Jiangshan Yu, David Kozhaya, Jérémie Decouchant, Paulo Esteves-Veríssimo
Existing proof-of-work cryptocurrencies cannot tolerate attackers controlling more than 50 percent of the network's computing power at any time, but assume that such a condition happening is “unlikely”. However, recent attack sophistication, e.g., where attackers can rent mining capacity to obtain a majority of computing power temporarily, render this assumption unrealistic. This paper proposes RepuCoin, the first system to provide guarantees even when more than 50 percent of the system's computing power is temporarily dominated by an attacker. RepuCoin physically limits the rate of voting power growth of the entire system. In particular, RepuCoin defines a miner's power by its `reputation', as a function of its work integrated over the time of the entire blockchain, rather than through instantaneous computing power, which can be obtained relatively quickly and/or temporarily. As an example, after a single year of operation, RepuCoin can tolerate attacks compromising 51 percent of the network's computing resources, even if such power stays maliciously seized for almost a whole year. Moreover, RepuCoin provides better resilience to known attacks, compared to existing proof-of-work systems, while achieving a high throughput of 10000 transactions per second (TPS).
Kristián Košťál, Pavol Helebrandt, Matej Belluš, Michal Ries · 5 authors
Nowadays, we are surrounded by a large number of IoT (Internet of Things) devices and sensors. These devices are designed to make life easier and more comfortable. Blockchain technology, especially its mass application, is becoming a term number one. Adoption of blockchain into enterprise networks still has a few challenges that need to be tackled. Utilizing blockchain can bring increased security and efficiency of network maintenance. The key feature of the blockchain, immutability, brings resistance to unauthorized modifications. The whole history of device configuration changes is stored in the blockchain, hence recovery after incidents is very straightforward. This paper extends our previous studies. We are introducing an improved architecture for management and monitoring of IoT devices using a private blockchain. The majority of the system is built on a chaincode, which handles CRUD (Create, Read, Update, Delete) operations as well as encryption and access control. Device configuration files are stored in the blockchain. When a modification occurs, the device downloads a new configuration in a simple manner. The chaincode receives notification whether setup was successful and this history is available for administrators. Our results show that such a system is possible and dissemination of configuration changes to IoT devices can be secured by the blockchain. The key novelty of our solution is a distributed management of configuration files of IoT devices in enterprise networks utilizing blockchain technology. This is essentially improving security and storage options for configurations in the blockchain.
A decentralized application (dapp for short) refers to an application that is executed by multiple users over a decentralized network. In recent years, the number of dapp keeps fast growing, mainly due to the popularity of blockchain technology. Despite the increasing importance of dapps as a typical application type that is assumed to promote the adoption of blockchain, little is known on what, how, and how well dapps are used in practice. In addition, the insightful knowledge of whether and how a traditional application can be transformed to a dapp is yet missing. To bridge the knowledge gap, this paper presents a comprehensive empirical study on an extensive dataset of 734 dapps that are collected from three popular open dapp marketplaces, i.e., ethereum, state of the dapp, and DAppRadar. We analyze the popularity of dapps, and summarize the patterns of how smart contracts are organized in a dapp. Based on the findings, we draw some implications to help dapp developers and users better understand and deploy dapps.
PAI Coin's Proof-of-Work (PoW) consensus mechanism utilizes the double SHA-256 hashing protocol-- the same mechanism used by Bitcoin Core. This compatibility with classic Bitcoin-style mining provides low barrier to entry for PAI Coin mining, consequently rendering the PAI Coin network vulnerable to so-called 51% attacks, among others. To mitigate such risks, this paper proposes a hybrid Proof-of-Work, Proof-of-Stake (PoS) consensus mechanism and provides a detailed technical analysis of how such a mechanism would counter some of the PAI Coin network's inherent vulnerabilities, if successfully implemented. A detailed technical outline of blockchain-based PoW & PoS consensus, including their advantages and disadvantages, when used both independently and in the context of the hybrid model, is provided. An economic analysis of attacking a hybrid-powered PAI Coin network is presented, and a final recommendation for future development of PAI Coin consensus is made.
PAI Coin's Proof-of-Work (PoW) consensus mechanism utilizes the double SHA-256 hashing protocol-- the same mechanism used by Bitcoin Core. This compatibility with classic Bitcoin-style mining provides low barrier to entry for PAI Coin mining, consequently rendering the PAI Coin network vulnerable to so-called 51% attacks, among others. To mitigate such risks, this paper proposes a hybrid Proof-of-Work, Proof-of-Stake (PoS) consensus mechanism and provides a detailed technical analysis of how such a mechanism would counter some of the PAI Coin network's inherent vulnerabilities, if successfully implemented. A detailed technical outline of blockchain-based PoW & PoS consensus, including their advantages and disadvantages, when used both independently and in the context of the hybrid model, is provided. An economic analysis of attacking a hybrid-powered PAI Coin network is presented, and a final recommendation for future development of PAI Coin consensus is made.
