View source for Finance:Blockchain

{{short description|Distributed data store for digital transactions}}
{{pp-semi|small=yes}}

A '''blockchain''' is a [[Distributed ledger|distributed ledger]] with growing lists of [[Record (computer science)|records]] (''blocks'') that are securely linked together via [[Cryptographic hash function|cryptographic hashes]].{{R|fortune20160515|nyt20160521}}<ref name="te20151031" /><ref name="cryptocurrencytech">{{Cite book |last1=Narayanan |first1=Arvind |title=Bitcoin and cryptocurrency technologies: a comprehensive introduction |last2=Bonneau |first2=Joseph |last3=Felten |first3=Edward |last4=Miller |first4=Andrew |last5=Goldfeder |first5=Steven |date=2016 |publisher=Princeton University Press |isbn=978-0-691-17169-2 |location=Princeton, New Jersey}}</ref> Each block contains a cryptographic hash of the previous block, a [[Trusted timestamping|timestamp]], and transaction data (generally represented as a [[Merkle tree]], where [[Node (computer science)|data nodes]] are represented by leaves). Since each block contains information about the previous block, they effectively form a ''chain'' (compare linked list data structure), with each additional block linking to the ones before it. Consequently, blockchain transactions are irreversible in that, once they are recorded, the data in any given block cannot be altered retroactively without altering all subsequent blocks.

Blockchains are typically managed by a [[Peer-to-peer|peer-to-peer (P2P)]] computer network for use as a public [[Distributed ledger|distributed ledger]], where nodes collectively adhere to a consensus algorithm [[Communication protocol|protocol]] to add and validate new transaction blocks. Although blockchain records are not unalterable, since [[Fork (blockchain)|blockchain forks]] are possible, blockchains may be considered [[Secure by design|secure by design]] and exemplify a distributed computing system with high [[Byzantine fault tolerance]].<ref>{{Cite news |last1=Iansiti |first1=Marco |last2=Lakhani |first2=Karim R. |date=January 2017 |title=The Truth About Blockchain |work=Harvard Business Review |publisher=[[Organization:Harvard University|Harvard University]] |location=Cambridge, Massachusetts|url=https://hbr.org/2017/01/the-truth-about-blockchain |url-status=live |access-date=January 17, 2017 |archive-url=https://web.archive.org/web/20170118052537/https://hbr.org/2017/01/the-truth-about-blockchain |archive-date=18 January 2017 |quote=The technology at the heart of bitcoin and other virtual currencies, blockchain is an open, distributed ledger that can record transactions between two parties efficiently and in a verifiable and permanent way. |df=dmy-all}}</ref>

A blockchain was created by a person (or group of people) using the name (or [[Pseudonym|pseudonym]]) Satoshi Nakamoto in 2008 to serve as the public [[Distributed ledger|distributed ledger]] for [[Software:Bitcoin|bitcoin]] [[Finance:Cryptocurrency|cryptocurrency]] transactions, based on previous work by [[Biography:Stuart Haber|Stuart Haber]], [[Biography:W. Scott Stornetta|W. Scott Stornetta]], and [[Biography:Dave Bayer|Dave Bayer]].<ref>{{Cite web|first=Daniel|last=Oberhaus|title=The World's Oldest Blockchain Has Been Hiding in the New York Times Since 1995|url=https://www.vice.com/en/article/j5nzx4/what-was-the-first-blockchain|date=August 27, 2018|access-date=October 9, 2021|website=Vice|language=en}}</ref> The implementation of the blockchain within bitcoin made it the first digital currency to solve the [[Finance:Double-spending|double-spending]] problem without the need for a trusted authority or central [[Server (computing)|server]]. The [[Software:Bitcoin|bitcoin]] design has inspired other applications{{R|te20151031|nyt20160521}} and blockchains that are readable by the public and are widely used by cryptocurrencies. The blockchain may be considered a type of [[Finance:Payment rail|payment rail]].<ref>{{Cite web |first=Bernard|last=Lunn|date=10 February 2018 |title=Blockchain may finally disrupt payments from Micropayments to credit cards to SWIFT |url=https://dailyfintech.com/2018/02/10/bitcoin-will-finally-disrupt-the-credit-card-rails/ |url-status=live |archive-url=https://web.archive.org/web/20180927005613/https://dailyfintech.com/2018/02/10/bitcoin-will-finally-disrupt-the-credit-card-rails/ |archive-date=27 September 2018 |access-date=November 18, 2018 |website=dailyfintech.com}}</ref>

Private blockchains have been proposed for business use. ''Computerworld'' called the marketing of such privatized blockchains without a proper security model "snake oil";<ref name="cw20160905" /> however, others have argued that permissioned blockchains, if carefully designed, may be more decentralized and therefore more secure in practice than permissionless ones.<ref name="cryptocurrencytech" /><ref name="auto">{{Cite journal |last1=Bakos |first1=Yannis |last2=Halaburda |first2=Hanna |last3=Mueller-Bloch |first3=Christoph |date=February 2021 |title=When Permissioned Blockchains Deliver More Decentralization Than Permissionless |journal=Communications of the ACM |volume=64 |issue=2 |pages=20–22 |doi=10.1145/3442371 |s2cid=231704491}}</ref>

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== History ==
[[File:2011-2021_blockchain_transactions.jpg|600px|thumb|[[Software:Bitcoin|Bitcoin]], Ethereum and Litecoin transactions per day (January 2011 – January 2021)]]
Cryptographer [[Biography:David Chaum|David Chaum]] first proposed a blockchain-like protocol in his 1982 dissertation "Computer Systems Established, Maintained, and Trusted by Mutually Suspicious Groups."<ref>{{Cite journal |last1=Sherman |first1=Alan T. |last2=Javani |first2=Farid |last3=Zhang |first3=Haibin |last4=Golaszewski |first4=Enis |date=January 2019 |title=On the Origins and Variations of Blockchain Technologies |journal=IEEE Security Privacy |volume=17 |issue=1 |pages=72–77 |arxiv=1810.06130 |doi=10.1109/MSEC.2019.2893730 |issn=1558-4046 |s2cid=53114747}}</ref> Further work on a cryptographically secured chain of blocks was described in 1991 by [[Biography:Stuart Haber|Stuart Haber]] and [[Biography:W. Scott Stornetta|W. Scott Stornetta]].<ref name="cryptocurrencytech" /><ref>{{Cite journal |last1=Haber |first1=Stuart |last2=Stornetta |first2=W. Scott |date=January 1991 |title=How to time-stamp a digital document |journal=Journal of Cryptology |volume=3 |issue=2 |pages=99–111 |citeseerx=10.1.1.46.8740 |doi=10.1007/bf00196791 |s2cid=14363020}}</ref> They wanted to implement a system wherein document [[Physics:Timestamp|timestamps]] could not be tampered with. In 1992, Haber, Stornetta, and [[Biography:Dave Bayer|Dave Bayer]] incorporated [[Merkle tree]]s into the design, which improved its efficiency by allowing several document certificates to be collected into one block.<ref name="cryptocurrencytech" /><ref>{{Cite book |last1=Bayer |first1=Dave |last2=Haber |first2=Stuart |last3=Stornetta |first3=W. Scott |title=Sequences II |chapter=Improving the Efficiency and Reliability of Digital Time-Stamping |date=March 1992 |work=Sequences |isbn=978-1-4613-9325-2 |volume=2 |pages=329–334 |citeseerx=10.1.1.71.4891 |doi=10.1007/978-1-4613-9323-8_24}}</ref> Under their company Surety, their document certificate hashes have been published in ''{{wipe|The New York Times}}'' every week since 1995.<ref name=":0">{{Cite web |last=Oberhaus |first=Daniel |date=2018-08-27 |title=The World's Oldest Blockchain Has Been Hiding in the New York Times Since 1995 |url=https://www.vice.com/en/article/j5nzx4/what-was-the-first-blockchain |access-date=2021-10-09 |website=www.vice.com |language=en}}</ref>

The first decentralized blockchain was conceptualized by a person (or group of people) known as Satoshi Nakamoto in 2008. Nakamoto improved the design in an important way using a [[Hashcash]]-like method to [[Timestamp-based concurrency control|timestamp]] blocks without requiring them to be signed by a trusted party and introducing a difficulty parameter to stabilize the rate at which blocks are added to the chain.{{r|cryptocurrencytech}} The design was implemented the following year by Nakamoto as a core component of the [[Finance:Cryptocurrency|cryptocurrency]] [[Software:Bitcoin|bitcoin]], where it serves as the public ledger for all transactions on the network.{{R|te20151031}}

In August 2014, the bitcoin blockchain file size, containing records of all transactions that have occurred on the network, reached 20&nbsp;GB ([[Gigabyte|gigabyte]]s).<ref>{{Cite book |last1=Nian |first1=Lam Pak |title=Handbook of Digital Currency: Bitcoin, Innovation, Financial Instruments, and Big Data |last2=Chuen |first2=David LEE Kuo |publisher=Academic Press |year=2015 |isbn=978-0-12-802351-8 |editor-last=Chuen |editor-first=David LEE Kuo |page=319 |chapter=A Light Touch of Regulation for Virtual Currencies}}</ref> In January 2015, the size had grown to almost 30&nbsp;GB, and from January 2016 to January 2017, the bitcoin blockchain grew from 50&nbsp;GB to 100&nbsp;GB in size. The ledger size had exceeded 200 GB by early 2020.<ref>{{Cite web |title=Blockchain Size |url=https://www.blockchain.com/en/charts/blocks-size?scale=1&timespan=all&showDataPoints=true |url-status=live |archive-url=https://web.archive.org/web/20200519024720/https://www.blockchain.com/en/charts/blocks-size?scale=1&timespan=all&showDataPoints=true |archive-date=19 May 2020 |access-date=25 February 2020}}</ref>

The words ''block'' and ''chain'' were used separately in Satoshi Nakamoto's original paper, but were eventually popularized as a single word, ''blockchain,'' by 2016.<ref>{{Cite book |last=Johnsen |first=Maria |date=12 May 2020 |url=https://books.google.com/books?id=uVbjDwAAQBAJ&pg=PA6 |title=Blockchain in Digital Marketing: A New Paradigm of Trust |publisher=Maria Johnsen |isbn=979-8-6448-7308-1|page=6|language=en}}</ref>

According to [[Company:Accenture|Accenture]], an application of the [[Physics:Diffusion of innovations|diffusion of innovations]] theory suggests that blockchains attained a 13.5% adoption rate within financial services in 2016, therefore reaching the [[Physics:Early adopter|early adopter]]s' phase.<ref>{{Cite news |date=27 June 2016 |title=The future of blockchain in 8 charts |work=Raconteur |url=http://raconteur.net/business/the-future-of-blockchain-in-8-charts |url-status=live |access-date=3 December 2016 |archive-url=https://web.archive.org/web/20161202234125/http://raconteur.net/business/the-future-of-blockchain-in-8-charts |archive-date=2 December 2016}}</ref> Industry trade groups joined to create the Global Blockchain Forum in 2016, an initiative of the [[Organization:Chamber of Digital Commerce|Chamber of Digital Commerce]].

In May 2018, [[Company:Gartner|Gartner]] found that only 1% of [[Chief information officer|CIOs]] indicated any kind of blockchain adoption within their organisations, and only 8% of CIOs were in the short-term "planning or [looking at] active experimentation with blockchain".<ref>{{Cite news |date=4 May 2018 |title=Hype Killer - Only 1% of Companies Are Using Blockchain, Gartner Reports {{!}} Artificial Lawyer |language=en-GB |work=Artificial Lawyer |url=https://www.artificiallawyer.com/2018/05/04/hype-killer-only-1-of-companies-are-using-blockchain-gartner-reports/ |url-status=live |access-date=2018-05-22 |archive-url=https://web.archive.org/web/20180522111623/https://www.artificiallawyer.com/2018/05/04/hype-killer-only-1-of-companies-are-using-blockchain-gartner-reports/ |archive-date=22 May 2018}}</ref> For the year 2019 Gartner reported 5% of CIOs believed blockchain technology was a 'game-changer' for their business.<ref>Kasey Panetta. (31 October 2018). "Digital Business: CIO Agenda 2019: Exploit Transformational Technologies." [https://www.gartner.com/smarterwithgartner/cio-agenda-2019-exploit-transformational-technologies/ Gartner website] Retrieved 27 March 2021.</ref>

== Structure and design ==
[[File:Blockchain.svg|thumb|150px|Blockchain formation. The main chain (black) consists of the longest series of blocks from the genesis block (green) to the current block. Orphan blocks (purple) exist outside of the main chain.]]
A blockchain is a [[Decentralized computing|decentralized]], [[Distributed computing|distributed]], and often public, digital ledger consisting of records called ''blocks'' that are used to record transactions across many computers so that any involved block cannot be altered retroactively, without the alteration of all subsequent blocks.{{R|te20151031}}<ref>{{Cite news |last=Armstrong |first=Stephen |date=7 November 2016 |title=Move over Bitcoin, the blockchain is only just getting started |magazine=Wired |url=https://www.wired.co.uk/article/unlock-the-blockchain |url-status=live |access-date=2016-11-09 |archive-url=https://web.archive.org/web/20161108130946/http://www.wired.co.uk/article/unlock-the-blockchain |archive-date=8 November 2016}}</ref> This allows the participants to verify and audit transactions independently and relatively inexpensively.<ref>{{Cite journal |last1=Catalini |first1=Christian |last2=Gans |first2=Joshua S. |date=23 November 2016 |title=Some Simple Economics of the Blockchain |journal=SSRN |url=http://www.nber.org/papers/w22952.pdf |url-status=live |doi=10.2139/ssrn.2874598 |hdl=1721.1/130500 |ssrn=2874598 |archive-url=https://web.archive.org/web/20200306014931/https://www.nber.org/papers/w22952.pdf |archive-date=6 March 2020 |access-date=16 September 2019 |s2cid=46904163}}</ref> A blockchain database is managed autonomously using a [[Peer-to-peer|peer-to-peer]] network and a distributed timestamping server. They are [[Authentication|authenticated]] by [[Social:Mass collaboration|mass collaboration]] powered by [[Social:Collective|collective]] [[Philosophy:Self-interest|self-interest]]s.<ref>{{Cite magazine |last1=Tapscott |first1=Don |last2=Tapscott |first2=Alex |date=8 May 2016 |title=Here's Why Blockchains Will Change the World |url=http://fortune.com/2016/05/08/why-blockchains-will-change-the-world/ |magazine=Fortune |archive-url=https://web.archive.org/web/20161113134748/http://fortune.com/2016/05/08/why-blockchains-will-change-the-world/ |archive-date=13 November 2016 |access-date=16 November 2016 |author-link1=Don Tapscott |url-status=live}}</ref> Such a design facilitates [[Robustness (computer science)|robust]] [[Workflow|workflow]] where participants' uncertainty regarding data security is marginal. The use of a blockchain removes the characteristic of infinite [[Finance:Reproduction (economics)|reproducibility]] from a digital asset. It confirms that each unit of value was transferred only once, solving the long-standing problem of double-spending. A blockchain has been described as a ''value-exchange protocol''.<ref>{{Cite magazine |last=Bheemaiah |first=Kariappa |date=January 2015 |title=Block Chain 2.0: The Renaissance of Money |url=https://www.wired.com/insights/2015/01/block-chain-2-0/ |magazine=Wired |archive-url=https://web.archive.org/web/20161114001509/https://www.wired.com/insights/2015/01/block-chain-2-0/ |archive-date=14 November 2016 |access-date=13 November 2016 |url-status=live}}</ref> A blockchain can maintain [[Social:Title (property)|title rights]] because, when properly set up to detail the exchange agreement, it provides a record that compels [[Finance:Offer and acceptance|offer and acceptance]].{{citation needed|date=June 2022}}

