Abstract. The purpose of a consensus protocol is to keep a distributed network of nodes “in sync,” even in the presence of an unpredictable communication network and adversarial behavior by some of the participating nodes. In the permissionless setting relevant to modern blockchain protocols, these nodes may be operated by a large number of unknown players, with each player free to use multiple identifiers and to start or stop running the protocol at any time. Establishing that a permissionless consensus protocol is “secure” thus requires both a distributed computing argument (that the protocol guarantees consistency and liveness unless the fraction of adversarial participation is sufficiently large) and an economic argument (that carrying out an attack would be prohibitively expensive for a potential attacker). There is a mature toolbox for assembling arguments of the former type; the goal of this paper is to lay the foundations for arguments of the latter type. For example, the Ethereum protocol is oft-claimed to be “more economically secure” after “the merge,” meaning in its current proof-of-stake incarnation relative to the (proof-of-work) original. What, formally, does this assertion mean? Is it true? Could there be alternative protocols that are “still more economically secure” than Ethereum? How do the answers depend on the assumptions imposed on, for example, the reliability of message delivery or the active participation of non-malicious players? An ideal permissionless consensus protocol would, in addition to satisfying standard consistency and liveness guarantees, render consistency violations prohibitively expensive for the attacker without collateral damage to honest participants—for example, by programatically confiscating an attacker’s resources without reducing the value of honest participants’ resources, as is the intention for slashing in a proof-of-stake protocol. We make this idea precise with our notion of the EAAC (expensive to attack in the absence of collapse) property and prove the following results: (1) In the synchronous and dynamically available setting (in which the communication network is reliable but nonmalicious players may be periodically inactive), with an adversary that controls at least one-half of the overall resources, no protocol can be EAAC. In particular, this result rules out EAAC for all typical longest-chain protocols (be they proof-of-work or proof-of-stake). (2) In the partially synchronous and quasi-permissionless setting (in which resource-controlling non-malicious players are always active but the communication network may suffer periods of unreliability), with an adversary that controls at least one-third of the overall resources, no protocol can be EAAC. In particular, slashing in a proof-of-stake protocol cannot achieve its intended purpose if message delays cannot be bounded a priori. (3) In the synchronous and quasi-permissionless setting, there is a proof-of-stake protocol with slashing that, provided the adversary controls less than two-thirds of the overall stake, satisfies the EAAC property. Thus, while only “classical security” is possible in the dynamically available or partially synchronous settings, proof-of-stake protocols with slashing can obtain additional “economic security” in the quasi-permissionless and synchronous settings. All three results are optimal with respect to the size of the adversary. With respect to Ethereum, our work formalizes the potential security benefits of proof-of-stake sybil-resistance coupled with slashing and the common belief that the merge has increased Ethereum’s economic security. Our work also provides mathematical justifications for several key design decisions behind the post-merge Ethereum protocol, ranging from long cooldown periods for unstaking to economic penalties for inactivity.
The dynamic and unpredictable nature of network environments poses a significant challenge for distributed systems, particularly those relying on consensus algorithms for state management and fault tolerance. To address this challenge, this article introduces a novel simulation model designed to study the impact of unstable network connections on clusters running consensus algorithms. The model is engineered to mimic varying degrees of network instability, including latency fluctuations and connection disruptions, which are characteristic of real-world distributed systems. Our proposed model represents a significant advancement in the simulation of distributed networks. It employs a sophisticated network emulation layer capable of generating a wide spectrum of unstable network conditions. The core of the model is a highly configurable consensus mechanism simulator that allows for the adjustment of key parameters such as heartbeat intervals, election timeouts, and message loss rates. This level of configurability enables a comprehensive analysis of consensus behaviors under different network scenarios. The article focuses on the methodology behind the development of the model, detailing the theoretical underpinnings and the implementation strategies used to ensure a realistic representation of network instability. We also discuss the potential applications of the model, which extend beyond academic research into practical domains where distributed ledger technologies and distributed databases are prevalent. Through the deployment of this model, researchers and system architects can gain deeper insights into the resilience and adaptability of consensus algorithms. The model serves as a tool for preemptively identifying and addressing potential issues in distributed systems, facilitating the development of more robust and reliable technologies. In summary, the article showcases the design and capabilities of a new model that enables an in-depth understanding of the delicate interplay between network instability and consensus efficiency. By focusing on the model itself, the article aims to lay a foundation for future studies and improvements in the field of distributed systems.
