Ghareeb Falazi, Uwe Breitenbücher, Frank Leymann, Stefan Schulte · 5 authors
Blockchains have become increasingly important in recent years and have expanded their applicability to many domains beyond finance and cryptocurrencies. This adoption has particularly increased with the introduction of smart contracts, which are immutable, user-defined programs directly deployed on blockchain networks. However, many scenarios require business transactions to simultaneously access smart contracts on multiple, possibly heterogeneous blockchain networks while ensuring the atomicity and isolation of these transactions, which is not natively supported by current blockchain systems. Therefore, in this work, we introduce the Transactional Cross-Chain Smart Contract Invocation (TCCSCI) approach, which supports such distributed business transactions while ensuring their global atomicity and serializability. The approach introduces the concept of Resource Manager Smart Contracts (RMSCs), and 2PC for Blockchains (2PC4BC), a client-driven Atomic Commit Protocol (ACP) specialized for blockchain-based distributed transactions. We validate our approach using a prototypical implementation, evaluate its introduced overhead, and prove its correctness.
Joachim Neu, Srivatsan Sridhar, Lei Yang, David Tse
Classic BFT consensus protocols guarantee safety and liveness for all clients if fewer than one-third of replicas are faulty. However, in applications such as high-value payments, some clients may want to prioritize safety over liveness. Flexible consensus allows each client to opt for a higher safety resilience, albeit at the expense of reduced liveness resilience. We present the first construction that allows optimal safety--liveness tradeoff for every client simultaneously. This construction is modular and is realized as an add-on applied on top of an existing consensus protocol. The add-on consists of an additional round of voting and permanent locking done by the replicas, to sidestep a sub-optimal quorum-intersection-based constraint present in previous solutions. We adapt our construction to the existing Ethereum protocol to derive optimal flexible confirmation rules that clients can adopt unilaterally without requiring system-wide changes. This is possible because existing Ethereum protocol features can double as the extra voting and locking. We demonstrate an implementation using Ethereum's consensus API.
Traditional blockchain systems still struggle with limited throughput, particularly those compatible with EVM, which are crucial in many blockchain applications. One of the main reasons arises from serial execution, which doesn’t exploit parallelism in transaction execution. Although some recent literature introduced concurrency control mechanisms to execute transactions in parallel, they do not work efficiently in real-world blockchains where proposers and validators have different execution contexts, which means varying execution deterministic levels and execution quantities.
Abstract This paper presents a quantitative model to assess the performance of a NFT (Non-Fungible Token)-centered chain as referred to as a NFT Chain in this paper. The model was introduced in [17] and more extensive simulations are conducted and the results are presented in this work. NFT chain in general stores its data distributed across on chain (e.g., NFT registration ledger data and an address pointing at the data located off chain such as meta data table and ultimate digital asset's data) due to the high cost to store the potentially high volume of data for digital assets. Therefore, it is expected that the overall performance of NFT chain is primarily to be dominated and bound by the off-chain performance. The proposed performance model employing an embedded Markovian queueing process model, tracks a bivariate state of the NFT chain such that \(\left(\varvec{i},\varvec{j}\right)\) where \(\varvec{i}\) stochastically tracks the number of slots of the transactions executed on chain and \(\varvec{j}\) stochastically tracks the number of transactions off chain as well, and the states transition as determined by \({\varvec{\lambda }}_{\varvec{o}\varvec{n}}\), \({\varvec{\lambda }}_{\varvec{o}\varvec{f}\varvec{f}}\), \(\varvec{\mu }\), and the number of slots in the current block. Extensive numerical simulations are performed to validate the efficacy of the model. The primary set of variables used in the simulations consists of \({\varvec{\lambda }}_{\varvec{o}\varvec{n}}\), \({\varvec{\lambda }}_{\varvec{o}\varvec{f}\varvec{f}}\), \(\varvec{\mu }\) and the average number of slots of the transactions during a block posting, \(\varvec{L}\), is simulated based on both \({\varvec{L}}_{\varvec{o}\varvec{n}}\)and \({\varvec{L}}_{\varvec{o}\varvec{f}\varvec{f}}\); and the average waiting time \(\varvec{W}\) based on both \({\varvec{W}}_{\varvec{o}\varvec{n}}\)and \({\varvec{W}}_{\varvec{o}\varvec{f}\varvec{f}}\), in an intermingled manner in order to take into account of the nature of NFT transactions executed across on- and off-chain without loss of generality. The simulation results in [17] has demonstrated a good agreement with the expected and intuitive trends. The results of more extensive simulations are presented in this paper to further demonstrate the efficacy and versatility of the proposed model. Ultimately, the proposed NFT chain model will serve as a sound theoretical foundation for the design of NFT chains from the performance's perspective.
