Christian Berger, Sadok Ben Toumia, Hans P. Reiser
The novel blockchain generation of Byzantine fault-tolerant (BFT) state machine replication (SMR) protocols focuses on scalability and performance to meet the requirements of distributed ledger technology (DLT), e.g., decentralization and geographic dispersion. Validating scalability and performance of BFT protocol implementations requires careful evaluation. While experiments with real protocol deployments usually offer the best realism, they are costly and time-consuming. In this paper, we explore simulation of unmodified BFT protocol implementations as a method for cheap and rapid protocol evaluation: We can accurately forecast the performance of a BFT protocol while experimentally scaling its environment, i.e., by varying the number of nodes or geographic dispersion. Our approach is resource-friendly and preserves application-realism, since existing BFT frameworks can be simply plugged into the simulation engine without requiring code modifications or re-implementation.
Consensus - loosely defined as global agreement on the state of a decentralised network across its mutually untrusting participants - is an essential ingredient for decentralisation. At the same time, its scalability remains the Achilles' heel of distributed systems. A number of ongoing R&D efforts aim at scaling blockchain networks up to hundreds of thousands of transactions per second. Yet even such performance targets can be seen as modest when the goal is to bring traditional web workloads to the decentralised web (Web3), requiring the handling of billions of transactions per second, large volumes of data, complex workloads and applications, and hard latency requirements. The goal of this workshop is to foster scientific exchange across a wider community in consensus research and adjacent fields, by disseminating and providing a forum for discussion of upcoming impactful research with a practical twist.
Waterfall is a highly-scalable smart contract platform for the development of decentralized applications (dapps) and financial services. The distributed protocol is based on Directed Acyclic Graphs (DAGs) with fast finality Proof-of-Stake (PoS) consensus. The Waterfall platform consists of the Coordinating and Shard networks achieving high transaction throughput due to parallelized block production. The DAG structure facilitates scalability, which is one of the main challenges of decentralized technologies. The Coordinating network maintains a register of Validators, and also assigns block producers, committee members, and leaders in each time slot. In addition, the linearization and finalization of the distributed ledger are performed in the Coordinating network increasing overall security and synchronization.
In this article, a credit identity ring optimization blockchain algorithm (CRBFT) based on practical Byzantine fault tolerance (PBFT) is proposed to address the security problem for the network of Internet of Things (IoT). The contributions of this work are given as follows. First, combined with the edge computing architecture, CRBFT introduces the improved credit grading protocol and the improved ring signature scheme into the blockchain network, rewards or punishes the nodes through their behavior, changes the way of selecting the primary node, and ensures that the identity of the primary node will not be disclosed, so as to prevent the primary node from adaptive attack by Byzantine nodes, improve the reliability of the nodes participating in the consensus, and enhance the security of the system. Second, in order to reduce the communication traffic among nodes, CRBFT optimizes the consensus protocol, which not only reduces the time complexity of the traffic in the consensus stage from O (${n}^{{2}}$) to O (${n}$) but also improves the consensus efficiency of the system while ensuring the system security. Finally, CRBFT aims to measure the performance of CRBFT. This article is simulated and tested in three aspects: throughput (transactions per second), consistency delay, and communication overhead. Performance evaluation shows that CRBFT achieves lower communication overhead than PBFT. When the number of nodes is the same, CRBFT can obtain higher TPS and lower consistency delay. The results show that compared with PBFT, CRBFT can provide very competitive results.
Blockchain is a Byzantine fault tolerant (BFT) system wherein decentralized nodes execute consensus protocols to drive the agreement process on new blocks added to a distributed ledger. Generally, two-round communications among [Formula: see text] nodes are required to tolerate up to [Formula: see text] faults in BFT-based consensus networks. This communication pattern corresponds to the worse-case scenario of consensus achievement, even under asynchronous network conditions. Nevertheless, it is not uncommon for a network to operate under better conditions, where a consensus can be reached with a lower communication cost. Hence, with the addition of a faster optimistic path toward an agreement, the idea of dual-mode consensus has been proposed as a promising approach to enhance the performance of asynchronous BFT protocols. However, this opportunity is not completely exploited by existing dual-mode protocols as the fast path can be followed only in a nonfaulty and synchronous network. This article presents a novel dual-mode protocol consisting of fast and backup subprotocols. To create different consensus committees for fast and backup-mode operations, the network contains both active and passive nodes. A consensus can be expedited through a fast-mode operation when majority of the active nodes can communicate synchronously. Under non-ideal conditions, the backup protocol takes over the agreement process from its fast-mode counterpart without starting over the suspended round. The safety and liveness of the proposed protocol are guaranteed with lower communication costs, which balance the trade-off between protocol efficiency and availability.
