Bitcoins are sent from user to user on the peer-to-peer bitcoin network directly, without the need for intermediaries.:4,5 Transactions are verified by network nodes through cryptography and recorded in a public distributed ledger called a blockchain. Bitcoin was invented by an unknown person or group of people using the name Satoshi Nakamoto and released as open-source software in 2009. Bitcoins are created as a reward for a process known as mining. They can be exchanged for other currencies, products, and services. Research produced by the University of Cambridge estimates that in 2017, there were 2.9 to 5.8 million unique users using a cryptocurrency wallet, most of them using bitcoin.
Bitcoin's proponents consider the following to be its positive qualities:
independence from world governments, banks and corporations
no central authority to censor or interfere with transactions
a good store of value, akin to "digital gold"
relatively low cost and fast peer-to-peer transactions between people regardless of geographic location
Bitcoin's critics consider the following to be its negative qualities:
^July 2016 to approximately June 2020, halved approximately every four years
The domain name "bitcoin.org" was registered on 18 August 2008. In November 2008, a link to a paper authored by Satoshi Nakamoto titled Bitcoin: A Peer-to-Peer Electronic Cash System was posted to a cryptography mailing list. Nakamoto implemented the bitcoin software as open source code and released it in January 2009. The identity of Nakamoto remains unknown.
In January 2009, the bitcoin network was created when Nakamoto mined the first block of the chain, known as the genesis block. Embedded in the coinbase of this block was the following text:
The Times 03/Jan/2009 Chancellor on brink of second bailout for banks.
Nakamoto is estimated to have mined 1 million bitcoins before disappearing in 2010, when he handed the network alert key and control of the code repository over to Gavin Andresen. Andresen later became lead developer at the Bitcoin Foundation. Andresen then sought to decentralize control. This left opportunity for controversy to develop over the future development path of bitcoin.
2011 - 2012
Prices were extremely volatile in 2011, starting at $0.30 per bitcoin, growing 1,656% for the year to $5.27. Prices rose to $31.50 on June 8, a 10,500% increase from January 1. Within a month the price had crashed to $11.00, a 65% decline. The next month if fell to $7.80, and in another month to $4.77, for an overall 85% decline in the ninety days from the June 8 high.
Litecoin was an early bitcoin spinoff or altcoin, starting in October 2011. Many altcoins have been created since.
In 2012 bitcoin prices started at $5.27 growing 153% to $13.30 for the year. By January 9 the price had risen to $7.38, but then crashed by 49% over the next 16 days. The price then rose to $16.41 on August 17, but fell by 57% over the next three days.
The Bitcoin Foundation was founded in September 2012 to "accelerate the global growth of bitcoin through standardization, protection, and promotion of the open source protocol". The founders included Gavin Andresen and Charlie Shrem.
2013 - 2016
In 2013 prices started at $13.30 rising 5,691% to $770 by January 1, 2014.
In March 2013 the blockchain temporarily split into two independent chains with different rules. The two blockchains operated simultaneously for six hours, each with its own version of the transaction history. Normal operation was restored when the majority of the network downgraded to version 0.7 of the bitcoin software. The Mt. Gox exchange briefly halted bitcoin deposits and the price dropped by 23% to $37 before recovering to previous level of approximately $48 in the following hours.
The US Financial Crimes Enforcement Network (FinCEN) established regulatory guidelines for "decentralized virtual currencies" such as bitcoin, classifying American bitcoin miners who sell their generated bitcoins as Money Service Businesses (MSBs), that are subject to registration or other legal obligations.
In April, payment processors BitInstant and Mt. Gox experienced processing delays due to insufficient capacity resulting in the bitcoin price dropping from $266 to $76 before returning to $160 within six hours.
The bitcoin price rose to $259 on April 10, but then crashed by 83% over the next 3 days.
On 15 May 2013, the US authorities seized accounts associated with Mt. Gox after discovering that it had not registered as a money transmitter with FinCEN in the US.
Bitcoin's price rose to $755 on 19 November and crashed by 50% to $378 the same day. On 30 November 2013 the price reached $1,163 before starting a long-term crash, declining by 87% to $152 in January 2015.
