We propose LazyLedger, a design for distributed ledgers where the blockchain\nis optimised for solely ordering and guaranteeing the availability of\ntransaction data. Responsibility for executing and validating transactions is\nshifted to only the clients that have an interest in specific transactions\nrelating to blockchain applications that they use. As the core function of the\nconsensus system of a distributed ledger is to order transactions and ensure\ntheir availability, consensus participants do not necessarily need to be\nconcerned with the contents of those transactions. This reduces the problem of\nblock verification to data availability verification, which can be achieved\nprobabilistically with sub-linear complexity, without downloading the whole\nblock. The amount of resources required to reach consensus can thus be\nminimised, as transaction validity rules can be decoupled from consensus rules.\nWe also implement and evaluate several example LazyLedger applications, and\nvalidate that the workload of clients of specific applications does not\nsignificantly increase when the workload of other applications that use the\nsame chain increase.\n
Quartierstrom creates a peer-to-peer marketplace for locally generated solar power. The marketplace is implemented as a smart contract on a permissioned blockchain governed by all prosumers. Two privacy-by-design concepts are presented which guarantee that the users individual load profile is not leaked to any third party despite using a blockchain. The first approach leverages UTXO based coin mixing protocols in combination with an account-based on-chain smart contract. The second approach relies on an off-chain smart contract running in trusted execution environments.
Although the emergence of the programmable smart contract makes blockchain systems easily embrace a wider range of industrial areas, how to execute smart contracts efficiently becomes a big challenge nowadays. Due to the existence of Byzantine nodes, the mechanism of executing smart contracts is quite different from that in database systems, so that existing successful concurrency control protocols in database systems cannot be employed directly. Moreover, even though smart contract execution follows a two-phase style, i.e, the miner node executes a batch of smart contracts in the first phase and the validators replay them in the second phase, existing parallel solutions only focus on the optimization in the first phase, but not including the second phase. In this paper, we propose a novel efficient concurrency control scheme which is the first one to do optimization in both phases. Specifically, (i) in the first phase, we give a variant of OCC (Optimistic Concurrency Control) protocol based on {\em batching} feature to improve the concurrent execution efficiency for the miner and produce a schedule log with high parallelism for validators. Also, a graph partition algorithm is devised to divide the original schedule log into small pieces and further reduce the communication cost; and (ii) in the second phase, we give a deterministic OCC protocol to replay all smart contracts efficiently on multi-core validators where all cores can replay smart contracts independently. Theoretical analysis and extensive experimental results illustrate that the proposed scheme outperforms state-of-art solutions significantly.
Providing security and privacy for the Internet of Things (IoT) applications while ensuring a minimum level of performance requirements is an open research challenge. Recently, blockchain offers a promising solution to overcome the current peer-to-peer networks limitations. In the context of IoT, Byzantine fault tolerance (BFT)-based consensus protocols are used due to the energy efficiency advantage over other consensus protocols. The consensus process in BFT is done by electing a group of authenticated nodes. The elected nodes will be responsible for ensuring the data blocks' integrity through defining a total order on the blocks and preventing the concurrently appended blocks from containing conflicting data. However, the blockchain consensus layer contributes the most performance overhead. Therefore, a performance study needs to be conducted especially for the IoT applications that are subject to maximum delay constraints. In this paper, we obtain a mathematical expression to calculate the end-to-end delay with different network configurations, i.e., number of network hops and replica machines. We validate the proposed analytical model with simulation. Our results show that the unique characteristics of IoT traffic have an undeniable impact on the end-to-end delay requirement.
Dumitrel Loghin, Gang Chen, Tien Tuan Anh Dinh, Beng Chin Ooi · 5 authors
Motivated by the massive energy usage of blockchain, on the one hand, and by significant performance improvements in low-power, wimpy systems, on the other hand, we perform an in-depth time-energy analysis of blockchain systems on low-power nodes in comparison to high-performance nodes. We use three low-power systems to represent a wide range of the performance-power spectrum, while covering both x86/64 and ARM architectures. We show that low-end wimpy nodes are struggling to run full-fledged blockchains mainly due to their small and low-bandwidth memory. On the other hand, wimpy systems with balanced performance-to-power ratio achieve reasonable performance while saving significant amounts of energy. For example, Jetson TX2 nodes achieve around 80% and 30% of the throughput of Parity and Hyperledger, respectively, while using 18x and 23x less energy compared to traditional brawny servers with Intel Xeon CPU.
