In blockchain, the consensus algorithm is a core component that governs the trust among the participants in the blockchain activities. However, the exiting consensus algorithms suffer from performance bottleneck such as low throughput, high delay, unstable performance, sustainability issues and vulnerability to targeted attacks. In this paper, we propose a new consortium blockchain consensus algorithm, referred to as Weighted Byzantine Fault Tolerance (WBFT) consensus algorithm that improves system throughput and consensus delay. We introduce a dynamic weighting mechanism for consensus nodes, which enhances the security of blockchain system by weakening the influence of malicious nodes and reduces the probability of malicious behavior. We validate the performance of WBFT experimentally and compare it against Practical Byzantine Fault Tolerance (PBFT) and Reputation-Based Byzantine Fault-Tolerance (RBFT) based approaches. The results show that WBFT substantially outperforms PBFT and RBFT in terms of system throughput, consensus delay and security.
Limited scalability and transaction costs are, among others, some of the critical issues that hamper a wider adoption of distributed ledger technologies (DLT). That is particularly true for the Ethereum blockchain, which, so far, has been the ecosystem with the highest adoption rate. Quite a few solutions, especially on the Ethereum side of things, have been attempted in the last few years. Most of them adopt the approach to offload transactions from the blockchain mainnet, a.k.a. Level 1 (L1), to a separate network. Such systems are collectively known as Level 2 (L2) systems. While mitigating the scalability issue, the adoption of L2 introduces additional drawbacks: users have to trust that the L2 system has correctly performed transactions or, conversely, high computational power is required to prove transactions correctness. In addition, significant technical knowledge is needed to set up and manage such an L2 system. To tackle such limitations, we propose 1DLT: a novel system that enables rapid and trustless deployment of an Ethereum Virtual Machine based blockchain that overcomes those drawbacks.
Norine Coenen, Bernd Finkbeiner, Jana Hofmann, Julia Tillman
Smart contracts are small but highly security-critical programs that implement wallets, token systems, auctions, crowd funding systems, elections, and other multi-party transactions on the blockchain. A broad range of methods has been developed to ensure that a smart contract is functionally correct. However, smart contracts often additionally need to satisfy certain hyperproperties, such as symmetry, determinism, or an information flow policy. In this paper, we show how a synthesis method for smart contracts can ensure that the contract satisfies its desired hyperproperties. We build on top of a recently developed synthesis approach from specifications in the temporal logic TSL. We present HyperTSL, an extension of TSL for the specification of hyperproperties of infinite-state software. As a preprocessing step, we show how to detect if a hyperproperty has an equivalent formulation as a (simpler) trace property. Finally, we describe how to refine a synthesized contract to adhere to its HyperTSL specification.
Due to its minimal energy requirement the PoS consensus protocol has become an attractive alternative to PoW in modern cryptocurrencies. In this protocol the chance of being selected as a block proposer in each round is proportional to the current stake of any node. Thus, nodes with higher stakes will achieve more block rewards, resulting in the so-called rich-getting-richer problem. In this paper, we introduce a new block reward mechanism called the FRD (Fair Reward Distribution) mechanism, in which for each block produced, in addition to a major reward given to the block proposer, a small reward is given to all other nodes. We prove that this reward mechanism makes the PoS protocol fairer in terms of concentration of wealth by developing on the Bagchi-Pal urn model.
Payment channel networks (PCNs) enhance the scalability of blockchains by allowing parties to conduct transactions off-chain, i.e, without broadcasting every transaction to all blockchain participants. To conduct transactions, a sender and a receiver can either establish a direct payment channel with a funding blockchain transaction or leverage existing channels in a multi-hop payment. The security of PCNs usually relies on the synchrony of the underlying blockchain, i.e., evidence of misbehavior needs to be published on the blockchain within a time limit. Alternative payment channel proposals that do not require blockchain synchrony rely on quorum certificates and use a committee to register the transactions of a channel. However, these proposals do not support multi-hop payments, a limitation we aim to overcome. In this paper, we demonstrate that it is in fact impossible to design a multi-hop payment protocol with both network asynchrony and faulty channels, i.e., channels that may not correctly follow the protocol. We then detail two committee-based multi-hop payment protocols that respectively assume synchronous communications and possibly faulty channels, or asynchronous communication and correct channels. The first protocol relies on possibly faulty committees instead of the blockchain to resolve channel disputes, and enforces privacy properties within a synchronous network. The second one relies on committees that contain at most f faulty members out of 3f+1 and successively delegate to each other the role of eventually completing a multi-hop payment. We show that both protocols satisfy the security requirements of a multi-hop payment and compare their communication complexity and latency.
