Sam Blackshear, Andrey Chursin, George Danezis, Anastasios Kichidis · 12 authors
Sui Lutris is the first smart-contract platform to sustainably achieve sub-second finality. It achieves this significant decrease by employing consensusless agreement not only for simple payments but for a large variety of transactions. Unlike prior work, Sui Lutris neither compromises expressiveness nor throughput and can run perpetually without restarts. Sui Lutris achieves this by safely integrating consensuless agreement with a high-throughput consensus protocol that is invoked out of the critical finality path but ensures that when a transaction is at risk of inconsistent concurrent accesses, its settlement is delayed until the total ordering is resolved. Building such a hybrid architecture is especially delicate during reconfiguration events, where the system needs to preserve the safety of the consensusless path without compromising the long-term liveness of potentially misconfigured clients. We thus develop a novel reconfiguration protocol, the first to provably show the safe and efficient reconfiguration of a consensusless blockchain. Sui Lutris is currently running in production and underpins the Sui smart-contract platform. Combined with the use of Objects instead of accounts it enables the safe execution of smart contracts that expose objects as a first-class resource. In our experiments Sui Lutris achieves latency lower than 0.5 seconds for throughput up to 5,000 certificates per second (150k ops/s with transaction blocks), compared to the state-of-the-art real-world consensus latencies of 3 seconds. Furthermore, it gracefully handles validators crash-recovery and does not suffer visible performance degradation during reconfiguration.
Dmitry A. Zaitsev, Tatiana R. Shmeleva, Zeyu Zhou, Ding Liu
The reliability of consensus protocols establishes the basis for cryptocurrency cybersecurity. Formal and simulation techniques are appreciated for the verification of proof-of-work agreement protocols, because the formal techniques development process frequently requires a series of assumptions, leading to somewhat unrealistic models. A conventional colored Petri net model, presented by the authors in a previous study, allowed us to refine the Keller and Böhme consensus protocol by applying the simulation technique. In this study, we developed a reenterable colored Petri net model representing a general construct for model-driven development and refinement of consensus protocols and the corresponding software. A considerable benefit of a reenterable model is the invariance of its structure with respect to the net topology, number of attached nodes, and parameters of their software and hardware, which are represented as the marking of dedicated places. Switching of topology tags associated with dynamic objects represents the basic principle of reenterable model functioning. It is shown that, having the same characteristics, in bounds of admissible error of some 2-3%, the reenterable model results in 6 times speed-up of the simulation process and a drastic decrease in time for model editing, especially when the number of nodes exceeds a hundred. Thus, a reenterable model is a valuable complement to possible formal models that allows us to obtain express-evaluations of characteristics in a rather short time and with an acceptable level of adequacy.
Digital currencies have become an increasingly popular topic of discussion in recent years. Digital currencies are virtual forms of currency that operate outside the traditional banking system. They are based on cryptographic technologies and are often decentralized, meaning they are not controlled by a central authority. The most well-known digital currency is Bitcoin, but there are many other types of digital currencies in existence. Digital currencies can be used to purchase goods and services online or transferred between users directly without intermediaries like banks. They have gained popularity due to their potential for increased security, transparency, and efficiency in financial transactions. In today's digital currency, a variety of digital currencies emerge in an endless stream, and crypto technology is also constantly developing to improve the security of digital currency payments. In section 2, this paper briefly introduces several common digital currencies and encryption algorithms, and in section 3, this paper introduces these typical digital currencies in detail through the analysis of representative literature. Bitcoin is mainly encrypted based on blockchain technology, and its encryption principle is mainly divided into three parts: public key encryption, hash function, and proof of work. Ethereum is a distributed blockchain platform with encryption principles similar to Bitcoin, including public key encryption and hashing algorithms. Ripple is a distributed cryptocurrency. Its encryption principle mainly adopts the public-private key encryption system. In terms of encryption technology, blockchain technology, the Hash algorithm and symmetric and asymmetric encryption are also popular encryption algorithms in digital currencies.
