The concept of decentralized digital currency, as well as alternative applications like property registries, has been around for decades, but none has produced viable production implementations until now. The anonymous e-cash protocols of the 1980s and 1990s were mostly reliant on a cryptographic primitive known as Chaumian blinding (after its developer, David Chaum). Chaumian blinding provided these new currencies with high degrees of privacy, but their underlying protocols largely failed to gain traction because of their reliance on a centralized intermediary. In 1998, Wei Dai's b-money became the first proposal to introduce the idea of creating money through solving computational puzzles as well as decentralized consensus, but the proposal was scant on details as to how decentralized consensus could actually be implemented. In 2005, Hal Finney introduced a concept of "reusable proofs of work" a system that uses ideas from b-money together with Adam Back's computationally difficult Hashcash (http://hashcash.org) puzzles to create a concept for a cryptocurrency, but this once again fell short of the ideal by relying on trusted computing as a backend. As we all know, the blockchain concept was implemented as a core component of the digital currency Bitcoin. This critical and perhaps first production implementation of the blockchain made it the first digital currency to solve the double-spending problem, without the use of a trusted authority or central server. The Bitcoin design, which we examine briefly in the next section, has been the inspiration for other implementations we will explore in the chapters to come.
As we mentioned, when the financial crisis of 2008 was in full throttle, Bitcoin (BTC), a decentralized currency, was implemented for the first time in practice by Satoshi Nakamoto. Bitcoin combines established primitives for managing ownership through public key cryptography with a consensus algorithm for keeping track of who owns coins, known as proof-of-work. The mechanism behind proof-of-work simultaneously solves two problems. First, it provides an effective consensus algorithm, allowing nodes in the network to collectively agree on a set of updates to the state of the Bitcoin ledger. Second, it provides a mechanism for allowing free entry into the consensus process, solving the political problem of deciding who gets to influence the consensus, while simultaneously preventing Sybil attacks - that is, attacks where a reputation system is subverted by forging identities in peer-to-peer networks. It is named after a case study of a woman diagnosed with dissociative identity disorder. It works by substituting a formal barrier to participation, such as the requirement to be registered as a unique entity on a particular list, with an economic barrier - the weight of a single node in the consensus voting process is directly proportional to the computing power that the node brings. More recently, an alternative approach has been proposed called proof- of-stake, calculating the weight of a node as being proportional to its currency holdings and not its computational resources. The discussion concerning the relative merits of the two approaches will be examined in the chapters that address the Ethereum-based blockchain and derivatives thereof. At this junction in 2018, all blockchain platforms are still evolving and will continue to do so for the foreseeable futures. As Bitcoin is the most widely used, we will explore it in some detail in the next sections.
Source: Source: Blockchain: A Practical Guide to Developing Business, Law, and Technology Solutions 1st Edition by Joseph J. Bambara