5 Consensus Algorithms

Consensus is a fundamental problem in distributed systems. Since the 1970s this problem has been researched in the context of distributed systems, but recently, with the advent of blockchain technology, a renewed interest has arisen in developing distributed consensus algorithms that are suitable for blockchain networks. In this chapter, we will explore the underlying techniques behind distributed consensus algorithms, their inner workings, and new algorithms that have been specifically developed for blockchain networks.

In addition, we will introduce various well-known algorithms in a traditional distributed systems arena that can also be implemented in blockchain networks with some modifications, such as Paxos, Raft, and PBFT. We will also explore other mechanisms that have been introduced specifically for blockchain networks such as Proof of Work (PoW), Proof of Stake (PoS), and modified versions of traditional consensus such as Istanbul Byzantine Fault Tolerant (IBFT), which is a modified, blockchained version of the Practical Byzantine Fault Tolerant (PBFT) algorithm, suitable for a blockchain network. Along the way, we'll cover the following topics:

• Introducing the consensus problem
• Analysis and design
• Classification
• Algorithms
• Choosing an algorithm

Before we delve into specific algorithms, we first need to understand some fundamental concepts and an overview of the consensus problem.