Blockchain technology has been quite popular during recent years and it finally seems to present a significant rise with respect to its use for real-world applications. This advancement has brought up a critical challenge that public blockchain systems face, which is scalability. Most of the currently deployed systems fail to cope with increasing usage. In order to provide the promised security guarantees, large delays and high usage fees are imposed for submitted transactions and thus widespread adoption of the technology is hindered. A number of different approaches have been proposed to increase the capacity of blockchain systems with respect to processing transactions. The present survey focuses on one of the most popular ones, that of state channels, and to the extent of our knowledge constitutes the first collective survey of research in this field. An extensive analysis of relevant publications is conducted and a general view on the domain is provided. We have identified the limitations discussed through all relevant research efforts along with the various features that differentiate proposed designs. A comparison between retrieved papers is carried out on the basis of those limitations and features. Finally, future research directions are analysed while the role of state channels in the general public blockchain ecosystem is also discussed.
Decentralized cryptocurrencies have gathered increasing interest in the past few years, raising hopes of a new era of non-sovereign electronic money. Unfortunately, cryptocurrencies perform poorly as actual money due to their unacceptably volatile purchasing power. "Stablecoins" aiming to reduce this volatility, on the other hand, tend to peg to an external currency like the US dollar, gravely weakening the decentralization that makes cryptocurrencies so attractive.
Blockchain technologies have been rapidly enhanced in recent years. However, its scalability still has limitations in terms of throughput and broadcast delay as the network and the amount of transaction data increase. To improve scalability of blockchain networks, we propose a novel approach named PiChu that accelerates block propagation in blockchain networks by pipelining and verifying chunks of a block in parallel. Accelerating block propagation reduces the mining interval and chance of fork occurring, which in turn increases throughput. Our approach can be applied to the blockchain networks either directly or with a minor modification to the consensus. Through an extensive and large scale simulations, we validate that the proposed PiChu scheme significantly enhances the scalability of blockchain networks. For instance, a 64 MB block can be broadcasted in just 80 seconds in a blockchain network with a million nodes. The efficiency of PiChu broadcasting increases with bigger block sizes and a larger number of nodes in the network.
Kejiao Li, Hui Li, Han Wang, Huiyao An · 7 authors
The blockchain has a great vogue in recent years, and its core consensus algorithms also become the focus of research. At present, most of the research on consensus mechanisms are oriented to the public blockchain and based on existing consensus mechanisms or sophisticated distributed algorithms. Various application scenarios have been developed based on the consortium blockchain, while few researchers pay attention to customize consistency algorithms. Moreover, there is a trade-off between security and performance in designing consensus mechanisms. We propose a novel consensus algorithm called Proof of Vote (PoV), where the distributed nodes controlled by consortium members could reach consensus and come to a decentralized arbitration by voting. PoV separates the voting rights and bookkeeping rights with the essential idea of establishing different security identities for network nodes. Contrary to the third-party intermediary or uncontrollable public awareness, the production and verification of PoV blocks are decided by the voting results among the core consortium members. We theoretically prove that PoV blocks can reach transaction finality by only one confirmation. Compared with the total traffic complexity of BFT-based consensus, PoV has just that of O( ), which is a great improvement when the number of nodes is over 100.
Most existing blockchain schemes are based on the design concept “openness and transparency” to realize data security, which usually require transaction data to be presented in the form of plaintext. However, it inevitably brings the issues with respect to data privacy and operating performance. In this paper, we proposed a novel blockchain scheme called Cipherchain, which can process and maintain transaction data in the form of ciphertext while the characteristics of immutability and auditability are guaranteed. Specifically in our scheme, transactions can be encrypted locally based on a searchable encryption scheme called multi-user public key encryption with conjunctive keyword search (mPECK), and can be accessed by multiple specific participants after appended to the globally consistent distributed ledger. By introducing execution-consensus-update paradigm of transaction flow, Cipherchain cannot only make it possible for transaction data to exist in the form of ciphertext, but also guarantee the overall system performance not greatly affected by cryptographic operations and other local execution work. In addition, Cipherchain is a promising scheme to realize the technology combination of “blockchain+cloud computing” and “permissioned blockchain+public blockchain”.