Logically, a blockchain can be seen as consisting of several layers:<ref>{{cite journal |last1=Chen |first1=Huashan |last2=Pendleton |first2=Marcus |last3=Njilla |first3=Laurent |last4=Xu |first4=Shouhuai |title=A Survey on Ethereum Systems Security: Vulnerabilities, Attacks, and Defenses |journal=ACM Computing Surveys |date=12 June 2020 |volume=53 |issue=3 |pages=3–4 |doi=10.1145/3391195 |arxiv=1908.04507 |s2cid=199551841 |issn=0360-0300}}</ref>
* infrastructure (hardware)
* [[Network layer|networking]] (node discovery, information propagation<ref>{{Cite thesis |title=Structured Information Flow (SIF) Framework for Automating End-to-End Information Flow for Large Organizations |url=https://vtechworks.lib.vt.edu/handle/10919/31148 |publisher=Virginia Tech |date=2006-02-02 |language=en |first=Bhatia |last=Shishir}}</ref> and verification)
* [[Consensus (computer science)|consensus]] ([[Finance:Proof of work|proof of work]], [[Finance:Proof of stake|proof of stake]])
* data (blocks, transactions)
* [[Application layer|application]] ([[Finance:Smart contract|smart contract]]s/[[Finance:Decentralized application|decentralized application]]s, if applicable)

===Blocks===
Blocks hold batches of valid [[Transaction processing|transactions]] that are hashed and encoded into a [[Merkle tree]].<ref name="te20151031" /> Each block includes the cryptographic hash of the prior block in the blockchain, linking the two. The linked blocks form a chain.<ref name="te20151031" /> This [[Iteration|iterative]] process confirms the integrity of the previous block, all the way back to the initial block, which is known as the ''genesis block'' (Block 0).<ref>{{Cite web |title=Genesis Block Definition |url=https://www.investopedia.com/terms/g/genesis-block.asp |access-date=2022-08-10 |website=Investopedia |language=en}}</ref><ref name="hadc" /> To assure the integrity of a block and the data contained in it, the block is usually [[Digital signature|digitally signed]].{{sfn|Knirsch|Unterweger|Engel|2019|page=2}}

Sometimes separate blocks can be produced concurrently, creating a temporary [[Fork (blockchain)|fork]]. In addition to a secure [[Hash-based cryptography|hash-based]] history, any blockchain has a specified algorithm for scoring different versions of the history so that one with a higher score can be selected over others. Blocks not selected for inclusion in the chain are called orphan blocks.<ref name="hadc" /> Peers supporting the database have different versions of the history from time to time. They keep only the highest-scoring version of the database known to them. Whenever a peer receives a higher-scoring version (usually the old version with a single new block added) they extend or overwrite their own database and retransmit the improvement to their peers. There is never an absolute guarantee that any particular entry will remain in the best version of history forever. Blockchains are typically built to add the score of new blocks onto old blocks and are given incentives to extend with new blocks rather than overwrite old blocks. Therefore, the probability of an entry becoming superseded decreases exponentially<ref name="bsm">{{Cite web |last=Antonopoulos |first=Andreas |date=20 February 2014 |title=Bitcoin security model: trust by computation |url=http://radar.oreilly.com/2014/02/bitcoin-security-model-trust-by-computation.html |url-status=live |archive-url=https://web.archive.org/web/20161031132328/http://radar.oreilly.com/2014/02/bitcoin-security-model-trust-by-computation.html |archive-date=31 October 2016 |access-date=19 November 2016 |website=Radar |publisher=O'Reilly}}</ref> as more blocks are built on top of it, eventually becoming very low.{{R|te20151031}}{{r|t12|p=ch. 08}}{{r|paper}} For example, bitcoin uses a [[Finance:Proof-of-work system|proof-of-work system]], where the chain with the most cumulative proof-of-work is considered the valid one by the network. There are a number of methods that can be used to demonstrate a sufficient level of [[Computation|computation]]. Within a blockchain the computation is carried out redundantly rather than in the traditional segregated and [[Parallel computing|parallel]] manner.<ref>{{Cite web |title=Permissioned Blockchains |url=https://monax.io/explainers/permissioned_blockchains/ |url-status=live |archive-url=https://web.archive.org/web/20161120154948/https://monax.io/explainers/permissioned_blockchains/ |archive-date=20 November 2016 |access-date=20 November 2016 |website=Explainer |publisher=Monax}}</ref>

====Block time====
The ''block time'' is the average time it takes for the network to generate one extra block in the blockchain. By the time of block completion, the included data becomes verifiable. In cryptocurrency, this is practically when the transaction takes place, so a shorter block time means faster transactions. The block time for [[Finance:Ethereum|Ethereum]] is set to between 14 and 15 seconds, while for bitcoin it is on average 10 minutes.<ref>{{Cite book |last1=Kumar |first1=Randhir |last2=Tripathi |first2=Rakesh |title=2019 Fifth International Conference on Image Information Processing (ICIIP) |chapter=Implementation of Distributed File Storage and Access Framework using IPFS and Blockchain |date=November 2019 |publisher=IEEE |pages=246–251 |doi=10.1109/iciip47207.2019.8985677 |isbn=978-1-7281-0899-5 |s2cid=211119043}}</ref>

==== Hard forks ====
{{Excerpt|Fork (blockchain)|Hard fork}}

=== Decentralization ===
By storing data across its [[Peer-to-peer|peer-to-peer network]], the blockchain eliminates some risks that come with data being held centrally.{{R|te20151031}} The decentralized blockchain may use ad hoc [[Message passing|message passing]] and [[Distributed networking|distributed networking]].<ref>{{Cite journal |last1=Hughes |first1=Laurie |last2=Dwivedi |first2=Yogesh K. |last3=Misra |first3=Santosh K. |last4=Rana |first4=Nripendra P. |last5=Raghavan |first5=Vishnupriya |last6=Akella |first6=Viswanadh |date=December 2019 |title=Blockchain research, practice and policy: Applications, benefits, limitations, emerging research themes and research agenda |url=https://linkinghub.elsevier.com/retrieve/pii/S0268401219302014 |journal=International Journal of Information Management |language=en |volume=49 |pages=114–129 |doi=10.1016/j.ijinfomgt.2019.02.005|hdl=10454/17473 |s2cid=116666889 |hdl-access=free }}</ref> 

In a so-called "51% attack" a central entity gains control of more than half of a network and can then manipulate that specific blockchain record at will, allowing [[Finance:Double-spending|double-spending]].<ref>{{Cite web|last=Roberts|first=Jeff John|title=Bitcoin Spinoff Hacked in Rare '51% Attack'|url=https://fortune.com/2018/05/29/bitcoin-gold-hack/|date=29 May 2018|access-date=27 December 2022|work=Fortune|language=en|archive-url=https://web.archive.org/web/20211222000248/https://fortune.com/2018/05/29/bitcoin-gold-hack/|archive-date=22 December 2021}}</ref>

Blockchain security methods include the use of [[Public-key cryptography|public-key cryptography]].{{r|primer|p=5}} A ''public key'' (a long, random-looking string of numbers) is an address on the blockchain. Value tokens sent across the network are recorded as belonging to that address. A ''private key'' is like a password that gives its owner access to their digital assets or the means to otherwise interact with the various capabilities that blockchains now support. Data stored on the blockchain is generally considered incorruptible.{{R|te20151031}}

Every [[Node (networking)|node]] in a decentralized system has a copy of the blockchain. [[Data quality]] is maintained by massive database [[Replication (computing)|replication]]<ref>{{Cite book |last=Raval |first=Siraj |url={{google books|fvywDAAAQBAJ|plainurl =yes}} |title=Decentralized Applications: Harnessing Bitcoin's Blockchain Technology |publisher=O'Reilly Media, Inc. |year=2016 |isbn=978-1-4919-2452-5 |pages=[{{google books|fvywDAAAQBAJ|page =1|plainurl =yes}} 1]–[{{google books |chapter=What Is a Decentralized Application? |oclc=968277125 |access-date=6 November 2016 |chapter-url={{google books|fvywDAAAQBAJ|page =1|plainurl =yes}} |via=Google Books |fvywDAAAQBAJ |plainurl=yes}} 2]}}</ref> and [[Computational trust|computational trust]]. No centralized "official" copy exists and no user is "trusted" more than any other.{{r|primer}} Transactions are broadcast to the network using the software. Messages are delivered on a [[Best-effort delivery|best-effort]] basis. Early blockchains rely on energy-intensive mining nodes to validate transactions,<ref name="hadc" /> add them to the block they are building, and then [[Broadcasting (networking)|broadcast]] the completed block to other nodes.{{R|t12|p=ch. 08}} Blockchains use various time-stamping schemes, such as [[Finance:Proof-of-work system|proof-of-work]], to serialize changes.{{r|kopstein}} Later consensus methods include [[Finance:Proof-of-stake|proof of stake]].<ref name="hadc">{{Cite book |last1=Bhaskar |first1=Nirupama Devi |title=Handbook of Digital Currency |last2=Chuen |first2=David LEE Kuo |year=2015 |isbn=978-0-12-802117-0 |pages=45–65 |chapter=Bitcoin Mining Technology |doi=10.1016/B978-0-12-802117-0.00003-5}}</ref> The growth of a decentralized blockchain is accompanied by the risk of [[Centrality|centralization]] because the computer resources required to process larger amounts of data become more expensive.<ref>{{Cite web |last1=Gervais |first1=Arthur |last2=Karame |first2=Ghassan O. |last3=Capkun |first3=Vedran |last4=Capkun |first4=Srdjan |title=Is Bitcoin a Decentralized Currency? |url=https://www.infoq.com/articles/is-bitcoin-a-decentralized-currency/ |url-status=live |archive-url=https://web.archive.org/web/20161010042659/https://www.infoq.com/articles/is-bitcoin-a-decentralized-currency/ |archive-date=10 October 2016 |access-date=11 October 2016 |website=InfoQ |publisher=InfoQ & IEEE computer society}}</ref>

==== Finality ====
Finality is the level of confidence that the well-formed block recently appended to the blockchain will not be revoked in the future (is "finalized") and thus can be trusted. Most distributed blockchain protocols, whether [[Finance:Proof of work|proof of work]] or [[Finance:Proof of stake|proof of stake]], cannot guarantee the finality of a freshly committed block, and instead rely on "probabilistic finality": as the block goes deeper into a blockchain, it is less likely to be altered or reverted by a newly found consensus.<ref name="Deirmentzoglou et al">{{cite journal | last1 = Deirmentzoglou | first1 = Evangelos | last2 = Papakyriakopoulos | first2 = Georgios | last3 = Patsakis | first3 = Constantinos | title = A Survey on Long-Range Attacks for Proof of Stake Protocols | journal = [[Engineering:IEEE Access|IEEE Access]] | date = 2019 | volume = 7 | pages = 28712–28725 | eissn = 2169-3536 | doi = 10.1109/ACCESS.2019.2901858 | pmid = | bibcode = 2019IEEEA...728712D | s2cid = 84185792 | doi-access = free }}</ref>

[[Byzantine fault tolerance]]-based proof-of-stake protocols purport to provide so called "absolute finality": a randomly chosen validator proposes a block, the rest of validators vote on it, and, if a supermajority decision approves it, the block is irreversibly committed into the blockchain.<ref name="Deirmentzoglou et al"/> A modification of this method, an "economic finality", is used in practical protocols, like the Casper protocol used in [[Finance:Ethereum|Ethereum]]: validators which sign two different blocks at the same position in the blockchain are subject to "slashing", where their leveraged stake is forfeited.<ref name="Deirmentzoglou et al"/>

=== Openness ===
Open blockchains are more [[Usability|user-friendly]] than some traditional ownership records, which, while open to the public, still require physical access to view. Because all early blockchains were permissionless, controversy has arisen over the blockchain definition. An issue in this ongoing debate is whether a private system with verifiers tasked and authorized (permissioned) by a central authority should be considered a blockchain.{{R|t16|t10|t11|t8|t9}} Proponents of permissioned or private chains argue that the term "blockchain" may be applied to any '''data structure'''<!-- bolded per WP:MOSBOLD as a redirect target --> that batches data into time-stamped blocks. These blockchains serve as a distributed version of [[multiversion concurrency control (MVCC) in databases.{{R|t4}} Just as MVCC prevents two transactions from concurrently modifying a single object in a database, blockchains prevent two transactions from spending the same single output in a blockchain.<ref name="tapscott201605">{{Cite book|last1=Tapscott|first1=Don|title=The Blockchain Revolution: How the Technology Behind Bitcoin is Changing Money, Business, and the World|last2=Tapscott|first2=Alex|date=May 2016|publisher=Portfolio/Penguin |isbn=978-0-670-06997-2|author-link2=Alex Tapscott}}</ref>{{rp|30–31}} Opponents say that permissioned systems resemble traditional corporate databases, not supporting decentralized data verification, and that such systems are not hardened against operator tampering and revision.{{R|t16|t11}} Nikolai Hampton of ''Computerworld'' said that "many in-house blockchain solutions will be nothing more than cumbersome databases," and "without a clear security model, proprietary blockchains should be eyed with suspicion."<ref name="cw20160905" /><ref>{{Cite news |last=Barry |first=Levine |date=11 June 2018 |title=A new report bursts the blockchain bubble |publisher=MarTech |url=https://martechtoday.com/a-new-report-bursts-the-blockchain-bubble-216959 |url-status=live |access-date=13 July 2018 |archive-url=https://web.archive.org/web/20180713232406/https://martechtoday.com/a-new-report-bursts-the-blockchain-bubble-216959 |archive-date=13 July 2018}}</ref>

==== Permissionless (public) blockchain ====
An advantage to an open, permissionless, or public, blockchain network is that guarding against bad actors is not required and no [[Access control|access control]] is needed.<ref name="bsm" /> This means that applications can be added to the network without the approval or trust of others, using the blockchain as a [[Transport layer|transport layer]].<ref name="bsm" />

Bitcoin and other cryptocurrencies currently secure their blockchain by requiring new entries to include proof of work. To prolong the blockchain, bitcoin uses [[Hashcash]] puzzles. While Hashcash was designed in 1997 by [[Biography:Adam Back|Adam Back]], the original idea was first proposed by [[Biography:Cynthia Dwork|Cynthia Dwork]] and [[Biography:Moni Naor|Moni Naor]] and Eli Ponyatovski in their 1992 paper "Pricing via Processing or Combatting Junk Mail".

