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Zcash
Zcash logo
Unit
SymbolZEC‎
Demographics
Date of introduction28 October 2016; 8 years ago (2016-10-28)
User(s)Worldwide
Issuance
AdministrationDecentralized[note 1]
Valuation
Supply growthedit
This article contains special characters. Without proper rendering support, you may see question marks, boxes, or other symbols.

Zcash is a cryptocurrency. This page is under creation and more information can be found at https://z.cash/

Etymology and orthography

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Design

Blockchain

See also: Blockchain (database)

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Units

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Ownership

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Transactions

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Mining

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Practicalities

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Energy consumption

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Supply

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Transaction fees

Wallets

Reference implementation

Privacy

Fungibility

History

Alexa rank Site
33[2] PayPal[3]
41[4] Microsoft[5]
328[6] Dell[7]
329[8] Newegg[9]
505[10] Overstock.com[11]
512[12] Expedia[13]
1,981[14] TigerDirect[15]
5,674[16] Dish Network[17]
7,038[18] Zynga[19]
30,565[20] Time Inc.[21]
176,903[22] PrivateFly[23]
253,983[24] Virgin Galactic[25]
348,010[26] Dynamite Entertainment[27]
1,145,668[28] Clearly Canadian[29]
n.a. Sacramento Kings[30]

Acceptance by nonprofits

The Electronic Frontier Foundation,[31] Greenpeace,[32] The Mozilla Foundation,[33] and The Wikimedia Foundation.[34] Some U.S. political candidates, including New York City Democratic Congressional candidate Jeff Kurzon have said they would accept campaign donations in bitcoin.[35] In late 2013 the University of Nicosia became the first university in the world to accept bitcoins.[36]

Use in retail transactions

File:V0cgp31.jpg
Bitcoin ATM in The D Las Vegas Casino. An early retail adopter of bitcoin

Due to the design of bitcoin, all retail figures are only estimates.[37][38] According to Tim Swanson, head of business development at a Hong Kong-based cryptocurrency technology company, in 2014, daily retail purchases made with bitcoin were worth about $2.3 million.[38] He estimates that, as of February 2015, fewer than 5,000 bitcoins per day (worth roughly $1.2 million at the time) were being used for retail transactions,[37] and concluded that in 2014 "it appears there has been very little if any increase in retail purchases using bitcoin."[37]

Financial institutions

Bitcoin companies have had difficulty opening traditional bank accounts because lenders have been leery of bitcoin's links to illicit activity.[39] According to Antonio Gallippi, a co-founder of BitPay, "banks are scared to deal with bitcoin companies, even if they really want to".[40] In 2014, the National Australia Bank closed accounts of businesses with ties to bitcoin,[41] and HSBC refused to serve a hedge fund with links to bitcoin.[42] Australian banks in general have been reported as closing down bank accounts of operators of businesses involving the currency;[43] this has become the subject of an investigation by the Australian Competition and Consumer Commission.[43] Nonetheless, Australian banks have keenly adopted the blockchain technology on which bitcoin is based.[44]

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."[45]

In June 2014, the first bank that converts deposits in currencies instantly to bitcoin without any fees was opened in Boston.[46]

As an investment

Some Argentinians have bought bitcoins to protect their savings against high inflation or the possibility that governments could confiscate savings accounts.[47] During the 2012–2013 Cypriot financial crisis, bitcoin purchases in Cyprus rose due to fears that savings accounts would be confiscated or taxed.[48] 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.[49] Also, c. 2012 an attempt was made by the Winklevoss twins (who in April 2013 claimed they owned nearly 1% of all bitcoins in existence[50]) to establish a bitcoin ETF.[51] As of early 2015, they have announced plans to launch a New York-based bitcoin exchange named Gemini,[52] which has received approval to launch on 5 October 2015.[53] On 4 May 2015, Bitcoin Investment Trust started trading on the OTCQX market as GBTC.[54] Forbes started publishing arguments in favor of investing in December 2015.[55]

In 2013 and 2014, the European Banking Authority[56] and the Financial Industry Regulatory Authority (FINRA), a United States self-regulatory organization,[57] warned that investing in bitcoins carries significant risks. Forbes named bitcoin the best investment of 2013.[58] In 2014, Bloomberg named bitcoin one of its worst investments of the year.[59] In 2015, bitcoin topped Bloomberg's currency tables.[60]

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.[61][62] In May 2015, Intercontinental Exchange Inc., parent company of the New York Stock Exchange, announced a bitcoin index initially based on data from Coinbase transactions.[63]

