Study of consensus protocols and improvement of the Federated Byzantine Agreement (FBA) algorithm

At a present time, it has been proven that blockchain technology has influenced to a great extent the way of human interaction in a digital world. The operation of the blockchain systems allows the peers to implement digital transactions in a Peer to Peer (P2P) network in a direct way without the need of third parties. Each blockchain determines different rules for the record of the transactions in the ledger. The transactions are inserted in blocks and each one, in turn, is appended to the chain (ledger) based on different consensus algorithms. Once blocks have been inserted in the chain, the consensus has been reached and the blocks with corresponding transactions are considered immutable. This thesis analyses the main features of the blockchain and how the consensus can be achieved through the different kinds of consensus algorithms. In addition, a detailed reference for Stellar and Federated Byzantine Agreement (FBA) consensus protocols is made in order to explain these algorithms, their limitations as well as their improvement. The development of a reputation mechanism is necessary to the improvement of above algorithms

Performance Analysis of Reputation based Proof of Credibility Consensus Mechanism for Blockchain based Applications

Blockchain is a decentralized transaction and data management technology first developed for the Bitcoin cryptocurrency. Blockchain technology is gaining popularity due to its core attributes which provides security, anonymity and data integrity without any involvement of third party. Consensus mechanism is a procedure by which all peers in the blockchain network agrees to a common agreement on the current state of the distributed ledger. It plays vital role in increasing efficiency of any blockchain environment. Though we have many consensus mechanisms working currently in different areas but they still lack in parameters like status of validators, latency, node failure etc. In Our proposed algorithm Proof of credibility, we have tried to incorporate all above factors in it. We have also implemented two or more factors of proposed algorithm and have evaluated and compared with existing consensus algorithm. In future research we aim to implement RPoC in any blockchain network and then we will evaluate it in terms of different evaluation parameters such as performance, security, scalability

BLOXY: Providing Transparent and Generic BFT-Based Ordering Services for Blockchains

With the wide-spread use of blockchain technology, Byzantine fault-tolerant (BFT) protocols are explored as a means to achieve consensus on which transactions should be processed next. BFT protocols are not a one-size-fits-all solution: they should be chosen according to the blockchain's use case, which can range from supply chain management to decentralised storage, requiring specialisation e.g. regarding throughput, latency, or level of decentralisation. Previously, consensus protocols were usually hardcoded into the blockchain infrastructure and could not be exchanged, therefore inhibiting flexible use of an otherwise generic blockchain infrastructure. Hyperledger Fabric claims to provide modular consensus and support for crash-fault and Byzantine fault tolerant protocols. However, integrating a BFT protocol has shown that Fabric's architecture is currently not well-suited for this fault model as it requires substantial changes and thereby breaks Fabric's modularity. This also has to be repeated for each integrated BFT protocol. In this paper, we present Bloxy, a blockchain-aware trusted proxy running on the replica that encapsulates all BFT client functionality. Bloxy enables transparent access to generic BFT frameworks and preserves Fabric's modularity even for the Byzantine fault model. It runs inside a trusted execution environment based on Intel's Software Guard Extensions. Bloxy offers blockchain-specific communication mechanisms as well as short-term block storage to handle crashes or disconnects to ensure that all nodes receive block updates. We implemented two Bloxy-based ordering services based on PBFT and the hybrid BFT protocol Hybster. Our evaluation shows that our approach increases throughput by up to 71% compared to directly integrated BFT protocols

STUDY OF CONSENSUS PROTOCOLS AND IMPROVEMENT OF THE DELEGATED BYZANTINE FAULT TOLERANCE (DBFT) ALGORITHM

Nowadays, blockchain is one of the most popular and innovate technologies over the world. Although this technology appears for first time in the Bitcoin cryptocurrency, in recent years, a lot of researchers and industries from different fields such as banking, financial, supply chain management, etc. have given more involved than ever before. The blockchain is implemented in decentralized and distributed ledgers in peer-to-peer (p2p) networks where non-trusting peers can implement digital asset transactions without the need of central authority. Then, other peers in the network, according specific rules determined by the network, validate these transactions, insert them in the block and append the block in the chain (ledger). The key contribution for the proper operation of the blockchain is the consensus protocols. Through these protocols, all the peers in the network or the majority of them, they have to reach an agreement for a specific block in order to insert it in the chain based on different blockchains rules. In this master thesis, we will analyze in depth the general architecture of the blockchain and various consensus protocols that implemented in different blockchains in order to be able to improve the Delegated Byzantine Fault Tolerance (DBFT) consensus algorithm, which is used in the NEO blockchain technology. Finally, a development of a reputation mechanism is needed based on the improvement of the DBFT algorithm in order to measure the reputation of the peers for a specific day

