A common logo from the bitcoin reference client
|Date of introduction||3 January 2009|
|Production||25 bitcoins per block (approximately every ten minutes) until mid 2016, and then afterwards 12.5 bitcoins per block for 4 years until next halving. This halving continues until 2110-2140.|
|Source||Number of bitcoins in circulation|
|Method||Increase in the supply|
|10−6||bit or μBTC|
Bitcoin is a software-based payment system described by Satoshi Nakamoto[note 1] in 2008, and introduced as open-source software in 2009. Payments are recorded in a public ledger using its own unit of account, which is also called bitcoin.[note 2] Payments work peer-to-peer without a central repository or single administrator, which has led the US Treasury to call bitcoin a decentralized virtual currency in contrast to centralized virtual currencies such as Liberty Reserve. Although its status as a currency is disputed, media reports often refer to bitcoin as a cryptocurrency or digital currency.
Bitcoins are created as a reward for payment processing work in which users offer their computing power to verify and record payments into the public ledger. Called mining, individuals or companies engage in this activity in exchange for transaction fees and newly created bitcoins. Besides mining, bitcoins can be obtained in exchange for fiat money, products, and services. Users can send and receive bitcoins electronically for an optional transaction fee using wallet software on a personal computer, mobile device, or a web application.
Bitcoin as a form of payment for products and services has seen growth, and merchants have an incentive to accept the digital currency because fees are lower than the 2–3% typically imposed by credit card processors. The European Banking Authority has warned that bitcoin lacks consumer protections. Unlike credit cards, any fees are paid by the purchaser not the vendor. Bitcoins can be stolen and chargebacks are impossible. Commercial use of bitcoin is currently small compared to its use by speculators, which has fueled price volatility.
Bitcoin has been a subject of scrutiny amid concerns that it can be used for illegal activities. In October 2013 the US FBI shut down the Silk Road online black market and seized 144,000 bitcoins worth US$28.5 million at the time. The US is considered bitcoin-friendly compared to other governments. In China, buying bitcoins with yuan is subject to restrictions, and bitcoin exchanges are not allowed to hold bank accounts.
- 1 Overview
- 2 History
- 3 Economics
- 4 Reception
- 5 Legal status and regulation
- 6 Criminal activity
- 7 Risk
- 8 Security
- 9 In the media
- 10 See also
- 11 Notes
- 12 References
- 13 External links
The most important part of the bitcoin system is a public ledger that records financial transactions in bitcoins. This is accomplished without the intermediation of any single, central authority, as long as mining is decentralized. Instead, multiple intermediaries exist in the form of computer servers running bitcoin software. By connecting over the Internet, these servers form a network that anyone can join. Transactions of the form payer X wants to send Y bitcoins to payee Z are broadcast to this network using readily available software applications. Bitcoin servers can validate these transactions, add them to their copy of the ledger, and then broadcast these ledger additions to other servers.
The block chain ledger
All bitcoin transfers are recorded in a computer file that acts as a public ledger called the block chain, which everyone can examine. Where a conventional ledger records the transfer of actual bills or promissory notes that exist apart from it, bitcoins are simply entries in the block chain and do not exist outside of it.
Maintaining the block chain is called mining, and those who do are rewarded with newly created bitcoins and transaction fees. Miners may be located anywhere in the world; they process payments by verifying each transaction as valid and adding it to the block chain. As of 2014 payment processing is rewarded with 25 newly created bitcoins per block added to the block chain. To claim the reward, a special transaction called a coinbase is included with the processed payments. All bitcoins in circulation can be traced back to such coinbase transactions. The bitcoin protocol specifies that the reward for adding a block will be halved approximately every four years. Eventually, the reward will be removed entirely when an arbitrary limit of 21 million bitcoins is reached c. 2140, and transaction processing will then be rewarded by transaction fees solely. Paying a transaction fee is optional, but may speed up confirmation of the transaction. Payers have an incentive to include such fees because doing so means their transaction will likely be added to the block chain sooner; miners can choose which transactions to process and prefer to include those that pay fees.
As of 2013 mining had become quite competitive, and the process has been compared to an arms race as ever more specialized technology is utilized. The most efficient mining hardware makes use of custom designed application-specific integrated circuits, which outperform general purpose CPUs and use less power as well. Without access to these purpose built machines, a bitcoin miner is unlikely to earn enough to even cover the cost of the electricity used in his or her efforts.
- Mining pools
The individual odds of winning the reward for adding a block to the block chain decrease alongside an increase in the number of miners. Many miners participate, but the reward for each block can only go to a single bitcoin address. As of 2014 it has become common for miners to join organized mining pools, which split the work and the reward among all participants and make mining a less risky endeavor. Even for those who join pools, the cost of the electricity necessary to mine may outweigh the bitcoin rewards from doing so.
The public nature of bitcoin means that, while those who use it are not identified by name, transactions can be linked to individuals and companies. All transactions are recorded into a public ledger, the block chain, and are viewable by everyone. Additionally, many jurisdictions require exchanges, where people can buy and sell bitcoins for cash, to collect personal information. The privacy concerns of some who use bitcoins are sufficient to cause them to take additional steps to cover their tracks. In order to obfuscate the link between individual and transaction, a different bitcoin address for each transaction can be used, and others rely on so-called mixing services that allow users to trade bitcoins whose transaction history implicates them for coins with different transaction histories.