The rapid advancement of technology has brought about profound changes in various spheres of our society. Among these improvements, the Internet of Things (IoT) stands out as a transformative force, revolutionizing visibility across diverse domains. By furnishing real-time data and insights, IoT empowers businesses to refine their operations and significantly enhance overall efficiency. However, the decentralized nature of IoT architecture presents a substantial challenge in terms of security. As technology proliferates, security emerges as a paramount concern, particularly in safeguarding IoT devices and the data they generate against unauthorized access, data breaches, and potential harm. Simultaneously, the imperative for real-time data streaming underscores the need for a rapid dissemination protocol as a fundamental requirement. Our proposed solution adeptly addresses both of these critical aspects by integrating BDLS, a promising Byzantine Fault Tolerance (BFT) protocol, with Hyperledger Fabric for IoT devices. This integration not only enhances security but also ensures the rapid and secure dissemination of data. Through rigorous evaluation, our study demonstrates the outstanding performance of BDLS Fabric integration in terms of throughput (TPS), surpassing CFT-type protocols and numerous other proposed solutions utilizing PBFT, thereby reinforcing the importance of security in IoT deployments. Moreover, by securing the edge servers and the cloud replica using Hyperledger Fabric-BDLS integration, our solution fortifies the IoT ecosystem against potential threats, establishing a robust foundation for future innovations in distributed ledger technology.
Lucian Trestioreanu, Flaviene Scheidt, Wazen M. Shbair, Jérôme François · 6 authors
With the large increase in the adoption of blockchain technologies, their underlying peer-to-peer networks must also scale with the demand. In this context, previous works highlighted the importance of ensuring efficient and resilient communication for the underlying consensus and replication mechanisms. However, they were mainly focused on mainstream, Proof-of-Work-based Distributed Ledger Technologies like Bitcoin or Ethereum. In this paper, the problem is investigated in the context of consensus-validation based blockchains, like the XRP Ledger. The latter relies on a Federated Byzantine Agreement (FBA) consensus mechanism which is proven to have a good scalability in regards to transaction throughput. However, it is known that significant increases in the size of the XRP Ledger network would be challenging to achieve. The main reason is the flooding mechanism used to disseminate the messages related to the consensus protocol, which creates many duplicates in the network. Squelching is a recent solution proposed for limiting this duplication, however, it was never evaluated quantitatively in real-life scenarios involving the XRPL production network. In this paper, our aim is to assess this mechanism using a real-life controllable testbed and the XRPL production network, to assess its benefit and compare it to alternative solutions relying on Named Data Networking and on a gossip-based approach.
This paper introduces the Proof of Sampling (PoSP) protocol, a Nash Equilibrium-based verification mechanism, and its application to decentralized machine learning inference through spML. Our protocol has a pure strategy Nash Equilibrium, compelling rational participants to act honestly. It economically disincentivizes dishonest behavior, making it costly for participants to compromise the network's integrity. In our spML protocol, we apply PoSP to decentralized inference for AI applications via a novel cryptographic protocol. The resulting protocol is much more efficient than zero knowledge proof based approaches. Moreover, we anticipate that the PoSP protocol could be effectively utilized for designing verification mechanisms within Actively Validated Services (AVS) in restaking solutions. We further expect that the PoSP protocol could be applied to a variety of other decentralized applications. Our approach enhances the reliability and efficiency of decentralized systems, paving the way for a new generation of decentralized applications.
Ulysse Pavloff, Yackolley Amoussou-Guenou, Sara Tucci-Piergiovanni
In May 2023, the Ethereum blockchain experienced its first inactivity leak, a mechanism designed to reinstate chain finalization amid persistent network disruptions. This mechanism aims to reduce the voting power of validators who are unreachable within the network, reallocating this power to active validators. This paper investigates the implications of the inactivity leak on safety within the Ethereum blockchain. Our theoretical analysis reveals scenarios where actions by Byzantine validators expedite the finalization of two conflicting branches, and instances where Byzantine validators reach a voting power exceeding the critical safety threshold of one-third. Additionally, we revisit the probabilistic bouncing attack, illustrating how the inactivity leak can result in a probabilistic breach of safety, potentially allowing Byzantine validators to exceed the one-third safety threshold. Our findings uncover how penalizing inactive nodes can compromise blockchain properties, particularly in the presence of Byzantine validators capable of coordinating actions.
