Carsten Baum, Samuel Dittmer, Peter Schöll, Xiao Wang
Abstract A zero-knowledge proof is a cryptographic protocol where a prover can convince a verifier that a statement is true, without revealing any further information except for the truth of the statement. This article is a survey of recent developments in building practical zero-knowledge proof systems using vector oblivious linear evaluation (VOLE), a tool from secure two-party computation. In this work, we attempt to systematize the recent works on VOLE-based Zero-Knowledge proofs and make the state of the art accessible in one document.
Juanjuan Li, Xiaolong Liang, Rui Qin, Fei–Yue Wang
Decentralized Autonomous Organizations (DAOs) have been gaining popularity in recent years due to their promise of realizing the decentralized Web 3.0. However, most DAOs rely heavily on token-centric value systems as well as allocate decision-making authority and yield-sharing rights according to the held tokens, which often lead to monopolization of power and rights. To address this issue, this paper contributes to propose a truly democratic organization model, named True Autonomous Organizations and Operations (TAOs), that does not count upon tokens and is guided by principles of contribution-based and on-demand allocation. We first discuss the design of TAOs, including their infrastructures, power structures, and value systems, and then provide a technical roadmap for implementing TAOs in the DeSci context. This research can provide a valuable guidance for the construction and application of TAOs.
Christian Berger, Sadok Ben Toumia, Hans P. Reiser
Recent Byzantine fault-tolerant (BFT) state machine replication (SMR) protocols increasingly focus on scalability to meet the requirements of distributed ledger technology (DLT). Validating the performance of scalable BFT protocol implementations requires careful evaluation. Our solution uses network simulations to forecast the performance of BFT protocols while experimentally scaling the environment. Our method seamlessly plug-and-plays existing BFT implementations into the simulation without requiring code modification or re-implementation, which is often time-consuming and error-prone. Furthermore, our approach is also significantly cheaper than experiments with real large-scale cloud deployments. In this paper, we first explain our simulation architecture, which enables scalable performance evaluations of BFT systems through high-performance network simulations. We validate the accuracy of these simulations for predicting the performance of BFT systems by comparing simulation results with measurements of real systems deployed on cloud infrastructures. We found that simulation results display a reasonable approximation at a larger system scale, because the network eventually becomes the dominating factor limiting system performance. In the second part of our paper, we use our simulation method to evaluate the performance of PBFT and BFT protocols from the "blockchain generation", such as HotStuff and Kauri, in large-scale and realistic wide-area network scenarios, as well as under induced faults.
In this paper, we propose GreenCoin – an energy-efficient cryptocurrency system with mining protocols designed to favor locations with relatively higher availability of renewable energy. Traditionally, crypto coin mining involves solving complex mathematical problems by high-end computing devices consuming an enormous amount of electricity, thus adversely affecting net carbon emissions. To reduce cost and emissions, GreenCoin uses a modified proof of stake (PoS) consensus algorithm, which itself is more energy efficient compared to other state-of-the-art methods. Our modified PoS algorithm, called Green PoS (GPoS), allows GreenCoin to favor nodes (with reward and privilege) located in regions with higher availability of renewable energy. We present a detailed system architecture of GreenCoin and explain the operating method of GPoS. We also provide results from empirical studies demonstrating the renewable energy-aware approach of GreenCoin.
Mustafa Ibrahim Alnajjar, Mehmet Sabır Kiraz, Ali H. Al‐Bayatti, Süleyman Kardaş
A distributed ledger is a shared and synchronized database across multiple designated nodes, often referred to as miners, validators, or peers. These nodes record, distribute, and access data to ensure security and transparency. However, these nodes can be compromised and manipulated by selectively choosing which user transactions to include, exclude, or reorder, thereby gaining an unfair advantage. This is known as a miner/maximal extractable value (MEV) attack. Existing solutions can be classified into various categories, such as MEV auction platforms and time-based ordering properties, which rely on private transaction Mempools. In this paper, we first identify some architectural weaknesses inherent in the latest proposals that divide the block creation and execution roles into separate functions: block builders and block executors. The existing schemes mainly suffer from the verifiability of the decryption process, where a corrupted builder or executor can simply deny the inclusion of specific targeted transactions by exploiting the fact that all transactions are in plain format. To address this, we propose an enhanced version that incorporates a verifiable decryption process. On a very high level, within our proposal, whenever an Executor or a Builder performs a decryption, the decrypted values must be broadcasted. This enables any entity in the network to publicly verify whether the decryption was executed correctly, thus preventing malicious behavior by either party from going undetected. We also define a new adversary model for MEV and conduct a comprehensive security analysis of our protocol against all kinds of potential adversaries related to MEV. Finally, we present the performance analysis of the proposed solution.
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Physical Unclonable Functions (PUFs) and Hardware Security
This paper presents secure mempool designs under asymmetric DoS attacks. We formulate safety definitions under two abstract DoSes, namely eviction- and locking-based attacks. We propose a safe transaction admission framework for securing mempools, named saferAd, that achieves both eviction- and locking-safety. The proven security stems from an upper bound of the attack damage under locking DoSes and a lower bound of the attack cost under eviction DoSes. The evaluation by replaying real transaction traces shows saferAd incurs negligible latency or insignificant change of validator revenue.
