Hyoungsung Kim, Jaehyuk Jang, Sangjun Park, Heung-No Lee
The error-correction code based proof-of-work (ECCPoW) algorithm is based on a low-density parity-check (LDPC) code. The ECCPoW is possible to impair ASIC with its time-varying capability of the parameters of LDPC code. Previous researches on the ECCPoW algorithm have presented its theory and implementation on Bitcoin. But they do not discuss how stable the block generation time is. A finite mean block generation time (BGT) and none heavy-tail BGT distribution are the ones of the focus in this study. In the ECCPoW algorithm, BGT may show a long-tailed distribution due to time-varying cryptographic puzzles. Thus, it is of interest to see if the BGT distribution is not heavy-tailed and if it shows a finite mean. If the distribution is heavy-tailed, then confirmation of a transaction cannot be guaranteed. We present implementation, simulation, and validation of ECCPoW Ethereum. In implementation, we explain how the ECCPoW algorithm is integrated into Ethereum 1.0 as a new consensus algorithm. In the simulation, we perform a multinode simulation to show that the ECCPoW Ethereum works well with automatic difficulty change. In the validation, we present the statistical results of the two-sample Anderson-Darling test to show that the distribution of BGT satisfies the necessary condition of the exponential distribution. Our implementation is downloadable at https://github.com/cryptoecc/ETH-ECC.
Abstract The distributed ledger or blockchain technologies originated from the Bitcoin have been rapidly widespread in recent years. However, it also gives incentive to malicious users who would like to break the system or take advantage of it (steal money, hide some information stored in the ledger, isolate a particular node from the rest of the network, and so forth). Thus, research focusing on overcoming potential attacks to distributed ledgers is required. In this article, we focus on attacks that damage underlying networks of distributed ledgers. Underlying networks offer useful communication primitives such as an atomic broadcast, however, such attacks may degrade the property of the primitives and make distributed ledgers relying on the primitives no longer work. Hence we should design algorithms to make the distributed ledgers still work even when some attacks degrade the primitives. As the first study for such situations, we consider a problem to implement distributed ledgers tolerating the degradation of an underlying atomic broadcast service that distributed ledgers are relying on. We consider the case where the uniform agreement property of the atomic broadcast is degraded, and propose new algorithms that could ensure to reach eventual consistency despite degraded atomic broadcast.
Lei Zhang, Hao Xu, Oluwakayode Onireti, Muhammad Ali Imran · 5 authors
Blockchain is built on a peer-to-peer network that relies on frequent communications among distributively located nodes. In particular, the consensus mechanisms (CMs), which play a pivotal role in blockchain, are communication resource-demanding and largely determine blockchain security bounds (i.e., fault tolerances) and other key performance metrics such as transaction throughput, latency and scalability. Most blockchain systems are designed in a stable wired communication network running in advanced devices under the assumption of sufficient communication resource provision. However, it is envisioned that the majority of blockchain node peers will be connected through the wireless network in the future. Constrained by the highly dynamic wireless channel and scarce frequency spectrum, communication can significantly affect blockchain's key performance metrics. Hence, in this article, we present wireless blockchain networks (WBN) under various commonly used CMs and we answer the question of how much communication resource is needed to run such a network. We first present the role of communication in the four stages of the blockchain procedure. We then discuss the relationship between the communication resource provision and the WBNs performance, for three of the most used blockchain CMs, namely, Proof-of-Work (PoW), practical Byzantine Fault Tolerant (PBFT) and Raft. Finally, we provide analytical and simulated results to show the impact of the communication resource provision on block-chain performance.
Smart Contracts based cryptocurrencies such as Ethereum are becoming increasingly popular in various domains: but with this increase in popularity comes a significant decrease in throughput and efficiency. Smart Contracts are executed by every miner in the system serially without any parallelism, both inter and intra-Smart Contracts. Such a serial execution inhibits the scalability required to obtain extremely high throughput pertaining to computationally intensive tasks deployed with such Smart Contracts. While significant advancements have been made in the field of concurrency, from GPU architectures that enable massively parallel computation to tools such as MapRe-duce that distributed computing to several nodes connected in the system to achieve higher performance in distributed systems, none are incorporated in blockchain-based distributed computing. The team proposes a novel blockchain that allows public nodes in a permission-independent blockchain to deploy and run Smart Contracts that provide concurrency-related functionalities within the Smart Contract framework. In this paper, the researchers present “ConCurrency,” a blockchain network capable of handling big data-based computations. The technique is based on currently used distributed system paradigms, such as MapReduce, while also allowing for fundamental parallelly computable problems. Concurrency is achieved using a sharding protocol incorporated with consensus mechanisms to ensure high scalability, high reliability, and better efficiency. A detailed methodology and a comprehensive analysis of the proposed blockchain further indicate a significant increase in throughput for parallelly computable tasks, as detailed in this paper.
