cryptocurrency

A cryptocurrency (or crypto currency) is a digital asset designed to work as a medium of exchange that uses cryptography to secure its transactions, to control the creation of additional units, and to verify the transfer of assets.[1][2][3] Cryptocurrencies are a type of digital currencies, alternative currencies and virtual currencies. Cryptocurrencies use decentralized control[4] as opposed to centralized electronic money and central banking systems.[5] The decentralized control of each cryptocurrency works through a blockchain, which is a public transaction database, functioning as a distributed ledger.[6]

Bitcoin, created in 2009, was the first decentralized cryptocurrency.[7] Since then, numerous other cryptocurrencies have been created.[8] These are frequently called altcoins, as a blend of alternative coin.[9][10][11]

Contents
1 Formal definition
2 Overview
3 Architecture
3.1 Blockchain
3.2 Timestamping
3.2.1 Proof-of-work schemes
3.2.2 Proof-of-stake and combined schemes
3.3 Mining
3.4 Wallets
3.5 Anonymity
4 Economics
4.1 Competition in cryptocurrency markets
4.2 Transaction fees
5 Legality
5.1 U.S. tax status
5.2 The legal concern of an unregulated global economy
5.3 Loss, theft, and fraud
5.4 Darknet markets
5.5 Fundings – ICOs
6 Cryptocurrency in gaming
6.1 Lotteries
6.2 Online casinos & dice sites
7 Academic studies
8 Criticism
8.1 Causing a rise in GPU prices
9 History
9.1 Publicity
10 See also
11 References
12 Further reading
13 External links
Formal definition
According to Jan Lansky, a cryptocurrency is a system that meets all of the following six conditions:[12]

The system does not require a central authority, distributed achieve consensus on its state.
The system keeps an overview of cryptocurrency units and their ownership.
The system defines whether new cryptocurrency units can be created. If new cryptocurrency units can be created, the system defines the circumstances of their origin and how to determine the ownership of these new units.
Ownership of cryptocurrency units can be proved exclusively cryptographically.
The system allows transactions to be performed in which ownership of the cryptographic units is changed. A transaction statement can only be issued by an entity proving the current ownership of these units.
If two different instructions for changing the ownership of the same cryptographic units are simultaneously entered, the system performs at most one of them.
In March 2018, the word "cryptocurrency" was added to the Merriam-Webster Dictionary.[13]

Overview
Decentralized cryptocurrency is produced by the entire cryptocurrency system collectively, at a rate which is defined when the system is created and which is publicly known. In centralized banking and economic systems such as the Federal Reserve System, corporate boards or governments control the supply of currency by printing units of fiat money or demanding additions to digital banking ledgers. In case of decentralized cryptocurrency, companies or governments cannot produce new units, and have not so far provided backing for other firms, banks or corporate entities which hold asset value measured in it. The underlying technical system upon which decentralized cryptocurrencies are based was created by the group or individual known as Satoshi Nakamoto.[14]

As of September 2017, over a thousand cryptocurrency specifications exist; most are similar to and derive from the first fully implemented decentralized cryptocurrency, bitcoin. Within cryptocurrency systems the safety, integrity and balance of ledgers is maintained by a community of mutually distrustful parties referred to as miners: members of the general public using their computers to help validate and timestamp transactions, adding them to the ledger in accordance with a particular timestamping scheme.[15] Miners have a financial incentive to maintain the security of a cryptocurrency ledger.[14]

Most cryptocurrencies are designed to gradually decrease production of currency, placing an ultimate cap on the total amount of currency that will ever be in circulation, mimicking precious metals.[1][16] Compared with ordinary currencies held by financial institutions or kept as cash on hand, cryptocurrencies can be more difficult for seizure by law enforcement.[1] This difficulty is derived from leveraging cryptographic technologies.

Architecture
Blockchain
Main article: Blockchain
The validity of each cryptocurrency's coins is provided by a blockchain. A blockchain is a continuously growing list of records, called blocks, which are linked and secured using cryptography.[14][17] Each block typically contains a hash pointer as a link to a previous block,[17] a timestamp and transaction data.[18] By design, blockchains are inherently resistant to modification of the data. It is "an open, distributed ledger that can record transactions between two parties efficiently and in a verifiable and permanent way".[19] For use as a distributed ledger, a blockchain is typically managed by a peer-to-peer network collectively adhering to a protocol for validating new blocks. Once recorded, the data in any given block cannot be altered retroactively without the alteration of all subsequent blocks, which requires collusion of the network majority.

