A cryptocurrency (or crypto currency) is a digital asset designed to work as a medium of exchange using cryptography to secure the transactions, to control the creation of additional units, and to verify the transfer of assets. Cryptocurrencies are classified as a subset of digital currencies and are also classified as a subset of alternative currencies and virtual currencies.
Bitcoin, created in 2009, was the first decentralized cryptocurrency. Since then, numerous cryptocurrencies have been created. These are frequently called altcoins, as a blend of bitcoin alternative. Bitcoin and its derivatives use decentralized control as opposed to centralized electronic money/centralized banking systems. The decentralized control is related to the use of bitcoin's blockchain transaction database in the role of a distributed ledger.
Bitcoin is a worldwide cryptocurrency and digital payment system called the first decentralized digital currency, as the system works without a central repository or single administrator. It was invented by an unknown person or group of people under the name Satoshi Nakamoto and released as open-source software in 2009. The system is peer-to-peer, and transactions take place between users directly, without an intermediary. These transactions are verified by network nodes and recorded in a public distributed ledger called a blockchain.
From Wikipedia - Bitcoin
A blockchain – originally block chain – is a continuously growing list of records, called blocks, which are linked and secured using cryptography. Each block typically contains a hash pointer as a link to a previous block, a timestamp and transaction data. By design, blockchains are inherently resistant to modification of the data. A blockchain can serve as "an open, distributed ledger that can record transactions between two parties efficiently and in a verifiable and permanent way." For use as a distributed ledger, a blockchain is typically managed by a peer-to-peer network collectively adhering to a protocol for validating new blocks. Once recorded, the data in any given block cannot be altered retroactively without the alteration of all subsequent blocks, which requires collusion of the network majority.
"Blockchain technology is complex, but the idea is simple. At its most basic, blockchain is a vast, global distributed ledger or database running on millions of devices and open to anyone, where not just information but anything of value – money, titles, deeds, music, art, scientific discoveries, intellectual property, and even votes – can be moved and stored securely and privately. On the blockchain, trust is established, not by powerful intermediaries like banks, governments and technology companies, but through mass collaboration and clever code. Blockchains ensure integrity and trust between strangers. They make it difficult to cheat." - Don Tapscott and Alex Tapscott, Harvard Business Review
Introduced in 2008, Bitcoin was heralded for its potential to disrupt the traditional banking model for businesses and consumers alike.
Cryptocurrencies have enjoyed some success; Bitcoin is now the largest cryptocurrency, with the total number of Bitcoins currently valued at approximately USD$70 billion. Research produced by Cambridge University concluded this year that there are between 2.9 million and 5.8 million unique users actively using a cryptocurrency wallet.
In this research, we’ve looked at governmental attitudes toward cryptocurrencies, not limited to Bitcoin alone. The picture produced across the world is patchy. Some countries have become global advocates, while others have actively banned cryptocurrencies completely, with various shades in between.
The most notable disrupter is Japan, which has passed a law accepting Bitcoin as legal tender. At the other end of the spectrum, Bangladesh passed a law in 2014 stating that anybody caught using the virtual currency could be jailed under the country’s strict anti-money-laundering laws.
Whatever the individual case for a country, the growth in cryptocurrencies in the last decade has shown that there is strong momentum around this new technology.
From Cryptocurrencies by Country, Thomson Reuters: Dividends Magazine | October 25, 2017
Bitcoin uses public-key cryptography, peer-to-peer networking, and proof-of-work to process and verify payments. Bitcoins are sent (or signed over) from one address to another with each user potentially having many, many addresses. Each payment transaction is broadcast to the network and included in the blockchain so that the included bitcoins cannot be spent twice. After an hour or two, each transaction is locked in time by the massive amount of processing power that continues to extend the blockchain. Using these techniques, Bitcoin provides a fast and extremely reliable payment network that anyone can use.
Mining is the process of adding transaction records to Bitcoin's public ledger of past transactions (and a "mining rig" is a colloquial metaphor for a single computer system that performs the necessary computations for "mining"). This ledger of past transactions is called the block chain as it is a chain of blocks. The block chain serves to confirm transactions to the rest of the network as having taken place. Bitcoin nodes use the block chain to distinguish legitimate Bitcoin transactions from attempts to re-spend coins that have already been spent elsewhere.
Mining is intentionally designed to be resource-intensive and difficult so that the number of blocks found each day by miners remains steady. Individual blocks must contain a proof of work to be considered valid. This proof of work is verified by other Bitcoin nodes each time they receive a block. Bitcoin uses the hashcash proof-of-work function.
The primary purpose of mining is to allow Bitcoin nodes to reach a secure, tamper-resistant consensus. Mining is also the mechanism used to introduce Bitcoins into the system: Miners are paid any transaction fees as well as a "subsidy" of newly created coins. This both serves the purpose of disseminating new coins in a decentralized manner as well as motivating people to provide security for the system.
Bitcoin mining is so called because it resembles the mining of other commodities: it requires exertion and it slowly makes new currency available at a rate that resembles the rate at which commodities like gold are mined from the ground.