Myoungwon Oh, Sujin Ha, Jin Hyuk Yoon, Kang‐Won Lee · 6 authors
Distributed ledger technology faces scalability problems due to a long commit time despite recent successes for cryptocurrency. Small group consensus studies have improved this scalability of distributed ledgers. However, they still have problems of the consensus process itself. For example, most blockchain systems perform serialized block proposal and consensus processing, guarantee the finality with high overhead, and handle byzantine nodes inefficiently. To address these problems, we propose a consensus system, named graph learning byzantine fault tolerance (GL BFT), which offers high parallelism and low latency under Byzantine fault. To do this, we enable a parallel pipelined agreement by separating the block proposal and the consensus process. Second, we devise two techniques of merging blocks and commit learning to guarantee the finality with little overhead. Finally, we present a path learning approach which chooses optimal paths to handle Byzantine fault. The proposed GL BFT can achieve instant finality with low message overhead among a small group of nodes even if Byzantine nodes exit. Also, we evaluate its performance on an open source blockchain protocol. Experimental results show that our design reduces data traffic required by the consensus up to 30%, one transaction is finalized within a few seconds, and optimal performance is maintained.
The goal of this article is to extend the ideas concerning Bracha-Toueg asynchronous Byzantine Fault Tolerant consensus algorithm and Baird's Hashgraph consensus. We propose a family of atomic broadcast algorithms, which Hashgraph consensus is closely related to. We also do preliminary comparative algorithm speed analysis which shows that some members of the family seriously outperform Hashgraph consensus. These algorithms can also be readily used as a base of proof-of-stake consensuses. In appendix we provide an extension of Hashgraph gossip protocol, which efficiently handles byzantine fault information exchange between nodes.
One of the key challenges in the collaboration within heterogeneous multi-robot systems is the optimization of the amount and type of data to be shared between robots with different sensing capabilities and computational resources. In this paper, we present a novel approach to managing collaboration terms in heterogeneous multi-robot systems with blockchain technology. Leveraging the extensive research of consensus algorithms in the blockchain domain, we exploit key technologies in this field to be integrated for consensus in robotic systems. We propose the utilization of proof of work systems to have an online estimation of the available computational resources at different robots. Furthermore, we define smart contracts that integrate information about the environment from different robots in order to evaluate and rank the quality and accuracy of each of the robots' sensor data. This means that the key parameters involved in heterogeneous robotic collaboration are integrated within the Blockchain and estimated at all robots equally without explicitly sharing information about the robots' hardware or sensors. Trustability is based on the verification of data samples that are submitted to the blockchain within each data exchange transaction and validated by other robots operating in the same environment. Initial results are reported which show the viability of the concepts presented in this paper.
Distributed Leger Technologies (DLTs), most notably Blockchain technologies, bring decentralised platforms that eliminate a single trusted third party and avoid the notorious single point of failure vulnerability. Since Nakamoto's Bitcoin cryptocurrency system, an enormous number of decentralised applications have been proposed on top of these technologies, aiming at more transparency and trustworthiness than their traditional counterparts. These applications spread over a lot of areas, e.g. financial services, healthcare, transportation, supply chain management, and cloud computing. While Blockchain brings transparency and decentralised trust intuitively due to the consensus of a (very large) group of nodes (or, miners), it introduces very subtle implications for other desirable properties such as privacy. In this work, we demonstrate these subtle implications for Blockchain-based searchable encryption solutions, which are one specific use case of cloud computing services. These solutions rely on Blockchain to achieve both the standard privacy property and the new fairness property, which requires that search operations are carried out faithfully and are rewarded accordingly. We show that directly replacing the server in an existing searchable encryption solution with a Blockchain will cause undesirable operational cost, privacy loss, and security vulnerabilities. The analysis results indicate that a dedicated server is still needed to achieve the desired privacy guarantee. To this end, we propose two frameworks which can be instantiated based on most existing searchable encryption schemes. Through analysing these two frameworks, we affirmatively show that a carefully engineered Blockchain-based solution can achieve the desired fairness property while preserving the privacy guarantee of the original searchable encryption scheme simultaneously.
The 3XORSUM problem aims to find (x, y, z) such that x + y + z = 0 over {0, 1}d, with each variable drawn from one of 3 randomly generated lists. In addition to being of interest in its own right, this problem has cryptographic applications including proof of stake methods in Blockchain.The 3XORSUM problem is also related to the integer 3SUM problem from theoretical computer science on which there is extensive recent literature. It is conjectured that the integer 3SUM problem has complexity $\tilde \Omega \left({{n^2}}\right)$ for lists of size O(n).Wagner [10] has presented an algorithm with complexity Õ(2d/3) for finding a 4XORSUM solution (x + y + z + w = 0) with each variable drawn from one of 4 randomly generated lists of size O(2d/3) with members from {0, 1}d.We present an algorithm which solves the 3XORSUM problem for randomly generated binary vectors from {0, 1}dwith time and memory complexity Õ(n) = Õ(2d/3). This substantially improves results from [1], [8]. Our algorithm has applications to blockchains and other cryptographic problems.