In Bitcoin, to independently verify whether new transactions are correct or not, a type of a node called "Full Node" has to hold the whole of historical transactions. The transactions are stored in ledger called "Blockchain. " Blockchain is an append-only data structure. Thus, to operate Full Nodes, the required storage capacity would grow too large for resource-constrained devices. Due to the limitation, the existing lightweight node scheme is that a node relies on other Full Nodes. In this thesis, to reduce storage capacity with keeping the independence of each node, we propose a storage load balancing scheme "KARAKASA" using Distributed Hash Table (DHT). In KARAKASA, nodes distributedly keep the whole blockchain among DHT networked nodes. We evaluated KARAKASA from the view of storage capacity and independence. As a result, a node in a cluster does not need to trust other nodes. We concluded that nodes in a DHT cluster can behave like Full Nodes without holding the whole blockchain.
The blockchain is the underlying technology of the Bitcoin cryptocurrency, and it has created much excitement in the technology and research communities. A blockchain is a distributed ledger collectively maintained by a peer‐to‐peer network of participants who in Bitcoin are known as miners. This key innovation enables cryptocurrencies such as Bitcoin to operate in a decentralized manner with no intermediaries such as financial institutions. But the blockchain can be used to record things other than cryptocurrency transactions. While many of the concepts of Bitcoin build on what have been around since the 1980s and 1990s, the designer(s) of it have made important assumptions that make it work along with the use of an incentive protocol, leading to a major breakthrough from traditional academic thinking. In this paper, we present the state‐of‐the‐art of blockchain and cryptocurrencies along with research challenges and opportunities that would be of interest to researchers getting into this exciting field.
Following the recent increase in smart factories and smart cities and the fourth industrial revolution, the number of IoT devices has been increasing and accordingly, the security of IoT devices has also become an important issue. However, due to reasons such as the low performance of IoT devices, the currently existing security solutions can be hardly applied and even if safe firmware is supplied, security problems may arise due to attacks such as man-in-the-middle attacks and roll-back attacks. To resolve such problems, we propose a new firmware management architecture using blockchains and IPFS (The InterPlanetary File System). Using IPFS can ensure the integrity of the firmware. However, IoT device version management and IPFS URL integrity cannot be guaranteed. Therefore, IoT devices are enabled to be provided with firmware information and updated through blockchian networks to ensure the integrity of the IPFS URL, and an IoT devices management function is provided. The proposed system enables safe firmware distribution and update, and IoT devices' security level is expected to be higher. Through the proposed system, safe firmware distribution and update will become possible and IoT device security levels are expected to be enhanced.
Md. Ashraf Uddin, Andrew Stranieri, Iqbal Gondal, Venki Balasubramanian
Blockchains have been widely used in Internet of Things(IoT) applications including smart cities, smart home and smart governance to provide high levels of security and privacy. In this article, we advance a Blockchain based decentralized architecture for the storage of IoT data produced from smart home/cities. The architecture includes a secure communication protocol using a sign-encryption technique between power constrained IoT devices and a Gateway. The sign encryption also preserves privacy. We propose that a Software Agent executing on the Gateway selects a Miner node using performance parameters of Miners. Simulations demonstrate that the recommended Miner selection outperforms Proof of Works selection used in Bitcoin and Random Miner Selection.
The Internet of Things (IoT) promises technical solutions to many important societal problems relating to the environment, healthcare, transportation, etc. One approach to making IoT solutions more cost-effective is the idea of horizontal integration, where sensors and actuators are shared between different applications. In such environments, economic transactions between system components are used to pay for data and services. Blockchain-based overlay networks have been developed to provide such financial mechanism for IoT devices with sufficient processing power and operating system support. However, no practical solutions for low-end devices exist. In addition, existing solutions also require setting up multiple blockchain accounts for a single administrative domain, which incurs high fees when consolidating those accounts. In this paper, we propose a Ticket-Based Verification Protocol, which defines two separate logical entities, contract manager and transaction verifier. Our design limits the need for high-performance embedded systems to only one unit per administrative domain and reduces the processing and networking overhead other IoT devices in that domain.
With the widespread of Bitcoin, blockchain has been focused by researchers from many fields, such as digital cryptocurrencies, finance security exchange, decentralized trade platform and so on. However, the operation efficiency (about 10min/per block) has limited its practical application except of Bitcoin. In this paper, we conduct further research based on the existing hybrid blockchain architectures, say N + X Hybrid Blockchain, which may significantly improve blockchain efficiency with the negligible cost of security. Moreover, we gave an evaluation model for the feedback process of nodes in the N+X Hybrid Blockchain and obtained optimal strategies. For the application of Energy Internet (EI), we proposed a scheduling mechanism based on the above evaluation model, and given an algorithm to implement it.