Venture capital

Venture capitalists, such as Peter Thiel's Founders Fund, which invested US$3 million in BitPay, do not purchase bitcoins themselves, instead funding bitcoin infrastructure like companies that provide payment systems to merchants, exchanges, wallet services, etc.[64] 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,[65] at the time called 'mystery buyer'.[66] The company's goal is to fund 100 bitcoin businesses within 2–3 years with $10,000 to $20,000 for a 6% stake.[65] Investors also invest in bitcoin mining.[67] According to a 2015 study by Paolo Tasca, bitcoin startups raised almost $1 billion in three years (Q1 2012 – Q1 2015).[68]

Political economy

The decentralization of money offered by virtual currencies like bitcoin has its theoretical roots in the Austrian school of economics,[69] especially with Friedrich von Hayek in his book Denationalisation of Money: The Argument Refined, in which he advocates a complete free market in the production, distribution and management of money to end the monopoly of central banks.[70]

Bitcoin appeals to tech-savvy libertarians, because it so far exists outside the institutional banking system and the control of governments.[71] However, researchers looking to uncover the reasons for interest in bitcoin did not find evidence in Google search data that this was linked to libertarianism.[72]

Bitcoin's appeal reaches from left wing critics, "who perceive the state and banking sector as representing the same elite interests, […] recognising in it the potential for collective direct democratic governance of currency"[73] and socialists proposing their "own states, complete with currencies",[74] to right wing critics suspicious of big government, at a time when activities within the regulated banking system were responsible for the severity of the financial crisis of 2007–08,[75] "because governments are not fully living up to the responsibility that comes with state-sponsored money".[76] Bitcoin has been described as "remov[ing] the imbalance between the big boys of finance and the disenfranchised little man, potentially allowing early adopters to negotiate favourable rates on exchanges and transfers – something that only the very biggest firms have traditionally enjoyed".[77] Two WSJ journalists describe bitcoin in their book as "about freeing people from the tyranny of centralised trust".[78]

Main article: Legality of bitcoin by country

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. Likewise, various government agencies, departments, and courts have classified bitcoins differently. Regulations and bans that apply to bitcoin probably extend to similar cryptocurrency systems.[79]

In April 2013, Steven Strauss, a Harvard public policy professor, suggested that governments could outlaw bitcoin,[80] and this possibility was mentioned again by a bitcoin investment vehicle in a July 2013 report to a regulator.[51] However, the vast majority of nations have not done so as of 2014. It is illegal in Bangladesh,[81] Bolivia,[82] Ecuador.[83]

In China in December 2013 the Chinese government declared that “bitcoin is not a currency and should not be circulated and used in the market as a currency.” 'While people there are free to buy and sell it, financial institutions have been warned away'.[84]

Criminal activity

The use of bitcoin by criminals has attracted the attention of financial regulators, legislative bodies, law enforcement, and the media.[85] The FBI prepared an intelligence assessment,[86] the SEC has issued a pointed warning about investment schemes using virtual currencies,[85] and the U.S. Senate held a hearing on virtual currencies in November 2013.[87]

Several news outlets have asserted that the popularity of bitcoins hinges on the ability to use them to purchase illegal goods.[88][89] 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."[72]

Theft

There have been many cases of bitcoin theft.[90] One way this is accomplished involves a third party accessing the private key to a victim's bitcoin address,[91] or of an online wallet.[92] If the private key is stolen, all the bitcoins from the compromised address can be transferred. In that case, the network does not have any provisions to identify the thief, block further transactions of those stolen bitcoins, or return them to the legitimate owner.[51]

Theft also occurs at sites where bitcoins are used to purchase illicit goods. In late November 2013, an estimated $100 million in bitcoins were allegedly stolen from the online illicit goods marketplace Sheep Marketplace, which immediately closed.[93] Users tracked the coins as they were processed and converted to cash, but no funds were recovered and no culprits identified.[93] 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.[94]

Sites where users exchange bitcoins for cash or store them in "wallets" are also targets for theft. Inputs.io, an Australian wallet service, was hacked twice in October 2013 and lost more than $1 million in bitcoins.[95] In late February 2014 Mt. Gox, one of the largest virtual currency exchanges, filed for bankruptcy in Tokyo amid reports that bitcoins worth $350 million had been stolen.[96] 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.[97] Poloniex, a digital currency exchange, reported on March 2014 that it lost bitcoins valued at around $50,000.[98] In January 2015 UK-based bitstamp, the third busiest bitcoin exchange globally, was hacked and $5 million in bitcoins were stolen.[99] February 2015 saw a Chinese exchange named BTER lose bitcoins worth nearly $2 million to hackers.[100]

