Received September 27, 2020, accepted October 8, 2020, date of publication October 12, 2020, date of current version

October 23, 2020.

Digital Object Identifier 10.1109/ACCESS.2020.3030491

Focus on Blockchain: A Comprehensive

Survey on Academic and Application
YIJUN ZOU1 , TING MENG 2,3 , PENG ZHANG2,3 , WENZHEN ZHANG2,3 , AND HUIYANG LI4
1 E-Commerce Laboratory, School of Economics and Management, Beijing University of Posts and Telecommunications, Beijing 100876, China
2 School of Software Engineering, Beijing University of Posts and Telecommunications, Beijing 100876, China
3 Key Laboratory of Trustworthy Distributed Computing and Service, Ministry of Education, Beijing University of Posts and Telecommunications, Beijing

100876, China
4 Department of Computer Science and Engineering, The University of Texas at Arlington, Arlington, TX 76019, USA

Corresponding author: Ting Meng (mengting@bupt.edu.cn)

This work was supported in part by the National Natural Science Foundation of China under Grant 61170273, and in part by the China
Scholarship Council under Grant [2013]3050.

ABSTRACT As a decentralized distributed ledger, blockchain has developed rapidly since its birth and
has been highly valued by governments, academia, and industry. Start in the financial field, blockchain
technology has been rapidly applied to various fields such as the Internet of Things, supply chain, and
healthcare. Blockchain technology has made sufficient development and innovation, but it also faces many
challenges, such as security, scalability, and waste of resources. This paper starts with the development
history of blockchain and combines the characteristics and technical principles of it to analyze the current
academic research status and application scenarios. Meanwhile, this paper analyzes the existing outstanding
blockchain projects and elaborates on their key advantages and current challenges. With discussing the
ongoing development trend of blockchain, the development direction, and the research trend of blockchain
in the future, this paper provides a useful reference for related research.

INDEX TERMS Blockchain, academic, application, projects, consensus algorithm, smart contract, security,
development trend.

I. INTRODUCTION to mine a block and the higher the chance of obtaining a

Since the concept of blockchain was first proposed in Satoshi reward. Nevertheless, the Proof-of-Work (PoW) mechanism
Nakamoto’s paper [1], it has developed rapidly from a pro- still has problems, such as waste of computing resources
totype concept into a hot technology in the past decade. and low efficiency, so the consensus mechanism of Proof-of-
Technically, blockchain is a combination of blocks linked Stake (PoS) [3] and Delegated Proof-of-Stake (DPoS) [4] has
by hash functions, and its essence is a distributed ledger been proposed successively. Blockchain is based on a peer-
based on asymmetric encryption algorithms. It is an inte- to-peer network, where distributed ledger books are stored
grated and innovative technology which integrates cryptog- on each node to complete peer-to-peer transactions. Based
raphy, distributed system, network security and others. The on consensus protocols and P2P networks, to extend the
emergence of blockchain has changed the past pattern of availability of blockchain, the concept of smart contracts was
transactions that had to rely on trusted third-party institutions. proposed. Generally speaking, smart contract is a contract
The central institution can no longer restrict both parties written in code. If it can meet the conditions, it is auto-
of the transaction, and each transaction is verified by more matically enforced without an intermediary’s need to estab-
than half of the participants in the network [2], making a lish trust. However, once mistakes are in the smart contract,
truly distributed peer-to-peer transaction possible. To ensure the consequences can be disastrous [5]. Smart contracts are
network consistency in the blockchain, Nakamoto proposed widely used to defend against distributed denial of service
a Proof-of-Work (PoW) consensus mechanism, which means (DDoS) attacks, design voting protocols, and build decentral-
that the more work a miner does, the more likely it is ized applications (DAPPS).
With the continuous development of blockchain tech-
The associate editor coordinating the review of this manuscript and nology, the concept of blockchain has expanded from the
approving it for publication was Wei Yu . financial field to other fields, such as healthcare, IoT and
This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 License.
187182 For more information, see https://creativecommons.org/licenses/by-nc-nd/4.0/ VOLUME 8, 2020
Y. Zou et al.: Focus on Blockchain: A Comprehensive Survey on Academic and Application

supply chain, etc. It has been continuously combined with II. BLOCKCHAIN BACKGROUND
other application scenarios, gradually heading in the direction A. BLOCKCHAIN CONCEPTS
of ‘‘blockchain +’’ [6]. Various universities and research Satoshi Nakamoto first proposed the concept of blockchain,
institutions attach great importance to this technology and which is a Proof-of-Work chain based on hash. It is used
publish a large number of academic achievements related for online transactions without any financial institution [1].
to blockchain. At present, there are a large number of lit- In this part, we explain the concept of blockchain based on
erature reviews about blockchain techniques, such as the different subject backgrounds and perspectives and summa-
technical architecture [7]–[8], security and privacy [9]–[11], rize the following directions.
network security [12]. And some discussion on a specific At the technical level, blockchain can be regarded as a
area of blockchain [13]–[15] has been raised. The paper [16] technology built on the basis of a series of encryption algo-
presents a comprehensive introduction to the blockchain’s rithms, storage technologies, and peer-to-peer networks, with
architecture, principles and applications from a more tech- features including ‘‘unalterable’’, ‘‘consensus mechanism’’
nical perspective. Unlike the above papers, our paper starts and ‘‘decentralized’’. At the database level, blockchain can
from the perspective of academics and application. It focuses be thought as a giant ledger for bookkeeping [17], [18].
more on academic data information statistics and industry At the economic level, blockchain can build a reliable trust
applications to show the development status and blockchain foundation for both parties who know nothing about trans-
trend. Therefore, this paper is devoted to the holistic research actions with equal and credible. In summary, blockchain is
of blockchain, as shown in Figure 1. 1) Comprehensively an innovative integration solution of multiple existing tech-
expound the concept and characteristics of blockchain from nologies that integrates cryptography technology, distributed
the background and development history. 2) Analyze the consistency protocol, network security, and other related
academic community’s attention to the blockchain, and sum- technologies [19].
marize the latest research results. 3) Analyze the application
scenarios and actual implementation projects of blockchain in B. BLOCKCHAIN PAST AND PRESENT
various fields. 4) Elaborate on the advantages and challenges As shown in Figure 2, from ‘‘New Directions in Cryptogra-
of blockchain under the current situation. 5) Predict and phy’’ published by Diffie and Hellman in 1976 to Libra pro-
discuss the technology development trend and industry trend posed by Facebook in 2019 [20]–[25], blockchain technology
of blockchain. We hope that the work in this paper can provide is constantly developing and improving.
a useful reference for subsequent studies.

FIGURE 2. The Foundation and Development History of Blockchain.

C. BLOCKCHAIN CHARACTERISTIC AND CLASSIFICATION

There are four of the most important features of blockchain.
• Anonymity:The anonymity of blockchain means that
everyone has a virtual identity on the blockchain. For
example, Bitcoin users anonymously hold public keys
for transactions, and public keys are not unique [1].
• Decentralization: The decentralization of blockchain
means that no central institution is needed, and every
FIGURE 1. The Structure of Blockchain Holistic Research. node is equivalent. It has become the core technology

VOLUME 8, 2020 187183

 Y. Zou et al.: Focus on Blockchain: A Comprehensive Survey on Academic and Application

of digital cryptocurrencies, such as Bitcoin and

Ethereum [26].
• Tamper-resistance:The tamper-resistance of blockchain
means that any transaction information stored in the
blockchain cannot be tampered during and after the
process of block generation [10]. The data structure
of the blockchain is formed by orderly linking blocks
containing transaction information.
• Traceability:The traceability of blockchain means that
transaction sources can be tracked through data storage
structure and chain structure. L. Xiao et al. designed
a blockchain-based traceable IP copyright protection
algorithm [27], X. Li et al. researched critical technolo-
gies of the logistics information traceability model [28].
Blockchain can be classified into the public chain, alliance
chain, and private chain. These three types of blockchains
have some common characteristics: They use a distributed
P2P network for transactions. They all rely on the consen-
sus algorithm to synchronize network transaction data and
require that each transaction need digitally signed before
being added to the chain [30]. The details of the three
blockchains are as follows.
• Public Chain: It refers to the blockchain where anyone
in the world can enter the system at any time to read data,
send verifiable transactions, and complete accounting.
The public chain mainly includes Bitcoin and Ethereum.
• Alliance Chain:It refers to the blockchain with several
institutions participating in the management. Each insti-
tution runs one or more nodes. The data only allows
different institutions in the system to read, write and send
a transaction, and record transaction data together. The
alliance chain is represented by Hyperledger. Besides,
Jingjing Gu et al. built an alliance blockchain framework
to detect malicious code in malware [31].
• Private Chain: It refers to the blockchain whose writing
permission is controlled by an organization or institu-
tion. The qualification of participating nodes will be
strictly restricted, and its writing permission is in the
hands of only one organization. Private chains are gen-
erally used as internal audits in practical applications.
The applications based on private chain technology
are mainly the Linux Foundation and R3CEV Corda
platforms.

D. BLOCKCHAIN INFRASTRUCTURE
The blockchain architecture consists of six different layers,
as shown in Figure 3.
• Data Layer:This layer encapsulates the chain structure
of the underlying data block, and the related digital
signature and time stamp technology, which is the most
underlying data structure in the whole blockchain tech-
nology.
• Network Layer: Including P2P network, communica-
FIGURE 3. The Infrastructure of Blockchain.
tion mechanism, and verification mechanism.

