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Yli-Huumo, Jesse; Ko, Deokoon; Choi, Sujin; Park, Sooyong; Smolander, Kari
Where Is Current Research on Blockchain Technology? - A Systematic Review
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DOI:
10.1371/journal.pone.0163477
Published: 03/10/2016
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Please cite the original version:
Yli-Huumo, J., Ko, D., Choi, S., Park, S., & Smolander, K. (2016). Where Is Current Research on Blockchain
Technology? - A Systematic Review. PloS one, 10(11), [e0163477].
https://doi.org/10.1371/journal.pone.0163477
RESEARCH ARTICLE
Where Is Current Research on Blockchain
Technology?—A Systematic Review
Jesse Yli-Huumo
1
, Deokyoon Ko
2
, Sujin Choi
4
*, Sooyong Park
2
, Kari Smolander
3
1 Dept. of Innovation and Software, Lappeenranta University of Technology, Lappeenranta, Finland, 2 Dept.
of Computer Science & Engineering, Sogang University, Seoul, South Korea, 3 Dept. of Computer Science,
Aalto University, Helsinki, Finland, 4 Sogang Institute of Advanced Technology, Sogang University, Seoul,
South Korea
*
sujinchoi@sogang.ac.kr
Abstract
Blockchain is a decentralized transaction and data management technology developed first
for Bitcoin cryptocurrency. The interest in Blockchain technology has been increasing since
the idea was coined in 2008. The reason for the interest in Blockchain is its central attri-
butes that provide security, anonymity and data integrity without any third party organiza-
tion in control of the transactions, and therefore it creates interesting research areas,
especially from the perspective of technical challenges and limitations. In this research, we
have conducted a systematic mapping study with the goal of collecting all relevant research
on Blockchain technology. Our objective is to understand the current research topics, chal-
lenges and future directions regarding Blockchain technology from the technical perspec-
tive. We have extracted 41 primary papers from scientific databases. The results show that
focus in over 80% of the papers is on Bitcoin system and less than 20% deals with other
Blockchain applications including e.g. smart contracts and licensing. The majority of
research is focusing on revealing and improving limitations of Blockchain from privacy and
security perspectives, but many of the proposed solutions lack concrete evaluation on their
effectiveness. Many other Blockchain scalability related challenges including throughput
and latency have been left unstudied. On the basis of this study, recommendations on
future research directions are provided for researchers.
Introduction
Currency transactions between persons or companies are often centralized and controlled by a
third party organization. Making a digital payment or currency transfer requires a bank or
credit card provider as a middleman to complete the transaction. In addition, a transaction
causes a fee from a bank or a credit card company. The same process applies also in several
other domains, such as games, music, software etc. The transaction system is typically central-
ized, and all data and information are controlled and managed by a third party organization,
rather than the two principal entities involved in the transaction. Blockchain technology has
PLOS ONE | DOI:10.1371/journal.pone.0163477 October 3, 2016 1 / 27
a11111
OPEN ACCESS
Citation: Yli-Huumo J, Ko D, Choi S, Park S,
Smolander K (2016) Where Is Current Research on
Blockchain Technology?—A Systematic Review.
PLoS ONE 11(10): e0163477. doi:10.1371/journal.
pone.0163477
Editor: Houbing Song, West Virginia University,
UNITED STATES
Received: May 10, 2016
Accepted: September 9, 2016
Published: October 3, 2016
Copyright: © 2016 Yli-Huumo et al. This is an open
access article distributed under the terms of the
Creative Commons Attribution License, which
permits unrestricted use, distribution, and
reproduction in any medium, provided the original
author and source are credited.
Data Availability Statement: All relevant data are
within the paper.
Funding: The author(s) received no specific
funding for this work.
Competing Interests: The authors have declared
that no competing interests exist.
been developed to solve this issue. The goal of Blockchain technology is to create a decentral-
ized environment where no third party is in control of the transactions and data.
Blockchain is a distributed database solution that maintains a continuously growing list of
data records that are confirmed by the nodes participating in it. The data is recorded in a public
ledger, including information of every transaction ever completed. Blockchain is a decentral-
ized solution which does not require any third party organization in the middle. The informa-
tion about every transaction ever completed in Blockchain is shared and available to all nodes.
This attribute makes the system more transparent than centralized transactions involving a
third party. In addition, the nodes in Blockchain are all anonymous, which makes it more
secure for other nodes to confirm the transactions. Bitcoin was the first application that intro-
duced Blockchain technology. Bitcoin created a decentralized environment for cryptocurrency,
where the participants can buy and exchange goods with digital money.