It has further been suggested that bitcoin payments should not be considered more anonymous than credit card payments.
Buying and selling
Bitcoins can be bought and sold with many different currencies from individuals and companies. Bitcoins may be purchased in person or at a bitcoin ATM in exchange for cash currency. Participants in online exchanges offer bitcoin buy and sell bids. Using an online exchange to obtain bitcoins entails some risk, and according to one study, 45% of exchanges fail and take client bitcoins with them. Since bitcoin transactions are irreversible, sellers of bitcoins must take extra measures to ensure they have received traditional funds from the buyer.
While wallets are often described as being a place to hold or store bitcoins, due to the nature of the system, bitcoins are inseparable from the block chain transaction ledger. Perhaps a better way to define a wallet is something "that stores the digital credentials for your bitcoin holdings" and allows you to access (and spend) them. Bitcoin uses public-key cryptography, in which two cryptographic keys, one public and one private, are generated. The public key can be thought of as an account number or name and the private key, ownership credentials. At its most basic, a wallet is a collection of these keys. Most bitcoin software also includes the ability to make transactions, however.
Perhaps better termed physical wallets, physical bitcoins are ubiquitous in media coverage and combine a novelty coin with a private key printed on paper, metal, wood, or plastic. Physical bitcoins aren't widely seen outside of pictures in news article, but for those serious about security, storing private keys on paper printouts or in offline data storage devices is the best option.
Bitcoin client software called a bitcoin wallet allows a user to transact bitcoins. A wallet program generates and stores private keys, and communicates with peers on the bitcoin network. The first wallet program called Bitcoin-Qt was released in 2009 by Satoshi Nakamoto as open source code. It can be used as a desktop wallet for payments or as a server utility for merchants and other payment services. Bitcoin-Qt, also called Satoshi client is sometimes referred to as the reference client because it serves to define the bitcoin protocol and acts as a standard for other implementations. As of version 0.9, Bitcoin-Qt has been renamed Bitcoin Core to more accurately describe its role in the network. When making a purchase with a mobile device, QR codes are used ubiquitously to simplify transactions. Several server software implementations of the bitcoin protocol exist. So-called full nodes on the network validate transactions and blocks they receive, and relay them to connected peers.
The ownership of bitcoins associated with a certain bitcoin address can be demonstrated with knowledge of the private key belonging to the address. For the owner, it is important to protect the private key from loss or theft. If a private key is lost, the user cannot prove ownership by other means. The coins are then lost and cannot be recovered. Because anyone with knowledge of the private key can take ownership of any associated bitcoins, theft can occur when a private key is revealed or stolen.
- Security, theft, and loss
Integral to bitcoin security is the prevention of unauthorized transactions from an individual's wallet. A bitcoin transaction permanently transfers ownership to a new address, a string having the form of random letters and numbers derived from public keys by application of a hash function and encoding scheme. The corresponding private keys act as a safeguard for the owner; a valid payment message from an address must contain the associated public key and a digital signature proving possession of the associated private key. Because anyone with a private key can spend all of the bitcoins associated with the corresponding address, protection of private keys is quite important. Loss of a private key may result in theft, which has occurred on numerous occasions. The practical day-to-day security of bitcoin wallets is an ongoing concern. Risk of theft can be reduced by generating keys offline on an uncompromised computer and saving them on external storage or paper printouts.
Bitcoins can be lost. In 2013 one user said he lost 7,500 bitcoins, worth $7.5m at the time, when he discarded a hard drive containing his private key. Bitcoins can also be found. In March 2014, former bitcoin exchange Mt. Gox reported it found an "old wallet, which was used before June 2011 [that] held about 200,000 bitcoins".
Bitcoin was first mentioned in a 2008 research paper published under the name Satoshi Nakamoto. It is unknown who Satoshi Nakamoto is. In 2009, an exploit in an early bitcoin client was found that allowed large numbers of bitcoins to be created.
In March 2013, a technical glitch caused a fork in the block chain, with one half of the network adding blocks to one version of the chain and the other half adding to another. For six hours two bitcoin networks operated at the same time, each with its own version of the transaction history. The core developers called for a temporary halt to transactions, sparking a sharp sell-off. Normal operation was restored when the majority of the network downgraded to version 0.7 of the bitcoin software.
Some mainstream websites began accepting bitcoins c. 2013. WordPress started in November 2012 followed by OKCupid in April 2013, Atomic Mall in November 2013, TigerDirect and Overstock.com in January 2014, Expedia in June 2014, and Newegg in July 2014. Certain non-profit or advocacy groups such as the Electronic Frontier Foundation allow bitcoin donations. (Although this organization stopped accepting bitcoins in 2011 and began again in 2013.)
The first law enforcement events occurred in May 2013. Assets belonging to the Mt. Gox exchange were seized by Department of Homeland Security, and the Silk Road drug market website was shut down by the FBI.