187184 VOLUME 8, 2020

Y. Zou et al.: Focus on Blockchain: A Comprehensive Survey on Academic and Application

• Consensus Layer: It is one of the core technologies of

blockchain and the blockchain community’s governance
mechanism to make highly decentralized nodes reach a
consensus in the decentralized blockchain network.
• Incentive Layer:The incentive layer is the mining
mechanism. You can get as many rewards as you con-
tribute to the blockchain system. With this incentive
mechanism, nodes in the entire network can be encour-
aged to participate in data recording and maintenance on
the blockchain.
• Contract Layer: This layer encapsulates various
scripts, algorithms, and smart contracts, which is based
on the programmable characteristics of the blockchain.
• Application Layer: The ‘‘blockchain +’’ as we know
is at the application layer. This layer encapsulates var-
ious application scenarios and cases of the blockchain.
The transaction’s main content includes the formation
of blocks by miners’ package trading, and the verifi-
FIGURE 4. The Transaction Process of Blockchain.
cation of the blocks excavated by miners’ mining and
broadcasting. To ensure the security and integrity of
the transaction in the system, the construction of the
transaction address also use multiple hash encryption. achievements published has increased dramatically, espe-
cially from 2017 to 2019.
From the survey of IEEE database, there are more and
E. BLOCKCHAIN TRANSACTION PROCESS more discussions on blockchain in recent years. And univer-
In addition, taking bitcoin as an example, blockchain transac- sities and research institutions have invested more scientific
tion has seven steps, as shown in Figure 4. The transaction’s research strength in the field of blockchain, which plays an
main content includes the formation of blocks by miners’ important role in the mature application and further develop-
package trading, and the verification of the blocks excavated ment of blockchain.
by miners’ mining and broadcasting. To ensure the security
and integrity of the transaction in the system, the construc- b: ACM
tion of the transaction address also adopts multiple hash This part investigates the total number of blockchain papers
encryption. in ACM database from since 2008, including the number pub-
lished by different universities and the collection in different
III. ACADEMIC RESEARCH STATISTICS ACM journals and conferences. The research results show in
A. STATISTICAL RESEARCH ON BLOCKCHAIN LITERATURE the Figure 6(a)-(c).
To make better statistics on blockchain’s research status, According to the ACM library, we can conclude that
we searched the four major databases, including IEEE, ACM, the number of blockchain related papers has surged in the
Springer and Elsevier. It can help us make a portrait of the past five years. Different universities competing to publish
blockchain academic research’s current situation, and facil- papers and putting forward different viewpoints, which have
itate us to examine the popularity and future trends of the played an important role in the development of blockchain
blockchain. The following databases selecting results on aca- technology.
demic research achievements of blockchain used advanced
search methods to filter achievements. The number of papers c: SPRINGER
from the four databases used blockchain as the keyword, then This part investigates the total number of blockchain related
the other features, such as conferences and journals, univer- academic achievements published in the Springer database
sities and institutions, used more search items combining the since 2008. The research results show in the Figure 7(a)-(b).
blockchain keyword with the corresponding labels. According to the papers retrieved from the database,
no blockchain related papers were published in 2011 and
1) LITERATURE ANALYSIS OF EACH DATABASE before. Since 2012, the number of publications of related
a: IEEE papers has gradually increased, and it can be seen that the
This part investigates the total number of blockchain- research on blockchain is becoming more and more pop-
related academic achievements published in IEEE database, ular. From only two papers in early 2012 to two thou-
the publication status of universities, the conferences with sand in 2019, more than two thousand related papers have
more publications, since 2008. The research results show been published since 2020, which can be said to be quite
in the Figure 5(a)-(c). Since 2013, the number of blockchain popular.

VOLUME 8, 2020 187185

 Y. Zou et al.: Focus on Blockchain: A Comprehensive Survey on Academic and Application

FIGURE 5. (a). The number of blockchain related achievements in IEEE. (b). The universities of blockchain related papers published in IEEE. (c). The
conferences of blockchain related papers published in IEEE.

187186 VOLUME 8, 2020

Y. Zou et al.: Focus on Blockchain: A Comprehensive Survey on Academic and Application

FIGURE 7. (a). The number of blockchain related papers published in

Springer. (b). The conferences of blockchain related papers published in
Springer.

d: ELSEVIER
The research results show in the Figure 8(a)-(b).
By August 2020, there were 981 records and 10 journals that
had published papers. Academic Research on blockchain has
various types of results, most of which are Research Article,
and the access type is also developing towards open access.
With 2014 as the starting point, attention has been grad-
ually rising, the academic research achievements have been
increasing year by year, and the blockchain has been increas-
ingly influential in the world.

2) OVERALL LITERATURE ANALYSIS

According to the survey of these four major databases,
the number of blockchain papers is increasing year by year.
FIGURE 6. (a). The number of blockchain related papers published As the year 2020 is not over, the number of papers has
in ACM. (b). The conferences and journals of blockchain related papers
published in ACM. (c). The universities of blockchain related papers
decreased slightly. The results show in the Figure 9. Peo-
published in ACM. ple’s enthusiasm for blockchain research is also increasing.

VOLUME 8, 2020 187187

 Y. Zou et al.: Focus on Blockchain: A Comprehensive Survey on Academic and Application

FIGURE 9. The total number of papers published in four major databases.

of talent supply and demand has also become a hot topic in

the industry, and the entire industry urgently needs a large
number of professionals. In a short period, the situation of
talent supply and demand mismatch in blockchain is still
difficult to change. In addition, we investigated the situation
of blockchain labs opened by universities around the world,
and statistically summarized the corresponding websites of
the labs, as shown in TABLE 1.

C. BLOCKCHAIN TECHNOLOGY LATEST RESEARCH

RESULT
1) CONSENSUS ALGORITHM FIELD
Driven by previous research, the PoW algorithm used by
the Bitcoin system came into being. Unfortunately, many
other research results show that the PoW algorithm have
many defects, such as energy waste and security issues.
FIGURE 8. (a). The number of blockchain related papers published in Philip Daian [32] stated that these huge computing power
Elsevier. (b). The journals of blockchain related papers published in had no effect on society except for protecting the secu-
Elsevier.
rity of the Bitcoin network. To prevent the generation of
large mining pools, Miller [33] proposed a new mecha-
Especially from 2017 to 2019, the number of papers has nism to design the PoW puzzles as non-outsourced puzzles.
exploded. But at present, we believe that the development In addition to the security problem of the PoW algorithm,
of blockchain is still in the early stage, and the future devel- Eyal raised another problem: the payment system using the
opment prospects are still very broad to explore and study. PoW algorithm is not suitable for real-time payment [34],
In addition to theoretical research, practical research also and proposed a new consensus model called Bitcoin-NG,
needs more attention. which speeds up the confirmation time of transactions. Som-
polinsky and Zohar [35] proposed the GHOST strategy to
B. BLOCKCHAIN RESEARCH SITUATION IN UNIVERSITIES reduce the block generation time while being able to handle
With the continuous development of blockchain technol- the problem of forks and prevent double-spending attacks.
ogy, various universities and research institutions have also Vivek Bagaria et al. [36] proposed a new blockchain proof
begun to pay attention to blockchain. The number of uni- protocol called Prism, which can resist 51% attacks, thereby
versities offering blockchain courses is constantly increasing, improving the security of the system.
which also proves the importance of blockchain technology. PoS was proposed because of the unfair mining of PoW.
At present, the world is facing a shortage of blockchain Nxt is the first electronic currency with a 100% Proof of Stake
talents. This contradiction between supply and demand has (PoS) mechanism. The more coin miners have, the greater
given the market a vast imagination, which is the reason that chance to mine the next block. Kiayias et al. [37] used
the current colleges and universities are offering blockchain Follow-the-Satoshi program to implement the PoS con-
courses. With the rapid development of blockchain technol- sensus, claiming that the leader election should be com-
ogy in various industries around the world, the imbalance pleted randomly by calculating entropy. To overcome the

187188 VOLUME 8, 2020

Y. Zou et al.: Focus on Blockchain: A Comprehensive Survey on Academic and Application

TABLE 1. Global University Blockchain Lab.

limitations of the existing PoS in terms of fairness and secu- developed other types of consensus algorithms in recent
rity, Lee et al. [38] proposed a new protocol called Proof of years. Blocki and Zhou [40] proposed the Proof of Human
Sharing (PoS) based on fairness and dynamic sharing man- puzzle. The ingenious design of this puzzle is to mine a new
agement. Larimer’s idea was to use rights and interests as the block. It cannot simply depend on the hardware devices, and
evidence of voting [4], rather than the opportunity to mine human participation is also required. Proof of Space [41] is
new block. This consensus algorithm is called Delegated the other consensus algorithm based on proof types, and they
Proof of Stake (DPoS). Some people think that the consen- do not use the concepts of PoW and PoS algorithms. In Proof
sus algorithm used by PPCoin is the first variation of PoS. of Burn, miners must send their coins to an address that
Bentov et al. [39] proposed a solution called Proof of Activity ‘‘burns’’ them, which means others cannot use these coins.
(PoA). This PoA consensus combining PoW and PoS not In Proof of Space, miners invest their money in hard drives,
only solves the double spending attack, but also deals with which is much cheaper than investing in the equipment used
the Tragedy of the commons caused by the PoW consensus. by the PoW algorithm.
TABLE 2 compares the PoW, PoS algorithm, and the combi- This consensus is performed in a special environment
nation of them from multiple angles. called the Trusted Execution Environment (TEE) [42].
In addition to the above mainstream consensus algo- Milutinovic [29] proposed the Proof of Luck consensus algo-
rithms used in the blockchains, many scholars have also rithm, which is also performed in the TEE environment.

VOLUME 8, 2020 187189

 Y. Zou et al.: Focus on Blockchain: A Comprehensive Survey on Academic and Application

TABLE 2. Comparison of Main Consensus Algorithms. verification. Matetic et al. [48] proposed a new Bitcoin pro-
tection method for light client competition, which provided
significant protection for light clients. Ting Cai et al. designed
a Blockchain-Assisted Trust Access Authentication System
for Solid [49]. With the increasing interest of blockchain in
academic research and industry, the security and privacy of
blockchain will attract considerable attention gradually.

4) SCALABILITY FIELD
Scalability is defined as the ability of a system, network,
These emerging consensus algorithms have also made out- or process to handle increasing workloads, or to expand its
standing contributions to the development of blockchain. potentiality for accommodating this growth. For the cur-
rent blockchain, scalability is a problem that prevents it
from being accepted by the mainstream. Currently, Visa,
2) SMART CONTRACT FIELD
the fastest payment network, can process approximately
The smart contract is similar to the upgraded version of many
24,000 payments per second. However, due to the use of
electronic contracts. When the contract meets the conditions,
blockchain, the transaction speed of most cryptocurrencies
it will automatically execute. And at the same time, it can
is inferior and cannot meet demand. At present, it seems
receive and store information. Because of the decentraliza-
that increasing the block size and Lightning Network are
tion, tamper-resistance, and traceability characteristics in the
the only two mode options for expanding the Bitcoin sys-
blockchain. The developers propose to embed the smart con-
tem, but this is actually just the two mainstream methods
tract into the blockchain to avoid malicious tampering of the
currently favored by BCH and BTC [50]. In fact, there are
contract conditions. However, the widely used cryptocurren-
many other suggestions for improving throughput, including
cies do not support complex smart contracts. Das et al. [43]
sidechains, which can ease the pressure on the network with-
proposed the practical framework called FastKitten, which is
out having to switch to a hosting solution similar to Light-
used to execute complex smart contracts at a low cost. In addi-
ning Network. In addition, Payment Channel Network (PCN)
tion, the privacy of smart contracts is the main obstacle to its
has become the most widely deployed solution to alleviate
widespread adoption. Steffen et al. [44] proposed zkay lan-
the scalability problem, allowing most transactions between
guage, which introduced the definition of privacy type of pri-
two users to be handled outside the chain. On this basis,
vate value owners, hid private data with a primitive password,
Malavolta et al. [51] studied and designed a secure and
and then enhanced the correctness of update state through
private PCNS. Smart contract is a kind of automatic imple-
Non-Interactive Zero-Knowledge (NIZK) proof, to solve the
mentation protocol, and the scalability challenge hinders its
privacy problem of smart contracts.
further adoption. Based on this, Dziembowski et al. [52]
proposed State Channel Network (SCN), which can create
3) SECURITY AND PRIVACY FIELD
and close state channels without blockchain interaction, and
The essential security characteristics of the blockchain allow to sign contracts with any number of organizations.
come from the advancement of cryptographic technology Although different blockchains vary in scalability, the dif-
and the design and implementation of the Bitcoin system. ferences between projects are increasing in the process. This
Rui Zhang et al. summarized the inherent security trend will bring great progress to solve the scalability problem
attributes of the blockchain and the parts that need to be of cryptocurrency, and gradually form a perfect solution.
strengthened [10].
Among them, consistency, tamper-resistance, prevention
IV. BLOCKCHAIN APPLICATION SCENARIO
of DDoS attacks, resistance to double-spending attacks, and
A. BLOCKCHAIN APPLICATION INDUSTRY
the use of pseudonyms are all more common mature security
attributes in blockchain, while, unlinkability, confidentiality, The main advantages of blockchain are no intermediary par-
and resistance to majority 51% consensus attacks need to ticipation, efficient and transparent process, low cost, and
be strengthened. In addition, Ganesh et al. [45] proposed high data security. Based on the above advantages, the appli-
a privacy-protected version of the PoS protocol, defining cation of blockchain is very extensive, as shown in TABLE 3,
the concept of anonymous verifiable random functions, and which can penetrate many industries. At present, many lit-
strengthening the security of the PoS protocol. Zhang and eratures divide the application industry of blockchain into
Preneel [46] proposed the future direction of more secure financial industry and non-financial industry. A more detailed
PoW protocols and pointed out several common pitfalls in classification is discussed in this paper.
PoW security analysis.
Rodler et al. [47] have proposed a new smart contract secu- 1) FINANCIAL FIELD
rity technology that protects deployed contracts in a back- Digital currency is the most widely used and accepted appli-
ward compatible manner through runtime monitoring and cation of blockchain. The most familiar one is bitcoin, which

187190 VOLUME 8, 2020

Y. Zou et al.: Focus on Blockchain: A Comprehensive Survey on Academic and Application

TABLE 3. Blockchain Application Scenario.