Alpesh Bhudia, Anna Cartwright, Edward Cartwright, Darren Hurley-Smith · 5 authors
Consensus algorithms facilitate agreement on and resolution of blockchain functions, such as smart contracts and transactions. Ethereum uses a Proof-of-Stake (PoS) consensus mechanism, which depends on financial incentives to ensure that validators perform certain duties and do not act maliciously. Should a validator attempt to defraud the system, legitimate validators will identify this and then staked cryptocurrency is `burned' through a process of slashing. In this paper, we show that an attacker who has compromised a set of validators could threaten to perform malicious actions that would result in slashing and thus, hold those validators to ransom. We use game theory to study how an attacker can coerce payment from a victim, for example by deploying a smart contract to provide a root of trust shared between attacker and victim during the extortion process. Our game theoretic model finds that it is in the interests of the validators to fully pay the ransom due to a lack of systemic protections for validators. Financial risk is solely placed on the victim during such an attack, with no mitigations available to them aside from capitulation (payment of ransom) in many scenarios. Such attacks could be disruptive to Ethereum and, likely, to many other PoS networks, if public trust in the validator system is eroded. We also discuss and evaluate potential mitigation measures arising from our analysis of the game theoretic model.
Ethereum has established itself as a highly decentralized and reliable blockchain network and serves as the de facto standard. However, using public blockchains in enterprise applications can be challenging due to concerns about confidentiality and transaction finality. As a result, consortium and private blockchains, which limit participation to specific nodes, are also commonly used. But these consortium blockchains also have limitations, such as limited node participation due to performance constraints imposed by the consensus algorithm. In this study, by using ZK-rollups as a messaging means, we would connect consortium blockchains via public Ethereum as a hub. We examined a mechanism to balance both mathematically reliable interoperability and maintaining the secrecy of the information and the finality. The concept was actually implemented, to confirm the interoperability of simple money transfer transactions. And also, the way to handle secret information and the finality was theoretically organized.
The consensus algorithm of Bitcoin, namely proof-of-work (PoW), has been criticized for its high energy consumption and centralization of mining power. PoW needs a lot of processing power to execute cryptographic problems and verify network transactions. In contrast, Chia's consensus mechanism is based on proofs-of-space (PoSpace), which utilizes disk space rather than computing power. PoSpace involves generating a large amount of verifiable storage space on the network and requires less energy consumption than PoW. This paper presents a comparative analysis of the algorithms used by Bitcoin, Ethereum, and Chia. The paper simulates the PoW and PoSpace processes by Java and compares both mechanisms' memory, CPU usage, and time consumption using VisualVM. The experiment results show that PoSpace costs less space and time resources than PoW. The former is more energy-efficient and decentralized.