In a practical blockchain system based on the Practical Byzantine Fault Tolerance (PBFT) protocol, the voting nodes can fail at any time due to non-Byzantine errors, such as autonomous shutdowns, device crashes, and communication link failures caused by mobility or obstacles. These errors may cause voting nodes to exit the PBFT-based blockchain system unpredictably, resulting in a variable number of voting nodes available at any given time. To maintain optimal performance and consistency while adapting a PBFT-based blockchain system to this dynamic change, this paper proposes an extension to the PBFT protocol by introducing a repair process for failed nodes. The new PBFT-based blockchain system with repairable voting nodes is then analyzed for performance and reliability analysis by using multi-dimensional Markov processes, queueing theory, and the first passage time method. Additionally, we validate the accuracy of our theoretical findings by conducting numerical examples and simulation experiments. These experiments demonstrate that the introduction of a repair process can improve the performance and reliability of the PBFT-based blockchain system. Furthermore, we illustrate how various system parameters impact the performance measures of the PBFT-based blockchain system with repairable voting nodes. We hope that the methodology and results presented in this paper will establish a common framework for deriving theoretical analysis of existing PBFT-based blockchain systems and inspire future research efforts in this field.
In the realm of Distributed Ledgers (DLs), a solution to enhancing maximum peak throughput involves establishing multiple independent blockchains that evolve concurrently. However, an excess of parallel chains in comparison to the application's demands can result in increased latency in content delivery, squandered bandwidth, and heightened computational strain on network nodes.
This article examines the significant challenges encountered in implementing sharding within distributed replication systems. It identifies the impediments of achieving consensus among large participant sets, leading to scalability, throughput, and performance limitations. These issues primarily arise due to the message complexity inherent in consensus mechanisms. In response, we investigate the potential of sharding to mitigate these challenges, analyzing current implementations within distributed replication systems. Additionally, we offer a comprehensive review of replication systems, encompassing both classical distributed databases as well as Distributed Ledger Technologies (DLTs) employing sharding techniques. Through this analysis, the article aims to provide insights into addressing the scalability and performance concerns in distributed replication systems.
Smart contracts have played a pivotal role in the evolution of blockchains and Decentralized Applications (DApps). As DApps continue to gain widespread adoption, multiple smart contract languages have been and are being made available to developers, each with its distinctive features, strengths, and weaknesses. In this paper, we examine the smart contract languages used in major blockchain platforms, with the goal of providing a comprehensive assessment of their main properties. Our analysis targets the programming languages rather than the underlying architecture: as a result, while we do consider the interplay between language design and blockchain model, our main focus remains on language-specific features such as usability, programming style, safety and security. To conduct our assessment, we propose an original benchmark which encompasses a wide, yet manageable, spectrum of key use cases that cut across all the smart contract languages under examination. • We give an abstract overview of smart contract platforms, discussing the impact of different design choices. • We illustrate by examples how different design choices give rise to different programming styles for smart contracts. • We consider 6 leading smart contract languages: Solidity (Ethereum), Rust (Solana), Aiken (Cardano), PyTeal (Algorand), Move (Aptos), SmartPy (Tezos). • We develop an open-source benchmark of use cases of smart contracts, implemented in all the languages in our selection. • Based on our benchmark, we evaluate smart contract languages focussing on their security, code readability, usability, and functionalities.
Bank of Italy, Carlo Gola, Guido Befani, Patrizio Fiorenza · 7 authors
The work provides a method for classifying blockchains and crypto-assets, facilitating their comparison for business and regulatory purposes. Blockchains - and more generally systems based on Distributed Ledger Technology (DLT) - adopt different technologic configurations, each distinguished by the activities performed, technical characteristics, and governance structures. Particular noteworthy is the difference between some DLTs, which integrate automated organizational procedures with traditional decision-making processes, and others that adopt entirely algorithmic governance. Equally complex is the task of identifying types of crypto-assets, also known as digital tokens, generated and transferred through this technology. The work outlines the primary characteristics of DLTs and crypto-assets, utilizing ‘switching circuits’ to visually represent or express them in a simple formula. The proposed methodology, applicable both in the EU and in the US, untangles a given DLT/crypto ecosystem and reassembles it through logic maps, facilitating the identification of the technologic, economic, and legal features and overcoming the risk of a rigid and easily outdated taxonomy. The ultimate purpose of the paper is to propose a working method capable of accommodating every possible configuration of DLT and digital token and their potential evolutions. Practical examples of regulatory application and two case studies (Ethereum and Polkadot) are provided
Networked computing power is a critical utility in the era of artificial intelligence. This paper presents a novel Physical Infrastructure Finance (PinFi) protocol designed to facilitate the distribution of computing power within networks in a decentralized manner. Addressing the core challenges of coordination, pricing, and liquidity in decentralized physical infrastructure networks (DePIN), the PinFi protocol introduces a distinctive dynamic pricing mechanism. It enables providers to allocate excess computing resources to a "dissipative" PinFi liquidity pool, distinct from traditional DeFi liquidity pools, ensuring seamless access for clients at equitable, market-based prices. This approach significantly reduces the costs of accessing computing power, potentially to as low as 1% compared to existing services, while simultaneously enhancing security and dependability. The PinFi protocol is poised to transform the dynamics of supply and demand in computing power networks, setting a new standard for efficiency and accessibility.
