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Bitcoin

Prevailing bitcoin logo

DenominationsPluralbitcoinsSymbol₿ (Unicode: U+20BF ₿ BITCOIN SIGN (HTML ₿))^[a]Ticker symbolBTC, XBT^[b]Precision10⁻⁸Subunits 1⁄1000millibitcoin 1⁄100000000satoshi^[2]DevelopmentOriginal author(s)Satoshi NakamotoWhite paper"Bitcoin: A Peer-to-Peer Electronic Cash System"^[4]Implementation(s)Bitcoin CoreInitial release0.1.0 / 9 January 2009 (12 years ago) (2009-01-09)Latest release0.21.1 / 2 May 2021 (25 days ago) (2021-05-02)^[3]Code repositoryhttps://github.com/bitcoin/bitcoinDevelopment statusActiveWebsitebitcoin.orgLedgerLedger start3 January 2009 (12 years ago) (2009-01-03)Timestamping schemeProof-of-work (partial hash inversion)Hash functionSHA-256Issuance scheduleDecentralized (block reward)
Initially ₿50 per block, halved every 210,000 blocks^[7]Block reward₿6.25^[c]Block time10 minutesBlock explorerMany implementationsCirculating supply₿18,660,000 (as of 20 March 2021^[update])Supply limit₿21,000,000^[5][d]

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1. ^ The symbol was encoded in Unicode version 10.0 at position U+20BF ₿ BITCOIN SIGN in the Currency Symbols block in June 2017.^[1]\n' + '
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2. ^ Compatible with ISO 4217.\n' + '
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3. ^ May 2020 to approximately 2024, halved approximately every four years\n' + '
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4. ^ The supply will approach, but never reach, ₿21 million. Issuance will permanently halt c. 2140 at ₿20,999,999.9769.^{[6]:ch. 8}\n' + '
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This article contains special characters. Without proper rendering support, you may see question marks, boxes, or other symbols.

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Bitcoin (₿) is a decentralized digital currency, without a central bank or single administrator, that can be sent from user to user on the peer-to-peer bitcoin network without the need for intermediaries.^[7] 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.^[8] The currency began use in 2009^[9] when its implementation was released as open-source software.^{[6]:ch. 1}\n' + '

Bitcoins are created as a reward for a process known as mining. They can be exchanged for other currencies, products, and services,^[10] but the real-world value of the coins is extremely volatile.^[11] 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.^[12] Users choose to participate in the digital currency for a number of reasons: ideologies such as commitment to anarchism, decentralization and libertarianism, convenience, using the currency as an investment and pseudonymity of transactions. Increased use has led to a desire among governments for regulation in order to tax, facilitate legal use in trade and for other reasons (such as investigations for money laundering and price manipulation).\n' + '

Bitcoin has been criticized for its use in illegal transactions, the large amount of electricity (and thus carbon footprint) used by mining, price volatility, and thefts from exchanges. Some economists and commentators have characterized it as a speculative bubble at various times. Bitcoin has also been used as an investment, although several regulatory agencies have issued investor alerts about bitcoin.^[11][13][14]\n' + '

The word bitcoin was defined in a white paper published on 31 October 2008.^[4][15] It is a compound of the words bit and coin.^[16] 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.^[17] The Wall Street Journal,^[18] The Chronicle of Higher Education,^[19] and the Oxford English Dictionary^[16] advocate the use of lowercase bitcoin in all cases.\n' + '

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History

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Creation

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The domain name bitcoin.org was registered on 18 August 2008.^[20] On 31 October 2008, a link to a paper authored by Satoshi Nakamoto titled Bitcoin: A Peer-to-Peer Electronic Cash System^[4] was posted to a cryptography mailing list.^[21] Nakamoto implemented the bitcoin software as open-source code and released it in January 2009.^[22][23][9] Nakamoto's identity remains unknown.^[8]\n' + '

On 3 January 2009, the bitcoin network was created when Nakamoto mined the starting block of the chain, known as the genesis block.^[24][25] Embedded in the coinbase of this block was the text "The Times 03/Jan/2009 Chancellor on brink of second bailout for banks".^[9] 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.^[26]:18\n' + '

The receiver of the first bitcoin transaction was cypherpunk Hal Finney, who had created the first reusable proof-of-work system (RPoW) in 2004.^[27] Finney downloaded the bitcoin software on its release date, and on 12 January 2009 received ten bitcoins from Nakamoto.^[28][29] Other early cypherpunk supporters were creators of bitcoin predecessors: Wei Dai, creator of b-money, and Nick Szabo, creator of bit gold.^[24] In 2010, the first known commercial transaction using bitcoin occurred when programmer Laszlo Hanyecz bought two Papa John's pizzas for ₿10,000.^[30]\n' + '

Blockchain analysts estimate that Nakamoto had mined about one million bitcoins^[31] 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.^[32][33] 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.^[34][33]\n' + '

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2011–2012

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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 in bitcoins, worth about $214 million.^[35]:222\n' + '

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.^[36]\n' + '

In 2012, bitcoin prices started at $5.27, growing to $13.30 for the year.^[36] 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.^[37]\n' + '

The Bitcoin Foundation was founded in September 2012 to promote bitcoin's development and uptake.^[38]\n' + '

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.^[39] The software previously used Berkeley DB for database management. Developers switched to LevelDB in release 0.8 in order to reduce blockchain synchronization time.^{[citation needed]} The update to this release resulted in a minor blockchain fork on 11 March 2013. The fork was resolved shortly afterwards.^{[citation needed]} 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.^{[citation needed]} 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.^{[citation needed]}\n' + '

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2013–2016

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In 2013, prices started at $13.30 rising to $770 by 1 January 2014.^[36]\n' + '

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.^[40] During the split, the Mt. Gox exchange briefly halted bitcoin deposits and the price dropped by 23% to $37^[40][41] before recovering to the previous level of approximately $48 in the following hours.^[42]\n' + '

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.^[43][44][45]\n' + '

In April, exchanges BitInstant and Mt. Gox experienced processing delays due to insufficient capacity^[46] resulting in the bitcoin price dropping from $266 to $76 before returning to $160 within six hours.^[47] The bitcoin price rose to $259 on 10 April, but then crashed by 83% to $45 over the next three days.^[37]\n' + '

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.^[48][49] 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.^[50] The FBI seized about ₿30,000^[51] in October 2013 from the dark web website Silk Road, following the arrest of Ross William Ulbricht.^[52][53][54] These bitcoins were sold at blind auction by the United States Marshals Service to venture capital investor Tim Draper.^[51] 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.^[37]\n' + '

On 5 December 2013, the People's Bank of China prohibited Chinese financial institutions from using bitcoins.^[55] After the announcement, the value of bitcoins dropped,^[56] and Baidu no longer accepted bitcoins for certain services.^[57] Buying real-world goods with any virtual currency had been illegal in China since at least 2009.^[58]\n' + '

In 2014, prices started at $770 and fell to $314 for the year.^[36] On 30 July 2014, the Wikimedia Foundation started accepting donations of bitcoin.^[59]\n' + '

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.^[36]\n' + '

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.^[60] Bitcoin Core 0.12.1 was released on 15 April 2016, and enabled multiple soft forks to occur concurrently.^[61] Around 100 contributors worked on Bitcoin Core 0.13.0 which was released on 23 August 2016.\n' + '

In July 2016, the CheckSequenceVerify soft fork activated.^[62]\n' + '

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.^{[citation needed]} The patch which was originally finalised in April, and 35 developers were engaged to deploy it.^{[citation needed]} 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.^{[63][non-primary source needed]} The 0.13.1 release endured extensive testing and research leading to some delays in its release date.^{[citation needed]} SegWit prevents various forms of transaction malleability.^{[64][non-primary source needed]}\n' + '

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2017–2019

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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.^[65] SegWit was subsequently activated on the network on 24 August 2017. The bitcoin price rose almost 50% in the week following SegWit's approval.^[65] On 21 July 2017, bitcoin was trading at $2,748, up 52% from 14 July 2017's $1,835.^[65] 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.^[66] \n' + '

Prices started at $998 in 2017 and rose to $13,412.44 on 1 January 2018,^[36] after reaching its all-time high of $19,783.06 on 17 December 2017.^[67]\n' + '

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.^[37] The percentage of bitcoin trading in the Chinese renminbi fell from over 90% in September 2017 to less than 1% in June 2018.^[68]\n' + '

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.^[69][70] The price on 1 January 2019 was $3,747, down 72% for 2018 and down 81% since the all-time high.^[69][71]\n' + '

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.^{[72][non-primary source needed]}\n' + '

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.^[73] Bitcoin's price was affected even though other cryptocurrencies were stolen at Coinrail and Bancor as investors worried about the security of cryptocurrency exchanges.^[74][75][76] In September 2019 the Intercontinental Exchange (the owner of the NYSE) began trading of bitcoin futures on its exchange called Bakkt.^[77] Bakkt also announced that it would launch options on bitcoin in December 2019.^[78] In December 2019, YouTube removed bitcoin and cryptocurrency videos, but later restored the content after judging they had "made the wrong call."^[79]\n' + '

In February 2019, Canadian cryptocurrency exchange Quadriga Fintech Solutions failed with approximately $200 million missing.^[80] By June 2019 the price had recovered to $13,000.^[81]\n' + '

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2020–present

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According to CoinMetrics and Forbes, on 11 March 281,000 bitcoins were sold by owners who held them 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.^[81] During the week of 11 March 2020 as a result of the COVID-19 pandemic, 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.^[81] On 13 March 2020, bitcoin fell below $4000 during a broad COVID-19 pandemic related market selloff, after trading above $10,000 in February 2020.^[82]\n' + '

In August 2020, MicroStrategy invested $250 million in bitcoin as a treasury reserve asset.^[83] In October 2020, Square, Inc. put approximately 1% of their total assets ($50 million) in bitcoin.^[84] In November 2020, PayPal announced that all users in the US could buy, hold, or sell bitcoin using PayPal.^[85] On 30 November 2020, bitcoin hit a new all-time high of $19,860 topping the previous high from December 2017.^[86] Alexander Vinnik, founder of BTC-e, was convicted and sentenced to 5 years in prison for money laundering in France while refusing to testify during his trial.^[87] In December 2020 Massachusetts Mutual Life Insurance Company announced it has purchased $100 million in bitcoin, or roughly 0.04% of its general investment account.^[88]\n' + '

On 19 January 2021, Elon Musk placed #Bitcoin in his Twitter profile tweeting "In retrospect, it was inevitable", which caused the price to briefly rise about $5000 in an hour to $37,299.^[89] On 25 January 2021 Microstrategy announced it continued to buy bitcoin and as of the same date it had holdings of ₿70,784 worth $2.38 billion.^[90] On 8 February 2021 Tesla's announcement that it had purchased $1.5 billion in bitcoin and planned to start accepting bitcoin as payment for vehicles pushed the bitcoin price to an all-time high of $44,141.^[91] On 18 February 2021, Elon Musk said that "owning bitcoin was only a little better than holding conventional cash, but that the slight difference made it a better asset to hold".^[92]\n' + '

It was announced in September 2020, that the Canton of Zug (in Switzerland) will start to accept tax payments in bitcoin from February 2021.^[93][94]\n' + '

