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1

Introduction

Since its inception, blockchain emerged as a disruptive and distributed technology for

the IoT industry as introduced by the Bitcoin Whitepaper and its subsequent proven

application. Blockchain is regarded as a subset of Distributed Ledger Technologies

[1]. However, at present, the terms “blockchain” and “distributed ledger technology”

are often interchangeably used. Blockchain has hardly left any field untouched.

This chapter, thus, acts as a primer for blockchain and allied technologies being

used for privacy preservation [2] and identity management [3] and presents current

blockchain engines geared towards ledger interoperability. We start by discussing

self-sovereign identity [4], Decentralized Identifiers (DID) [5], and Zero-Knowledge

Proof[6]—threecornerstonesofblockchain-basedprivacypreservationplatforms[7]

along with mentioning recent works related to the aforementioned terms. We then

present two case studies. First, we review the Polkadot protocol [8], which has seen

a rise at the time of writing due to its ability to facilitate cross-platform distributed

ledger operations. We also present the overviews on other similar platforms dedi-

cated to interoperability such as Cosmos and Ark. As a second case study, we discuss

the Sovrin Network—pioneers of DIDs and self-sovereign identity. We also review

the open-sourced framework Hyperledger Indy [9], which helps in building similar

networks for identity management [10]. The latter is open-sourced by the Sovrin

Foundation itself and currently hosted at the Linux Foundation under active status.

Given that we are already in the NISQ-era of Quantum Computing where a substan-

tial amount of work is being done on proposing novel applications of near-term

noisy quantum, blockchain has come under scrutiny due to its reliance on crypto-

graphic protocols deemed to be surpassable. For instance, RSA—one of the staples in

encryptionofcommunicationcanbebrokencourtesyofShor’sAlgorithminquantum

computing. While this is not an immediate possibility, it still exists as an eventuality.

For this reason, recent trends indicate research being done on improving the existing

blockchain and distributed ledger technology platform. The chapter, thus, concludes

with a discussion of the recent works in making distributed ledger technologies robust

and quantum-resilient in terms of consensus and overall architecture.

In this chapter, we first give a survey on blockchain in Internet of Things (IoT)

[11] and Industrial Internet of Things (IIoT) [12], which is in Sect. 2. Section 3

describes blockchain used for identity management using zero knowledge proof,

decentralized identity, and others. It also presents a case study on Hyperledger Indy—

a Distributed Ledger Framework that uses ZKPs and DIDs to facilitate secure identity

with selective disclosure. Section 4 describes blockchain and interoperability using

the case study of Polkadot and contemporary survey of other popular interoperability

solutions, which exist at the time of writing. Section 5 describes some of the open

challenges, and we conclude the chapter in Sect. 6.