Computer Networks 198 (2021) 108395 Available online 8 August 2021 1389-1286/© 2021 Elsevier B.V. All rights reserved. Blockchain -based Initiatives: Current state and challenges Shadab Alam a , Mohammed Shuaib a , Wazir Zada Khan b , Sahil Garg c , Georges Kaddoum c , M. Shamim Hossain d , Yousaf Bin Zikria e, * a College of Computer Science & IT, Jazan University, Jazan, Saudi Arabia b Department of Computer Science, Capital University of Science and Technology, Islamabad, Pakistan c Ecole de technologie sup’erieure, Universit’e du Qu’ebec, Montr’eal QC H3C 1K3, Canada d Department of Software Engineering, College of Computer and Information Sciences, King Saud University, Riyadh 11543, Saudi Arabia e Department of Information and Communication Engineering, Yeungnam University, Gyeongsan 38541, South Korea A R T I C L E INFO Keywords: Blockchain Blockchain Initiatives Challenges for blockchain Distributed ledger Smart contracts E-Government ABSTRACT Blockchain is considered a distributed ledger that can transact securely and trustfully without involving any third party. It has caused a lot of interest in various sectors, like government, finance, banking, etc. Blockchain technology is suitable for areas where multiple data storage and transaction types generally require the third party to authenticate the transactions involving transaction cost and authentication issues. In this paper, various aspects of Blockchain technology applications in public concern sectors have been analyzed in detail. This paper also reviews the multiple case studies and implementations of Blockchain technology in these sectors and their current status that provide a detailed insight into all the aspects of its application. This paper finally comes up with various implementation requirements in Government, Health, Finance, Economics, and Energy. Further, it identifies the challenges in successfully implementing Blockchain technology in these mentioned sectors to provide a reference for future deployments. 1. Introduction Blockchain technology’s inception is considered from Satoshi Nakamoto’s famous paper on Bitcoin that describes Blockchain tech- nology as a means of direct financial transaction between parties without and trusted third party [1]. It is a decentralized ledger in which all transactions are safely accumulated in blocks, with each block con- nected to the next in a chain. When a new block is attached to the chain, it is appended. The Blockchain consists of a distributed database con- taining records of all the transactions and events, and it is a special form of distributed ledger that maintains a log of stored data in the form of the ledger in which a new transaction or information can be appended at the end. It does not allow any modification in the already stored data items. Any newly created data is not directly added instantly, but it is collected in batches in the form of a block, and then these blocks are further approved by consensus algorithms then only these data items are added into the existing Blockchain. A sample transaction in the Blockchain has been depicted in Fig. 1. Researchers have classified the Blockchain into three types [2,3]: a Public Blockchain: It allows anyone to create, modify, and validate the block, and every node can participate in the consensus process. Every user having similar resources possesses equal authority in creating a new node. It is also known as Permissionless or Public Permissionless Blockchain. b Private Blockchain: It allows only a set of certified users in the network to make, modify, and create transactions inside the ledger. Only a limited number of users can be allowed in the consensus and new block generation. It is also referred to as Permissioned or Private Permissioned Blockchain. c Hybrid (federated) blockchain: This type of Blockchain is a mixture of public and private Blockchain that makes a balance between these two and offers attributes of both. It allows each user to participate in the consensus mechanism but allows only certain users to create a new node explicitly designated. It is also considered a Public Per- missioned Blockchain. The high level of investment by Governments and enterprises in implementing Blockchain technology for various initiatives is an indi- cator of potential benefits. Various pilot projects based on are ongoing, * Corresponding author. E-mail address: yousafbinzikria@ynu.ac.kr (Y.B. Zikria). Contents lists available at ScienceDirect Computer Networks journal homepage: www.elsevier.com/locate/comnet https://doi.org/10.1016/j.comnet.2021.108395 Received 18 December 2020; Received in revised form 24 March 2021; Accepted 2 August 2021