A major bitcoin exchange, Bitfinex, was hacked and nearly 120,000 bitcoins (around $60m) was stolen in 2016. Bitfinex was forced to suspend its trading. The theft is the second largest bitcoin heist ever, dwarfed only by Mt. Gox theft in 2014. According to Forbes, "All of Bitfinex’s customers,... will stand to lose money. The company has announced a haircut of 36.067% across the board."[101]

Black markets

Main article: Darknet market

A CMU researcher estimated that in 2012, 4.5% to 9% of all transactions on all exchanges in the world were for drug trades on a single deep web drugs market, Silk Road.[102] Child pornography,[103] murder-for-hire services,[104] and weapons[105] are also allegedly available on black market sites that sell in bitcoin. Due to the anonymous nature and the lack of central control on these markets, it is hard to know whether the services are real or just trying to take the bitcoins.[106]

Several deep web black markets have been shut by authorities. In October 2013 Silk Road was shut down by U.S. law enforcement[107][108][109] leading to a short-term decrease in the value of bitcoin.[110] In 2015, the founder of the site was sentenced to life in prison.[111] Alternative sites were soon available, and in early 2014 the Australian Broadcasting Corporation reported that the closure of Silk Road had little impact on the number of Australians selling drugs online, which had actually increased.[112] In early 2014, Dutch authorities closed Utopia, an online illegal goods market, and seized 900 bitcoins.[113] In late 2014, a joint police operation saw European and American authorities seize bitcoins and close 400 deep web sites including the illicit goods market Silk Road 2.0.[114] Law enforcement activity has resulted in several convictions. In December 2014, Charlie Shrem was sentenced to two years in prison for indirectly helping to send $1 million to the Silk Road drugs site,[115] and in February 2015, its founder, Ross Ulbricht, was convicted on drugs charges and faces a life sentence.[116]

Some black market sites may seek to steal bitcoins from customers. The bitcoin community branded one site, Sheep Marketplace, as a scam when it prevented withdrawals and shut down after an alleged bitcoins theft.[117] In a separate case, escrow accounts with bitcoins belonging to patrons of a different black market were hacked in early 2014.[94]

According to the Internet Watch Foundation, a UK-based charity, bitcoin is used to purchase child pornography, and almost 200 such websites accept it as payment. Bitcoin isn't the sole way to purchase child pornography online, as Troels Oertling, head of the cybercrime unit at Europol, states, "Ukash and Paysafecard... have [also] been used to pay for such material." However, the Internet Watch Foundation lists around 30 sites that exclusively accept bitcoins.[103] Some of these sites have shut down, such as a deep web crowdfunding website that aimed to fund the creation of new child porn.[118][better source needed] Furthermore, hyperlinks to child porn websites have been added to the blockchain as arbitrary data can be included when a transaction is made.[119][120]

Money laundering

Bitcoins may not be ideal for money laundering because all transactions are public.[121] Authorities, including the European Banking Authority[56] the FBI,[86] and the Financial Action Task Force of the G7[122] have expressed concerns that bitcoin may be used for money laundering. In early 2014, an operator of a U.S. bitcoin exchange was arrested for money laundering.[123] A report by UK's Treasury and Home Office named "UK national risk assessment of money laundering and terrorist financing" (2015 October) found that, of the twelve methods examined in the report, bitcoin carries the lowest risk of being used for money laundering, with the most common money laundering method being the banks.[124]

Ponzi scheme

In a 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.[125] In July 2013 the U.S. Securities and Exchange Commission charged the company and its founder in 2013 "with defrauding investors in a Ponzi scheme involving bitcoin".[125] In September 2014 the judge fined Bitcoin Savings & Trust and its owner $40 million for operating a bitcoin Ponzi scheme.[126]

Malware

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 almost 150 types of bitcoin malware.[127]

Unauthorized mining

In June 2011, Symantec warned about the possibility that botnets could mine covertly for bitcoins.[128] Malware used the parallel processing capabilities of GPUs built into many modern video cards.[129] 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.[130]

In mid-August 2011, bitcoin mining botnets were detected,[131] and less than three months later, bitcoin mining trojans had infected Mac OS X.[132]

In April 2013, electronic sports organization E-Sports Entertainment was accused of hijacking 14,000 computers to mine bitcoins; the company later settled the case with the State of New Jersey.[133]

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.[134]

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.[135] 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.[136]

Several reports of employees or students using university or research computers to mine bitcoins have been published.[137]

Malware stealing

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.[138] Many of these also log keystrokes to record passwords, often avoiding the need to crack the keys.[138] 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.[139] This method is effective because bitcoin transactions are irreversible.