On 5 December 2013, the People's Bank of China prohibited Chinese financial institutions from using bitcoins. After the announcement, the value of bitcoins dropped, and Baidu no longer accepted bitcoins for certain services. Buying real-world goods with any virtual currency had been illegal in China since at least 2009.
In 2014 prices started at $770 and fell 59% to $314 for the year.
In February 2014 the Mt. Gox exchange, the largest bitcoin exchange at the time, said that 850,000 bitcoins had been stolen from its customers, amounting to almost $500 million. Bitcoin's price fell by almost half, from $867 to $439 (a 49% drop). Prices remained low until late 2016.
In 2015 prices started at $314 and rose 38% to $434 for the year. In 2016 prices rose 130% to $998 on January 1, 2017.
2017 - 2018
Bitcoin prices in 2017 were exceptionally volatile, starting at $998 and rising 1,245% to $13,412.44 on January 1, 2018. On December 17 bitcoin's price reached an all time high of $19,666 and then fell 70% to $5,920 on February 6, 2018.
China banned trading in bitcoin, with the first steps taken in September 2017, and a complete ban starting 1 February 2018. Bitcoin prices then fell from $9,052 to $6,914 on 5 February 2018. The percentage of bitcoin trading in renminbi fell from over 90% in September 2017 to less than 1% in June.
Throughout the rest of the first half of 2018, bitcoin's price fluctuated between $11,480 and $5,848. On July 1, 2018 bitcoin's price was $6,469.
Bitcoin prices were negatively affected by several hacks or thefts from cryptocurrency exchanges, including thefts from Coincheck in January 2018, Coinrail and Bithumb in June, and Bancor in July. For the first six months of 2018, $761 million worth of cryptocurrencies was reported stolen from exchanges. Bitcoin's price was affected even though other cryptocurrencies were stolen at Coinrail and Bancor, as investors worried about the overall security of cryptocurrencies.
On 1 August 2017, a hard fork of bitcoin was created, known as Bitcoin Cash. Bitcoin Cash has a larger block size limit and had an identical blockchain at the time of fork. On 24 October 2017 another hard fork, Bitcoin Gold, was created. Bitcoin Gold changes the proof-of-work algorithm used in mining.
As disagreements around scaling bitcoin heated up, several hard forks were proposed. Bitcoin XT was one proposal that aimed for 24 transactions per second. In order to accomplish this, it proposed increasing the block size from 1 megabyte to 8 megabytes. When Bitcoin XT was declined, some community members still wanted block sizes to increase. In response, a group of developers launched Bitcoin Classic, which intended to increase the block size to only 2 megabytes. Bitcoin Unlimited set itself apart by allowing miners to decide on the size of their blocks, with nodes and miners limiting the size of blocks they accept, up to 16 megabytes.
Bitcoin Core developer Peter Wuille presented the idea of Segregated Witness (SegWit) in late 2015. SegWit is a soft fork – a backward-compatible rule update &ndash that aims to reduce the size of each bitcoin transaction, thereby allowing more transactions to take place at once. Some developers and users decided to initiate a hard fork - Bitcoin Cash - in order to avoid the protocol updates SegWit brought about.
Bitcoin Gold was a hard fork that followed several months later in October 2017 that changed the proof-of-work algorithm with the aim of restoring mining functionality to basic graphics processing units (GPU), as the developers felt that mining had become too specialized.Bitcoin Private, launched in March 2018, added the ability to keep certain details private in a transaction, in contrast to bitcoin which has a transparent transaction history.
The blockchain is a public ledger that records bitcoin transactions. It is implemented as a chain of blocks, each block containing a hash of the previous block up to the genesis block[a] of the chain. A novel solution was designed to do this without any trusted central authority: the maintenance of the blockchain is performed by a network of communicating nodes running bitcoin software. Transactions of the form payer X sends Y bitcoins to payee Z are broadcast to this network using readily available software applications. Nevertheless, the "trustless" design requires "each and every user to download and verify the history of all transactions ever made, including amount paid, payer, payee and other details." 