Servio Palacios, Aaron Ault, James V. Krogmeier, Bharat Bhargava · 5 authors
This paper introduces AGAPECert, an Auditable, Generalized, Automated, Privacy-Enabling, Certification framework capable of performing auditable computation on private data and reporting real-time aggregate certification status without disclosing underlying private data. AGAPECert utilizes a novel mix of trusted execution environments, blockchain technologies, and a real-time graph-based API standard to provide automated, oblivious, and auditable certification. Our technique allows a privacy-conscious data owner to run pre-approved Oblivious Smart Contract code in their own environment on their own private data to produce Private Automated Certifications. These certifications are verifiable, purely functional transformations of the available data, enabling a third party to trust that the private data must have the necessary properties to produce the resulting certification. Recently, a multitude of solutions for certification and traceability in supply chains have been proposed. These often suffer from significant privacy issues because they tend to take a" shared, replicated database" approach: every node in the network has access to a copy of all relevant data and contract code to guarantee the integrity and reach consensus, even in the presence of malicious nodes. In these contexts of certifications that require global coordination, AGAPECert can include a blockchain to guarantee ordering of events, while keeping a core privacy model where private data is not shared outside of the data owner's own platform. AGAPECert contributes an open-source certification framework that can be adopted in any regulated environment to keep sensitive data private while enabling a trusted automated workflow.
Ertem Nusret Tas, David Tse, Fangyu Gai, Sreeram Kannan · 6 authors
Bitcoin is the most secure blockchain in the world, supported by the immense hash power of its Proof-of-Work miners. Proof-of-Stake chains are energy-efficient, have fast finality but face several security issues: susceptibility to non-slashable long-range safety attacks, low liveness resilience and difficulty to bootstrap from low token valuation. We show that these security issues are inherent in any PoS chain without an external trusted source, and propose a new protocol, Babylon, where an off-the-shelf PoS protocol checkpoints onto Bitcoin to resolve these issues. An impossibility result justifies the optimality of Babylon. A use case of Babylon is to reduce the stake withdrawal delay: our experimental results show that this delay can be reduced from weeks in existing PoS chains to less than 5 hours using Babylon, at a transaction cost of less than 10K USD per annum for posting the checkpoints onto Bitcoin.
Marco Benedetti, Francesco De Sclavis, Marco Favorito, Giuseppe Galano · 7 authors
Distributed Ledger Technologies (DLTs), when managed by a few trusted validators, require most but not all of the machinery available in public DLTs. In this work, we explore one possible way to profit from this state of affairs. We devise a combination of a modified Practical Byzantine Fault Tolerant (PBFT) protocol and a revised Flexible Round-Optimized Schnorr Threshold Signatures (FROST) scheme, and then we inject the resulting proof-of-authority consensus algorithm into Bitcoin (chosen for the reliability, openness, and liveliness it brings in), replacing its PoW machinery. The combined protocol may operate as a modern, safe foundation for digital payment systems and Central Bank Digital Currencies (CBDC).
This perspective highlights some recent progress on the research of Byzantine fault tolerant (BFT) consensus protocol in the era of blockchains, including both partially synchronous BFT and asynchronous BFT protocols, their fundamental building blocks, and their variants.