This paper proposes a, namely, asynchronous chain and presents a Variable Bulk Arrival and Asynchronous Bulk Service (VBAABS) model of the type in order to provide a quantitative method to design an asynchronous chain as a basis in its initial theoretical design stage. Note that the proposed chain is precisely and namely asynchronous along with adaptive-sized blocks in a proactive manner versus the conventional chain that controls the block posting in a strictly synchronous manner to the fixed-sized blocks. The model of the type (i.e., VBAVBS) is considered as the theoretical and quantitative baseline model for the proposed model, namely, an adaptive chain model, yet with a rather reactively dynamic size of blocks, while the proposed asynchronous model carries a proactively dynamic (or adaptive) size of blocks. The proposed asynchronous chain model assumes variable bulk arrivals of transactions in Poisson distribution, i.e., , where represents the number of slots across all the mined transactions, and variable asynchronous services of transactions, each of which applies to a block potentially of different capacity in terms of the number of slots in it, in exponential time, i.e., , for being posted in the current block, namely, VBAABS. The major quantitative distinction between the adaptive model, i.e., VBAVBS, and the asynchronous model, i.e., VBAABS, is that in VBAVBS, every state , where , transitions back into while in VBAABS, every state , where , transitions back into , where , as well as back into , and is the state in which the transaction up in execution is to be discarded, in other words, that the current block capacity is in excess of the required capacity for the transaction in execution to result in a potentially excessive delay as much as than an otherwise ordinarily fully synchronous block posting delay that is as much as . VBAABS will reveal the performance advantages of the asynchronous chain versus the baseline chain, i.e., VBASBS [30] and the adaptive chain, i.e., VBAVBS, with respect to the average time for a slot to wait in the block and the average spatial requirement by the slots in the block, in a quantitative manner. Extensive numerical simulations are conducted on Matlab. Further, for feasibility validation purpose, an asynchronous chain algorithm will be developed and implemented by redesigning the Ethereum open source and analyzed.
Muhammed F. Esgin, Oğuzhan Ersoy, Veronika Kuchta, Julian Loss · 8 authors
In this work, we study the blockchain leader election problem. The purpose of such protocols is to elect a leader who decides on the next block to be appended to the blockchain, for each block proposal round. Solutions to this problem are vital for the security of blockchain systems. We introduce an efficient blockchain leader election method with security based solely on standard assumptions for cryptographic hash functions (rather than public-key cryptographic assumptions) and that does not involve a racing condition as in Proof-of-Work based approaches. Thanks to the former feature, our solution provides the highest confidence in security, even in the post-quantum era. A particularly scalable application of our solution is in the Proof-of-Stake setting, and we investigate our solution in the Algorand blockchain system. We believe our leader election approach can be easily adapted to a range of other blockchain settings.
Daniël Reijsbergen, Aung Htein Maw, Jingchi Zhang, Tien Tuan Anh Dinh · 5 authors
A plethora of different blockchain platforms have emerged in recent years, but many of them operate in silos. As such, there is a need for reliable cross-chain communication to enable blockchain interoperability. Blockchain interoperability is challenging because transactions can typically not be reverted – as such, if one transaction is committed then the protocol must ensure that all related transactions are committed as well. Existing interoperability approaches, e.g., Cosmos and Polkadot, are limited in the sense that they only support interoperability between their own subchains, or require intrusive changes to existing blockchains. To overcome this limitation, we propose PIEChain, a general, Kafka-based cross-chain communication framework. We utilize PIEChain for a practical case study: a cross-chain auction in which users who hold tokens on multiple chains bid for a ticket sold on another chain. PIEChain is the first publicly available, practical implementation of a general framework for cross-chain communication.
The original FlexiChain and its descendants are a revolutionary distributed ledger technology (DLT) for cyber-physical systems (CPS) and their embedded systems (ES). FlexiChain, a DLT implementation, uses cryptography, distributed ledgers, peer-to-peer communications, scalable networks, and consensus. FlexiChain facilitates data structure agreements. This thesis offers a Block Directed Acyclic Graph (BDAG) architecture to link blocks to their forerunners to speed up validation. These data blocks are securely linked. This dissertation introduces Proof of Rapid Authentication, a novel consensus algorithm. This innovative method uses a distributed file to safely store a unique identifier (UID) based on node attributes to verify two blocks faster. This study also addresses CPS hardware security. A system of interconnected, user-unique identifiers allows each block's history to be monitored. This maintains each transaction and the validators who checked the block to ensure trustworthiness and honesty. We constructed a digital version that stays in sync with the distributed ledger as all nodes are linked by a NodeChain. The ledger is distributed without compromising node autonomy. Moreover, FlexiChain Layer 0 distributed ledger is also introduced and can connect and validate Layer 1 blockchains. This project produced a DAG-based blockchain integration platform with hardware security. The results illustrate a practical technique for creating a system depending on diverse applications' needs. This research's design and execution showed faster authentication, less cost, less complexity, greater scalability, higher interoperability, and reduced power consumption.