Network nodes can validate transactions, add them to their copy of the ledger, and then broadcast these ledger additions to other nodes. The blockchain is a distributed database – to achieve independent verification of the chain of ownership of any and every bitcoin amount, each network node stores its own copy of the blockchain. Approximately once every 10 minutes, a new group of accepted transactions, a block, is created, added to the blockchain, and quickly published to all nodes. This allows bitcoin software to determine when a particular bitcoin amount has been spent, which is necessary in order to prevent double-spending in an environment without central oversight. Whereas a conventional ledger records the transfers of actual bills or promissory notes that exist apart from it, the blockchain is the only place that bitcoins can be said to exist in the form of unspent outputs of transactions.:ch. 5
Number of bitcoin transactions per month (logarithmic scale)
Transactions are defined using a Forth-like scripting language.:ch. 5 Transactions consist of one or more inputs and one or more outputs. When a user sends bitcoins, the user designates each address and the amount of bitcoin being sent to that address in an output. To prevent double spending, each input must refer to a previous unspent output in the blockchain. The use of multiple inputs corresponds to the use of multiple coins in a cash transaction. Since transactions can have multiple outputs, users can send bitcoins to multiple recipients in one transaction. As in a cash transaction, the sum of inputs (coins used to pay) can exceed the intended sum of payments. In such a case, an additional output is used, returning the change back to the payer. Any input satoshis not accounted for in the transaction outputs become the transaction fee.
The unit of account of the bitcoin system is a bitcoin. Ticker symbols used to represent bitcoin are BTC[b] and XBT.[c] Its Unicode character is ₿.:2 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 0.00000001 bitcoins, one hundred millionth of a bitcoin. A millibitcoin equals 0.001 bitcoins, one thousandth of a bitcoin or 100,000 satoshis.
Though transaction fees are optional, miners can choose which transactions to process and prioritize those that pay higher fees. Miners may choose transactions based on the fee paid relative to their storage size, not the absolute amount of money paid as a fee. These fees are generally measured in satoshis per byte (sat/b). The size of transactions is dependent on the number of inputs used to create the transaction, and the number of outputs.:ch. 8
Simplified chain of ownership. In reality, a transaction can have more than one input and more than one output.
In the blockchain, bitcoins are registered to bitcoin addresses. Creating a bitcoin address is 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 mathematically unfeasible and so users can tell others and 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 for that. To be able to spend the bitcoins, the owner must know the corresponding private key and digitally sign the transaction. The network verifies the signature using the public key.:ch. 5
If the private key is lost, the bitcoin network will not recognize any other evidence of ownership; the coins are then unusable, and effectively lost. For example, in 2013 one user claimed to have lost 7,500 bitcoins, worth $7.5 million at the time, when he accidentally discarded a hard drive containing his private key. A backup of his key(s) would have prevented this.
About 20% of all bitcoins are believed to be lost. The lost coins would have a market value of about $20 billion at July 2018 prices. . Approximately 1 million bitcoins have been stolen, which would have a value of about $7 billion at July 2018 prices.
Amateur bitcoin mining with a small ASIC. This was when difficulty was much lower, and is no longer feasible.
Mining is a record-keeping service done through the use of computer processing power.[e] Miners keep the blockchain consistent, complete, and unalterable by repeatedly grouping newly broadcast transactions into a block, which is then broadcast to the network and verified by recipient nodes. Each block contains a SHA-256cryptographic hash of the previous block, thus linking it to the previous block and giving the blockchain its name.:ch. 7
To be accepted by the rest of the network, a new block must contain a so-called proof-of-work (PoW). The system used is based on Adam Back's 1997 anti-spam scheme, Hashcash. 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.: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, ...:ch. 8) before meeting the difficulty target.
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.: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.
The proof-of-work system, alongside the chaining of blocks, makes modifications of the blockchain extremely hard, as an attacker must modify all subsequent blocks in order for the modifications of one block to be accepted. As new blocks are mined all the time, the difficulty of modifying a block increases as time passes and the number of subsequent blocks (also called confirmations of the given block) increases.
Computing power is often bundled together or "pooled" 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.