Rachid Guerraoui, Petr Kuznetsov, Matteo Monti, Matej Pavlovič · 5 authors
Many blockchain-based algorithms, such as Bitcoin, implement a decentralized asset transfer system, often referred to as a cryptocurrency. As stated in the original paper by Nakamoto, at the heart of these systems lies the problem of preventing double-spending; this is usually solved by achieving consensus on the order of transfers among the participants. In this paper, we treat the asset transfer problem as a concurrent object and determine its consensus number, showing that consensus is, in fact, not necessary to prevent double-spending. We first consider the problem as defined by Nakamoto, where only a single process---the account owner---can withdraw from each account. Safety and liveness need to be ensured for correct account owners, whereas misbehaving account owners might be unable to perform transfers. We show that the consensus number of an asset transfer object is $1$. We then consider a more general $k$-shared asset transfer object where up to $k$ processes can atomically withdraw from the same account, and show that this object has consensus number $k$. We establish our results in the context of shared memory with benign faults, allowing us to properly understand the level of difficulty of the asset transfer problem. We also translate these results in the message passing setting with Byzantine players, a model that is more relevant in practice. In this model, we describe an asynchronous Byzantine fault-tolerant asset transfer implementation that is both simpler and more efficient than state-of-the-art consensus-based solutions. Our results are applicable to both the permissioned (private) and permissionless (public) setting, as normally their differentiation is hidden by the abstractions on top of which our algorithms are based.
A Coordination Blockchain is a blockchain with the task of coordinating activities of multiple private blockchains. This paper discusses the pros and cons of using Ethereum MainNet, the public Ethereum blockchain, as a Coordination Blockchain. The requirements Ethereum MainNet needs to fulfil to perform this role are discussed within the context of Ethereum Private Sidechains, a private blockchain technology which allows many blockchains to be operated in parallel, and allows atomic crosschain transactions to execute across blockchains. Ethereum MainNet is a permissionless network which aims to offer strong authenticity, integrity, and non-repudiation properties, that incentivises good behaviour using crypto economics. This paper demonstrates that Ethereum MainNet does deliver these properties. It then provides a comprehensive review of the features of Ethereum Private Sidechains, with a focus on the potential usage of Coordination Blockchains for these features. Finally, the merits of using Ethereum MainNet as a Coordination Blockchain are assessed. For Ethereum Private Sidechains, we found that Ethereum MainNet is best suited to storing long term static data that needs to be widely available, such as the Ethereum Registration Authority information. However, due to Ethereum MainNet's probabilistic finality, it is not well suited to information that needs to be available and acted upon immediately, such as the Sidechain Public Keys and Atomic Crosschain Transaction state information that need to be accessible prior to the first atomic crosschain transaction being issued on a sidechain. Although this paper examined the use of Ethereum MainNet as a Coordination Blockchain within reference to Ethereum Private Sidechains, the discussions and observations of the typical tasks a Coordination blockchain may be expected to perform are applicable more widely to any multi-blockchain system.
A Coordination Blockchain is a blockchain with the task of coordinating\nactivities of multiple private blockchains. This paper discusses the pros and\ncons of using Ethereum MainNet, the public Ethereum blockchain, as a\nCoordination Blockchain. The requirements Ethereum MainNet needs to fulfil to\nperform this role are discussed within the context of Ethereum Private\nSidechains, a private blockchain technology which allows many blockchains to be\noperated in parallel, and allows atomic crosschain transactions to execute\nacross blockchains. Ethereum MainNet is a permissionless network which aims to\noffer strong authenticity, integrity, and non-repudiation properties, that\nincentivises good behaviour using crypto economics. This paper demonstrates\nthat Ethereum MainNet does deliver these properties. It then provides a\ncomprehensive review of the features of Ethereum Private Sidechains, with a\nfocus on the potential usage of Coordination Blockchains for these features.\nFinally, the merits of using Ethereum MainNet as a Coordination Blockchain are\nassessed. For Ethereum Private Sidechains, we found that Ethereum MainNet is\nbest suited to storing long term static data that needs to be widely available,\nsuch as the Ethereum Registration Authority information. However, due to\nEthereum MainNet's probabilistic finality, it is not well suited to information\nthat needs to be available and acted upon immediately, such as the Sidechain\nPublic Keys and Atomic Crosschain Transaction state information that need to be\naccessible prior to the first atomic crosschain transaction being issued on a\nsidechain. Although this paper examined the use of Ethereum MainNet as a\nCoordination Blockchain within reference to Ethereum Private Sidechains, the\ndiscussions and observations of the typical tasks a Coordination blockchain may\nbe expected to perform are applicable more widely to any multi-blockchain\nsystem.\n
Transaction throughput, confirmation latency and confirmation reliability are fundamental performance measures of any blockchain system in addition to its security. In a decentralized setting, these measures are limited by two underlying physical network attributes: communication capacity and speed-of-light propagation delay. Existing systems operate far away from these physical limits. In this work we introduce Prism, a new proof-of-work blockchain protocol, which can achieve 1) security against up to 50% adversarial hashing power; 2) optimal throughput up to the capacity C of the network; 3) confirmation latency for honest transactions proportional to the propagation delay D, with confirmation error probability exponentially small in CD ; 4) eventual total ordering of all transactions. Our approach to the design of this protocol is based on deconstructing the blockchain into its basic functionalities and systematically scaling up these functionalities to approach their physical limits.
