2.4.7. Blockchain Technology

Blockchain (BC) which was first introduced by Satoshi Takemoto in 2008 is a decentralized database originally designed for financial-related applications. It is the underlying technology of bitcoin—a peer-to-peer electronic cash system in which a virtual currency called bitcoin is circulated in the online economy without a central controller [117]. This approach entails the mutual performance of transactions using a distributed online ledger. If the transaction meets the requirement, it is unanimously validated by the nodes (called miners) in the network [118]. The transactions once validated are linked (or chained) to older transactions forming shapes that look like a group of blocks chained together, hence the name Blockchain. Hash as was explained by [119] is a mathematical algorithm that produces a string of characters called hash value which is used to sign digital signatures as a means of validating that the requestor is the rightful person. Blockchain can be classified as public (permission-less), Private (permissioned), or Consortium (hybrid) Blockchain technologies [120]. The public Blockchain (PBC) is open for anybody to join. PBC is fully decentralized and transactions are open for all to read and write to. Prove of work (POW) is the consensus mechanism in which every node will participate making the process resource-demanding and time-consuming. An example of public Blockchain is bitcoin. Consortium Blockchain is partially decentralized while private Blockchain is fully centralized. Private Blockchain and consortium are restricted to participating organizations. Consensus is performed using proof of stake (POS) or other, variants of consensus mechanism in private and consortium Blockchain.

The distributed data storage and management feature of Blockchain is appealing and is expected to play a major role in resolving the privacy issues inherent in data management architectures in the existing contact tracing applications. The study reported in [109] lays credence to this assertion. In this research, the authors evaluated the feasibility of integrating Blockchain with IoT devices (RFID) in the deployment of contact tracing systems. Their prototype was developed using Ethereum Blockchain taking advantage of its smart contract. The evaluation performed on the prototype shows that the approach is cost-effective. A similar framework was proposed in [109] using a public Blockchain network (PBN) where an infected person can share his contact list by initiating a transaction. Upon successful approval and addition of the new block, other users can confirm their status by initiating a query transaction on the Blockchain network. Another Blockchain-based contact tracing framework was proposed by [121] where the authors opined that with their framework, infection risk for international travels is reduced. Their proposal also ensures that contact tracing of users can be achieved in a privacy-preserving manner.