As a distributed ledger technology, blockchain has found widespread use in a variety of industries, including finance, the Internet of Things (IoT), healthcare, and manufacturing. This technology addresses the trust issue by converting a low-trust centralized ledger into a highly trusted distributed ledger maintained by various entities. Consensus algorithms are one of the fundamental building blocks of the blockchain, controlling how nodes cooperate and synchronize data to perform secure and reliable activities in a decentralized setting. This paper examines the extant mainstream consensus algorithms, introduces six representative consensus algorithms, analyses their benefits and drawbacks, and discusses the application scenarios and suitability of each consensus algorithm in various blockchain platforms.
A distributed and decentralized ledger widely used in the computer science and financial fields called blockchain has provided safe and fast transactions for multiple parties. Also, check the transaction by each node on the blockchain. The consensus mechanism is the core of the blockchain. It lets all the nodes reach an agreement for those transactions, which ensures security and accuracy and make Bitcoin valuable and popular. Two of the most mainstream Consensus mechanisms are Proof of Work (PoW) and Proof of Stake (PoS), and Proof of Authority (PoA) is the new one that will apply in the future. Many discourses talk about consensus mechanisms, most of which are review papers. Those papers mainly show a specific aspect of a consensus mechanism or introduce the primary notion, but they rarely explain the corresponding relationship between theories and cryptocurrency. So, the purpose is to give a clear structure, connect the consensus mechanism to its application and simplify the reader's understanding. This paper aims to provide an overview of the consensus mechanism, including its general definition, concepts of different mechanism variants, and advantages and disadvantages. For the structure below, the essay introduces the notion of consensus mechanism and how PoW, PoS, and PoA work. Then summarize the papers based on these three consensus mechanisms, describing the theories of many consensus mechanisms and comparing the advantages and disadvantages. The essay also creates a comparison table about these three consensus mechanisms to embody the content above the stem better.
The broad topic of this thesis is the design and analysis of Bitcoin custody systems. Both the technology and threat landscape are evolving constantly. Therefore, custody systems, defence strategies, and risk models should be adaptive too. We introduce Bitcoin custody by describing the different types, design principles, phases and functions of custody systems. We review the technology stack of these systems and focus on the fundamentals; key-management and privacy. We present a perspective we call the systems view. It is an attempt to capture the full complexity of a custody system, including technology, people, and processes. We review existing custody systems and standards. We explore Bitcoin covenants. This is a mechanism to enforce constraints on transaction sequences. Although previous work has proposed how to construct and apply Bitcoin covenants, these require modifying the consensus rules of Bitcoin, a notoriously difficult task. We introduce the first detailed exposition and security analysis of a deleted-key covenant protocol, which is compatible with current consensus rules. We demonstrate a range of security models for deleted-key covenants which seem practical, in particular, when applied in autonomous (user-controlled) custody systems. We conclude with a comparative analysis with previous proposals. Covenants are often proclaimed to be an important primitive for custody systems, but no complete design has been proposed to validate that claim. To address this, we propose an autonomous custody system called Ajolote which uses deleted-key covenants to enforce a vault sequence. We evaluate Ajolote with; a model of its state dynamics, a privacy analysis, and a risk model. We propose a threat model for custody systems which captures a realistic attacker for a system with offline devices and user-verification. We perform ceremony analysis to construct the risk model.
Sharding is a critical technique that enhances the scalability of blockchain technology. However, existing protocols often assume adversarial nodes in a general term without considering the different types of attacks, which limits transaction throughput at runtime because attacks on liveness could be mitigated. There have been attempts to increase transaction throughput by separately handling the attacks; however, they have security vulnerabilities. This paper introduces Reticulum, a novel sharding protocol that overcomes these limitations and achieves enhanced scalability in a blockchain network without security vulnerabilities.<br/><br/>Reticulum employs a two-phase design that dynamically adjusts transaction throughput based on runtime adversarial attacks on either or both liveness and safety. It consists of `control' and `process' shards in two layers corresponding to the two phases. Process shards are subsets of control shards, with each process shard expected to contain at least one honest node with high confidence. Conversely, control shards are expected to have a majority of honest nodes with high confidence. Reticulum leverages unanimous voting in the first phase to involve fewer nodes in accepting/rejecting a block, allowing more parallel process shards. The control shard finalizes the decision made in the first phase and serves as a lifeline to resolve disputes when they surface.<br/><br/>Experiments demonstrate that the unique design of Reticulum empowers high transaction throughput and robustness in the face of different types of attacks in the network, making it superior to existing sharding protocols for blockchain networks.