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Design

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Bitcoin is based on an elliptic curve called secp256k1 and encrypted with the ECDSA algorithm.^{[95][better source needed]} The equation for the Bitcoin secp256k1 curve is $\backslash n\text{'}\; +\; \text{'}\backslash n\text{'}\; +\; \text{'}\backslash n\text{'}\; +\; \text{'}y\backslash n\text{'}\; +\; \text{'}\backslash n\text{'}\; +\; \text{'}\backslash n\text{'}\; +\; \text{'}$²=$\backslash n\text{'}\; +\; \text{'}\backslash n\text{'}\; +\; \text{'}\backslash n\text{'}\; +\; \text{'}x\backslash n\text{'}\; +\; \text{'}\backslash n\text{'}\; +\; \text{'}\backslash n\text{'}\; +\; \text{'}$³+7.^{[96][better source needed]} Bitcoin has a proposed Bitcoin Improvement Proposal (BIP) that would add support for Schnorr signatures.^[97]:101\n' + '

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Units and divisibility

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The unit of account of the bitcoin system is a bitcoin. Ticker symbols used to represent bitcoin are BTC^[a] and XBT.^[b][101]:2 Its Unicode character is ₿.^[1] Small amounts of bitcoin used as alternative units are millibitcoin (mBTC), and satoshi (sat). Named in homage to bitcoin's creator, a satoshi is the smallest amount within bitcoin representing 1⁄100000000 bitcoins, one hundred millionth of a bitcoin.^[2] A millibitcoin equals 1⁄1000 bitcoins; one thousandth of a bitcoin or 100,000 satoshis.^[102]\n' + '

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Blockchain

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The bitcoin blockchain is a public ledger that records bitcoin transactions.^[105] It is implemented as a chain of blocks, each block containing a hash of the previous block up to the genesis block^[c] of the chain. A network of communicating nodes running bitcoin software maintains the blockchain.^{[35]:215–219} Transactions of the form payer X sends Y bitcoins to payee Z are broadcast to this network using readily available software applications.\n' + '

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.^[106] 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.^{[6]:ch. 5}\n' + '

Individual blocks, public addresses and transactions within blocks can be examined using a blockchain explorer.^{[citation needed]}\n' + '

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Supply

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The successful miner finding the new block is allowed by the rest of the network to reward themselves with newly created bitcoins and transaction fees.^[107] As of 11 May 2020^[update],^{[citation needed]} the reward amounted to 6.25 newly created bitcoins per block added to the blockchain,^{[citation needed]} plus any transaction fees from payments processed by the block. To mine half of the supply of bitcoins took four years but the remainder will take another 120 years, because of an artificial process called "bitcoin halving" according to which miners are compensated by fewer BTC as time goes on.^{[citation needed]} To claim the reward, a special transaction called a coinbase is included with the processed payments.^{[6]:ch. 8} All bitcoins in existence have been created in such coinbase transactions. The bitcoin protocol specifies that the reward for adding a block will be halved every 210,000 blocks (approximately every four years). Eventually, the reward will decrease to zero, and the limit of 21 million bitcoins^[d] will be reached c. 2140; the record keeping will then be rewarded solely by transaction fees.^[108]\n' + '

In other words, Nakamoto set a monetary policy based on artificial scarcity at bitcoin's inception that the total number of bitcoins could never exceed 21 million. New bitcoins are created roughly every ten minutes and the rate at which they are generated drops by half about every four years until all will be in circulation.^[109]\n' + '

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Transactions

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Transactions are defined using a Forth-like scripting language.^{[6]: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.^[110] 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.^[110] Any input satoshis not accounted for in the transaction outputs become the transaction fee.^[110]\n' + '

Though transaction fees are optional, miners can choose which transactions to process and prioritize those that pay higher fees.^[110] 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.^{[6]:ch. 8}\n' + '

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. Eventually the block size limit of one megabyte created problems for transaction processing, such as increasing transaction fees and delayed processing of transactions.^[111] Andreas Antonopoulos has stated Lightning Network is a potential scaling solution and referred to lightning as a second layer routing network.^{[6]:ch. 8}\n' + '

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Ownership

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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.^{[6]: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.^{[6]:ch. 5}\n' + '

If the private key is lost, the bitcoin network will not recognize any other evidence of ownership;^[35] the coins are then unusable, and effectively lost. For example, in 2013 one user claimed to have lost 7,500 bitcoins, worth $7.5 million at the time, when he accidentally discarded a hard drive containing his private key.^[112] 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.^[113]\n' + '

To ensure the security of bitcoins, the private key must be kept secret.^{[6]: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.^[114] As of December 2017^[update], around 980,000 bitcoins have been stolen from cryptocurrency exchanges.^[115]\n' + '

Regarding ownership distribution, as of 16 March 2018, 0.5% of bitcoin wallets own 87% of all bitcoins ever mined.^[116]\n' + '

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Mining

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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.^[105] Each block contains a SHA-256 cryptographic hash of the previous block,^[105] thus linking it to the previous block and giving the blockchain its name.^{[6]:ch. 7[105]}\n' + '

To be accepted by the rest of the network, a new block must contain a proof-of-work (PoW).^[105] The system used is based on Adam Back's 1997 anti-spam scheme, Hashcash.^{[120][failed verification][4]} The PoW 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.^{[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, ...^{[6]:ch. 8}) before meeting the difficulty target.\n' + '

Every 2,016 blocks (approximately 14 days at roughly 10 min per block), 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.^{[6]:ch. 8} 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.^[121]\n' + '

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.^[122] 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.^[105]\n' + '

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.^[123]\n' + '

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Wallets

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The first wallet program, simply named Bitcoin, and sometimes referred to as the Satoshi client, was released in 2009 by Satoshi Nakamoto as open-source software.^[9] In version 0.5 the client moved from the wxWidgets user interface toolkit to Qt, and the whole bundle was referred to as Bitcoin-Qt.^[124] After the release of version 0.9, the software bundle was renamed Bitcoin Core to distinguish itself from the underlying network.^[125][126] Bitcoin Core is, perhaps, the best known implementation or client. Alternative clients (forks of Bitcoin Core) exist, such as Bitcoin XT, Bitcoin Unlimited,^[34] and Parity Bitcoin.^[127]\n' + 'List of bitcoin forks\n' + '

A wallet stores the information necessary to transact bitcoins. While wallets are often described as a place to hold^[128] or store bitcoins, due to the nature of the system, bitcoins are inseparable from the blockchain transaction ledger. A wallet is more correctly defined as something that "stores the digital credentials for your bitcoin holdings" and allows one to access (and spend) them.^{[6]:ch. 1, glossary} Bitcoin uses public-key cryptography, in which two cryptographic keys, one public and one private, are generated.^[129] At its most basic, a wallet is a collection of these keys.\n' + '

There are several modes which wallets can operate in. They have an inverse relationship with regards to trustlessness and computational requirements.\n' + '

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• Full clients verify transactions directly by downloading a full copy of the blockchain (over 150 GB as of January 2018^[update]).^[130] They are the most secure and reliable way of using the network, as trust in external parties is not required. Full clients check the validity of mined blocks, preventing them from transacting on a chain that breaks or alters network rules.^{[6]:ch. 1} Because of its size and complexity, downloading and verifying the entire blockchain is not suitable for all computing devices.
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• Lightweight clients consult full nodes to send and receive transactions without requiring a local copy of the entire blockchain (see simplified payment verification – SPV). This makes lightweight clients much faster to set up and allows them to be used on low-power, low-bandwidth devices such as smartphones. When using a lightweight wallet, however, the user must trust full nodes, as it can report faulty values back to the user. Lightweight clients follow the longest blockchain and do not ensure it is valid, requiring trust in full nodes.^[131]

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Third-party internet services called online wallets offer similar functionality but may be easier to use. In this case, credentials to access funds are stored with the online wallet provider rather than on the user's hardware.^[132] As a result, the user must have complete trust in the online wallet provider. A malicious provider or a breach in server security may cause entrusted bitcoins to be stolen. An example of such a security breach occurred with Mt. Gox in 2011.^[133]\n' + '

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Physical wallets store the credentials necessary to spend bitcoins offline and can be as simple as a paper printout of the private key:^{[6]:ch. 10} a paper wallet or more advanced such as a hardware wallet. A paper wallet is created with a keypair generated on a computer with no internet connection; the private key is written or printed onto the paper^[g] and then erased from the computer. The paper wallet can then be stored in a safe physical location for later retrieval. Bitcoins stored using a paper wallet are said to be in cold storage.^[134]:39\n' + '

Cameron and Tyler Winklevoss, the founders of the Gemini Trust Co. exchange, reported that they had cut their paper wallets into pieces and stored them in envelopes distributed to safe deposit boxes across the United States.^[135] Through this system, the theft of one envelope would neither allow the thief to steal any bitcoins nor deprive the rightful owners of their access to them.^[136]\n' + '

Physical wallets can also take the form of metal token coins^[137] with a private key accessible under a security hologram in a recess struck on the reverse side.^[138]:38 The security hologram self-destructs when removed from the token, showing that the private key has been accessed.^[139] Originally, these tokens were struck in brass and other base metals, but later used precious metals as bitcoin grew in value and popularity.^[138]:80 Coins with stored face value as high as ₿1000 have been struck in gold.^{[138]:102–104} The British Museum's coin collection includes four specimens from the earliest series^[138]:83 of funded bitcoin tokens; one is currently on display in the museum's money gallery.^[140] In 2013, a Utahn manufacturer of these tokens was ordered by the Financial Crimes Enforcement Network (FinCEN) to register as a money services business before producing any more funded bitcoin tokens.^{[137][138]:80}\n' + '

Another type of physical wallet called a hardware wallet keeps credentials offline while facilitating transactions.^[141] The hardware wallet acts as a computer peripheral and signs transactions as requested by the user, who must press a button on the wallet to confirm that they intended to make the transaction. Hardware wallets never expose their private keys, keeping bitcoins in cold storage even when used with computers that may be compromised by malware.^{[134]:42–45}\n' + '

\n' + '

Decentralization

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Bitcoin is decentralized thus:^[7]\n' + '

\n' + '

• Bitcoin does not have a central authority.^[7]
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• There is no central server; the bitcoin network is peer-to-peer.^[9]
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• There is no central storage; the bitcoin ledger is distributed.^[142]
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• The ledger is public; anybody can store it on their computer.^{[6]:ch. 1}
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• There is no single administrator;^[7] the ledger is maintained by a network of equally privileged miners.^{[6]:ch. 1}
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• Anybody can become a miner.^{[6]:ch. 1}
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• The additions to the ledger are maintained through competition. Until a new block is added to the ledger, it is not known which miner will create the block.^{[6]:ch. 1}
\n' + '
• The issuance of bitcoins is decentralized. They are issued as a reward for the creation of a new block.^[107]
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• Anybody can create a new bitcoin address (a bitcoin counterpart of a bank account) without needing any approval.^{[6]:ch. 1}
\n' + '
• Anybody can send a transaction to the network without needing any approval; the network merely confirms that the transaction is legitimate.^[143]:32

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Conversely, researchers have pointed out at a "trend towards centralization". Although bitcoin can be sent directly from user to user, in practice intermediaries are widely used.^{[35]:220–222} Bitcoin miners join large mining pools to minimize the variance of their income.^{[35]:215, 219–222[144]:3[145]} Because transactions on the network are confirmed by miners, decentralization of the network requires that no single miner or mining pool obtains 51% of the hashing power, which would allow them to double-spend coins, prevent certain transactions from being verified and prevent other miners from earning income.^[146] As of 2013^[update] just six mining pools controlled 75% of overall bitcoin hashing power.^[146] In 2014 mining pool Ghash.io obtained 51% hashing power which raised significant controversies about the safety of the network. The pool has voluntarily capped their hashing power at 39.99% and requested other pools to act responsibly for the benefit of the whole network.^[147] Around the year 2017, over 70% of the hashing power and 90% of transactions were operating from China.^[148]\n' + '