Decentralized Finance (DeFi) has emerged as a contemporary competitive as well as complementary to traditional centralized finance systems. As of 23rd January 2024, per Defillama approximately USD 55 billion is the total value locked on the DeFi applications on all blockchains put together. A Byzantine Fault Tolerant (BFT) State Machine Replication (SMR) protocol, popularly known as the consensus protocol, is the central component of a blockchain. If forks are possible in a consensus protocol, they can be misused to carry out double spending attacks and can be catastrophic given high volumes of finance that are transacted on blockchains. Formal verification of the safety of consensus protocols is the golden standard for guaranteeing that forks are not possible. However, it is considered complex and challenging to do. This is reflected by the fact that not many complex consensus protocols are formally verified except for Tendermint and QBFT. We focus on Supra's Pipelined Moonshot consensus protocol. Similar to Tendermint's formal verification, we too model Pipelined Moonshot using IVy and formally prove that for all network sizes, as long as the number of Byzantine validators is less than one thirds, the protocol does not allow forks, thus proving that Pipelined Moonshot is safe and double spending cannot be done using forks. The IVy model and proof of safety is available on Github.
Ethereum's current Gasper consensus mechanism, which combines the Latest Message Driven Greediest Heaviest Observed SubTree (LMD-GHOST) fork choice rule with the probabilistic Casper the Friendly Finality Gadget (FFG) finality overlay, finalizes transactions in 64 to 95 blocks, an approximate 15-minute delay. This finalization latency impacts user experience and exposes the network to short-term chain reorganization risks, potentially enabling transaction censorship or frontrunning by validators without severe penalties. As the ecosystem pursues a rollup-centric roadmap to scale Ethereum into a secure global settlement layer, faster finality allows cross-layer and inter-rollup communication with greater immediacy, reducing capital inefficiencies. Single slot finality (SSF), wherein transactions are finalized within the same slot they are proposed, promises to advance the Ethereum protocol and enable better user experiences by enabling near-instant economic finality. This thesis systematically studies distributed consensus protocols through propose-vote-merge, PBFT-inspired, and graded agreement families - scrutinizing their capacities to enhance or replace LMD-GHOST. The analysis delves into the intricate tradeoffs between safety, liveness, and finality, shedding light on the challenges and opportunities in designing an optimal consensus protocol for Ethereum. It also explores different design decisions and mechanisms by which single slot or fast finality can be enabled, including cumulative finality, subsampling, and application-layer fast finality. Furthermore, this work introduces SSF-enabled and streamlined fast finality constructions based on a single-vote total order broadcast protocol. The insights and recommendations in this thesis provide a solid foundation for the Ethereum community to make informed decisions regarding the future direction of the protocol's consensus.
We study long-term equilibria that arise in the token monetary policy, or tokenomics, design of proof-of-stake (PoS) blockchain systems that engage utility maximizing users and validators. Validators are system maintainers who get rewarded with tokens for performing the work necessary for the system to function properly, while users compete and pay with such tokens for getting a desired portion of the system service. <br/><br/>We study how the system service provision and suitable rewards schemes together can lead to equilibria with the following desirable characteristics (1) viability: the system keeps parties engaged, (2) decentralization and skin-in-the-game: multiple sufficiently invested validators are participating, (3) stability: the price path of the underlying token used to transact with the system does not change widely over time, and (4) feasibility: the mechanism is easy to implement as a smart contract, e.g., it does not require a fiat reserve on-chain to perform token buybacks or to perform bookkeeping of exponentially growing token holdings.<br/><br/>Our analysis enables us to put forward a novel generic mechanism for blockchain monetary policy that we call quantitative rewarding (QR). We investigate how to implement QR in single-token and two-token proof of stake (PoS) blockchain systems. The latter are systems that utilize one token for the users to pay the transaction fees and a different token for the validators to participate in the PoS protocol and get rewarded. Our approach demonstrates a concrete advantage of the two-token setting in terms of the ability of the QR mechanism to be realized effectively and provide good equilibria. Our analysis also reveals an inherent limitation of the single token setting in terms of implementing an effective blockchain monetary policy - a distinction that is, to the best of our knowledge, highlighted for the first time.licy - a distinction that is, to the best of our knowledge, highlighted for the first time.