In October 2013, Chinese internet giant Baidu had allowed clients of website security services to pay with bitcoins. During November 2013, the China-based bitcoin exchange BTC China overtook the Japan-based Mt. Gox and the Europe-based Bitstamp to become the largest bitcoin trading exchange by trade volume. On 19 November 2013, the value of a bitcoin on the Mt. Gox exchange soared to a peak of US$900 after a United States Senate committee hearing was told that virtual currencies were a legitimate financial service. On the same day, one bitcoin traded for over RMB¥6780 (US$1100) in China. 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.
With roughly 12 million existing bitcoins as of November 2013, the new price increased the market cap for bitcoin to at least US$7.2 billion. By 23 November 2013, the total market capitalization of bitcoin exceeded US$10 billion for the first time.
In the US two men were arrested in January 2014 on charges of money-laundering using bitcoins including Charlie Shrem, the head of defunct bitcoin exchange BitInstant and a vice chairman of the Bitcoin Foundation. Shrem allegedly allowed the other arrested party to purchase large quantities of bitcoins for use on black-market websites.
In early February 2014, one of the largest bitcoin exchanges, Mt. Gox, suspended withdrawals citing technical issues. By the end of the month, Mt. Gox had filed for bankruptcy protection in Japan amid reports that 744,000 bitcoins had been stolen. Originally a site for trading Magic: The Gathering cards, Mt. Gox once was the dominant bitcoin exchange although prior to the collapse its popularity had waned.
Classification as money
Bitcoin is often referred to as a currency, but it does not conform to widely used definitions of money. Economists generally agree that to qualify as money, something must be a store of value, a medium of exchange, and a unit of account. Bitcoin has some way to go if it wants to meet these criteria. It does best as a medium of exchange. (About 1,000 bricks and mortar businesses were willing to accept payment in bitcoins as of November 2013 in addition to more than 35,000 online merchants.) The bitcoin market currently suffers from volatility, limiting the ability of bitcoins to act as a stable store of value, and, although bitcoins are the unit of account for the block chain, bitcoin does not see use as a unit of account outside of it. Where people are allowed to buy with bitcoins, prices are not denominated in bitcoins.
Others feel being a widely accepted or common medium of exchange is sufficient for something to be considered money. Still more believe money must be both a medium of exchange and a unit of account. Others think money has four characteristics. It must be: a medium of exchange, a unit of account, a store of value, and a standard of deferred payments.
The People's Bank of China has stated that bitcoin "is fundamentally not a currency". According to the director of the Institute for Money, Technology and Financial Inclusion at the University of California-Irvine there is "an unsettled debate about whether bitcoin is a currency or payment protocol". Despite this, in the media bitcoin is commonly referred to with terms that include the word currency such as digital currency, digital cash, virtual currency, electronic money, or cryptocurrency. Some media outlets do make a distinction between "real" money and bitcoins, however.
Price and volatility
To improve access to price information and increase transparency, on 30 April 2014 Bloomberg LP announced plans to list prices from bitcoin companies Kraken and Coinbase on its 320.000 subscription financial data terminals.
According to Mark T. Williams of Boston University, the volatility of bitcoin is over seven times that of gold and over eight times that of the S&P 500. The Bitcoin Foundation contends that high volatility is due to insufficient liquidity while a Forbes journalist claims that it is related to the uncertainty of its long-term value. As of 2014, pro-bitcoin venture capitalists argue the greatly increased trading volume that planned high-frequency trading exchanges are hoped to bring will decrease price volatility. Volatility has little effect on the utility of bitcoin as a payment processing system.
The price of bitcoins has gone through various 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 2012-2013 Cypriot Financial Crisis, the bitcoin price began to rise, reaching a peak of US$266 on 10 April 2013, before crashing to around US$50. At the end of 2013, the cost of one bitcoin rose to the all-round peak of US$1135, but fell to the price of US$693 three days later.[better source needed] In 2014 the price fell sharply, and as of April remained depressed at little more than half that of 2013.
Alternative to national currencies
Bitcoins are used by some Argentinians as an alternative to the official currency, which is stymied by inflation and strict capital controls, to protect their savings against inflation or the possibility that governments could confiscate savings accounts. It's been suggested that during the 2012–2013 Cypriot financial crisis bitcoin purchases rose due to fears that savings accounts would be confiscated or taxed.
Bitcoin has been labelled a speculative bubble by many including Former Federal Reserve Chairman Alan Greenspan and economist John Quiggin. Two lead software developers of bitcoin, Gavin Andresen and Mike Hearn, have warned that bubbles may occur. Nobel Laureate Robert Shiller said that bitcoin "exhibited many of the characteristics of a speculative bubble." Others reject the label and see bitcoin's quick rise in price as nothing more than normal economic forces at work.
