Introduction

Introduction

Dryly speaking, the goal of this zeroth part is to establish a theoretical understanding and terminology that will serve us well in the following parts of the book. That is, I want to have a unified source that could be used to initiate anyone into discussing any of the advanced disparate topics that I plan to cover in the following parts.

However, my true goal is to get the reader excited about the theory of decentralized consensus. Why? Because it is beautiful. It is a theory elementary enough to make approachable to a relatively broad audience, while deep enough to provide (with some effort) rewarding a-ha! moments that will make many readers feeling smarter than they were before reading. While not requiring high proficiency in any particular branch of math, consensus theory provides a nice sight-seeing tour through the reals of probability, combinatorics, graph theory, game theory, cryptography, algorithmics, and so on. And if all of that isn't enough, the story of this scientific paradigm shift is wrapped in mystery, espionage, and aspirations for a better world.

That being said, this is not a historical review. While I do point out major milestones, I present the theory in a uniform, modern approach, one that naturally risen to consolidate the many different works and ideas that diverged from Satoshi et al.'s original work.

I am hopeful that any reader could better appreciate cryptocurrencies and the struggles they are facing with the tools and thought frameworks in this volume, even if they do not decide to apply this insight to study GHOSTDAG.

Overview

Our journey will be divided into six chapters. In the first, we visit the place where it all began: the Byzantine generals problem, and consider Byzantine fault tolerance and where it stands with regards to proof-of-work.

The second chapter will be all about block chain protocols, starting from a systemic framework for describing them as chain selection rules and culminating with the two most ubiquitous examples: the Heaviest Chain Rule and GHOST.

In the third chapter, we dive deep into security, of blockchains and in general. We discuss what a security property even is before isolating the common security properties used for block chains. We will describe safety, liveness, and confirmation time and, for the mathier audience, we will also sketch the proof of Bitcoin's security.

In the fourth chapter we will expend the ideas of the second chapter to define the blockDAG paradigm by replacing selection rules with ordering rules, and generalize some of the security discussion of the third chapter to this extended context.