To be competitive with centralized applications, consensus protocols in blockchains must provide minimal latency while being able to scale to thousands of participants in order to preserve a high level of decentralization. A common way to minimize latency is to augment a consensus protocol with a fast track, which ensures that a decision is reached in just a couple of message delays in favorable conditions. However, it is a challenging task to preserve safety and good performance when these favorable conditions do not hold. To the best of our knowledge, all existing Byzantine fault-tolerant consensus protocols with fast tracks require view change protocols with quadratic authenticator complexity. In this paper, we provide the first solution to Byzantine consensus with fast track with a linear view change. The protocol incurs no asymptotic overhead over the baseline while reducing the latency in favorable conditions by a factor of 2. Our construction is based on a novel type of cryptographic proofs, which we call Proofs of Exclusivity (or PoE for short), which may be of independent interest. While our protocol for constructing a PoE comes at no extra costs in latency or asymptotic complexities, it does require some extra computation. To make sure that it does not impair the overall performance, we also show how to apply accountability and proofs of misbehavior in order to reduce to zero the overhead incurred by the computation of a PoE. More precisely, our mechanism guarantees that whenever this overhead is not zero, then automatically honest participants obtain a publicly verifiable proof that a well-identified malicious participant openly misbehaved. In this case, the overhead of computing a few extra threshold signatures for the Proof of Exclusivity can be seen as a relatively small price to get rid of a malicious participant.
The thesis addresses the problem of scalability in decentralized blockchains in the context of the trade-off between transaction throughput and hardware requirements to participate in the network. Rollups are presented, that is technologies to verify on-chain blocks executed off-chain by minimizing the assumptions of trust. The variant of the Optimistic Rollups, in particular of Optimism and the use of invalidity proofs through interactive binary search and of the Validity Rollups, in particular of StarkNet, and the use of validity proofs through STARKs are discussed. Finally, the two solutions are compared on withdrawal time, on the cost of transactions and techniques to minimize it, on the possibility of applying the technology recursively, on compatibility with Ethereum and on the licenses used.
Web 3.0 enables user-generated contents and user-selected authorities. With the help of decentralized wireless edge computing architectures, Web 3.0 allows users to read, write, and own contents. A core technology that enables Web 3.0 goals is blockchain, which provides security services by recording content in a decentralized and transparent manner. However, the explosion of on-chain recorded contents and the fast-growing number of users cause increasingly unaffordable computing and storage resource consumption. A promising paradigm is to analyze the semantic information of contents that can convey precisely the desired meanings without consuming many resources. In this article, we propose a unified blockchainse-mantic ecosystems framework for wireless edge intelligence-enabled Web 3.0. Our framework consists of six key components to exchange semantic demands. We then introduce an Oracle-based proof of semantic mechanism to implement on-chain and off-chain interactions of Web 3.0 ecosystems on semantic verification algorithms while maintaining on-chain and off-chain service security. An adaptive Deep Reinforcement Learning-based sharding mechanism on Oracle is designed to improve interaction efficiency, which can facilitate Web 3.0 ecosystems to deal with varied semantic demands. Finally, a case study is presented to show that the proposed framework can dynamically adjust settines according to varied semantic demands.
Ertem Nusret Tas, John R. Adler, Mustafa Al-Bassam, Ismail Khoffi · 6 authors
Accountability, the ability to provably identify protocol violators, gained prominence as the main economic argument for the security of proof-of-stake (PoS) protocols. Rollups, the most popular scaling solution for blockchains, typically use PoS protocols as their parent chain. We define accountability for rollups, and present an attack that shows the absence of accountability on existing designs. We provide an accountable rollup design and prove its security, both for the traditional `enshrined' rollups and for sovereign rollups, an emergent alternative built on lazy blockchains, tasked only with ordering and availability of the rollup data.