One way of investing in bitcoins is to buy and hold them as a long-term, high-risk investment. FINRA, a United States self-regulatory organization, warns that investing in bitcoins carries significant risks. The European Banking Authority warns that the risks of investment go beyond a potential fall in the value of bitcoins. Bitcoins may be of limited value to unsophisticated investors. Risk hasn't deterred some such as the Winklevoss twins, who made a US$1.5 million personal investment and attempted to launch a bitcoin ETF. Other investors, like Peter Thiel's Founders Fund, which invested US$3 million, don't purchase bitcoins themselves instead funding bitcoin infrastructure like companies that provide payment systems to merchants, exchanges, and wallet services, etc. Investors also invest in bitcoin mining.
Growth of the bitcoin supply is predefined by the bitcoin protocol. Currently there are over twelve million bitcoins in circulation with an approximate creation rate of 25 every ten minutes. The total supply is capped at an arbitrary limit of 21 million, and every four years the creation rate is halved. This means new bitcoins will continue to be released for more than a hundred years.
Financial journalists and analysts, economists, and investors have attempted to predict the possible future value of bitcoin. Economist John Quiggin stated, "bitcoins will attain their true value of zero sooner or later, but it is impossible to say when." In 2013, Bank of America FX and Rate Strategist David Woo forecast a maximum fair value per bitcoin of $1,300. Bitcoin investor Cameron Winklevoss stated in 2013 that the "[s]mall bull case scenario for bitcoin is... 40,000 USD a coin". In late 2013, finance professor Mark Williams forecast a bitcoin would be worth less than ten US dollars by July 2014.
On its political economy
It has been claimed that bitcoin is a currency that reflects a new type of capitalism, named “distributed” capitalism. This new iteration of capitalism conforms to the characteristics of the network era and utilizes the peer-to-peer infrastructures to achieve capital accumulation. Bitcoin is designed to allow multiple users, though in a competitive framework. It might appear as though it exists outside the financial system, but by promoting scarcity and competition this project aggravates the over-accumulation of capital and exacerbates the social inequalities that it is supposed to combat  According to some scholars, bitcoin should be viewed like a new technology, not just a currency: It has paved the way for new types of currencies that utilize new technological infrastructures and whose dynamics should not be ignored.
Some economists have responded positively to bitcoin, including François R. Velde, Senior Economist at the Chicago Fed, who described it as "an elegant solution to the problem of creating a digital currency." Paul Krugman and Brad DeLong have found fault with bitcoin questioning why it should act as a reasonably stable store of value or whether there is a floor on their value. Economist John Quiggin has criticized bitcoin as "the final refutation of the efficient-market hypothesis".
David Andolfatto, a 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.
Free software movement activist Richard Stallman has criticized the lack of anonymity and called for reformed development. PayPal President David A. Marcus calls bitcoin a "great place to put assets" but claims it will not be a currency until price volatility is reduced. As bitcoins proved popular, they have been increasingly covered by comics around the world.
Acceptance by merchants
Established firms that accept bitcoins include Atomic Mall, Clearly Canadian, Dish Network, Overstock.com, the Sacramento Kings, TigerDirect, Virgin Galactic, Zynga and Newegg.
As of 2014, bitcoin companies have had difficulty opening traditional bank accounts because lenders have been leery of bitcoin's links to illicit activity. According to a co-founder of one such company, BitPay, "banks are scared to deal with bitcoin companies, even if they really want to". Yet, some financial institutions have been bullish on bitcoin. In a 2013 report, Bank of America Merrill Lynch stated that "we believe bitcoin can become a major means of payment for e-commerce and may emerge as a serious competitor to traditional money-transfer providers. As a medium of exchange, bitcoin has clear potential for growth and that in a long-term fair-value analysis maximum market capitalization for bitcoins could be $15 billion." In June 2014, the first bank that converts deposits in currencies instantly to Bitcoin without any fees, for further transactions, was opened in Boston.
Concurrent with Bloomberg LP, 33% owned by Merrill Lynch launching pricing information is the development of high-frequency trading firms by Atlas ATS in New York and Hong Kong and one from London-based Coinfloor, claiming to be the first auditable bitcoin exchange, and a SecondMarket project of an exchange for institutional investors.
A US government auction of almost 30,000 bitcoins seized in October 2013 from the Silk Road on 30 June 2014 by the US Marshals Service was said to increase legitimacy of the currency. The 45 registered bidders, each of whom put down a deposit of $200,000 made 63 bids.
Legal and journalistic opinions
Bitcoins have been evaluated and treated in various ways around the world. While it may appear that a lively debate over the nature of bitcoins is occurring, the different classifications are likely more reflective of what rules apply to bitcoin in a specific jurisdiction than what bitcoin really is. Magistrate Judge Amos Maazant of a Texas court classified bitcoins as currency. A German court found bitcoin to be a unit of account. The Finnish Government judged it to be a commodity. The People's Bank of China has stated that bitcoin "is fundamentally not a currency".
A WSJ journalist declared bitcoins a commodity in December 2013. A Forbes journalist referred to bitcoins as digital collectible. Two University of Amsterdam computer scientists proposed the term 'money-like informational commodity' in order "to allow for a systematic discussion of its development through all stages including an initial stage and a possible demise without being constrained by the implications of it being a money or a near-money".