In 2016, [[Finance:Venture capital|venture capital]] investment for blockchain-related projects was weakening in the USA but increasing in China.<ref name="btt17" /> Bitcoin and many other cryptocurrencies use open (public) blockchains. {{asof|2018|04}}, bitcoin has the highest [[Finance:Cryptocurrency#Price trends|market capitalization]].

==== Permissioned (private) blockchain ====
Permissioned blockchains use an access control layer to govern who has access to the network.<ref name="btit">{{Cite news |last=Bob Marvin |date=30 August 2017 |title=Blockchain: The Invisible Technology That's Changing the World |work=PC MAG Australia |publisher=ZiffDavis, LLC |url=http://au.pcmag.com/amazon-web-services/46389/feature/blockchain-the-invisible-technology-thats-changing-the-world |url-status=live |access-date=25 September 2017 |archive-url=https://web.archive.org/web/20170925180800/http://au.pcmag.com/amazon-web-services/46389/feature/blockchain-the-invisible-technology-thats-changing-the-world |archive-date=25 September 2017}}</ref> It has been argued that permissioned blockchains can guarantee a certain level of decentralization, if carefully designed, as opposed to permissionless blockchains, which are often centralized in practice.<ref name="auto" />

===== Disadvantages of permissioned blockchain =====
Nikolai Hampton argued in ''Computerworld'' that "There is also no need for a '51 percent' attack on a private blockchain, as the private blockchain (most likely) already controls 100 percent of all block creation resources. If you could attack or damage the blockchain creation tools on a private corporate server, you could effectively control 100 percent of their network and alter transactions however you wished."<ref name="cw20160905" /> This has a set of particularly profound adverse implications during a [[Finance:Financial crisis|financial crisis]] or [[Finance:Debt crisis|debt crisis]] like the [[Finance:Financial crisis of 2007–08|financial crisis of 2007–08]], where politically powerful actors may make decisions that favor some groups at the expense of others,<ref>{{Cite web |last1=O'Keeffe, M. |last2=Terzi, A. |date=7 July 2015 |title=The political economy of financial crisis policy |url=http://bruegel.org/2015/07/the-political-economy-of-financial-crisis-policy/ |url-status=live |archive-url=https://web.archive.org/web/20180519025919/http://bruegel.org/2015/07/the-political-economy-of-financial-crisis-policy/ |archive-date=19 May 2018 |access-date=8 May 2018 |website=Bruegel}}</ref> and "the bitcoin blockchain is protected by the massive group mining effort. It's unlikely that any private blockchain will try to protect records using gigawatts of computing power — it's time-consuming and expensive."<ref name="cw20160905" /> He also said, "Within a private blockchain there is also no 'race'; there's no incentive to use more power or discover blocks faster than competitors. This means that many in-house blockchain solutions will be nothing more than cumbersome databases."<ref name="cw20160905">{{Cite magazine |last=Hampton |first=Nikolai |date=5 September 2016 |title=Understanding the blockchain hype: Why much of it is nothing more than snake oil and spin |url=https://www2.computerworld.com.au/article/606253/understanding-blockchain-hype-why-much-it-nothing-more-than-snake-oil-spin/ |magazine=Computerworld |archive-url=https://web.archive.org/web/20160906171838/http://www.computerworld.com.au/article/606253/understanding-blockchain-hype-why-much-it-nothing-more-than-snake-oil-spin/ |archive-date=6 September 2016 |access-date=2016-09-05 |url-status=live}}</ref>

==== Blockchain analysis ====
The [[Blockchain analysis|analysis of public blockchains]] has become increasingly important with the popularity of [[Software:Bitcoin|bitcoin]], [[Finance:Ethereum|Ethereum]], [[Finance:Litecoin|litecoin]] and other cryptocurrencies.<ref>{{Cite journal |last=Dr Garrick Hileman & Michel Rauchs |year=2017 |title=GLOBAL CRYPTOCURRENCY BENCHMARKING STUDY |url=https://cdn.crowdfundinsider.com/wp-content/uploads/2017/04/Global-Cryptocurrency-Benchmarking-Study.pdf |url-status=live |journal=Cambridge Centre for Alternative Finance |publisher=University of Cambridge Judge Business School |archive-url=https://web.archive.org/web/20190515100308/https://cdn.crowdfundinsider.com/wp-content/uploads/2017/04/Global-Cryptocurrency-Benchmarking-Study.pdf |archive-date=15 May 2019 |access-date=15 May 2019 |via=crowdfundinsider}}</ref> A blockchain, if it is public, provides anyone who wants access to observe and analyse the chain data, given one has the know-how. The process of understanding and accessing the flow of crypto has been an issue for many cryptocurrencies, crypto exchanges and banks.<ref>{{Cite journal |last=Raymaekers |first=Wim |date=March 2015 |title=Cryptocurrency Bitcoin: Disruption, challenges and opportunities |url=https://www.ingentaconnect.com/content/hsp/jpss/2015/00000009/00000001/art00005 |url-status=live |archive-url=https://web.archive.org/web/20190515100259/https://www.ingentaconnect.com/content/hsp/jpss/2015/00000009/00000001/art00005 |archive-date=15 May 2019 |access-date=2019-05-15 |journal=Journal of Payments Strategy & Systems |volume=9 |issue=1 |pages=30–46 |language=en}}</ref><ref>{{Cite news |date=2019-03-03 |title=Why Crypto Companies Still Can't Open Checking Accounts |language=en |url=https://www.bloomberg.com/news/articles/2019-03-03/why-crypto-companies-still-can-t-open-checking-accounts |url-status=live |access-date=2019-06-04 |archive-url=https://web.archive.org/web/20190604091359/https://www.bloomberg.com/news/articles/2019-03-03/why-crypto-companies-still-can-t-open-checking-accounts |archive-date=4 June 2019}}</ref> The reason for this is accusations of blockchain-enabled cryptocurrencies enabling illicit [[Darknet market|dark market]] trade of drugs, weapons, money laundering, etc.<ref>{{Cite journal |last=Christian Brenig, Rafael Accorsi & Günter Müller |date=Spring 2015 |title=Economic Analysis of Cryptocurrency Backed Money Laundering |url=https://aisel.aisnet.org/cgi/viewcontent.cgi?article=1019&context=ecis2015_cr |url-status=live |journal=Association for Information Systems AIS Electronic Library (AISeL) |archive-url=https://web.archive.org/web/20190828223207/https://aisel.aisnet.org/cgi/viewcontent.cgi?article=1019&context=ecis2015_cr |archive-date=28 August 2019 |access-date=15 May 2019}}</ref> A common belief has been that cryptocurrency is private and untraceable, thus leading many actors to use it for illegal purposes. This is changing and now specialised tech companies provide blockchain tracking services, making crypto exchanges, law-enforcement and banks more aware of what is happening with crypto funds and [[Finance:Fiat money|fiat]]-crypto exchanges. The development, some argue, has led criminals to prioritise the use of new cryptos such as [[Finance:Monero (cryptocurrency)|Monero]].<ref>{{Cite news |last=Greenberg |first=Andy |date=25 January 2017 |title=Monero, the Drug Dealer's Cryptocurrency of Choice, Is on Fire |magazine=Wired |url=https://www.wired.com/2017/01/monero-drug-dealers-cryptocurrency-choice-fire/ |url-status=live |access-date=2019-05-15 |archive-url=https://web.archive.org/web/20181210020727/https://www.wired.com/2017/01/monero-drug-dealers-cryptocurrency-choice-fire/ |archive-date=10 December 2018 |issn=1059-1028}}</ref><ref>{{Cite web |last=Orcutt |first=Mike |title=It's getting harder to hide money in Bitcoin |url=https://www.technologyreview.com/s/608763/criminals-thought-bitcoin-was-the-perfect-hiding-place-they-thought-wrong/ |access-date=2019-05-15 |website=MIT Technology Review |language=en-US}}</ref><ref>{{Cite news |date=15 May 2019 |title=Explainer: 'Privacy coin' Monero offers near total anonymity |language=en |work=Reuters |url=https://uk.reuters.com/article/us-crypto-currencies-altcoins-explainer-idUKKCN1SL0F0 |url-status=live |access-date=2019-05-15 |archive-url=https://web.archive.org/web/20190515075334/https://uk.reuters.com/article/us-crypto-currencies-altcoins-explainer-idUKKCN1SL0F0 |archive-date=15 May 2019}}</ref>
===Standardisation===

In April 2016, Standards Australia submitted a proposal to the [[Organization:International Organization for Standardization|International Organization for Standardization]] to consider developing standards to support blockchain technology. This proposal resulted in the creation of ISO Technical Committee 307, Blockchain and Distributed Ledger Technologies.<ref name="Blockchain">{{cite web |title=Blockchain |url=https://www.standards.org.au/engagement-events/flagship-projects/blockchain |website=standards.org.au |publisher=Standards Australia |access-date=21 June 2021}}</ref> The technical committee has working groups relating to blockchain terminology, reference architecture, security and privacy, identity, smart contracts, governance and interoperability for blockchain and DLT, as well as standards specific to industry sectors and generic government requirements.<ref name="ISO/TC 307 Blockchain and distributed ledger technologies">{{cite web |title=ISO/TC 307 Blockchain and distributed ledger technologies |url=https://www.iso.org/committee/6266604.html |website=iso.org |date=15 September 2020 |publisher=ISO |access-date=21 June 2021}}</ref>{{secondary source needed|date=January 2022}} More than 50 countries are participating in the standardization process together with external liaisons such as the [[Organization:Society for Worldwide Interbank Financial Telecommunication|Society for Worldwide Interbank Financial Telecommunication]] (SWIFT), the European Commission, the [[Organization:International Federation of Surveyors|International Federation of Surveyors]], the [[Organization:International Telecommunication Union|International Telecommunication Union]] (ITU) and the United Nations Economic Commission for Europe (UNECE).<ref name="ISO/TC 307 Blockchain and distributed ledger technologies"/>

Many other national standards bodies and open standards bodies are also working on blockchain standards.<ref>{{cite web |last1=Deshmukh |first1=Sumedha |last2=Boulais |first2=Océane |last3=Koens |first3=Tommy |title=Global Standards Mapping Initiative: An overview of blockchain technical standards |url=http://www3.weforum.org/docs/WEF_GSMI_Technical_Standards_2020.pdf |website=weforum.org |publisher=World Economic Forum |access-date=23 June 2021}}</ref> These include the [[Organization:National Institute of Standards and Technology|National Institute of Standards and Technology]]<ref name="BLOCKCHAIN Overview">{{cite journal |title=Blockchain Overview |date=25 September 2019 |url=https://www.nist.gov/blockchain |journal=NIST |access-date=21 June 2021}}</ref> (NIST), the [[Organization:European Committee for Electrotechnical Standardization|European Committee for Electrotechnical Standardization]]<ref name="CEN and CENELEC publish a White Paper on standards in Blockchain & Distributed Ledger Technologies">{{cite web |title=CEN and CENELEC publish a White Paper on standards in Blockchain & Distributed Ledger Technologies |url=https://www.cencenelec.eu/news/brief_news/Pages/TN-2018-085.aspx |website=cencenelec.eu |publisher=CENELEC |access-date=21 June 2021}}</ref> (CENELEC), the [[Organization:Institute of Electrical and Electronics Engineers|Institute of Electrical and Electronics Engineers]]<ref name="Standards">{{cite web |title=Standards |url=https://blockchain.ieee.org/standards |website=ieee.org |publisher=IEEE Blockchain |access-date=21 June 2021}}</ref> (IEEE), the Organization for the Advancement of Structured Information Standards ([[Organization:OASIS|OASIS]]), and some individual participants in the [[Organization:Internet Engineering Task Force|Internet Engineering Task Force]]<ref name="An Interoperability Architecture for Blockchain/DLT Gateways draft-hardjono-blockchain-interop-arch-02">{{cite web |last1=Hardjono |first1=Thomas |title=An Interoperability Architecture for Blockchain/DLT Gateways |url=https://www.ietf.org/id/draft-hardjono-blockchain-interop-arch-02.txt |website=ietf.org |publisher=IETF |access-date=21 June 2021}}</ref> (IETF).

===Centralized blockchain===
Although most of blockchain implementation are decentralized and distributed, [[Company:Oracle Corporation|Oracle]] launched a centralized blockchain table feature in [[Software:Oracle Database|Oracle 21c database]]. The Blockchain Table in [[Software:Oracle Database|Oracle 21c database]] is a centralized blockchain which provide immutable feature. Compared to decentralized blockchains, centralized blockchains normally can provide a higher throughput and lower latency of transactions than consensus-based distributed blockchains.<ref name="OracleBlockchainDetails" /><ref name="OracleBlockchainTable" />

==Types==
Currently, there are at least four types of blockchain networks — public blockchains, private blockchains, [[Organization:Consortium|consortium]] blockchains and hybrid blockchains.

===Public blockchains===
A public blockchain has absolutely no access restrictions. Anyone with an [[Internet]] connection can send [[Finance:Financial transaction|transactions]] to it as well as become a validator (i.e., participate in the execution of a [[Consensus (computer science)|consensus protocol]]).<ref>{{Cite web |title=How Companies Can Leverage Private Blockchains to Improve Efficiency and Streamline Business Processes |url=https://perfectial.com/blog/leveraging-private-blockchains-improve-efficiency-streamline-business-processes/ |website=Perfectial}}</ref>{{sps|date=April 2018}} Usually, such networks offer [[Finance:Incentive|economic incentives]] for those who secure them and utilize some type of a [[Finance:Proof-of-stake|proof-of-stake]] or proof-of-work algorithm.

Some of the largest, most known public blockchains are the bitcoin blockchain and the Ethereum blockchain.

===Private blockchains===
A private blockchain is permissioned.<ref name="btit" /> One cannot join it unless invited by the network administrators. Participant and validator access is [[Closed platform|restricted]]. To distinguish between open blockchains and other peer-to-peer decentralized database applications that are not open ad-hoc compute clusters, the terminology Distributed Ledger (DLT) is normally used for private blockchains.

===Hybrid blockchains===
A hybrid blockchain has a combination of centralized and decentralized features.<ref>[Distributed Ledger Technology: Hybrid Approach, Front-to-Back Designing and Changing Trade Processing Infrastructure, By Martin Walker, First published:, 24 OCT 2018 {{ISBN|978-1-78272-389-9}}]</ref> The exact workings of the chain can vary based on which portions of centralization and decentralization are used.