According to researchers, other parts of the ecosystem are also "controlled by a small set of entities", notably the maintenance of the client software, online wallets and simplified payment verification (SPV) clients.^[146]\n' + '

\n' + '

Privacy & Fungibility

\n' + '

Bitcoin is pseudonymous, meaning that funds are not tied to real-world entities but rather bitcoin addresses. Owners of bitcoin addresses are not explicitly identified, but all transactions on the blockchain are public. In addition, transactions can be linked to individuals and companies through "idioms of use" (e.g., transactions that spend coins from multiple inputs indicate that the inputs may have a common owner) and corroborating public transaction data with known information on owners of certain addresses.^[149] Additionally, bitcoin exchanges, where bitcoins are traded for traditional currencies, may be required by law to collect personal information.^[150] To heighten financial privacy, a new bitcoin address can be generated for each transaction.^[151]\n' + '

Wallets and similar software technically handle all bitcoins as equivalent, establishing the basic level of fungibility. Researchers have pointed out that the history of each bitcoin is registered and publicly available in the blockchain ledger, and that some users may refuse to accept bitcoins coming from controversial transactions, which would harm bitcoin's fungibility.^[152] For example, in 2012, Mt. Gox froze accounts of users who deposited bitcoins that were known to have just been stolen.^[153]\n' + '

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Ideology

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Satoshi Nakamoto stated in his white paper that: "The root problem with conventional currencies is all the trust that's required to make it work. The central bank must be trusted not to debase the currency, but the history of fiat currencies is full of breaches of that trust."^[154]\n' + '

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Austrian economics roots

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According to the European Central Bank, the decentralization of money offered by bitcoin has its theoretical roots in the Austrian school of economics, especially with Friedrich von Hayek in his book Denationalisation of Money: The Argument Refined,^[155] in which Hayek advocates a complete free market in the production, distribution and management of money to end the monopoly of central banks.^[156]:22\n' + '

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Anarchism and libertarianism

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According to The New York Times, libertarians and anarchists were attracted to the philosophical idea behind bitcoin. Early bitcoin supporter Roger Ver said: "At first, almost everyone who got involved did so for philosophical reasons. We saw bitcoin as a great idea, as a way to separate money from the state."^[154] The Economist describes bitcoin as "a techno-anarchist project to create an online version of cash, a way for people to transact without the possibility of interference from malicious governments or banks".^[157] Economist Paul Krugman argues that cryptocurrencies like bitcoin are "something of a cult" based in "paranoid fantasies" of government power.^[158]\n' + '

\n' + '

External video The Declaration Of Bitcoin's Independence, BraveTheWorld, 4:38^[159]

Nigel Dodd argues in The Social Life of Bitcoin that the essence of the bitcoin ideology is to remove money from social, as well as governmental, control.^[160] Dodd quotes a YouTube video, with Roger Ver, Jeff Berwick, Charlie Shrem, Andreas Antonopoulos, Gavin Wood, Trace Meyer and other proponents of bitcoin reading The Declaration of Bitcoin's Independence. The declaration includes a message of crypto-anarchism with the words: "Bitcoin is inherently anti-establishment, anti-system, and anti-state. Bitcoin undermines governments and disrupts institutions because bitcoin is fundamentally humanitarian."^[160][159]\n' + '

David Golumbia says that the ideas influencing bitcoin advocates emerge from right-wing extremist movements such as the Liberty Lobby and the John Birch Society and their anti-Central Bank rhetoric, or, more recently, Ron Paul and Tea Party-style libertarianism.^[161] Steve Bannon, who owns a "good stake" in bitcoin, considers it to be "disruptive populism. It takes control back from central authorities. It's revolutionary."^[162]\n' + '

A 2014 study of Google Trends data found correlations between bitcoin-related searches and ones related to computer programming and illegal activity, but not libertarianism or investment topics.^[163]\n' + '

\n' + '

Economics

\n' + '\n' + '\n' + '

Bitcoin is a digital asset designed to work in peer-to-peer transactions as a currency.^[4][164] Bitcoins have three qualities useful in a currency, according to The Economist in January 2015: they are "hard to earn, limited in supply and easy to verify."^[165] Per some researchers, as of 2015^[update], bitcoin functions more as a payment system than as a currency.^[35]\n' + '

Economists define money as serving the following three purposes: a store of value, a medium of exchange, and a unit of account.^[166] According to The Economist in 2014, bitcoin functions best as a medium of exchange.^[166] However, this is debated, and a 2018 assessment by The Economist stated that cryptocurrencies met none of these three criteria.^[157]\n' + 'Yale economist Robert J. Shiller writes that bitcoin has potential as a unit of account for measuring the relative value of goods, as with Chile's Unidad de Fomento, but that "Bitcoin in its present form [...] doesn't really solve any sensible economic problem".^[167]\n' + '

According to research by Cambridge University, between 2.9 million and 5.8 million unique users used a cryptocurrency wallet in 2017, most of them for bitcoin. The number of users has grown significantly since 2013, when there were 300,000–1.3 million users.^[12]\n' + '

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Acceptance by merchants

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The overwhelming majority of bitcoin transactions take place on a cryptocurrency exchange, rather than being used in transactions with merchants.^[168] Delays processing payments through the blockchain of about ten minutes make bitcoin use very difficult in a retail setting. Prices are not usually quoted in units of bitcoin and many trades involve one, or sometimes two, conversions into conventional currencies.^[35] Merchants that do accept bitcoin payments may use payment service providers to perform the conversions.^[169]\n' + '

In 2017 and 2018 bitcoin's acceptance among major online retailers included only three of the top 500 U.S. online merchants, down from five in 2016.^[168] Reasons for this decline include high transaction fees due to bitcoin's scalability issues and long transaction times.^[170]\n' + '

Bloomberg reported that the largest 17 crypto merchant-processing services handled $69 million in June 2018, down from $411 million in September 2017. Bitcoin is "not actually usable" for retail transactions because of high costs and the inability to process chargebacks, according to Nicholas Weaver, a researcher quoted by Bloomberg. High price volatility and transaction fees make paying for small retail purchases with bitcoin impractical, according to economist Kim Grauer. However, bitcoin continues to be used for large-item purchases on sites such as Overstock.com, and for cross-border payments to freelancers and other vendors.^[171]\n' + '

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Financial institutions

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Bitcoins can be bought on digital currency exchanges.\n' + '

Per researchers, "there is little sign of bitcoin use" in international remittances despite high fees charged by banks and Western Union who compete in this market.^[35] The South China Morning Post, however, mentions the use of bitcoin by Hong Kong workers to transfer money home.^[172]\n' + '

In 2014, the National Australia Bank closed accounts of businesses with ties to bitcoin,^[173] and HSBC refused to serve a hedge fund with links to bitcoin.^[174] Australian banks in general have been reported as closing down bank accounts of operators of businesses involving the currency.^[175]\n' + '

On 10 December 2017, the Chicago Board Options Exchange started trading bitcoin futures,^[176] followed by the Chicago Mercantile Exchange, which started trading bitcoin futures on 17 December 2017.^[177]\n' + '

In September 2019 the Central Bank of Venezuela, at the request of PDVSA, ran tests to determine if bitcoin and ether could be held in central bank's reserves. The request was motivated by oil company's goal to pay its suppliers.^[178]\n' + '

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As an investment

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The Winklevoss twins have purchased bitcoin. In 2013, The Washington Post reported a claim that they owned 1% of all the bitcoins in existence at the time.^[179]\n' + '

Other methods of investment are bitcoin funds. The first regulated bitcoin fund was established in Jersey in July 2014 and approved by the Jersey Financial Services Commission.^[180]\n' + '

Forbes named bitcoin the best investment of 2013.^[181] In 2014, Bloomberg named bitcoin one of its worst investments of the year.^[182] In 2015, bitcoin topped Bloomberg's currency tables.^[183]\n' + '

According to bitinfocharts.com, in 2017 there are 9,272 bitcoin wallets with more than $1 million worth of bitcoins.^[184] The exact number of bitcoin millionaires is uncertain as a single person can have more than one bitcoin wallet.\n' + '

In August 2020, MicroStrategy invested in Bitcoin.^[185][186]\n' + '

In May 2021, the Bitcoin's market share on exchanges dropped from 70% to 45% as investors pursued altcoins.^[187]\n' + '

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Venture capital

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Peter Thiel's Founders Fund invested US$3 million in BitPay.^[188] In 2012, an incubator for bitcoin-focused start-ups was founded by Adam Draper, with financing help from his father, venture capitalist Tim Draper, one of the largest bitcoin holders after winning an auction of 30,000 bitcoins,^[189] at the time called "mystery buyer".^[190] The company's goal is to fund 100 bitcoin businesses within 2–3 years with $10,000 to $20,000 for a 6% stake.^[189] Investors also invest in bitcoin mining.^[191] According to a 2015 study by Paolo Tasca, bitcoin startups raised almost $1 billion in three years (Q1 2012 – Q1 2015).^[192]\n' + '

\n' + '

Price and volatility

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The price of bitcoins has gone through cycles of appreciation and depreciation referred to by some as bubbles and busts.^[193] In 2011, the value of one bitcoin rapidly rose from about US$0.30 to US$32 before returning to US$2.^[194] In the latter half of 2012 and during the 2012–13 Cypriot financial crisis, the bitcoin price began to rise,^[195] reaching a high of US$266 on 10 April 2013, before crashing to around US$50. On 29 November 2013, the cost of one bitcoin rose to a peak of US$1,242.^[196] In 2014, the price fell sharply, and as of April remained depressed at little more than half 2013 prices. As of August 2014^[update] it was under US$600.^[197]\n' + '

According to Mark T. Williams, as of 30 September 2014^[update], bitcoin has volatility seven times greater than gold, eight times greater than the S&P 500, and 18 times greater than the US dollar.^[198] Hodl is a meme created in reference to holding (as opposed to selling) during periods of volatility. Unusual for an asset, bitcoin weekend trading during December 2020 was higher than for weekdays.^[199] Hedge funds (using high leverage and derivates)^[200] have attempted to use the volatility to profit from downward price movements. At the end of January 2021, such positions were over $1 billion, their highest of all time.^[201][202]\n' + 'As of 8 February 2021^[update], the closing price of bitcoin equals US$44,797.^[203]\n' + '

\n' + '

Legal status, tax and regulation

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Because of bitcoin's decentralized nature and its trading on online exchanges located in many countries, regulation of bitcoin has been difficult. However, the use of bitcoin can be criminalized, and shutting down exchanges and the peer-to-peer economy in a given country would constitute a de facto ban.^[204] The legal status of bitcoin varies substantially from country to country and is still undefined or changing in many of them. Regulations and bans that apply to bitcoin probably extend to similar cryptocurrency systems.^[192]\n' + '

According to the Library of Congress, an "absolute ban" on trading or using cryptocurrencies applies in nine countries: Algeria, Bolivia, Egypt, Iraq, Morocco, Nepal, Pakistan, Vietnam, and the United Arab Emirates. An "implicit ban" applies in another 15 countries, which include Bahrain, Bangladesh, China, Colombia, the Dominican Republic, Indonesia, Kuwait, Lesotho, Lithuania, Macau, Oman, Qatar, Saudi Arabia and Taiwan.^[205]\n' + '

In October 2020, the Islamic Republic News Agency announced pending regulations that would require bitcoin miners in Iran to sell bitcoin to the Central Bank of Iran, and the central bank would use it for imports.^[206] Iran, as of October 2020, had issued over 1,000 bitcoin mining licenses.^[206] The Iranian government initially took a stance against cryptocurrency, but later changed it after seeing that digital currency could be used to circumvent sanctions.^[207] The US Office of Foreign Assets Control listed two Iranians and their bitcoin addresses as part of its Specially Designated Nationals and Blocked Persons List for their role in the 2018 Atlanta cyberattack whose ransom was paid in bitcoin.^[208]\n' + '