Legal status and regulation
Few governments have moved to regulate bitcoin and similar private currencies. According to the European Central Bank, traditional financial sector regulation is not applicable because bitcoin does not involve traditional financial actors. Under other regimes, existing rules have been extended to include bitcoin and bitcoin companies. Steven Strauss, a Harvard public policy professor, suggested in April 2013 governments could outlaw bitcoin, a possibility that was mentioned in a 2013 SEC filing made by a bitcoin investment vehicle. A detailed survey of forty foreign jurisdictions and the European Union is maintained by the US Library of Congress.
Bitcoin is banned by the Bolivian central bank.
The Canadian government announced in February 2014 that it was going to regulate bitcoin under existing anti-money laundering and counter-terrorist financing legislation. In Quebec, The Financial Markets Authority stated in regards to bitcoin ATMs, that it would prosecute any violation of the Securities Act, the Derivatives Act, or the Money Services Business Act.
China restricted bitcoin exchange for local currency in December 2013. On 10 April 2014 the People’s Bank of China ordered banks and all third-party payment services to stop dealing with anyone in the bitcoin business. The ruling de-funds all Chinese bitcoin trading websites, as they will no longer have bank accounts in China.
The use of bitcoins is not regulated in Cyprus. On 11 December 2013, the Central Bank of Cyprus issued a statement on bitcoins, stating that "it considers the use of any kind of virtual money as particularly dangerous, given that it is not under any regulatory system and its operation is unchecked." 
- Hong Kong
Pre-existing Hong Kong law covers acts of fraud and money laundering involving virtual commodities.
Digital or virtual currencies such as Bitcoin have gained widespread acceptance in India despite a natural scepticism to assets not backed by tangible entities such as land. After the RBI warning in December 2013, a number of Bitcoin operators shut shop. The actions of the ED (enforcement directorate) and the I-T (income-tax) department have sent tremors throughout the mainstream Bitcoin community in India, if only for the reason that there is still no official regulation on how companies involved in dealing with digital currencies should comply with anti-money laundering and financial transaction laws.
A spokesman for Bank Indonesia reportedly issued a statement on Bitcoin in December 2013, saying that "bitcoin is a potential payment method, but it’s different than ordinary currency... It is not regulated by the central bank so there are risks... At the moment, we’re studying bitcoin and we have no plan to issue a regulation on it."
No laws in Japan regulate the use of bitcoins. Haruhiko Kuroda, governor of the Bank of Japan (BOJ), stated in December, 2013, that BOJ was "researching issues of bitcoins, but I have nothing to say regarding bitcoins at the moment."
- Russian Federation
On 27 January 2014, the Central Bank of the Russian Federation issued a statement entitled "On Using Virtual Currencies, Specifically Bitcoin, in Transactions." According to the statement, the Central Bank views the services of Russian legal entities aimed at assisting in the exchange of bitcoins for goods, services, or currencies as a "dubious activity" associated with money laundering and terrorism financing, and recommends that Russian individuals and legal entities refrain from transactions involving bitcoins.
The Monetary Authority of Singapore may require bitcoin intermediaries to collect personal details of their customers and report suspicious activity similar to what it requires from money changers.
In the US the first step of regulation occurred in July 2011, when the US Department of Treasury's Financial Crimes Enforcement Network added "other value that substitutes for currency" to its definition of Money services businesses. In 2013 the Treasury issued new rules regarding virtual currencies, whereby exchanges (but not users) are considered money transmitters and must comply with rules to prevent money laundering and terrorist financing. Besides obtaining personal details of clients, bitcoin exchanges must verify that their customers are not on the Office of Foreign Asset Control’s Specially Designated Nationals list. In April 2014, the Treasury confirmed that bitcoin cloud mining and escrow services are not classified as money transmitters.
The US Government Accountability Office reviewed virtual currencies upon the request of the Senate Finance Committee and in May 2013 recommended that the IRS formulate tax guidance for bitcoin businesses. On 25 March 2014, in time for 2013 tax filing, the IRS issued a guidance that virtual currency is treated as property for US federal tax purposes and that "an individual who 'mines' virtual currency as a trade or business [is] subject to self-employment tax."
In January 2014, the US Securities and Exchange Commission (SEC) was “very focused” on whether Bitcoin-denominated stock exchanges were illegal, per its enforcement administrator and was inquiring into the gambling site SatoshiDice listing shares on Bitcoin exchange MPEx. In May it warned investors that "both fraudsters and promoters of high-risk investment schemes may target Bitcoin users." The SEC charged and settled with the former owner of SatoshiDice in June 2014 for selling securities without registering with the SEC.
On 8 May 2014, the US Federal Election Commission issued draft guidance to US politicians who want to receive Bitcoin donations. The Commission declined to declare bitcoins currency, opting to deem them items "of value."
In May 2014, Brett Stapper, the co-founder of Falcon Global Capital, registered to lobby members of Congress and federal agencies on issues related to Bitcoin.