FIGURE 10. The Advantages of ‘‘Blockchain + IoT’’.

used to be synonymous with blockchain. Digital currency IoT’s needs, a lightweight, scalable blockchain (LSB) is pro-
is the beginning of the combination of the blockchain and posed [56], which guarantees the privacy of IoT. In terms
financial field. of identity authentication, Wazid et al. [57] designed the
At present, there are hundreds of digital currencies in the universal authentication key management protocol UAKMP
market. PRCash [53], a blockchain currency that can pay for the IoT security, which protects users’ privacy and iden-
quickly and has a good level of user privacy and regulatory tity. In terms of data sharing, the IoT design based on the
control, providing a new regulatory mechanism for transac- blockchain can use the blockchain as an auditable storage
tions using cryptographic promises, and regulating expen- layer and a distributed access control layer to achieve flexible
diture limits of zero-knowledge proof. It realizes a more access control management and secure data sharing [58].
effective security method of blockchain in the financial field. In terms of credibility verification, a framework with layers,
Avgouleas et al. [55] built a comprehensive blockchain-based intersect, and self-organization Blockchain Structures (BCS)
framework that can perfectly express the relevant securities is proposed, helping us build trust, significantly reduce costs,
trading logic with codes, realize real-time asset transfer, and and reduce human errors, to protect data security and privacy
accelerate the speed of transaction liquidation. Meanwhile, better for IoT [59]. Integrating blockchain and IoT will bring
blockchain technology can optimize the global financial many advantages to solving IoT’s shortcomings, which can
infrastructure, achieve sustainable development, and create break the existing multiple information islands, promote the
more effective systems than now. They also explore the chal- horizontal flow of information, and multi-party collaboration.
lenges and opportunities of implementing blockchain tech- ‘‘Blockchain + IoT’’ will promote a new round of technology
nology in the banking industry [54]. Therefore, the appli- integration and innovation.
cation of blockchain in the financial field has dramatically
improved security and speed. 3) SUPPLY CHAIN FIELD
It is real that supply chain management systems lack suf-
2) IOT FIELD ficient efficiency and transparency, thus trying to integrate
In addition to the financial field, the Internet of Things may every part in the supply chain is still a difficult problem.
be the field combines with blockchain to produce the most Based on blockchain technology characteristics, Li et al. [60]
sparks, as shown in Figure 10. proposed a new customs supervision model to solve the
IoT and blockchain are two different technologies. IoT problems, the poor customs supervision management, low
represents a large number of data collection devices, while efficiency and high cost in cross-border import e-commerce
blockchain ensures that they do not tamper the data. However, retail business. In terms of the supervision system prob-
the IoT still lacks effective means in the construction of lems from the traditional food industry, such as indus-
the network credit system and value system, and there are trial chain deficiency, data dispersion, and so on, it is a
still many problems in equipment security, identity authen- risk and an area of concern for systems where there is a
tication, data privacy and public, etc. In terms of security need for a high-reliability solution. The Hierarchical Multi-
and privacy, to provide end-to-end security that meets the Domain Block Chain (HMDBC) network structure and the

VOLUME 8, 2020 187191

 Y. Zou et al.: Focus on Blockchain: A Comprehensive Survey on Academic and Application

secondary inspection mechanism proposed by Tao et al. [61] 5) EDUCATION FIELD

is quite appropriate. Moreover, Blockchain technology can With the general trend in the development and trans-
solve some of the most pressing issues in the supply chain, formation of global education, blockchain technology is
as it provides new methods to record, transmit, and share expected to play an important role in the construction of the
data. It is visible, just like the information on the Internet, ‘‘Internet + education’’ ecology. An in-depth discussion on
for every aspect of the transaction process with blockchain the educational application with blockchain technology, and
technology used in the supply chain. Blockchain technol- its benefits that blockchain technology can bring to education
ogy can also be combined in the supply chain to throw is conducted by Alammary et al. [68]. M. Han et al. use
light on every product [62] for gaining customer confidence blockchain to provide proof of achievements for academic
from global markets. Schmidt et al. [63] used the transac- transcripts issued by education providers [69]. There is a
tion cost theory to explain how the blockchain affected the global trust education framework [70], based on blockchain to
supply chain and believed that the effective and transparent verify the academic certificates and course credits of college
nature of the blockchain helped the supply chain reduce students. By means of ensuring the consistency between local
transaction costs. Blockchain technology helps the supply education certificates and credits, it can ensure a comprehen-
chain network establish a shared and secure information sive understanding about students’ performance. On account
flow record and provides a ‘‘shared version of events’’ for of the application of blockchain technology in the education
supply chain transactions, processes, and partner networks. field is still in its infancy, the potential of blockchain in the
Therefore, blockchain will combine supply chain with great education field is not consummate yet.
chemistry.
6) HEALTHCARE FIELD
Blockchains can also be applied to many scenarios in health-
4) SOCIAL WELFARE FIELD care, especially in the data sharing of clinical medicine sce-
In recent years, a series of dishonest donations on the Internet nario, which has great potential to overcome the trust prob-
has aroused many netizens’ attention and enthusiasm. Trust lem and technical problems. In the field of ‘‘blockchain +
is significant for charity, once people lose trust in others, healthcare’’, the most cases are medical tracing.
it is difficult to rebuild. Due to the blockchain advantages of Chaudhari et al. [71] constructed a medical tracking system
decentralization, transparency, and information traceability, based on blockchain, which aims to solve the trust prob-
the problems that have been criticized by people in this field lem in the process of data sharing. Xia et al. [72] built a
will be solved one by one if these advantages are applied medical device traceability system by combining traditional
to the field of public welfare and charity. According to the tracking systems with blockchain technology, using alliance
above advantages, there is an innovative charity logistics plat- chain and smart contract. The blockchain system is able
form [64] based on the Ethereum platform, combined with the to records the whole process data of drugs, including the
unique responsibility system and appraisal report mechanism, product information, logistics data, storage data, sales data,
for achieving the data consistency of the chain and the real and consumption terminal purchase data. Once the link data is
state, as well as the authenticity and transparency of charity added to the blockchain, it cannot be tampered. Blockchain is
logistics data. Once add the data of public welfare projects mainly used in medical data storage, drug anti-counterfeiting
to the blockchain that the moment user donates to the end, traceability, gene data secure storage, etc. The characteristics
every link in the process will be recorded on the chain in detail of blockchain can help us fully trace the flow of drugs
and all information process relevant cannot be changed arti- from manufacturers to end-users, and identify the counterfeit
ficially. Sun et al. [65] regarded blockchain as an electronic drugs [73]. In general scenarios, personal case data is kept
log of transactions and other information in commercial by the hospital, while centralized data storage has many
and charitable activities, enabling secure transfers, reducing advantages, such as high efficiency, easy to operate. However,
fraud, retaining tracking evidence, improving transparency, data stored in this way is highly likely to be lost. Once the data
reducing costs, and increasing efficiency. Blockchain-based is lost, it will cause very serious consequences. To solve this
charitable donations may also be more complicated, donors problem, Rouhani et al. [74] proposed a secure distributed
can design a smart contract to release certain donations in medical data asset management system, which can help
specific conditions [66]. Jain and Simha [67] designed a dis- patients and medical staff effectively exchange medical data
tributed ledger application and stakeholder incentives, such while ensuring the security and privacy of private medical
as accountability, transparency and flexibility, to increase data. Abdullah et al. [75] introduced a medical data manage-
social welfare. For charity, the transparency from blockchain ment system based on blockchain technology, which encrypts
technology can ensure that donors clearly understand and patients’ data to ensure users’ privacy. The data stored in
check the flow of their funds. The tamper-resistance ensures a hospital alone is not comprehensive enough. The privacy
that financial information will not be tampered with and of medical cases and the anti-counterfeiting of drugs are
anonymity also protects the privacy of donors. Therefore, both crucial links. ‘‘Blockchain + healthcare’’ can gradually
blockchain technology can be regarded as the best medicine solve these problems, expecting to be popularized as soon as
for charity. possible.