Yu‐Jin Kwon, Jian Liu, Minjeong Kim, Dawn Song · 5 authors
Bitcoin uses blockchain technology and proof-of-work (PoW) mechanism where nodes spend computing resources and earn rewards in return for spending these resources. This incentive system has caused power to be significantly biased towards a few nodes, called mining pools. In fact, poor decentralization appears not only in PoW-based coins but also in coins adopting other mechanisms such as proof-of-stake (PoS) and delegated proof-of-stake (DPoS). In this paper, we target this centralization issue. To this end, we first define (m, \varepsilon, δ)-decentralization as a state that satisfies 1) there are at least m participants running a node and 2) the ratio between the total resource power of nodes run by the richest and δ-th percentile participants is less than or equal to 1+\varepsilon. To see if it is possible to achieve good decentralization, we introduce sufficient conditions for the incentive system of a blockchain to reach (m, \varepsilon, δ)-decentralization. When satisfying the conditions, a blockchain system can reach full decentralization with probability 1. However, to achieve this, the blockchain system should be able to assign a positive Sybil cost, where the Sybil cost is defined as the difference between the cost for one participant running multiple nodes and the total cost for multiple participants each running one node. On the other hand, we prove that when there is no Sybil cost, the probability of reaching (m, \varepsilon, δ)-decentralization is upper bounded by a value close to 0, considering a large rich-poor gap. To determine the conditions that each system cannot satisfy, we also analyze protocols of all PoW, PoS, and DPoS coins in the top 100 coins according to our conditions. Finally, we conduct data analysis of these coins to validate our theory.
Various start-up developers and academic researchers have investigated the\nusage of blockchain as a data storage medium due to the advantages offered by\nits tamper-proof and decentralized nature. However, there have not been many\nattempts to provide a standard platform for virtually storing the states of\nunique tangible entities and their subsequent modifications. In this paper, we\npropose NFTracer, a non-fungible token tracking proof-of-concept based on\nHyperledger Composer and Hyperledger Fabric Blockchain. To achieve the\ncapabilities of our platform, we use NFTracer to build an artwork auction and a\nreal estate auction, which vary in technical complexity and demonstrate the\nadvantages of being able to track entities and their resulting modifications in\na decentralized manner. We also present its accompanying modular architecture\nand system components, and discuss possible future works on NFTracer.\n
The development of blockchain technologies has enabled the trustless execution of so-called smart contracts, i.e. programs that regulate the exchange of assets (e.g., cryptocurrency) between users. In a decentralized blockchain, the state of smart contracts is collaboratively maintained by a peer-to-peer network of mutually untrusted nodes, which collect from users a set of transactions (representing the required actions on contracts), and execute them in some order. Once this sequence of transactions is appended to the blockchain, the other nodes validate it, re-executing the transactions in the same order. The serial execution of transactions does not take advantage of the multi-core architecture of modern processors, so contributing to limit the throughput. In this paper we propose a true concurrent model of smart contract execution. Based on this, we show how static analysis of smart contracts can be exploited to parallelize the execution of transactions.
Blockchain technologies and smart contracts were considered for their potential to provide tremendous benefits as decision support tools to the next generation of warfighters. An investigative team focused on novel security-enhanced information gathering and decision support Artificial-Intelligence (AI) based software agents that will serve as decision support co-pilots when commanders are developing real-time multi-domain orders of battle. As a core construct for this architecture, smart contracts allow for the governance of these systems to be time-bound and/or condition-bound. This disruptive technology propels progress made with distributed multi-agent systems with the numerous security benefits of blockchain technologies. Methods for implementing intelligent computing agents that follow and execute the logic embedded in a contract model will provide a transparent record of agents, chain of trust and chain of custody on the blockchain. This paper will explore mechanisms for maintaining a hierarchy of smart contracts allowing reasoning and decision support over different aspects of the overall command structure. Finally, the potential for maintaining multiple levels of classification across communication channels for platforms tasked with collection and reconnaissance missions will explored.
The recent adoption of blockchain technologies and open permissionless networks suggest the importance of peer-to-peer atomic cross-chain transaction protocols. Users should be able to atomically exchange tokens and assets without depending on centralized intermediaries such as exchanges. Recent peer-to-peer atomic cross-chain swap protocols use hashlocks and timelocks to ensure that participants comply to the protocol. However, an expired timelock could lead to a violation of the all-or-nothing atomicity property. An honest participant who fails to execute a smart contract on time due to a crash failure, denial of service attacks or even network delays might end up losing assets. Although a crashed participant is the only participant who ends up worse off, current proposals are unsuitable for atomic cross-chain transactions in asynchronous environments where crash failures and network delays are the norm. In this paper, we present AC 3 WN, the first decentralized all-or-nothing atomic cross-chain commitment protocol. The redeem and refund events of the smart contracts that exchange assets are modeled as conflicting events. An open permissionless network of witnesses is used to guarantee that conflicting events could never simultaneously occur and either all smart contracts in an atomic cross-chain transaction are redeemed or all of them are refunded.
