we set up multiple test networks for each DAG and blockchain framework and conducted broad performance measurements to have a mutual basis for comparison between the different solutions. Using the transactions per second numbers of each technology, we created a side-by-side evaluation that allows for a direct scalability estimation of the systems. Our findings support the fact that, due to their internal, more parallelly oriented data structure, DAG-based solutions offer significantly higher transaction throughput in comparison to blockchain-based platforms. Although, due to their relatively early maturity state, fully DAG-based platforms need to further evolve in their feature set to reach the same level of programmability and spread as modern blockchain platforms. With our findings at hand, developers of modern digital storage systems are able to reasonably determine whether to use a DAG-based distributed ledger technology solution in their production environment, i.e., replacing a database system with a DAG platform. Furthermore, we provide two real-world application scenarios, one being smart grid communication and the other originating from trusted supply chain management, that benefit from the introduction of DAG-based technologies.
Operators of low-Earth-orbit (LEO) non-geostationary satellite networks, also known as mega-constellations, are required by current regulations to share all available satellite spectrum. This paper proposes a consensus mechanism to facilitate spectrum sharing with accountability by multiple operators, a subset of which may even be adversarial. A distributed ledger is used to securely record and track the state of consensus on spectrum usage, including interference incidents and the corresponding responsible parties. A key challenge is that operators generally do not have initial agreement due to noise in their analog measurements. To address this, two categories of spectrum-sharing solutions are studied in detail. The first category employs an exact Byzantine fault tolerant (BFT) agreement model; the second category utilizes an approximate BFT agreement model. Practical considerations were taken into account regarding the BFT agreements, substantiated by numerical findings on the feasibility of the proposed solutions within the context of non-geostationary orbit satellite networks (NGSO).
The potential of the Internet of Vehicles (IoV) to reduce on-board system costs in autonomous vehicles through shared intelligence is considerable. However, it still faces significant challenges, including concerns over data breaches and privacy, inefficiencies and limited fault tolerance in centralized management, and the challenge of ensuring data accuracy. This letter marks the inaugural report from a series of IEEE Transactions on Intelligent Vehicles (TIV) Trustworthy IoV Workshops, which aim to address these issues. In these workshops, we explore the concept of a decentralized IoV (DeIoV), underpinned by decentralized autonomous organizations and operations (DAOs), to facilitate trustworthy interactions between vehicles and other entities. The proposed DeIoV is structured in two layers: the local DAO layer and the global DAO layer. This dual-layer architecture distinguishes between real-time and non-real-time decision-making tasks, aiding in their efficient completion. To ensure data security, integrity, and accuracy, we employ blockchain technology and smart contracts, which allow for mutual verification among adjacent members and utilize encryption algorithms. A reputation value-based voting mechanism for decision-making is also introduced, which helps prevent the monopolization of power through token-based systems, a common issue in traditional DAOs. Ultimately, we believe that DeIoV has the potential to create a trustworthy IoV ecosystem, contributing significantly to safe, secure, and collaborative autonomous driving.
William Frederic O. Wells, Glenn Walter V. Lim, Cedric Angelo M. Festin, Wilson M. Tan
Private blockchains are uncompetitive with the throughput of distributed databases. HotStuff(RS) is a recent BFT-SMR consensus protocol that is supposedly a faster alter-native to the established IBFT and QBFT protocols. Despite its promise, HS remains untested in private Ethereum blockchains. Previous work evaluates HS as a standalone protocol but never in a blockchain environment due to the difficulty of implementing BFT-SMR protocols. Our work addresses this gap by implementing and evaluating Basic HotStuff(BHS), a HS variant that trades latency for simplicity, against IBFT and QBFT in a private Ethereum blockchain. We create a consensus module for BHS in GoQuorum 22.7.4 and measure the performance of BHS, IBFT, and QBFT under varying (i) network sizes, (ii) transaction loads, and (iii) network conditions. Our work shows that, at scale, BHS significantly outperforms IBFT and QBFT under low-bandwidth conditions and has the lightest network traffic under all network conditions.