Gabriel Antonio F. Rebello, Gustavo F. Camilo, Lucas C. B. Guimarães, Lucas Airam C. de Souza · 5 authors
Consensus protocols for blockchain-based systems are crucial and the most complex part of the blockchain. The proof-of-work consensus protocol of Bitcoin cryptocurrency is the most popular, but it presents a low transaction rate and high energy consumption. This paper analyzes the main quorum-based consensus protocols for blockchains that are alternatives with higher throughput and energy-efficient. The paper focuses on Byzantine fault-tolerant protocols as they are more robust to security attacks. We classify and analyze quorum-based consensus protocols according to their main characteristics and performance, highlighting the flaws and the specific attacks that affect each consensus protocol and presenting countermeasures.1
Currently there exist many blockchains with weak trust guarantees, limiting applications and participation. Existing solutions to boost the trust using a stronger blockchain, e.g., via checkpointing, requires the weaker blockchain to give up sovereignty. In this paper, we propose a family of protocols in which multiple blockchains interact to create a combined ledger with boosted trust. We show that even if several of the interacting blockchains cease to provide security guarantees, the combined ledger continues to be secure - our Trustboost protocols achieve the optimal threshold of tolerating the insecure blockchains. This optimality, along with the necessity of blockchain interactions, is formally shown within the classic shared memory model, tackling the long standing open challenge of solving consensus in the presence of both Byzantine objects and processes. Furthermore, our proposed construction of Trustboost simply operates via smart contracts and require no change to the underlying consensus protocols of the participating blockchains, a form of "consensus on top of consensus''. The protocols are lightweight and can be used on specific (e.g., high value) transactions; we demonstrate the practicality by implementing and deploying Trustboost as cross-chain smart contracts in the Cosmos ecosystem using approximately 3,000 lines of Rust code, made available as open source [52]. Our evaluation shows that using 10 Cosmos chains in a local testnet, Trustboost has a gas cost of roughly $2 with a latency of 2 minutes per request, which is in line with the cost on a high security chain such as Bitcoin or Ethereum.
Sina Kamali, Shayan Shabihi, Fakharian, Mohammad Taha, Alireza Arbabi · 7 authors
The consensus protocol is the core of a blockchain system which guarantees its secure and stable operation. Proof of Activity (PoA) is a consensus protocol that tries to address some of the issues pertinent to the most widely used protocols, such as Proof of Stake (PoS) and Proof of Work (PoW). However, it still needs to solve the issues regarding high energy consumption, significant resources required, high mining latency, and the need for private blockchains. In this paper, we propose Redefined Proof of Activity (RPoA), a new consensus protocol that builds on top of some of the best features of the existing protocols, such as PoW, PoS, and PoA, and values active service provided by users on the network. Our approach tries to address the issues above and falls in the service-based protocols category that gives mining credit to users as they serve on the network.
Ulysse Pavloff, Yackolley Amoussou-Guenou, Sara Tucci-Piergiovanni
Ethereum has undergone a recent change called \textit{the Merge}, which made Ethereum a Proof-of-Stake blockchain, shifting closer to BFT consensus. Ethereum, which wished to keep the best of the two protocol designs (BFT and Nakomoto-style), now has a convoluted consensus protocol as its core. The result is a blockchain being possibly produced in a tree-like form while participants try to finalize blocks. We categorize different attacks jeopardizing the liveness of the protocol. The Ethereum community has responded by creating patches against some of them. We discovered a new attack on the patched protocol. To support our analysis, we propose a new high-level formalization of the properties of liveness and availability of the Ethereum blockchain, and we provide a pseudo-code. We believe this formalization to be helpful for other analyses as well. Our results yield that the Ethereum Proof-of-Stake has safety but only probabilistic liveness. The probability of the liveness is influenced by the parameter describing the time frame allowed for validators to change their mind about the current main chain.
As transaction fees skyrocket today, blockchains become increasingly expensive, hurting their adoption in broader applications. This work tackles the saving of transaction fees for economic blockchain applications. The key insight is that other than the existing "default" mode to execute application logic fully on-chain, i.e., in smart contracts, and in fine granularity, i.e., user request per transaction, there are alternative execution modes with advantages in cost-effectiveness. On Ethereum, we propose a holistic middleware platform supporting flexible and secure transaction executions, including off-chain states and batching of user requests. Furthermore, we propose control-plane schemes to adapt the execution mode to the current workload for optimal runtime cost. We present a case study on the institutional accounts (e.g., coinbase.com) intensively sending Ether on Ethereum blockchains. By collecting real-life transactions, we construct workload benchmarks and show that our work saves 18% ~ 47% per invocation than the default baseline while introducing 1.81 ~ 16.59 blocks delay.
