Sanaz Taheri-Boshrooyeh, Ali Utkan Şahin, Yahya Hassanzadeh-Nazarabadi, Öznur Özkasap
Skip Graphs belong to the family of Distributed Hash Table (DHT) structures that are utilized as routing overlays in various peer-to-peer applications including blockchains, cloud storage, and social networks. In a Skip Graph overlay, any misbehavior of peers during the routing of a query compromises the system functionality. Guard is the first authenticated search mechanism for Skip Graphs, enables reliable search operation in a fully decentralized manner. In this demo paper, we present a proof-of-concept implementation of Guard on Skip Graph nodes as well as a deployment demo scenario.
LightChain is the first Distributed Hash Table (DHT)-based blockchain with a logarithmic asymptotic message and memory complexity. In this demo paper, we present the software architecture of our open-source implementation of LightChain, as well as a novel deployment scenario of the entire LightChain system on a single machine aiming at results reproducibility.
Yahya Hassanzadeh-Nazarabadi, Ali Utkan Şahin, Öznur Özkasap, Alptekin Küpçü
SkipSim is an offline Skip Graph simulator that enables Skip Graph-based algorithms including blockchains and P2P cloud storage to be simulated while preserving their scalability and decentralized nature. To the best of our knowledge, it is the first Skip Graph simulator that provides several features for experimentation on Skip Graph-based overlay networks. In this demo paper, we present SkipSim features, its architecture, as well as a sample blockchain demo scenario.
Permissioned Blockchains are increasingly considered in enterprise use-cases, many of which do not require geo-distribution, or even disallow it due to legislation. Examples include country-wide networks, such as Alastria, or those deployed using cloud-based platforms such as IBM Blockchain Platform. We expect these blockchains to eventually run in environments with high bandwidth and low latency modern networks, as well as, advanced programmable hardware accelerators in servers. Even though there is renewed interest in BFT consensus algorithms with various proposals targeting Permissioned Blockchains, related work does not optimize for fast networks and does not incorporate hardware accelerators -- we make the case that doing so will pay off in the long run. To this end, we re-implemented the seminal PBFT algorithm in a way that allows us to measure different configurations of the protocol. Through this we explore the benefits of various common optimization strategies and show that the protocol is unlikely to saturate more than 10Gbps networks without relying on specialized hardware-based offloading. We discuss two concrete ways in which the cost of consensus in Permissioned Blockchains could be reduced in high speed networking environments, namely, offloading to SmartNICs and implementing the protocol on standalone FPGAs.
In the general setting, consensus cannot be solved if an adversary controls a third of the system. Yet, blockchain participants typically reach consensus "eventually" despite an adversary controlling a minority of the system. Exceeding this $\frac{1}{3}$ cap is made possible by tolerating transient disagreements, where distinct participants select distinct blocks for the same index, before eventually agreeing to select the same block. Until now, no blockchain could tolerate an attacker controlling a majority of the system. In this paper, we present Zero-Loss Blockchain (ZLB), the first blockchain that tolerates an adversary controlling more than half of the system. ZLB is an open blockchain that combines recent theoretical advances in accountable Byzantine agreement to exclude undeniably deceitful replicas. progressively reduces the portion of deceitful replicas below $\frac{1}{3}$, and reaches consensus. Geo-distributed experiments show that ZLB outperforms HotStuff and is almost as fast as the scalable Red Belly Blockchain that cannot tolerate $n/3$ faults.
Chuka Oham, Regio Michelin, Salil S. Kanhere, Raja Jurdak · 5 authors
The ubiquity of connecting technologies in smart vehicles and the incremental automation of its functionalities promise significant benefits, including a significant decline in congestion and road fatalities. However, increasing automation and connectedness broadens the attack surface and heightens the likelihood of a malicious entity successfully executing an attack. In this paper, we propose a Blockchain based Framework for sEcuring smaRt vehicLes (B-FERL). B-FERL uses permissioned blockchain technology to tailor information access to restricted entities in the connected vehicle ecosystem. It also uses a challenge-response data exchange between the vehicles and roadside units to monitor the internal state of the vehicle to identify cases of in-vehicle network compromise. In order to enable authentic and valid communication in the vehicular network, only vehicles with a verifiable record in the blockchain can exchange messages. Through qualitative arguments, we show that B-FERL is resilient to identified attacks. Also, quantitative evaluations in an emulated scenario show that B-FERL ensures a suitable response time and required storage size compatible with realistic scenarios. Finally, we demonstrate how B-FERL achieves various important functions relevant to the automotive ecosystem such as trust management, vehicular forensics and secure vehicular networks.
