Bitcoin (abbreviation: BTC[a] or XBT;[b] sign: ₿) is a protocol which implements a public, permanent, and decentralized ledger.
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 The word “bitcoin” was defined in a white paper published on October 31, 2008. It is a compound of the words bit and coin.
The Library of Congress reports that, as of November 2021, nine countries have fully banned bitcoin use, and a further forty-two have implicitly banned it. A few governments have used bitcoin in some capacity. El Salvador has adopted Bitcoin as legal tender, although use by merchants remains low. Ukraine has accepted cryptocurrency donations to fund the resistance to the 2022 Russian invasion. Iran has used bitcoin to bypass sanctions.
In 2018, Bitcoin has been described as an economic bubble by at least eight recipients of the Nobel Memorial Prize in Economic Sciences.
The environmental effects of bitcoin are substantial. Its proof-of-work algorithm for bitcoin mining is designed to be computationally difficult, which requires the consumption of increasing quantities of electricity, the generation of which has contributed to climate change. According to the University of Cambridge, bitcoin has emitted an estimated 200 million tonnes of carbon dioxide since its launch, or about 0.04% of all carbon dioxide released since 2009.
The domain name bitcoin.org was registered on 18 August 2008. On 31 October 2008, a link to a paper authored by Satoshi Nakamoto titled Bitcoin: A Peer-to-Peer Electronic Cash System was posted to a cryptography mailing list. Nakamoto implemented the bitcoin software as open-source code and released it in January 2009. Nakamoto’s identity remains unknown.
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.
On 3 January 2009, the bitcoin network was created when Nakamoto mined the starting block of the chain, known as the genesis block. Embedded in the coinbase of this block was the text “The Times 03/Jan/2009 Chancellor on brink of second bailout for banks”. This note references a headline published by The Times and has been interpreted as both a timestamp and a comment on the instability caused by fractional-reserve banking. 18
The receiver of the first bitcoin transaction was Hal Finney, who had created the first reusable Proof-of-work system system (RPoW) in 2004. Finney downloaded the bitcoin software on its release date, and on 12 January 2009 received ten bitcoins from Nakamoto. Other early cypherpunk supporters were creators of bitcoin predecessors: Wei Dai, creator of b-money, and Nick Szabo, creator of bit gold. In 2010, the first known commercial transaction using bitcoin occurred when programmer Laszlo Hanyecz bought two Papa John’s pizzas for ₿10,000 from Jeremy Sturdivant..
Blockchain analysts estimate that Nakamoto had mined about one million bitcoins. before disappearing in 2010 when he handed the network alert key and control of the code repository over to Gavin Andresen. Andresen later became lead developer at the Bitcoin Foundation. Andresen then sought to decentralize control. This left opportunity for controversy to develop over the future development path of bitcoin, in contrast to the perceived authority of Nakamoto’s contributions.
After early “proof-of-concept” transactions, the first major users of bitcoin were black markets, such as Silk Road. During its 30 months of existence, beginning in February 2011, Silk Road exclusively accepted bitcoins as payment, transacting ₿9.9 million, worth about $214 million. 222
In 2011, the price started at $0.30 per bitcoin, growing to $5.27 for the year. The price rose to $31.50 on 8 June. Within a month, the price fell to $11.00. The next month it fell to $7.80, and in another month to $4.77.
In 2012, bitcoin prices started at $5.27, growing to $13.30 for the year. By 9 January the price had risen to $7.38, but then crashed by 49% to $3.80 over the next 16 days. The price then rose to $16.41 on 17 August, but fell by 57% to $7.10 over the next three days.
The Bitcoin Foundation was founded in September 2012 to promote bitcoin’s development and uptake.
On 1 November 2011, the reference implementation Bitcoin-Qt version 0.5.0 was released. It introduced a front end that used the Qt user interface toolkit. The software previously used Berkeley DB for database management. Developers switched to LevelDB in release 0.8 in order to reduce blockchain synchronization time. The update to this release resulted in a minor blockchain fork on 11 March 2013. The fork was resolved shortly afterwards. Seeding nodes through IRC was discontinued in version 0.8.2. From version 0.9.0 the software was renamed to Bitcoin Core. Transaction fees were reduced again by a factor of ten as a means to encourage microtransactions. Although Bitcoin Core does not use OpenSSL for the operation of the network, the software did use OpenSSL for remote procedure calls. Version 0.9.1 was released to remove the network’s vulnerability to the Heartbleed bug.
In 2013, prices started at $13.30 rising to $770 by 1 January 2014.