Ignacio Amores-Sesar, Christian Cachin, Tedeschi, Enrico
Avalanche is a blockchain consensus protocol with exceptionally low latency and high throughput. This has swiftly established the corresponding token as a top-tier cryptocurrency. Avalanche achieves such remarkable metrics by substituting proof of work with a random sampling mechanism. The protocol also differs from Bitcoin, Ethereum, and many others by forming a directed acyclic graph (DAG) instead of a chain. It does not totally order all transactions, establishes a partial order among them, and accepts transactions in the DAG that satisfy specific properties. Such parallelism is widely regarded as a technique that increases the efficiency of consensus. Despite its success, Avalanche consensus lacks a complete abstract specification and a matching formal analysis. To address this drawback, this work provides first a detailed formulation of Avalanche through pseudocode. This includes features that are omitted from the original whitepaper or are only vaguely explained in the documentation. Second, the paper gives an analysis of the formal properties fulfilled by Avalanche in the sense of a generic broadcast protocol that only orders related transactions. Last but not least, the analysis reveals a vulnerability that affects the liveness of the protocol. A possible solution that addresses the problem is also proposed.
The concept of verifiable delay functions has received attention from researchers since it was first proposed in 2018. The applications of verifiable delay are also widespread in blockchain research, such as: computational timestamping, public random beacons, resource-efficient blockchains, and proofs of data replication. This paper introduces the concept of verifiable delay functions and systematically summarizes the types of verifiable delay functions. Firstly, the description and characteristics of verifiable delay functions are given, and weak verifiable delay functions, incremental verifiable delay functions, decodable verifiable delay functions, and trapdoor verifiable delay functions are introduced respectively. The construction of verifiable delay functions generally relies on two security assumptions: algebraic assumption or structural assumption. Then, the security assumptions of two different verifiable delay functions are described based on cryptography theory. Secondly, a post-quantum verifiable delay function based on super-singular isogeny is introduced. Finally, the paper summarizes the blockchain-related applications of verifiable delay functions.
Blockchain platforms have gained popularity in recent years and integrated with other digital technologies like Internet of Things (IoT) and Artificial Intelligence (AI) for multiple-business purposes. Software aging is a common issue in many long-running software systems, but little has been experienced in the context of blockchain platforms. To narrow this gap, this work aims to characterize potential software aging issues in the Cardano blockchain platform that is considered the largest cryptocurrency adopting proof-of-stake. By performing statistical analysis on the measurement data of the Cardano blockchain deployed in two environments with different configurations, we found a symptom of software aging through memory degradation that was confirmed by the Mann-Kendall test. By analyzing the running processes, we identify the cardano-node (the main process of the platform) as the process possibly responsible for such degradation.
Aleksandr I. Filippov, Artem Barger, Vladimir Popov, Oleg Abdrashitov
We have recently become witnesses of the constantly growing adoption of distributed ledger technology utilized in various domains, whereas for enterprise-grade solutions, the most prominent platform is Hyperledger Fabric [1]. However, the lack of a trusted source of time within the platform poses certain limitations in how this platform could be used. In particular, there is no built-in mechanism to ensure the expiration of the signing certificates during the validation phase of the transactions processing pipeline, which introduces severe concern from the platform’s usability and security point of view. Therefore, we would like to introduce a solution that incorporates Byzantine Fault Tolerant source of time into Hyperledger Fabric, where the suggested approach utilizes opened sourced implementation of SmartBFT [2] distributed consensus protocol.
Aimen Djari, Emmanuelle Anceaume, Sara Tucci-Piergiovanni
The arrival of Bitcoin [1] drove the shift to decentralized ecosystems through the exchange of transactions without intermediary. However, one of the main challenges that need to face permissionless blockchains are scalability and security. In this paper, we present a performance evaluation of Sycomore++, a permissionless graph-based distributed ledger whose main feature is to dynamically self-adapt the number of created blocks to the current number of submitted transactions, and compare them with the ones of Bitcoin and Sycomore, a graph-based distributed ledger. Our evaluation relies on agent-based simulations to evaluate the capability of these distributed ledgers to address the aforementioned challenges, within different execution contexts.
