Bitcoin
Bitcoin (₿) is a decentralized digital currency that can be transferred on the peer-to-peer bitcoin network. Bitcoin transactions are verified by network nodes through cryptography and recorded in a public distributed ledger called a blockchain. The cryptocurrency was invented in 2008 by an unknown person or group of people using the name Satoshi Nakamoto.The currency began use in 2009, when its implementation was released as open-source software.: ch. 1
Bitcoin has been described as an economic bubble by at least eight Nobel Memorial Prize in Economic Sciences recipients
The word bitcoin was defined in a white paper published on 31 October 2008. It is a compound of the words bit and coin. No uniform convention for bitcoin capitalization exists; some sources use Bitcoin, capitalized, to refer to the technology and network and bitcoin, lowercase, for the unit of account.The Wall Street Journal, The Chronicle of Higher Education, and the Oxford English Dictionary advocate the use of lowercase bitcoin in all cases.
A few local and national governments are officially using bitcoin in some capacity; El Salvador and the Central African Republic have adopted Bitcoin as legal tender, while Ukraine is accepting bitcoin donations to fund the resistance against the Russian invasion.
Design
Units and divisibility
The unit of account of the bitcoin system is the bitcoin. Currency codes for representing bitcoin are BTC[a] and XBT.: 2 Its Unicode character is ₿. One bitcoin is divisible to eight decimal places.: ch. 5 Units for smaller amounts of bitcoin are the millibitcoin (mBTC), equal to 1⁄1000 bitcoin, and the satoshi (sat), which is the smallest possible division, and named in homage to bitcoin's creator, representing 1⁄100000000 (one hundred millionth) bitcoin.100,000 satoshis are one mBTC.
Blockchain
The bitcoin blockchain is a public ledger that records bitcoin transactions. It is implemented as a chain of blocks, each block containing a cryptographic hash of the previous block up to the genesis block[c] in the chain. A network of communicating nodes running bitcoin software maintains the blockchain.: 215–219 Transactions of the form payer X sends Y bitcoins to payee Z are broadcast to this network using readily available software applications.
Network nodes can validate transactions, add them to their copy of the ledger, and then broadcast these ledger additions to other nodes. To achieve independent verification of the chain of ownership each network node stores its own copy of the blockchain.At varying intervals of time averaging to every 10 minutes, a new group of accepted transactions, called a block, is created, added to the blockchain, and quickly published to all nodes, without requiring central oversight. This allows bitcoin software to determine when a particular bitcoin was spent, which is needed to prevent double-spending. A conventional ledger records the transfers of actual bills or promissory notes that exist apart from it, but the blockchain is the only place that bitcoins can be said to exist in the form of unspent outputs of transactions.: ch. 5
Mining
Mining is a record-keeping service done through the use of computer processing power.[f] Miners keep the blockchain consistent, complete, and unalterable by repeatedly grouping newly broadcast transactions into a block, which is then broadcast to the network and verified by recipient nodes. Each block contains a SHA-256 cryptographic hash of the previous block, thus linking it to the previous block and giving the blockchain its name.: ch. 7
To be accepted by the rest of the network, a new block must contain a proof-of-work (PoW).[g] The PoW requires miners to find a number called a nonce (number used once), such that when the block content is hashed along with the nonce, the result is numerically smaller than the network's difficulty target.[6]: ch. 8 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 the ascending natural numbers: 0, 1, 2, 3, ...) before a result happens to be less than the difficulty target. Because the difficulty target is extremely small compared to a typical SHA-256 hash, block hashes have many leading zeros[6]: ch. 8 as can be seen in this example block hash:
By adjusting this difficulty target, the amount of work needed to generate a block can be changed. Every 2,016 blocks (approximately 14 days given roughly 10 minutes per block), nodes deterministically adjust the difficulty target based on the recent rate of block generation, 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.: ch. 8 As of April 2022, it takes on average 122 sextillion (122 thousand billion billion) attempts to generate a block hash smaller than the difficulty target. Computations of this magnitude are extremely expensive and utilize specialized hardware.
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.
Computing power is often bundled together by a Mining pool to reduce variance in miner income. Individual mining rigs often have to wait for long periods to confirm a block of transactions and receive payment. In a pool, all participating miners get paid every time a participating server solves a block. This payment depends on the amount of work an individual miner contributed to help find that block.