\n' + '

Regulatory warnings

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The U.S. Commodity Futures Trading Commission has issued four "Customer Advisories" for bitcoin and related investments.^[13] A July 2018 warning emphasized that trading in any cryptocurrency is often speculative, and there is a risk of theft from hacking, and fraud.^[209] In May 2014 the U.S. Securities and Exchange Commission warned that investments involving bitcoin might have high rates of fraud, and that investors might be solicited on social media sites.^[210] An earlier "Investor Alert" warned about the use of bitcoin in Ponzi schemes.^[211]\n' + '

The European Banking Authority issued a warning in 2013 focusing on the lack of regulation of bitcoin, the chance that exchanges would be hacked, the volatility of bitcoin's price, and general fraud.^[212] FINRA and the North American Securities Administrators Association have both issued investor alerts about bitcoin.^[213][214]\n' + '

\n' + '

Price manipulation investigation

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An official investigation into bitcoin traders was reported in May 2018.^[215] The U.S. Justice Department launched an investigation into possible price manipulation, including the techniques of spoofing and wash trades.^{[216][217][218]}\n' + '

The U.S. federal investigation was prompted by concerns of possible manipulation during futures settlement dates. The final settlement price of CME bitcoin futures is determined by prices on four exchanges, Bitstamp, Coinbase, itBit and Kraken. Following the first delivery date in January 2018, the CME requested extensive detailed trading information but several of the exchanges refused to provide it and later provided only limited data. The Commodity Futures Trading Commission then subpoenaed the data from the exchanges.^[219][220]\n' + '

State and provincial securities regulators, coordinated through the North American Securities Administrators Association, are investigating "bitcoin scams" and ICOs in 40 jurisdictions.^[221]\n' + '

Academic research published in the Journal of Monetary Economics concluded that price manipulation occurred during the Mt Gox bitcoin theft and that the market remains vulnerable to manipulation.^[222] The history of hacks, fraud and theft involving bitcoin dates back to at least 2011.^[223]\n' + '

Research by John M. Griffin and Amin Shams in 2018 suggests that trading associated with increases in the amount of the Tether cryptocurrency and associated trading at the Bitfinex exchange account for about half of the price increase in bitcoin in late 2017.^[224][225]\n' + '

J.L. van der Velde, CEO of both Bitfinex and Tether, denied the claims of price manipulation: "Bitfinex nor Tether is, or has ever, engaged in any sort of market or price manipulation. Tether issuances cannot be used to prop up the price of bitcoin or any other coin/token on Bitfinex."^[226]\n' + '

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Analysis

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External video Cryptocurrencies: looking beyond the hype, Hyun Song Shin, Bank for International Settlements, 2:48^[227]

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The Bank for International Settlements summarized several criticisms of bitcoin in Chapter V of their 2018 annual report. The criticisms include the lack of stability in bitcoin's price, the high energy consumption, high and variable transactions costs, the poor security and fraud at cryptocurrency exchanges, vulnerability to debasement (from forking), and the influence of miners.^{[227][228][229]}\n' + '

François R. Velde, Senior Economist at the Chicago Fed, described bitcoin as "an elegant solution to the problem of creating a digital currency".^[230] David Andolfatto, Vice President at the Federal Reserve Bank of St. Louis, stated that bitcoin is a threat to the establishment, which he argues is a good thing for the Federal Reserve System and other central banks, because it prompts these institutions to operate sound policies.^{[119]:33[231][232]}\n' + '

\n' + '

Economic concerns

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Bitcoin, along with other cryptocurrencies, has been described as an economic bubble by at least eight Nobel Memorial Prize in Economic Sciences laureates at various times, including Robert Shiller on 1 March 2014,^[167] Joseph Stiglitz on 29 November 2017,^[233] and Richard Thaler on 21 December 2017.^[234][235] On 29 January 2018, a noted Keynesian economist Paul Krugman has described bitcoin as "a bubble wrapped in techno-mysticism inside a cocoon of libertarian ideology",^[158] on 2 February 2018, professor Nouriel Roubini of New York University has called bitcoin the "mother of all bubbles",^[236] and on 27 April 2018, a University of Chicago economist James Heckman has compared it to the 17th-century tulip mania.^[235]\n' + '

Journalists, economists, investors, and the central bank of Estonia have voiced concerns that bitcoin is a Ponzi scheme.^{[237][238][239][240]} In April 2013, Eric Posner, a law professor at the University of Chicago, stated that "a real Ponzi scheme takes fraud; bitcoin, by contrast, seems more like a collective delusion."^[241] A July 2014 report by the World Bank concluded that bitcoin was not a deliberate Ponzi scheme.^[242]:7 In June 2014, the Swiss Federal Council examined concerns that bitcoin might be a pyramid scheme, and concluded that "since in the case of bitcoin the typical promises of profits are lacking, it cannot be assumed that bitcoin is a pyramid scheme."^[243]:21\n' + '

\n' + '

Energy consumption and carbon footprint

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Bitcoin has been criticized for the amount of electricity consumed by mining.\n' + '

As of 2015^[update], estimated combined electricity consumption attributed to mining was 166.7 megawatts and by 2017, was estimated to be between one and four gigawatts of electricity.^[244][165] In 2018, bitcoin was estimated by to use 2.55 to 3.572 GW, or around 6% of the total power consumed by the global banking sector.^{[245][246][247]} In July 2019 BBC reported bitcoin consumes about 7 gigawatts, 0.2% of the global total, or equivalent to that of Switzerland.^[248] A 2021 estimate from the University of Cambridge suggests bitcoin consumes more than 178 (TWh) annually, ranking it in the top 30 energy consumers if it were a country.^[249]\n' + '

Bitcoin is mined in places like Iceland where geothermal energy is cheap and cooling Arctic air is free.^[250] Bitcoin miners are known to use hydroelectric power in Tibet, Quebec, Washington (state), and Austria to reduce electricity costs.^[245][251] Miners are attracted to suppliers such as Hydro Quebec that have energy surpluses.^[252] \n' + '

According to a University of Cambridge study, much of bitcoin mining is done in China, where electricity is subsidized by the government.^[253][254] A significant part of Bitcoin mining is powered by cheap electricity in Xinjiang, which mostly comes from coal power.^[255][256] In April 2021 a coal mine explosion in the province coincided with a 35% drop in hashing power and a flash crash in price.^[257][255] In other provinces, such as Hunan and Sichuan, mining farms use more hydropower, however these account for at most 4% of hash power. According to Alex de Vries, renewable energy is not a good match for Bitcoin mining as 24/7 operations are best for ROI on mining devices.^[257] In 2021, a US company purchased the Greenidge coal power plant and converted it to burn natural gas for the sole purpose of mining bitcoin, which has proven to be highly profitable, in spite of protests of local residents against air pollution and thermal pollution.^[258]\n' + '

Concerns about bitcoin's environmental impact relate bitcoin's energy consumption to carbon emissions.^[259][260] The difficulty of translating the energy consumption into carbon emissions lies in the decentralized nature of bitcoin impeding the localization of miners to examine the electricity mix used. The results of recent studies analyzing bitcoin's carbon footprint vary.^{[261][262][263][264]} A study published in Nature Climate Change in 2018 claims that bitcoin "could alone produce enough CO
2 emissions to push warming above 2 °C within less than three decades."^[263] However, other researchers criticized this analysis, arguing the underlying scenarios were inadequate, leading to overestimations.^{[265][266][267]} According to studies published in Joule and American Chemical Society in 2019, bitcoin's annual energy consumption results in annual carbon emission ranging from 17^[247] to 22.9 MtCO
2 which is comparable to the level of emissions of countries as Jordan and Sri Lanka or Kansas City.^[264] George Kamiya, writing for the International Energy Agency, says that "predictions about bitcoin consuming the entire world's electricity" are sensational, but that the area "requires careful monitoring and rigorous analysis".^[268]\n' + '

\n' + '

Use in illegal transactions

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Bitcoin held at exchanges are vulnerable to theft through phishing, scamming, and hacking. As of December 2017^[update], around 980,000 bitcoins have been stolen from cryptocurrency exchanges.^[115]\n' + '

The use of bitcoin by criminals has attracted the attention of financial regulators, legislative bodies, law enforcement, and the media.^[269] Bitcoin gained early notoriety for its use on the Silk Road. The U.S. Senate held a hearing on virtual currencies in November 2013.^[270] The U.S. government claimed that bitcoin was used to facilitate payments related to Russian interference in the 2016 United States elections.^[271] However, a 2021 study led by former CIA director Michael Morell showed that broad generalizations about the use of bitcoin in illicit finance are significantly overstated and that blockchain analysis is an effective crime fighting and intelligence gathering tool.^[272]\n' + '

Several news outlets have asserted that the popularity of bitcoins hinges on the ability to use them to purchase illegal goods.^[164][273] Nobel-prize winning economist Joseph Stiglitz says that bitcoin's anonymity encourages money laundering and other crimes.^[274][275]\n' + '

In 2014, researchers at the University of Kentucky found "robust evidence that computer programming enthusiasts and illegal activity drive interest in bitcoin, and find limited or no support for political and investment motives".^[163] Australian researchers have estimated that 25% of all bitcoin users and 44% of all bitcoin transactions are associated with illegal activity as of April 2017^[update]. There were an estimated 24 million bitcoin users primarily using bitcoin for illegal activity. They held $8 billion worth of bitcoin, and made 36 million transactions valued at $72 billion.^[276][277]\n' + '

\n' + '

Software implementation

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The start screen under Fedora

Original author(s)Satoshi NakamotoInitial release2009Stable release0.20.1 (2 August 2020; 9 months ago (2020-08-02)) [±]\n' + 'Repositorygithub.com/bitcoin/bitcoinWritten inC++Operating systemLinux, Windows, macOSTypeCryptocurrencyLicenseMIT LicenseWebsitebitcoincore.org

\n' + '

Bitcoin Core is free and open-source software that serves as a bitcoin node (the set of which form the bitcoin network) and provides a bitcoin wallet which fully verifies payments. It is considered to be bitcoin's reference implementation.^[278] Initially, the software was published by Satoshi Nakamoto under the name "Bitcoin", and later renamed to "Bitcoin Core" to distinguish it from the network.^[279] It is also known as the Satoshi client.^[280]\n' + '

The MIT Digital Currency Initiative funds some of the development of Bitcoin Core.^[281] The project also maintains the cryptography library libsecp256k1.^[282]\n' + '

Bitcoin Core includes a transaction verification engine and connects to the bitcoin network as a full node.^[280] Moreover, a cryptocurrency wallet, which can be used to transfer funds, is included by default.^[282] The wallet allows for the sending and receiving of bitcoins. It does not facilitate the buying or selling of bitcoin. It allows users to generate QR codes to receive payment.\n' + '

The software validates the entire blockchain, which includes all bitcoin transactions ever. This distributed ledger which has reached more than 235 gigabytes in size as of Jan 2019, must be downloaded or synchronized before full participation of the client may occur.^[280] Although the complete blockchain is not needed all at once since it is possible to run in pruning mode. A command line-based daemon with a JSON-RPC interface, bitcoind, is bundled with Bitcoin Core. It also provides access to testnet, a global testing environment that imitates the bitcoin main network using an alternative blockchain where valueless "test bitcoins" are used. Regtest or Regression Test Mode creates a private blockchain which is used as a local testing environment.^[283] Finally, bitcoin-cli, a simple program which allows users to send RPC commands to bitcoind, is also included.\n' + '