===Sidechains===
A sidechain is a designation for a blockchain ledger that runs in parallel to a primary blockchain.<ref>{{Cite book |last=Siraj Raval |url=https://books.google.com/books?id=fvywDAAAQBAJ&pg=PA22 |title=Decentralized Applications: Harnessing Bitcoin's Blockchain Technology |date=18 July 2016 |publisher="O'Reilly Media, Inc." |isbn=978-1-4919-2452-5 |pages=22–}}</ref><ref>{{Cite book |last=Niaz Chowdhury |url=https://books.google.com/books?id=_HatDwAAQBAJ&pg=PA22 |title=Inside Blockchain, Bitcoin, and Cryptocurrencies |date=16 August 2019 |publisher=CRC Press |isbn=978-1-00-050770-6 |pages=22–}}</ref> Entries from the primary blockchain (where said entries typically represent digital assets) can be linked to and from the sidechain; this allows the sidechain to otherwise operate independently of the primary blockchain (e.g., by using an alternate means of record keeping, alternate [[Consensus (computer science)|consensus algorithm]], etc.).<ref>{{US patent|10438290}}</ref>{{better source needed|date=November 2021}}

===Consortium blockchain===
A consortium blockchain is a type of blockchain that combines elements of both public and private blockchains. In a consortium blockchain, a group of organizations come together to create and operate the blockchain, rather than a single entity. The consortium members jointly manage the blockchain network and are responsible for validating transactions. Consortium blockchains are permissioned, meaning that only certain individuals or organizations are allowed to participate in the network. This allows for greater control over who can access the blockchain and helps to ensure that sensitive information is kept confidential.

Consortium blockchains are commonly used in industries where multiple organizations need to collaborate on a common goal, such as supply chain management or financial services. One advantage of consortium blockchains is that they can be more efficient and scalable than public blockchains, as the number of nodes required to validate transactions is typically smaller. Additionally, consortium blockchains can provide greater security and reliability than private blockchains, as the consortium members work together to maintain the network. Some examples of consortium blockchains include [[Social:Quorum|Quorum]] and [[Hyperledger]].<ref>{{cite journal | title = Consortium Blockchains: Overview, Applications and Challenges | first1 = Omar | last1 = Dib | first2 = Kei-Leo | last2 = Brousmiche | first3 = Antoine | last3 = Durand | first4 = Eric | last4 = Thea | first5=  Elyes Ben | last5 = Hamida | journal = International Journal on Advances in Telecommunications | volume = 11 | issue = 1/2 | pages = 51–64 }}</ref>

== Uses ==
[[File:Bitcoin.svg|thumb|220x220px|[[Software:Bitcoin|Bitcoin's]] transactions are recorded on a publicly viewable blockchain.]]
Blockchain technology can be integrated into multiple areas. The primary use of blockchains is as a [[Distributed ledger|distributed ledger]] for [[Finance:Cryptocurrency|cryptocurrencies]] such as [[Software:Bitcoin|bitcoin]]; there were also a few other operational products that had matured from [[Proof of concept|proof of concept]] by late 2016.<ref name="btt17">{{Cite web |last=Ovenden |first=James |title=Blockchain Top Trends In 2017 |url=https://channels.theinnovationenterprise.com/articles/blockchain-top-trends-in-2017 |url-status=live |archive-url=https://web.archive.org/web/20161130143727/https://channels.theinnovationenterprise.com/articles/blockchain-top-trends-in-2017 |archive-date=30 November 2016 |access-date=4 December 2016 |publisher=The Innovation Enterprise}}</ref> As of 2016, some businesses have been testing the technology and conducting low-level implementation to gauge blockchain's effects on organizational efficiency in their [[Finance:Back office|back office]].<ref>{{Cite news |last=Katie Martin |date=27 September 2016 |title=CLS dips into blockchain to net new currencies |work=Financial Times |url=https://www.ft.com/content/c905b6fc-4dd2-3170-9d2a-c79cdbb24f16 |url-status=live |access-date=7 November 2016 |archive-url=https://web.archive.org/web/20161109152317/https://www.ft.com/content/c905b6fc-4dd2-3170-9d2a-c79cdbb24f16 |archive-date=9 November 2016}}</ref>

In 2019, it was estimated that around $2.9 billion were invested in blockchain technology, which represents an 89% increase from the year prior. Additionally, the International Data Corp has estimated that corporate investment into blockchain technology will reach $12.4 billion by 2022.<ref>{{Cite news|first=Michael|last=Castillo|date=16 April 2019|title=blockchain 50: Billion Dollar Babies|work=Financial Website|publisher=SourceMedia|url=https://www.forbes.com/sites/michaeldelcastillo/2019/04/16/blockchain-50-billion-dollar-babies/|access-date=1 February 2021}}</ref> Furthermore, According to [[Company:PricewaterhouseCoopers|PricewaterhouseCoopers]] (PwC), the second-largest professional services network in the world, blockchain technology has the potential to generate an annual business value of more than $3 trillion by 2030. PwC's estimate is further augmented by a 2018 study that they have conducted, in which PwC surveyed 600 business executives and determined that 84% have at least some exposure to utilizing blockchain technology, which indicates a significant demand and interest in blockchain technology.<ref>{{Cite news|first=Steve|last=Davies|date=2018|title=PwC's Global Blockchain Survey|work=Financial Website|publisher=SourceMedia|url=https://www.pwc.com/gx/en/industries/technology/blockchain/blockchain-in-business.html|access-date=1 February 2021}}</ref>

In 2019, the BBC World Service radio and podcast series ''[[History:50 Things That Made the Modern Economy|Fifty Things That Made the Modern Economy]]'' identified blockchain as a technology that would have far-reaching consequences for economics and society. The economist and ''Financial Times'' journalist and broadcaster Tim Harford discussed why the underlying technology might have much wider applications and the challenges that needed to be overcome.<ref>{{Cite web |title=BBC Radio 4 - Things That Made the Modern Economy, Series 2, Blockchain |url=https://www.bbc.co.uk/programmes/m0008b9v |access-date=2022-10-14 |website=BBC |language=en-GB}}</ref> His first broadcast was on June 29, 2019.

The number of blockchain wallets quadrupled to 40 million between 2016 and 2020.<ref>{{Cite news|first=Shanhong|last=Liu|date=13 March 2020|title=Blockchain - Statistics & Facts|work=Statistics Website|publisher=SourceMedia|url=https://www.statista.com/topics/5122/blockchain/#dossierSummary__chapter6|access-date=17 February 2021}}</ref>

A paper published in 2022 discussed the potential use of blockchain technology in [[Social:Sustainable management|sustainable management]].<ref>{{Cite journal |last1=Du |first1=Wenbo |last2=Ma |first2=Xiaozhi |last3=Yuan |first3=Hongping |last4=Zhu |first4=Yue |date=2022-08-01 |title=Blockchain technology-based sustainable management research: the status quo and a general framework for future application |url=https://doi.org/10.1007/s11356-022-21761-2 |journal=Environmental Science and Pollution Research |language=en |volume=29 |issue=39 |pages=58648–58663 |doi=10.1007/s11356-022-21761-2 |issn=1614-7499 |pmc=9261142 |pmid=35794327|bibcode=2022ESPR...2958648D }}</ref>

=== Cryptocurrencies ===
{{main|Finance:Cryptocurrency}}
Most cryptocurrencies use blockchain technology to record transactions. For example, the [[Finance:Bitcoin network|bitcoin network]] and [[Finance:Ethereum|Ethereum]] network are both based on blockchain.

The criminal enterprise Silk Road, which operated on [[Software:Tor (anonymity network)|Tor]], utilized cryptocurrency for payments, some of which the US federal government has seized through research on the blockchain and [[Social:Forfeiture (law)|forfeiture.]]<ref>KPIX-TV. (5 November 2020). "Silk Road: Feds Seize $1 Billion In Bitcoins Linked To Infamous Silk Road Dark Web Case; 'Where Did The Money Go'". [https://www.cbsnews.com/sanfrancisco/news/silk-road-feds-seize-1-billlion-in-bitcoins-linked-to-infamous-silk-road-dark-web-case-where-did-the-money-go/ KPIX website]{{Dead link|date=October 2022|bot=InternetArchiveBot|fix-attempted=yes}} Retrieved 28 March 2021.</ref>

[[Finance:Legality of bitcoin by country or territory|Governments have mixed policies]] on the legality of their citizens or banks owning cryptocurrencies. China implements blockchain technology in several industries including a [[Finance:Central bank digital currency|national digital currency]] which launched in 2020.<ref>Aditi Kumar and Eric Rosenbach. (20 May 2020). "Could China's Digital Currency Unseat the Dollar?: American Economic and Geopolitical Power Is at Stake". [https://www.foreignaffairs.com/articles/china/2020-05-20/could-chinas-digital-currency-unseat-dollar Foreign Affairs website] Retrieved 31 March 2021.</ref> To strengthen their respective currencies, Western governments including the European Union and the United States have initiated similar projects.<ref>Staff. (16 February 2021). "The Economist Explains: What is the fuss over central-bank digital currencies?" [https://www.economist.com/the-economist-explains/2021/02/16/what-is-the-fuss-over-central-bank-digital-currencies The Economist website] Retrieved 1 April 2021.</ref>

=== Smart contracts ===
{{main|Finance:Smart contract}}
Blockchain-based [[Finance:Smart contract|smart contract]]s are proposed contracts that can be partially or fully executed or enforced without human interaction.<ref>{{Cite book |last=Franco |first=Pedro |url=https://books.google.com/books?id=YHfCBwAAQBAJ |title=Understanding Bitcoin: Cryptography, Engineering and Economics |publisher=John Wiley & Sons |year=2014 |isbn=978-1-119-01916-9 |page=9 |access-date=4 January 2017 |archive-url=https://web.archive.org/web/20170214204859/https://books.google.com/books?id=YHfCBwAAQBAJ |archive-date=14 February 2017 |url-status=live |via=Google Books}}</ref> One of the main objectives of a smart contract is [[Engineering:Automation|automated]] [[Social:Escrow|escrow]]. A key feature of smart contracts is that they do not need a trusted third party (such as a trustee) to act as an intermediary between contracting entities — the blockchain network executes the contract on its own. This may reduce friction between entities when transferring value and could subsequently open the door to a higher level of transaction automation.<ref>{{Cite book| vauthors = Casey M |url=https://www.worldcat.org/oclc/1059331326|title=The impact of blockchain technology on finance : a catalyst for change|date=16 July 2018|isbn=978-1-912179-15-2|location=London, UK|oclc=1059331326}}</ref> An [[Organization:International Monetary Fund|IMF]] staff discussion from 2018 reported that smart contracts based on blockchain technology might reduce [[Moral hazard|moral hazard]]s and optimize the use of contracts in general. But "no viable smart contract systems have yet emerged." Due to the lack of widespread use, their legal status was unclear.<ref>{{Cite journal |last1=Governatori |first1=Guido |last2=Idelberger |first2=Florian |last3=Milosevic |first3=Zoran |last4=Riveret |first4=Regis |last5=Sartor |first5=Giovanni |last6=Xu |first6=Xiwei |year=2018 |title=On legal contracts, imperative and declarative smart contracts, and blockchain systems |journal=Artificial Intelligence and Law |language=en |volume=26 |issue=4 |pages=33 |doi=10.1007/s10506-018-9223-3 |s2cid=3663005}}</ref><ref>{{Cite book |url=https://www.imf.org/external/pubs/ft/sdn/2016/sdn1603.pdf |title=Virtual Currencies and Beyond: Initial Considerations |publisher=International Monetary Fund |year=2016 |isbn=978-1-5135-5297-2 |series=IMF Discussion Note |page=23 |access-date=2018-04-19 |archive-url=https://web.archive.org/web/20180414210721/https://www.imf.org/external/pubs/ft/sdn/2016/sdn1603.pdf |archive-date=14 April 2018 |url-status=live}}</ref>

===Financial services===
According to ''Reason'', many banks have expressed interest in implementing [[Distributed ledger|distributed ledger]]s for use in [[Finance:Banking|banking]] and are cooperating with companies creating private blockchains,<ref>{{Cite news |last=Epstein |first=Jim |date=6 May 2016 |title=Is Blockchain Technology a Trojan Horse Behind Wall Street's Walled Garden? |work=Reason |url=http://reason.com/reasontv/2016/05/06/bitcoin-consensus-blockchain-wall-street |url-status=live |access-date=2016-06-29 |archive-url=https://web.archive.org/web/20160708170429/http://reason.com/reasontv/2016/05/06/bitcoin-consensus-blockchain-wall-street |archive-date=8 July 2016 |quote=mainstream misgivings about working with a system that's open for anyone to use. Many banks are partnering with companies building so-called private blockchains that mimic some aspects of Bitcoin's architecture except they're designed to be closed off and accessible only to chosen parties. ... [but some believe] that open and permission-less blockchains will ultimately prevail even in the banking sector simply because they're more efficient.}}</ref><ref>{{Cite news |last=Redrup |first=Yolanda |date=29 June 2016 |title=ANZ backs private blockchain, but won't go public |work=Australia Financial Review |url=http://www.afr.com/technology/anz-backs-private-blockchain-but-wont-go-public-20160629-gpuf9z |url-status=live |access-date=2016-07-07 |archive-url=https://web.archive.org/web/20160703103852/http://www.afr.com/technology/anz-backs-private-blockchain-but-wont-go-public-20160629-gpuf9z |archive-date=3 July 2016 |quote=Blockchain networks can be either public or private. Public blockchains have many users and there are no controls over who can read, upload or delete the data and there are an unknown number of pseudonymous participants. In comparison, private blockchains also have multiple data sets, but there are controls in place over who can edit data and there are a known number of participants.}}</ref><ref>{{Cite web |last=Shah |first=Rakesh |date=1 March 2018 |title=How Can The Banking Sector Leverage Blockchain Technology? |url=http://www.postboxcommunications.com/blog/can-banking-sector-leverage-blockchain-technology/ |url-status=live |archive-url=https://web.archive.org/web/20180317232141/http://www.postboxcommunications.com/blog/can-banking-sector-leverage-blockchain-technology/ |archive-date=17 March 2018 |website=PostBox Communications |publisher=PostBox Communications Blog |quote=Banks preferably have a notable interest in utilizing Blockchain Technology because it is a great source to avoid fraudulent transactions. Blockchain is considered hassle free, because of the extra level of security it offers.}}</ref> and according to a September 2016 [[Company:IBM|IBM]] study, this is occurring faster than expected.<ref>{{Cite news |last=Kelly, Jemima |date=28 September 2016 |title=Banks adopting blockchain 'dramatically faster' than expected: IBM |work=Reuters |url=https://www.reuters.com/article/us-tech-blockchain-ibm-idUSKCN11Y28D |url-status=live |access-date=2016-09-28 |archive-url=https://web.archive.org/web/20160928163048/http://www.reuters.com/article/us-tech-blockchain-ibm-idUSKCN11Y28D |archive-date=28 September 2016 |df=dmy-all}}</ref>

Banks are interested in this technology not least because it has the potential to speed up [[Finance:Back office|back office]] settlement systems.<ref>{{Cite news |last=Arnold |first=Martin |date=23 September 2013 |title=IBM in blockchain project with China UnionPay |work=Financial Times |url=https://www.ft.com/content/719f4e7e-80e1-11e6-bc52-0c7211ef3198 |url-status=live |access-date=7 November 2016 |archive-url=https://web.archive.org/web/20161109152822/https://www.ft.com/content/719f4e7e-80e1-11e6-bc52-0c7211ef3198 |archive-date=9 November 2016}}</ref> Moreover, as the blockchain industry has reached early maturity institutional appreciation has grown that it is, practically speaking, the infrastructure of a whole new financial industry, with all the implications which that entails.<ref>{{Cite web|url=https://corpgov.law.harvard.edu/2022/01/28/blockchain-in-the-banking-sector-a-review-of-the-landscape-and-opportunities/|title=Blockchain in the Banking Sector: A Review of the Landscape and Opportunities|first1=Arvind|last1=Ravichandran|first2=Christopher|last2=Fargo|first3=David|last3=Kappos|first4=David|last4=Portilla|first5=John|last5=Buretta|first6=Minh Van|last6=Ngo|first7=Sasha|last7=Rosenthal-Larrea|date=28 January 2022}}</ref>