The successful miner finding the new block is rewarded with newly created bitcoins and transaction fees. As of 9 July 2016, the reward amounted to 12.5 newly created bitcoins per block added to the blockchain. To claim the reward, a special transaction called a coinbase is included with the processed payments.: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[f] will be reached c. 2140; the record keeping will then be rewarded by transaction fees solely.
In other words, bitcoin's inventor Nakamoto set a monetary policy based on artificial scarcity at bitcoin's inception that there would only ever be 21 million bitcoins in total. Their numbers are being released roughly every ten minutes and the rate at which they are generated would drop by half every four years until all were in circulation.
A wallet stores the information necessary to transact bitcoins. While wallets are often described as a place to hold or store bitcoins, due to the nature of the system, bitcoins are inseparable from the blockchain transaction ledger. A better way to describe a wallet is something that "stores the digital credentials for your bitcoin holdings" and allows one to access (and spend) them. Bitcoin uses public-key cryptography, in which two cryptographic keys, one public and one private, are generated. At its most basic, a wallet is a collection of these keys.
There are three modes which wallets can operate in. They have an inverse relationship with regards to trustlessness and computational requirements.
Full clients verify transactions directly by downloading a full copy of the blockchain (over 150 GB As of January 2018). 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. Because of its size and complexity, downloading and verifying the entire blockchain is not suitable for all computing devices.
Lightweight clients consult full clients 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 the server to a certain degree, 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 miners.
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. As a result, the user must have complete trust in the 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. This has led to the often-repeated meme "Not your keys, not your bitcoin".
Bitcoin paper wallet
Trezor hardware wallet
Physical wallets store offline the credentials necessary to spend bitcoins. One notable example was a novelty coin with these credentials printed on the reverse side.Paper wallets are simply paper printouts.
Another type of wallet called a hardware wallet keeps credentials offline while facilitating transactions.
The first wallet program – simply named "Bitcoin" – was released in 2009 by Satoshi Nakamoto as open-source code. 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". After the release of version 0.9, the software bundle was renamed "Bitcoin Core" to distinguish itself from the underlying network. It is sometimes referred to as the "Satoshi client".
Bitcoin was designed not to need a central authority and the bitcoin network is considered to be decentralized. However, researchers have pointed out a visible "trend towards centralization" by the means of miners joining large mining pools to minimise the variance of their income. According to researchers, other parts of the ecosystem are also "controlled by a small set of entities", notably online wallets and simplified payment verification (SPV) clients.
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. As of 2013 just six mining pools controlled 75% of overall bitcoin hashing power.
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.
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. Additionally, bitcoin exchanges, where bitcoins are traded for traditional currencies, may be required by law to collect personal information.
To heighten financial privacy, a new bitcoin address can be generated for each transaction. For example, hierarchical deterministic wallets generate pseudorandom "rolling addresses" for every transaction from a single seed, while only requiring a single passphrase to be remembered to recover all corresponding private keys. Researchers at Stanford University and Concordia University have also shown that bitcoin exchanges and other entities can prove assets, liabilities, and solvency without revealing their addresses using zero-knowledge proofs. "Bulletproofs," a version of Confidential Transactions proposed by Greg Maxwell, have been tested by Professor Dan Boneh of Stanford. Other solutions such Merkelized Abstract Syntax Trees (MAST), pay-to-script-hash (P2SH) with MERKLE-BRANCH-VERIFY, and "Tail Call Execution Semantics", have also been proposed to support private smart contracts.
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.
The blocks in the blockchain were originally limited to 32 megabyte 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.
On 24 August 2017 (at block 481,824), Segregated Witness (SegWit) went live. Transactions contain some data which is only used to verify the transaction, and does not otherwise effect the movement of coins. SegWit introduces a new transaction format that moves this data into a new field in a backwards-compatible way. The segregated data, the so-called witness, is not sent to non-SegWit nodes and therefore does not form part of the blockchain as seen by legacy nodes. This lowers the size of the average transaction in such nodes' view, thereby increasing the block size without incurring the hard fork implied by other proposals for block size increases. Thus, per computer scientist Jochen Hoenicke, the actual block capacity depends on the ratio of SegWit transactions in the block, and on the ratio of signature data. Based on his estimate, if the ratio of SegWit transactions is 50%, the block capacity may be 1.25 megabytes. According to Hoenicke, if native SegWit addresses from Bitcoin Core version 0.16.0 are used, and SegWit adoption reaches 90 to 95%, a block size of up to 1.8 megabytes is possible.