A P2P Networking Simulation Framework For Blockchain Studies

Recently, blockchain becomes a disruptive technology of building distributed applications (DApps). Many researchers and institutions have devoted their resources to the development of more effective blockchain technologies and innovative applications. However, with the limitation of computing power and financial resources, it is hard for researchers to deploy and test their blockchain innovations in a large-scape physical network. Hence, in this dissertation, we proposed a peer-to-peer (P2P) networking simulation framework, which allows to deploy and test (simulate) a large-scale blockchain system with thousands of nodes in one single computer. We systematically reviewed existing research and techniques of blockchain simulator and evaluated their advantages and disadvantages. To achieve generality and flexibility, our simulation framework lays the foundation for simulating blockchain network with different scales and protocols. We verified our simulation framework by deploying the most famous three blockchain systems (Bitcoin, Ethereum and IOTA) in our simulation framework. We demonstrated the effectiveness of our simulation framework with the following three case studies: (a) Improve the performance of blockchain by changing key parameters or deploying new directed acyclic graph (DAG) structure protocol; (b) Test and analyze the attack response of Tangle-based blockchain (IOTA) (c) Establish and deploy a new smart grid bidding system for demand side in our simulation framework. This dissertation also points out a series of open issues for future research

Deconstructing Blockchains: A Comprehensive Survey on Consensus, Membership and Structure

It is no exaggeration to say that since the introduction of Bitcoin, blockchains have become a disruptive technology that has shaken the world. However, the rising popularity of the paradigm has led to a flurry of proposals addressing variations and/or trying to solve problems stemming from the initial specification. This added considerable complexity to the current blockchain ecosystems, amplified by the absence of detail in many accompanying blockchain whitepapers. Through this paper, we set out to explain blockchains in a simple way, taming that complexity through the deconstruction of the blockchain into three simple, critical components common to all known systems: membership selection, consensus mechanism and structure. We propose an evaluation framework with insight into system models, desired properties and analysis criteria, using the decoupled components as criteria. We use this framework to provide clear and intuitive overviews of the design principles behind the analyzed systems and the properties achieved. We hope our effort will help clarifying the current state of blockchain proposals and provide directions to the analysis of future proposals

Tenderbake - A Solution to Dynamic Repeated Consensus for Blockchains

First-generation blockchains provide probabilistic finality: a block can be revoked, albeit the probability decreases as the block "sinks" deeper into the chain. Recent proposals revisited committee-based BFT consensus to provide deterministic finality: as soon as a block is validated, it is never revoked. A distinguishing characteristic of these second-generation blockchains over classical BFT protocols is that committees change over time as the participation and the blockchain state evolve. In this paper, we push forward in this direction by proposing a formalization of the Dynamic Repeated Consensus problem and by providing generic procedures to solve it in the context of blockchains. Our approach is modular in that one can plug in different synchronizers and single-shot consensus. To offer a complete solution, we provide a concrete instantiation, called {{Tenderbake}}, and present a blockchain synchronizer and a single-shot consensus algorithm, working in a Byzantine and partially synchronous system model with eventually synchronous clocks. In contrast to recent proposals, our methodology is driven by the need to bound the message buffers. This is essential in preventing spamming and run-time memory errors. Moreover, {{Tenderbake}} processes can synchronize with each other without exchanging messages, leveraging instead the information stored in the blockchain

Blockchains basées sur du Consensus Répété

International audienceLes blockchains basées sur le consensus sont considérées aujourd'hui comme étant parmi les alternatives les plus viables aux blockchains utilisant un mécanisme de Proof-of-work (Bitcoin, Ethereum,. . .), ces dernières étant très énergivores et ne garantissent pas une cohérence forte. Elles ont pour but d'offrir des garanties de cohérence forte (pas de fourches) dans un système ouvert grâce à : (i) un ensemble de validateurs qui produit un bloc via une variante du protocole de consensus Practical Byzantine Fault Tolerant (PBFT), et (ii) un mécanisme de sélection qui choisit dynamiquement les noeuds qui seront validateurs pour le bloc suivant. Dans cet article, nous caractérisons précisément le problème que tentent de résoudre ces protocoles de blockchains. Nous étudions Tendermint. Nos contributions sont les suivantes : nous formalisons pour la première fois le protocole Tendermint, puis nous présentons le modèle et les hypothèses précis sous lesquels il atteint son objectif. Nous prouvons que dans un système ultimement synchrone et avec une hypothèse supplémentaire, une légère modification du protocole résout une variante (i) du consensus pour la production d'un bloc, et une variante (ii) du consensus répété pour construire la chaîne de bloc ; cela si strictement moins d'un tiers des validateurs est atteint de fautes Byzantines. Nous nous sommes ensuite intéressés à l'étude de l'équité du mécanisme de récompense dans ces blockchains. Cette étude préliminaire permet d'établir que garantir (ultimement) l'équité de la récompense requiert une communication (ultimement) synchrone