Yustus Eko Oktian, Elizabeth Nathania Witanto, Sandra Kumi, Sang-Gon Lee
The payment of a subscription-based model for the cloud service is regularly operated with the association of the bank as a centralized trustful third party. This system taxes the parties involved by requiring them to pay high transaction costs to the bank. In this paper, we propose a protocol to enable Fixed Subscription and Pay As You Go Subscription payments in the cloud service without the use of the third party. We achieve this goal by decentralizing the payment with blockchain. In return, this decentralized system generates low transaction costs. We implement our idea in the form of two smart contracts in Ethereum network. We also evaluate the security properties of our protocol. Based on the performance analysis, we can argue that all of the operations in the smart contract produces reasonable gas costs and the contracts are usable in the real network.
Manisa Pipattanasomporn, Saifur Rahman, Murat Kuzlu
Over the past decade, high penetration of rooftop solar photovoltaics (PV) has been observed in many countries. The availability of rooftop solar PV at customer premises has transformed a house into an energy prosumer that can both consume and export electricity. With proper regulations in place, homeowners can become a market participant who can buy and sell excess solar electricity in a peer-to-peer (P2P) trading environment. With the emerging blockchain technology, it will be possible to securely keep track of such solar electricity exchange without a third party oversight. The objective of this paper is to discuss the conceptual architecture of the blockchain-based platform for exchange of solar electricity in a neighborhood. Several open-source blockchain platforms are reviewed, including Hyperledger, Ethereum and Corda. Experiments developed on one of the well-known open-source blockchain platforms are discussed that describe how a P2P exchange of solar electricity can be set up in a laboratory environment.
Recently, blockchain techniques have been widely used in finance, e-commerce and sharing economy, owing to its decentralization, openness and permission-less properties. In cybersecurity, a blockchain-based framework Sapiens Chain is proposed, which aims to provide decentralized and trustable cybersecurity services while protecting the privacy of the anonymous users. However, how to select an optimal service provider in Sapiens Chain remains challenging. In this paper, we tackle the novel problem of scheduling nodes in Sapiens Chain, which covers and rewards the nodes based on their performance with the history of providing cybersecurity services, and thus attracting more and more users to anticipate cybersecurity services. Under the scheduling algorithm, we propose to select nodes for different tasks by unifying the interest of each user, such as the bandwidth, the computing resource, and the activation degree. The experimental results demonstrate the efficiency and effectiveness of our method.
Blockchains were designed to solve the problem of double-spending in cryptocurrencies, and the success of the Bitcoin design has generated vastly more interest than previous proposals for digital currencies. Blockchains are being used in other areas as well, but the design choices that made blockchains effective for cryptocurrencies often do not fit well with other applications. In this paper we review the properties of distributed ledger technology (DLT) for use in typical data management applications and show how two recently developed distributed ledger ideas can be used to retain valuable aspects of blockchain while simplifying design and adding new but often necessary capabilities to permissioned distributed ledger applications. In particular, we are interested in the ability to delete or modify blocks, and the ability to provide a timestamping mechanism to provide a highly accurate time for applications that are time order dependent.
Alberto Sonnino, Shehar Bano, Mustafa Al-Bassam, George Danezis
We present a family of replay attacks against sharded distributed ledgers, that target cross-shard consensus protocols, such as the recently proposed Chainspace and Omniledger. They allow an attacker, with network access only, to double-spend or lock resources with minimal efforts. The attacker can act independently without colluding with any nodes, and succeed even if all nodes are honest; most of the attacks can also exhibit themselves as faults under periods of asynchrony. These attacks are effective against both shard-led and client-led cross-shard consensus approaches. Finally, we present Byzcuit - a new cross-shard consensus protocol that is immune to those attacks. We implement a prototype of Byzcuit and evaluate it on a real cloud-based testbed, showing that our defenses impact performance minimally, and overall performance surpasses previous works.