Checkpoints which have been hard coded into the client are used only to prevent Denial of Service attacks against nodes which are initially syncing the chain. For this reason the checkpoints included are only as of several years ago.^{[284][285][failed verification]} A one megabyte block size limit was added in 2010 by Satoshi Nakamoto. This limited the maximum network capacity to about three transactions per second.^[286] Since then, network capacity has been improved incrementally both through block size increases and improved wallet behavior. A network alert system was included by Satoshi Nakamoto as a way of informing users of important news regarding bitcoin.^[287] In November 2016 it was retired. It had become obsolete as news on bitcoin is now widely disseminated.\n' + '

Bitcoin Core includes a scripting language inspired by Forth that can define transactions and specify parameters.^[288] ScriptPubKey is used to "lock" transactions based on a set of future conditions. scriptSig is used to meet these conditions or "unlock" a transaction. Operations on the data are performed by various OP_Codes. Two stacks are used - main and alt. Looping is forbidden.\n' + '

Bitcoin Core uses OpenTimestamps to timestamp merge commits.^[289]\n' + '

The original creator of the bitcoin client has described their approach to the software's authorship as it being written first to prove to themselves that the concept of purely peer-to-peer electronic cash was valid and that a paper with solutions could be written. The lead developer is Wladimir J. van der Laan, who took over the role on 8 April 2014.^[290] Gavin Andresen was the former lead maintainer for the software client. Andresen left the role of lead developer for bitcoin to work on the strategic development of its technology.^[290] Bitcoin Core in 2015 was central to a dispute with Bitcoin XT, a competing client that sought to increase the blocksize.^[291] Over a dozen different companies and industry groups fund the development of Bitcoin Core.\n' + '

\n' + '

In popular culture

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Term "HODL"

\n' + '

Hodl (/ˈhɒdəl/ HOD-əl; often written HODL) is slang in the cryptocurrency community for holding a cryptocurrency rather than selling it.^[292] A person who does this is known as a Hodler. It originated in a December 2013 post on the Bitcoin Forum message board by an apparently inebriated user who posted with a typo in the subject, "I AM HODLING."^[293] It is often humorously suggested to be a backronym to "hold on for dear life".^[294] In 2017, Quartz listed it as one of the essential slang terms in Bitcoin culture, and described it as a stance, "to stay invested in bitcoin and not to capitulate in the face of plunging prices."^[295] TheStreet.com referred to it as the "favorite mantra" of Bitcoin holders.^[296] Bloomberg News referred to it as a "mantra" for holders during market routs.^[297]\n' + '

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Literature

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In Charles Stross' 2013 science fiction novel, Neptune's Brood, the universal interstellar payment system is known as "bitcoin" and operates using cryptography.^[298] Stross later blogged that the reference was intentional, saying "I wrote Neptune's Brood in 2011. Bitcoin was obscure back then, and I figured had just enough name recognition to be a useful term for an interstellar currency: it'd clue people in that it was a networked digital currency."^[299]\n' + '

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Film

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The 2014 documentary The Rise and Rise of Bitcoin portrays the diversity of motives behind the use of bitcoin by interviewing people who use it. These include a computer programmer and a drug dealer.^[300] The 2016 documentary Banking on Bitcoin is an introduction to the beginnings of bitcoin and the ideas behind cryptocurrency today.^[301]\n' + '

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Academia

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In September 2015, the establishment of the peer-reviewed academic journal Ledger (ISSN 2379-5980) was announced. It covers studies of cryptocurrencies and related technologies, and is published by the University of Pittsburgh.^[302] The journal encourages authors to digitally sign a file hash of submitted papers, which will then be timestamped into the bitcoin blockchain. Authors are also asked to include a personal bitcoin address in the first page of their papers.^[303][304]\n' + '

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See also

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Notes

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References

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External links

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Wikimedia Commons has media related to Bitcoin.

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• Bitcoin.org website
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• Bitcoin at Curlie

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A barcode or bar code is a method of representing data in a visual, machine-readable form. Initially, barcodes represented data by varying the widths and spacings of parallel lines. These barcodes, now commonly referred to as linear or one-dimensional (1D), can be scanned by special optical scanners, called barcode readers, of which there are several types. Later, two-dimensional (2D) variants were developed, using rectangles, dots, hexagons and other patterns, called matrix codes or 2D barcodes, although they do not use bars as such. 2D barcodes can be read using purpose-built 2D optical scanners, which exist in a few different forms. 2D barcodes can also be read by a digital camera connected to a microcomputer running software that takes a photographic image of the barcode and analyzes the image to deconstruct and decode the 2D barcode. A mobile device with an inbuilt camera, such as smartphone, can function as the latter type of 2D barcode reader using specialized application software. (The same sort of mobile device could also read 1D barcodes, depending on the application software.)\n' + '

The barcode was invented by Norman Joseph Woodland and Bernard Silver and patented in the US in 1951.^[1] The invention was based on Morse code^[2] that was extended to thin and thick bars. However, it took over twenty years before this invention became commercially successful. An early use of one type of barcode in an industrial context was sponsored by the Association of American Railroads in the late 1960s. Developed by General Telephone and Electronics (GTE) and called KarTrak ACI (Automatic Car Identification), this scheme involved placing colored stripes in various combinations on steel plates which were affixed to the sides of railroad rolling stock. Two plates were used per car, one on each side, with the arrangement of the colored stripes encoding information such as ownership, type of equipment, and identification number.^[3] The plates were read by a trackside scanner, located for instance, at the entrance to a classification yard, while the car was moving past.^[4] The project was abandoned after about ten years because the system proved unreliable after long-term use.^[3]\n' + '

Barcodes became commercially successful when they were used to automate supermarket checkout systems, a task for which they have become almost universal. The Uniform Grocery Product Code Council had chosen, in 1973, the barcode design developed by George Laurer. Laurer's barcode, with vertical bars, printed better than the circular barcode developed by Woodland and Silver.^[5] Their use has spread to many other tasks that are generically referred to as automatic identification and data capture (AIDC). The first scanning of the now-ubiquitous Universal Product Code (UPC) barcode was on a pack of Wrigley Company chewing gum in June 1974 at a Marsh supermarket in Troy, Ohio, using scanner produced by Photographic Sciences Corporation.^[6][5] QR codes, a specific type of 2D barcode, have recently become very popular due to the growth in smartphone ownership.^[7]\n' + '

Other systems have made inroads in the AIDC market, but the simplicity, universality and low cost of barcodes has limited the role of these other systems, particularly before technologies such as radio-frequency identification (RFID) became available after 1995.\n' + '

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History

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This article duplicates the scope of other articles, specifically, Universal Product Code#History. Please discuss this issue on the talk page and edit it to conform with Wikipedia's Manual of Style. (December 2013)

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In 1948 Bernard Silver, a graduate student at Drexel Institute of Technology in Philadelphia, Pennsylvania, US overheard the president of the local food chain, Food Fair, asking one of the deans to research a system to automatically read product information during checkout.^[8] Silver told his friend Norman Joseph Woodland about the request, and they started working on a variety of systems. Their first working system used ultraviolet ink, but the ink faded too easily and was expensive.^[9]\n' + '

Convinced that the system was workable with further development, Woodland left Drexel, moved into his father's apartment in Florida, and continued working on the system. His next inspiration came from Morse code, and he formed his first barcode from sand on the beach. "I just extended the dots and dashes downwards and made narrow lines and wide lines out of them."^[9] To read them, he adapted technology from optical soundtracks in movies, using a 500-watt incandescent light bulb shining through the paper onto an RCA935 photomultiplier tube (from a movie projector) on the far side. He later decided that the system would work better if it were printed as a circle instead of a line, allowing it to be scanned in any direction.\n' + '

On 20 October 1949, Woodland and Silver filed a patent application for "Classifying Apparatus and Method", in which they described both the linear and bull's eye printing patterns, as well as the mechanical and electronic systems needed to read the code. The patent was issued on 7 October 1952 as US Patent 2,612,994.^[1] In 1951, Woodland moved to IBM and continually tried to interest IBM in developing the system. The company eventually commissioned a report on the idea, which concluded that it was both feasible and interesting, but that processing the resulting information would require equipment that was some time off in the future.\n' + '

IBM offered to buy the patent, but the offer was not accepted. Philco purchased the patent in 1962 and then sold it to RCA sometime later.^[9]\n' + '

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Collins at Sylvania

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During his time as an undergraduate, David Jarrett Collins worked at the Pennsylvania Railroad and became aware of the need to automatically identify railroad cars. Immediately after receiving his master's degree from MIT in 1959, he started work at GTE Sylvania and began addressing the problem. He developed a system called KarTrak using blue and red reflective stripes attached to the side of the cars, encoding a six-digit company identifier and a four-digit car number.^[9] Light reflected off the colored stripes was read by photomultiplier vacuum tubes.^[10]\n' + '

The Boston and Maine Railroad tested the KarTrak system on their gravel cars in 1961. The tests continued until 1967, when the Association of American Railroads (AAR) selected it as a standard, Automatic Car Identification, across the entire North American fleet. The installations began on 10 October 1967. However, the economic downturn and rash of bankruptcies in the industry in the early 1970s greatly slowed the rollout, and it was not until 1974 that 95% of the fleet was labeled. To add to its woes, the system was found to be easily fooled by dirt in certain applications, which greatly affected accuracy. The AAR abandoned the system in the late 1970s, and it was not until the mid-1980s that they introduced a similar system, this time based on radio tags.^[11]\n' + '

The railway project had failed, but a toll bridge in New Jersey requested a similar system so that it could quickly scan for cars that had purchased a monthly pass. Then the U.S. Post Office requested a system to track trucks entering and leaving their facilities. These applications required special retroreflector labels. Finally, Kal Kan asked the Sylvania team for a simpler (and cheaper) version which they could put on cases of pet food for inventory control.\n' + '

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Computer Identics Corporation

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In 1967, with the railway system maturing, Collins went to management looking for funding for a project to develop a black-and-white version of the code for other industries. They declined, saying that the railway project was large enough, and they saw no need to branch out so quickly.\n' + '

Collins then quit Sylvania and formed the Computer Identics Corporation.^[9] As its first innovations, Computer Identics moved from using incandescent light bulbs in its systems, replacing them with helium–neon lasers, and incorporated a mirror as well, making it capable of locating a barcode up to several feet in front of the scanner. This made the entire process much simpler and more reliable, and typically enabled these devices to deal with damaged labels, as well, by recognizing and reading the intact portions.\n' + '

Computer Identics Corporation installed one of its first two scanning systems in the spring of 1969 at a General Motors (Buick) factory in Flint, Michigan.^[9] The system was used to identify a dozen types of transmissions moving on an overhead conveyor from production to shipping. The other scanning system was installed at General Trading Company's distribution center in Carlstadt, New Jersey to direct shipments to the proper loading bay.\n' + '

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Universal Product Code

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In 1966, the National Association of Food Chains (NAFC) held a meeting on the idea of automated checkout systems. RCA, who had purchased the rights to the original Woodland patent, attended the meeting and initiated an internal project to develop a system based on the bullseye code. The Kroger grocery chain volunteered to test it.\n' + '

In the mid-1970s, the NAFC established the Ad-Hoc Committee for U.S. Supermarkets on a Uniform Grocery-Product Code to set guidelines for barcode development. In addition, it created a symbol-selection subcommittee to help standardize the approach. In cooperation with consulting firm, McKinsey & Co., they developed a standardized 11-digit code for identifying products. The committee then sent out a contract tender to develop a barcode system to print and read the code. The request went to Singer, National Cash Register (NCR), Litton Industries, RCA, Pitney-Bowes, IBM and many others.^[12] A wide variety of barcode approaches was studied, including linear codes, RCA's bullseye concentric circle code, starburst patterns and others.\n' + '