Blockchains are secure by design and are an example of a distributed computing system with high Byzantine fault tolerance. Decentralized consensus has therefore been achieved with a blockchain.[20] It solves the double spending problem without the need of a trusted authority or central server.

The block time is the average time it takes for the network to generate one extra block in the blockchain.[21] Some blockchains create a new block as frequently as every five seconds.[22] By the time of block completion, the included data becomes verifiable. This is practically when the money transaction takes place, so a shorter block time means faster transactions.[citation needed]

Timestamping
Cryptocurrencies use various timestamping schemes to avoid the need for a trusted third party to timestamp transactions added to the blockchain ledger.

Proof-of-work schemes
The first timestamping scheme invented was the proof-of-work scheme. The most widely used proof-of-work schemes are based on SHA-256 and scrypt.[23] The latter now dominates over the world of cryptocurrencies, with at least 480 confirmed implementations.[24]

Some other hashing algorithms that are used for proof-of-work include CryptoNight, Blake, SHA-3, and X11.

Proof-of-stake and combined schemes
Some cryptocurrencies use a combined proof-of-work/proof-of-stake scheme.[23] The proof-of-stake is a method of securing a cryptocurrency network and achieving distributed consensus through requesting users to show ownership of a certain amount of currency. It is different from proof-of-work systems that run difficult hashing algorithms to validate electronic transactions. The scheme is largely dependent on the coin, and there's currently no standard form of it.

Mining

Hashcoin mine
In cryptocurrency networks, mining is a validation of transactions. For this effort, successful miners obtain new cryptocurrency as a reward. The reward decreases transaction fees by creating a complementary incentive to contribute to the processing power of the network. The rate of generating hashes, which validate any transaction, has been increased by the use of specialized machines such as FPGAs and ASICs running complex hashing algorithms like SHA-256 and Scrypt.[25] This arms race for cheaper-yet-efficient machines has been on since the day the first cryptocurrency, bitcoin, was introduced in 2009.[25] With more people venturing into the world of virtual currency, generating hashes for this validation has become far more complex over the years, with miners having to invest large sums of money on employing multiple high performance ASICs. Thus the value of the currency obtained for finding a hash often does not justify the amount of money spent on setting up the machines, the cooling facilities to overcome the enormous amount of heat they produce, and the electricity required to run them.[25][26]

Some miners pool resources, sharing their processing power over a network to split the reward equally, according to the amount of work they contributed to the probability of finding a block. A "share" is awarded to members of the mining pool who present a valid partial proof-of-work.

One company is operating data centers for mining operations at Canadian oil and gas field sites, due to low gas prices.[27]

Given the economic and environmental concerns associated with mining, various "minerless" cryptocurrencies are undergoing active development.[28][29][30] Unlike conventional blockchains, some directed acyclic graph cryptocurrencies utilise a pay-it-forward system, whereby each account performs minimally heavy computations on two previous transactions to verify. Other cryptocurrencies like Nano utilise a block-lattice structure whereby each individual account has its own blockchain. With each account controlling its own transactions, no traditional proof-of-work mining is required, allowing for feeless, instantaneous transactions.[31][better source needed]

As of February 2018, the Chinese Government halted trading of virtual currency, banned initial coin offerings and shut down mining. Some Chinese miners have since relocated to Canada.[32] According to a February 2018 report from Fortune,[33] Iceland has become a haven for cryptocurrency miners in part because of its cheap electricity. Prices are contained because nearly all of the country’s energy comes from renewable sources, prompting more mining companies to consider opening operations in Iceland. However, the cryptocurrency mania might have gone a little too far in Iceland. The region’s energy company says bitcoin mining is becoming so popular that the country will likely use more electricity to mine coins than power homes in 2018.

In March 2018, a town in Upstate New York put an 18 month moratorium on all cryptocurrency mining in an effort to preserve natural resources and the "character and direction" of the city.[34]

Wallets