Orestis Alpos, Christian Cachin, Giorgia Azzurra Marson, Luca Zanolini
Modern blockchains support a variety of distributed applications beyond cryptocurrencies, including smart contracts -- which let users execute arbitrary code in a distributed and decentralized fashion. Regardless of their intended application, blockchain platforms implicitly assume consensus for the correct execution of a smart contract, thus requiring that all transactions are totally ordered. It was only recently recognized that consensus is not necessary to prevent double-spending in a cryptocurrency (Guerraoui et al., PODC'19), contrary to common belief. This result suggests that current implementations may be sacrificing efficiency and scalability because they synchronize transactions much more tightly than actually needed. In this work, we study the synchronization requirements of Ethereum's ERC20 token contract, one of the most widely adopted smart contacts. Namely, we model a smart-contract token as a concurrent object and analyze its consensus number as a measure of synchronization power. We show that the richer set of methods supported by ERC20 tokens, compared to standard cryptocurrencies, results in strictly stronger synchronization requirements. More surprisingly, the synchronization power of ERC20 tokens depends on the object's state and can thus be modified by method invocations. To prove this result, we develop a dedicated framework to express how the object's state affects the needed synchronization level. Our findings indicate that ERC20 tokens, as well as other token standards, are more powerful and versatile than plain cryptocurrencies, and are subject to dynamic requirements. Developing specific synchronization protocols that exploit these dynamic requirements will pave the way towards more robust and scalable blockchain platforms.
Ashar Ahmad, Muhammad Saad, Joongheon Kim, DaeHun Nyang · 5 authors
Blockchain-based audit systems use “Practical Byzantine Fault Tolerance” (PBFT) consensus protocol which suffers from a high message complexity and low scalability. Alternatives to PBFT have not been tested in blockchain-based audit systems since no blockchain testbed supports the execution and benchmarking of different consensus protocols in a unified testing environment. In this paper, we address this gap by developing a blockchain testbed capable of executing and testing five consensus protocols in a blockchain network; namely PBFT, Proof-of-Work (PoW), Proof-of-Stake (PoS), Proof-of-Elapsed Time (PoET), and Clique. We carry out performance evaluation of those consensus algorithms using data from a real-world audit system. Our results show that the Clique protocol is best suited for blockchain-based audit systems, based on scalability features.
Big data applications put significant latency and throughput demands on distributed storage systems. Meeting these demands requires storage systems to use a significant amount of infrastructure resources, such as network capacity and storage devices. Resource demands largely depend on the workloads and can vary significantly over time. Moreover, demand hotspots can move rapidly between different infrastructure locations. \n \nExisting storage systems are largely infrastructure-oblivious as they are designed to support a broad range of hardware and deployment scenarios. Most only use basic configuration information about the infrastructure to make important placement and routing decisions. In the case of cloud-based storage systems, cloud services have their own infrastructure-specific limitations, such as minimum request sizes and maximum number of concurrent requests. By ignoring infrastructure-specific details, these storage systems are unable to react to resource demand changes and may have additional inefficiencies from performing redundant network operations. As a result, provisioning enough resources for these systems to address all possible workloads and scenarios would be cost prohibitive. \n \nThis thesis studies the performance problems in commonly used distributed storage systems and introduces novel infrastructure-aware design methods to improve their performance. First, it addresses the problem of slow reads due to network congestion that is induced by disjoint replica and path selection. Selecting a read replica separately from the network path can perform poorly if all paths to the pre-selected endpoints are congested. Second, this thesis looks at scalability limitations of consensus protocols that are commonly used in geo-distributed key value stores and distributed ledgers. Due to their network-oblivious designs, existing protocols redundantly communicate over highly oversubscribed WAN links, which poorly utilize network resources and limits consistent replication at large scale. Finally, this thesis addresses the need for a cloud-specific realtime storage system for capital market use cases. Public cloud infrastructures provide feature-rich and cost-effective storage services. However, existing realtime timeseries databases are not built to take advantage of cloud storage services. Therefore, they do not effectively utilize cloud services to provide high performance while minimizing deployment cost. \n \nThis thesis presents three systems that address these problems by using infrastructure-aware design methods. Our performance evaluation of these systems shows that infrastructure-aware design is highly effective in improving the performance of large scale distributed storage systems.