JCLedger is a BlockChain-based distributed ledger for JointCloud that can improve the reliability and convenience of cloud resource exchanges by empowering cooperation among multiple clouds. The biggest challenge for the implementation of JCLedger is the approach to consensus. The existing consensus algorithms for the public BlockChain, such as proof of work (PoW) or proof of stake (PoS) does not apply to the JointCloud, because they require a massive computing power with a low throughput or monopoly risk. In this paper, we propose a practical Byzantine-fault-tolerance (PBFT)-based consensus algorithm called proof of previous transactions (PoPT), in which the accountants are selected by a specific hash function from a certain number of candidates. The candidates are chosen according to the users' participation in JointCloud, and only candidates that join the PBFT-based consensus process instead of all users. We also propose a new BlockChain structure for parallel accounting to improve the scalability of JCLedger, and a consistent hashing algorithm is used to assign the transactions to different accountants. Simulation experiments show that the PoPT can shield the unequal computing power of the users to provide them equal accounting opportunities, and the parallel accounting can handle the massive and high-frequency transactions in JointCloud more efficiently.
Recentemente tem havido um interesse crescente na tecnologia de ledger distribuídos e aplicações de blockchain. Algoritmos tradicionais como PBFT e novos algoritmos como Proof of Work (PoW), Proof of Stake (PoS) e algoritmos híbridos foram desenvolvidos para lidar com a abertura desses sistemas. No entanto, estas Soluções não apresentam boa escalabilidade com o alto número de servidores ou dependem de uma criptomoeda subjacente. Estruturas hierárquicas como Steward ou Fireplug, apresentam melhor escalabilidade com um possível número de réplicas crescente, porém não lidam com o modelo competitivo esperado no ambiente blockchain. Neste artigo é proposta uma arquitetura hierárquica para lidar com o modelo competitivo do ambiente blockchain que também escala (horizontalmente) com o número de réplicas.
Renlord Yang, Toby Murray, Paul Rimba, Udaya Parampalli
Ethereum's Gas mechanism attempts to set transaction fees in accordance with the computational cost of transaction execution: a cost borne by default by every node on the network to ensure correct smart contract execution. Gas encourages users to author transactions that are efficient to execute and in so doing encourages node diversity, allowing modestly resourced nodes to join and contribute to the security of the network. However, the effectiveness of this scheme relies on Gas costs being correctly aligned with observed computational costs in reality. In this work, we performed the first large scale empirical study to understand to what degree this alignment exists in practice, by collecting and analyzing Tera-bytes worth of nanosecond-precision transaction execution traces. Besides confirming potential denial-of-service vectors, our results also shed light on the role of I/O in transaction costs which remains poorly captured by the current Gas cost model. Finally, our results suggest that under the current Gas cost model, nodes with modest computational resources are disadvantaged compared to their better resourced peers, which we identify as an ongoing threat to node diversity and network decentralization.
Permissioned blockchains have evolved as an alternative to permissionless blockchains for various closed business environments. In this paper, we develop FRChain, a scalable and high-performant consensus protocol for permissioned blockchains, which is resilient to different types of node and network failures. FRChain uses collective signing over multicast trees for block propagation and block validation. The protocol ensures safety and liveness as long as a majority of the nodes can participate in the protocol correctly. Further, we also demonstrate a technique for replacing failed nodes with correct ones. We have implemented and tested FRChain spread across a 5000 node blockchain network over two different data centers - (a) 35 Softlayer Cloud VMs located across Melbourne, Milan and San Jose, (b) Amazon VPC with 30 Amazon EC2 instances spread across Mumbai, Singapore, Tokyo and Frankfurt. Our experiments show that FRChain is scalable in terms of both transaction throughput and network size.
In massive, dynamic and distributed P2P networks like Bitcoin, where thousands of updates occur per second, it is hard to obtain an accurate topology representing the structure of the network as a graph with nodes and links by using the traditional local measurement approaches based on batches, offline data, or on the discovery of the topology around a small set of nodes and then combine them to discover an approximate network topology. All of which present some limitation when applying them on blockchain-based networks. In this paper, we propose a topology discovery system, which performs a real-time data collection and analysis for Bitcoin P2P links with the use of a customized version of the Page-Rank algorithm that assembles incoming nodes information for deeper graph analysis processing. The topology discovery system allows us to gain knowledge on the Bitcoin network size, the network stability in term of well-connected Bitcoin nodes, as well as some data regarding the Bitcoin nodes geolocation.