Proof-of-stake (PoS) is a promising approach for designing efficient blockchains, where block proposers are randomly chosen with probability proportional to their stake. A primary concern with PoS systems is the "rich getting richer" phenomenon, whereby wealthier nodes are more likely to get elected, and hence reap the block reward, making them even wealthier. In this paper, we introduce the notion of equitability, which quantifies how much a proposer can amplify her stake compared to her initial investment. Even with everyone following protocol (i.e., honest behavior), we show that existing methods of allocating block rewards lead to poor equitability, as does initializing systems with small stake pools and/or large rewards relative to the stake pool. We identify a \emph{geometric} reward function, which we prove is maximally equitable over all choices of reward functions under honest behavior and bound the deviation for strategic actions; the proofs involve the study of optimization problems and stochastic dominances of Polya urn processes, and are of independent mathematical interest. These results allow us to provide a systematic framework to choose the parameters of a practical incentive system for PoS cryptocurrencies.
Halil Ibrahim Ozercan, Atalay Mert Ileri, Erman Ayday, Can Alkan
Genomics data introduce a substantial computational burden as well as data privacy and ownership issues. Data sets generated by high-throughput sequencing platforms require immense amounts of computational resources to align to reference genomes and to call and annotate genomic variants. This problem is even more pronounced if reanalysis is needed for new versions of reference genomes, which may impose high loads to existing computational infrastructures. Additionally, after the compute-intensive analyses are completed, the results are either kept in centralized repositories with access control, or distributed among stakeholders using standard file transfer protocols. This imposes two main problems: (1) Centralized servers become gatekeepers of the data, essentially acting as an unnecessary mediator between the actual data owners and data users; and (2) servers may create single points of failure both in terms of service availability and data privacy. Therefore, there is a need for secure and decentralized platforms for data distribution with user-level data governance. A new technology, blockchain, may help ameliorate some of these problems. In broad terms, the blockchain technology enables decentralized, immutable, incorruptible public ledgers. In this Perspective, we aim to introduce current developments toward using blockchain to address several problems in omics, and to provide an outlook of possible future implications of the blockchain technology to life sciences.
Open access
Blockchain Technology Applications and Security
Nanocluster Synthesis and Applications
Innovative Microfluidic and Catalytic Techniques Innovation
Nowadays, blockchain is becoming a synonym for distributed ledger technology. However, blockchain is only one of the specializations in the field and is currently well-covered in existing literature, but mostly from a cryptographic point of view. Besides blockchain technology, a new paradigm is gaining momentum: directed acyclic graphs. The contribution presented in this paper is twofold. Firstly, the paper analyzes distributed ledger technology with an emphasis on the features relevant to distributed systems. Secondly, the paper analyses the usage of directed acyclic graph paradigm in the context of distributed ledgers, and compares it with the blockchain-based solutions. The two paradigms are compared using representative implementations: Bitcoin, Ethereum and Nano. We examine representative solutions in terms of the applied data structures for maintaining the ledger, consensus mechanisms, transaction confirmation confidence, ledger size, and scalability.