Daniel M. Kane, Andreas Fackler, Adam Gągol, Damian Straszak
There has been recently a lot of progress in designing efficient partially synchronous BFT consensus protocols that are meant to serve as core consensus engines for Proof of Stake blockchain systems. While the state-of-the-art solutions attain virtually optimal performance under this theoretical model, there is still room for improvement, as several practical aspects of such systems are not captured by this model. Most notably, during regular execution, due to financial incentives in such systems, one expects an overwhelming fraction of nodes to honestly follow the protocol rules and only few of them to be faulty, most likely due to temporary network issues. Intuitively, the fact that almost all nodes behave honestly should result in stronger confidence in blocks finalized in such periods, however it is not the case under the classical model, where finality is binary. We propose Highway, a new consensus protocol that is safe and live in the classical partially synchronous BFT model, while at the same time offering practical improvements over existing solutions. Specifically, block finality in Highway is not binary but is expressed by fraction of nodes that would need to break the protocol rules in order for a block to be reverted. During periods of honest participation finality of blocks might reach well beyond 1/3 (as what would be the maximum for classical protocols), up to even 1 (complete certainty). Having finality defined this way, Highway offers flexibility with respect to the configuration of security thresholds among nodes running the protocol, allowing nodes with lower thresholds to reach finality faster than the ones requiring higher levels of confidence.
David Hyland-Wood, Peter Robinson, Roberto Saltini, Sandra Johnson · 5 authors
Integration of space-based communications infrastructure within 5G networks presents specific challenges for spacecraft, namely a necessary rationalization of currently patchy communications security and the assurance of identity when conducting high-level spacecraft tasking and control operations. This chapter presents approaches to addressing both issues via the deployment of an enterprise Ethereum blockchain modified with a consensus algorithm appropriate for access by spacecraft. We discuss the applicability of enterprise Ethereum blockchains to the problem of spacecraft communication security, analyze the properties of blockchain consensus algorithms suitable for use with spacecraft, and suggest information architectures to allow secure spacecraft integration into 5G networks.
The conventional architecture of vehicular ad hoc networks (VANETs) with a centralized approach has difficulty overcoming the increasing complexity of intelligent transportation system (ITS) applications as well as challenges in providing large amounts of data storage, trust management, and information security. Therefore, vehicular edge computing networks (VECNets) have emerged to provide massive storage resources with powerful computing on network edges. However, a centralized server in VECNets is insufficient due to potential data leakage and security risks as it can still allow a single point of failure (SPoF). We propose consortium blockchain and smart contracts to ensure a trustworthy environment for secure data storage and sharing in the system to address these challenges. Practical byzantine fault tolerance (PBFT) is utilized because it is suitable for consortium blockchain to audit publicly, store data sharing, and records the whole consensus process. It can defend against system failures with or without symptoms to reach an agreement among consensus participants. Furthermore, we use an incentive mechanism to motivate the vehicle to contribute and honestly share their data. The simulation results satisfy the proposed model’s design goals by increasing vehicular networks’ performance in general.
In the Ethereum ecosystem, the transfer of value between users is often realized by the use of tokens that represent digital assets. Ether is the default token and the de facto currency used for transactions and for initializing smart contracts on the network. Ethereum also supports the creation of new kinds of tokens that can represent any commonly traded commodities as digital assets. All tokens are implemented using the standard protocol, so the tokens are compatible with any Ethereum wallet on the network. The tokens are distributed to users interested in the given specific use case through an Initial Coin Offering (ICO). In this chapter, we will focus our attention on tokens created for a very specific use case: high-performance computing (HPC). More precisely, we will discuss a model of distributed HPC where miners offer computational resources for a task and get rewarded in some form of Ethereum token.
