623 research outputs found
The Curses of Blockchain Decentralization
Decentralization, which has backed the hyper growth of many blockchains,
comes at the cost of scalability. To understand this fundamental limitation,
this paper proposes a quantitative measure of blockchain decentralization, and
discusses its implications to various trust models and consensus algorithms.
Further, we identify the major challenges in blockchain decentralization. Our
key findings are that true decentralization is hard to achieve due to the
skewed mining power and that a fully decentralized blockchain inherently limits
scalability as it incurs a throughput upper bound and prevents scaling smart
contract execution. To address these challenges, we outline three research
directions to explore the trade-offs between decentralization and scalability
A Survey on Blockchain Interoperability: Past, Present, and Future Trends
Blockchain interoperability is emerging as one of the crucial features of
blockchain technology, but the knowledge necessary for achieving it is
fragmented. This fact makes it challenging for academics and the industry to
seamlessly achieve interoperability among blockchains.
Given the novelty and potential of this new domain, we conduct a literature
review on blockchain interoperability, by collecting 262 papers, and 70 grey
literature documents, constituting a corpus of 332 documents. From those 332
documents, we systematically analyzed and discussed 80 documents, including
both peer-reviewed papers and grey literature.
Our review classifies studies in three categories: Cryptocurrency-directed
interoperability approaches, Blockchain Engines, and Blockchain Connectors.
Each category is further divided into sub-categories based on defined criteria.
We discuss not only studies within each category and subcategory but also
across categories, providing a holistic overview of blockchain
interoperability, paving the way for systematic research in this domain. Our
findings show that blockchain interoperability has a much broader spectrum than
cryptocurrencies.
The present survey leverages an interesting approach: we systematically
contacted the authors of grey literature papers and industry solutions to
obtain an updated view of their work. Finally, this paper discusses supporting
technologies, standards, use cases, open challenges, and provides several
future research directions.Comment: For any comments or suggestions, contact rafael.belchior AT
t\'ecnico.ulisboa.p
Evolutionary Game for Consensus Provision in Permissionless Blockchain Networks with Shard
With the development of decentralized consensus protocols, permissionless
blockchains have been envisioned as a promising enabler for the general-purpose
transaction-driven, autonomous systems. However, most of the prevalent
blockchain networks are built upon the consensus protocols under the
crypto-puzzle framework known as proof-of-work. Such protocols face the
inherent problem of transaction-processing bottleneck, as the networks achieve
the decentralized consensus for transaction confirmation at the cost of very
high latency. In this paper, we study the problem of consensus formation in a
system of multiple throughput-scalable blockchains with sharded consensus.
Specifically, the protocol design of sharded consensus not only enables
parallelizing the process of transaction validation with sub-groups of
processors, but also introduces the Byzantine consensus protocols for
accelerating the consensus processes. By allowing different blockchains to
impose different levels of processing fees and to have different
transaction-generating rate, we aim to simulate the multi-service provision
eco-systems based on blockchains in real world. We focus on the dynamics of
blockchain-selection in the condition of a large population of consensus
processors. Hence, we model the evolution of blockchain selection by the
individual processors as an evolutionary game. Both the theoretical and the
numerical analysis are provided regarding the evolutionary equilibria and the
stability of the processors' strategies in a general case
Read-Uncommitted Transactions for Smart Contract Performance
Smart contract transactions demonstrate issues of performance and correctness
that application programmers must work around. Although the blockchain
consensus mechanism approaches ACID compliance, use cases that rely on frequent
state changes are impractical due to the block publishing interval of
seconds. The effective isolation level is Read-Committed, only revealing state
transitions at the end of the block interval. Values read may be stale and not
match program order, causing many transactions to fail when a block is
committed. This paper perceives the blockchain as a transactional data
structure, using this analogy in the development of a new algorithm,
Hash-Mark-Set (HMS), that improves transaction throughput by providing a
Read-Uncommitted view of state variables. HMS creates a directed acyclic graph
(DAG) from the pending transaction pool. The transaction order derived from the
DAG is used to provide a Read-Uncommitted view of the data for new
transactions, which enter the DAG as they are received. An implementation of
HMS is provided, interoperable with Ethereum and ready for use in smart
contracts. Over a wide range of transaction mixes, HMS is demonstrated to
improve throughput. A side product of the implementation is a new technique,
Runtime Argument Augmentation (RAA), that allows smart contracts to communicate
with external data services before submitting a transaction. RAA has use cases
beyond HMS and can serve as a lightweight replacement for blockchain oracles.Comment: Accepted to ICDCS 2019, Dallas, Texas.