In a blockchain network, a rule set called consensus mechanism is used to create and finalize a block. In a proof-of-stake (PoS), consensus-based blockchain network, nodes become validators, minters, or stakeholders’ nodes to complete the consensus mechanism. In these networks, when a node becomes a validator node, its details need to be saved because the details of the validators are used in the network for many important decisions, such as selecting block proposers for the consensus process. In this paper, we present Sea Shield, which uses a validator chain to save a node’s information when it becomes a validator or leaves its responsibility as a validator in the PoS-based blockchain network. The validator chain is a blockchain that can run with the main chain of a PoS-based blockchain. The internal features of the validator chain are similar to those of the blockchain. We designed and simulated a consensus mechanism to create and finalize the block for the validator chain with no forks. We present a process by which a node may join or unjoin as a validator in a PoS-based blockchain network to improve the overall security of the main chain-consensus process.
As the potential of directed acyclic graph (DAG)-based distributed ledgers in IoT systems unfolds, a need arises to understand their intricate dynamics in real-world scenarios. It is well known that discrete event simulations can provide high-fidelity evaluations of protocols. However, there is a lack of public discrete event simulators capable of assessing DAG-based distributed ledgers. In this paper, a discrete-event-based distributed ledger simulator is introduced, with which we investigate a custom Python-based implementation of IOTA's Tangle DAG protocol. The study reveals the dynamics of Tangle (particularly Poisson processes in transaction dynamics), the efficiency and intricacies of the random walk in Tangle, and the quantitative assessment of node convergence. Furthermore, the research underscores the significance of weight updates without depth limitations and provides insights into the role, challenges, and implications of the coordinator/validator in DAG architectures. The results are striking, and although the findings are reported only for Tangle, they demonstrate the need for adaptable and versatile discrete event simulators for DAG architectures and tip selection methodologies in general.
In this paper, we present a watchdog blockchain network (WDN) that allows for simultaneous scalability and decentralization enhancements. Because of the blockchain trilemma, achieving high levels of security, scalability, and decentralization simultaneously is challenging. Typically, public blockchains are fully decentralized at the expense of scalability, whereas private blockchains achieve high scalability at the expense of decentralization. A WDN is proposed to compensate for the low-level decentralization of a private blockchain while maintaining its high-level scalability. A WDN may prevent arbitrary forgery, alteration, and deletion of distributed ledgers in private blockchains owing to weak decentralization. However, the transaction throughput gap between the WDN and the private blockchain can be a significant obstacle in operating a WDN with a private blockchain. Therefore, the WDN in this study has been designed to back up data on the private blockchain in real time over a distributed network environment. The WDN features a network-aware consensus protocol that can quickly complete the consensus process of the three phases. To this end, modern network technologies such as GossipSub, quick UDP internet connections (QUIC), and Google remote procedure call (GRPC) have been appropriately adopted for the WDN. To demonstrate the system performance of the WDN, a blockchain system was fully implemented in the form of docker containers. Furthermore, we verified the feasibility of the WDN by developing decentralized applications (DApps).
Wireless community networks (WCNs) represent bottom-up network infrastructures facing the following challenges: (1) Managing diverse devices, (2) Establishing effective real-time incentives, (3) Addressing anomalies, attacks, and faults, and (4) Ensuring data integrity verification. Inspired by [2], we introduce the decentralized wireless community network (DeWCN) concept, enabling community members to contribute resources to a common resource pool in a verifiable and incentivized manner. Consensus participants, selected from conflict-free network areas, maintain a distributed ledger with partial Byzantine fault tolerance for transparency and protocol automation. By leasing out storage, computing, and bandwidth resources with globally agreed-upon contributions, individuals can receive real-time cost compensation.