[[Social:Bank|Bank]]s such as [[Company:UBS|UBS]] are opening new research labs dedicated to blockchain technology in order to explore how blockchain can be used in financial services to increase efficiency and reduce costs.<ref>{{Cite news |date=24 August 2016 |title=UBS leads team of banks working on blockchain settlement system |work={{wipe|Reuters}} |url=https://www.reuters.com/article/us-banks-blockchain-ubs-idUSKCN10Z147 |url-status=live |access-date=13 May 2017 |archive-url=https://web.archive.org/web/20170519073429/http://www.reuters.com/article/us-banks-blockchain-ubs-idUSKCN10Z147 |archive-date=19 May 2017}}</ref><ref>{{Cite web |title=Cryptocurrency Blockchain |url=https://www.capgemini.com/beyond-the-buzz/cryptocurrency-blockchain |url-status=live |archive-url=https://web.archive.org/web/20161205202317/https://www.capgemini.com/beyond-the-buzz/cryptocurrency-blockchain |archive-date=5 December 2016 |access-date=13 May 2017 |website=capgemini.com}}</ref>

[[Company:Berenberg Bank|Berenberg]], a German bank, believes that blockchain is an "overhyped technology" that has had a large number of "proofs of concept", but still has major challenges, and very few success stories.<ref>{{Cite news |last=Kelly |first=Jemima |date=31 October 2017 |title=Top banks and R3 build blockchain-based payments system |work=Reuters |url=https://www.reuters.com/article/us-banks-blockchain-r3/top-banks-and-r3-build-blockchain-based-payments-system-idUSKBN1D00ZB |url-status=live |access-date=9 July 2018 |archive-url=https://web.archive.org/web/20180710011735/https://www.reuters.com/article/us-banks-blockchain-r3/top-banks-and-r3-build-blockchain-based-payments-system-idUSKBN1D00ZB |archive-date=10 July 2018}}</ref>

The blockchain has also given rise to [[Finance:Initial coin offering|initial coin offering]]s (ICOs) as well as a new category of digital asset called security token offerings (STOs), also sometimes referred to as digital security offerings (DSOs).<ref>{{Cite web |title= Are Token Assests the Securities of Tomorrow? | date = February 2019 | work = Deloitte |url= https://www2.deloitte.com/content/dam/Deloitte/lu/Documents/technology/lu-token-assets-securities-tomorrow.pdf |url-status=live |archive-url=https://web.archive.org/web/20190623225917/https://www2.deloitte.com/content/dam/Deloitte/lu/Documents/technology/lu-token-assets-securities-tomorrow.pdf |archive-date=23 June 2019 |access-date=26 September 2019}}</ref> STO/DSOs may be conducted privately or on public, regulated stock exchange and are used to tokenize traditional assets such as company shares as well as more innovative ones like intellectual property, real estate,<ref>{{cite news |first=Jeff |last=Hammerberg |date=November 7, 2021 |url=https://www.washingtonblade.com/2021/11/07/potential-impact-of-blockchain-on-real-estate/ |title=Potential impact of blockchain on real estate |work=Washington Blade}}</ref> art, or individual products. A number of companies are active in this space providing services for compliant [[Tokenization (data security)|tokenization]], private STOs, and public STOs.

===Games===
{{main|Finance:Blockchain game}}
Blockchain technology, such as cryptocurrencies and [[Finance:Non-fungible token|non-fungible token]]s (NFTs), has been used in video games for [[Finance:Video game monetization|monetization]]. Many [[Games as a service|live-service games]] offer in-game customization options, such as character skins or other in-game items, which the players can earn and trade with other players using in-game currency. Some games also allow for trading of virtual items using real-world currency, but this may be illegal in some countries where video games are seen as akin to gambling, and has led to gray market issues such as [[Skin gambling|skin gambling]], and thus publishers typically have shied away from allowing players to earn real-world funds from games.<ref name="Verge-Valve">{{cite news |last1=Clark |first1=Mitchell |title=Valve bans blockchain games and NFTs on Steam, Epic will try to make it work |url=https://www.theverge.com/2021/10/15/22728425/valve-steam-blockchain-nft-crypto-ban-games-age-of-rust |access-date=8 November 2021 |work=The Verge |date=15 October 2021 |language=en}}</ref> Blockchain games typically allow players to trade these in-game items for cryptocurrency, which can then be exchanged for money.<ref name="inverse blockchain games">{{cite web | url = https://www.inverse.com/gaming/blockchain-games-online-gaming | title = Blockchain Games Twist The Fundamentals Of Online Gaming | first = Mo | last = Mozuch | date = April 29, 2021 | access-date = November 4, 2021 | work = Inverse }}</ref>

The first known game to use blockchain technologies was ''[[Software:CryptoKitties|CryptoKitties]]'', launched in November 2017, where the player would purchase NFTs with Ethereum cryptocurrency, each NFT consisting of a [[Software:Virtual pet|virtual pet]] that the player could breed with others to create offspring with combined traits as new NFTs.<ref>{{Cite news |date=22 February 2018 |title=Internet firms try their luck at blockchain games |work=Asia Times |url=https://asiatimes.com/article/internet-firms-try-luck-blockchain-games/ |access-date=2018-02-28}}</ref><ref name="inverse blockchain games"/> The game made headlines in December 2017 when one virtual pet sold for more than {{wipe|United States dollar}}100,000.<ref>{{Cite news |last=Evelyn Cheng |date=6 December 2017 |title=Meet CryptoKitties, the $100,000 digital beanie babies epitomizing the cryptocurrency mania |publisher={{wipe|CNBC}} |url=https://www.cnbc.com/2017/12/06/meet-cryptokitties-the-new-digital-beanie-babies-selling-for-100k.html |url-status=live |access-date=2018-02-28 |archive-url=https://web.archive.org/web/20181120115903/https://www.cnbc.com/2017/12/06/meet-cryptokitties-the-new-digital-beanie-babies-selling-for-100k.html |archive-date=20 November 2018}}</ref> ''CryptoKitties'' also illustrated scalability problems for games on Ethereum when it created significant congestion on the Ethereum network in early 2018 with approximately 30% of all Ethereum transactions{{clarify|over what period of time? a day? a week? forever since 2018?|date=October 2021}} being for the game.<ref>{{Cite news |last=Laignee Barron |date=13 February 2018 |title=CryptoKitties is Going Mobile. Can Ethereum Handle the Traffic? |work=Fortune |url=http://fortune.com/2018/02/13/cryptokitties-ethereum-ios-launch-china-ether/ |url-status=live |access-date=2018-09-30 |archive-url=https://web.archive.org/web/20181028041832/http://fortune.com/2018/02/13/cryptokitties-ethereum-ios-launch-china-ether/ |archive-date=28 October 2018}}</ref><ref>{{Cite news |date=12 May 2017 |title=CryptoKitties craze slows down transactions on Ethereum |url=https://www.bbc.com/news/technology-42237162 |url-status=live |archive-url=https://web.archive.org/web/20180112143517/http://www.bbc.com/news/technology-42237162 |archive-date=12 January 2018}}</ref>

By the early 2020s, there had not been a breakout success in video games using blockchain, as these games tend to focus on using blockchain for speculation instead of more traditional forms of gameplay, which offers limited appeal to most players. Such games also represent a high risk to investors as their revenues can be difficult to predict.<ref name="inverse blockchain games"/> However, limited successes of some games, such as ''Axie Infinity'' during the COVID-19 pandemic, and corporate plans towards metaverse content, refueled interest in the area of GameFi, a term describing the intersection of video games and financing typically backed by blockchain currency, in the second half of 2021.<ref>{{cite web | url = https://www.bloomberg.com/news/features/2021-10-30/what-is-the-metaverse-where-crypto-nft-capitalism-collide-in-games-like-axie | title = Into the Metaverse: Where Crypto, Gaming and Capitalism Collide | first1 = Charlie | last1 = Wells | first2 = Misrylena | last2 = Egkolfopoulou | date = October 30, 2021 | access-date = November 11, 2021 | work = {{wipe|Bloomberg News}} }}</ref> Several major publishers, including [[Company:Ubisoft|Ubisoft]], [[Company:Electronic Arts|Electronic Arts]], and Take Two Interactive, have stated that blockchain and NFT-based games are under serious consideration for their companies in the future.<ref>{{cite web | url = https://arstechnica.com/gaming/2021/11/big-name-publishers-see-nfts-as-a-big-part-of-gamings-future/ | title = Big-name publishers see NFTs as a big part of gaming's future | first = Kyle | last = Orland | date = November 4, 2021 | access-date = November 4, 2021 | work = [[Ars Technica]] }}</ref>

In October 2021, [[Company:Valve Corporation|Valve Corporation]] banned blockchain games, including those using cryptocurrency and [[Finance:Non-fungible token|NFTs]], from being hosted on its [[Software:Steam (service)|Steam]] digital storefront service, which is widely used for personal computer gaming, claiming that this was an extension of their policy banning games that offered in-game items with real-world value. Valve's prior history with gambling, specifically [[Skin gambling|skin gambling]], was speculated to be a factor in the decision to ban blockchain games.<ref name=pcgamer/> Journalists and players responded positively to Valve's decision as blockchain and NFT games have a reputation for scams and fraud among most PC gamers,<ref name="Verge-Valve"/><ref name=pcgamer>{{cite news |last1=Knoop |first1=Joseph |title=Steam bans all games with NFTs or cryptocurrency |url=https://www.pcgamer.com/steam-bans-nfts-cryptocurrencies-blockchain/ |access-date=8 November 2021 |work=PC Gamer |date=15 October 2021 |language=en}}</ref> and [[Company:Epic Games|Epic Games]], which runs the Epic Games Store in competition to Steam, said that they would be open to accepted blockchain games in the wake of Valve's refusal.<ref>{{cite web | url = https://www.theverge.com/2021/10/15/22729050/epic-game-store-open-to-blockchain-cryptocurrency-nft-games | title= Epic says it's 'open' to blockchain games after Steam bans them | first=  Mitchell | last =Clark | date= October 15, 2021 | access-date = November 11, 2021 | work = [[The Verge]] }}</ref>

===Supply chain===
There have been several different efforts to employ blockchains in [[Social:Supply chain management|supply chain management]].
* '''Precious commodities mining''' — Blockchain technology has been used for tracking the origins of gemstones and other precious commodities. In 2016, ''{{wipe|The Wall Street Journal}}'' reported that the blockchain technology company Everledger was partnering with [[Company:IBM|IBM]]'s blockchain-based tracking service to trace the origin of diamonds to ensure that they were ethically mined.<ref>{{Cite news |last=Nash |first=Kim S. |date=14 July 2016 |title=IBM Pushes Blockchain into the Supply Chain |work={{wipe|The Wall Street Journal}} |url=https://www.wsj.com/articles/ibm-pushes-blockchain-into-the-supply-chain-1468528824 |url-status=live |access-date=2016-07-24 |archive-url=https://web.archive.org/web/20160718032702/http://www.wsj.com/articles/ibm-pushes-blockchain-into-the-supply-chain-1468528824 |archive-date=18 July 2016}}</ref> As of 2019, the Diamond Trading Company (DTC) has been involved in building a diamond trading supply chain product called Tracer.<ref name="Wharton, Gstettner July 30, 2019">{{Cite web |last=Gstettner |first=Stefan |date=July 30, 2019 |title=How Blockchain Will Redefine Supply Chain Management |url=https://knowledge.wharton.upenn.edu/article/blockchain-supply-chain-management |access-date=28 August 2020 |website=Knowledge@Wharton |publisher=The Wharton School of the University of Pennsylvania}}</ref>
* '''Food supply''' — As of 2018, [[Company:Walmart|Walmart]] and [[Company:IBM|IBM]] were running a trial to use a blockchain-backed system for [[Supply chain|supply chain]] monitoring for lettuce and spinach — all nodes of the blockchain were administered by Walmart and were located on the IBM [[Cloud computing|cloud]].<ref>{{Cite news |last1=Corkery |first1=Michael |last2=Popper |first2=Nathaniel |date=24 September 2018 |title=From Farm to Blockchain: Walmart Tracks Its Lettuce |work=The New York Times |url=https://www.nytimes.com/2018/09/24/business/walmart-blockchain-lettuce.html |url-status=live |access-date=5 December 2018 |archive-url=https://web.archive.org/web/20181205103719/https://www.nytimes.com/2018/09/24/business/walmart-blockchain-lettuce.html |archive-date=5 December 2018}}</ref>
* '''Fashion industry''' — There is an opaque relationship between brands, distributors, and customers in the fashion industry, which will prevent the sustainable and stable development of the fashion industry. Blockchain makes up for this shortcoming and makes information transparent, solving the difficulty of sustainable development of the industry.<ref>{{Cite journal |date=2021-06-08 |title=Blockchain basics: Utilizing blockchain to improve sustainable supply chains in fashion |url=https://www.emerald.com/insight/content/doi/10.1108/SD-03-2021-0028/full/html |journal=Strategic Direction |language=en |volume=37 |issue=5 |pages=25–27 |doi=10.1108/SD-03-2021-0028 |s2cid=241322151 |issn=0258-0543}}</ref>
*'''Motor vehicles''' — [[Company:Mercedes-Benz|Mercedes-Benz]] and partner Icertis developed a blockchain prototype used to facilitate consistent documentation of contracts along the supply chain so that the ethical standards and contractual obligations required of its direct suppliers can be passed on to second tier suppliers and beyond.<ref>Mercedes-Benz Group AG, [https://group.mercedes-benz.com/innovation/blockchain-2.html Once round the block, please!], accessed 24 August 2023</ref><ref>Green, W., [https://www.cips.org/supply-management/news/2019/february/mercedes-tests-blockchain-to-improve-supply-chain-transparency/ Mercedes tests blockchain to improve supply chain transparency], ''Supply Management'', published 25 February 2019, accessed 24 August 2023</ref> In another project, the company uses blockchain technology to track the emissions of climate-relevant gases and the amount of secondary material along the supply chain for its battery cell manufacturers.<ref>Mercedes-Benz AG, [https://media.mercedes-benz.com/article/ff705327-be61-4b15-9eee-2c1a53c9b0e6 Mercedes-Benz Cars drives "Ambition2039" in the supply chain: blockchain pilot project provides transparency on CO₂ emissions], published 30 January 2020, accessed 24 August 2023</ref>