A system of zero-knowledge proofs on graph signatures has been proposed, where a graph can be signed, and the owner of the graph signature can prove a graph relation such as the connectivity and isolation of any two vertexes on the graph without disclosing all information about the graph. The correctness of the graph information is guaranteed by the signature. One of the applications is a virtualized infrastructure, where an infrastructure provider manages a distributed system, and each tenant is allocated a specific portion of this infrastructure for use. Tenants need to check with the provider that their resources are properly connected (connectivity) and that their resources are properly separated from the resources of other tenants (isolation). On the other hand, the provider cannot simply disclose the entire infrastructure topology to each tenant. Using the zero-knowledge proof system on graph signatures, both requirements can be addressed. Previously, an efficient zero-knowledge proof system on graph signatures using a bilinear-map accumulator has been proposed, where the verification time and the size of the proof data do not depend on the number of graph vertexes and edges. However, this system has two problems. First, since the proof does not include labels, it is not possible to prove the connectivity considering network bandwidth and cost. Second, since it assumes undirected graphs, it cannot handle applications on directed graphs such as network flows. In this paper, we extend the previous system and propose a zero-knowledge proof system of the connectivity for directed graphs where each edge has labels. We implemented our system on a PC using a pairing library and evaluate it by measuring the processing times. Compared to the conference version of this paper, we show the formal definitions and the security proofs of our proposed system, and add implementation-based evaluations reflecting the application to the virtualized infrastructure.
Existing distributed ledger systems ensure the integrity and availability of information, but they lack built-in mechanisms to ensure the confidentiality of transaction data recorded in the ledger. Any intruder can obtain all transaction data by downloading a copy of the ledger and trace the relationships between transactions and accounts. Thus, additional mechanisms are needed to ensure the confidentiality of transactions. One solution to this problem is to use a zero-knowledge proof protocol. This article discusses the use of zero-knowledge proof to ensure the confidentiality of transactions in distributed ledger systems. We consider both the UTXO-model and the account model.
Muhammad Ikram Mohd Rashid, Imran Rasool, Nazir Ahmad Zafar, Hamra Afzaal
The Ethereum 2.0 Beacon chain is a big step toward improving the security, scalability, and decentralization. It is based on the Proof of Stake (PoS) consensus protocol that maintains the validator status, attestation details, and many more. The term validator is introduced in the PoS consensus protocol and its work is to propose blocks and vote for them by becoming a committee member to add those blocks to the blockchain. We address the problem related to validator’s voluntary exit to vanish its active status and do its formal verification using the SPIN Model checker. There does not exist much research in this area as it was introduced recently in 2020. Further, this is the first work on formal verification of the beacon chain using the SPIN model checker. In this work, we formally specify the validator exit process of the Ethereum 2.0 Beacon Chain using the formal specification language, i.e., Process or Protocol Meta Language (PROMELA). We create a program graph for this process through the SPIN Model checker and describe safety and liveness properties using Linear temporal logic (LTL) in the form of a formula. The formal verification is performed to ensure correctness by giving the program graph and LTL formulas as input to the SPIN model checker whether the properties are satisfied with the program graph
Davide Frey, Lucie Guillou, Michel Raynal, François Taı̈ani
This paper explores the territory that lies between best-effort Byzantine-Fault-Tolerant Conflict-free Replicated Data Types (BFT CRDTs) and totally ordered distributed ledgers, such as those implemented by Blockchains. It formally characterizes a novel class of distributed objects that only requires a First In First Out (FIFO) order on the object operations from each process (taken individually). The formalization leverages Mazurkiewicz traces to define legal sequences of operations and ensure both Strong Eventual Consistency (SEC) and Pipleline Consistency (PC). The paper presents a generic algorithm that implements this novel class of distributed objects both in a crash- and Byzantine setting. It also illustrates the practical interest of the proposed approach using four instances of this class of objects, namely money transfer, Petri nets, multi-sets, and concurrent work stealing dequeues.
Maximum Extractable Value (MEV) refers to the maximum benefit obtained from the Decentralized Finance (DeFi) protocol during the block production process by utilizing the power of transaction ordering in the block. Although MEV plays a role in incentivizing the efficiency of DeFi projects, excessive abuse of this power can pose a series of problems and challenges to the blockchain, including an increased risk of chain forks. The State Sharding technique can fundamentally enhance the scalability of blockchain, but its consensus security also faces the potential threat of MEV. To mitigate the negative impact of MEV on state sharding, a scheme combining the Proposer-Builder Separation (PBS) and the State Merge is proposed. This scheme allows high-performance nodes to synchronize the state of adjacent shards and form a higher-level virtual shard, establishing a logical relationship resembling a complete binary tree among the shards. And through role separation, nodes participate in consensus within a leaf shard and composite virtual shards. At the same time, they can participate in block construction and seize MEV opportunities in other shards that are already synchronized. By confining transaction ordering authority outside the consensus shards, the security risk to the State Sharding consensus network from the MEV is reduced. However completely eliminating the MEV threats is very difficult and requires further research. Analytical and simulation-based validation shows that the proposed approach can mitigate the issue of decreased resistance to censorship and incentivize nodes to fully utilize their performance by leveraging MEV opportunities, thereby improving the blockchain's throughput capacity.