As of June 2014[update], there are no new rules at the state level, although the New York State Department of Financial Services intended to propose regulations no later than the end of the second quarter of 2014. As of 11 March 2014[update], it officially invited bitcoin exchanges to apply with them. In June 2014 California Assemblyman Roger Dickinson (D-Sacramento) drafted legislation (Assembly Bill 129) to legalize Bitcoin and all other alternative and digital currency, such as Litecoin, Dogecoin, Starbucks Stars, and Amazon Coins. However, Dickinson "thinks the federal government should regulate the cryptocurrency" and said "I saw this legislation as a ways of cleaning up the code in California to conform to reality".
The 2013 G7's Financial Action Task Force published guidance for Internet-based payment services that defines "exchangers buying or selling digital currency for cash (or other digital currencies) [...] as a virtual bureau de change" and warns that "Internet-based payment services that allow third party funding from anonymous sources may face an increased risk of [money laundering/terrorist financing]" concluding that this may "pose challenges to countries in [anti-money laundering/counter terrorist financing] regulation and supervision."
Bitcoins have been associated with online criminal behavior and so-called cybercriminals. Used to obfuscate online transactions, bitcoins are seized when deep web black markets are shut by authorities. Criminal activities have stigmatized the currency and attracted the attention of financial regulators, legislative bodies, and law enforcement. CNN has referred to bitcoin as a "shady online currency [that is] starting to gain legitimacy in certain parts of the world," and The Washington Post calls it "the currency of choice for seedy online activities." The FBI stated in a 2012 report that "bitcoin will likely continue to attract cyber-criminals who view it as a means to move or steal funds." Criminal activity involving bitcoin has largely centered around theft, money laundering, the use of botnets for mining, and the use of bitcoins in exchange for illegal items or services. "Like cash, it can be used for ill as well as for good." Certain nation states may feel that its use in circumventing capital controls is also undesirable. Despite claims made by non-profit Bitcoin Foundation that "cryptography is the reason no one can steal bitcoins," theft is widespread.
In 2012, it was estimated that 4.5% to 9% of all transactions of all bitcoin exchanges in the world were for drug trades on a single deep web drugs market, Silk Road. The bulk of bitcoin purchases during the time were speculative in nature, so drugs must have constituted a greater percentage of the actual goods purchased with bitcoins c. 2012. Silk Road was shut by US law enforcement in October 2013 leading to a short-term fall in the value of bitcoin. Alternative sites were soon available, and in early 2014 the Australian Broadcasting Corporation reported that the closure of the Silk Road had little impact on the number of Australians selling drugs online, which had actually increased.
Several news outlets have asserted that the popularity of bitcoins hinges on the ability to use them to purchase illegal goods. Non-drug transactions were thought to be far less than the number involved in the purchase of drugs, and roughly one half of all transactions made using bitcoin c. 2013 were bets placed at a single online gambling website, Satoshi Dice. One source stated online gun dealers use bitcoin to sell arms without background checks. The bitcoin community branded one site, Sheep Marketplace, as a scam when it prevented withdrawals and shut down after an alleged bitcoins theft. In a separate case, escrow accounts with bitcoins belonging to patrons of a different black market were hacked in early 2014.
Bitcoins may not be ideal for money laundering because all transactions are public. Authorities have expressed concerns, however. The European Banking Authority and the FBI have both stated that bitcoin may be used for money laundering. In early 2014, an operator of a US bitcoin exchange was arrested for money laundering.
Various journalists, US economist Nouriel Roubini, and the head of the Estonian central bank have voiced concerns that bitcoin may be a Ponzi scheme. Bitcoin supporters disagree. A 2012 report by the European Central Bank states, "it [is not] easy to assess whether or not the bitcoin system actually works like a pyramid or Ponzi scheme."
In an alleged Ponzi scheme that utilized bitcoins, The Bitcoin Savings and Trust promised investors up to 7 percent weekly interest, and raised at least 700,000 bitcoins from 2011 to 2012. The SEC charged the company and its founder in 2013 "with defrauding investors in a Ponzi scheme involving bitcoin...".
A theft is an unauthorized transfer from a bitcoin address using the private key to unlock the address. Because transactions are irreversible and the identity of users difficult to unmask, it is rare that stolen bitcoins are recovered and returned. Theft occurs on a regular basis despite claims made by the Bitcoin Foundation that theft is impossible. Generating and storing keys offline mitigates the risk of theft. Most large-scale thefts occur at exchanges or online wallet services that store the private keys of many users. The thief hacks an online wallet service by finding a bug in its website or spreading malware to computers holding the private keys 
Many high-profile thefts have been reported. In late November 2013, an estimated $100 million in bitcoins were stolen from the online illicit goods marketplace Sheep Marketplace, which immediately closed. Users tracked the coins as they were processed and converted to cash, but no funds were recovered and no culprits identified. A different black market, Silk Road 2, stated that during a February 2014 hack bitcoins valued at $2.7 million were taken from escrow accounts. In late February 2014 Mt. Gox, one of the largest virtual currency exchanges, filed for bankruptcy in Tokyo after its computer system was hacked and approximately $477 million in bitcoins were stolen. Flexcoin, a bitcoin storage specialist based in Alberta, Canada, shut down on March 2014 after saying it discovered a theft of about $650,000 in bitcoins. Poloniex, a digital currency exchange, reported on March 2014 that it lost bitcoins valued at around $50,000.