Tao Yan, Shengnan Li, Benjamin Kraner, Luyao Zhang · 5 authors
Ethereum 2.0, as the preeminent smart contract blockchain platform, guarantees the precise execution of applications without third-party intervention. At its core, this system leverages the Proof-of-Stake (PoS) consensus mechanism, which utilizes a stochastic process to select validators for block proposal and validation, consequently rewarding them for their contributions. However, the implementation of blockchain technology often diverges from its central tenet of decentralized consensus, presenting significant analytical challenges. Our study collects consensus reward data from the Ethereum Beacon chain and conducts a comprehensive analysis of reward distribution and evolution, categorizing them into attestation, proposer and sync committee rewards. To evaluate the degree of decentralization in PoS Ethereum, we apply several inequality indices, including the Shannon entropy, the Gini Index, the Nakamoto Coefficient, and the Herfindahl-Hirschman Index (HHI). Our comprehensive dataset is publicly available on Harvard Dataverse, and our analytical methodologies are accessible via GitHub, promoting open-access research. Additionally, we provide insights on utilizing our data for future investigations focused on assessing, augmenting, and refining the decentralization, security, and efficiency of blockchain systems.
Sharding is a promising solution to enhance the scalability of blockchain. However, previous sharding systems adopt the lock-based cross-shard protocol to exclusively handle one-shot cross-shard transactions, leading to low-efficiency executions and unavailable calls when handling complex cross-shard contracts that introduce multi-shot cross-shard transactions to invoke multiple contracts managed by different shards.In this paper, we aim to enable efficient execution of arbitrarily complex cross-shard contracts in blockchain sharding systems. First, we perform a calling-flow analysis on Ethereum contracts with more than 180 million real-world transactions and find that about 30% transactions invoke complex contracts. Then, motivated by the properties of these complex contracts, we propose an off-chain execution model, called ShardCon, to achieve efficient executions for complex cross-shard contracts by decoupling the contract execution from the cross-shard consensus. Next, we introduce a cross-shard contract execution engine and a contract-driven deployment rule to the overheads introduced by off-chain executions. Moreover, to adapt to the multi-chain property of a sharding system, we introduce an off-chain state atomic commit protocol. Finally, we implement a prototype and evaluate it with concrete cross-shard contracts, showing that ShardCon can achieve more than 10x increase in throughput and 2x decrease in confirmation latency than the state-of-the-art sharding systems.
Renan Lima Baima, Loïck Chovet, Eduard Hartwich, Abhishek Bera · 7 authors
In the new space economy, space agencies, large enterprises, and start-ups aim to launch space multi-robot systems (MRS) for various in-situ resource utilization (ISRU) purposes, such as mapping, soil evaluation, and utility provisioning. However, these stakeholders' competing economic interests may hinder effective collaboration on a centralized digital platform. To address this issue, neutral and transparent infrastructures could facilitate coordination and value exchange among heterogeneous space MRS. While related work has expressed legitimate concerns about the technical challenges associated with blockchain use in space, we argue that weighing its potential economic benefits against its drawbacks is necessary. This paper presents a novel architectural framework and a comprehensive set of requirements for integrating blockchain technology in MRS, aiming to enhance coordination and data integrity in space exploration missions. We explored distributed ledger technology (DLT) to design a non-proprietary architecture for heterogeneous MRS and validated the prototype in a simulated lunar environment. The analyses of our implementation suggest global ISRU efficiency improvements for map exploration, compared to a corresponding group of individually acting robots, and that fostering a coopetitive environment may provide additional revenue opportunities for stakeholders.
Cryptocurrencies such as Bitcoin and Ethereum are gaining popularity thanks to their prominent advantages compared to legacy financial transaction systems. However, they require all participants to reach a consensus on the order of transactions, which fundamentally limits their performance in terms of confirmation latency and throughput, thus hindering their further deployment. Off-chain payment network is the state-of-the-art approach of solving this performance issue. Unfortunately, all existing payment networks are based on payment channels, which bring extra overhead, cost and vulnerabilities. In this paper, by leveraging trusted monotonic counters, we propose monoCash, the first off-chain payment network that is channel-free, thereby it is one-hop, routing-free, concurrency-friendly, rebalancing-free and wormhole-resilient. We implement and deploy monoCash on a wide area network of 3,000 nodes. The benchmark shows that it provides a throughput up to 30,000 transactions per second (higher than credit card systems, e.g., VISA).