Blockchains add transactions to a distributed shared ledger by arriving at consensus on sets of transactions contained in blocks. This provides a total ordering on a set of global transactions. However, total ordering is not enough to satisfy application semantics under the Byzantine fault model. This is due to the fact that malicious miners and clients can collaborate to add their own transactions ahead of correct clients' transactions in order to gain application level and financial advantages. These attacks fall under the umbrella of front-running attacks. Therefore, total ordering is not strong enough to preserve application semantics. In this paper, we propose causality preserving total order as a solution to this problem. The resulting Blockchains will be stronger than traditional consensus based blockchains and will provide enhanced security ensuring correct application semantics in a Byzantine setting.
Zahra Sharifian, Hossein Saidi, Ali Fanian, T. Aaron Gulliver
One of the main problems in Nakamoto consensus is the creation of orphan blocks and sub-chains which reduce throughput and can lead to unfairness and network abuse. This paper proposes a new approach to change the behavior in dealing with these blocks. In the proposed method, almost all correct mined blocks at any height are made final by adding a small database to the blocks. This acts as distributed supervision to improve system security and encourage honest miner behavior. By preventing conflicting transactions from being finalized and detecting exceptional circumstances, the proposed method also preserves the important blockchain features of safety and liveness. To demonstrate the practicality of this approach, its main parameter is obtained using real network data for Bitcoin. In addition, simulation results are given for Bitcoin and other scenarios with different block sizes and block times which indicate that the proposed method improves the throughput.
The Algorand consensus protocol is interesting both in theory and in practice. On the theoretical side, to achieve adaptive security, it introduces the novel idea of player replaceability, where each step of the protocol is executed by a different randomly selected committee whose members remain secret until they send their first and only message. The protocol provides consistency under arbitrary network conditions and liveness under intermittent network partitions. On the practical side, the protocol is used to secure the Algorand cryptocurrency, whose total value is approximately 850M at the time of writing.
Resilience is vital to blockchain systems and helps them automatically adapt and continue providing their service when adverse situations occur, e.g., node crashing and data discarding. However, due to the vulnerabilities in their implementation, blockchain systems may fail to recover from the error situations, resulting in permanent service disruptions. Such vulnerabilities are called resilience issues.
We study the problem of committee selection in the context of proof-of-stake consensus mechanisms or distributed ledgers. These settings determine a family of participating parties---each of which has been assigned a non-negative ''stake''---and are subject to an adversary that may corrupt a subset of the parties. The challenge is to select a committee of participants that accurately reflects the proportion of corrupt and honest parties, as measured by stake, in the full population. The trade-off between committee size and the probability of selecting a committee that over-represents the corrupt parties is a fundamental factor in both security and efficiency of proof-of-stake consensus, as well as committee-run layer-two protocols.