=== Domain names ===

There are several different efforts to offer [[Domain name|domain name]] services via the blockchain. These domain names can be controlled by the use of a private key, which purports to allow for uncensorable websites. This would also bypass a registrar's ability to suppress domains used for fraud, abuse, or illegal content.<ref name=techrepublic>{{Cite news |last1=Sanders |first1=James |last2=August 28 |title=Blockchain-based Unstoppable Domains is a rehash of a failed idea |url=https://www.techrepublic.com/article/blockchain-based-unstoppable-domains-is-a-rehash-of-a-failed-idea/ |url-status=live |archive-url=https://web.archive.org/web/20191119015118/https://www.techrepublic.com/article/blockchain-based-unstoppable-domains-is-a-rehash-of-a-failed-idea/ |archive-date=19 November 2019 |access-date=2020-04-16 |website=TechRepublic |date=28 August 2019 |language=en}}</ref>

[[Namecoin]] is a cryptocurrency that supports the ".bit" [[Top-level domain|top-level domain]] (TLD). Namecoin was forked from bitcoin in 2011. The .bit TLD is not sanctioned by [[Organization:ICANN|ICANN]], instead requiring an [[Alternative DNS root|alternative DNS root]].<ref name=techrepublic/> As of 2015, .bit was used by 28 websites, out of 120,000 registered names.<ref name=orcutt>{{cite news |last1=Orcutt |first1=Mike |title=The ambitious plan to reinvent how websites get their names |url=https://www.technologyreview.com/2019/06/04/239039/the-ambitious-plan-to-make-the-internets-phone-book-more-trustworthy/ |access-date=May 17, 2021 |work=MIT Technology Review |date=June 4, 2019 |language=en}}</ref> Namecoin was dropped by [[Organization:OpenNIC|OpenNIC]] in 2019, due to malware and potential other legal issues.<ref>{{cite news |last1=Cimpanu |first1=Catalin |title=OpenNIC drops support for .bit domain names after rampant malware abuse |url=https://www.zdnet.com/article/opennic-drops-support-for-bit-domain-names-after-rampant-malware-abuse/ |access-date=May 17, 2021 |work=ZDNet |date=July 17, 2019 |language=en}}</ref> Other blockchain alternatives to ICANN include ''The Handshake Network'',<ref name=orcutt/> ''EmerDNS'', and ''Unstoppable Domains''.<ref name=techrepublic/>

Specific TLDs include ".eth", ".luxe", and ".kred", which are associated with the Ethereum blockchain through the Ethereum Name Service (ENS). The .kred TLD also acts as an alternative to conventional [[Finance:Cryptocurrency wallet|cryptocurrency wallet]] addresses as a convenience for transferring cryptocurrency.<ref>{{Cite web |date=2020-03-06 |title=.Kred launches as dual DNS and ENS domain |url=https://domainnamewire.com/2020/03/06/kred-blockchain-domain/ |url-status=live |archive-url=https://web.archive.org/web/20200308175635/https://domainnamewire.com/2020/03/06/kred-blockchain-domain/ |archive-date=8 March 2020 |access-date=2020-04-16 |website=Domain Name Wire {{!}} Domain Name News |language=en-US}}</ref>

=== Other uses ===
{{anchor|Lightweight blockchain}}
Blockchain technology can be used to create a permanent, public, transparent ledger system for compiling data on sales, tracking digital use and payments to content creators, such as wireless users<ref>K. Kotobi, and S. G. Bilen, [http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=8269834 "Secure Blockchains for Dynamic Spectrum Access : A Decentralized Database in Moving Cognitive Radio Networks Enhances Security and User Access"], IEEE Vehicular Technology Magazine, 2018.</ref> or musicians.<ref>{{Cite web |date=22 September 2016 |title=Blockchain Could Be Music's Next Disruptor |url=http://fortune.com/2016/09/22/blockchain-music-disruption/ |url-status=live |archive-url=https://web.archive.org/web/20160923180800/http://fortune.com/2016/09/22/blockchain-music-disruption/ |archive-date=23 September 2016}}</ref> The Gartner 2019 CIO Survey reported 2% of higher education respondents had launched blockchain projects and another 18% were planning academic projects in the next 24 months.<ref>Susan Moore. (16 October 2019). "Digital Business: 4 Ways Blockchain Will Transform Higher Education". [https://www.gartner.com/smarterwithgartner/4-ways-blockchain-will-transform-higher-education/ Gartner website] Retrieved 27 March 2021.</ref> In 2017, [[Company:IBM|IBM]] partnered with ASCAP and PRS for Music to adopt blockchain technology in music distribution.<ref>{{Cite web |date=9 April 2017 |title=ASCAP, PRS and SACEM Join Forces for Blockchain Copyright System |url=http://www.musicbusinessworldwide.com/ascap-prs-sacem-join-forces-blockchain-copyright-system/ |url-status=live |archive-url=https://web.archive.org/web/20170410050815/http://www.musicbusinessworldwide.com/ascap-prs-sacem-join-forces-blockchain-copyright-system/ |archive-date=10 April 2017 |publisher=Music Business Worldwide |df=dmy-all}}</ref> Imogen Heap's Mycelia service has also been proposed as a blockchain-based alternative "that gives artists more control over how their songs and associated data circulate among fans and other musicians."<ref>{{Cite magazine |last1=Burchardi, K. |last2=Harle, N. |date=20 January 2018 |title=The blockchain will disrupt the music business and beyond |url=https://www.wired.co.uk/article/blockchain-disrupting-music-mycelia |url-status=live |magazine=Wired UK |archive-url=https://web.archive.org/web/20180508040911/https://www.wired.co.uk/article/blockchain-disrupting-music-mycelia |archive-date=8 May 2018 |access-date=8 May 2018}}</ref><ref>{{Cite web |last=Bartlett |first=Jamie |date=6 September 2015 |title=Imogen Heap: saviour of the music industry? |url=https://www.theguardian.com/music/2015/sep/06/imogen-heap-saviour-of-music-industry |url-status=live |archive-url=https://web.archive.org/web/20160422213153/http://www.theguardian.com/music/2015/sep/06/imogen-heap-saviour-of-music-industry |archive-date=22 April 2016 |access-date=18 June 2016 |website=The Guardian}}</ref>

New distribution methods are available for the [[Finance:Insurance|insurance]] industry such as [[Peer-to-peer insurance|peer-to-peer insurance]], parametric insurance and microinsurance following the adoption of blockchain.<ref>{{Cite web |last1=Wang |first1=Kevin |last2=Safavi |first2=Ali |date=29 October 2016 |title=Blockchain is empowering the future of insurance |url=https://techcrunch.com/2016/10/29/blockchain-is-empowering-the-future-of-insurance/ |url-status=live |archive-url=https://web.archive.org/web/20161107160418/https://techcrunch.com/2016/10/29/blockchain-is-empowering-the-future-of-insurance/ |archive-date=7 November 2016 |access-date=7 November 2016 |website=Tech Crunch |publisher=AOL Inc}}</ref><ref>{{Cite journal |last1=Gatteschi |first1=Valentina |last2=Lamberti |first2=Fabrizio |last3=Demartini |first3=Claudio |last4=Pranteda |first4=Chiara |last5=Santamaría |first5=Víctor |date=20 February 2018 |title=Blockchain and Smart Contracts for Insurance: Is the Technology Mature Enough? |journal=Future Internet |language=en |volume=10 |issue=2 |pages=20 |doi=10.3390/fi10020020 |doi-access=free}}</ref> The [[Sharing economy|sharing economy]] and IoT are also set to benefit from blockchains because they involve many collaborating peers.<ref>{{Cite web |title=Blockchain reaction: Tech companies plan for critical mass |url=http://www.ey.com/Publication/vwLUAssets/ey-blockchain-reaction-tech-companies-plan-for-critical-mass/$FILE/ey-blockchain-reaction.pdf |url-status=live |archive-url=https://web.archive.org/web/20161114001423/http://www.ey.com/Publication/vwLUAssets/ey-blockchain-reaction-tech-companies-plan-for-critical-mass/$FILE/ey-blockchain-reaction.pdf |archive-date=14 November 2016 |access-date=13 November 2016 |publisher=Ernst & Young |page=5}}</ref> The use of blockchain in libraries is being studied with a grant from the U.S. Institute of Museum and Library Services.<ref>Carrie Smith. [https://americanlibrariesmagazine.org/2019/03/01/library-blockchain-reaction/ Blockchain Reaction: How library professionals are approaching blockchain technology and its potential impact.] {{Webarchive|url=https://web.archive.org/web/20190912044927/https://americanlibrariesmagazine.org/2019/03/01/library-blockchain-reaction/ |date=12 September 2019}} ''American Libraries'' March 2019.</ref>

Other blockchain designs include [[Hyperledger]], a collaborative effort from the [[Organization:Linux Foundation|Linux Foundation]] to support blockchain-based distributed ledgers, with projects under this initiative including Hyperledger Burrow (by Monax) and Hyperledger Fabric (spearheaded by IBM).<ref>{{Cite web |date=9 January 2018 |title=IBM Blockchain based on Hyperledger Fabric from the Linux Foundation |url=https://www.ibm.com/blockchain/hyperledger.html |url-status=live |archive-url=https://web.archive.org/web/20171207035925/https://www.ibm.com/blockchain/hyperledger.html |archive-date=7 December 2017 |access-date=2018-01-18 |website=IBM.com |language=en-US}}</ref><ref>{{Cite news |last=Hyperledger |date=22 January 2019 |title=Announcing Hyperledger Grid, a new project to help build and deliver supply chain solutions! |url=https://www.hyperledger.org/blog/2019/01/22/announcing-hyperledger-grid-a-new-project-to-help-build-and-deliver-supply-chain-solutions |url-status=live |access-date=8 March 2019 |archive-url=https://web.archive.org/web/20190204125611/https://www.hyperledger.org/blog/2019/01/22/announcing-hyperledger-grid-a-new-project-to-help-build-and-deliver-supply-chain-solutions |archive-date=4 February 2019}}</ref><ref>{{Cite news |last=Mearian |first=Lucas |date=23 January 2019 |title=Grid, a new project from the Linux Foundation, will offer developers tools to create supply chain-specific applications running atop distributed ledger technology |work=Computerworld |url=https://www.computerworld.com/article/3336036/blockchain/linuxs-hyperledger-to-give-developers-supply-chain-building-blocks.html |url-status=live |access-date=8 March 2019 |archive-url=https://web.archive.org/web/20190203225703/https://www.computerworld.com/article/3336036/blockchain/linuxs-hyperledger-to-give-developers-supply-chain-building-blocks.html |archive-date=3 February 2019}}</ref> Another is Quorum, a permissioned private blockchain by [[Company:JPMorgan Chase|JPMorgan Chase]] with private storage, used for contract applications.<ref>{{Cite web |title=Why J.P. Morgan Chase Is Building a Blockchain on Ethereum |url=http://fortune.com/2016/10/04/jp-morgan-chase-blockchain-ethereum-quorum/ |url-status=live |archive-url=https://web.archive.org/web/20170202033844/http://fortune.com/2016/10/04/jp-morgan-chase-blockchain-ethereum-quorum/ |archive-date=2 February 2017 |access-date=2017-01-24 |website=Fortune}}</ref>

[[Company:Oracle Corporation|Oracle]] introduced a blockchain table feature in its [[Software:Oracle database|Oracle 21c database]].<ref name="OracleBlockchainDetails">{{Cite web|title=Details: Oracle Blockchain Table
|url=https://docs.oracle.com/en/database/oracle/oracle-database/21/nfcon/details-oracle-blockchain-table-282449857.html|access-date=2022-01-01|archive-url=https://web.archive.org/web/20210120232657/https://docs.oracle.com/en/database/oracle/oracle-database/21/nfcon/details-oracle-blockchain-table-282449857.html|archive-date=2021-01-20|url-status=live}}</ref><ref name="OracleBlockchainTable">{{Cite web|title=Oracle Blockchain Table|url=https://docs.oracle.com/en/database/oracle/oracle-database/21/nfcon/oracle-blockchain-table-268779556.html|access-date=2022-01-01|archive-url=https://web.archive.org/web/20210516130824/https://docs.oracle.com/en/database/oracle/oracle-database/21/nfcon/oracle-blockchain-table-268779556.html|archive-date=2021-05-16|url-status=live}}</ref>

Blockchain is also being used in peer-to-peer energy trading.<ref>{{Cite journal |title=Blockchain technology in the energy sector: A systematic review of challenges and opportunities |year=2019 |doi=10.1016/j.rser.2018.10.014 |last1=Andoni |first1=Merlinda |last2=Robu |first2=Valentin |last3=Flynn |first3=David |last4=Abram |first4=Simone |last5=Geach |first5=Dale |last6=Jenkins |first6=David |last7=McCallum |first7=Peter |last8=Peacock |first8=Andrew |journal=Renewable and Sustainable Energy Reviews |volume=100 |pages=143–174 |s2cid=116422191 |doi-access=free }}</ref><ref>{{Cite web |title=This Blockchain-Based Energy Platform Is Building A Peer-To-Peer Grid |date=16 October 2017 |url=https://www.fastcompany.com/40479952/this-blockchain-based-energy-platform-is-building-a-peer-to-peer-grid |url-status=live |archive-url=https://web.archive.org/web/20200607085107/https://www.fastcompany.com/40479952/this-blockchain-based-energy-platform-is-building-a-peer-to-peer-grid |archive-date=7 June 2020 |access-date=7 June 2020}}</ref><ref>{{Cite web |title=Blockchain-based microgrid gives power to consumers in New York |url=https://www.newscientist.com/article/2079334-blockchain-based-microgrid-gives-power-to-consumers-in-new-york/ |url-status=live |archive-url=https://web.archive.org/web/20160322204730/https://www.newscientist.com/article/2079334-blockchain-based-microgrid-gives-power-to-consumers-in-new-york/ |archive-date=22 March 2016 |access-date=7 June 2020}}</ref>

'''Lightweight blockchains''', or simplified blockchains, are more suitable for [[Internet of things|internet of things]] (IoT) applications than conventional blockchains.<ref>{{Cite journal|last1=Alassaf|first1=Norah|last2=Gutub|first2=Adnan|last3=Parah|first3=Shabir A.|last4=Al Ghamdi|first4=Manal|date=December 2019|title=Enhancing speed of SIMON: A light-weight-cryptographic algorithm for IoT applications|url=http://link.springer.com/10.1007/s11042-018-6801-z|journal=Multimedia Tools and Applications|language=en|volume=78|issue=23|pages=32633–32657|doi=10.1007/s11042-018-6801-z|s2cid=254858308 |issn=1380-7501}}</ref> One experiment suggested that a lightweight blockchain-based network could accommodate up to 1.34 million authentication processes every second, which could be sufficient for resource-constrained IoT networks.<ref>{{Cite journal |last1=Khan |first1=Safiullah |last2=Lee |first2=Wai-Kong |last3=Hwang |first3=Seong Oun |date=2021 |title=AEchain: A lightweight blockchain for IoT applications |url=https://ieeexplore.ieee.org/document/9357973 |journal=IEEE Consumer Electronics Magazine |volume=11 |issue=2 |pages=64–76 |doi=10.1109/MCE.2021.3060373 |issn=2162-2256 |s2cid=234325223}}</ref>