https://theory.utdallas.edu/ICDCS2019/program.html#Session%202F 10 pages, 3
figure
VAPOR: a Value-Centric Blockchain that is Scale-out, Decentralized, and Flexible by Design
Blockchains is a special type of distributed systems that operates in unsafe
networks. In most blockchains, all nodes should reach consensus on all state
transitions with Byzantine fault tolerant algorithms, which creates bottlenecks
in performance. In this paper, we propose a new type of blockchains, namely
Value-Centric Blockchains (VCBs), in which the states are specified as values
(or more comprehensively, coins) with owners and the state transition records
are then specified as proofs of the ownerships of individual values. We then
formalize the "rational" assumptions that have been used in most blockchains.
We further propose a VCB, VAPOR, that guarantees secure value transfers if all
nodes are rational and keep the proofs of the values they owned, which is
merely parts of the whole state transition record. As a result, we show that
VAPOR enjoys significant benefits in throughput, decentralization, and
flexibility without compromising security.Comment: To be appeared in Financial Crypto 201
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
A Survey of State-of-the-Art on Blockchains: Theories, Modelings, and Tools
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
Towards Distributed Clouds
This review focuses on the evolution of cloud computing and distributed
ledger technologies (blockchains) over the last decade. Cloud computing relies
mainly on a conceptually centralized service provisioning model, while
blockchain technologies originate from a peer-to-peer and a completely
distributed approach. Still, noteworthy commonalities between both approaches
are often overlooked by researchers. Therefore, to the best of the authors
knowledge, this paper reviews both domains in parallel for the first time. We
conclude that both approaches have advantages and disadvantages. The advantages
of centralized service provisioning approaches are often the disadvantages of
distributed ledger approaches and vice versa. It is obviously an interesting
question whether both approaches could be combined in a way that the advantages
can be added while the disadvantages could be avoided. We derive a software
stack that could build the foundation unifying the best of these two worlds and
that would avoid existing shortcomings like vendor lock-in, some security
problems, and inherent platform dependencies
Untangling Blockchain: A Data Processing View of Blockchain Systems
Blockchain technologies are gaining massive momentum in the last few years.
Blockchains are distributed ledgers that enable parties who do not fully trust
each other to maintain a set of global states. The parties agree on the
existence, values and histories of the states. As the technology landscape is
expanding rapidly, it is both important and challenging to have a firm grasp of
what the core technologies have to offer, especially with respect to their data
processing capabilities. In this paper, we first survey the state of the art,
focusing on private blockchains (in which parties are authenticated). We
analyze both in-production and research systems in four dimensions: distributed
ledger, cryptography, consensus protocol and smart contract. We then present
BLOCKBENCH, a benchmarking framework for understanding performance of private
blockchains against data processing workloads. We conduct a comprehensive
evaluation of three major blockchain systems based on BLOCKBENCH, namely
Ethereum, Parity and Hyperledger Fabric. The results demonstrate several
trade-offs in the design space, as well as big performance gaps between
blockchain and database systems. Drawing from design principles of database
systems, we discuss several research directions for bringing blockchain
performance closer to the realm of databases.Comment: arXiv admin note: text overlap with arXiv:1703.0405
PolyShard: Coded Sharding Achieves Linearly Scaling Efficiency and Security Simultaneously
Today's blockchain designs suffer from a trilemma claiming that no blockchain
system can simultaneously achieve decentralization, security, and performance
scalability. For current blockchain systems, as more nodes join the network,
the efficiency of the system (computation, communication, and storage) stays
constant at best. A leading idea for enabling blockchains to scale efficiency
is the notion of sharding: different subsets of nodes handle different portions
of the blockchain, thereby reducing the load for each individual node. However,
existing sharding proposals achieve efficiency scaling by compromising on trust
- corrupting the nodes in a given shard will lead to the permanent loss of the
corresponding portion of data. In this paper, we settle the trilemma by
demonstrating a new protocol for coded storage and computation in blockchains.
In particular, we propose PolyShard: ``polynomially coded sharding'' scheme
that achieves information-theoretic upper bounds on the efficiency of the
storage, system throughput, as well as on trust, thus enabling a truly scalable
system. We provide simulation results that numerically demonstrate the
performance improvement over state of the arts, and the scalability of the
PolyShard system. Finally, we discuss potential enhancements, and highlight
practical considerations in building such a system
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