Nowadays, blockchain is becoming a synonym for distributed ledger technology.\nHowever, blockchain is only one of the specializations in the field and is\ncurrently well-covered in existing literature, but mostly from a cryptographic\npoint of view. Besides blockchain technology, a new paradigm is gaining\nmomentum: directed acyclic graphs. The contribution presented in this paper is\ntwofold. Firstly, the paper analyzes distributed ledger technology with an\nemphasis on the features relevant to distributed systems. Secondly, the paper\nanalyses the usage of directed acyclic graph paradigm in the context of\ndistributed ledgers, and compares it with the blockchain-based solutions. The\ntwo paradigms are compared using representative implementations: Bitcoin,\nEthereum and Nano. We examine representative solutions in terms of the applied\ndata structures for maintaining the ledger, consensus mechanisms, transaction\nconfirmation confidence, ledger size, and scalability.\n
K.W. Yeow, Abdullah Gani, Raja Wasim Ahmad, Joel J. P. C. Rodrigues · 5 authors
With the exponential rise in the number of devices, the Internet of Things (IoT) is geared toward edge-centric computing to offer high bandwidth, low latency, and improved connectivity. In contrast, legacy cloud-centric platforms offer deteriorated bandwidth and connectivity that affect the quality of service. Edge-centric Internet of Things-based technologies, such as fog and mist computing, offer distributed and decentralized solutions to resolve the drawbacks of cloud-centric models. However, to foster distributed edge-centric models, a decentralized consensus system is necessary to incentivize all participants to share their edge resources. This paper is motivated by the shortage of comprehensive reviews on decentralized consensus systems for edge-centric Internet of Things that elucidates myriad of consensus facets, such as data structure, scalable consensus ledgers, and transaction models. Decentralized consensus systems adopt either blockchain or blockchainless directed acyclic graph technologies, which serve as immutable public ledgers for transactions. This paper scrutinizes the pros and cons of state-of-the-art decentralized consensus systems. With an extensive literature review and categorization based on existing decentralized consensus systems, we propose a thematic taxonomy. The pivotal features and characteristics associated with existing decentralized consensus systems are analyzed via a comprehensive qualitative investigation. The commonalities and variances among these systems are analyzed using key criteria derived from the presented literature. Finally, several open research issues on decentralized consensus for edge-centric IoT are presented, which should be highlighted regarding centralization risk and deficiencies in blockchain/blockchainless solutions.
Andrew Miller, Iddo Bentov, Surya Bakshi, Ranjit Kumaresan · 5 authors
Bitcoin, Ethereum and other blockchain-based cryptocurrencies, as deployed today, cannot scale for wide-spread use. A leading approach for cryptocurrency scaling is a smart contract mechanism called a payment channel which enables two mutually distrustful parties to transact efficiently (and only requires a single transaction in the blockchain to set-up). Payment channels can be linked together to form a payment network, such that payments between any two parties can (usually) be routed through the network along a path that connects them. Crucially, both parties can transact without trusting hops along the route. In this paper, we propose a novel variant of payment channels, called Sprites, that reduces the worst-case "collateral cost" that each hop along the route may incur. The benefits of Sprites are two-fold. 1) In Lightning Network, a payment across a path of $\ell$ channels requires locking up collateral for $Θ(\ellΔ)$ time, where $Δ$ is the time to commit an on-chain transaction. Sprites reduces this cost to $O(\ell + Δ)$. 2) Unlike prior work, Sprites supports partial withdrawals and deposits, during which the channel can continue to operate without interruption. In evaluating Sprites we make several additional contributions. First, our simulation-based security model is the first formalism to model timing guarantees in payment channels. Our construction is also modular, making use of a generic abstraction from folklore, called the "state channel," which we are the first to formalize. We also provide a simulation framework for payment network protocols, which we use to confirm that the Sprites construction mitigates against throughput-reducing attacks.
Tyler Crain, Vincent Gramoli, Mikel Larrea, Michel Raynal
This paper presents a new Byzantine consensus algorithm targeting consortium blockchains. To this end, it first revisits the consensus validity property by requiring that the decided value satisfies a predefined predicate, which does not systematically exclude a value proposed only by Byzantine processes, thereby generalizing the validity properties found in the literature. Then, the paper presents a simple and modular Byzantine consensus algorithm that relies neither on a leader, nor on signatures, nor on randomization. It features the fastest multivalued reduction to binary consensus we know of and a time optimal binary Byzantine consensus algorithm. The multivalued reduction runs multiple instances of binary consensus concurrently, which result in a bitmask that is then applied to a vector of multivalued proposals to filter out a valid proposed value that is decided. To ensure eventual decision deterministically, the underlying binary consensus algorithm assumes eventual synchrony.
Tendermint is a new protocol for ordering events in a distributed network under adversarial conditions. More commonly known as consensus or atomic broadcast, the problem has attracted significant attention recently due to the widespread success of digital currencies, such as Bitcoin and Ethereum, which successfully solve the problem in public settings without a central authority. Tendermint modernizes classic academic work on the subject to provide a secure consensus protocol with accountability guarantees, as well as an interface for building arbitrary applications above the consensus. Tendermint is high performance, achieving thousands of transactions per second on dozens of nodes distributed around the globe, with latencies of about one second, and performance degrading moderately in the face of adversarial attacks.