Rob van Glabbeek, Vincent Gramoli, Pierre Tholoniat
We consider the problem of cross-chain payment whereby customers of different escrows---implemented by a bank or a blockchain smart contract---successfully transfer digital assets without trusting each other. Prior to this work, cross-chain payment problems did not require this success, or any form of progress. We demonstrate that it is possible to solve this problem when assuming synchrony, in the sense that each message is guaranteed to arrive within a known amount of time, but impossible to solve without assuming synchrony. Yet, we solve a weaker variant of this problem, where success is conditional on the patience of the participants, without assuming synchrony, and in the presence of Byzantine failures. We also discuss the relation with the recently defined cross-chain deals.
This paper presents LinSBFT, a Byzantine Fault Tolerance (BFT) protocol with the capacity of processing over 2000 smart contract transactions per second in production. LinSBFT applies to a permissionless, public blockchain system, in which there is no public-key infrastructure, based on the classic PBFT with 4 improvements: (\romannumeral1) LinSBFT achieves $O(n)$ worst-case communication volume, in contract to PBFT's $O(n^4)$; (\romannumeral2) LinSBFT rotates the leader of protocol randomly to reduce the risk of denial-of-service attacks on leader; and (\romannumeral3) each run of LinSBFT finalizes one block, which is robust against participants that are honest in one run of the protocol, and dishonest in another, and the set of participants is dynamic, which is update periodically. (\romannumeral4) LinSBFT helps the delayed nodes to catch up via a synchronization mechanism to promise the liveness. Further, in the ordinary case, LinSBFT involves only a single round of voting instead of two in PBFT, which reduces both communication overhead and confirmation time, and employs the \emph{proof-of-stake} scheme to reward all participants. Extensive experiments using data obtained from the Ethereum demonstrate that LinSBFT consistently and significantly outperforms existing in-production BFT protocols for blockchains.
One of the biggest challenges associated with connected and autonomous vehicles (CAVs) is to maintain and make use of vehicles health records (VHR). VHR can facilitate different entities to offer various services in a proactive, transparent, secure, reliable and in an efficient manner. The state-of-the-art solutions for maintaining the VHR are centralized in nature, mainly owned by manufacturer and authorized in-vehicle device developers. Owners, drivers, and other key service providers have limited accessibility and control to the VHR. We need to change the strategy from single or limited party access to multi-party access to VHR in an secured manner so that all stakeholders of intelligent transportation system (ITS) can be benefited from this. Any unauthorized attempt to alter the data should also be prevented. Blockchain is one such potential candidate, which can facilitate the sharing of such data among different participating organizations and individuals. For example, owners, manufacturers, trusted third parties, road authorities, insurance companies, charging stations, and car selling ventures can access VHR stored on the blockchain in a permissioned, secured, and with a higher level of confidence. In this paper, a blockchain-based decentralized secure system for V-CARE is proposed to manage records in an interoperable framework that leads to improved ITS services in terms of safety, availability, reliability, efficiency, and maintenance. Insurance based on pay-how-you-drive (PHYD), and sale and purchase of used vehicles can also be made more transparent and reliable without compromising the confidentiality and security of sensitive data.
Charles Tim Batista Garrocho, Célio Marcio Soares Ferreira, Carlos Frederico Marcelo da Cunha Cavalcanti, Ricardo Augusto Rabelo Oliveira
Industrial Internet of Things is a new milestone that will require new industry paradigms and investments. In this context, cyber-physical systems are considered the bridge to the fourth revolution. Centralized approaches and observance of real-time constraints are two important challenges that must be overcome for the advancement of Industry 4.0. To solve these problems, a blockchain-based vertical integration architecture of the process automation systems is proposed in which it performs the control and monitoring of industrial processes. Proof of concept experiments reveal the feasibility and performance of the proposal.