Blockchain could be used in detecting counterfeits by associating unique identifiers to products, documents and shipments, and storing records associated with transactions that cannot be forged or altered.<ref>{{Cite journal|last1=Ma|first1=Jinhua|last2=Lin|first2=Shih-Ya|last3=Chen|first3=Xin|last4=Sun|first4=Hung-Min|last5=Chen|first5=Yeh-Cheng|last6=Wang|first6=Huaxiong|date=2020|title=A Blockchain-Based Application System for Product Anti-Counterfeiting|journal=IEEE Access|volume=8|pages=77642–77652|doi=10.1109/ACCESS.2020.2972026|bibcode=2020IEEEA...877642M |s2cid=214205788|issn=2169-3536|doi-access=free|hdl=10356/145745|hdl-access=free}}</ref><ref>{{Cite book|last1=Alzahrani|first1=Naif|last2=Bulusu|first2=Nirupama|title=Proceedings of the 1st Workshop on Cryptocurrencies and Blockchains for Distributed Systems |chapter=Block-Supply Chain |date=2018-06-15|series=CryBlock'18|location=Munich, Germany|publisher=Association for Computing Machinery|pages=30–35|doi=10.1145/3211933.3211939|isbn=978-1-4503-5838-5|s2cid=169188795}}</ref> It is however argued that blockchain technology needs to be supplemented with technologies that provide a strong binding between physical objects and blockchain systems,<ref>{{Cite journal|last1=Balagurusamy|first1=V. S. K.|last2=Cabral|first2=C.|last3=Coomaraswamy|first3=S.|last4=Delamarche|first4=E.|last5=Dillenberger|first5=D. N.|last6=Dittmann|first6=G.|last7=Friedman|first7=D.|last8=Gökçe|first8=O.|last9=Hinds|first9=N.|last10=Jelitto|first10=J.|last11=Kind|first11=A.|date=2019-03-01|title=Crypto anchors|url=https://ieeexplore.ieee.org/document/8645638|journal=IBM Journal of Research and Development|volume=63|issue=2/3|pages=4:1–4:12|doi=10.1147/JRD.2019.2900651|s2cid=201109790|issn=0018-8646}}</ref> as well as provisions for content creator verification ''ala'' [[Finance:Know your customer|KYC standards]].<ref>{{Cite conference |last=Jung |first=Seung Wook |date=23 June 2021 |editor-last=Lee |editor-first=Robert |title=A Novel Authentication System for Artwork Based on Blockchain |url=https://books.google.com/books?id=Sbk0EAAAQBAJ&dq=Verisart&pg=PA159 |format=eBook |conference=20th IEEE/ACIS International Summer Semi-Virtual Conference on Computer and Information Science (ICIS 2021) |series=Studies in Computational Intelligence |publisher=Springer |volume=985 |page=159 |via=[[Google Books]]}}</ref> The [[Organization:European Union Intellectual Property Office|EUIPO]] established an Anti-Counterfeiting Blockathon Forum, with the objective of "defining, piloting and implementing" an anti-counterfeiting infrastructure at the European level.<ref>{{Cite web|last=Brett|first=Charles|date=2018-04-18|title=EUIPO Blockathon Challenge 2018 -|url=https://www.enterprisetimes.co.uk/2018/04/18/euipo-blockathon-challenge-2018/|access-date=2020-09-01|website=Enterprise Times|language=en-GB}}</ref><ref>{{Cite web|title=EUIPO Anti-Counterfeiting Blockathon Forum|url=https://euipo.europa.eu/ohimportal/en/web/observatory/blockathon}}</ref> The Dutch Standardisation organisation NEN uses blockchain together with [[QR code|QR Codes]] to authenticate certificates.<ref>{{Cite web |title=PT Industrieel Management |url=https://privacy.vakmedianet.nl/ptindustrieelmanagement/?ref=https%3A%2F%2Fwww.ptindustrieelmanagement.nl%2Fhse%2Fnieuws%2F2020%2F06%2Fnen-innoveert-certificatencheck-en-blockchain-1013171%3F_ga%3D2.11339894.336094574.1598975931-710406553.1598975931 |access-date=2020-09-01 |website=PT Industrieel Management |archive-date=24 May 2022 |archive-url=https://web.archive.org/web/20220524211503/https://privacy.vakmedianet.nl/ptindustrieelmanagement/?ref=https%3A%2F%2Fwww.ptindustrieelmanagement.nl%2Fhse%2Fnieuws%2F2020%2F06%2Fnen-innoveert-certificatencheck-en-blockchain-1013171%3F_ga%3D2.11339894.336094574.1598975931-710406553.1598975931 |url-status=dead }}</ref>

Beijing and Shanghai are among the cities designated by China to trial blockchain applications as January 30, 2022.<ref>{{cite news | url=https://www.reuters.com/world/china/china-selects-pilot-zones-application-areas-blockchain-project-2022-01-30/ | title=China selects pilot zones, application areas for blockchain project | newspaper=Reuters | date=31 January 2022 }}</ref> In Chinese legal proceedings, blockchain technology was first accepted as a method for authenticating internet evidence by the Hangzhou Internet Court in 2019 and has since been accepted by other Chinese courts.<ref name=":9222">{{Cite book |last=Šimalčík |first=Matej |title=Contemporary China: a New Superpower? |publisher=[[Company:Routledge|Routledge]] |year=2023 |isbn=978-1-03-239508-1 |editor-last=Kironska |editor-first=Kristina |chapter=Rule by Law |editor-last2=Turscanyi |editor-first2=Richard Q.}}</ref>{{Rp|page=|pages=123-125}}

==Blockchain interoperability==

With the increasing number of blockchain systems appearing, even only those that support cryptocurrencies, blockchain interoperability is becoming a topic of major importance. The objective is to support transferring assets from one blockchain system to another blockchain system. Wegner{{R|wegner}} stated that "[[Engineering:Interoperability|interoperability]] is the ability of two or more software components to cooperate despite differences in language, interface, and execution platform". The objective of blockchain interoperability is therefore to support such cooperation among blockchain systems, despite those kinds of differences.

There are already several blockchain interoperability solutions available.{{R|survey}} They can be classified into three categories: cryptocurrency interoperability approaches, blockchain engines, and blockchain connectors.

Several individual IETF participants produced the draft of a blockchain interoperability architecture.{{R|ietf-draft}}

== Energy consumption concerns ==

Some cryptocurrencies use blockchain mining — the peer-to-peer computer computations by which transactions are validated and verified. This requires a large amount of energy. In June 2018, the [[Organization:Bank for International Settlements|Bank for International Settlements]] criticized the use of public proof-of-work blockchains for their high energy consumption.<ref>{{Cite web |last=Hyun Song Shin |date=June 2018 |title=Chapter V. Cryptocurrencies: looking beyond the hype |url=https://www.bis.org/publ/arpdf/ar2018e5.pdf |url-status=live |archive-url=https://web.archive.org/web/20180618080358/https://www.bis.org/publ/arpdf/ar2018e5.pdf |archive-date=18 June 2018 |access-date=19 June 2018 |website=BIS 2018 Annual Economic Report |publisher=Bank for International Settlements |quote=Put in the simplest terms, the quest for decentralised trust has quickly become an environmental disaster.}}</ref><ref>{{Cite news |last=Janda |first=Michael |date=18 June 2018 |title=Cryptocurrencies like bitcoin cannot replace money, says Bank for International Settlements |publisher=ABC (Australia) |url=http://www.abc.net.au/news/2018-06-18/cryptocurrencies-cannot-replace-money-bis/9879448 |url-status=live |access-date=18 June 2018 |archive-url=https://web.archive.org/web/20180618072225/http://www.abc.net.au/news/2018-06-18/cryptocurrencies-cannot-replace-money-bis/9879448 |archive-date=18 June 2018}}</ref><ref>{{Cite news |last=Hiltzik |first=Michael |date=18 June 2018 |title=Is this scathing report the death knell for bitcoin? |work=Los Angeles Times |url=https://latimes.com/business/hiltzik/la-fi-hiltzik-bitcoin-bank-20180618-story.html |url-status=live |access-date=19 June 2018 |archive-url=https://web.archive.org/web/20180618233532/http://www.latimes.com/business/hiltzik/la-fi-hiltzik-bitcoin-bank-20180618-story.html |archive-date=18 June 2018}}</ref>

Early concern over the high energy consumption was a factor in later blockchains such as [[Cardano (blockchain platform)|Cardano]] (2017), [[Finance:Solana (blockchain platform)|Solana]] (2020) and [[Finance:Polkadot (cryptocurrency)|Polkadot]] (2020) adopting the less energy-intensive [[Finance:Proof of stake|proof-of-stake]] model. Researchers have estimated that Bitcoin consumes 100,000 times as much energy as proof-of-stake networks.<ref>{{Cite news |last=Ossinger |first=Joanna |date=2 February 2022 |title=Polkadot Has Least Carbon Footprint, Crypto Researcher Says |work=Bloomberg |url=https://www.bloomberg.com/news/articles/2022-02-02/polkadot-has-smallest-carbon-footprint-crypto-researcher-says |access-date=1 June 2022}}</ref><ref>{{Cite web |last=Jones |first=Jonathan Spencer |date=13 September 2021 |title=Blockchain proof-of-stake – not all are equal |url=https://www.smart-energy.com/industry-sectors/new-technology/proof-of-stake-blockchains-not-all-are-equal/ |website=www.smart-energy.com |access-date=26 February 2022 |archive-date=25 September 2021 |archive-url=https://web.archive.org/web/20210925061707/https://www.smart-energy.com/industry-sectors/new-technology/proof-of-stake-blockchains-not-all-are-equal/ |url-status=dead }}</ref>

In 2021, a study by [[Organization:University of Cambridge|Cambridge University]] determined that Bitcoin (at 121 terawatt-hours per year) used more electricity than Argentina (at 121TWh) and the Netherlands (109TWh).<ref>Criddle, Christina (February 20, 2021) [https://www.bbc.com/news/technology-56012952 "Bitcoin consumes 'more electricity than Argentina'."] BBC News. (Retrieved April 26, 2021.)</ref> According to Digiconomist, one bitcoin transaction required 708 kilowatt-hours of electrical energy, the amount an average U.S. household consumed in 24 days.<ref>Ponciano, Jonathan (March 9, 2021) [https://www.forbes.com/sites/jonathanponciano/2021/03/09/bill-gates-bitcoin-crypto-climate-change/ "Bill Gates Sounds Alarm On Bitcoin's Energy Consumption–Here's Why Crypto Is Bad For Climate Change."] Forbes.com. (Retrieved April 26, 2021.)</ref>

In February 2021, U.S. Treasury secretary [[Biography:Janet Yellen|Janet Yellen]] called Bitcoin "an extremely inefficient way to conduct transactions", saying "the amount of energy consumed in processing those transactions is staggering".<ref>Rowlatt, Justin (February 27, 2021) [https://www.bbc.com/news/science-environment-56215787 "How Bitcoin's vast energy use could burst its bubble."] BBC News. (Retrieved April 26, 2021.)</ref> In March 2021, [[Biography:Bill Gates|Bill Gates]] stated that "Bitcoin uses more electricity per transaction than any other method known to mankind", adding "It's not a great climate thing."<ref>Sorkin, Andrew et al. (March 9, 2021) [https://www.nytimes.com/2021/03/09/business/dealbook/bill-gates-bitcoin.html "Why Bill Gates Is Worried About Bitcoin."] ''New York Times''. (Retrieved April 25, 2021.)</ref>

Nicholas Weaver, of the [[Organization:International Computer Science Institute|International Computer Science Institute]] at the [[Organization:University of California, Berkeley|University of California, Berkeley]], examined blockchain's online security, and the [[Physics:Efficient energy use|energy efficiency]] of proof-of-work public blockchains, and in both cases found it grossly inadequate.<ref>{{Cite web |last=Illing |first=Sean |date=April 11, 2018 |title=Why Bitcoin is bullshit, explained by an expert |url=https://www.vox.com/conversations/2018/4/11/17206018/bitcoin-blockchain-cryptocurrency-weaver |url-status=live |archive-url=https://web.archive.org/web/20180717041640/https://www.vox.com/conversations/2018/4/11/17206018/bitcoin-blockchain-cryptocurrency-weaver |archive-date=17 July 2018 |access-date=17 July 2018 |website=Vox}}</ref><ref>{{Cite web |last=Weaver |first=Nicholas |title=Blockchains and Cryptocurrencies: Burn It With Fire |url=https://www.youtube.com/watch?v=xCHab0dNnj4 |url-status=live |archive-url=https://web.archive.org/web/20190219015620/https://www.youtube.com/watch?v=xCHab0dNnj4 |archive-date=19 February 2019 |access-date=17 July 2018 |website=YouTube video |publisher=Berkeley School of Information}}</ref> The 31TWh-45TWh of electricity used for bitcoin in 2018 produced 17-23 million tonnes of {{CO2}}.<ref>{{Cite journal |last1=Köhler |first1=Susanne |last2=Pizzol |first2=Massimo |date=20 November 2019 |title=Life Cycle Assessment of Bitcoin Mining |journal=Environmental Science & Technology |volume=53 |issue=23 |pages=13598–13606 |bibcode=2019EnST...5313598K |doi=10.1021/acs.est.9b05687 |pmid=31746188|doi-access=free}}</ref><ref>{{Cite journal |last1=Stoll |first1=Christian |last2=Klaaßen |first2=Lena |last3=Gallersdörfer |first3=Ulrich |year=2019 |title=The Carbon Footprint of Bitcoin |journal=Joule |volume=3 |issue=7 |pages=1647–1661 |doi=10.1016/j.joule.2019.05.012 |doi-access=free}}</ref> By 2022, the University of Cambridge and Digiconomist estimated that the two largest proof-of-work blockchains, Bitcoin and Ethereum, together used twice as much electricity in one year as the whole of Sweden, leading to the release of up to 120 million tonnes of {{CO2}} each year.<ref>{{Cite news|url=https://www.business-standard.com/article/international/us-lawmakers-begin-probe-into-bitcoin-miners-high-energy-use-122012900282_1.html#:~:text=Eight+US+lawmakers+have+come,being+felt+across+the+globe|title=US lawmakers begin probe into Bitcoin miners' high energy use|newspaper=Business Standard India |date=29 January 2022|via=Business Standard}}</ref>

Some cryptocurrency developers are considering moving from the proof-of-work model to the [[Finance:Proof-of-stake|proof-of-stake]] model.<ref>Cuen, Leigh (March 21, 2021) [https://techcrunch.com/2021/03/21/the-debate-about-cryptocurrency-and-energy-consumption/ "The debate about cryptocurrency and data consumption."] TechCrunch. (Retrieved April 26, 2021.)</ref>