This work aims to discuss the currently ongoing efforts towards the implementation of a fully autonomous and decentralized consensus mechanism based on Proof-of-Stake. We focus on the technical challenges arising from adopting a committeeless Proof-of-Stake consensus protocol (CPoS) where the global state of the entire peer-to-peer network is used to converge to a distributed consensus instead of relying on a validation committee. Specifically, we analyse the performance and security tradeoffs of the protocol. Since the CPoS protocol is very sensitive to its configuration parameters, we investigate their full impact on the blockchain performance and propose improvements to previous works in the area.
Blockchain and other decentralized databases, known as distributed ledgers, are designed to store information online where all trusted network members can update the data with transparency. The dynamics of ledger's development can be mathematically represented by a directed acyclic graph (DAG). One essential property of a properly functioning shared ledger is that all network members holding a copy of the ledger agree on a sequence of information added to the ledger, which is referred to as consensus and is known to be related to a structural property of DAG called one-endedness. In this paper, we consider a model of distributed ledger with sequential stochastic arrivals that mimic attachment rules from the IOTA cryptocurrency. We first prove that the number of leaves in the random DAG is bounded by a constant infinitely often through the identification of a suitable martingale, and then prove that a sequence of specific events happens infinitely often. Combining those results we establish that, as time goes to infinity, the IOTA DAG is almost surely one-ended.
Elmira Ebrahimi, Ehsan Khamespanah, Marjan Sirjani, Siamak Mohammadi
Conducting interactions between shared-purpose organizations that are not entirely trustworthy of each other without centralized oversight is an idea that emerged with the advent of private blockchains such as Hyperledger Fabric and its smart contracts. It is critical to check contracts to ensure their proper functionality, as organizations may collaborate with competitors. Due to the new architecture of Hyperledger Fabric, tools in this area are limited. To formally verify the source code of contracts, we mapped Fabric contract concepts into the Rebeca modeling language. Rebeca is an actor-based language that enables the modeling of concurrent and distributed systems and is supported by a model checking tool, Afra. We have identified vulnerabilities such as deadlock and starvation by examining the desired properties. Using the model checking approach, we could debug the code and hence benefit from speeding up the transactions, creating fewer extra blocks, requiring less storage space to store the ledger, and avoiding wasting computing resources.
Solana has quickly emerged as a popular platform for building decentralized applications (DApps), such as marketplaces for non-fungible tokens (NFTs). A key reason for its success are Solana's low transaction fees and high performance, which is achieved in part due to its stateless programming model. Although the literature features extensive tooling support for smart contract security, current solutions are largely tailored for the Ethereum Virtual Machine. Unfortunately, the very stateless nature of Solana's execution environment introduces novel attack patterns specific to Solana requiring a rethinking for building vulnerability analysis methods. In this paper, we address this gap and propose FuzzDelSol, the first binary-only coverage-guided fuzzing architecture for Solana smart contracts. FuzzDelSol faithfully models runtime specifics such as smart contract interactions. Moreover, since source code is not available for the large majority of Solana contracts, FuzzDelSol operates on the contract's binary code. Hence, due to the lack of semantic information, we carefully extracted low-level program and state information to develop a diverse set of bug oracles covering all major bug classes in Solana. Our extensive evaluation on 6049 smart contracts shows that FuzzDelSol's bug oracles find bugs with a high precision and recall. To the best of our knowledge, this is the largest evaluation of the security landscape on the Solana mainnet.
Traditional blockchains cannot achieve the same transaction throughput as Web2, so their use cases are limited. Therefore, state sharding has been proposed to improve transaction throughput by dividing the blockchain network and managing states and transactions in parallel. However, Nightshade in the NEAR Protocol, a type of state sharding, provides a rollback protocol to cancel the generation of blocks containing inconsistent transaction results because processing cross-shard transactions (CSTXs) in a 2-phase commit may cause state inconsistency. We present a new attack that interferes with the generation of new blocks by repeatedly executing CSTXs that certainly causes state inconsistency, causing continuous rollback. We also propose a block-generation protocol called Synchro to incorporate all the state changes of each CSTX into the same block by coordinating the block prior to approving transactions in each shard. Synchro eliminates the occurrence of the state inconsistency caused by the CSTXs and the necessity of the rollback protocol. We use zero-knowledge proof to make Synchro scalable in the global validation phase. Although the actual overhead of the zero-knowledge proof has not yet been evaluated, we show that Synchro could achieve the same transaction throughput as Nightshade theoretically, depending on the future innovations in zero-knowledge proof techniques.
Motivated by proof-of-stake (PoS) blockchains such as Ethereum, two key desiderata have recently been studied for Byzantine-fault tolerant (BFT) state-machine replication (SMR) consensus protocols: Finality means that the protocol retains consistency, as long as less than a certain fraction of validators are malicious, even in partially-synchronous environments that allow for temporary violations of assumed network delay bounds. Accountable safety means that in any case of inconsistency, a certain fraction of validators can be identified to have provably violated the protocol. Earlier works have developed impossibility results and protocol constructions for these properties separately. We show that accountable safety implies finality, thereby unifying earlier results.