In March 2013 the blockchain temporarily split into two independent chains with different rules due to a bug in version 0.8 of the bitcoin software. The two blockchains operated simultaneously for six hours, each with its own version of the transaction history from the moment of the split. Normal operation was restored when the majority of the network downgraded to version 0.7 of the bitcoin software, selecting the backwards-compatible version of the blockchain. As a result, this blockchain became the longest chain and could be accepted by all participants, regardless of their bitcoin software version. During the split, the Mt. Gox exchange briefly halted bitcoin deposits and the price dropped by 23% to $37 before recovering to the previous level of approximately $48 in the following hours.
The US Financial Crimes Enforcement Network (FinCEN) established regulatory guidelines for “decentralized virtual currencies” such as bitcoin, classifying American bitcoin miners who sell their generated bitcoins as Money Service Businesses (MSBs), that are subject to registration or other legal obligations.
In April, exchanges BitInstant and Mt. Gox experienced processing delays due to insufficient capacity resulting in the bitcoin price dropping from $266 to $76 before returning to $160 within six hours. The bitcoin price rose to $259 on 10 April, but then crashed by 83% to $45 over the next three days.
On 15 May 2013, US authorities seized accounts associated with Mt. Gox after discovering it had not registered as a money transmitter with FinCEN in the US. On 23 June 2013, the US Drug Enforcement Administration listed ₿11.02 as a seized asset in a United States Department of Justice seizure notice pursuant to 21 U.S.C. § 881. This marked the first time a government agency had seized bitcoin, likely by either seizing a computer with an unencrypted wallet, or through a sting operation. The FBI seized about ₿30,000 in October 2013 from the dark web website Silk Road, following the arrest of Ross William Ulbricht. These bitcoins were sold at blind auction by the United States Marshals Service to venture capital investor Tim Draper. Bitcoin’s price rose to $755 on 19 November and crashed by 50% to $378 the same day. On 30 November 2013, the price reached $1,163 before starting a long-term crash, declining by 87% to $152 in January 2015.
On 5 December 2013, the People’s Bank of China prohibited Chinese financial institutions from using bitcoin. After the announcement, the value of bitcoin dropped, and Baidu no longer accepted bitcoins for certain services. Buying real-world goods with any virtual currency had been illegal in China since at least 2009.
In 2015, prices started at $314 and rose to $434 for the year. In 2016, prices rose and climbed up to $998 by 1 January 2017.
Release 0.10 of the software was made public on 16 February 2015. It introduced a consensus library which gave programmers easy access to the rules governing consensus on the network. In version 0.11.2 developers added a new feature which allowed transactions to be made unspendable until a specific time in the future.
In July 2016, the CheckSequenceVerify soft fork activated. In August 2016, the Bitfinex cryptocurrency exchange platform was hacked in the second-largest breach of a Bitcoin exchange platform up to that time, and ₿119,756, worth about $72 million at the time, were stolen.
In October 2016, Bitcoin Core’s 0.13.1 release featured the “Segwit” soft fork that included a scaling improvement aiming to optimize the bitcoin blocksize. The patch was originally finalized in April, and 35 developers were engaged to deploy it. This release featured Segregated Witness (SegWit) which aimed to place downward pressure on transaction fees as well as increase the maximum transaction capacity of the network. The 0.13.1 release endured extensive testing and research leading to some delays in its release date. SegWit prevents various forms of transaction malleability.
Research produced by the University of Cambridge estimated that in 2017, there were 2.9 to 5.8 million unique users using a cryptocurrency wallet, most of them using bitcoin. On 15 July 2017, the controversial Segregated Witness [SegWit] software upgrade was approved (“locked-in”). Segwit was intended to support the Lightning Network as well as improve scalability. SegWit was subsequently activated on the network on 24 August 2017. The bitcoin price rose almost 50% in the week following SegWit’s approval. On 21 July 2017, bitcoin was trading at $2,748, up 52% from 14 July 2017’s $1,835. Supporters of large blocks who were dissatisfied with the activation of SegWit forked the software on 1 August 2017 to create Bitcoin Cash, becoming one of many forks of bitcoin such as Bitcoin Gold.
Prices started at $998 in 2017 and rose to $13,412.44 on 1 January 2018, after reaching its all-time high of $19,783.06 on 17 December 2017.
China banned trading in bitcoin, with first steps taken in September 2017, and a complete ban that started on 1 February 2018. Bitcoin prices then fell from $9,052 to $6,914 on 5 February 2018. The percentage of bitcoin trading in the Chinese renminbi fell from over 90% in September 2017 to less than 1% in June 2018.
Throughout the rest of the first half of 2018, bitcoin’s price fluctuated between $11,480 and $5,848. On 1 July 2018, bitcoin’s price was $6,343. The price on 1 January 2019 was $3,747, down 72% for 2018 and down 81% since the all-time high.
In September 2018, an anonymous party discovered and reported an invalid-block denial-of-server vulnerability to developers of Bitcoin Core, Bitcoin ABC and Bitcoin Unlimited. Further analysis by bitcoin developers showed the issue could also allow the creation of blocks violating the 21 million coin limit and CVE-2018-17144 was assigned and the issue resolved.