Bitcoin-related malware includes software that steals bitcoins from users using a variety of techniques, software that uses infected computers to mine bitcoins, and different types of ransomware, which disable computers or prevent files from being accessed until some payment is made. Security company Dell SecureWorks said in February 2014 that it had identified 146 types of bitcoin malware; about half of it undetectable with standard antivirus scanners.
In June 2011, Symantec warned about the possibility that botnets could mine covertly for bitcoins. Malware used the parallel processing capabilities of GPUs built into many modern video cards. Although the average PC with an integrated graphics processor is virtually useless for bitcoin mining, tens of thousands of PCs laden with mining malware could produce some results.
German police arrested two people in December 2013 who customized existing botnet software to perform bitcoin mining, which police said had been used to mine at least $950,000 worth of bitcoins.
For four days in December 2013 and January 2014, Yahoo Europe hosted an ad containing bitcoin mining malware that infected an estimated two million computers. The software, called Sefnit, was first detected in mid-2013 and has been bundled with many software packages. Microsoft has been removing the malware through its Microsoft Security Essentials and other security software since January 2014.
Malware stealing bitcoins
Some malware can steal private keys for bitcoin wallets allowing the bitcoins themselves to be stolen. The most common type searches computers for cryptocurrency wallets to upload to a remote server where they can be cracked and their coins stolen. Many of these also log keystrokes to record passwords, often avoiding the need to crack the keys. A different approach detects when a bitcoin address is copied to a clipboard and quickly replaces it with a different address, tricking people into sending bitcoins to the wrong address. This method is effective because bitcoin transactions are irreversible.
Cases of theft
One virus, spread through the Pony botnet, was reported in February 2014 to have stolen up to $220,000 in cryptocurrencies including 335 bitcoins from 85 wallets. Security company Trustwave, which tracked the malware, reports that its latest version was able to steal 30 types of digital currency.
A type Mac malware active in August 2013, Bitvanity posed as a vanity wallet address generator and stole addresses and private keys from other bitcoin client software. A different trojan for Mac OS X, called CoinThief was reported in February 2014 to be responsible for multiple bitcoin thefts, including one user who lost 20 bitcoins. The software was hidden in versions of some cryptocurrency apps on Download.com and MacUpdate.
Another type of bitcoin-related malware is ransomware. One program called Cryptolocker, typically spread through legitimate-looking email attachments, encrypts the hard drive of an infected computer, then displays a countdown timer and demands a ransom, usually two bitcoins, to decrypt it. Police in Massachusetts said they paid a 2 bitcoin ransom in November 2013, worth more than $1,300 at the time, to decrypt one of their hard drives. Linkup, a combination ransomware and bitcoin mining program that surfaced in February 2014, disables internet access and demands credit card information to restore it, while secretly mining bitcoins.
Core developers could stop maintaining the bitcoin protocol unless they are paid.
There are two main ways the blockchain ledger can be corrupted to steal bitcoins: by fraudulently adding to or modifying it. The bitcoin system protects the blockchain against both using a combination of digital signatures and cryptographic hashes.
The Addition Attack and digital signatures
Payers and payees are identified in the blockchain by their public cryptographic keys: most bitcoin transfers are from one public key to a different public key. (Actually, hashes of these keys are used in the blockchain, and are called "bitcoin addresses".) In principle, an attacker Eve could steal money from Alice and Bob by simply adding transactions to the blockchain ledger like Alice pays Eve 100 bitcoins, Bob pays Eve 100 bitcoins, and so on, using of course these people's bitcoin addresses instead of their names. The bitcoin protocol prevents this kind of theft by requiring every transfer to be digitally signed with the payer's private key; only signed transfers can be added to the blockchain ledger. Since Eve cannot forge Alice's signature, Eve cannot defraud Alice by adding an entry to the blockchain equivalent to Alice pays Eve 100 bitcoins. At the same time, anyone can verify Alice's signature using her public key, and therefore that she has authorized any transaction in the blockchain where she is the payer.
The Modification Attack and mining
The other principal way to steal bitcoins would be to modify blockchain ledger entries. Eve could buy something from Alice, like a sofa, by adding a signed entry to the blockchain ledger equivalent to Eve pays Alice 100 bitcoins. Later, after receiving the sofa, Eve could modify that blockchain ledger entry to read instead: Eve pays Alice 1 bitcoin, or even delete the entry. Digital signatures cannot prevent this attack: Eve can simply sign her entry again after modifying it.
To prevent modification attacks, the bitcoin system first requires entries be added to the blockchain not one at a time, but in groups or blocks. More importantly, each block must be accompanied by a cryptographic hash of three things: the hash of the previous block, the block itself, and a number called a nonce. A hash of only the first two items will, like any cryptographic hash, always have a fixed number of bits (e.g. 256 for SHA-256). The nonce is a number which, when included, yields a hash with a specified number of leading zero bits. Because cryptographic hashes are essentially random, in the sense that their output cannot be predicted from their inputs, there is only one known way to find the nonce: to try out integers one after the other, e.g. 1, then 2, then 3, and so on. This process is called mining. The larger the number of leading zeros, the longer on average it will take to find a requisite nonce. The bitcoin system constantly adjusts the number of leading zeros so that the average time to find a nonce is about ten minutes. That way, as computer hardware gets faster over the years, the bitcoin protocol will simply require more leading zero bits to make mining always last about ten minutes.