Rafael Belchior, Jan Süßenguth, Qi Feng, Thomas Hardjono · 6 authors
Blockchain interoperability conflates the need for distributed systems to communicate with third- party systems without the existence of a canonical chain or orchestration layer. As there is not “a chain to rule them all” (due to reasons such as performance, privacy, and market forces), these distributed systems rely on exchanging data and value across network boundaries. Interconnected systems achieve a higher value than the sum of their parts, similar to how the Internet emerged as a set of isolated Local Area Networks (LANs) - and, by force of surprising synergies, such networks fundamentally transformed society, forever. Concurrently, in the last decade, we have witnessed the astonishing development of blockchain technologies, which seem more connected than ever: via bridges [13, 15, 16, 31], oracles [45], and other interoperability mechanisms [4, 9, 17, 48, 89]. These recent developments have, slowly but steadily, contributed to the improvement of the scalability of blockchain networks, as well as providing new functionality and use cases [66], but there is still a long way to go until mass adoption. In this paper, we will dive into the rabbit hole of blockchain interoperability and explain why it is needed, what has been done in the last decade, and where it is going.
With the increasing popularity of Web 3.0, tokenomics is becoming even more important as a scientific discipline. Tokenomics auditing is a new area of interest in the context of Web 3.0 whose aim is to stress test the design and structure of token economies, to ensure they are robust and safe. The importance of this area has increased considering multiple project failures and fraud that were witnessed in the recent history of the space. In this paper we present a framework to audit the tokenomics of blockchain-based projects. The auditing framework can be used by stakeholders to audit their tokens and by investors to assess the risks associated with investing in a given token. We demonstrate how this framework can be applied to assess risks and improve the structure of a token economy. We give three examples: First, an example is based on a real case study of a newly launched DeFi protocol called Algem which was the original inspiration for this protocol. Then, we perform retrospective study of Terra/Luna. Finally, we show how that framework could be used for the analysis of Ethereum 2.0. While the auditing framework is not without its shortcomings, it represents the first attempt at standardising tokenomics auditing. Therefore, this provides a foundation upon which the community will build and improve, as tokenomics auditing matures as a framework.
Named-Data Networking (NDN) is a novel network that secures network communication by fetching semantically named and secured data. All data packets in NDN are signed by producers and verified by data consumers. Therefore, it is vital to have producers' certificates available all the time. In this paper, we describe the design of CLedger, a secure distributed certificate ledger, to ensure certificate availability in NDN. CLedger logs certificate records in an immutable Directed Acyclic Graph (DAG) structure and replicates the DAG among a set of distributed loggers. We implemented CLedger using NDN's pub/sub API, and evaluated our design through an emulated deployment setting. Our initial evaluation results show that CLedger is effective, efficient, and resilient to failures.
Caspar Schwarz-Schilling, Fahad Saleh, Thomas Thiery, Jennifer Pan · 6 authors
We propose a model suggesting that honest-but-rational consensus participants may play timing games, and strategically delay their block proposal to optimize MEV capture, while still ensuring the proposal's timely inclusion in the canonical chain. In this context, ensuring economic fairness among consensus participants is critical to preserving decentralization. We contend that a model grounded in honest-but-rational consensus participation provides a more accurate portrayal of behavior in economically incentivized systems such as blockchain protocols. We empirically investigate timing games on the Ethereum network and demonstrate that while timing games are worth playing, they are not currently being exploited by consensus participants. By quantifying the marginal value of time, we uncover strong evidence pointing towards their future potential, despite the limited exploitation of MEV capture observed at present.