Cong Yue, Tien Tuan Anh Dinh, Zhongle Xie, Meihui Zhang · 7 authors
Verifiable ledger databases protect data history against malicious tampering. Existing systems, such as blockchains and certificate transparency, are based on transparency logs --- a simple abstraction allowing users to verify that a log maintained by an untrusted server is append-only. They expose a simple key-value interface without transactions. Building a practical database from transparency logs, on the other hand, remains a challenge. In this paper, we explore the design space of verifiable ledger databases along three dimensions: abstraction, threat model, and performance. We survey existing systems and identify their two limitations, namely, the lack of transaction support and the inferior efficiency. We then present GlassDB, a distributed database system that addresses these limitations under a practical threat model. GlassDB inherits the verifiability of transparency logs, but supports transactions and offers high performance. It extends a ledgerlike key-value store with a data structure for efficient proofs, and adds a concurrency control mechanism for transactions. GlassDB batches independent operations from concurrent transactions when updating the core data structures. In addition, we design a new benchmark for evaluating verifiable ledger databases, by extending YCSB and TPC-C benchmarks. Using this benchmark, we compare GlassDB against four baselines: reimplemented versions of three verifiable databases, and a verifiable map backed by a transparency log. Experimental results demonstrate that GlassDB is an efficient, transactional, and verifiable ledger database system.
Haoqian Zhang, Louis-Henri Merino, Vero Estrada-Galiñanes, Bryan Ford
Front-running, the practice of benefiting from advanced knowledge of pending transactions, has proliferated in the cryptocurrency space with the emergence of decentralized finance. Front-running causes devastating losses to honest participants—estimated at $280M each month—and endangers the fairness of the ecosystem. We present Flash Freezing Flash Boys (F3B), an architecture to address front-running attacks by relying on a commit-and-reveal scheme where the contents of a transaction are encrypted and later revealed by a decentralized secret-management committee (SMC) when the transaction has been committed by the underlying consensus layer. To maintain legacy compatibility, we design F3B to be agnostic to the underlying consensus algorithm and compatible with existing smart contracts. A preliminary exploration of F3B shows that with a secret-management committee consisting of 8 and 128 members, F3B presents between 0.1 and 2.2 seconds of transaction-processing latency, respectively.
Margarita Capretto, Martín Ceresa, Antonio Fernández Anta, Antonio Russo · 5 authors
Blockchain technologies are facing a scalability challenge, which must be overcome to guarantee a wider adoption of the technology. This scalability issue is mostly caused by the use of consensus algorithms to guarantee the total order of the chain of blocks (and of the operations within each block). However, total order is often overkilling, since important advanced applications of smart-contracts do not require a total order of all the operations. Hence, if a more relaxed partial order (instead of a total order) is allowed under certain safety conditions, a much higher scalability can be achieved. In this paper, we propose a distributed concurrent data type, called Setchain, that allows implementing this partial order and increases significantly blockchain scalability. A Setchain implements a grow-only set object whose elements are not totally ordered, unlike conventional blockchain operations. When convenient, the Setchain allows forcing a synchronization barrier that assigns permanently an epoch number to a subset of the latest elements added. With the Setchain, operations in the same epoch are not ordered, while operations in different epochs are. We present different Byzantine-tolerant implementations of Setchain, prove their correctness and report on an empirical evaluation of a direct implementation. Our results show that Setchain is orders of magnitude faster than consensus-based ledgers to implement grow-only sets with epoch synchronization. Since the Setchain barriers can be synchronized with block consolidation, Setchain objects can be used as a sidechain to implement many smart contract solutions with much faster operations than on basic blockchains.
Luciano Freitas de Souza, Andrei Tonkikh, Adda-Akram Bendoukha, Sara Tucci-Piergiovanni · 7 authors
In a single secret leader election protocol (SSLE), one of the system participants is chosen and, unless it decides to reveal itself, no other participant can identify it. SSLE has a great potential in protecting blockchain consensus protocols against denial of service (DoS) attacks. However, all existing solutions either make strong synchrony assumptions or have expiring registration, meaning that they require elected processes to re-register themselves before they can be re-elected again. This, in turn, prohibits the use of these SSLE protocols to elect leaders in partially-synchronous consensus protocols as there may be long periods of network instability when no new blocks are decided and, thus, no new registrations (or re-registrations) are possible. In this paper, we propose Homomorphic Sortition -- the first asynchronous SSLE protocol with non-expiring registration, making it the first solution compatible with partially-synchronous leader-based consensus protocols. Homomorphic Sortition relies on Threshold Fully Homomorphic Encryption (ThFHE) and is tailored to proof-of-stake (PoS) blockchains, with several important optimizations with respect to prior proposals. In particular, unlike most existing SSLE protocols, it works with arbitrary stake distributions and does not require a user with multiple coins to be registered multiple times. Our protocol is highly parallelizable and can be run completely off-chain after setup. Some blockchains require a sequence of rounds to have non-repeating leaders. We define a generalization of SSLE, called Secret Leader Permutation (SLP) in which the application can choose how many non-repeating leaders should be output in a sequence of rounds and we show how Homomorphic Sortition also solves this problem.