However, even though Blockchain seems to be a suitable solution for conducting transac-
tions by using cryptocurrencies,it has still some technical challenges and limitations that need
to be studied and addressed. High integrity of transactions and security, as well as privacy of
nodes are needed to prevent attacks and attempts to disturb transactions in Blockchain [
1]. In
addition, confirming transactions in the Blockchain requires a computational power.
It is important to identify what topics have been already studied and addressed in Block-
chain and what are currently the biggest challenges and limitations that need further studies.
To address these questions, we decided to use a systematic mapping study process [
2] to iden-
tify relevant papers related to Blockchain. In the systematic mapping study, we applied a well-
designed research protocol to search for material in scientific databases. The produced map of
current research on Blockchain will help other researchers and practitioners in identifying pos-
sible research areas and questions for future research.
Although cryptocurrenciesare also a business and management topic, we decided to narrow
down the research topic to the technical perspective of Blockchain. Our objective was to find
and map all papers with technical viewpoints on Blockchain. We were interested in finding
Blockchain research topics related to various technical areas, such as security, performance,
data integrity, privacy, and scalability.
The rest of the paper is organized as follows. Section 2 introduces the background of Block-
chain and Bitcoin. In addition, we present some already identified challenges and technical lim-
itations of Blockchain technology. In Section 3, we describe the applied research methodology
and the process of collecting relevant research papers. Section 4 presents the results of the gath-
ered papers and extracted data. Section 5 presents the identified classification schemes. Section
6 discusses the study and answers the research questions. Section 7 concludes the paper.
Background
Blockchain, mostly known as the technology running the Bitcoin cryptocurrency, is a public
ledger system maintaining the integrity of transaction data [
1]. Blockchain technology was first
used when the Bitcoin cryptocurrency was introduced. To this day, Bitcoin is still the most
commonly used application using Blockchain technology [
3]. Bitcoin is a decentralized digital
currency payment system that consists of a public transaction ledger called Blockchain [
4]. The
essential feature of Bitcoin is the maintainability of the value of the currency without any orga-
nization or governmental administration in control. The number of transfers and users in the
Bitcoin network is constantly increasing [
5]. In addition, the conversions with traditional cur-
rencies, e.g. KRW, EUR and USD, occur constantly in currency exchange markets [
6][7]. Bit-
coin has therefore gained the attention of various communities and is currently the most
successful digital currency using Blockchain technology [
6].
Where Is Current Research on Blockchain Technology?—A Systematic Review
PLOS ONE | DOI:10.1371/journal.pone.0163477 October 3, 2016 2 / 27
Bitcoin uses the public key infrastructure (PKI) mechanism [8]. In PKI, the user has one
pair of public and private keys. The public key is used in the address of the user Bitcoin wallet,
and the private key is for the authentication of the user. The transaction of Bitcoin consists of
the public key of the sender, multiple public keys of the receiver, and the value transferred. In
about ten minutes, the transaction will be written in a block. This new block is then linked to a
previously written block. All blocks, including information about every transaction made, are
stored in the disk storage of the users, called nodes. All the nodes store information about all
recorded transactions of the Bitcoin network and check the correctness of each new transaction
made by using previous blocks. The nodes are rewarded by checking the correctness of transac-
tions. This method is called mining, and it is confirmed with Proof-of-Work, which is one of
the main concepts of Blockchain technology. When all transactions are successfully confirmed,
a consensus exists between all the nodes. The new blocks are linked to previous blocks and all
the blocks are aligned in one continuous chain. This chain of blocks is the public ledger tech-
nique of Bitcoin, called Blockchain.
Blockchain is the decentralized managing technique of Bitcoin, designed for issuing and
transferring money for the users of the Bitcoin currency. This technique can support the public
ledger of all Bitcoin transactions that have ever been executed, without any control of a third
party organization [
1]. The advantage of Blockchain is that the public ledger cannot be modi-
fied or deleted after the data has been approved by all nodes. This is why Blockchain is well-
known of its data integrity and security characteristics. Blockchain technology can also be
applied to other types of uses. It can for example create an environment for digital contracts
and peer-to-peer data sharing in a cloud service [
1]. The strong point of Blockchain technique,
data integrity, is the reason why its use extends also to other services and applications.
Blockchain technology has also some technical challenges and limitations that have been
identified. Swan [
1] presents seven technical challenges and limitations for the adaptation of
Blockchain technology in the future:
• Throughput: The potential throughput of issues in the Bitcoin network is currently maxi-
mized to 7tps (transactions per second). Other transaction processing networks are VISA
(2,000tps) and Twitter (5,000tps). When the frequency of transactions in Blockchain
increases to similar levels, the throughput of the Blockchain network needs to be improved.