This system prevents modification attacks in part because an attacker has to recalculate all the hashes of the blocks after the modified one. In the example above, if Eve wants to change 100 bitcoins to 1 bitcoin, she will not only have to recompute the hash of the block that transaction is in, but of all the blocks that come after it; she will have to recreate the chain of blocks. Although she could do this in principle, it would take her about ten minutes on average per block. Concurrently, the network will continue to add blocks at a much faster rate than Eve alone can mine. Eve would have to recalculate all the blocks before the network could add a new one, or at least catch up with or overtake the network's miners. To achieve this would require roughly as much computing power as all existing bitcoin miners combined which would be prohibitively expensive and, if the bitcoin network is large enough, essentially unfeasible. Moreover, due to the financial incentives of mining new bitcoins, it would make more economic sense for Eve to devote her resources to normal bitcoin mining instead. Thus the system protects against fraudulent blockchain modifications by making them expensive and, if the attacker is rational, unappealing because they make less financial sense than becoming a miner. The more miners there are, the more expensive and less feasible such attacks become, making the whole system even more secure.
Bitcoin system is based on an innovative solution of a problem common to all digital currency and payment schemes: that of so-called double-spending. With paper money or physical coins, when the payer transfers money to the payee, the payer cannot keep a copy of that dollar bill or coin. With digital money, which is just a computer file, this is not the case, and the payer could in principle spend the same money again and again, copying the file over and over. With bitcoin, when Eve offers to pay Alice some bitcoins, Alice can always first check the blockchain ledger to verify that Eve actually owns that many bitcoins. Of course, Eve could try to pay many people simultaneously; but bitcoin can defend against that. If Eve offers to pay Alice some bitcoins in exchange for goods, Alice can stipulate that she will not deliver the goods until Eve's payment to Alice appears in the blockchain, which typically involves waiting about ten minutes.
Types of attacks
If the transaction has no confirmations, shops and services which accept payment can be exposed to a so-called race attack. For example, two transactions are created for the same funds to be sent to different shops/services. System rules ensure that only one of those transactions can be added to the block chain.
Shops can take numerous precautions to reduce this type of attack. It is always good to consider whether you should accept transactions without any confirmation.
Another type of attack. Shops or services which accept transactions without any confirmation are affected. A Finney attack is an attack which requires the participation of a miner to premine a block sending the money to be defrauded back to the fraudster. The risk of such an attack cannot be reduced to nothing regardless of the preventative measures taken by shops or services, but it does require the participation of a miner and an ideal combination of contributing factors. It is no mean feat, the miner risks a potential loss of the block reward. Just as with the other type of attack, the shop or service must seriously consider its policies concerning transactions without any confirmation.
Also called an attack with confirmation, this is a combination of the 2 aforementioned attacks which gives the perpetrator the ability to spend funds twice simply with a confirmation.
Brute force attack
This attack is possible even if the shop or service is expecting several transaction confirmations. It requires the attacker to be in possession of relatively high-performance hardware (hash frequency).
The perpetrator sends a transaction to the shop paying for a product/service and at the same time continues looking for a connection in the block chain (block chain fork) which recognizes this transaction. After a certain number of confirmations, the shop sends the product. If the perpetrator has found more than n blocks at this point, he breaks his block chain fork and regains his money, but if the perpetrator has not succeeded in doing this, the attack can be deemed a failure and the funds are sent to the shop, as should be the case.
The success of this attack depends on the speed (hash frequency) of the attacker and the number of confirmations for the shop/service. For example, if the attacker possesses 10% of the calculation power of the bitcoin network and the shop expects 6 confirmations for a successful transaction, the probability of success of such an attack will be 0.1%.
If the perpetrator controls more than 50% of the bitcoin network power, the probability of success of the aforementioned attack will be 100%. By virtue of the fact that the perpetrator can generate blocks more often than the other part of the network, he can create his own block chain until it becomes longer than the "integral" part of the network.
In the media
A bitcoin documentary film called The Rise and Rise of Bitcoin made its debut at the Tribeca Film Festival in New York on 23 April 2014, chronicling bitcoin's origins to its explosive growth in 2013.
In Fall 2014, undergraduate students at the Massachusetts Institute of Technology will receive $100 in bitcoins "to better understand this emerging technology". A student had the idea of a Bitcoin Club and raised more than half a million dollars from a high frequency trader.
- It is not known whether the name "Satoshi Nakamoto" is real or a pseudonym, or whether it represents one person or a group of people.
- There is no uniform convention for bitcoin capitalization. Some sources use Bitcoin, capitalized, to refer to the technology and network and bitcoin, lowercase, to refer to the unit of account. The WSJ and The Chronicle of Higher Education advocate use of lowercase bitcoin in all cases, however. This article follows the latter convention.
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