187192 VOLUME 8, 2020

Y. Zou et al.: Focus on Blockchain: A Comprehensive Survey on Academic and Application

7) GOVERNMENT FIELD lifestyle of the whole society and may set off a new energy
Blockchain can reduce official fraud, improve efficiency, and revolution.
reduce costs. The ideal state is to achieve a completely paper-
less digital government and minimize corruption. The use of B. BLOCKCHAIN PROJECT
blockchain in taxation may change how the government col- Blockchain technology can help organizations and institu-
lects and disburses funds and improve efficiency [76]. Many tions build trust among, while reducing the cost of trust. In the
countries have adopted blockchain technology to implement blockchain boom, technology giants, venture companies, and
the electronic voting system and realize ‘‘voter authentication academic institutions have joined in and launched one project
and result saving’’. However, the traditional electronic voting after another. According to the classification of blockchain
system has the risk that the data is not open and transparent application industry in the previous section, we sort out the
enough, and it is easy to be tampered with and forged; the projects of corresponding industries, as shown in Figure 11.
user’s private information is exposed; the voters are unable
to verify the voting results [77]. Nadar et al. [78] proposed a 1) FINANCIAL FIELD PROJECTS
new method to realize decentralized voting system by using • Digital currency projects: Digital currency is the
blockchain. Shahzad and Crowcroft [79] proposed a frame- project that has the most public contact among
work to ensure data security by using effective hash tech- blockchain projects, and is mainly used for transactions
nology. The paper introduced the concept of block sealing, such as ordinary currency. At present, there are more
which helps make the blockchain more adjustable to meet than one thousand kinds of digital currency in the world.
the security needs of the voting process. In daily life, many Among them, the more successful projects are bitcoin,
scenarios require identity authentication, such as through ETH, Litecoin, Monero, EOS, Ripple.
border customs, airport security, cashing checks or opening • Global payment projects:With the continuous devel-
bank accounts. The government needs to prove and manage opment of credit card payments and mobile payments
the identity. In many cases, identity is easy to be forged. in recent years, the traditional cash payments in reality
And blockchain can help to solve the problem of identity have been gradually away from people’s lives. Com-
authentication. Kuperberg et al. [80] conducted a thorough pared with the traditional global payment mentioned
analysis of the opportunities brought by the combination of above, the global payment system and settlement func-
the latest blockchain technology and the electronic identity tion of the blockchain is unique and epoch-making. The
document (EID) issued by the government, including the following is a list of some blockchain global payment
existing implementation and pilot. Odelu [81] proposed a new projects.
key management mechanism of blockchain based on user a: InterLedger PROJECT OF RIPPLE
authentication and analyzed the mechanism strictly, which Ripple, American finance and technology company, has
showed that the proposed protocol could resist all kinds of
launched the InterLedger project. This project is a practitioner
possible attacks. The combination of blockchain and govern-
of global cross-border payment based on blockchain. The
ment services can maximize the efficiency of work. Utilizing
purpose is to create a unified global unified payment standard
technical means can increase the people’s trust and build a
and a unified network financial communication protocol.
safer society. At present, banks in more than ten countries have joined
the project to cooperate, and in addition, they have received
8) ENERGY FIELD
support from companies such as Apple and Microsoft.
Blockchain technology, as a new database technology, can b: STELLAR PROJECT OF IBM
increase the mutual trust of multi-stakeholders in the energy IBM launched the blockchain global payment system World
network. Its decentralization, openness, and transparency are Wire, in which Stellar protocol constitutes a key part of
in line with the concept of the energy network and have the technical framework for real-time cross-border payment.
attracted more and more attention in energy field. At present, Stellar’s new platform enables real-time clearing and settle-
the application of blockchain in energy field mainly focuses ment of cross-border transactions. IBM believes that World
on distributed intelligent energy systems and energy sharing. Wire can integrate with any existing payment system at any
Mengelkamp et al. [82] provides a distributed market plat- time and support payment at any scale, any destination and
form for energy producers and consumers to trade energy any asset type in a high security environment.
without centralized institutions. Gao et al. [83] combined
smart grid with blockchain technology, and use smart con- c: LIBRA PROJECT OF FACEBOOK
tract to establish trading procedures to provide trust between Libra’s mission is to build a simple, borderless currency
participants on the network. The system is proved to be very and global payment system for billions of people. Libra is
effective since users can monitor how to use electricity. When composed of three parts, which will work together to create a
the energy meets the blockchain, the collision and blending more inclusive financial system: a) It is based on a secure,
of the two are related to the long-term and overall situation, scalable, and reliable blockchain. b) It is backed by asset
which will have a significant impact on the production and reserves that give it intrinsic value. c) It is governed by an

VOLUME 8, 2020 187193

 Y. Zou et al.: Focus on Blockchain: A Comprehensive Survey on Academic and Application

FIGURE 11. Blockchain Project Classification.

independent Libra association whose mission is to promote platform has completed the first real-time cross-border finan-
the development of this financial ecosystem. cial transaction.
• Financial services project:Scenarioization of financial
services is a trend, and blockchain will make many 2) IOT FIELD PROJECTS
changes to traditional financial models and business pro- a: AMBROSUS
cesses. Blockchain reconstructs the financial services Ambrosus is a blockchain-powered IoT network for food and
scene, connects the bank’s financial system and services pharmaceutical enterprises, enabling secure and frictionless
to the scene, and makes the information more symmet- dialogue. The core technology is a decentralized protocol by
rical and transparent. combining various sensors, smart contracts on AMB-NET,
secure storage and robust developer tools components for
d: BSAVE PROJECT tracking, storing and transmitting, thus it can be used in
In March 2019, British Basve company launched research on supply chain, IoT and health-care application scenarios.
a platform providing users with online storage bitcoin asset,
b: CHAIN OF THING (CoT)
so that users can directly obtain income from their bitcoin
assets. The company’s goal is to fundamentally simplify the Chain of Things (CoT) plays an important role of bitcoin and
process of online savings and investment, fully exploit the blockchain technology in providing a better foundation for
financial service potential of digital currency, and provide securing IoT and securing data from IoT devices. Dubbed
convenience for people all over the world. the 4th industrial revolution, the ‘Internet of Things’ will
consist of a vast network of sensor nodes that will generate
e: CORDA PROJECT an unprecedented flow of global data. These devices will
R3, a global blockchain alliance organization, has been quietly execute smart contracts with physical actuators that
committed to developing a third-party financial transaction will manage many aspects of our future lives.
platform with the help of blockchain technology. Corda
c: IOTA
project is a distributed ledger launched by R3 which uses
blockchain technology to record and manage financial con- It is not only a blockchain but also a feeless and open secure
tracts. Corda is used to recording, manage, and synchronize trust layer, protocol for IoT and scalable distributed ledger.
financial contracts between traditional financial institutions, The tangle, characteristic of its network, immutably records
which is largely inspired by the blockchain system, excluding the exchange of data and value for ensuring the trustworthy
some designs that are not suitable for banking application and tamper-resistance of information. It enables new possibil-
scenarios. ities in many fields and will continue to enrich technological
maturity and others.
f: WE.TRADE PROJECT
We.trade a financial trading blockchain platform jointly d: SLOCK.IT
developed by nine well-known banks, which aims to Based on the Ethereum network, Slock.it with the name of a
provide enterprises with the tracking of fund flow and Universal Sharing Network (USN) is an open marketplace for
transaction management, and improve the efficiency of real and virtual products renting, sharing or selling. It enables
cross-border financial transactions. The We.trade blockchain humans and machines to securely participate in the evolving

187194 VOLUME 8, 2020

Y. Zou et al.: Focus on Blockchain: A Comprehensive Survey on Academic and Application

economy of things. Slock.it brings a better transaction envi- c: BLOCKCHAIN ARCHITECTURE

ronment, and benefits IoT and financial industry. In October 2019, National Science Foundation (NSF) funded
the University of California, Berkeley to research blockchain
3) SUPPLY CHAIN FIELD PROJECTS architecture for resource-constrained devices. The goal of
a: SKUCHAIN this project is to develop a new framework and protocol
It is a pioneer of empowering enterprises using blockchain toolkit so that resource-constrained computers can play an
to strengthen collaboration across supply chains. By using important role in ensuring the security of distributed systems.
Popcodes traceability, brackets smart contracts and This resource constrained blockchain architecture will enable
ZK-collaboration technologies, it helps customers solve innovation and development in the IoT, healthcare, supply
transparent problems of products with their various infras- chain and other fields.
tructure developed tools. There is no doubt that Skuchain is an d: MEDILEDGER
outstanding achiever with its products and a vigorous assistor
The MediLedger Project was launched in 2017 and it became
for empowering in supply chain scenario.
a fully decentralized peer-to-peer and blockchain network.
MediLedger meets the emerging needs of the prescription
b: PROVENANCE
medicine supply chain through redefining the potential of
It is a platform brings the supply chain to the shopper with blockchain for the pharmaceutical sector, it plays an impor-
the concentration on products’ story. Using digital passport tant role in healthcare field.
for product traceable and the blockchain based platform for
transparency, it unites of citizens and businesses in a system 5) EDUCATION FIELD PROJECTS
to build trust and meaningful relationships with customers in a: BLOCKCERTS
supply chain scenario. Blockcerts Project set up an open standard for creating,
issuing, viewing, and verifying blockchain-based certificates.
c: EVERLEDGER This project aims at helping individuals to process and share
It is a digital platform based on blockchain secure technolo- their own official records like academic credentials profes-
gies, the aim is to contribute greater clarity and confidence sional licenses, workforce development and more.
in transparent marketplaces with the help business surface
b: APPII
and converge information. Based on blockchain, combined
APPII is a subproject of Applied Blockchain, which designed
AI, Intelligent labelling and nanotech together, it attaches
a platform underpinned by blockchain and digital signatures
transparency and temper-resistance to IoT and supply chain
as a way to create a single immutable record of an individual’s
among produce and transmit process.
experience. APII develop a smart contract data store for each
user with controls over third party access to that data. APPII
d: TradeLens
is a meaningful practice of combining blockchain with the
It is one of interconnected ecosystem of supply chain, education industry.
absorbed in freeing people from legacy data systems and
making trade easy. Using IBM Blockchain Platform which c: ODEM
is based on Hyperledger Fabric is to let goods accessible and It is an on-demand education market built on the Ethereum
traceable by every part the goods relevant. It benefits many blockchain. The platform brings together students, educa-
industries including ports, ocean carriers, shippers, etc., and tors, and service providers who develop and participate in
brings vitality to supply chain. education programs. Once students and educators begin their
education programs ODEM smart contract can seamlessly
4) SOCIAL WAELFARE AND HEALTHCARE FIELD PROJECTS manage payments from the beginning to the end of a long-
a: OXFAM term contract. ODEM is revolutionizing the way educators
It is a charity dedicating to help people beat poverty. It is and students plan, connect, and book educational programs.
partnered to carry out a blockchain program that permitted d: TURING CHAIN
blockchain-backed vouchers to deliver credit and introduces
Turing Chain Project aim to use AI and blockchain technol-
blockchain into rice which known as BlocRice program.
ogy to construct a public chain of natural language commu-
It is delighted to know that social welfare can make use of
nication to realize Turing test. Turing Chain is capable of
blockchain technology for effective and credible assistance.
redefining traditional educational certificates and eventually
enabling unified and sustainable records tracking for educa-
b: PATIENTORY
tional industry.
Founded for making a difference in healthcare improvement,
it combines people who could be doctors, patients, caregivers 6) GOVERNMENT AND ENERGY FIELD PROJECTS
etc. together for better treatment. Applied in healthcare sce- a: ARCHANGEL
nario, it will gain more new form of relevant technology that Archangel Project can deliver long-term sustainability of
could be regarded as healthcare future tense. digital archives through new transformational blockchain