Bitcoin prices were negatively affected by several hacks or thefts from cryptocurrency exchanges, including thefts from Coincheck in January 2018, Bithumb in June, and Bancor in July. For the first six months of 2018, $761 million worth of cryptocurrencies was reported stolen from exchanges. Bitcoin’s price was affected even though other cryptocurrencies were stolen at Coinrail and Bancor as investors worried about the security of cryptocurrency exchanges. In September 2019, the Intercontinental Exchange (the owner of the NYSE) began trading of bitcoin futures on its exchange called Bakkt. Bakkt also announced that it would launch options on bitcoin in December 2019. In December 2019, YouTube removed bitcoin and cryptocurrency videos, but later restored the content after judging they had “made the wrong call”.
In February 2019, Canadian cryptocurrency exchange Quadriga Fintech Solutions failed with approximately $200 million missing. By June 2019 the price had recovered to $13,000.
On 13 March 2020, bitcoin fell below $4,000 during a broad market selloff, after trading above $10,000 in February 2020. On 11 March 2020, 281,000 bitcoins were sold, held by owners for only thirty days. This compared to ₿4,131 that had laid dormant for a year or more, indicating that the vast majority of the bitcoin volatility on that day was from recent buyers. During the week of 11 March 2020, cryptocurrency exchange Kraken experienced an 83% increase in the number of account signups over the week of bitcoin’s price collapse, a result of buyers looking to capitalize on the low price. These events were attributed to the onset of the COVID-19 pandemic.
In August 2020, MicroStrategy invested $250 million in bitcoin as a treasury reserve asset. In October 2020, Square, Inc. placed approximately 1% of total assets ($50 million) in bitcoin. In November 2020, PayPal announced that US users could buy, hold, or sell bitcoin. On 30 November 2020, the bitcoin value reached a new all-time high of $19,860, topping the previous high of December 2017. Alexander Vinnik, founder of BTC-e, was convicted and sentenced to five years in prison for money laundering in France while refusing to testify during his trial. In December 2020, Massachusetts Mutual Life Insurance Company announced a bitcoin purchase of US$100 million, or roughly 0.04% of its general investment account.
On 19 January 2021, Elon Musk placed the handle #Bitcoin in his Twitter profile, tweeting “In retrospect, it was inevitable”, which caused the price to briefly rise about $5,000 in an hour to $37,299. On 25 January 2021, Microstrategy announced that it continued to buy bitcoin and as of the same date it had holdings of ₿70,784 worth $2.38 billion. On 8 February 2021 Tesla’s announcement of a bitcoin purchase of US$1.5 billion and the plan to start accepting bitcoin as payment for vehicles, pushed the bitcoin price to $44,141. On 18 February 2021, Elon Musk stated that “owning bitcoin was only a little better than holding conventional cash, but that the slight difference made it a better asset to hold”. After 49 days of accepting the digital currency, Tesla reversed course on 12 May 2021, saying they would no longer take bitcoin due to concerns that “mining” the cryptocurrency was contributing to the consumption of fossil fuels and climate change. The decision resulted in the price of bitcoin dropping around 12% on 13 May. During a July bitcoin conference, Musk suggested Tesla could possibly help bitcoin miners switch to renewable energy in the future and also stated at the same conference that if bitcoin mining reaches, and trends above 50 percent renewable energy usage, that “Tesla would resume accepting bitcoin.” The price for bitcoin rose after this announcement.
In June 2021, the Taproot network software upgrade was approved, adding support for Schnorr signatures, improved functionality of Smart contracts and Lightning Network. The upgrade was activated in November.
In September 2021, Bitcoin in El Salvador became legal tender, alongside the US dollar.
On 16 October 2021, the SEC approved the ProShares Bitcoin Strategy ETF, a cash-settled futures exchange-traded fund (ETF). The first bitcoin ETF in the United States gained 5% on its first trading day on 19 October 2021.
On 25 March 2022, Pavel Zavalny stated that Russia might accept bitcoin for payment for oil and gas exports, in response to sanctions stemming from the 2022 Russian invasion of Ukraine.
On 27 April 2022 Central African Republic adopted bitcoin as legal tender alongside the CFA franc.
On May 10, 2022, the bitcoin price fell to $31,324, as a result of a collapse of a UST stablecoin experiment named Terra, with bitcoin down more than 50% since the November 2021 high. By June 13, 2022, the Celsius Network (a decentralized finance loan company) halted withdrawals and resulted in the bitcoin price falling below $20,000.
In May 2022, following a vote by Wikipedia editors the previous month, the Wikimedia Foundation announced it would stop accepting donations in bitcoin or other cryptocurrencies—eight years after it had first started taking contributions in bitcoin.