This paper explores the potential for improving blockchain performance through the implementation of an adaptive consensus machine. Blockchains, as immutable distributed ledgers, have found applications in various domains such as cryptocurrency, supply chains, healthcare, and more. The two main types of blockchains are permissionless and permissioned, each with its own advantages and limitations. The proposal suggests monitoring transaction metrics on the blockchain to enable the adaptive machine to adjust operational parameters of the consensus protocol or even switch to a different consensus strategy. This autonomic approach aims to enhance the overall performance of the blockchain by utilizing self-defined policies and goals. The paper discusses the use of off-chain structures for recording transactions and the trade-offs between latency and cost. Furthermore, it highlights the potential improvements that can be achieved by adapting classic consensus algorithms in permissioned blockchains. By incorporating adaptive and autonomic techniques, blockchain platforms can achieve enhanced efficiency and performance.
Zhuo Cai, Soroush Farokhnia, Amir Kafshdar Goharshady, S. Hitarth
Modern programmable blockchains have built-in support for smart contracts, i.e. âprograms that are stored on the blockchain and whose state is subject to consensus. After a smart contract is deployed on the blockchain, anyone on the network can interact with it and call its functions by creating transactions. The blockchain protocol is then used to reach a consensus about the order of the transactions and, as a direct corollary, the state of every smart contract. Reaching such consensus necessarily requires every node on the network to execute all function calls. Thus, an attacker can perform DoS by creating expensive transactions and function calls that use considerable or even possibly infinite time and space. To avoid this, following Ethereum, virtually all programmable blockchains have introduced the concept of âgasâ. A fixed hard-coded gas cost is assigned to every atomic operation and the user who calls a function has to pay for its total gas usage. This technique ensures that the protocol is not vulnerable to DoS attacks, but it has also had significant unintended consequences. Out-of-gas errors, i.e. âwhen a user misunderestimates the gas usage of their function call and does not allocate enough gas, are a major source of security vulnerabilities in Ethereum. We focus on the well-studied problem of automatically finding upper-bounds on the gas usage of a smart contract. This is a classical problem in the blockchain community and has also been extensively studied by researchers in programming languages and verification. In this work, we provide a novel approach using theorems from polyhedral geometry and real algebraic geometry, namely Farkasâ Lemma, Handelmanâs Theorem, and Putinarâs Positivstellensatz, to automatically synthesize linear and polynomial parametric bounds for the gas usage of smart contracts. Our approach is the first to provide completeness guarantees for the synthesis of such parametric upper-bounds. Moreover, our theoretical results are independent of the underlying consensus protocol and can be applied to smart contracts written in any language and run on any blockchain. As a proof of concept, we also provide a tool, called âAsparagusâ that implements our algorithms for Ethereum contracts written in Solidity. Finally, we provide extensive experimental results over 24,188 real-world smart contracts that are currently deployed on the Ethereum blockchain. We compare Asparagus against GASTAP, which is the only previous tool that could provide parametric bounds, and show that our method significantly outperforms it, both in terms of applicability and the tightness of the resulting bounds. More specifically, our approach can handle 80.56% of the functions (126,269 out of 156,735) in comparison with GASTAPâs 58.62%. Additionally, even on the benchmarks where both approaches successfully synthesize a bound, our bound is tighter in 97.85% of the cases.