VOLUME 8, 2020 187195

 Y. Zou et al.: Focus on Blockchain: A Comprehensive Survey on Academic and Application

• Decentralization: decentralization is a decentralized

distributed structure. The whole network has no central
hardware or mechanism, which is the core advantage
of blockchain. Decentralization is a key selling point of
most public blockchain platforms [84]. Decentralization
removes the existence of intermediaries and reduces the
cost of intermediaries, which makes blockchain widely
used.
• Collective maintainability: collective maintainability
is built on the basis of decentralization. Without the par-
ticipation of the third party, all nodes need to be united,
FIGURE 12. Advantages and Challenges of Blockchain Technology. and all parties have clear rights and responsibilities to
maintain the normal operation of the blockchain. It can
technology solutions that will ensure both accessibility better maintain the stability and security of the entire
and integrity of digital archives. By deploying Archangel, blockchain system [85].
the credibility of archives was improved, which not just for • Trust-free: Trust-free is to remove the third-party
study reference, but for matters as serious as legal cases, trust [84], which is manifested in two aspects: one is
official investigations. to trust the authenticity of the historical behavior of the
data on the chain; the other is to trust the future behavior
b: ENERCHAIN
constrained by rules and mechanisms.
• Traceability:traceability means that the data on the
Enerchain is a blockchain based application developed by
chain can be found. Currently, many studies take advan-
POTON company. The Enerchain Project has shown that
tage of the traceability of blockchain [87-88]. We can
applying blockchain technology in energy markets promises
track the data in the blockchain, which is convenient for
more efficient operational processes and less transaction cost.
supervision and tracking.
• Tamper-resistance: Blocks are linked by hash val-
c: ENERGY WEB CHAIN
ues, and the ledger is stored on multiple nodes,
The Energy Web Chain is a public blockchain platform making the tamper-resistance advantage possible [89].
designed for the energy industry, launched in 2019. It imple- Tamper-resistance can ensure that we have enough trust
ments a virtual machine like public Ethereum, which allow in the blockchain data. We do not need to spend time and
developers to write smart contracts and decentralized appli- energy to verify the authenticity of the data, but uncon-
cation on the platform. The Energy Web Chain provides the ditionally trust the authenticity of the data, which is
foundational digital infrastructure for the energy industry determined by the tamper-resistance of the blockchain.
with the advantages of blockchain. • Openness: openness ensures the openness of the sys-
tem. Apart from the fact that the private informa-
d: LO3 ENERGY tion of all parties to the transaction is encrypted,
It builds a blockchain based platform named Exergy, to record the blockchain data is open to everyone. Anyone can
and process grid edge data. They combine industry expertise query the blockchain data and develop relevant appli-
with advancements in blockchain technology to deliver a new cations through an open interface, so the information of
frontier in energy. the whole system is highly transparent [90].
• Anonymity: the nature of anonymity in blockchain is
V. BLOCKCHAIN ADVANTAGES AND CHALLENGES different from our traditional understanding.
With the continuous development of blockchain applications, More accurately, blockchain has pseudonyms, not real
blockchain technology becomes more and more popular. This names. Everyone has a virtual identity independent of
strong development power from the requirements of various the real identity on the blockchain. The decentralized
industries makes the blockchain technology progress with model determines the transparency of data disclosure,
each passing day, and the achievements of various industries but all the things the virtual identity does are transparent,
more attractive. However, there are advantages and disadvan- and transparency directly leads to privacy problems.
tages, we summarize the advantages and challenges faced by The form of anonymity ensures our privacy to a certain
the blockchain shown in Figure 12 and describe them in detail extent [91].
below.
B. BLOCKCHAIN CHALLENGES
A. BLOCKCHAIN ADVANTAGES 1) SECURITY-RELATED CHALLENGE
Blockchain is equipped with decentralization, collective a: BLOCKCHAIN UNDERLYING CODE
maintainability, trustless, traceability, tamper-resistance, There are several specific security holes in the architecture
openness, and anonymity etc. advantages. and implementation of blockchain technology. Blockchain

187196 VOLUME 8, 2020

Y. Zou et al.: Focus on Blockchain: A Comprehensive Survey on Academic and Application

security vulnerabilities are usually related to the consen- At the same time, due to the anonymity of the blockchain
sus mechanism used to confirm and validate transactions. digital currency, bitcoin often appears in the dark network
These security vulnerabilities include DDoS, block discard- transactions, money laundering crimes and virus blackmail
ing, eclipse attack [92], selfish mining, Sybil attack [93], programs. Laws and regulations could impact how far and
51% attack, double spend attack [94]. Blockchain projects how fast the technology could develop [97]. The events indi-
are open-source. The characteristics of open source are con- cate that our blockchain related regulatory system and means
ducive to the development and promotion of blockchain, but are not advanced enough, which provides an opportunity for
also provide opportunities for attackers. The lack of code crime.
evaluation in blockchain leads to frequent security events,
which limits the development of blockchain. 4) INDUSTRIAL APPLICATION CHALLENGE
b: POTENTIAL HACKING The slow promotion of standardization and the lack of inno-
vation in business models are the biggest obstacles to imple-
Blockchain design limits the attack of some hackers. For
menting blockchain technology in the industry. Currently,
example, if a hacker wants to tamper with the blockchain’s
the blockchain implementation still lacks industry best prac-
data, he needs to have 51% computing power. But the benefits
tices and standards for reference. At the same time, the appli-
of using 51% computing power to attack the whole system
cation of blockchain faces policy risks. By summarizing
are not as much as the benefits of using 51% computing
the existing implementation difficulties, it is hoped that it
power to mine normally, so, hackers will not choose to attack
will help the implementation and landing of subsequent
blockchain in an ideal state. Due to the immense attack-
blockchain solutions.
ing cost to perform the 51% attack, it was considered very
unlikely for a long period [95]. However, we just have to
consider such a situation. Hackers are not only trying to 5) RESOURCE WASTE CHALLENGE
obtain benefits, but only want to destroy or show their own Blockchain is a large ledger of distributed storage, each node
technical advantages. Under strict planning and organization, keeps a ledger, but repeated data storage will cause serious
the possibility of blockchain system being broken is also waste of storage resources. Taking bitcoin as an example,
theoretically there. the mining process will produce high power consumption.
Cambridge University uses the Cambridge bitcoin electric-
c: THREATS FROM QUANTUM COMPUTERS ity consumption index (CBECI) to track the use of bitcoin
In data storage, blockchain uses public-key encryption, digi- power, which shows that the electricity consumption of bit-
tal signature, hash function and other cryptographic compo- coin accounts for 0.20% of the total electricity consump-
nents. To meet the needs of higher privacy protection, some tion of the world every year, 0.17% of the total electricity
blockchain schemes also need ring signature, zero knowledge production of the world every year, which exceeds the total
proof and other privacy protection technologies. The secu- electricity consumption of Austria or Colombia and other
rity of these cryptographic components directly affects the countries electricity.
security of blockchain data. In the short term, these cryptog-
raphy technologies will not be threatened, but with the rise 6) SPACE STORAGE CHALLENGE
of quantum computing, the existing cryptography algorithms Each node in the blockchain must save complete backup data.
may face a devastating blow. As the amount of transaction data increase, the storage space
it takes up is also increasing. Taking bitcoin as an example,
2) SCALABILITY-RELATED CHALLENGE there are more than 600000 blocks on the main chain at
Due to the increase in the number of participants in the present, and the synchronous and complete block data needs
blockchain system, there is another challenge in the scalabil- more than 200G of space, which has a very high demand for
ity and computing resources of the system. Scalability is still a storage space resources. It is a crucial problem restricting the
key barrier when the blockchain technology is widely used in development of the blockchain.
real business environments [96]. With the increasing scale of
nodes in the blockchain system, the broadcast mode adopted 7) TALENT SHORTAGE CHALLENGE
by blockchain technology may lead to data delay and network The whole blockchain industry is still in the early stage of
performance degradation, or even paralysis. In addition, with development, similar to the Internet industry in the 1990s
the increase in data volume, the efficiency of query and data or the early 21st century, few people really understand
mining has been difficult to meet people’s needs. blockchain. Moreover, blockchain is the integration of var-
ious technologies, including cryptography, economics, and
3) LEGAL SUPERVISION CHALLENGE computer science, which is more complicated than the Inter-
As blockchain technology has been widely concerned in net and has a higher threshold for in-depth research. There-
recent years, the corresponding legal provisions are not per- fore, blockchain related technical talents have been very
fect. Many countries and regions have different attitudes scarce, which is the pain point restricting the development
towards blockchain, lacking a unified regulatory standard. of the whole industry.

VOLUME 8, 2020 187197

 Y. Zou et al.: Focus on Blockchain: A Comprehensive Survey on Academic and Application

VI. BLOCKCHAIN DEVELOPMENT TREND social tools, games, trading platforms, etc. We can develop
A. BLOCKCHAIN TECHNOLOGY DEVELOPMENT TREND DApp directly on the basis of the valuable resource of data.
Blockchain itself is a comprehensive technology, and it hasn’t
2) FROM DIGITAL CURRENCY TO NON-FINANCIAL FIELD
been around for a long time, so there is still a long way to go.
From a technical perspective, the future development trend of In the future, blockchain can be used as a general-purpose
the blockchain is roughly as follows. technology to accelerate the penetration of digital currency
into other fields and carry out innovative integration with var-
ious industries. The development of blockchain mainly will
1) UNSTRUCTURED CHAIN STORAGE be involved by two camps. The first camp is cryptocurrency.
Structured block data in blockchain storage has certain Starting from currency, it will gradually advance to the field
advantages. But like today’s big data technology, it uses of asset management, deposit and certificate, and penetrate
unstructured data processing technology. Therefore, once the the field of credit investigation. The second is the IT camp,
blockchain can efficiently accept and process unstructured starting from information sharing, to build the credit core at
data, a blockchain technology belonging to the future Internet low cost, and gradually cover all fields.
will come. However, improving the chain structure is a very
high technical threshold, and it is also a significant challenge 3) IOT AND BLOCKCHAIN
to the technical level of the research and development team. Blockchain provides a secure and scalable framework for
communication between IoT facilities, and therefore brings
many advantages [101]–[103]. Undoubtedly, blockchain and
2) CONSENSUS ALGORITHM
the IoT are one of the best combinations in this era.
Consensus algorithm is the key part to the development We believe that, in the future, the contribution of the two
of blockchain technology, is the foundation of the whole technologies to human beings and the whole society will be
blockchain trust, and affects the transaction processing abil- endless and hard to inestimable.
ity, security and scalability of blockchain. The PoW consen-
sus algorithm used by Bitcoin has strong anti-attack ability, 4) BLOCKCHAIN AND ARTIFICIAL INTELLIGENCE
and good performance in solving data consistency, but con- The cooperation between AI and blockchain can make a
suming too much energy is the disadvantage. Some consensus difference in privacy protection, energy consumption, scal-
algorithms proposed in the later stage can solve the problem ability, efficiency and security [104]. Artificial intelligence
of energy consumption to a certain extent, but they still have is to cultivate the centralized intelligence on the closed data
significant limitations and functional degradation. Consensus platform, while blockchain is to promote the centralized
algorithm plays an important role in the whole blockchain, application in the open data environment. If we can find the
and any progress of consensus algorithm could dramatically right way to make two technologies work together, a little
change the development process of blockchain in the future. collision can produce a huge spark in an instant.
The future consensus algorithm will develop to superior per-
formance, high adaptability and scalability [98]. 5) BLOCKCHAIN DATA ANALYSIS
Since blockchain technology has been widely concerned,
3) CROSS-CHAIN TECHNOLOGY accumulated a large amount of user transaction data. In this
A single blockchain is an information island, and there age when data represent value, all data are our wealth. The
are two completely closed worlds between one chain to data of blockchain has the characteristics of openness, which
another. To realize the mutual communication of blockchain, provides unprecedented opportunities for researchers to ana-
cross-chain technology emerged. However, the existing lyze blockchain data and solve related problems [105-107].
blockchain technology is not mature, it is impossible to Nowadays, there are some worrying problems in blockchain,
expand in the infrastructure. At present, there are many such as private information disclosure, illegal financial activ-
researches on cross-chain technology [99-100], but most of ities, and so on. On the basis of blockchain value mining,
them are studying cross chain exchange between digital cur- analyzing the privacy of blockchain and discovering the char-
rencies, which is not revolutionary. The actual cross-chain acteristics of illegal behavior can help us build a safe and legal
technology is far from what we expected. Perhaps, when we blockchain environment.
break through the fixed block structure, cross-chain tech-
VII. CONCLUSION
nology will have a qualitative leap. Therefore, cross-chain
Blockchain technology, with its characteristics of anonymity,
technology is the direction we should strive to study in the
decentralization, traceability and non-tampering, has set off
future.
a wave of research in academic and social applications.
This paper introduces the development background and
B. BLOCKCHAIN INDUSTRY DEVELOPMENT TREND basic concepts of blockchain, analyzes and summarizes the
1) BLOCK DATA APPLICATION DEVELOPMENT eight application scenarios of blockchain by investigating
Block data can be used not only as data records, but also the blockchain related researches of many universities and
as input of programs to help other applications, such as research institutions, and then investigates the physical imple-