In the spring of 1971, RCA demonstrated their bullseye code at another industry meeting. IBM executives at the meeting noticed the crowds at the RCA booth and immediately developed their own system. IBM marketing specialist Alec Jablonover remembered that the company still employed Woodland, and he^[who?] established a new facility in Raleigh-Durham Research Triangle Park to lead development.\n' + '

In July 1972, RCA began an 18-month test in a Kroger store in Cincinnati. Barcodes were printed on small pieces of adhesive paper, and attached by hand by store employees when they were adding price tags. The code proved to have a serious problem; the printers would sometimes smear ink, rendering the code unreadable in most orientations. However, a linear code, like the one being developed by Woodland at IBM, was printed in the direction of the stripes, so extra ink would simply make the code "taller" while remaining readable. So on 3 April 1973, the IBM UPC was selected as the NAFC standard. IBM had designed five versions of UPC symbology for future industry requirements: UPC A, B, C, D, and E.^[13]\n' + '

NCR installed a testbed system at Marsh's Supermarket in Troy, Ohio, near the factory that was producing the equipment. On 26 June 1974, Clyde Dawson pulled a 10-pack of Wrigley's Juicy Fruit gum out of his basket and it was scanned by Sharon Buchanan at 8:01 am. The pack of gum and the receipt are now on display in the Smithsonian Institution. It was the first commercial appearance of the UPC.^[14]\n' + '

In 1971, an IBM team was assembled for an intensive planning session, threshing out, 12 to 18 hours a day, how the technology would be deployed and operate cohesively across the system, and scheduling a roll-out plan. By 1973, the team were meeting with grocery manufacturers to introduce the symbol that would need to be printed on the packaging or labels of all of their products. There were no cost savings for a grocery to use it, unless at least 70% of the grocery's products had the barcode printed on the product by the manufacturer. IBM projected that 75% would be needed in 1975. Yet, although this was achieved, there were still scanning machines in fewer than 200 grocery stores by 1977.^[15]\n' + '

Economic studies conducted for the grocery industry committee projected over $40 million in savings to the industry from scanning by the mid-1970s. Those numbers were not achieved in that time-frame and some predicted the demise of barcode scanning. The usefulness of the barcode required the adoption of expensive scanners by a critical mass of retailers while manufacturers simultaneously adopted barcode labels. Neither wanted to move first and results were not promising for the first couple of years, with Business Week proclaiming "The Supermarket Scanner That Failed" in a 1976 article.^[14][16]\n' + '

On the other hand, experience with barcode scanning in those stores revealed additional benefits. The detailed sales information acquired by the new systems allowed greater responsiveness to customer habits, needs and preferences. This was reflected in the fact that about 5 weeks after installing barcode scanners, sales in grocery stores typically started climbing and eventually leveled off at a 10–12% increase in sales that never dropped off. There was also a 1–2% decrease in operating cost for those stores, and this enabled them to lower prices and thereby to increase market share. It was shown in the field that the return on investment for a barcode scanner was 41.5%. By 1980, 8,000 stores per year were converting.^[15]\n' + '

Sims Supermarkets were the first location in Australia to use barcodes, starting in 1979.^[17]\n' + '

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Industrial adoption

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In 1981, the United States Department of Defense adopted the use of Code 39 for marking all products sold to the United States military. This system, Logistics Applications of Automated Marking and Reading Symbols (LOGMARS), is still used by DoD and is widely viewed as the catalyst for widespread adoption of barcoding in industrial uses.^[18]\n' + '

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Use

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Barcodes are widely used around the world in many contexts. In stores, UPC barcodes are pre-printed on most items other than fresh produce from a grocery store. This speeds up processing at check-outs and helps track items and also reduces instances of shoplifting involving price tag swapping, although shoplifters can now print their own barcodes.^[19] Barcodes that encode a book's ISBN are also widely pre-printed on books, journals and other printed materials. In addition, retail chain membership cards use barcodes to identify customers, allowing for customized marketing and greater understanding of individual consumer shopping patterns. At the point of sale, shoppers can get product discounts or special marketing offers through the address or e-mail address provided at registration.\n' + '

Barcodes are widely used in the healthcare and hospital settings, ranging from patient identification (to access patient data, including medical history, drug allergies, etc.) to creating SOAP Notes^[20] with barcodes to medication management. They are also used to facilitate the separation and indexing of documents that have been imaged in batch scanning applications, track the organization of species in biology,^[21] and integrate with in-motion checkweighers to identify the item being weighed in a conveyor line for data collection.\n' + '

They can also be used to keep track of objects and people; they are used to keep track of rental cars, airline luggage, nuclear waste, registered mail, express mail and parcels. Barcoded tickets (which may be printed by the customer on their home printer, or stored on their mobile device) allow the holder to enter sports arenas, cinemas, theatres, fairgrounds, and transportation, and are used to record the arrival and departure of vehicles from rental facilities etc. This can allow proprietors to identify duplicate or fraudulent tickets more easily. Barcodes are widely used in shop floor control applications software where employees can scan work orders and track the time spent on a job.\n' + '

Barcodes are also used in some kinds of non-contact 1D and 2D position sensors. A series of barcodes are used in some kinds of absolute 1D linear encoder. The barcodes are packed close enough together that the reader always has one or two barcodes in its field of view. As a kind of fiducial marker, the relative position of the barcode in the field of view of the reader gives incremental precise positioning, in some cases with sub-pixel resolution. The data decoded from the barcode gives the absolute coarse position. An "address carpet", such as Howell's binary pattern and the Anoto dot pattern, is a 2D barcode designed so that a reader, even though only a tiny portion of the complete carpet is in the field of view of the reader, can find its absolute X,Y position and rotation in the carpet.^[22][23]\n' + '

2D barcodes can embed a hyperlink to a web page. A mobile device with an inbuilt camera might be used to read the pattern and browse the linked website, which can help a shopper find the best price for an item in the vicinity. Since 2005, airlines use an IATA-standard 2D barcode on boarding passes (Bar Coded Boarding Pass (BCBP)), and since 2008 2D barcodes sent to mobile phones enable electronic boarding passes.^[24]\n' + '

Some applications for barcodes have fallen out of use. In the 1970s and 1980s, software source code was occasionally encoded in a barcode and printed on paper (Cauzin Softstrip and Paperbyte^[25] are barcode symbologies specifically designed for this application), and the 1991 Barcode Battler computer game system used any standard barcode to generate combat statistics.\n' + '

Artists have used barcodes in art, such as Scott Blake's Barcode Jesus, as part of the post-modernism movement.\n' + '

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Symbologies

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The mapping between messages and barcodes is called a symbology. The specification of a symbology includes the encoding of the message into bars and spaces, any required start and stop markers, the size of the quiet zone required to be before and after the barcode, and the computation of a checksum.\n' + '

Linear symbologies can be classified mainly by two properties:\n' + '

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Continuous vs. discrete

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• Characters in discrete symbologies are composed of n bars and n − 1 spaces. There is an additional space between characters, but it does not convey information, and may have any width as long as it is not confused with the end of the code.
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• Characters in continuous symbologies are composed of n bars and n spaces, and usually abut, with one character ending with a space and the next beginning with a bar, or vice versa. A special end pattern that has bars on both ends is required to end the code.

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Two-width vs. many-width

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• A two-width, also called a binary bar code, contains bars and spaces of two widths, "wide" and "narrow". The precise width of the wide bars and spaces is not critical; typically it is permitted to be anywhere between 2 and 3 times the width of the narrow equivalents.
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• Some other symbologies use bars of two different heights (POSTNET), or the presence or absence of bars (CPC Binary Barcode). These are normally also considered binary bar codes.
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• Bars and spaces in many-width symbologies are all multiples of a basic width called the module; most such codes use four widths of 1, 2, 3 and 4 modules.

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Some symbologies use interleaving. The first character is encoded using black bars of varying width. The second character is then encoded by varying the width of the white spaces between these bars. Thus characters are encoded in pairs over the same section of the barcode. Interleaved 2 of 5 is an example of this.\n' + '

Stacked symbologies repeat a given linear symbology vertically.\n' + '

The most common among the many 2D symbologies are matrix codes, which feature square or dot-shaped modules arranged on a grid pattern. 2D symbologies also come in circular and other patterns and may employ steganography, hiding modules within an image (for example, DataGlyphs).\n' + '

Linear symbologies are optimized for laser scanners, which sweep a light beam across the barcode in a straight line, reading a slice of the barcode light-dark patterns. Scanning at an angle makes the modules appear wider, but does not change the width ratios. Stacked symbologies are also optimized for laser scanning, with the laser making multiple passes across the barcode.\n' + '

In the 1990s development of charge-coupled device (CCD) imagers to read barcodes was pioneered by Welch Allyn. Imaging does not require moving parts, as a laser scanner does. In 2007, linear imaging had begun to supplant laser scanning as the preferred scan engine for its performance and durability.\n' + '

2D symbologies cannot be read by a laser, as there is typically no sweep pattern that can encompass the entire symbol. They must be scanned by an image-based scanner employing a CCD or other digital camera sensor technology.\n' + '

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Barcode readers

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The earliest, and still the cheapest, barcode scanners are built from a fixed light and a single photosensor that is manually moved across the barcode. Barcode scanners can be classified into three categories based on their connection to the computer. The older type is the RS-232 barcode scanner. This type requires special programming for transferring the input data to the application program. Keyboard interface scanners connect to a computer using a PS/2 or AT keyboard–compatible adaptor cable (a "keyboard wedge"). The barcode's data is sent to the computer as if it had been typed on the keyboard.\n' + '

Like the keyboard interface scanner, USB scanners do not need custom code for transferring input data to the application program. On PCs running Windows the human interface device emulates the data merging action of a hardware "keyboard wedge", and the scanner automatically behaves like an additional keyboard.\n' + '

Most modern smartphones are able to decode barcode using their built-in camera. Google's mobile Android operating system can use their own Google Lens application to scan QR codes, or third party apps like Barcode Scanner to read both one-dimensional barcodes and QR codes. Nokia's Symbian operating system featured a barcode scanner,^[26] while mbarcode^[27] is a QR code reader for the Maemo operating system. In Apple iOS 11, the native camera app can decode QR codes and can link to URLs, join wireless networks, or perform other operations depending on the QR Code contents.^[28] Other paid and free apps are available with scanning capabilities for other symbologies or for earlier iOS versions.^[29] With BlackBerry devices, the App World application can natively scan barcodes and load any recognized Web URLs on the device's Web browser. Windows Phone 7.5 is able to scan barcodes through the Bing search app. However, these devices are not designed specifically for the capturing of barcodes. As a result, they do not decode nearly as quickly or accurately as a dedicated barcode scanner or portable data terminal.^{[citation needed]}\n' + '

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Quality control and verification

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It is common for producers and users of bar codes to have a quality management system which includes verification and validation of bar codes.^[30] Barcode verification examines scanability and the quality of the barcode in comparison to industry standards and specifications.^[31] Barcode verifiers are primarily used by businesses that print and use barcodes. Any trading partner in the supply chain can test barcode quality. It is important to verify a barcode to ensure that any reader in the supply chain can successfully interpret a barcode with a low error rate. Retailers levy large penalties for non-compliant barcodes. These chargebacks can reduce a manufacturer's revenue by 2% to 10%.^[32]\n' + '

A barcode verifier works the way a reader does, but instead of simply decoding a barcode, a verifier performs a series of tests. For linear barcodes these tests are:\n' + '