One virus, spread through the Pony botnet, was reported in February 2014 to have stolen up to $220,000 in cryptocurrencies including bitcoins from 85 wallets.[140] Security company Trustwave, which tracked the malware, reports that its latest version was able to steal 30 types of digital currency.[141]

A type of 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.[142] A different trojan for Mac OS X, called CoinThief was reported in February 2014 to be responsible for multiple bitcoin thefts.[142] The software was hidden in versions of some cryptocurrency apps on Download.com and MacUpdate.[142]

Ransomware

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.[143] Massachusetts police 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.[144] 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.[143]

Security

Various potential attacks on the bitcoin network and its use as a payment system, real or theoretical, have been considered. The bitcoin protocol includes several features that protect it against some of those attacks, such as unauthorized spending, double spending, forging bitcoins, and tampering with the blockchain. Other attacks, such as theft of private keys, require due care by users.[145][146][147][148][149][150][151]

Unauthorized spending

Unauthorized spending is mitigated by bitcoin's implementation of public-private key cryptography. For example; when Alice sends a bitcoin to Bob, Bob becomes the new owner of the bitcoin. Eve observing the transaction might want to spend the bitcoin Bob just received, but she cannot sign the transaction without the knowledge of Bob's private key.[145]

Double spending

A specific problem that an internet payment system must solve is double-spending, whereby a user pays the same coin to two or more different recipients. An example of such a problem would be if Eve sent a bitcoin to Alice and later sent the same bitcoin to Bob. The bitcoin network guards against double-spending by recording all bitcoin transfers in a ledger (the blockchain) that is visible to all users, and ensuring for all transferred bitcoins that they haven't been previously spent.[145]: 4 

Race attack

If Eve offers to pay Alice a bitcoin in exchange for goods and signs a corresponding transaction, it is still possible that she also creates a different transaction at the same time sending the same bitcoin to Bob. By the rules, the network accepts only one of the transactions. This is called a race attack, since there is a race which transaction will be accepted first. Alice can reduce the risk of race attack stipulating that she will not deliver the goods until Eve's payment to Alice appears in the blockchain.[146]

A variant race attack (which has been called a Finney attack by reference to Hal Finney) requires the participation of a miner. Instead of sending both payment requests (to pay Bob and Alice with the same coins) to the network, Eve issues only Alice's payment request to the network, while the accomplice tries to mine a block that includes the payment to Bob instead of Alice. There is a positive probability that the rogue miner will succeed before the network, in which case the payment to Alice will be rejected. As with the plain race attack, Alice can reduce the risk of a Finney attack by waiting for the payment to be included in the blockchain.[147]

History modification

Each block that is added to the blockchain, starting with the block containing a given transaction, is called a confirmation of that transaction. Ideally, merchants and services that receive payment in bitcoin should wait for at least one confirmation to be distributed over the network, before assuming that the payment was done. The more confirmations that the merchant waits for, the more difficult it is for an attacker to successfully reverse the transaction in a blockchain—unless the attacker controls more than half the total network power, in which case it is called a 51% attack.[148]

Deanonymisation of clients

Along with transaction graph analysis, which may reveal connections between bitcoin addresses (pseudonyms),[149][150] there is a possible attack[151] which links a user's pseudonym to its IP address. If the peer is using Tor, the attack includes a method to separate the peer from the Tor network, forcing them to use their real IP address for any further transactions. The attack makes use of bitcoin mechanisms of relaying peer addresses and anti-DoS protection. The cost of the attack on the full bitcoin network is under €1500 per month.[151]

Data in the blockchain

While it is possible to store any digital file in the blockchain, the larger the transaction size, the larger any associated fees become.[152] Various items have been embedded, including URLs to child pornography, an ASCII art image of Ben Bernanke, material from the Wikileaks cables, prayers from bitcoin miners, and the original bitcoin whitepaper.[153]

In academia

In the fall of 2014, undergraduate students at the Massachusetts Institute of Technology (MIT) each received bitcoins worth $100 "to better understand this emerging technology". The bitcoins were not provided by MIT but rather the MIT Bitcoin Club, a student-run club.[154][155]

In art, entertainment, and media

Films

A documentary film called The Rise and Rise of Bitcoin (late 2014) features interviews with people who use bitcoin, such as a computer programmer and a drug dealer.[156]

Music

Several lighthearted songs celebrating bitcoin have been released.[157]

Literature

In Charles Stross' science fiction novel Neptune's Brood (2014), a modification of bitcoin is used as the universal interstellar payment system. The functioning of the system is a major plot element of the book.[158]

Television

In early 2015, the CNN series Inside Man featured an episode about bitcoin. Filmed in July 2014, it featured Morgan Spurlock living off of bitcoins for a week to figure out whether the world is ready for a new kind of money.[159]

See also

Template:Wikipedia books

Notes

  1. ^ Bitcoin does not have a central authority.[1]

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