187198 VOLUME 8, 2020

Y. Zou et al.: Focus on Blockchain: A Comprehensive Survey on Academic and Application

mentation projects of blockchain in various fields. Finally, [15] N. O. Nawari and S. Ravindran, ‘‘Blockchain and the built environ-
we summarize the advantages and challenges of blockchain ment: Potentials and limitations,’’ J. Building Eng., vol. 25, Sep. 2019,
Art. no. 100832.
technology and put forward the future development trend of [16] W. Gao, W. G. Hatcher, and W. Yu, ‘‘A survey of blockchain: Techniques,
blockchain technology. Through the above analysis, we draw applications, and challenges,’’ in Proc. 27th Int. Conf. Comput. Commun.
the following conclusions. In recent years, the research on Netw. (ICCCN), Hangzhou, China, Jul. 2018, pp. 1–11, doi: 10.1109/
ICCCN.2018.8487348.
blockchain technology has been widely carried out in var- [17] D. Yaga, P. Mell, N. Roby, and K. Scarfone, ‘‘Blockchain technology
ious universities, and the quantity and quality of published overview,’’ NIST, Gaithersburg, MD, USA, Tech. Rep. 8202, 2018.
papers have been further improved. As a result, a variety of [18] Z. Zheng, S. Xie, H.-N. Dai, X. Chen, and H. Wang, ‘‘Blockchain chal-
lenges and opportunities: A survey,’’ Int. J. Web Grid Services, vol. 14,
blockchain projects have been generated in different fields, no. 4, pp. 352–375, 2018.
with a wide range of application scenarios, which can be [19] C. Decker and R. Wattenhofer, ‘‘Information propagation in the bitcoin
combined with the Internet of Things, supply chain, medical network,’’ in Proc. IEEE P2P, Trento, Italy, Sep. 2013, pp. 1–10.
and other fields. But the technology still faces challenges [20] W. Diffie and M. Hellman, ‘‘New directions in cryptography,’’ IEEE
Trans. Inf. Theory, vol. 22, no. 6, pp. 644–654, Nov. 1976.
such as security, scalability, and waste of resources. We, [21] R. L. Rivest, A. Shamir, and L. Adleman, ‘‘A method for obtaining digital
therefore, proposed the future blockchain development trend. signatures and public-key cryptosystems,’’ Commun. ACM, vol. 21, no. 2,
In terms of technology, it will develop towards unstructured pp. 120–126, Feb. 1978.
[22] R. C. Merkle, ‘‘Protocols for public key cryptosystems,’’ in Proc. IEEE
chain storage and cross chain technology. While in industry, Symp. Secur. Privacy, Oakland, CA, USA, Apr. 1980, pp. 122–133.
it will develop in the direction of ‘‘blockchain +’’ and inte- [23] L. Lamport, R. Shostak, and M. Pease, ‘‘The byzantine generals prob-
grate more closely with different fields. The development of lem,’’ ACM Trans. Program. Lang. Syst., vol. 4, no. 3, pp. 382–401,
Jul. 1982.
blockchain relies on the close connection between academia [24] N. Koblitz, ‘‘Elliptic curve cryptosystems,’’ Math. Comput., vol. 48,
and industry and focuses on the combination of industry no. 177, pp. 203–209, 1987.
and research, to make it better and faster for the benefit of [25] L. Lamport, ‘‘The part-time parliament,’’ ACM Trans. Comput. Syst.,
vol. 16, no. 2, pp. 133–169, May 1998.
mankind.
[26] X. Li, Y. Mei, J. Gong, F. Xiang, and Z. Sun, ‘‘A blockchain pri-
vacy protection scheme based on ring signature,’’ IEEE Access, vol. 8,
REFERENCES pp. 76765–76772, 2020.
[27] L. Xiao, W. Huang, Y. Xie, W. Xiao, and K.-C. Li, ‘‘A blockchain-
[1] S. Nakamoto. (2008). Bitcoin: A Peer-to-Peer Electronic Cash System. based traceable IP copyright protection algorithm,’’ IEEE Access, vol. 8,
[Online]. Available: https://bitcoin.org/bitcoin.pdf pp. 49532–49542, 2020.
[2] M. Crosby, P. Pattanayak, S. Verma, and V. Kalyanaraman, ‘‘Blockchain [28] X. Li, F. Lv, F. Xiang, Z. Sun, and Z. Sun, ‘‘Research on key technologies
technology: Beyond bitcoin,’’ Appl. Innov., vol. 2, pp. 6–10, Jun. 2016. of logistics information traceability model based on consortium chain,’’
[3] I. Bentov, C. Lee, A. Mizrahi, and M. Rosenfeld, ‘‘Proof of activity: IEEE Access, vol. 8, pp. 69754–69762, 2020.
Extending bitcoin’s proof of work via proof of stake,’’ ACM SIGMET- [29] M. Milutinovic, W. He, H. Wu, and M. Kanwal, ‘‘Proof of luck:
RICS Perform. Eval. Rev., vol. 42, no. 3, pp. 34–37, Dec. 2014. An efficient blockchain consensus protocol,’’ in Proc. 1st Workshop Syst.
[4] D. Larimer, ‘‘Delegated proof-of-stake (DPoS),’’ EOS, Bitshare White Softw. Trusted Execution (SysTEX), Trento, Italy, 2016, pp. 1–6.
Paper 1.0, 2014. [30] M. C. Kus Khalilov and A. Levi, ‘‘A survey on anonymity and privacy in
[5] A. Kosba, A. Miller, E. Shi, Z. Wen, and C. Papamanthou, ‘‘Hawk: bitcoin-like digital cash systems,’’ IEEE Commun. Surveys Tuts., vol. 20,
The blockchain model of cryptography and privacy-preserving smart no. 3, pp. 2543–2585, 3rd Quart., 2018.
contracts,’’ in Proc. IEEE Symp. Secur. Privacy (SP), San Jose, CA, USA, [31] J. Gu, B. Sun, X. Du, J. Wang, Y. Zhuang, and Z. Wang, ‘‘Consortium
May 2016, pp. 839–858. blockchain-based malware detection in mobile devices,’’ IEEE Access,
[6] K. Christidis and M. Devetsikiotis, ‘‘Blockchains and smart contracts for vol. 6, pp. 12118–12128, 2018.
the Internet of Things,’’ IEEE Access, vol. 4, pp. 2292–2303, 2016. [32] P. Daian, I. Eyal, A. Juels, and E. G. Sirer, ‘‘(Short Paper) piecework:
[7] J. Yli-Huumo, D. Ko, S. Choi, S. Park, and K. Smolander, ‘‘Where Generalized outsourcing control for proofs of work,’’ in Proc. Int. Conf.
is current research on blockchain technology?—A systematic review,’’ Financial Cryptogr. Data Secur., Sliema, Malta, 2017, pp. 182–190.
PLoS ONE, vol. 11, no. 10, Oct. 2016, Art. no. e0163477. [33] A. Miller, A. Kosba, J. Katz, and E. Shi, ‘‘Nonoutsourceable scratch-
off puzzles to discourage bitcoin mining coalitions,’’ in Proc. 22nd ACM
[8] M. Belotti, N. Bozic, G. Pujolle, and S. Secci, ‘‘A vademecum on
SIGSAC Conf. Comput. Commun. Secur. (CCS), Denver, CO, USA, 2015,
blockchain technologies: When, which, and how,’’ IEEE Commun. Sur-
pp. 680–691.
veys Tuts., vol. 21, no. 4, pp. 3796–3838, 4th Quart., 2019, doi: 10.1109/
[34] I. Eyal, A. E. Gencer, E. G. Sirer, and R. Van Renesse, ‘‘Bitcoin-NG:
COMST.2019.2928178.
A scalable blockchain protocol,’’ in Proc. USENIX Conf. Netw. Syst.
[9] T. Salman, M. Zolanvari, A. Erbad, R. Jain, and M. Samaka, ‘‘Security
Design Implement. (NSDI), Santa Clara, CA, USA, 2016, pp. 45–59.
services using blockchains: A state of the art survey,’’ IEEE Commun.
[35] Y. Sompolinsky and A. Zohar, ‘‘Secure high-rate transaction processing
Surveys Tuts., vol. 21, no. 1, pp. 858–880, 1st Quart., 2019, doi: 10.
in bitcoin,’’ in Proc. Int. Conf. Financial Cryptogr. Data Secur., San Juan,
1109/COMST.2018.2863956.
Puerto Rico, 2015, pp. 507–527.
[10] R. Zhang, R. Xue, and L. Liu, ‘‘Security and privacy on blockchain,’’ [36] V. Bagaria, S. Kannan, D. Tse, G. Fanti, and P. Viswanath, ‘‘Prism:
ACM Comput. Surv., vol. 52, no. 3, pp. 1–34, 2019. Deconstructing the blockchain to approach physical limits,’’ in Proc.
[11] E. Zaghloul, T. Li, M. W. Mutka, and J. Ren, ‘‘Bitcoin and blockchain: ACM SIGSAC Conf. Comput. Commun. Secur., New York, NY, USA,
Security and privacy,’’ IEEE Internet Things J., vol. 7, no. 10, Nov. 2019, pp. 585–602.
pp. 1028–10313, Oct. 2020, doi: 10.1109/JIOT.2020.3004273. [37] A. Kiayias, A. Russell, B. David, and R. Oliynykov, ‘‘Ouroboros:
[12] P. J. Taylor, T. Dargahi, A. Dehghantanha, R. M. Parizi, and A provably secure proof-of-stake blockchain protocol,’’ in Proc. Annu.
K.-K.-R. Choo, ‘‘A systematic literature review of blockchain cyber Int. Cryptol. Conf., Santa Barbara, CA, USA, 2017, pp. 357–388.
security,’’ Digit. Commun. Netw., vol. 6, no. 2, pp. 147–156, May 2020. [38] D. R. Lee, Y. Jang, and H. Kim, ‘‘Poster: A proof-of-stake (PoS)
[13] X. Wang, X. Zha, W. Ni, R. P. Liu, Y. J. Guo, X. Niu, and K. Zheng, ‘‘Sur- blockchain protocol using fair and dynamic sharding management,’’ in
vey on blockchain for Internet of Things,’’ Comput. Commun., vol. 136, Proc. ACM SIGSAC Conf. Comput. Commun. Secur., New York, NY,
pp. 10–29, Feb. 2019. USA, Nov. 2019, pp. 2553–2555.
[14] A. Ahl, M. Yarime, K. Tanaka, and D. Sagawa, ‘‘Review of blockchain- [39] I. Bentov, C. Lee, A. Mizrahi, and M. Rosenfeld, ‘‘Proof of activity:
based distributed energy: Implications for institutional development,’’ Extending Bitcoin’s proof of work via proof of stake,’’ ACM SIGMET-
Renew. Sustain. Energy Rev., vol. 107, pp. 200–211, Jun. 2019. RICS Perform. Eval. Rev., vol. 42, no. 3, pp. 34–37, Dec. 2014.