Blockchain technology has gained widespread use. However, it faces several challenges including throughput, transaction delay, security, and decentralization. This paper presents the Avalon protocol based on a novel Proof-of-Market (PoM) consensus mechanism to address these issues. PoM is a type of Proof-of-Work (PoW) consensus that incorporates market-driven leader election and shifts PoW from mining pools to consumers based on transactions. The matching incentive mechanism makes PoM incentive compatible. PoM decouples the scalability and security of Bitcoin, which means that Avalon can optimize the capacity and interval of blocks without compromising other performance goals. Our analysis shows that Avalon can tolerate malicious nodes possessing up to$\bf{1/3}$of the network's total computational power. Furthermore, the implementation of Avalon is similar to Bitcoin and is highly concise. We evaluate the performance of Avalon through a simulated network of over$\bf{1,000}$nodes. Experimental results demonstrate that Avalon can achieve a throughput of$\bf{4,000}$TPS (transactions per second), which is significantly better than state-of-the-art schemes ($\bf{10\boldsymbol{\times}}$Bitcoin-NG,$\bf{5\boldsymbol{\times}}$ByzCoin, and$\bf{4\boldsymbol{\times}}$Algorand). Additionally, it has a transaction confirmation delay of up to$\bf{40}$s, which is twice better than Bitcoin-NG and ByzCoin while experiencing only minimal blockchain splits and maintaining excellent decentralization.
Soosan Naderi Mighan, Jelena Mišić, Vojislav B. Mišić
We present a comprehensive analytical model for block and transaction distribution in the Ethereum P2P network. We model the data distribution protocol in which a node forwards a full block (transaction) to some of its peers and its hash to others, and combine this model with the connectivity and transmission models to obtain input and output data rates, which are then fed into a priority M/G/1 Jackson network queuing system in which blocks are given preference over transactions, and transactions are further grouped into two priority classes according to gasprice. Block and transaction delivery times are found to be mainly determined by node connectivity and network size, and prioritization provides faster service for higher priority transactions. We also model an Eclipse-like attack that degrades data delivery times and block finalization time, i.e., the time for a block to be officially confirmed, by reducing network connectivity, and show that its impact can be countered by adjusting the portion of peers which receive a full block. Lastly, we determine the probability of uncle blocks being included in the longer chain and demonstrate how the Eclipse attack affects this probability.
A Distributed Concensus System (DCS) is a key component for a distributed system, maintaining and consenting over distributed state, as often required in distributed filesystems, cryptocurrencies and other applications. The prevalent mechanism to distribute the information needed to reach consensus in a DCS is through an iterative diffusion with the goal of distributing the (updated) information to at least the majority of DCS participants. Such diffusion is not just costly in maintaining the needed communication relations but also incurs latency in performing the diffusion itself. When looking closer at the goal of achieving the majority rule, however, one may wonder of the lack of multicast being used for achieving the same goal. This paper thus returns to the original intention of how to distribute information to a large set of users and outlines reasons for why multicast has not been widely used thus far. We evaluate the potential gain in doing so, based on an analytical model for the diffusion latency in an iterative diffusion DCS, bounded through empirical studies in an Ethereum system.
Mohammad M. Jalalzai, Jianyu Niu, Chen Feng, Fangyu Gai
he HotStuff protocol is a recent breakthrough in Byzantine Fault Tolerant (BFT) consensus that enjoys both responsiveness and linear view change by creatively adding a round to classic two-round BFT protocols like PBFT. Despite its great advantages, HotStuff has a few limitations. First, the additional round of communication during normal cases results in higher latency. Second, HotStuff is vulnerable to certain performance attacks, which can significantly deteriorate its throughput and latency. To address these limitations, we propose a new two-round BFT protocol called Fast-HotStuff, which enjoys responsiveness and efficient view change that is comparable to the linear view-change in terms of performance. Our Fast-HotStuff has lower latency and is more robust against the performance attacks that HotStuff is susceptible to.
As a subset of distributed systems, blockchain technology is equally bound by the CAP trilemma. Specifically, no distributed system can satisfy consistency, availability, and partition tolerance simultaneously. Informally, the innovative blockchain trilemma has been theorized to include security, scalability, and decentralization. While many software approaches on blockchains claim to solve the trilemma problem, almost all known approaches have been proven to involve tradeoffs and fail to reach the upper bounds, meaning they do not achieve the theoretical limit value in each term of a trilemma. In this article, we propose a general trilemma based on the above two trilemmas. For permissioned blockchains, we then describe a system framework called GBT-CHAIN to solve the G eneral B lockchain T rilemma. In the proposed framework, the consensus and data layer, the network layer, and the physical layer work in cooperation. According to our theoretical proof and experimental analysis, the three properties of the trilemma consisting of consistency, scalability, and partition tolerance are perfectly satisfied without tradeoffs. Our results demonstrate that the general blockchain trilemma is resolved by combining consensus algorithms and physical topologies, in particular for permissioned blockchains.
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.