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• Edge contrast (EC)^[33]\n' + '
  • The difference between the space reflectance (Rs) and adjoining bar reflectance (Rb). EC=Rs-Rb
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• Minimum bar reflectance (Rb)^[33]\n' + '
  • The smallest reflectance value in a bar.
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• Minimum space reflectance (Rs)^[33]\n' + '
  • The smallest reflectance value in a space.
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• Symbol contrast (SC)^[33]\n' + '
  • Symbol Contrast is the difference in reflectance values of the lightest space (including the quiet zone) and the darkest bar of the symbol. The greater the difference, the higher the grade. The parameter is graded as either A, B, C, D, or F. SC=Rmax-Rmin
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• Minimum edge contrast (ECmin)^[33]\n' + '
  • The difference between the space reflectance (Rs) and adjoining bar reflectance (Rb). EC=Rs-Rb
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• Modulation (MOD)^[33]\n' + '
  • The parameter is graded either A, B, C, D, or F. This grade is based on the relationship between minimum edge contrast (ECmin) and symbol contrast (SC). MOD=ECmin/SC The greater the difference between minimum edge contrast and symbol contrast, the lower the grade. Scanners and verifiers perceive the narrower bars and spaces to have less intensity than wider bars and spaces; the comparison of the lesser intensity of narrow elements to the wide elements is called modulation. This condition is affected by aperture size.
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• Inter-character gap^[33]\n' + '
  • In discrete barcodes, the space that disconnects the two contiguous characters. When present, inter-character gaps are considered spaces (elements) for purposes of edge determination and reflectance parameter grades.
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• Defects
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• Decode^[33]\n' + '
  • Extracting the information which has been encoded in a bar code symbol.
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• Decodability^[33]\n' + '
  • Can be graded as A, B, C, D, or F. The Decodability grade indicates the amount of error in the width of the most deviant element in the symbol. The less deviation in the symbology, the higher the grade. Decodability is a measure of print accuracy using the symbology reference decode algorithm.

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2D matrix symbols look at the parameters:\n' + '

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• Symbol contrast^[33]
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• Modulation^[33]
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• Decode^[33]
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• Unused error correction
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• Fixed (finder) pattern damage
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• Grid non-uniformity
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• Axial non-uniformity^[34]

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Depending on the parameter, each ANSI test is graded from 0.0 to 4.0 (F to A), or given a pass or fail mark. Each grade is determined by analyzing the scan reflectance profile (SRP), an analog graph of a single scan line across the entire symbol. The lowest of the 8 grades is the scan grade, and the overall ISO symbol grade is the average of the individual scan grades. For most applications a 2.5 (C) is the minimal acceptable symbol grade.^[35]\n' + '

Compared with a reader, a verifier measures a barcode's optical characteristics to international and industry standards. The measurement must be repeatable and consistent. Doing so requires constant conditions such as distance, illumination angle, sensor angle and verifier aperture. Based on the verification results, the production process can be adjusted to print higher quality barcodes that will scan down the supply chain.\n' + '

Bar code validation may include evaluations after use (and abuse) testing such as sunlight, abrasion, impact, moisture, etc.^[36]\n' + '

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Barcode verifier standards

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Barcode verifier standards are defined by the International Organization for Standardization (ISO), in ISO/IEC 15426-1 (linear) or ISO/IEC 15426-2 (2D).^{[citation needed]} The current international barcode quality specification is ISO/IEC 15416 (linear) and ISO/IEC 15415 (2D).^{[citation needed]} The European Standard EN 1635 has been withdrawn and replaced by ISO/IEC 15416. The original U.S. barcode quality specification was ANSI X3.182. (UPCs used in the US – ANSI/UCC5).^{[citation needed]} As of 2011 the ISO workgroup JTC1 SC31 was developing a Direct Part Marking (DPM) quality standard: ISO/IEC TR 29158.^[37]\n' + '

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Benefits

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In point-of-sale management, barcode systems can provide detailed up-to-date information on the business, accelerating decisions and with more confidence. For example:\n' + '

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• Fast-selling items can be identified quickly and automatically reordered.
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• Slow-selling items can be identified, preventing inventory build-up.
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• The effects of merchandising changes can be monitored, allowing fast-moving, more profitable items to occupy the best space.
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• Historical data can be used to predict seasonal fluctuations very accurately.
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• Items may be repriced on the shelf to reflect both sale prices and price increases.
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• This technology also enables the profiling of individual consumers, typically through a voluntary registration of discount cards. While pitched as a benefit to the consumer, this practice is considered to be potentially dangerous by privacy advocates.^[which?]

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Besides sales and inventory tracking, barcodes are very useful in logistics and supply chain management.\n' + '

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• When a manufacturer packs a box for shipment, a Unique Identifying Number (UID) can be assigned to the box.
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• A database can link the UID to relevant information about the box; such as order number, items packed, quantity packed, destination, etc.
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• The information can be transmitted through a communication system such as Electronic Data Interchange (EDI) so the retailer has the information about a shipment before it arrives.
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• Shipments that are sent to a Distribution Center (DC) are tracked before forwarding. When the shipment reaches its final destination, the UID gets scanned, so the store knows the shipment's source, contents, and cost.

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Barcode scanners are relatively low cost and extremely accurate compared to key-entry, with only about 1 substitution error in 15,000 to 36 trillion characters entered.^{[38][unreliable source?]} The exact error rate depends on the type of barcode.\n' + '

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Types of barcodes

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Linear barcodes

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A first generation, "one dimensional" barcode that is made up of lines and spaces of various widths that create specific patterns.\n' + '

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Example	Symbology	Continuous or discrete	Bar widths	Uses\n' + '
	Australia Post barcode	Discrete	4 bar heights	An Australia Post barcode as used on a business reply paid envelope and applied by automated sorting machines to other mail when initially processed in fluorescent ink .\n' + '
	Codabar	Discrete	Two	Old format used in libraries and blood banks and on airbills (out of date, but still widely used in libraries)\n' + '
	Code 25 – Non-interleaved 2 of 5	Continuous	Two	Industrial\n' + '
	Code 25 – Interleaved 2 of 5	Continuous	Two	Wholesale, libraries International standard ISO/IEC 16390\n' + '
	Code 11	Discrete	Two	Telephones (out of date)\n' + '
	Farmacode or Code 32	Discrete	Two	Italian pharmacode – use Code 39 (no international standard available)\n' + '
	Code 39	Discrete	Two	Various – international standard ISO/IEC 16388\n' + '
	Code 49	Continuous	Many	Various\n' + '
	Code 93	Continuous	Many	Various\n' + '
	Code 128	Continuous	Many	Various – International Standard ISO/IEC 15417\n' + '
	CPC Binary	Discrete	Two	\n' + '
	DX film edge barcode	Neither	Tall/short	Color print film\n' + '
	EAN 2	Continuous	Many	Addon code (magazines), GS1-approved – not an own symbology – to be used only with an EAN/UPC according to ISO/IEC 15420\n' + '
	EAN 5	Continuous	Many	Addon code (books), GS1-approved – not an own symbology – to be used only with an EAN/UPC according to ISO/IEC 15420\n' + '
	EAN-8, EAN-13	Continuous	Many	Worldwide retail, GS1-approved – International Standard ISO/IEC 15420\n' + '
	Facing Identification Mark	Discrete	Two	USPS business reply mail\n' + '
	GS1-128 (formerly named UCC/EAN-128), incorrectly referenced as EAN 128 and UCC 128	Continuous	Many	Various, GS1-approved – just an application of the Code 128 (ISO/IEC 15417) using the ANS MH10.8.2 AI Datastructures. It is not a separate symbology.\n' + '
	GS1 DataBar, formerly Reduced Space Symbology (RSS)	Continuous	Many	Various, GS1-approved\n' + '
	Intelligent Mail barcode	Discrete	4 bar heights	United States Postal Service, replaces both POSTNET and PLANET symbols (formerly named OneCode)\n' + '
	ITF-14	Continuous	Two	Non-retail packaging levels, GS1-approved – is just an Interleaved 2/5 Code (ISO/IEC 16390) with a few additional specifications, according to the GS1 General Specifications\n' + '
	ITF-6	Continuous	Two	Interleaved 2 of 5 barcode to encode an addon to ITF-14 and ITF-16 barcodes. The code is used to encode additional data such as items quantity or container weight\n' + '
	JAN	Continuous	Many	Used in Japan, similar to and compatible with EAN-13 (ISO/IEC 15420)\n' + '
	Japan Post barcode	Discrete	4 bar heights	Japan Post\n' + '
	KarTrak ACI	Discrete	Coloured bars	Used in North America on railroad rolling equipment\n' + '
	MSI	Continuous	Two	Used for warehouse shelves and inventory\n' + '
	Pharmacode	Discrete	Two	Pharmaceutical packaging (no international standard available)\n' + '
	PLANET	Continuous	Tall/short	United States Postal Service (no international standard available)\n' + '
	Plessey	Continuous	Two	Catalogs, store shelves, inventory (no international standard available)\n' + '
	PostBar	Discrete	4 bar heights	Canadian Post office\n' + '
	POSTNET	Discrete	Tall/short	United States Postal Service (no international standard available)\n' + '
	RM4SCC / KIX	Discrete	4 bar heights	Royal Mail / PostNL\n' + '
	RM Mailmark C	Discrete	4 bar heights	Royal Mail\n' + '
	RM Mailmark L	Discrete	4 bar heights	Royal Mail\n' + '
	Telepen	Continuous	Two	Libraries (UK)\n' + '
	Universal Product Code (UPC-A and UPC-E)	Continuous	Many	Worldwide retail, GS1-approved – International Standard ISO/IEC 15420\n' + '

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Matrix (2D) barcodes

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A matrix code, also termed a 2D barcode or simply a 2D code, is a two-dimensional way to represent information. It is similar to a linear (1-dimensional) barcode, but can represent more data per unit area.\n' + '