• Latency: To create sufficient security for a Bitcoin transaction block, it takes currently
roughly 10 minutes to complete one transaction. To achieve efficiency in security, more time
has to be spent on a block, because it has to outweigh the cost of double spending attacks.
Double-spending is the result of successful spending of money more than once [
9]. Bitcoin
protects against double spending by verifying each transaction added to the block chain, to
ensure that the inputs for the transaction have not been spent previously [
9]. This makes
latency a big issue in Blockchain currently. Making a block and confirming the transaction
should happen in seconds, while maintaining security. To complete a transaction e.g. in
VISA takes only a few seconds, which is a huge advantage compared to Blockchain.
• Size and bandwidth: At the moment, the size of a Blockchain in the Bitcoin network is over
50,000MB (February 2016). When the throughput increases to the levels of VISA, Blockchain
could grow 214PB in each year. The Bitcoin community assumes that the size of one block is
1MB, and a block is created every ten minutes [
10]. Therefore, there is a limitation in the num-
ber of transactions that can be handled (on average 500 transaction in one block) [11]. If the
Blockchain needs to control more transactions, the size and bandwidth issues have to be solved.
• Security: The current Blockchain has a possibility of a 51% attack. In a 51% attack a single
entity would have full control of the majority of the network’s mining hash-rate and would
Where Is Current Research on Blockchain Technology?—A Systematic Review
PLOS ONE | DOI:10.1371/journal.pone.0163477 October 3, 2016 3 / 27
be able to manipulate Blockchain. To overcome this issue, more research on security is
necessary.
• Waste d resources: Mining Bitcoin wastes huge amounts of energy ($15million/day). The
waste in Bitcoin is caused by the Proof-of-Work effort. There are some alternatives in indus-
try fields, such as proof-of-stake. With Proof-of-Work, the probability of mining a block
depends on the work done by the miner [
12]. However, in Proof-of-Stake, the resource that
is compared is the amount of Bitcoin a miner holds [
12]. For example, someone holding 1%
of the Bitcoin can mine 1% of the “Proof-of-Stake blocks” [12]. The issue with wasted
resources needs to be solved to have more efficient mining in Blockchain.
• Usability: The Bitcoin API for developing services is difficult to use. There is a need to
develop a more developer-friendly API for Blockchain. This could resemble REST APIs.
• Versioning, hard forks, multiple chains: A small chain that consists of a small number of
nodes has a higher possibility of a 51% attack. Another issue emerges when chains are split
for administrative or versioning purposes.
Overall, Blockchain as a technology has the potential to change the way how transactions
are conducted in everyday life. In addition, the applications of Blockchain are not limited to
cryptocurrencies,but the technology could be possibly applied in various environments where
some forms of transactions are done. The research on the possibilities of Blockchain in applica-
tions is certainly an interesting area for future research, but at the moment Blockchain suffers
from technical limitations and challenges. Anonymity, data integrity and security attributes set
a lot of interesting challenges and questions that need to be solved and assessed with high qual-
ity research. Scalability is also an issue that needs to be solved for future needs. Therefore, to
identify and understand the current status of research conducted on Blockchain, it is important
to gather all relevant research. It is then possible to evaluate what challenges and questions
have been tackled and answered, and what are the most problematic issues in Blockchain at the
moment.
Research methodology
Systematic mapping study was selected as the research methodology for this study. The goal of
a systematic mapping study is to provide an overview of a research area, to establish if research
evidence exists, and quantify the amount of evidence [
2]. In this study we follow the systematic
mapping process described by Petersen et al. [
13]. We also use guidelines for a systematic liter-
ature review described by Kitchenham and Charters [
2] to search for relevant papers. We
chose the systematic mapping process as our research methodology because our goal was to
explore the existing studies related to Blockchain technology. The results of the mapping study
would help us to identify and map research areas related to Blockchain technology and possible
research gaps. The process for the systematic mapping study is presented in
Fig 1, and consists
of five process steps and outcomes. The Prisma Checklist is provided in
S1 Checklist.
Definition of research questions
The first stage of the systematic mapping process is the definition of the research questions.
The goal of this study was to provide an overview of the current research on Blockchain tech-
nology. Therefore, we defined four research questions:
• RQ1: What research topics have been addressed in current research on Blockchain?
The main research question of this mapping study is to understand the current research top-
ics on Blockchain. By collecting all the relevant papers from scientific databases, we would be
Where Is Current Research on Blockchain Technology?—A Systematic Review
PLOS ONE | DOI:10.1371/journal.pone.0163477 October 3, 2016 4 / 27