7,511 research outputs found
A Survey of Distributed Consensus Protocols for Blockchain Networks
Since the inception of Bitcoin, cryptocurrencies and the underlying
blockchain technology have attracted an increasing interest from both academia
and industry. Among various core components, consensus protocol is the defining
technology behind the security and performance of blockchain. From incremental
modifications of Nakamoto consensus protocol to innovative alternative
consensus mechanisms, many consensus protocols have been proposed to improve
the performance of the blockchain network itself or to accommodate other
specific application needs.
In this survey, we present a comprehensive review and analysis on the
state-of-the-art blockchain consensus protocols. To facilitate the discussion
of our analysis, we first introduce the key definitions and relevant results in
the classic theory of fault tolerance which help to lay the foundation for
further discussion. We identify five core components of a blockchain consensus
protocol, namely, block proposal, block validation, information propagation,
block finalization, and incentive mechanism. A wide spectrum of blockchain
consensus protocols are then carefully reviewed accompanied by algorithmic
abstractions and vulnerability analyses. The surveyed consensus protocols are
analyzed using the five-component framework and compared with respect to
different performance metrics. These analyses and comparisons provide us new
insights in the fundamental differences of various proposals in terms of their
suitable application scenarios, key assumptions, expected fault tolerance,
scalability, drawbacks and trade-offs. We believe this survey will provide
blockchain developers and researchers a comprehensive view on the
state-of-the-art consensus protocols and facilitate the process of designing
future protocols.Comment: Accepted by the IEEE Communications Surveys and Tutorials for
publicatio
Blockchain Consensus Protocols in the Wild
A blockchain is a distributed ledger for recording transactions, maintained
by many nodes without central authority through a distributed cryptographic
protocol. All nodes validate the information to be appended to the blockchain,
and a consensus protocol ensures that the nodes agree on a unique order in
which entries are appended. Consensus protocols for tolerating Byzantine faults
have received renewed attention because they also address blockchain systems.
This work discusses the process of assessing and gaining confidence in the
resilience of a consensus protocols exposed to faults and adversarial nodes. We
advocate to follow the established practice in cryptography and computer
security, relying on public reviews, detailed models, and formal proofs; the
designers of several practical systems appear to be unaware of this. Moreover,
we review the consensus protocols in some prominent permissioned blockchain
platforms with respect to their fault models and resilience against attacks.
The protocol comparison covers Hyperledger Fabric, Tendermint, Symbiont,
R3~Corda, Iroha, Kadena, Chain, Quorum, MultiChain, Sawtooth Lake, Ripple,
Stellar, and IOTA
Correctness Analysis of IBFT
In this paper we analyse the correctness of Istanbul BFT (IBFT), which is a
Byzantine-fault-tolerant (BFT) proof-of-authority (PoA) blockchain consensus
protocol that ensures immediate finality. We show that the IBFT protocol does
not guarantee Byzantine-fault-tolerant consistency and liveness when operating
in an eventually synchronous network, and we propose modifications to the
protocol to ensure both Byzantine-fault-tolerant consistency and liveness in
eventually synchronous settings
Smart contracts that are smart and can function as legal contracts - A Review of Semantic Blockchain and Distributed Ledger Technologies
Blockchain and Distributed ledger Technologies are increasingly becoming key
enablers for vital innovation in financial services, manufacturing, government
and other industries. One of the biggest challenges though is the level of
support for semantics by most of the Block Chain and Distributed Ledger
technologies. This paper reviews and categorises common block chain and DLT
approaches and introduces a new approach to Blockchain / DLT promising to
resolve the semantic problems inherent in other Blockchain / DLT approache
The Blockchain Anomaly
Most popular blockchain solutions, like Bitcoin, rely on proof-of-work,
guaranteeing that the output of the consensus is agreed upon with high
probability. However, this probability depends on the delivery of messages and
that the computational power of the system is sufficiently scattered among
pools of nodes in the network so that no pool can mine more blocks faster than
the crowd. New approaches, like Ethereum, generalise the proof-of-work approach
by letting individuals deploy their own private blockchain with high
transaction throughput. As companies are starting to deploy private chains, it
has become crucial to better understand the guarantees blockchains offer in
such a small and controlled environment.