Distributed Ledger Technology is a powerful tool to support direct collaboration between organisations, without requiring full trust into a centralised infrastructure. By defining a program logic and access policies with smart contracts, all interactions are verified in the distributed network and the history of the data is recorded on the ledger. Blockchain implementations targeting enterprise use cases also provide means for private transactions, where the content of the transaction is only readable by authorized participants. Direct access to the ledger requires a node with reliable connection to the network and sufficient computational resources, which usually cannot be fulfilled with lightweight Internet of Things devices and mobile applications. We present an advanced system for accessing an enterprise Blockchain through dedicated gateway nodes, while preserving the functionality of private transactions. A hybrid approach is used to allow computation- and storage restricted clients to send private transactions through a central gateway, and use Light Ethereum Subprotocol to verify the data integrity based on proofs from distributed nodes. To increase the client-side security level, we introduce a dedicated Hardware Security Module for key management and efficient execution of the cryptographic primitives. A proof-of-concept implementation, using the Quorum Blockchain client and an extension for the Tessera transaction manager, validates the feasibility of the approach and can be used for further research in this field.
Focusing on the business alliance scenario in blockchains, this paper proposes a new consensus mechanism named proof of rest (PoR) and strong smart contracts. The block structure and logic of PoR consensus are described. And a consortium blockchain system supporting strong smart contracts is designed. We modify the difficulty value algorithm based on proof of work (PoW) and add adjustable parameters. The longer a node rests after creating a block, the less difficult it is to create another new block, hence the term PoR. The penalty for slack nodes, the joining and quitting of nodes, and the adjustment of the expected block creation time can all be accomplished using the strong smart contracts, so the consortium blockchain can realize self-renewal.
In decentralized finance (DeFi), lenders can offer flash loans to borrowers, i.e., loans that are only valid within a blockchain transaction and must be repaid with fees by the end of that transaction. Unlike normal loans, flash loans allow borrowers to borrow large assets without upfront collaterals deposits. Malicious adversaries use flash loans to gather large assets to exploit vulnerable DeFi protocols. In this paper, we introduce a new framework for automated synthesis of adversarial transactions that exploit DeFi protocols using flash loans. To bypass the complexity of a DeFi protocol, we propose a new technique to approximate the DeFi protocol functional behaviors using numerical methods (polynomial linear regression and nearest-neighbor interpolation). We then construct an optimization query using the approximated functions of the DeFi protocol to find an adversarial attack constituted of a sequence of functions invocations with optimal parameters that gives the maximum profit. To improve the accuracy of the approximation, we propose a novel counterexample driven approximation refinement technique. We implement our framework in a tool named FlashSyn. We evaluate FlashSyn on 16 DeFi protocols that were victims to flash loan attacks and 2 DeFi protocols from Damn Vulnerable DeFi challenges. FlashSyn automatically synthesizes an adversarial attack for 16 of the 18 benchmarks. Among the 16 successful cases, FlashSyn identifies attack vectors yielding higher profits than those employed by historical hackers in 3 cases, and also discovers multiple distinct attack vectors in 10 cases, demonstrating its effectiveness in finding possible flash loan attacks.