Jovan Nikolić, Nursultan Jubatyrov, Evangelos Pournaras
Large-scale decentralized systems of autonomous agents interacting via asynchronous communication often experience the following self-healing dilemma: fault detection inherits network uncertainties making a remote faulty process indistinguishable from a slow process. In the case of a slow process without fault, fault correction is undesirable as it can trigger new faults that could be prevented with fault tolerance that is a more proactive system maintenance. But in the case of an actual faulty process, fault tolerance alone without eventually correcting persistent faults can make systems underperforming. Measuring, understanding and resolving such self-healing dilemmas is a timely challenge and critical requirement given the rise of distributed ledgers, edge computing, the Internet of Things in several energy, transport and health applications. This paper contributes a novel and general-purpose modeling of fault scenarios during system runtime. They are used to accurately measure and predict inconsistencies generated by the undesirable outcomes of fault correction and fault tolerance as the means to improve self-healing of large-scale decentralized systems at the design phase. A rigorous experimental methodology is designed that evaluates 696 experimental settings of different fault scales, fault profiles and fault detection thresholds in a prototyped decentralized network of 3000 nodes. Almost 9 million measurements of inconsistencies were collected in a network, where each node monitors the health status of another node, while both can defect. The prediction performance of the modeled fault scenarios is validated in a challenging application scenario of decentralized and dynamic in-network data aggregation using real-world data from a Smart Grid pilot project. Findings confirm the origin of inconsistencies at design phase and provide new insights how to tune self-healing at an early stage. Strikingly, the aggregation accuracy is well predicted as shown by high correlations and low root mean square errors.
Academic publication of latest research results are crucial to advance the development of all disciplines. However, the current academic publication procedure lacks transparency in the review process, and reviewers do not have strong incentives to provide quality reviews for their peers. This may lead to misconducts in the review process, e.g. an anonymous reviewer may give biased comments to a paper without being noticed since the comments are seldom published for evaluation. In addition, it is ironic that the research community has to pay a lot to access papers reviewed by the community for free, though free sharing of research results is important for research advances.To address the above problems, we propose Open-Pub, a decentralized, transparent yet privacy-preserving academic publication scheme based on the blockchain technology. The blockchain promises transparency in the review process and provides an incentive mechanism based on cryptocurrency, but the privacy requirement in the double-blind review process still needs to be fulfilled. To this end, we first design a threshold identity-based group signature (TIBGS) using verifiable secret sharing to protect identity confidentiality. Then we develop a strong double-blind procedure to protect the identities of authors and reviewers. With this strong double-blind procedure, authors can choose to submit papers anonymously, and validators distribute papers anonymously to reviewers on the blockchain according to their research interests. This process is publicly recorded and traceable on the blockchain so as to realize transparent peer preview. To evaluate its efficiency, we implement Open-Pub based on Ethereum and conduct comprehensive experiments to evaluate its performance, including computation costs and processing delay. The experiment results show that Open-Pub is highly efficient in computation and processing anonymous transactions.
To draw a roadmap of current research activities of the blockchain community, we first conduct a brief overview of state-of-the-art blockchain surveys published in the recent 5 years. We found that those surveys are basically studying the blockchain-based applications, such as blockchain-assisted Internet of Things (IoT), business applications, security-enabled solutions, and many other applications in diverse fields. However, we think that a comprehensive survey towards the essentials of blockchains by exploiting the state-of-the-art theoretical modelings, analytic models, and useful experiment tools is still missing. To fill this gap, we perform a thorough survey by identifying and classifying the most recent high-quality research outputs that are closely related to the theoretical findings and essential mechanisms of blockchain systems and networks. Several promising open issues are also summarized finally for future research directions. We wish this survey can serve as a useful guideline for researchers, engineers, and educators about the cutting-edge development of blockchains in the perspectives of theories, modelings, and tools.
Classic Byzantine fault-tolerant consensus protocols forfeit liveness in the face of asynchrony in order to preserve safety, whereas most deployed blockchain protocols forfeit safety in order to remain live. In this work, we achieve the best of both worlds by proposing a novel abstractions called the finality gadget. A finality gadget allows for transactions to always optimistically commit but informs the clients that these transactions might be unsafe. As a result, a blockchain can execute transactions optimistically and only commit them after they have been sufficiently and provably audited. In this work, we formally model the finality gadget abstraction, prove that it is impossible to solve it deterministically in full asynchrony (even though it is stronger than consensus) and provide a partially synchronous protocol which is currently securing a major blockchain. This way we show that the protocol designer can decouple safety and liveness in order to speed up recovery from failures. We believe that there can be other types of finality gadgets that provide weaker safety (e.g., probabilistic) in order to gain more efficiency and this can depend on the probability that the network is not in synchrony.