In order to realize collaboration on a global scale, academic research requires often large quantities of data to be shared between geographically dispersed organizations. The requirement to protect and govern data in a network of loosely coupled, autonomous institutions is an incentive for decentralized solutions, where the participants are in full control of their data without trusting a third-party provider to store and process the data. In order to increase data availability and fault tolerance in decentralized collaborative systems, we propose a layer, which is based on replication and decentralized authority over the data. The solution consists of an idea of peer-sets, which are groups of peers implementing collective data management, a consensus protocol which synchronizes a distributed ledger between peers, and an atomic commitment protocol used to implement optional two-way references between documents. This architecture may be utilized in various decentralized collaborative data-sharing systems, such as Onedata.
Eventual consistency is a consistency model that favors liveness over safety. It is often used in large-scale distributed systems where models ensuring a stronger safety incur performance that are too low to be deemed practical. Eventual consistency tends to be uniformly applied within a system, but we argue a demand exists for differentiated eventual consistency, e.g. in blockchain systems. We propose update-query consistency with primaries and secondaries (UPS) to address this demand. UPS is a novel consistency mechanism that works in pair with our novel two-phase epidemic broadcast protocol gossip primary-secondary (GPS) to offer differentiated eventual consistency and delivery speed. We propose two complementary analyses of the broadcast protocol: a continuous analysis and a discrete analysis based on compartmental models used in epidemiology. Additionally, we propose the formal definition of a scalable consistency metric to measure the consistency trade-off at runtime. We evaluate UPS in two simulated worldwide settings: a one-million-node network and a network emulating that of the Ethereum blockchain. In both settings, UPS reduces inconsistencies experienced by a majority of the nodes and reduces the average message latency for the remaining nodes.
The advent of Ethereum opened up a pandora box of decentralized possibilities. While allowing for the replicated, decentralized computation of Turing-complete instructions, platforms such as Ethereum do not offer the possibility of direct, interactive, real-time processing of users’ inputs that could later affect the decentralized state machine. They cannot directly observe, replicate and authenticate users’ actions performed in real-time while presenting the results of these. They lack mechanics that would incentivize full-nodes to provide low-latency-constrained services to users in-between epochs of a decentralized state machine, thus pushing dApps’ developers towards hybrid architectures—ones employing centralized servers while not even considering certain applications, due to the aforementioned limitations. In this research paper, we explore our results of an attempt to create a ‘decentralized operating system’ user experience a reality. We propose an architecture which solves the problems of the responsiveness and finalization of multiple actions performed by users in real-time—without the need for users to pre-authenticate but after having presented a single, unitary consent to commit—through the hereby proposed Deferred Authentication mechanism. To allow for this, we employ an in-house developed #GridScript programming language, used by our decentralized state machine, along with a computer-vision-enabled and AI-aided mobile app (available for both iOS and Android). We introduce the concept of Decentralized Processing Threads (DPTs) and see how these enable fascinating possibilities. In addition, we look into how Access-Control-Lists (ACLs)-enabled, incentivized storage, incentivized Sybil-proof communication, embedded firewall apparatus, integrated off-the-chain payments, and crypto-incentivized off-the-chain storage aid such a system and thus render it as feasible. We highlight various interesting troubles we have encountered, such as state recovery after disconnects of the UI and the replication of its state across both nodes maintaining the network and web browsers. We depict ‘off-the-chain’ mechanics, which we use to reward for real-time services provided to users by nodes maintaining the network. We tackle crypto-incentivized WebRTC swarms not needing centralized servers for signaling. We look into a user-friendly approach to Non-Fungible Tokens (NFTs). The test-bed is readily available with multiple functional UI dApps already in place. Indeed, the paper presents UI and UX design decisions we have undertaken based on conclusions from statistical research results on a group of 50,341 volunteers over 4 years, which we have used to formulate what we codenamed as the Venice UI/UX design paradigm. We extend upon the notion of Token Pools to allow for the Sybil-proof incentivization of multiple-peers from a single data structure stored on the decentralized state machine.