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206 CHAPTER 8 BLOCKCHAIN IN HEALTHCARE: CHALLENGES AND SOLUTIONS

A hash algorithm: This hash algorithm is used in order to map random information into the definite
length of hash. A little in-hash data results in a big difference in actual data, which makes falsification
difficult in any data recorded by blockchain technology.
A digital signature: First used by Johnson et al. [43] as the elliptical curve digital signature algo-
rithm ECDSA. A digital signature is processed to prove the validity of the blockchain transmission.
Public and private keys are present in order to provide a double layer of authentication. Personal trans-
actions can be managed using the private key and external security can be managed using the
public key.
Forking: A forking of the blockchain happens when the chain of blocks diverges into two paths.
Since diverse participants need to agree on common rules, often more than one blockchain is generated.
However, after consensus and appropriate regulation, this forking problem is solved. Three types of
forking were mentioned by Castor [44]: hard fork, soft fork, and user centric fork.
Blockchain types: Blockchain technology is divided into three types based on its user-level per-
mission and scope in the healthcare sector by Linn and Koo [45]. Among the public, private, and con-
sortium layer, two types of blockchain are mostly used for organization of the healthcare sector. Fig. 8.9
elaborates on the different types of blockchain.
Consensus algorithm: Consensus algorithm is a process in blockchain technology by which any
new block (new transaction) is being approved by a set of legal nodes or distributed systems. Com-
monly used consensus protocols or mechanisms are discussed and compared in Table 8.1.

8.2.3 HOW BLOCKCHAIN WORKS
An example of a blockchain transaction is described in Fig. 8.10. First of all, the two parties decide to
perform a transaction or exchange information. A group of nodes associated to those parties approves
the legality of the transaction parties as well as the smart contract between them. After successful hash-
ing and consensus from every involved party with any aforementioned consensus algorithm, a new
block is finalized. Finally, a new block with detailed transaction information is added to the existing
block and the transaction finishes.
Prerequisites of blockchain technology: To set up this technology, the following prerequisites are
needed: several connected nodes (computers), a block data storing software or hashing software, a con-
sensus algorithm to make decisions, and finally a network system with fast Internet connectivity.

8.3 PRIVACY OF HEALTHCARE BIG DATA
Digital identity: A digital identity refers to any online identity of any individual or organization. A
digital identity consists of information or attributes related to any particular entity (individual, orga-
nization, or electronic device). The information contained in a digital identity allows assessment and
authentication of an entity on the web. However, through digital identity (online identity), any civil and
personal information associated with any online activities can be detected.
Personally identifiable information (PII): Any data or information that could lead to a specific
organization or individual is called personally identifiable information or PII. Nowadays, PII is also
knownas sensitive personal information (SPI) or personal data (PD) or personal information (PI) all over
the world. Any distinguishable information that can be used to separate the personal identity is also