A blockchain is a data structure that makes it possible to create a digital ledger of data and share it among a network of independent parties. There are many different types of blockchains.

·         Public blockchains: Public blockchains, such as Bitcoin, are large distributed networks that are run through a native token. They’re open for anyone to participate at any level and have open-source code that their community maintains.

·         Permissioned blockchains: Permissioned blockchains, such as Ripple, control roles that individuals can play within the network. They’re still large and distributed systems that use a native token. Their core code may or may not be open source.

·         Private blockchains: Private blockchains tend to be smaller and do not utilize a token. Their membership is closely controlled. These types of blockchains are favored by consortiums that have trusted members and trade confidential information.

All three types of blockchains use cryptography to allow each participant on any given network to manage the ledger in a secure way without the need for a central authority to enforce the rules. The removal of central authority from database structure is one of the most important and powerful aspects of blockchains.

Blockchains create permanent records and histories of transactions, but nothing is really permanent. The permanence of the record is based on the permanence of the network.

In the context of blockchains, this means that a large portion of a blockchain community would all have to agree to change the information and are incentivized not to change the data.

When data is recorded in a blockchain, it’s extremely difficult to change or remove it. When someone wants to add a record to a blockchain, also called a transaction or an entry, users in the network who have validation control verify the proposed transaction.

This is where things get tricky because every blockchain has a slightly different spin on how this should work and who can validate a transaction.

What blockchains do

A blockchain is a peer-to-peer system with no central authority managing data flow. One of the key ways to removing central control while maintaining data integrity is to have a large distributed network of independent users. This means that the computers that make up the network are in more than one location. These computers are often referred to as full nodes.

To prevent the network from being corrupted, not only are blockchains decentralized but they often also utilize a cryptocurrency. A cryptocurrency is a digital token that has a market value. Cryptocurrencies are traded on exchanges like stocks.

Cryptocurrencies work a little differently for each blockchain. Basically, the software pays the hardware to operate. The software is the blockchain protocol. Well-known blockchain protocols include Bitcoin, Ethereum, Ripple, Hyperledger, and Factom. The hardware consists of the full nodes that are securing the data in the network.

Why blockchains matter

Blockchains are now recognized as the “fifth evolution” of computing, the missing trust layer for the Internet. This is one of the reasons that so many people have become excited about this topic.

Blockchains can create trust in digital data. When information has been written into a blockchain database, it’s nearly impossible to remove or change it. This capability has never existed before.

When data is permanent and reliable in a digital format, you can transact business online in ways that, in the past, were only possible offline. Everything that has stayed analog, including property rights and identity, can now be created and maintained online.

Slow business and banking processes, such as money wires and fund settlements, can now be done nearly instantaneously. The implications for secure digital records are enormous for the global economy.

The first applications created were designed to piggyback on the secure digital value transfer that blockchains enable through the trading of their native tokens. These included things like the movement of money and assets. But the possibilities of the blockchain networks go far beyond the movement of value.

The Structure of Blockchains

Blockchains are composed of three core parts:

·         Block: A list of transactions recorded into a ledger over a given period. The size, period, and triggering event for blocks is different for every blockchain.

Not all blockchains are recording and securing a record of the movement of their cryptocurrency as their primary objective. But all blockchain do record the movement of their cryptocurrency or token. Think of the transaction as simply being the recording of data. Assigning a value to it (such as happens in a financial transaction) is used to interpret what that data means.

·         Chain: A hash that links one block to another, mathematically “chaining” them together. This is one of the most difficult concepts in blockchain to comprehend. It’s also the magic that glues blockchains together and allows them to create mathematical trust.

The hash in blockchain is created from the data that was in the previous block. The hash is a fingerprint of this data and locks blocks in order and time.

Although blockchains are a relatively new innovation, hashing is not. Hashing was invented over 30 years ago. This old innovation is being used because it creates a one-way function that cannot be decrypted.

A hashing function creates a mathematical algorithm that maps data of any size to a bit string of a fixed size. A bit string is usually 32 characters long, which then represents the data that was hashed.

The Secure Hash Algorithm (SHA) is one of some cryptographic hash functions used in blockchains. SHA-256 is a common algorithm that generates an almost-unique, fixed-size 256-bit (32-byte) hash. For practical purposes, think of a hash as a digital fingerprint of data that is used to lock it in place within the blockchain.

·         Network: The network is composed of “full nodes.” Think of them as the computer running an algorithm that is securing the network. Each node contains a complete record of all the transactions that were ever recorded in that blockchain.

The nodes are located all over the world and can be operated by anyone. It’s difficult, expensive, and time-consuming to operate a full node, so people don’t do it for free.

They’re incentivized to operate a node because they want to earn cryptocurrency. The underlying blockchain algorithm rewards them for their service. The reward is usually a token or cryptocurrency, like Bitcoin.

The terms Bitcoin and blockchain are often used interchangeably, but they’re not the same. Bitcoin has a blockchain. The Bitcoin blockchain is the underlying protocol that enables the secure transfer of Bitcoin.

The term Bitcoin is the name of the cryptocurrency that powers the Bitcoin network. The blockchain is a class of software, and Bitcoin is a specific cryptocurrency.

This is an edited extract from Blockchain For Dummies by Tiana Laurence (published by Wiley, June 2017).