The unit of account of the bitcoin system is the bitcoin. Currency codes for representing bitcoin are BTC 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.
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 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 as a digital ledger, bitcoins only exist by virtue of the blockchain; they are represented by the unspent outputs of transactions. ch. 5
Individual blocks, public addresses, and transactions within blocks can be examined using a blockchain explorer.
Transactions are defined using a Forth-like scripting language. ch. 5 Transactions consist of one or more inputs and one or more outputs. When a user sends bitcoins, the user designates each address and the amount of bitcoin being sent to that address in an output. To prevent double spending, each input must refer to a previous unspent output in the blockchain. The use of multiple inputs corresponds to the use of multiple coins in a cash transaction. Since transactions can have multiple outputs, users can send bitcoins to multiple recipients in one transaction. As in a cash transaction, the sum of inputs (coins used to pay) can exceed the intended sum of payments. In such a case, an additional output is used, returning the change back to the payer. Any input satoshis not accounted for in the transaction outputs become the transaction fee.
Though transaction fees are optional, miners can choose which transactions to process and prioritize those that pay higher fees. Miners may choose transactions based on the fee paid relative to their storage size, not the absolute amount of money paid as a fee. These fees are generally measured in satoshis per byte (sat/b). The size of transactions is dependent on the number of inputs used to create the transaction and the number of outputs.mch. 8
The blocks in the blockchain were originally limited to 32 megabytes in size. The block size limit of one megabyte was introduced by Satoshi Nakamoto in 2010.[clarification needed] Eventually, the block size limit of one megabyte created problems for transaction processing, such as increasing transaction fees and delayed processing of transactions. Andreas Antonopoulos has stated Lightning Network is a potential scaling solution and referred to lightning as a second-layer routing network. ch. 8
In the blockchain, bitcoins are registered to bitcoin addresses. Creating a bitcoin address requires nothing more than picking a random valid private key and computing the corresponding bitcoin address. This computation can be done in a split second. But the reverse, computing the private key of a given bitcoin address, is practically unfeasible.: ch. 4 Users can tell others or make public a bitcoin address without compromising its corresponding private key. Moreover, the number of valid private keys is so vast that it is extremely unlikely someone will compute a key pair that is already in use and has funds. The vast number of valid private keys makes it unfeasible that brute force could be used to compromise a private key. To be able to spend their bitcoins, the owner must know the corresponding private key and digitally sign the transaction. The network verifies the signature using the public key; the private key is never revealed. ch. 5
If the private key is lost, the bitcoin network will not recognize any other evidence of ownership; the coins are then unusable, and effectively lost. For example, in 2013 one user claimed to have lost ₿7,500, worth $7.5 million at the time, when he accidentally discarded a hard drive containing his private key. About 20% of all bitcoins are believed to be lost—they would have had a market value of about $20 billion at July 2018 prices.
To ensure the security of bitcoins, the private key must be kept secret. ch. 10 If the private key is revealed to a third party, e.g. through a data breach, the third party can use it to steal any associated bitcoins. As of December 2017, around ₿980,000 have been stolen from cryptocurrency exchanges.
Regarding ownership distribution, as of 28 December 2022, 9.62% of bitcoin addresses own 98.51% of all bitcoins ever mined. The largest of these addresses are thought to belong to exchanges, which are keeping their bitcoin in cold storage.
Mining is a record-keeping service done through the use of computer processing power. 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). The PoW requires miners to find a number called a nonce (a number used just once), such that when the block content is hashed along with the nonce, the result is numerically smaller than the network’s difficulty target. ch. 8 This PoW is easy for any node in the network to verify, but extremely time-consuming to generate. 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 ch. 8 as can be seen in this example block hash:0000000000000000000590fc0f3eba193a278534220b2b37e9849e1a770ca959
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 to 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 being generated continuously, the difficulty of modifying an old block increases as time passes and the number of subsequent blocks (also called confirmations of the given block) increases.
The vast majority of mining power is grouped together in mining pools to reduce variance in miner income. Independent miners may have to work for several years to mine a single block of transactions and receive payment. In a mining pool, all participating miners get paid every time any participant generates a block. This payment is proportionate to the amount of work an individual miner contributed to the pool.
Every 10 minutes, the successful miner finding the new block is allowed by the rest of the network to collect for themselves all transaction fees from transactions they included in the block, as well as a predetermined reward of newly created bitcoins. As of 11 May 2020, this reward is ₿6.25 in newly created bitcoins per block. To claim this reward, a special transaction called a coinbase is included in the block, with the miner as the payee. ch. 8 All bitcoins in existence have been created through this type of transaction. The bitcoin protocol specifies that the reward for adding a block will be reduced by half every 210,000 blocks (approximately every four years), until ₿21 million are generated. The last new bitcoin will be generated around the year 2140. After that, a successful miner would be rewarded by transaction fees only.
source : wikipedia
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