In this paper, we present the \emph{Blockchain Anomaly}, an execution that we
experienced when building our private chain at NICTA/Data61. Even though this
anomaly has never been acknowledged before, it may translate into dramatic
consequences for the user of blockchains. Named after the infamous Paxos
anomaly, this anomaly makes dependent transactions, like "Bob sends money to
Carole after he received money from Alice" impossible. This anomaly relies on
the fact that existing blockchains do not ensure consensus safety
deterministically: there is no way for Bob to make sure that Alice actually
sent him coins without Bob using an external mechanism, like converting these
coins into a fiat currency that allows him to withdraw. We also explore smart
contracts as a potential alternative to transactions in order to freeze coins,
and show implementations of smart contract that can suffer from the Blockchain
anomaly and others that may cope with it
Gosig: Scalable Byzantine Consensus on Adversarial Wide Area Network for Blockchains
Existing Byzantine fault tolerance (BFT) protocols face significant
challenges in the consortium blockchain scenario. On the one hand, we can make
little assumptions about the reliability and security of the underlying
Internet. On the other hand, the applications on consortium blockchains demand
a system as scalable as the Bit-coin but providing much higher performance, as
well as provable safety. We present a new BFT protocol, Gosig, that combines
crypto-based secret leader selection and multi-round voting in the protocol
layer with implementation layer optimizations such as gossip-based message
propagation. In particular, Gosig guarantees safety even in a network fully
controlled by adversaries, while providing provable liveness with
easy-to-achieve network connectivity assumption. On a wide area testbed
consisting of 140 Amazon EC2 servers spanning 14 cities on five continents, we
show that Gosig can achieve over 4,000 transactions per second with less than 1
minute transaction confirmation time
RepChain: A Reputation-based Secure, Fast and High Incentive Blockchain System via Sharding
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: Firstly, the throughput of
their random-based sharding system is not high enough as they did not leverage
the heterogeneity among validators. Secondly, to design an incentive mechanism
to promote cooperation could incur a huge overhead on their system. In this
paper, 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 which includes
transaction chain and reputation chain. For transaction chain, a Raft-based
synchronous consensus that can achieve high throughput has been presented. For
reputation chain, the synchronous Byzantine fault tolerance that combines
collective signing has been utilized to achieve a consensus 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 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
A New Hybrid Consensus Protocol: Deterministic Proof Of Work
The Decentralized-Consistent-Scale (DCS) Triangle defines three dimensions
that illustrate the tradeoffs of the blockchain consensus mechanism. In this
paper, we propose a new hybrid consensus protocol, called Deterministic Proof
of Work (DPoW), which can reach high levels of scalability and consistency
without significant reduction to decentralization. Our protocol introduces a
Map-reduce PoW mining algorithm to perform alongside Practical Byzantine Fault
Tolerance (PBFT) verification, which together allow for transactions to be
confirmed immediately, largely improving scalability. In addition, the protocol
is designed such that forking cannot occur, ensuring strong consistency and
security against a multitude of attacks. The Map-reduce PoW mining process
ensures that no single entity can control the network, guaranteeing
decentralization. We analyzed the security of our protocol by evaluating the
possibility of double spending attacks, and furthermore, conducted experiments
which demonstrate our claims.Comment: 6 figure
A Survey on Consensus Protocols in Blockchain for IoT Networks
The success of blockchain as the underlying technology for cryptocurrencies
has opened up possibilities for its use in other application domains as well.
The main advantages of blockchain for its potential use in other domains are
its inherent security mechanisms and immunity to different attacks. A
blockchain relies on a consensus method for agreeing on any new data. Most of
the consensus methods which are currently used for the blockchain of different
cryptocurrencies require high computational power and thus are not apt for
resource-constrained systems.
In this article, we discuss and survey the various blockchain based consensus
methods that are applicable to resource constrained IoT devices and networks. A
typical IoT network consists of several devices which have limited
computational and communications capabilities. Most often, these devices cannot
perform intensive computations and are starved for bandwidth. Therefore, we
discuss the possible measures that can be taken to reduce the computational
power and convergence time for the underlying consensus methods. We also talk
about some of the alternatives to the public blockchain like private blockchain
and tangle, along with their potential adoption for IoT networks. Furthermore,
we review the existing consensus methods that have been implemented and explore
the possibility of utilizing them to realize a blockchain based IoT network.
Some of the open research challenges are also put forward.Comment: This paper is submitted to IEEE Internet of Things Journal. It is
under revie
SoK: Tools for Game Theoretic Models of Security for Cryptocurrencies
Cryptocurrencies have garnered much attention in recent years, both from the
academic community and industry. One interesting aspect of cryptocurrencies is
their explicit consideration of incentives at the protocol level. Understanding
how to incorporate this into the models used to design cryptocurrencies has
motivated a large body of work, yet many open problems still exist and current
systems rarely deal with incentive related problems well. This issue arises due
to the gap between Cryptography and Distributed Systems security, which deals
with traditional security problems that ignore the explicit consideration of
incentives, and Game Theory, which deals best with situations involving
incentives. With this work, we aim to offer a systematization of the work that
relates to this problem, considering papers that blend Game Theory with
Cryptography or Distributed systems and discussing how they can be related.
This gives an overview of the available tools, and we look at their (potential)
use in practice, in the context of existing blockchain based systems that have
been proposed or implemented
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