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All about Bitcoin

Bitcoin is a digital asset and a payment system invented by Satoshi Nakamoto. Nakamoto introduced the idea on 31 October 2008 to a cryptography mailing list, and released it as open-source software in 2009. There have been several high profile claims to the identity of Satoshi Nakamoto; however, none of them have provided proof beyond doubt that back up their claims.

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 the blockchain, which uses bitcoin as its unit of account. Since the system works without a central repository or single administrator, the U.S. Treasury categorizes bitcoin as a decentralized virtual currency. Bitcoin is often called the first cryptocurrency, although prior systems existed and it is more correctly described as the first decentralized digital currency. Bitcoin is the largest of its kind in terms of total market value.

Bitcoins are created as a reward for payment processing work in which users offer their computing power to verify and record payments into a public ledger. This activity is called mining and miners are rewarded with transaction fees and newly created bitcoins. Besides being obtained by mining, bitcoins can be exchanged for other currencies, products, and services. When sending bitcoins, users can pay an optional transaction fee to the miners.

In February 2015, the number of merchants accepting bitcoin for products and services passed 100,000.[28] Instead of 2–3% typically imposed by credit card processors, merchants accepting bitcoins often pay fees in the range from 0% to less than 2%. Despite the fourfold increase in the number of merchants accepting bitcoin in 2014, the cryptocurrency did not have much momentum in retail transactions. The European Banking Authority and other sources have warned that bitcoin users are not protected by refund rights or chargebacks. The use of bitcoin by criminals has attracted the attention of financial regulators, legislative bodies, law enforcement, and media. Criminal activities are primarily centered around darknet markets and theft, though officials in countries such as the United States also recognize that bitcoin can provide legitimate financial services.

Mining
Relative mining difficulty, the scale is logarithmic.

A mining farm in Iceland
Mining is a record-keeping service. Miners keep the blockchain consistent, complete, and unalterable by repeatedly verifying and collecting newly broadcast transactions into a new group of transactions called a block. Each block contains a cryptographic hash of the previous block, using the SHA-256 hashing algorithm, which links it to the previous block thus giving the blockchain its name.

In order to be accepted by the rest of the network, a new block must contain a so-called proof-of-work. The proof-of-work requires miners to find a number called a nonce, such that when the block content is hashed along with the nonce, the result is numerically smaller than the network's difficulty target. This proof is easy for any node in the network to verify, but extremely time-consuming to generate, as for a secure cryptographic hash, miners must try many different nonce values (usually the sequence of tested values is 0, 1, 2, 3, … before meeting the difficulty target.

Every 2016 blocks (approximately 14 days), the difficulty target is adjusted based on the network's recent performance, with the aim of keeping the average time between new blocks at ten minutes. In this way the system automatically adapts to the total amount of mining power on the network.

Between 1 March 2014 and 1 March 2015, the average number of nonces miners had to try before creating a new block increased from 16.4 quintillion to 200.5 quintillion.

The proof-of-work system, alongside the chaining of blocks, makes modifications of the blockchain extremely hard, as an attacker must modify all subsequent blocks in order for the modifications of one block to be accepted. As new blocks are mined all the time, the difficulty of modifying a block increases as time passes and the number of subsequent blocks (also called confirmations of the given block) increases.