VOLUME 8, 2020 187199

 Y. Zou et al.: Focus on Blockchain: A Comprehensive Survey on Academic and Application

[40] J. Blocki and H. S. Zhou, ‘‘Designing proof of human-work puzzles for [62] M. Montecchi, K. Plangger, and M. Etter, ‘‘It’s real, trust me! Establishing
cryptocurrency and beyond,’’ in Proc. Theory Cryptogr. Conf., Berlin, supply chain provenance using blockchain,’’ Bus. Horizons, vol. 62, no. 3,
Germany, 2016, pp. 517–546. pp. 283–293, May 2019.
[41] S. Dziembowski, S. Faust, V. Kolmogorov, and K. Pietrzak, ‘‘Proofs of [63] C. G. Schmidt and S. M. Wagner, ‘‘Blockchain and supply chain relations:
space,’’ in Proc. Annu. Cryptol. Conf., Santa Barbara, CA, USA, 2015, A transaction cost theory perspective,’’ J. Purchasing Supply Manage.,
pp. 585–605. vol. 25, no. 4, Oct. 2019, Art. no. 100552.
[42] M. Sabt, M. Achemlal, and A. Bouabdallah, ‘‘Trusted execution envi- [64] J. Li, F. Qu, X. Tu, T. Fu, J. Guo, and J. Zhu, ‘‘Public philanthropy
ronment: What it is, and what it is not,’’ in Proc. IEEE Trust- logistics platform based on blockchain technology for social welfare
com/BigDataSE/ISPA, vol. 1, Aug. 2015, pp. 57–64. maximization,’’ in Proc. 8th Int. Conf. Logistics, Informat. Service Sci.
[43] P. Das, L. Eckey, T. Frassetto, D. Gens, K. Hostáková, P. Jauernig, (LISS), Aug. 2018, pp. 1–9.
S. Faust, and A.-R. Sadeghi, ‘‘FastKitten: Practical smart contracts on [65] D. Sun, W. Ying, X. Zhang, and L. Feng, ‘‘Developing a blockchain-
bitcoin,’’ in Proc. USENIX Secur. Symp., Berkeley, CA, USA, 2019, based loyalty programs system to hybridize business and charity: An
pp. 801–818. action design research,’’ in Proc. 40th Int. Conf. Inf. Syst. (ICIS), Munich,
[44] S. Steffen, B. Bichsel, M. Gersbach, N. Melchior, P. Tsankov, and Germany, 2019.
M. Vechev, ‘‘Zkay: Specifying and enforcing data privacy in smart [66] B. Reinsberg, ‘‘Blockchain technology and the governance of foreign
contracts,’’ in Proc. ACM SIGSAC Conf. Comput. Commun. Secur., aid,’’ J. Institutional Econ., vol. 15, no. 3, pp. 413–429, Jun. 2019.
New York, NY, USA, Nov. 2019, pp. 1759–1776. [67] S. Jain and R. Simha, ‘‘Blockchain for the common good: A digital
[45] C. Ganesh, C. Orlandi, and D. Tschudi, ‘‘Proof-of-stake protocols for currency for citizen philanthropy and social entrepreneurship,’’ in Proc.
privacy-aware blockchains,’’ in Proc. Annu. Int. Conf. Theory Appl. Cryp- IEEE Int. Conf. Internet Things (iThings) IEEE Green Comput. Commun.
tograph. Techn., Darmstadt, Germany, 2019, pp. 690–719. (GreenCom) IEEE Cyber, Phys. Social Comput. (CPSCom) IEEE Smart
[46] R. Zhang and B. Preneel, ‘‘Lay down the common metrics: Evaluating Data (SmartData), Jul. 2018, pp. 1387–1394.
proof-of-work consensus protocols’ security,’’ in Proc. IEEE Symp. Secur. [68] A. Alammary, S. Alhazmi, M. Almasri, and S. Gillani, ‘‘Blockchain-
Privacy (SP), San Francisco, CA, USA, May 2019, pp. 175–192. based applications in education: A systematic review,’’ Appl. Sci., vol. 9,
[47] M. Rodler, W. Li, G. O. Karame, and L. Davi, ‘‘Sereum: Protecting exist- no. 12, p. 2400, Jun. 2019.
ing smart contracts against re-entrancy attacks,’’ in Proc. Netw. Distrib. [69] M. Han, Z. Li, J. He, D. Wu, Y. Xie, and A. Baba, ‘‘A novel blockchain-
Syst. Secur. Symp., San Diego, CA, USA, 2019, pp. 1–15. based education records verification solution,’’ in Proc. 19th Annu. SIG
[48] S. Matetic, K. Wüst, M. Schneider, K. Kostianinen, G. Karame, and Conf. Inf. Technol. Edu., New York, NY, USA, Sep. 2018, pp. 178–183.
S. Capkun, ‘‘BITE: Bitcoin lightweight client privacy using trusted exe- [70] A. Srivastava, P. Bhattacharya, A. Singh, A. Mathur, O. Prakash, and
cution,’’ in Proc. USENIX Secur. Symp., Berkeley, CA, USA, 2019, R. Pradhan, ‘‘A distributed credit transfer educational framework based
pp. 783–900. on blockchain,’’ in Proc. 2nd Int. Conf. Adv. Comput., Control Commun.
[49] T. Cai, Z. Yang, W. Chen, Z. Zheng, and Y. Yu, ‘‘A blockchain-assisted Technol. (IAC3T), Allahabad, India, Sep. 2018, pp. 54–59.
trust access authentication system for solid,’’ IEEE Access, vol. 8,
[71] R. Chaudhari, R. Deshmukh, V. Bari, S. Rajput, and K. Rode, ‘‘Medicine
pp. 71605–71616, 2020.
traceability system using blockchain,’’ Int. J. Trend Sci. Res. Develop.,
[50] Y. Kwon, H. Kim, J. Shin, and Y. Kim, ‘‘Bitcoin vs. Bitcoin cash:
vol. 3, no. 4, pp. 346–349, 2019.
Coexistence or downfall of bitcoin cash?’’ in Proc. IEEE Symp. Secur.
[72] X. Xia, X. Lin, W. Dong, and Z. He, ‘‘Design of traceability system for
Privacy (SP), San Francisco, CA, USA, May 2019, pp. 935–951.
medical devices based on blockchain,’’ J. Phys., Conf. Ser., vol. 1314,
[51] G. Malavolta, P. Moreno-Sanchez, C. Schneidewind, A. Kate, and
Oct. 2019, Art. no. 012067.
M. Maffei, ‘‘Anonymous multi-hop locks for blockchain scalability and
[73] R. Kumar and R. Tripathi, ‘‘Traceability of counterfeit medicine supply
interoperability,’’ in Proc. Netw. Distrib. Syst. Secur. Symp., San Diego,
chain through blockchain,’’ in Proc. 11th Int. Conf. Commun. Syst. Netw.,
CA, USA, 2019, pp. 1–30.
Jan. 2019, pp. 568–570.
[52] S. Dziembowski, L. Eckey, S. Faust, J. Hessse, and K. Hostáková, ‘‘Multi-
party virtual state channels,’’ in Proc. Annu. Int. Conf. Theory Appl. [74] S. Rouhani, L. Butterworth, A. D. Simmons, D. G. Humphery, and
Cryptograph. Techn., Darmstadt, Germany, 2019, pp. 625–656. R. Deters, ‘‘MediChainTM: A secure decentralized medical data asset
[53] K. Wüst, K. Kostiainen, V. Čapkun, and S. Čapkun, ‘‘PRCash: Fast, management system,’’ in Proc. IEEE Int. Conf. Internet Things (iThings)
private and regulated transactions for digital currencies,’’ in Proc. Int. IEEE Green Comput. Commun. (GreenCom) IEEE Cyber, Phys. Social
Conf. Financial Cryptogr. Data Secur., Saint Kitts, Nevis, vol. 11598, Comput. (CPSCom) IEEE Smart Data (SmartData), Halifax, NS, Canada,
2019, pp. 158–178. Jul. 2018, pp. 1533–1538.
[54] L. Cocco, A. Pinna, and M. Marchesi, ‘‘Banking on blockchain: Costs [75] A. A. Alomar, M. Z. A. Bhuiyan, and A. Basu, S. Kiyomoto, and
savings thanks to the blockchain technology,’’ Future Internet, vol. 9, M. S. Rahman, ‘‘Privacy-friendly platform for healthcare data in cloud
no. 3, p. 25, Jun. 2017. based on blockchain environment,’’ Future Gener. Comput. Syst., vol. 95,
[55] E. Avgouleas and A. Kiayias, ‘‘The promise of blockchain technology for pp. 511–521, Jun. 2019.
global securities and derivatives markets: The new financial ecosystem [76] A. E. Nemade, S. S. Kadam, R. N. Choudhary, S. S. Fegade, and
and the ’holy grail’ of systemic risk containment,’’ Eur. Bus. Org. Law K. Agarwal, ‘‘Blockchain technology used in taxation,’’ in Proc. Int. Conf.
Rev., vol. 20, no. 1, pp. 81–110, 2019. Vis. Towards Emerg. Trends Commun. Netw. (ViTECoN), Vellore, India,
[56] A. Dorri, S. S. Kanhere, R. Jurdak, and P. Gauravaram, ‘‘LSB: Mar. 2019, pp. 1–4.
A lightweight scalable blockchain for IoT security and anonymity,’’ [77] S. Xiao, X. A. Wang, W. Wang, and H. Wang, ‘‘Survey on blockchain-
J. Parallel Distrib. Comput., vol. 134, pp. 180–197, Dec. 2019. based electronic voting,’’ in Proc. Int. Conf. Intell. Netw. Collaborative
[57] M. Wazid, A. K. Das, V. Odelu, N. Kumar, M. Conti, and M. Jo, ‘‘Design Syst., Oita, Japan, vol. 1035, 2019, pp. 559–567.
of secure user authenticated key management protocol for generic IoT [78] T. Nadar, M. Rawal, J. Patel, A. Shah, and A. S. Revathi, ‘‘A novel
networks,’’ IEEE Internet Things J., vol. 5, no. 1, pp. 269–282, Feb. 2018. approach to implement decentralized voting system using blockchain,’’
[58] H. Shafagh, L. Burkhalter, A. Hithnawi, and S. Duquennoy, ‘‘Towards in Proc. Int. Conf. Wireless Commun., vol. 36, 2020, pp. 471–479.
blockchain-based auditable storage and sharing of IoT data,’’ in Proc. [79] B. Shahzad and J. Crowcroft, ‘‘Trustworthy electronic voting using
Cloud Comput. Secur. Workshop (CCSW), New York, NY, USA, 2017, adjusted blockchain technology,’’ IEEE Access, vol. 7, pp. 24477–24488,
pp. 45–50. 2019.
[59] C. Qu, M. Tao, J. Zhang, X. Hong, and R. Yuan, ‘‘Blockchain based [80] M. Kuperberg, S. Kemper, and C. Durak, ‘‘Blockchain usage for
credibility verification method for IoT entities,’’ Secur. Commun. Netw., government-issued electronic IDs: A survey,’’ in Proc. Int. Conf. Adv. Inf.
vol. 2018, pp. 1–11, Jun. 2018. Syst. Eng., Rome, Italy, vol. 349, 2019, pp. 155–167.
[60] M. Li, S. P. Guan, and R. R. Du, ‘‘Research on the application of customs [81] V. Odelu, ‘‘IMBUA: Identity management on blockchain for biometrics-
supervision on cross-border import e-commerce retail business from the based user authentication,’’ in Proc. Int. Congr. Blockchain Appl., Ávila,
perspective of blockchain,’’ in Proc. 6th Int. Conf. Manage. Sci. Manage. Spain, vol. 1010, 2019, pp. 1–10.
Innov. (MSMI), 2019, pp. 1–5. [82] E. Mengelkamp, B. Notheisen, C. Beer, D. Dauer, and C. Weinhardt,
[61] Q. Tao, X. Cui, X. Huang, A. M. Leigh, and H. Gu, ‘‘Food safety super- ‘‘A blockchain-based smart grid: Towards sustainable local energy mar-
vision system based on hierarchical multi-domain blockchain network,’’ kets,’’ Comput. Sci.-Res. Develop., vol. 33, nos. 1–2, pp. 207–214,
IEEE Access, vol. 7, pp. 51817–51826, 2019. Feb. 2018.