Les preuves vérifiables de manière probabiliste (PCP, de l'anglais "probabilistically checkable proofs), les preuves interactives (IP, pour "interactive proofs") ou encore les preuves à divulgation nulle de connaissance ("zero-knowledge proofs") ont la particularité d'admettre une vérification probabilististe. Ces systèmes de preuves probabilistes interviennent dans les constructions de schémas de calcul vérifiable, des protocoles cryptographiques permettant de vérifier très rapidement qu'un long calcul a été correctement effectué. En 2016, un nouveau modèle de preuve a été introduit par Ben-Sasson, Chiesa et Spooner : celui des preuves interactives par oracle (IOP, pour "interactive oracle proofs"). Ce modèle généralise à la fois les PCPs et les IPs et a suscité beaucoup d'intérêt depuis son introduction. Le modèle IOP a mené à d'intéressants résultats théoriques sur les arguments non-interactifs succincts et transparents ainsi qu'à des déploiements industriels.Un problème récurrent dans les constructions de systèmes de preuves probabilistes est celui de tester efficacement la proximité à un code correcteur d'erreurs. Le but est de déterminer si un certain mot appartient à un code linéaire donné, ou bien s'il est éloigné de tout mot de ce code. Les tests de proximité à des codes polynomiaux peuvent être interprétés comme des tests de bas degré. Par exemple, un important sous-protocole utilisé dans de nombreuses constructions pratiques est un "IOP of Proximity" pour les codes de Reed-Solomon (Ben-Sasson et al., ICALP 2018).Dans cette thèse, nous proposons dans le modèle IOP des protocoles permettant de vérifier la proximité à des codes correcteur d'erreurs.En nous inspirant du test de proximité pour les codes de Reed-Solomon de Ben-Sasson et al., nous commençons par formuler un cadre abstrait et générique pour construire des "IOPs of Proximity" pour des codes linéaires et en analysons formellement les propriétés. Nous appliquons ensuite cette méthodologie à différentes familles de codes généralisant les codes de Reed-Solomon. Il s'agit d'une part de codes définis à partir d'évaluations de polynômes multivariés et, d'autre part, de codes de géométrie algrébrique définis sur des courbes. Nos protocoles permettent de tester la proximité à des codes présentant des propriétés attrayantes par rapport aux codes de Reed-Solomon (telles que des alphabets de petite taille), tout en ayant une efficacité similaire à la construction de Ben-Sasson et al.
Abstract We proposed a decentralized cryptocurrency protocol named proof of activity and stake in which participants have no admittance threshold and communicate in peer-to-peer network. Our protocol adopts the idea of stakeholders in proof of stake and combined it with the propagation activity to replace the resource-costly proof of work. It is also proposed to solve the contradiction of security and throughput, which discouraged the promotion of blockchain applications. With analysis of security assurance and performance, proof of activity and stake is proved to be robust and economical against double spending attack.
In the modern digital world, large-scale data and the analytic processing of the data make privacy-preserving computation even more critical. SMPC is a cryptographic protocol used to compute a function over the inputs of multiple parties such that the other party’s input is unknown. This then provides for computing in parallel with other participants, without requiring a coordinator, which, in today’s privacy-conscious world, is beneficial in avoiding using a central authority in data-entrusted activities. In a nutshell, a decentralized AI approach is based on distributed computing principles and the blockchain to create a solid architecture for SMPC implementation. In this manner, decentralized AI eliminates several drawbacks of data centralization, such as single points of failure and data breaches. SMPC and decentralized networks are the foundation of the privacy-preserving ML, where sensitive data train models without revealing the data points. Specifically, the growing necessity for protecting data with the help of laws like the GDPR and CCPA enhances SMPC’s application in decentralized AI. Blockchain technology extends this implementation by having additional qualities of having an unchangeable record and consensus mechanisms that guarantee computation reliability and openness. However, scalability, ITY, computational cost, and system compatibility are drawbacks to integrating decentralized AI and SMPC. Solving these needs more be a continuous effort in the search for cryptographic techniques in communication, network design, and protocol formation. The combination of decentralized AI and SMPC presents a new and revolutionary way of multi-party computation through data privacy and access to cooperation and innovation in sectors such as health, finance, and supply chain. With the development of technology, these intelligent computing applications of decentralized AI and SMPC will continue to develop and open up new areas for efficient and secure data usage.
Riyad Almakki, Lulwah AlSuwaidan, Shakir Khan, Abdul Rauf Baig · 6 authors
A new algorithm for practical Byzantine fault tolerance (PBFT), called score-PBFT or S-PBFT, is proposed to solve the problems of high communication overhead and low algorithm efficiency. This algorithm is based on the characteristics of the consortium chain. The scoring mechanism for nodes is added. All the nodes are broken up into consensus nodes, candidate nodes, and early nodes. To make sure the consensus nodes are as reliable as possible, the nodes are changed dynamically based on how each node is behaving. Improved: the election method for the controller node has been changed. The node’s score and behaviour are used as the election basis to make the algorithm more stable. In this paper, we want to improve the consensus protocol’s execution process, cut down on how many nodes are involved in the consensus process, simplify it, and make it more efficient. Results show that, when compared with the PBFT algorithm, the S-PBFT algorithm has a shorter consensus delay, less communication overhead and throughput, and better consensus node reliability.