Bitcoin does not necessarily work well as a currency. 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". Economists define money as a store of value, a medium of exchange, and a unit of account and agree that bitcoin does not meet all these criteria. As of March 2014, the bitcoin market suffered from volatility, limiting the ability of bitcoin to act as a stable store of value, and retailers accepting bitcoin use other currencies as their principal unit of account.
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 to 1.3 million users.
Acceptance by merchants
The overwhelming majority of bitcoin transactions take place on an exchange, rather than being used in transactions with merchants.
Merchants that accept bitcoin as payment may do so through bitcoin payment service providers such as Coinbase and BitPay. This allows merchants to avoid the volatility risk of accepting bitcoin payments directly by converting the received bitcoins to fiat money through the payment service provider.
In 2017 and 2018 bitcoin's acceptance among major online retailers included only three out of the top 500 online merchants, down from five in 2016. Reasons for this fall include high transaction fees due to bitcoin's scalability issues, long transaction times and a rise in value making consumers unwilling to spend it.
According to bitinfocharts.com, in 2017 there are 9,272 bitcoin wallets with more than $1 million worth of bitcoins. The exact number of bitcoin millionaires is uncertain as a single person can have more than one bitcoin wallet.
Venture capitalists, such as Peter Thiel's Founders Fund, which invested US$3 million in BitPay, do not purchase bitcoins themselves, but instead fund bitcoin infrastructure that provides payment systems to merchants, exchanges, wallet services, etc. 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, at the time called 'mystery buyer'. The company's goal is to fund 100 bitcoin businesses within 2–3 years with $10,000 to $20,000 for a 6% stake. Investors also invest in bitcoin mining. According to a 2015 study by Paolo Tasca, bitcoin startups raised almost $1 billion in three years (Q1 2012 – Q1 2015).
Price and volatility
Price[g](left y-axis, logarithmic scale) and volatility[h](right y-axis).
The price of bitcoins has gone through cycles of appreciation and depreciation referred to by some as bubbles and busts. In 2011, the value of one bitcoin rapidly rose from about US$0.30 to US$32 before returning to US$2. In the latter half of 2012 and during the 2012–13 Cypriot financial crisis, the bitcoin price began to rise, 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. In 2014, the price fell sharply, and as of April remained depressed at little more than half 2013 prices. As of August 2014 it was under US$600.
During their time as bitcoin developers, Gavin Andresen and Mike Hearn warned that bubbles may occur.
Because of bitcoin's decentralized nature, nation-states cannot shut down the network or alter its technical rules. 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".
The legal status of bitcoin varies substantially from country to country and is still undefined or changing in many of them. While some countries have explicitly allowed its use and trade, others have banned or restricted it. Regulations and bans that apply to bitcoin probably extend to similar cryptocurrency systems.
Bitcoin made its first historic appearance in a U.S. Supreme Court opinion (on Wisconsin Central Ltd. v. United States) regarding the changing definition of money on 21 June 2018.
The U.S. Commodity Futures Trading Commission has issued four "Customer Advisories" for bitcoin and related investments. A July 2018 warning emphasized that trading in any cryptocurrency is often speculative, the risk of theft from hacking, and fraud. A February 2018 advisory warned against investing an IRA fund into virtual currencies. A December 2017 advisory warned that virtual currencies are risky because:
the exchanges are not regulated or supervised by a government agency
the exchanges may lack system safeguards and customer protections
The U.S. Securities and Exchange Commission has also issued warnings. A May 2014 "Investor Alert" warned that investments involving bitcoin might have high rates of fraud, and that investors might be solicited on social media sites. An earlier "Investor Alert" warned about the use of bitcoin in Ponzi schemes.