Applications in the area of IoT and smart cities rely heavily on data to manage and control their operational environments. In such applications, machine learning and artificial intelligence algorithms help the government officials, city administrators, and industries to make an informed decision on managing their cities and factories using the data collected from various sources. As we step into the era where ”data is termed as new oil”, there is a need for protocols with support for selling and buying data without giving up the data ownership to third-parties. In this demo, we present Streaming Data Payment Protocol (SDPP), which is an application layer protocol for selling and buying data. SDPP uses blockchain and distributed ledger technology for micropayments and immutable storage of transaction records. In addition, our protocol has a built-in mechanism to set data granularity since the bulk transfer of data between a seller and a buyer may lead to a loss for the seller if the buyer terminates the connection after receiving the data without making a payment. In this demo, we present SDPP and explain how it can contribute to the emerging data economy using a proof-of-concept implementation that uses TCP protocol for data communication and IOTA as both cryptocurrency and a distributed ledger.
Matthias Grundmann, Marc Leinweber, Hannes Hartenstein
We explore challenges of and present a concept for a decentralized payment service which is based on trusted execution environments. The system guarantees that users can always cash out their funds without depending on the cooperation of other network members, hence minimizing the trust required in other network members. We present an overview of the system, motivate key components for a secure architecture and provide a communication protocol. We prove that the payment service users can cash out their funds at any time without any dependence on other network members.
Luigi Vigneri, Wolfgang Welz, Alon Gal, Vassil S. Dimitrov
Throughput is a key property for any distributed ledger technology. However, limited resources, such as bandwidth or node computational power, can lead to network congestion when nodes try to issue more transactions than the network can handle. Consequently, priority criteria are necessary to determine whether a transaction should be accepted or not. In this paper, we present a novel adaptive rate control algorithm for the Tangle, a new-generation distributed ledger allowing large throughput. Our approach combines various concepts, such as resource tests and Proof-of-Work with dynamic difficulty. Our algorithm not only serves as an anti-spam mechanism, but also achieves fair representation. This is to be contrasted with pure Proof-of-Work blockchains, which lead to wasteful mining races.
Carles Araguz, Marc Closa, Elisenda Bou‐Balust, Eduard Alarcón
The design of autonomous operational schemes for distributed, decentralized systems is expected to bring multiple qualities to systems of this kind. One of their instances are Earth-observing swarms of nano-satellites, in which their collective function targets global performance figures. The design of autonomous operations can be modelled as a collective scheduling problem subject to resource constraints. There are many system-wide qualities of interest, such as resiliency, adaptability, responsiveness, among others, that need specific frameworks to characterize the proposed solutions. This paper presents one such design-oriented tool that can evaluate these autonomous organization schemes-potentially for large-scale and highly heterogeneous scenarios with dynamic contexts and multiple time-scales-and illustrates its usage in the evaluation of an autonomous nano-satellite swarm that collectively optimizes revisit times.
This paper investigates the specification and verification of atomic swap multi-party transactions. It is argued that logics with the ability to express properties of strategies of players in a multi-agent setting are conceptually useful for this purpose, although ultimately, the less expressive setting of temporal logic suffices for verification of concrete implementations. This is illustrated through the use of a model checker to verify atomic swap smart contracts in on-chain and cross-chain settings.
As a decentralized distributed ledger technology,the main function of blockchain is to reach a consensus among untrusted nodes.In the blockchain,a suitable consensus mechanism can improve the blockchain performance and guarantee transaction data security.This paper proposes a new solution strategy for the “nothing at stake” problem in the Proof of Stakes(PoS).This strategy allows voting nodes to send agreement disagreement votes.If the node votes for a fork and the fork wins,the node will gain the profit.Otherwise,if the node votes against a fork and the fork fails,the node will also gain the profit.A smart contract is deployed on the Ethereum platform to validate the voting strategy.Results show that the proposed strategy can run normally and the nodes finally reach consensus.
In this paper, we address the performance analysis of Direct Acyclic Graph (DAG)-based cryptocurrency on the basis of its native structure. Several attempts on existing blockchain-based cryptocurrencies to resolve the limitation of the transaction processing rate has resulted in numerous form of solutions, such as side-chain, off-chain or data sharding. While those efforts are dedicated to overcome the limitation that the one-dimensional data structure has, a two-dimensional form of distributed ledger as known as DAG-based cryptocurrency has been emerged. Comparing with blockchain-based cryptocurrencies, DAG-based cryptocurrencies feature relatively faster issuance and confirmation of the transactions due to the individual processing method of the transactions. However, existing DAG-based cryptocurrencies also suffer from the instability of the performance, since the confirmation or validation delay can be varied by network condition such as transaction incoming rate. We derive the generic performance model of DAG-based cryptocurrency while varying the parameters. From the derived models, we propose some novel strategies to improve the performance of the DAG-based cryptocurrency system which encourages the participants of the cryptocurrency (both traders and nodes) to boost the transaction processing speed while keeping the ledger healthy. We show the effectiveness of our proposal by numerical statistics obtained by simulation, which results in maximum 46 percent of increase in our case.