Carlos Santiago, Shuyang Ren, Choonhwa Lee, Minsoo Ryu
In this paper, we present a novel Byzantine fault-tolerant consensus protocol for sharded blockchain networks that does not rely on expensive leader-driven communication. The proposed protocol selects a single block proposer at a time and uses threshold signatures as a voting mechanism to confirm the validity of the proposed block. By using a gossip-like communication scheme, each node can collect and recover the group signature within$\mathrm {O(log}N)$steps. With only one block proposer per consensus round, there is no possibility of conflicting blocks and resultant forks. Therefore, our consensus protocol requires only one round of one-way communication to achieve finality for each block. Our protocol guarantees safety and liveness while tolerating up to$f$faulty participants among$2f+1$nodes. Our performance study shows that the proposed protocol enables hundreds of nodes to participate in the agreement process, and can finalize large blocks in approximately 10 seconds.
Dezentrale Anwendungen werden, im Gegensatz zu zentralisierten Ansätzen, durch eine Unterstützergemeinschaft betrieben. Diese unterliegen keiner zentralen, kontrollierenden, eventuell sogar bösartigen Instanz. Viele Anwendungsgebiete werden durch dezentrale Ansätze abgedeckt. Beispiele hierfür sind dezentrale soziale Netzwerke, Währungen, Logbücher (engl. distributed ledger, i.e. blockchain). Durch eine breite Unterstützung sind die dezentralen Ansätze in der Lage, die marktbeherrschende Stellung einiger weniger Anbieter aufzubrechen und eine echte neutrale, offene Alternative anzubieten. Betrachtet man die Komponenten einer dezentralen Anwendung so trifft man auf der untersten Ebene auf die Hardwareebene, einzelne Peers die durch ein Netzwerk miteinander kommunizieren können und durch einen Operator verwaltet werden. Auf der höheren Anwendungsebene trifft man auf Benutzer, die auf die Dienste der Anwendung mit Hilfe von Operationen zugreifen und auf Daten der Anwendung, sogn. Verwaltungsstruktur. Die Hardwareebene stellt Ressourcen bereit, die durch die Anwendungsebene konsumiert werden. Leider leidet die Akzeptanz der dezentralen Anwendungen an Performanz der Operationen. Die Ursachen hierfür liegt in den unzureichenden Ressourcen der Hardware-Ebene oder ungünstiger Platzierung der Verwaltungsstruktur bezüglich ausgeführter Operationen. Die Ursache der unzureichenden Ressourcen in der Hardware-Ebene liegt u. A. an der absichtlichen Abwanderung der einzelnen Peers, aufgrund der dauerhaften Überlastung. In dieser Arbeit wird gezeigt, dass die günstige Platzierung der Verwaltungsstruktur bei gleichzeitig strikter Einhaltung der durch den Operator bereitgestellten Ressourcen dazu genutzt werden kann die Performanz der Operationen zu erhöhen. Damit werden die Bedürfnisse der Operatoren und Benutzer berücksichtigt, was auch zur verbesserten Akzeptanz der dezentralen Ansätze führt. Die Ergebnisse der gewählten Lösung zeigen, dass wenn ein einzelner Peer die ihm bekannten Teile der Verwaltungsstruktur optimal innerhalb seiner Nachbarschaft verschiebt, dies die Ausführungszeiten der Operationen reduziert. Somit wird ihre Performance deutlich verbessert.
The problem of transaction reordering in blockchains, also known as the blockchain anomaly [Christopher Natoli and Vincent Gramoli, 2016], can lead to fairness limitations [Kelkar et al., 2020] and front-running activities [Philip Daian et al., 2020] in cryptocurrency. To cope with this problem despite f < n/3 byzantine processes, Zhang et al. [Zhang et al., 2020] have introduced the ordering linearizability property ensuring that if two transactions or commands are perceived by all correct processes in the same order, then they are executed in this order. They proposed a generic distributed protocol that first orders commands and then runs a leader-based consensus protocol to agree on these orders, hence requiring at least 11 message delays. In this paper, we parallelize the ordering with the execution of the consensus to require only 6 message delays. For the ordering, we introduce the ordered reliable broadcast primitive suitable for broadcast-based cryptocurrencies (e.g., [Daniel Collins et al., 2020]). For the agreement, we build upon the DBFT leaderless consensus protocol [Tyler Crain et al., 2018] that was recently formally verified [Bertrand et al., 2021]. The combination is thus suitable to ensure ordering linearizability in consensus-based cryptocurrencies (e.g., [Tyler Crain et al., 2021]).