In this paper, we design, implement, and (partially-) evaluate a lightweight bridge (as a type of middleware) to connect the Bitcoin and Ethereum networks that were heterogeneously uncontactable before. Inspired by the recently introduced Bitcoin Request Comment (BRC-20) standard, we leverage the flexibility of Bitcoin inscriptions by embedding editable operations within each satoshi and mapping them to programmable Ethereum smart contracts. A user can initialize his/her requests from the Bitcoin network, subsequently triggering corresponding actions on the Ethereum network. We validate the lightweight nature of our solution and its ability to facilitate secure and seamless interactions between two heterogeneous ecosystems.
Open access
3 source records
Blockchain Technology Applications and Security
Physical Unclonable Functions (PUFs) and Hardware Security
In this article, we consider DAG-based distributed ledger technologies (DLTs), i.e., DLTs where each block can reference several previous blocks hence forming a directed acyclic graph of blocks (BDAG). Each block has a weight (usually a constant normalized to one) and our goal is to compute the heaviest sub-BDAG that does not contain conflicting blocks. First, we prove that computing such a sub-BDAG is NP-complete. Then, we show that the difficulty comes from concurrent conflicts and we present an optimal algorithm that is polynomial if the number of concurrent conflicts is bounded. We also give an efficient incremental version of our algorithm. Finally, we evaluate the performance of our algorithm on random BDAGs against an existing algorithm called GHOSTDAG and show that, in addition to being optimal, our algorithm is also more efficient in practice.
The processing of block lifecycles is essential to the efficiency of a blockchain, which consists of four steps: creation, execution, consensus, and validation. The permissionless blockchain systems typically had very limited transaction throughput because of the performance bottleneck of consensus protocols. With recent advances in consensus protocols, the execution and validation of transactions have become the new performance bottleneck. We propose a novel framework, called FastBlock, to speed up the execution and validation steps by introducing fine-grained concurrency. Our early design of FastBlock supported three key modules: (1) a symbolic execution-based analyzer that automatically identifies minimal atomic sections in each transaction; (2) a concurrent execution step that executes possibly conflicting transactions in parallel using hardware transactional memory; (3) a concurrent validation step that introduces a happen-before relation to deterministically re-execute transactions. The improved FastBlock presented in this article supports the nonce mechanism to schedule concurrent transactions from the same account. Moreover, we empirically study the impact of concurrency on Ethereum except for performance and shed light on potential optimizations of FastBlock. Finally, we implemented FastBlock and then evaluated the performance of FastBlock. Our result shows that the FastBlock outperforms state-of-art solutions significantly in performance: the execution step and validation step speed up to 3.0x and 2.3x on average over the original serial model, respectively, with eight concurrent threads. In addition, we evaluated the impact of the nonce mechanism, and the result shows that the performance loss caused by this mechanism is acceptable in practice.
This paper presents MindTheDApp, a toolchain designed specifically for the structural analysis of Ethereum-based Decentralized Applications (DApps), with a distinct focus on a complex network-driven approach. Unlike existing tools, our toolchain combines the power of ANTLR4 and Abstract Syntax Tree (AST) traversal techniques to transform the architecture and interactions within smart contracts into a specialized bipartite graph. This enables advanced network analytics to highlight operational efficiencies within the DApp's architecture. The bipartite graph generated by the proposed tool comprises two sets of nodes: one representing smart contracts, interfaces, and libraries, and the other including functions, events, and modifiers. Edges in the graph connect functions to smart contracts they interact with, offering a granular view of interdependencies and execution flow within the DApp. This network-centric approach allows researchers and practitioners to apply complex network theory in understanding the robustness, adaptability, and intricacies of decentralized systems. Our work contributes to the enhancement of security in smart contracts by allowing the visualisation of the network, and it provides a deep understanding of the architecture and operational logic within DApps. Given the growing importance of smart contracts in the blockchain ecosystem and the emerging application of complex network theory in technology, our toolchain offers a timely contribution to both academic research and practical applications in the field of blockchain technology.
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.
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.
Mustafa Ibrahim Alnajjar, Mehmet Sabır Kiraz, Ali H. AlâBayatti, SĂŒleyman KardaĆ
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.
Open access
2 source records
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.
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.
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.
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.