187200 VOLUME 8, 2020

Y. Zou et al.: Focus on Blockchain: A Comprehensive Survey on Academic and Application

[83] J. Gao, K. O. Asamoah, E. B. Sifah, A. Smahi, Q. Xia, H. Xia, X. Zhang, [105] D. Di Francesco Maesa, A. Marino, and L. Ricci, ‘‘Data-driven analysis of
and G. Dong, ‘‘GridMonitoring: Secured sovereign blockchain based bitcoin properties: Exploiting the users graph,’’ Int. J. Data Sci. Analytics,
monitoring on smart grid,’’ IEEE Access, vol. 6, pp. 9917–9925, 2018. vol. 6, no. 1, pp. 63–80, Aug. 2018.
[84] K. Wu, B. Peng, H. Xie, and Z. Huang, ‘‘An information entropy method [106] P. Zheng, Z. Zheng, X. Luo, X. Chen, and X. Liu, ‘‘A detailed and
to quantify the degrees of decentralization for blockchain systems,’’ in real-time performance monitoring framework for blockchain systems,’’
Proc. IEEE 9th Int. Conf. Electron. Inf. Emergency Commun. (ICEIEC), in Proc. 40th Int. Conf. Softw. Eng. Softw. Eng. Pract. (ICSE-SEIP),
Beijing, China, Jul. 2019, pp. 1–6. Gothenburg, Sweden, 2018, pp. 134–143.
[85] F. Wessling, C. Ehmke, O. Meyer, and V. Gruhn, ‘‘Towards blockchain [107] P. Tasca, A. Hayes, and S. Liu, ‘‘The evolution of the bitcoin economy:
tactics: Building hybrid decentralized software architectures,’’ in Proc. Extracting and analyzing the network of payment relationships,’’ J. Risk
IEEE Int. Conf. Softw. Archit. Companion (ICSA-C), Hamburg, Germany, Finance, vol. 19, no. 2, pp. 94–126, 2018.
Mar. 2019, pp. 234–237.
[86] F. Hawlitschek, B. Notheisen, and T. Teubner, ‘‘The limits of trust-free YIJUN ZOU was born in Jiangsu Province, China.
systems: A literature review on blockchain technology and trust in the He received the M.Sc. degree in management from
sharing economy,’’ Electron. Commerce Res. Appl., vol. 29, pp. 50–63, the University of International Business and Eco-
May 2018. nomics. He is currently pursuing the Ph.D. degree
[87] W. Hong, Y. Cai, Z. Yu, and X. Yu, ‘‘An agri-product traceability sys- in management science and engineering with the
tem based on IoT and blockchain technology,’’ in Proc. 1st IEEE Int.
Beijing University of Posts and Telecommunica-
Conf. Hot Inf.-Centric Netw. (HotICN), Shenzhen, China, Aug. 2018,
tions. He is also the Vice Director of the Depart-
pp. 254–255.
[88] J. Li and X. Wang, ‘‘Research on the application of blockchain in the
ment of Finance, BUPT. He is also the Account-
traceability system of agricultural products,’’ in Proc. 2nd IEEE Adv. ing Leader of the Chinese Central Government
Inf. Manage., Communicates, Electron. Autom. Control Conf. (IMCEC), Department. His research interests include big
Xi’an, China, May 2018, pp. 2637–2640. data, blockchain, data assets, and financial management.
[89] X. Liu, Z. Wang, C. Jin, F. Li, and G. Li, ‘‘A blockchain-based
medical data sharing and protection scheme,’’ IEEE Access, vol. 7, TING MENG received the B.S. degree in soft-
pp. 118943–118953, 2019. ware engineering from Yanshan University, China,
[90] S. V. Bojja, G. Fanti, and P. Viswanath, ‘‘Dandelion: Redesigning the in 2018. She is currently pursuing the M.S. degree
bitcoin network for anonymity,’’ ACM Meas. Anal. Comput. Syst., vol. 1,
with the School of Software Engineering, Beijing
no. 1, pp. 1–34, 2017.
University of Posts and Telecommunications. Her
[91] Q. Feng, D. He, S. Zeadally, M. K. Khan, and N. Kumar, ‘‘A survey
on privacy protection in blockchain system,’’ J. Netw. Comput. Appl., research interests include blockchain privacy pro-
vol. 126, pp. 45–58, Jan. 2019. tection, blockchain transaction data analysis, and
[92] A. Singh, T.-W. Ngan, P. Druschel, and D. S. Wallach, ‘‘Eclipse attacks network security.
on overlay networks: Threats and defenses,’’ in Proc. IEEE INFOCOM.
25TH IEEE Int. Conf. Comput. Commun., Barcelona, Spain, Apr. 2006,
pp. 1–12.
[93] J. R. Douceur, ‘‘The Sybil attack,’’ in Proc. Int. Workshop Peer-Peer Syst., PENG ZHANG received the B.S. degree in soft-
Cambridge, MA, USA, 2002, pp. 251–260. ware engineering from Shanxi University, China,
[94] G. Karame, E. Androulaki, and S. Capkun, ‘‘Two bitcoins at the price in 2018. He is currently pursuing the M.S.
of one? Double-spending attacks on fast payments in bitcoin,’’ IACR degree with the School of Software Engineering,
Cryptol. ePrint Arch., vol. 2012, no. 248, 2012. Beijing University of Posts and Telecommunica-
[95] S. Sayeed and H. Marco-Gisbert, ‘‘Assessing blockchain consensus and tions. His research interests include blockchain
security mechanisms against the 51% attack,’’ Appl. Sci., vol. 9, no. 9, privacy protection, blockchain consensus algo-
p. 1788, Apr. 2019. rithm, and network security.
[96] J. Xie, F. R. Yu, T. Huang, R. Xie, J. Liu, and Y. Liu, ‘‘A survey
on the scalability of blockchain systems,’’ IEEE Netw., vol. 33, no. 5,
pp. 166–173, Sep. 2019.
[97] A. A. Monrat, O. Schelen, and K. Andersson, ‘‘A survey of blockchain WENZHEN ZHANG received the B.S. degree in
from the perspectives of applications, challenges, and opportunities,’’
software engineering from the Beijing University
IEEE Access, vol. 7, pp. 117134–117151, 2019.
of Posts and Telecommunications, in 2019, where
[98] L. Ismail and H. Materwala, ‘‘A review of blockchain architecture and
consensus protocols: Use cases, challenges, and solutions,’’ Symmetry, she is currently pursuing the M.S. degree with
vol. 11, no. 10, p. 1198, 2019. the School of Software Engineering. Her research
[99] Q. Wang, S. Wang, P. Zhang, L. He, X. Li, S. Cheng, and S. Zhou, interests include blockchain privacy protection,
‘‘An achieving data exchange cross-chain alliance protocol,’’ J. Phys., blockchain, traction data analysis, and network
Conf. Ser., vol. 1213, Jun. 2019, Art. no. 042037. security.
[100] J. Y. Zie, J. C. Deneuville, J. Briffaut, and B. Nguyen, ‘‘Extending atomic
cross-chain swaps,’’ in Proc. DPM, Int. Workshop Data Privacy Manage.
CBT, Int. Workshop Cryptocurrencies Blockchain Technol., Luxembourg
City, Luxembourg, vol. 11737, 2019, pp. 219–229. HUIYANG LI was born in Taiyuan, Shanxi, China,
[101] D. Fakhri and K. Mutijarsa, ‘‘Secure IoT communication using in 1992. She received the B.S. degree in elec-
blockchain technology,’’ in Proc. Int. Symp. Electron. Smart Devices tronic information engineering from the Tian-
(ISESD), Bandung, Indonesia, Oct. 2018, pp. 1–6. jin College, University of Science & Technology
[102] H. Cui, Z. Chen, Y. Xi, H. Chen, and J. Hao, ‘‘IoT data management and
Beijing, Tianjin, China, in 2014, and the M.S.
lineage traceability: A blockchain-based solution,’’ in Proc. IEEE/CIC
degree in software engineering from The Univer-
Int. Conf. Commun. Workshops China (ICCC Workshops), Changchun,
China, Aug. 2019, pp. 239–244.
sity of Texas at Arlington, Arlington, TX, USA,
[103] M. S. Devi, R. Suguna, and P. M. Abhinaya, ‘‘Integration of blockchain in 2017, where she is currently pursuing the Ph.D.
and IoT in satellite monitoring process,’’ in Proc. IEEE Int. Conf. Electr., degree in computer science. Since 2018, she has
Comput. Commun. Technol. (ICECCT), Coimbatore, India, Feb. 2019, been a Research Assistant with the ACES Labora-
pp. 1–6. tory, The University of Texas at Arlington. Her research interests include the
[104] K. Salah, M. H. U. Rehman, N. Nizamuddin, and A. Al-Fuqaha, SLO Tail latency guaranteed data center job scheduling, blockchain, resource
‘‘Blockchain for AI: Review and open research challenges,’’ IEEE management in cloud, and edge computing.
Access, vol. 7, pp. 10127–10149, 2019.

VOLUME 8, 2020 187201