Distributed ledger technologies (DLT) usage is currently limited to a single platform as they do not have design-based interoperability capabilities. In general, it's challenging for a DLT to communicate with another one. Although several DLT solutions have been proposed and applied in specific application areas, building a general-purpose interoperability solution for any DLT remains a challenge. In previous work, we proposed a tailor-made interoperability solution between Hyperledger Fabric and Corda. This paper extends that work to enable interoperability between Hyperledger Fabric and Ethereum. The main contribution of this paper is to provide a new approach to enable interoperability between these two DLT. The approach follows a new request-response interaction model and future payments to enable the payments of services. A prototype was developed and evaluated through a case scenario, performance tests and cost analysis. Performance tests showed bottlenecks under heavy load scenarios due to Ethereum's design. Costs analysis showed that the approach is suitable for purchasing high-priced services. These promising results constitute a step forward in developing a general-purpose solution for DLT interoperability.
Andrei Constantinescu, Diana Ghinea, Lioba Heimbach, Zilin Wang · 5 authors
Traditional blockchain design gives miners or validators full control over transaction ordering, i.e., they can freely choose which transactions to include or exclude, as well as in which order. While not an issue initially, the emergence of decentralized finance has introduced new transaction order dependencies allowing parties in control of the ordering to make a profit by front-running others' transactions. In this work, we present the Decentralized Clock Network, a new approach for achieving fair transaction ordering. Users submit their transactions to the network's clocks, which run an agreement protocol that provides each transaction with a timestamp of receipt which is then used to define the transactions' order. By separating agreement from ordering, our protocol is efficient and has a simpler design compared to other available solutions. Moreover, our protocol brings to the blockchain world the paradigm of asynchronous fallback, where the algorithm operates with stronger fairness guarantees during periods of synchronous use, switching to an asynchronous mode only during times of increased network delay.
Martijn van Meerten, Burcu Kulahcioglu Ozkan, Annibale Panichella
Blockchain systems are prone to concurrency bugs due to the nondeterminism in the delivery order of messages between the distributed nodes. These bugs are hard to detect since they can only be triggered by a specific order or timing of concurrent events in the execution. Systematic concurrency testing techniques, which explore all possible delivery orderings of messages to uncover concurrency bugs, are not scalable to large distributed systems such as blockchains. Random concurrency testing methods search for bugs in a randomly generated set of executions and offer a practical testing method.In this paper, we investigate the effectiveness of random concurrency testing on blockchain systems using a case study on the XRP Ledger of the Ripple blockchain, which maintains one of the most popular cryptocurrencies in the market today. We test the Ripple consensus algorithm of the XRP Ledger by exploring different delivery orderings of consensus protocol messages. Moreover, we design an evolutionary algorithm to guide the random test case generation toward certain system behaviors to discover concurrency bugs more efficiently. Our case study shows that random concurrency testing is effective at detecting concurrency bugs in blockchains, and the evolutionary approach for test generation improves test efficiency. Our experiments could successfully detect the bugs we seeded in the Ripple source code. Moreover, we discovered a previously unknown concurrency bug in the production implementation of Ripple.
A significant portion of research on distributed ledgers has focused on circumventing the limitations of leader-based blockchains mainly in terms of scalability, decentralization and power consumption. Leaderless architectures based on directed acyclic graphs (DAGs) avoid many of these limitations altogether, but their increased flexibility and performance comes at the cost of increased design complexity, so their potential has remained largely unexplored. Management of write access to these ledgers presents a major challenge because ledger updates may be made in parallel, hence transactions cannot simply be serialised and prioritised according to token fees paid to validators. In this work, we propose an access control scheme for leaderless DAG-based ledgers which is based on consuming credits rather than paying fees in the base token. We outline a general model for this new approach and provide some simulation results showing promising performance boosts.