The Bank for International Settlements summarized many of the criticisms of bitcoin in Chapter V of their 2018 annual report. The criticisms include the lack of stability in bitcoin's price, the "environmental disaster" entailed by 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.
Tim Draper, a venture capitalist who has heavily invested in bitcoin, counters that bitcoin "is bigger than the internet. It's bigger than the iron age, the Renaissance. It's bigger than the industrial revolution."
Bitcoin has been criticized for the amounts of electricity consumed by mining. As of 2015, The Economist estimated that even if all miners used modern facilities, the combined electricity consumption would be 166.7 megawatts (1.46 terawatt-hours per year).
At the end of 2017, the global bitcoin mining activity was estimated to consume between 1 and 4 gigawatts of electricity.Politico noted that the banking sector today consumes about 6% of total global power, and even if bitcoin's consumption levels increased 100 fold from today's levels, bitcoin's consumption would still only amount to about 2% of global power consumption.
Inc. columnist, Joseph Steinberg, has even speculated that Bitcoin's technical shortcomings, including its use of "more electricity per day to operate than some Western countries" could ultimately threaten its viability, and transform it from the dominant cryptocurrency leader into the "MySpace of Cryptocurrencies."
Price manipulation investigation
An official investigation into bitcoin traders was reported in May 2018. The U.S. Justice Department launched an investigation into possible price manipulation, including the techniques of spoofing and wash trades. Traders in the U.S., the U.K, South Korea, and possibly other countries are being investigated. Brett Redfearn, head of the U.S. Securities and Exchange Commission's Division of Trading and Markets, had identified several manipulation techniques of concern in March 2018.
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.
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.
JL 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."
Ponzi scheme and pyramid scheme concerns
Various journalists, economists, and the central bank of Estonia have voiced concerns that bitcoin is a Ponzi scheme. In 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." A 2014 report by the World Bank concluded that bitcoin was not a deliberate Ponzi scheme.:7 The Swiss Federal Council:21 examined the concerns that bitcoin might be a pyramid scheme; it 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." In July 2017, billionaire Howard Marks referred to bitcoin as a pyramid scheme.
On 12 September 2017, Jamie Dimon, CEO of JP Morgan Chase, called bitcoin a "fraud" and said he would fire anyone in his firm caught trading it. Zero Hedge claimed that the same day Dimon made his statement, JP Morgan also purchased a large amount of bitcoins for its clients. In a January 2018 interview Dimon voiced regrets about his earlier remarks, and said "The blockchain is real. You can have cryptodollars in yen and stuff like that. ICOs ... you got to look at every one individually."
Use in illegal transactions
The use of bitcoin by criminals has attracted the attention of financial regulators, legislative bodies, law enforcement, and the media. In the United States, the FBI prepared an intelligence assessment, the SEC issued a pointed warning about investment schemes using virtual currencies, and the U.S. Senate held a hearing on virtual currencies in November 2013. The US government claimed that bitcoin was used to facilitate payments related to the Russian interference in the 2016 United States elections.
Nobel-prize winning economist Joseph Stiglitz says that bitcoin's anonymity encourages money laundering and other crimes, "If you open up a hole like bitcoin, then all the nefarious activity will go through that hole, and no government can allow that." He's also said that if "you regulate it so you couldn’t engage in money laundering and all these other [crimes], there will be no demand for Bitcoin. By regulating the abuses, you are going to regulate it out of existence. It exists because of the abuses."
Several news outlets have asserted that the popularity of bitcoins hinges on the ability to use them to purchase illegal goods. 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".
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. There were an estimated 24 million bitcoin users primarily using bitcoin for illegal activity, who held $8 billion worth of bitcoin, and made 36 million transactions valued at $72 billion.
A group of researches analyzed bitcoin transactions in 2016 and came to a conclusion that "some recent concerns regarding the use of bitcoin for illegal transactions at the present time might be overstated".