Alberto Sonnino, Shehar Bano, Mustafa Al-Bassam, George Danezis
We present a family of replay attacks against sharded distributed ledgers,\nthat target cross-shard consensus protocols, such as the recently proposed\nChainspace and Omniledger. They allow an attacker, with network access only, to\ndouble-spend or lock resources with minimal efforts. The attacker can act\nindependently without colluding with any nodes, and succeed even if all nodes\nare honest; most of the attacks can also exhibit themselves as faults under\nperiods of asynchrony. These attacks are effective against both shard-led and\nclient-led cross-shard consensus approaches. Finally, we present Byzcuit - a\nnew cross-shard consensus protocol that is immune to those attacks. We\nimplement a prototype of Byzcuit and evaluate it on a real cloud-based testbed,\nshowing that our defenses impact performance minimally, and overall performance\nsurpasses previous works.\n
Blockchain, which is a technology for distributedly managing ledger information over multiple nodes without a centralized system, has elicited increasing attention. Performing experiments on actual blockchains is difficult because a large number of nodes in wide areas are necessary. In this study, we developed a blockchain network simulator SimBlock for such experiments. Unlike the existing simulators, SimBlock can easily change behavior of nodes, so that it enables to investigate the influence of nodes' behavior on blockchains. We compared some simulation results with the measured values in actual blockchains to demonstrate the validity of this simulator. Furthermore, to show practical usage, we conducted two experiments which clarify the influence of neighbor node selection algorithms and relay networks on the block propagation time. The simulator could depict the effects of the two techniques on block propagation time. The simulator will be publicly available in a few months.
In today's blockchain system, designing a secure and high throughput blockchain on par with a centralized payment system is a difficult task. Sharding is one of the most worthwhile emerging technologies for improving the system throughput while maintain high-security level. However, previous sharding-related designs have two main limitations. First, the security and throughput of their random-based sharding system are not high enough as they did not leverage the heterogeneity among validators. Second, to design an incentive mechanism that promotes cooperation could incur a huge overhead on their system. In this article, we propose RepChain, a reputation-based secure and fast blockchain system via sharding, which also provides high incentive to stimulate node cooperation. RepChain utilizes reputation to explicitly characterize the heterogeneity among the validators and lay the foundation for the incentive mechanism. We propose a new double-chain architecture-a transaction chain and a reputation chain. For the transaction chain, an efficient Raft-based synchronous consensus has been presented. For the reputation chain, the synchronous Byzantine fault tolerance consensus that combines collective signing has been utilized to prevent the attack on both reputation score and the related transaction blocks. It supports a high throughput transaction chain with moderate generation speed. Moreover, we propose a reputation-based sharding and leader selection scheme. To analyze the security of RepChain, we propose a recursive formula to calculate the epoch security within only $\mathcal {O}(km^{2})$ time. Furthermore, we implement and evaluate RepChain on the Amazon Web Service platform. The results show our solution can enhance both throughout and security level of the existing sharding-based blockchain system.
Swapnoneel Roy, Faustina J. Anto Morais, Mehrdad Salimitari, Mainak Chatterjee
Protecting and securing data that reside at various hosts in the Internet has become more important than ever before because of the growing number of cyber attacks. Though there have been several studies related to denial of service and cache attacks, those studies are primarily based on simulations and investigations of attacks on real networks are still lacking.
Delay tolerant network (DTN) is successfully proposed for setting up emergency post disaster communication networks when normal communication infrastructure is incapacitated. Performance of such networks get affected by selfish nodes that do not participate in message forwarding. Thus, nodes must receive satisfactory rewards for cooperation. The available incentive schemes either rely on central trusted authorities or do not use an explicit and secure digital currency. Blockchain, a decentralized digital ledger of immutable transactions, is an attractive approach for addressing the incentive challenges in peer-to-peer networks that lack central trusted authorities. Bitcoin, the Blockchain based cryptocurrency, make it possible to devise practical credit based incentive schemes for such networks. In this paper, we propose a Blockchain based incentive scheme for DTN based post disaster communication network that uses Bitcoin to incentivize nodes for cooperation. The scheme uses a novel reward strategy to bring rationality in the incentivizing process.
<p style='text-indent:20px;'>In Bitcoin system, a transaction is given a priority value according to its attributes such as the remittance amount and fee, and transactions with high priorities are likely to be confirmed faster than those with low priorities. In this paper, we analyze the transaction-confirmation time for Bitcoin system. We model the transaction-confirmation process as a queueing system with batch service, M/<inline-formula><tex-math id="M1">\begin{document}$ \mbox{G}^B $\end{document}</tex-math></inline-formula>/1. We consider the joint distribution of numbers of transactions in system and the elapsed service time, deriving the mean transaction-confirmation time. Using the result, we derive the recursive formulae of mean transaction-confirmation times of an M/<inline-formula><tex-math id="M2">\begin{document}$ \mbox{G}^B $\end{document}</tex-math></inline-formula>/1 queue with priority service discipline. In numerical examples, we show the effect of the maximum block size on the mean transaction-confirmation time, investigating the accuracy region of our queueing model. We also discuss how the increase in micropayments, which are likely to be given low priorities, affects the transaction-confirmation time.