In this paper, we provide a new theoretical framework of pyramid Markov processes to solve some open and fundamental problems of blockchain selfish mining under a rigorous mathematical setting. We first describe a more general model of blockchain selfish mining with both a two-block leading competitive criterion and a new economic incentive mechanism. Then we establish a pyramid Markov process and show that it is irreducible and positive recurrent, and its stationary probability vector is matrix-geometric with an explicitly representable rate matrix. Also, we use the stationary probability vector to study the influence of many orphan blocks on the waste of computing resource. Next, we set up a pyramid Markov reward process to investigate the long-run average profits of the honest and dishonest mining pools, respectively. As a by-product, we build three approximative Markov processes and provide some new interesting interpretation on the Markov chain and the revenue analysis reported in the seminal work by Eyal and Sirer (2014). Note that the pyramid Markov (reward) processes can open up a new avenue in the study of blockchain selfish mining. Thus we hope that the methodology and results developed in this paper shed light on the blockchain selfish mining such that a series of promising research can be developed potentially.
Many blockchain systems today, including Bitcoin, rely on Proof of Work (PoW). Proof of work is crucial to the liveness and security of cryptocurrencies. The assumption when using PoW is that a lot of trial and error is required on average before a valid block is generated. One of the main concerns raised with regard to this kind of system is the inherent need to "waste" energy on "meaningless" problems. In fact, the Bitcoin system is believed to consume more electricity than several small countries. In this work we formally define three properties that are necessary for wasteless PoW systems: (1) solve "meaningful" problems (2) solve them efficiently and (3) be secure against double-spend attacks. These properties aim to create an open market for problem-solving, in which miners produce solutions to problems in the most efficient way (wasteless). The security of the system stems from the economical incentive created by the demand for solutions to these problems. We analyze these properties, and deduce constraints that must apply to such PoW systems. In our main result, we conclude that under realistic assumptions, the set of allowed problems must be preimage resistant functions in order to keep the system secure and efficient.
Jorge Peña Queralta, Li Qingqing, Zhuo Zou, Tomi Westerlund
This conceptual paper discusses how different aspects involving the autonomous operation of robots and vehicles will change when they have access to next-generation mobile networks. 5G and beyond connectivity is bringing together a myriad of technologies and industries under its umbrella. High-bandwidth, low-latency edge computing services through network slicing have the potential to support novel application scenarios in different domains including robotics, autonomous vehicles, and the Internet of Things. In particular, multi-tenant applications at the edge of the network will boost the development of autonomous robots and vehicles offering computational resources and intelligence through reliable offloading services. The integration of more distributed network architectures with distributed robotic systems can increase the degree of intelligence and level of autonomy of connected units. We argue that the last piece to put together a services framework with third-party integration will be next-generation low-latency blockchain networks. Blockchains will enable a transparent and secure way of providing services and managing resources at the Multi-Access Edge Computing (MEC) layer. We overview the state-of-the-art in MEC slicing, distributed robotic systems and blockchain technology to define a framework for services the MEC layer that will enhance the autonomous operations of connected robots and vehicles.
Mohammad M. Jalalzai, Chen Feng, Costas Busch, Golden G. Richard · 5 authors
The performance of partially synchronous BFT-based consensus protocols is highly dependent on the primary node. All participant nodes in the network are blocked until they receive a proposal from the primary node to begin the consensus process.Therefore, an honest but slack node (with limited bandwidth) can adversely affect the performance when selected as primary. Hermes decreases protocol dependency on the primary node and minimizes transmission delay induced by the slack primary while keeping low message complexity and latency. Hermes achieves these performance improvements by relaxing strong BFT agreement (safety) guarantees only for a specific type of Byzantine faults (also called equivocated faults). Interestingly, we show that in Hermes equivocating by a Byzantine primary is unlikely, expensive and ineffective. Therefore, the safety of Hermes is comparable to the general BFT consensus. We deployed and tested Hermes on 190 Amazon EC2 instances. In these tests, Hermes's performance was comparable to the state-of-the-art BFT protocol for blockchains (when the network size is large) in the absence of slack nodes. Whereas, in the presence of slack nodes Hermes out performed the state-of-the-art BFT protocol by more than 4x in terms of throughput as well as 15x in terms of latency.