Miguel Oliveira, Sumit Chauhan, Filipe Pereira, Carlos Felgueiras · 5 authors
"Industry 5.0" is the latest industrial revolution. A variety of cutting-edge technologies, including artificial intelligence, the Internet of Things (IoT), and others, come together to form it. Billions of devices are connected for high-speed data transfer, especially in a 5G-enabled industrial environment for information collection and processing. Most of the issues, such as access control mechanism, time to fetch the data from different devices, and protocols used, may not be applicable in the future as these protocols are based upon a centralized mechanism. This centralized mechanism may have a single point of failure along with the computational overhead. Thus, there is a need for an efficient decentralized access control mechanism for device-to-device (D2D) communication in various industrial sectors, for example, sensors in different regions may collect and process the data for making intelligent decisions. In such an environment, reliability, security, and privacy are major concerns as most of the solutions are based upon a centralized control mechanism. To mitigate the aforementioned issues, this paper provides the opportunities for and highlights some of the most impressive initiatives that help to curve the future. This new era will bring about significant changes in the way businesses operate, allowing them to become more cost-effective, more efficient, and produce higher-quality goods and services. As sensors are getting more accurate, cheaper, and have lower time responses, 5G networks are being integrated, and more industrial equipment and machinery are becoming available; hence, various sectors, including the manufacturing sector, are going through a significant period of transition right now. Additionally, the emergence of the cloud enables modern production models that use the cloud (both internal and external services), networks, and systems to leverage the cloud's low cost, scalability, increased computational power, real-time communication, and data transfer capabilities to create much smarter and more autonomous systems. We discuss the ways in which decentralized networks that make use of protocols help to achieve decentralization and how network meshes can grow to make things more secure, reliable, and cohere with these technologies, which are not going away anytime soon. We emphasize the significance of new design in regard to cybersecurity, data integrity, and storage by using straightforward examples that have the potential to lead to the excellence of distributed systems. This groundbreaking paper delves deep into the world of industrial automation and explores the possibilities to adopt blockchain for developing solutions for smart cities, smart homes, healthcare, smart agriculture, autonomous vehicles, and supply chain management within Industry 5.0. With an in-depth examination of various consensus mechanisms, readers gain a comprehensive understanding of the latest developments in this field. The paper also explores the current issues and challenges associated with blockchain adaptation for industrial automation and provides a thorough comparison of the available consensus, enabling end customers to select the most suitable one based on its unique advantages. Case studies highlight how to enable the adoption of blockchain in Industry 5.0 solutions effectively and efficiently, offering valuable insights into the potential challenges that lie ahead, particularly for smart industrial applications.
IOTA 2.0 addresses the dual challenge of dynamic availability and definite finality in distributed ledgers. By combining voting-based and proof-based consensus models, it allows users to strike a balance between these objectives. This innovative approach represents a significant advancement in the field, offering both dynamic availability and definite finality, all within the evolving landscape of distributed ledger technologies.
Huizhong Li, Yujie Chen, Shi Xiang, Xingqiang Bai · 9 authors
Enterprise-grade permissioned blockchain systems provide a promising infrastructure for data sharing and cooperation between different companies. However, performance bottlenecks seriously hinder the adoption of these systems in many industrial applications that process complex business logic and huge transaction volumes. Our research identifies two key factors that limit the system performance: 1) At the block level, the serial dependency of inter-block processing severely limits the system throughput. A new block must wait for the completion of all previous blocks. 2) At the transaction level, the lack of efficient intra-block transactions concurrency makes it difficult to achieve high performance, especially when dealing with multiple CPU-heavy contracts which are commonly used in industrial scenarios.
Blockchain has great application value in the field of finance, Internet of Things, digital copyright, decentralization is the most fundamental feature of blockchain. Decentralization increases the fault tolerance and security of the whole blockchain network, ensuring that the data cannot be tampered with, but decentralization greatly increases the amount of message communication in the whole system, so the whole blockchain network is very inefficient in the case of consensus of multiple nodes. The consensus algorithm is the core technology for implementing decentralization.In this paper, we propose a CG-PBFT consensus algorithm based on credit list grouping hierarchy, which aims to solve the problems of wasteful communication resources and inefficiency caused by too many broadcast messages in PBFT (Practical Byzantine Fault Tolerance algorithm). The implementation of the CG-PBFT algorithm is divided into three main steps: First, by selecting nodes with higher credit value as group leader nodes, the harm of malicious nodes to the whole consensus system can be significantly reduced. Second, the optimal grouping according to the communication delay between nodes can improve the efficiency of the whole consensus system. Finally, the intra-group consensus is performed first in the consensus phase, followed by the global consensus, which can significantly reduce the network overhead. Experiments demonstrate that the CG-PBFT consensus algorithm has lower network overhead, lower network latency, and higher Byzantine node fault tolerance.
Abstract Distributed ledgers, including blockchain and other decentralized databases, are designed to store information online where all trusted network members can update the data with transparency. The dynamics of a ledger’s development can be mathematically represented by a directed acyclic graph (DAG). In this paper, we study a DAG model that considers batch arrivals and random delay of attachment. We analyze the asymptotic behavior of this model by letting the arrival rate go to infinity and the inter-arrival time go to zero. We establish that the number of leaves in the DAG, as well as various random variables characterizing the vertices in the DAG, can be approximated by its fluid limit, represented as the solution to a set of delayed partial differential equations. Furthermore, we establish the stable state of this fluid limit and validate our findings through simulations.