Darcy Camargo, Andreas Penzkofer, Sebastian Müller, William H. Sanders
The robust construction of the ledger data structure is an essential ingredient for the safe operation of a distributed ledger. While in traditional linear blockchain systems, permission to append to the structure is leader-based, in Directed Acyclic Graph-based ledgers, the writing access can be organised leaderless. However, this leaderless approach relies on fair treatment of non-referenced blocks, i.e. tips, by honest block issuers. We study the impact of a deviation from the standard tip selection by a subset of block issuers with the aim of halting the confirmation of honest blocks entirely. W e provide models on this so-called orphanage of blocks and validate these through open-sourced simulation studies. A critical threshold for the adversary issuance rate is shown to exist, above which the tip pool becomes unstable, while for values below the orphanage decrease exponentially. We study the robustness of the protocol with an expiration time on tips, also called garbage collection, and modification of the parent references per block.
Many protocols in distributed computing rely on a source of randomness, usually called a random beacon, both for their applicability and security. This is especially true for proof-of-stake blockchain protocols in which the next miner or set of miners have to be chosen randomly and each party's likelihood to be selected is in proportion to their stake in the cryptocurrency. Current random beacons used in proof-of-stake protocols, such as Ouroboros and Algorand, have two fundamental limitations: Either (i)~they rely on pseudorandomness, e.g.~assuming that the output of a hash function is uniform, which is a widely-used but unproven assumption, or (ii)~they generate their randomness using a distributed protocol in which several participants are required to submit random numbers which are then used in the generation of a final random result. However, in this case, there is no guarantee that the numbers provided by the parties are uniformly random and there is no incentive for the parties to honestly generate uniform randomness. Most random beacons have both limitations. In this thesis, we provide a protocol for distributed generation of randomness. Our protocol does not rely on pseudorandomness at all. Similar to some of the previous approaches, it uses random inputs by different participants to generate a final random result. However, the crucial difference is that we provide a game-theoretic guarantee showing that it is in everyone's best interest to submit uniform random numbers. Hence, our approach is the first to incentivize honest behavior instead of just assuming it. Moreover, the approach is trustless and generates unbiased random numbers. It is also tamper-proof and no party can change the output or affect its distribution. Finally, it is designed with modularity in mind and can be easily plugged into existing distributed protocols such as proof-of-stake blockchains.
Bing-Yang Lin, Daria Dziubałtowska, Piotr Macek, Andreas Penzkofer · 5 authors
DAG-based DLTs allow for parallel, asynchronous writing access to a ledger. Consequently, the perception of the most recent blocks may differ considerably between nodes, and the underlying network properties of the P2P layer have a direct impact on the performance of the protocol. Moreover, the stronger inter-dependencies of several core components demand a more complex and complete approach to studying such DLTs. This paper presents an agent-based, open-sourced simulator for large-scale networks that implement the leaderless Tangle 2.0 consensus protocol. Its scope includes modelling the underlying peer-to-peer communication with network topology, package loss, heterogeneous latency, the gossip protocol with reliable broadcast qualities, the underlying DAG-based data structure, and the consensus protocol. The simulator allows us to explore the performance of the protocol in different network environments, as well as different attack scenarios.
Fabian Kirstein, Anton Altenbernd, Sonja Schimmler, Manfred Hauswirth
The Data Catalogue Vocabulary (DCAT) standard is a popular RDF vocabulary for publishing metadata about data catalogs and a valuable foundation for creating Knowledge Graphs. It has widespread application in the (Linked) Open Data and scientific communities. However, DCAT does not specify a robust mechanism to create and maintain persistent identifiers for the datasets. It relies on Internationalized Resource Identifiers (IRIs), that are not necessarily unique, resolvable and persistent. This impedes findability, citation abilities, and traceability of derived and aggregated data artifacts. As a remedy, we propose a decentralized identifier registry where persistent identifiers are managed by a set of collaborative distributed nodes. Every node gives full access to all identifiers, since an unambiguous state is shared across all nodes. This facilitates a common view on the identifiers without the need for a (virtually) centralized directory. To support this architecture, we propose a data model and network methodology based on a distributed ledger and the W3C recommendation for Decentralized Identifiers (DID). We implemented our approach as a working prototype on a five-peer test network based on Hyperledger Fabric.