In Bitcoin and Ethereum, nodes require large storage capacity to maintain all the blockchain data, such as transactions, UTXOs, and account states. As of May 2020, the storage size of the Bitcoin blockchain has expanded to 270 GB, and it will continue to increase. This storage requirement is a major hurdle to becoming a block proposer or validator. Although many studies have attempted to reduce the storage size, in the proposed methods, a node cannot keep all blocks or cannot generate a block. We propose an architecture called Trail that allows nodes to hold all blocks in a small storage and to generate and validate blocks and transactions. Trail does not depend on a consensus algorithm or fork choice rule. In this architecture, a client who issues transactions has the data to prove its own balances and can generate a transaction containing the proof of balances. The nodes in Trail do not store transactions, UTXOs and account balances: they keep only blocks. The blocksize is approximately 8 KB, which is 100 times smaller than that of Bitcoin. Further, the block size is constant regardless of the number of accounts and the number of transactions. Compared to traditional blockchains, clients who issue transactions must store additional data. However, we show that proper data archiving can keep the account device storage size small. Trail allows more users to be block proposers and validators and improves the decentralization of the blockchain.
This paper presents an architecture, based on Distributed Ledger Technologies (DLTs) and Decentralized File Storage (DFS) systems, to support the use of Personal Information Management Systems (PIMS). DLT and DFS are used to manage data sensed by mobile users equipped with devices with sensing capability. DLTs guarantee the immutability, traceability and verifiability of references to personal data, that are stored in DFS. In fact, the inclusion of data digests in the DLT makes it possible to obtain an unalterable reference and a tamper-proof log, while remaining compliant with the regulations on personal data, i.e. GDPR. We provide an experimental evaluation on the feasibility of the use of DFS. Three different scenarios have been studied: i) a proprietary IPFS approach with a dedicated node interfacing with the data producers, ii) a public IPFS service and iii) Sia Skynet. Results show that through proper configuration of the system infrastructure, it is viable to build a decentralized Personal Data Storage (PDS).
In recent years, there is an emerging trend that some computing services are moving from cloud to the edge of the networks. Compared to cloud computing, edge computing can provide services with faster response, lower expense, and more security. The massive idle computing resources closing to the edge also enhance the deployment of edge services. Instead of using cloud services from some primary providers, edge computing provides people with a great chance to actively join the market of computing resources. However, edge computing also has some critical impediments that we have to overcome. In this paper, we design an edge computing service platform that can receive and distribute the computing resources from the end-users in a decentralized way. Without centralized trade control, we propose a novel hierarchical smart contract-based decentralized technique to establish the trading trust among users and provide flexible smart contract interfaces to satisfy users. Our system also considers and resolves a variety of security and privacy challenges when utilizing the encryption and distributed access control mechanism. We implement our system and conduct extensive experiments to show the feasibility and effectiveness of our proposed system.
The interblockchain communication protocol (IBC) is an end-to-end, connection-oriented, stateful protocol for reliable, ordered, and authenticated communication between modules on separate distributed ledgers. IBC is designed for interoperation between heterogenous ledgers arranged in an unknown, dynamic topology, operating with varied consensus algorithms and state machines. The protocol realises this by specifying the sufficient set of data structures, abstractions, and semantics of a communication protocol which once implemented by participating ledgers will allow them to safely communicate. IBC is payload-agnostic and provides a cross-ledger asynchronous communication primitive which can be used as a constituent building block by a wide variety of applications.
Ali Alzubaidi, Karan Mitra, Pankesh Patel, Ellis Solaiman
Within cloud-based internet of things (IoT) applications, typically cloud providers employ Service Level Agreements (SLAs) to ensure the quality of their provisioned services. Similar to any other contractual method, an SLA is not immune to breaches. Ideally, an SLA stipulates consequences (e.g. penalties) imposed on cloud providers when they fail to conform to SLA terms. The current practice assumes trust in service providers to acknowledge SLA breach incidents and executing associated consequences. Recently, the Blockchain paradigm has introduced compelling capabilities that may enable us to address SLA enforcement more elegantly. This paper proposes and implements a blockchain-based approach for assessing SLA compliance and enforcing consequences. It employs a diagnostic accuracy method for validating the dependability of the proposed solution. The paper also benchmarks Hyperledger Fabric to investigate its feasibility as an underlying blockchain infrastructure concerning latency and transaction success/fail rates.
The utilisation of blockchain has moved beyond digital currency to other fields such as health, the Internet of Things, and education. In this paper, we present a systematic mapping study to collect and analyse relevant research on blockchain technology related to the higher education field. The paper concentrates on two main themes. First, it examines state of the art in blockchain-based applications that have been developed for educational purposes. Second, it summarises the challenges and research gaps that need to be addressed in future studies.