Blockchain-based IoT systems can manage IoT devices and achieve a high level of data integrity, security, and provenance. However, incorporating existing consensus protocols in many IoT systems limits scalability and leads to high computational cost and consensus latency. In addition, location-centric characteristics of many IoT applications paired with limited storage and computing power of IoT devices bring about more limitations, primarily due to the location-agnostic designs in blockchains. We propose a hierarchical and location-aware consensus protocol (LH-Raft) for IoT-blockchain applications inspired by the original Raft protocol to address these limitations. The proposed LH-Raft protocol forms local consensus candidate groups based on nodes' reputation and distance to elect the leaders in each sub-layer blockchain. It utilizes a threshold signature scheme to reach global consensus and the local and global log replication to maintain consistency for blockchain transactions. To evaluate the performance of LH-Raft, we first conduct an extensive numerical analysis based on the proposed reputation mechanism and the candidate group formation model. We then compare the performance of LH-Raft against the classical Raft protocol from both theoretical and experimental perspectives. We evaluate the proposed threshold signature scheme using Hyperledger Ursa cryptography library to measure various consensus nodes' signing and verification time. Experimental results show that the proposed LH-Raft protocol is scalable for large IoT applications and significantly reduces the communication cost, consensus latency, and agreement time for consensus processing.
In this paper we explore a context of application of Cob, a recently introduced Byzantine Fault Tolerant consensus protocol. Cob proves to be a leaderless consensus protocol which carries out the consensus process in parallel on each component of a list of events to be observed and recorded. We show how Cob can be used to define a consensus layer for scalable and sustainable blockchains. This layer is used to design consensus protocols based on sharding as a mean to achieve scalability, and on the fragmentation of time in time-slots (which get assigned to nodes that are instructed to create new blocks) as a mean to reduce the amount of computation and communication necessary for the maintenance of the distributed ledger. We explain why Cob is a viable candidate to implement such consensus layer through the introduction of an auxiliary blockchain that we name Synchronization Chain.
Sebastian Müller, Andreas Penzkofer, Nikita Polyanskii, Jonas Theis · 6 authors
The Unspent Transaction Output (UTXO) model is commonly used in the field of Distributed Ledger Technology (DLT) to transfer value between participants. One of its advantages is that it allows parallel processing of transactions, as independent transactions can be added in any order. This property of order invariance and parallelisability has potential benefits in terms of scalability. However, since the UTXO Ledger is an append-only data structure, this advantage is compromised through the presence of conflicting transactions. We propose an extended UTXO Ledger model that optimistically updates the ledger and keeps track of the dependencies of the possible conflicts. In the presence of a conflict resolution mechanism, we propose a method to reduce the extended ledger back to a consistent UTXO Ledger.
Classical and contemporary distributed consensus protocols, may they be for binary agreement, state machine replication, or blockchain consensus, require all protocol participants in a peer-to-peer system to agree on exactly the same information as part of the consensus payload. Although this model of consensus is extensively studied, and is useful for most consensus based decentralized applications, it falls short of defining correct distributed systems which mandate participant credential based privileged visibility into the consensus payload, through the consensus protocol itself. We introduce a new paradigm for distributed consensus, called functional blockchain consensus. Functional blockchain consensus allows each blockchain protocol participant to agree on some distinct sub-information of the list of transactions, as a function of the credentials of the participant in the blockchain system, instead of agreeing on the entire list of transactions. We motivate two adversary models, one with a standard crash-fault adversary and another with a novel rational-fault adversary, to compromise functional blockchain consensus. We then present two versions of a blockchain protocol called SightSteeple, that achieves functional blockchain consensus in the said fault models. SightSteeple relies on a novel combination of standard blockchain consensus and functional encryption, among other primitives, to achieve its goals of correctness. Finally, we discuss practical uses of functional blockchain consensus based asymmetric distributed ledgers, and motivate off-shoot constructions that can result from this new consensus paradigm.