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Example	Name	Notes\n' + '
	AR Code	A type of marker used for placing content inside augmented reality applications. Some AR Codes can contain QR codes inside, so that content AR content can be linked to.[39] See also ARTag.\n' + '
	Aztec Code	Designed by Andrew Longacre at Welch Allyn (now Honeywell Scanning and Mobility). Public domain. – International Standard: ISO/IEC 24778\n' + '
\n' + '	bCode\n' + '	A barcode designed for the study of insect behavior.[40] Encodes an 11 bit identifier and 16 bits of read error detection and error correction information. Predominately used for marking honey bees, but can also be applied to other animals.\n' + '
\n' + '	BEEtag\n' + '	A 25 bit (5x5) code matrix of black and white pixels that is unique to each tag surrounded by a white pixel border and a black pixel border. The 25-bit matrix consists of a 15-bit identity code, and a 10-bit error check.[41] It is designed to be a low-cost, image-based tracking system for the study of animal behavior and locomotion.\n' + '
\n' + '	BeeTagg\n' + '	A 2D barcode with honeycomb structures suitable for mobile tagging and was developed by the Swiss company connvision AG.\n' + '
\n' + '	Bokode\n' + '	A type of data tag which holds much more information than a barcode over the same area. They were developed by a team led by Ramesh Raskar at the MIT Media Lab. The bokode pattern is a tiled series of Data Matrix codes.\n' + '
\n' + '	Boxing\n' + '	A high-capacity 2D barcode is used on piqlFilm by Piql AS[42]\n' + '
	Code 1	Public domain. Code 1 is currently used in the health care industry for medicine labels and the recycling industry to encode container content for sorting.[43]\n' + '
\n' + '	Code 16K\n' + '	The Code 16K (1988) is a multi-row bar code developed by Ted Williams at Laserlight Systems (USA) in 1992. In the US and France, the code is used in the electronics industry to identify chips and printed circuit boards. Medical applications in the USA are well known. Williams also developed Code 128, and the structure of 16K is based on Code 128. Not coincidentally, 128 squared happened to equal 16,000 or 16K for short. Code 16K resolved an inherent problem with Code 49. Code 49's structure requires a large amount of memory for encoding and decoding tables and algorithms. 16K is a stacked symbology.[44][45]\n' + '
	ColorCode	ColorZip[46] developed colour barcodes that can be read by camera phones from TV screens; mainly used in Korea.[47]\n' + '
	Color Construct Code	Color Construct Code is one of the few barcode symbologies designed to take advantage of multiple colors.[48][49]\n' + '
	Cronto Visual Cryptogram\n' + '	The Cronto Visual Cryptogram (also called photoTAN) is a specialized color barcode, spun out from research at the University of Cambridge by Igor Drokov, Steven Murdoch, and Elena Punskaya.[50] It is used for transaction signing in e-banking; the barcode contains encrypted transaction data which is then used as a challenge to compute a transaction authentication number using a security token.[51]\n' + '
	CyberCode	From Sony.\n' + '
	d-touch	readable when printed on deformable gloves and stretched and distorted[52][53]\n' + '
	DataGlyphs	From Palo Alto Research Center (also termed Xerox PARC).[54]\n' + ' Patented.[55]\n' + 'DataGlyphs can be embedded into a half-tone image or background shading pattern in a way that is almost perceptually invisible, similar to steganography.[56][57]\n' + ' \n' + '
	Data Matrix	From Microscan Systems, formerly RVSI Acuity CiMatrix/Siemens. Public domain. Increasingly used throughout the United States. Single segment Data Matrix is also termed Semacode. – International Standard: ISO/IEC 16022.\n' + '
	Datastrip Code	From Datastrip, Inc.\n' + '
\n' + '	Digimarc Barcode\n' + '	The Digimarc Barcode is a unique identifier, or code, based on imperceptible patterns that can be applied to marketing materials, including packaging, displays, ads in magazines, circulars, radio and television[58]\n' + '
	digital paper	patterned paper used in conjunction with a digital pen to create handwritten digital documents. The printed dot pattern uniquely identifies the position coordinates on the paper.\n' + '
	DotCode	Standardized as AIM Dotcode Rev 3.0. Public domain. Used to track individual cigarette and pharmaceutical packages.\n' + '
	Dot Code A	Also known as Philips Dot Code.[59] Patented in 1988.[60]\n' + '
\n' + '	DWCode\n' + '	Introduced by GS1 US and GS1 Germany, the DWCode is a unique, imperceptible data carrier that is repeated across the entire graphics design of a package[61]\n' + '
	EZcode	Designed for decoding by cameraphones;[62] from ScanLife.[63]\n' + '
	Han Xin Barcode	Barcode designed to encode Chinese characters introduced by Association for Automatic Identification and Mobility in 2011.\n' + '
	High Capacity Color Barcode	HCCB was developed by Microsoft; licensed by ISAN-IA.\n' + '
	HueCode	From Robot Design Associates. Uses greyscale or colour.[64]\n' + '
	InterCode	From Iconlab, Inc. The standard 2D barcode in South Korea. All 3 South Korean mobile carriers put the scanner program of this code into their handsets to access mobile internet, as a default embedded program.\n' + '
\n' + ' \n' + ' \n' + '	JAB Code\n' + '	Just Another Bar Code is a colored 2D barcode. Square or rectangle. License free\n' + '
	MaxiCode	Used by United Parcel Service. Now public domain.\n' + '
\n' + '	mCode\n' + '	Designed by NextCode Corporation, specifically to work with mobile phones and mobile services.[65] It is implementing an independent error detection technique preventing false decoding, it uses a variable-size error correction polynomial, which depends on the exact size of the code.[66]\n' + '
	MMCC	Designed to disseminate high capacity mobile phone content via existing colour print and electronic media, without the need for network connectivity\n' + '
	NexCode	NexCode is developed and patented by S5 Systems.\n' + '
	Nintendo e-Reader#Dot code	Developed by Olympus Corporation to store songs, images, and mini-games for Game Boy Advance on Pokémon trading cards.\n' + '
	PDF417	Originated by Symbol Technologies. Public domain. – International standard: ISO/IEC 15438\n' + '
	Qode	American proprietary and patented 2D barcode from NeoMedia Technologies, Inc.[63]\n' + '
	QR code	Initially developed, patented and owned by Denso Wave for automotive components management; they have chosen not to exercise their patent rights. Can encode Latin and Japanese Kanji and Kana characters, music, images, URLs, emails. De facto standard for Japanese cell phones. Used with BlackBerry Messenger to pick up contacts rather than using a PIN code. The most frequently used type of code to scan with smartphones. Public Domain. – International Standard: ISO/IEC 18004\n' + '
	Screencode	Developed and patented[67][68] by Hewlett-Packard Labs. A time-varying 2D pattern using to encode data via brightness fluctuations in an image, for the purpose of high bandwidth data transfer from computer displays to smartphones via smartphone camera input. Inventors Timothy Kindberg and John Collomosse, publicly disclosed at ACM HotMobile 2008.[69]\n' + '
	ShotCode	Circular barcodes for camera phones. Originally from High Energy Magic Ltd in name Spotcode. Before that most likely termed TRIPCode.\n' + '
	Snapcode, also called Boo-R code	used by Snapchat, Spectacles, etc. US9111164B1[70][71][72]\n' + '
\n' + '	Snowflake Code\n' + '	A proprietary code developed by Electronic Automation Ltd. in 1981. It is possible to encode more than 100 numeric digits in a space of only 5mm x 5mm. User selectable error correction allows up to 40% of the code to be destroyed and still remain readable. The code is used in the pharmaceutical industry and has an advantage that it can be applied to products and materials in a wide variety of ways, including printed labels, ink-jet printing, laser-etching, indenting or hole punching.[44][73][74]\n' + '
	SPARQCode	QR code encoding standard from MSKYNET, Inc.\n' + '
\n' + '	Trillcode\n' + '	Designed for mobile phone scanning.[75] Developed by Lark Computer, a Romanian company.[66]\n' + '
	VOICEYE	Developed and patented by VOICEYE, Inc. in South Korea, it aims to allow blind and visually impaired people to access printed information. It also claims to be the 2D barcode that has the world's largest storage capacity.\n' + '

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Example images

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• First, Second and Third Generation Barcodes
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  GTIN-12 number encoded in UPC-A barcode symbol. First and last digit are always placed outside the symbol to indicate Quiet Zones that are necessary for barcode scanners to work properly\n' + '

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  EAN-13 (GTIN-13) number encoded in EAN-13 barcode symbol. First digit is always placed outside the symbol, additionally right quiet zone indicator (>) is used to indicate Quiet Zones that are necessary for barcode scanners to work properly\n' + '

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  "Wikipedia" encoded in Code 93\n' + '

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  "*WIKI39*" encoded in Code 39\n' + '

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  'Wikipedia" encoded in Code 128\n' + '

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  An example of a stacked barcode. Specifically a "Codablock" barcode.\n' + '

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  PDF417 sample\n' + '

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  Lorem ipsum boilerplate text as four segment Data Matrix 2D\n' + '

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  "This is an example Aztec symbol for Wikipedia" encoded in Aztec Code\n' + '

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  Text 'EZcode'\n' + '

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  High Capacity Color Barcode of the URL for Wikipedia's article on High Capacity Color Barcode\n' + '

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  "Wikipedia, The Free Encyclopedia" in several languages encoded in DataGlyphs\n' + '

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  Two different 2D barcodes used in film: Dolby Digital between the sprocket holes with the "Double-D" logo in the middle, and Sony Dynamic Digital Sound in the blue area to the left of the sprocket holes\n' + '

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  The QR Code for the Wikipedia URL. "Quick Response", the most popular 2D barcode. It is open in that the specification is disclosed and the patent is not exercised.^[76]\n' + '

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  MaxiCode example. This encodes the string "Wikipedia, The Free Encyclopedia"\n' + '

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  ShotCode sample\n' + '

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  detail of Twibright Optar scan from laser printed paper, carrying 32 kbit/s Ogg Vorbis digital music (48 seconds per A4 page)\n' + '

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  A KarTrak railroad Automatic Equipment Identification label on a caboose in Florida\n' + '

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In popular culture

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In architecture, a building in Lingang New City by German architects Gerkan, Marg and Partners incorporates a barcode design,^[77] as does a shopping mall called Shtrikh-kod (Russian for barcode) in Narodnaya ulitsa ("People's Street") in the Nevskiy district of St. Petersburg, Russia.^[78]\n' + '

In media, in 2011, the National Film Board of Canada and ARTE France launched a web documentary entitled Barcode.tv, which allows users to view films about everyday objects by scanning the product's barcode with their iPhone camera.^[79][80]\n' + '

In professional wrestling, the WWE stable D-Generation X incorporated a barcode into their entrance video, as well as on a T-shirt.^[81][82]\n' + '

In the TV series Dark Angel, the protagonist and the other transgenics in the Manticore X-series have barcodes on the back of their necks.\n' + '

In video games, the protagonist of the Hitman video game series has a barcode tattoo on the back of his head. Also, QR codes can be scanned for an extra mission on Watch Dogs.\n' + '

In the films Back to the Future Part II and The Handmaid's Tale, cars in the future are depicted with barcode licence plates.\n' + '

In the Terminator films, Skynet burns barcodes onto the inside surface of the wrists of captive humans (in a similar location to the WW2 concentration camp tattoos) as a unique identifier.\n' + '

In music, Dave Davies of The Kinks released a solo album in 1980, AFL1-3603, which featured a giant barcode on the front cover in place of the musician's head. The album's name was also the barcode number.\n' + '

The April 1978 issue of Mad Magazine featured a giant barcode on the cover, with the blurb "[Mad] Hopes this issue jams up every computer in the country...for forcing us to deface our covers with this yecchy UPC symbol from now on!"\n' + '

The 2018 videogame Judgment features QR Codes that protagonist Takayuki Yagami can photograph with his phone camera. These are mostly to unlock parts for Yagami's Drone.^[83]\n' + '

Interactive Textbooks were first published by Harcourt College Publishers to Expand Education Technology with Interactive Textbooks.^[84]\n' + '

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Designed barcodes

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Some brands integrate custom designs into barcodes (while keeping them readable) on their consumer products.\n' + '

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Hoaxes about barcodes

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There was minor skepticism from conspiracy theorists, who considered barcodes to be an intrusive surveillance technology, and from some Christians, pioneered by a 1982 book The New Money System 666 by Mary Stewart Relfe, who thought the codes hid the number 666, representing the "Number of the Beast".^[85] Old Believers, a separation of the Russian Orthodox Church, believe barcodes are the stamp of the Antichrist.^[86] Television host Phil Donahue described barcodes as a "corporate plot against consumers".^[87]\n' + '

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See also

\n' + '

• Automated identification and data capture (AIDC)
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• Barcode printer
\n' + '
• European Article Numbering-Uniform Code Council
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• Global Trade Item Number
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• Identifier
\n' + '
• Inventory control system
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• Object hyperlinking
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• Semacode
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• SMS barcode
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• SPARQCode (QR code)
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• List of GS1 country codes

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References

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Further reading

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External links

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Wikimedia Commons has media related to Barcode.

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• Barcode at Curlie
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• Barcode Glossary of Terms
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• Pros and cons and relative popularity of different 1D and 2D barcode codes.

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