Major thefts involving bitcoin 2012 - 2017, according to Bloomberg include
December 2017, NiceHash, a marketplace for crypto-mining reported $63 million worth of bitcoin stolen
November 2017, $31 million worth of tether tokens reported stolen and converted to bitcoins
April 2017, 4,000 bitcoins stolen from the YouBit exchange in April
August 2016, about $65 million worth of bitcoin stolen in the Bitfinex hack
May 2016, $2 million worth of bitcoin and ether stolen from the Gatecoin exchange
January 2015, $5 million worth of bitcoin stolen from the Bitstamp exchange
February 2014, the Mt. Gox exchange reports $480 million worth of bitcoin missing
September 2012, the BitFloor exchange reported about $250,000 worth of bitcoin stolen.
^Relative mining difficulty is defined as the ratio of the difficulty target on 9 January 2009 to the current difficulty target.
^It is misleading to think that there is an analogy between gold mining and bitcoin mining. The fact is that gold miners are rewarded for producing gold, while bitcoin miners are not rewarded for producing bitcoins; they are rewarded for their record-keeping services.
^The exact number is 20,999,999.9769 bitcoins.:ch. 8
^ abHyun Song Shin (June 2018). "Chapter V. Cryptocurrencies: looking beyond the hype"(PDF). BIS 2018 Annual Economic Report. Bank for International Settlements. Retrieved 19 June 2018. Put in the simplest terms, the quest for decentralised trust has quickly become an environmental disaster.
^Sparkes, Matthew (9 June 2014). "The coming digital anarchy". The Telegraph. London: Telegraph Media Group Limited. Archived from the original on 23 January 2015. Retrieved 7 January 2015.
^"Difficulty History" (The ratio of all hashes over valid hashes is D x 4,295,032,833, where D is the published "Difficulty" figure.). Blockchain.info. Archived from the original on 8 April 2015. Retrieved 26 March 2015.
^Janus Kopfstein (12 December 2013). "The Mission to Decentralize the Internet". The New Yorker. Archived from the original on 31 December 2014. Retrieved 30 December 2014. The network's 'nodes' – users running the bitcoin software on their computers – collectively check the integrity of other nodes to ensure that no one spends the same coins twice. All transactions are published on a shared public ledger, called the 'blockchain'.
^Ben-Sasson, Eli; Chiesa, Alessandro; Garman, Christina; Green, Matthew; Miers, Ian; Tromer, Eran; Virza, Madars (2014). "Zerocash: Decentralized Anonymous Payments from Bitcoin"(PDF). 2014 IEEE Symposium on Security and Privacy. IEEE computer society. Archived(PDF) from the original on 14 October 2014. Retrieved 31 October 2014.
^ ab"Monetarists Anonymous". The Economist. The Economist Newspaper Limited. 29 September 2012. Archived from the original on 20 October 2013. Retrieved 21 October 2013.
^Murphy, Kate (31 July 2013). "Virtual Currency Gains Ground in Actual World". The New York Times. Archived from the original on 14 October 2014. Retrieved 6 May 2014. A type of digital cash, bitcoins were invented in 2009 and can be sent directly to anyone, anywhere in the world.
^Bustillos, Maria (2 April 2013). "The Bitcoin Boom". The New Yorker. Condé Nast. Archived from the original on 27 July 2014. Retrieved 22 December 2013. Standards vary, but there seems to be a consensus forming around Bitcoin, capitalized, for the system, the software, and the network it runs on, and bitcoin, lowercase, for the currency itself.
^"China May Be Gearing Up to Ban Bitcoin". pastemagazine.com. Archived from the original on 3 October 2017. Retrieved 6 October 2017. The decentralized nature of bitcoin is such that it is impossible to “ban” the cryptocurrency, but if you shut down exchanges and the peer-to-peer economy running on bitcoin, it’s a de facto ban.
^Tasca, Paolo (7 September 2015). "Digital Currencies: Principles, Trends, Opportunities, and Risks". Social Science Research Network. SSRN2657598.
^Mooney, Chris; Mufson, Steven (19 December 2017). "Why the bitcoin craze is using up so much energy". The Washington Post. Archived from the original on 9 January 2018. Retrieved 11 January 2018. several experts told The Washington Post that bitcoin probably uses as much as 1 to 4 gigawatts, or billion watts, of electricity, roughly the output of one to three nuclear reactors.
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