==Academic research==
[[File:BlockchainPanelDiscussionAtIEEETechIgnite2017.jpg|thumb|Blockchain panel discussion at the first [[Organization:IEEE Computer Society|IEEE Computer Society]] TechIgnite conference]]
In October 2014, the MIT Bitcoin Club, with funding from MIT alumni, provided undergraduate students at the [[Organization:Massachusetts Institute of Technology|Massachusetts Institute of Technology]] access to $100 of bitcoin. The adoption rates, as studied by Catalini and Tucker (2016), revealed that when people who typically adopt technologies early are given delayed access, they tend to reject the technology.<ref>{{Cite journal |last1=Catalini |first1=Christian |last2=Tucker |first2=Catherine E. |date=11 August 2016 |title=Seeding the S-Curve? The Role of Early Adopters in Diffusion |journal=SSRN |doi=10.2139/ssrn.2822729 |ssrn=2822729 |s2cid=157317501 |url=http://www.netinst.org/Catalini_16-02.pdf}}</ref> Many universities have founded departments focusing on crypto and blockchain, including [[Organization:Massachusetts Institute of Technology|MIT]], in 2017. In the same year, [[Organization:University of Edinburgh|Edinburgh]] became "one of the first big European universities to launch a blockchain course", according to the ''Financial Times''.<ref>[https://www.ft.com/content/f736b04e-3708-11e7-99bd-13beb0903fa3 Arnold, M. (2017) "Universities add blockchain to course list", Financial Times: Masters in Finance, Retrieved 26 January 2022.]</ref>

===Adoption decision===
Motivations for adopting blockchain technology (an aspect of [[Physics:Diffusion of innovations|innovation adoptation]]) have been investigated by researchers. For example, Janssen, et al. provided a framework for analysis,<ref>{{Cite journal |last1=Janssen |first1=Marijn |last2=Weerakkody |first2=Vishanth |last3=Ismagilova |first3=Elvira |last4=Sivarajah |first4=Uthayasankar |last5=Irani |first5=Zahir |year=2020 |title=A framework for analysing blockchain technology adoption: Integrating institutional, market and technical factors |journal=International Journal of Information Management |publisher=Elsevier |volume=50 |pages=302–309 |doi=10.1016/j.ijinfomgt.2019.08.012 |s2cid=203129604 |doi-access=}}</ref> and Koens & Poll pointed out that adoption could be heavily driven by non-technical factors.<ref>{{Citation |last1=Koens |first1=Tommy |title=Euro-Par 2018: Parallel Processing Workshops |volume=11339 |pages=535–546 |year=2019 |series=Lecture Notes in Computer Science |chapter=The Drivers Behind Blockchain Adoption: The Rationality of Irrational Choices |doi=10.1007/978-3-030-10549-5_42 |isbn=978-3-030-10548-8 |last2=Poll |first2=Erik|hdl=2066/200787 |s2cid=57662305 |hdl-access=free }}</ref> Based on behavioral models, Li<ref>{{Cite book|chapter-url=https://doi.org/10.1145/3396743.3396750|archive-url=https://web.archive.org/web/20200605023137/https://dl.acm.org/doi/abs/10.1145/3396743.3396750|url-status=dead|first=Jerry|last=Li|title=Proceedings of the 2020 2nd International Conference on Management Science and Industrial Engineering |chapter=Blockchain Technology Adoption: Examining the Fundamental Drivers |date=7 April 2020|archive-date=5 June 2020|publisher=Association for Computing Machinery|pages=253–260|via=ACM Digital Library|doi=10.1145/3396743.3396750|isbn=9781450377065 |s2cid=218982506 }}</ref> has discussed the differences between adoption at the individual level and organizational levels.

=== Collaboration ===
Scholars in business and management have started studying the role of blockchains to support collaboration.<ref>{{Cite journal |last1=Hsieh |first1=Ying-Ying |last2=Vergne |first2=Jean-Philippe |last3=Anderson |first3=Philip |last4=Lakhani |first4=Karim |last5=Reitzig |first5=Markus |date=2019-02-12 |title=Correction to: Bitcoin and the rise of decentralized autonomous organizations |journal=Journal of Organization Design |volume=8 |issue=1 |pages=3 |doi=10.1186/s41469-019-0041-1 |issn=2245-408X |doi-access=free|hdl=10044/1/88332 |hdl-access=free }}</ref><ref>{{Cite journal |last1=Felin |first1=Teppo |last2=Lakhani |first2=Karim |year=2018 |title=What Problems Will You Solve With Blockchain? |journal=MIT Sloan Management Review}}</ref> It has been argued that blockchains can foster both cooperation (i.e., prevention of opportunistic behavior) and coordination (i.e., communication and information sharing). Thanks to reliability, transparency, traceability of records, and information immutability, blockchains facilitate collaboration in a way that differs both from the traditional use of contracts and from relational norms. Contrary to contracts, blockchains do not directly rely on the legal system to enforce agreements.<ref>{{Cite journal |last1=Beck |first1=Roman |last2=Mueller-Bloch |first2=Christoph |last3=King |first3=John Leslie |year=2018 |title=Governance in the Blockchain Economy: A Framework and Research Agenda |journal=Journal of the Association for Information Systems|pages=1020–1034 |doi=10.17705/1jais.00518 |s2cid=69365923 |url=https://aisel.aisnet.org/cgi/viewcontent.cgi?article=1835&context=jais}}</ref> In addition, contrary to the use of relational norms, blockchains do not require a trust or direct connections between collaborators.

===Blockchain and internal audit===
{{external media | width = 210px | float = right | video1= [https://www.youtube.com/watch?v=0UvVOMZqpEA Blockchain Basics & Cryptography], Gary Gensler, [[Organization:Massachusetts Institute of Technology|Massachusetts Institute of Technology]], 0:30<ref>{{cite web |last1=Popper |first1=Nathaniel |title=What is the Blockchain? Explaining the Tech Behind Cryptocurrencies (Published 2018) |url=https://www.nytimes.com/2018/06/27/business/dealbook/blockchains-guide-information.html |website=The New York Times |date=27 June 2018}}</ref>}}
The need for internal audits to provide effective oversight of organizational efficiency will require a change in the way that information is accessed in new formats.<ref>Hugh Rooney, Brian Aiken, & Megan Rooney. (2017). Q&A. Is Internal Audit Ready for Blockchain? ''Technology Innovation Management Review'', (10), 41.</ref> Blockchain adoption requires a framework to identify the risk of exposure associated with transactions using blockchain. The Institute of Internal Auditors has identified the need for internal auditors to address this transformational technology. New methods are required to develop audit plans that identify threats and risks. The Internal Audit Foundation study, ''Blockchain and Internal Audit,'' assesses these factors.<ref>Richard C. Kloch, Jr Simon J. Little, ''Blockchain and Internal Audit'' Internal Audit Foundation, 2019 {{ISBN|978-1-63454-065-0}}</ref> The American Institute of Certified Public Accountants has outlined new roles for auditors as a result of blockchain.<ref>Alexander, A. (2019). The audit, transformed: New advancements in technology are reshaping this core service. ''Accounting Today'', 33(1)</ref>

=== Journals ===
In September 2015, the first peer-reviewed academic journal dedicated to cryptocurrency and blockchain technology research, ''Ledger'', was announced. The inaugural issue was published in December 2016.<ref>{{Cite journal |last=Extance |first=Andy |date=30 September 2015 |title=The future of cryptocurrencies: Bitcoin and beyond |journal=Nature |volume=526 |issue=7571 |pages=21–23 |bibcode=2015Natur.526...21E |doi=10.1038/526021a |issn=0028-0836 |oclc=421716612 |pmid=26432223 |doi-access=free}}</ref> The journal covers aspects of [[Mathematics|mathematics]], [[Computer science|computer science]], [[Engineering:Engineering|engineering]], [[Philosophy:Law|law]], [[Finance:Economics|economics]] and [[Philosophy:Philosophy|philosophy]] that relate to cryptocurrencies.<ref>{{Cite book |title=Ledger (eJournal / eMagazine, 2015) |publisher=OCLC |oclc=910895894}}</ref><ref>{{Cite web |last=Hertig |first=Alyssa |date=15 September 2015 |title=Introducing Ledger, the First Bitcoin-Only Academic Journal |url=http://motherboard.vice.com/read/introducing-ledger-the-first-bitcoin-only-academic-journal |url-status=live |archive-url=https://web.archive.org/web/20170110172807/http://motherboard.vice.com/read/introducing-ledger-the-first-bitcoin-only-academic-journal |archive-date=10 January 2017 |access-date=10 January 2017 |website=Motherboard}}</ref> The journal encourages authors to [[Digital signature|digitally sign]] a [[Hash function|file hash]] of submitted papers, which are then [[Trusted timestamping|timestamped]] into the bitcoin blockchain. Authors are also asked to include a personal bitcoin address on the first page of their papers for non-repudiation purposes.<ref>{{Cite journal |last1=Rizun |first1=Peter R. |last2=Wilmer |first2=Christopher E. |last3=Burley |first3=Richard Ford |last4=Miller |first4=Andrew |year=2015 |title=How to Write and Format an Article for Ledger |url=http://ledger.pitt.edu/ojs/public/journals/1/AuthorGuide.pdf |url-status=live |journal=Ledger |volume=1 |issue=1 |pages=1–12 |doi=10.5195/LEDGER.2015.1 |doi-broken-date=31 January 2024 |issn=2379-5980 |oclc=910895894 |archive-url=https://web.archive.org/web/20150922190603/http://ledger.pitt.edu/ojs/public/journals/1/AuthorGuide.pdf |archive-date=22 September 2015 |access-date=11 January 2017}} {{Open access}}</ref>

==See also==
* [[Changelog]] – a record of all notable changes made to a project
* [[Medicine:Checklist|Checklist]] – an informational aid used to reduce failure
* [[Finance:Economics of digitization|Economics of digitization]]
* [[List of blockchains]]
* [[Privacy and blockchain]]
* [[Version control]] – a record of all changes (mostly of software project) in a form of a graph

==References==
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<ref name="fortune20160515">{{Cite news |last=Morris |first=David Z. |date=15 May 2016 |title=Leaderless, Blockchain-Based Venture Capital Fund Raises $100 Million, And Counting |work=Fortune |url=http://fortune.com/2016/05/15/leaderless-blockchain-vc-fund/ |url-status=live |access-date=2016-05-23 |archive-url=https://web.archive.org/web/20160521015602/http://fortune.com/2016/05/15/leaderless-blockchain-vc-fund/ |archive-date=21 May 2016}}</ref>
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<ref name="kopstein">{{Cite magazine |last=Kopfstein, Janus |date=12 December 2013 |title=The Mission to Decentralize the Internet |url=https://www.newyorker.com/tech/elements/the-mission-to-decentralize-the-internet |url-status=live |magazine=The New Yorker |archive-url=https://web.archive.org/web/20141231031044/http://www.newyorker.com/tech/elements/the-mission-to-decentralize-the-internet |archive-date=31 December 2014 |access-date=30 December 2014 |quote=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 'block chain.' |df=dmy-all}}</ref>
<ref name="te20151031">{{Cite news |date=31 October 2015 |title=Blockchains: The great chain of being sure about things |url=https://www.economist.com/news/briefing/21677228-technology-behind-bitcoin-lets-people-who-do-not-know-or-trust-each-other-build-dependable |url-status=live |newspaper=[[Finance:The Economist|The Economist]] |archive-url=https://web.archive.org/web/20160703000844/http://www.economist.com/news/briefing/21677228-technology-behind-bitcoin-lets-people-who-do-not-know-or-trust-each-other-build-dependable |archive-date=3 July 2016 |access-date=18 June 2016 |quote=The technology behind bitcoin lets people who do not know or trust each other build a dependable ledger. This has implications far beyond the crypto currency. |df=dmy-all}}</ref>
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<ref name="t9">{{Cite web |last=DeRose, Chris |date=26 June 2015 |title=Why the Bitcoin Blockchain Beats Out Competitors |url=http://www.americanbanker.com/bankthink/why-the-bitcoin-blockchain-beats-out-competitors-1075100-1.html |url-status=live |archive-url=https://web.archive.org/web/20160330060709/http://www.americanbanker.com/bankthink/why-the-bitcoin-blockchain-beats-out-competitors-1075100-1.html |archive-date=30 March 2016 |access-date=18 June 2016 |website=American Banker |df=dmy-all}}</ref>
<ref name="t10">{{Cite web |last=Reutzel, Bailey |date=13 July 2015 |title=A Very Public Conflict Over Private Blockchains |url=http://www.paymentssource.com/news/technology/a-very-public-confluct-over-private-blockchains-3021831-1.html |url-status=live |archive-url=https://web.archive.org/web/20160421112045/http://www.paymentssource.com/news/technology/a-very-public-confluct-over-private-blockchains-3021831-1.html |archive-date=21 April 2016 |access-date=18 June 2016 |website=PaymentsSource |publisher=SourceMedia, Inc. |location=New York, NY |df=dmy-all}}</ref>
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<ref name="survey">{{cite arXiv| last1 = Belchior| first1 = Rafael| last2 = Vasconcelos| first2 = André| last3 = Guerreiro| first3 = Sérgio| last4 = Correia| first4 = Miguel| date = May 2020| title = A Survey on Blockchain Interoperability: Past, Present, and Future Trends| class = cs.DC| eprint = 2005.14282}}</ref>
<ref name="ietf-draft">{{cite tech report | first1= T.| last1= Hardjono| first2= M.| last2= Hargreaves| first3= N.| last3= Smith | title= An Interoperability Architecture for Blockchain Gateways| number= draft-hardjono-blockchain-interop-arch-00| institution= IETF| date= October 2, 2020}}</ref>
}}

==Further reading==
{{Refbegin|30em}}
* {{Cite report |url=http://scet.berkeley.edu/wp-content/uploads/BlockchainPaper.pdf |title=BlockChain Technology: Beyond Bitcoin |last1=Crosby |first1=Michael |last2=Nachiappan |date=16 October 2015 |publisher=University of California, Berkeley |last3=Pattanayak |first3=Pradhan |last4=Verma |first4=Sanjeev |last5=Kalyanaraman |first5=Vignesh |access-date=2017-03-19 |series=Sutardja Center for Entrepreneurship & Technology Technical Report }}
* {{Cite book |last=Jaikaran |first=Chris |url=https://crsreports.congress.gov/product/pdf/R/R45116/3 |title=Blockchain: Background and Policy Issues |date=28 February 2018 |publisher=Congressional Research Service |location=Washington, DC |access-date=2 December 2018 |archive-date=2 December 2018 |archive-url=https://web.archive.org/web/20181202202739/https://crsreports.congress.gov/product/pdf/R/R45116/3 |url-status=dead }}
* {{Cite report |title=The Blockchain Revolution: An Analysis of Regulation and Technology Related to Distributed Ledger Technologies |last1=Kakavand |first1=Hossein |last2=De Sevres |first2=Nicolette Kost |date=12 October 2016 |publisher=Luther Systems & DLA Piper |last3=Chilton |first3=Bart |ssrn=2849251}}
* {{Cite web |last=Mazonka |first=Oleg |date=29 December 2016 |title=Blockchain: Simple Explanation |url=http://jrxv.net/x/16/chain.pdf |website=Journal of Reference |access-date=29 December 2016 |archive-date=7 August 2017 |archive-url=https://web.archive.org/web/20170807214027/http://jrxv.net/x/16/chain.pdf |url-status=dead }}
* {{Cite book |last1=Tapscott |first1=Don |title=Blockchain Revolution: How the Technology Behind Bitcoin Is Changing Money, Business and the World |last2=Tapscott |first2=Alex |date=2016 |publisher=Portfolio Penguin |isbn=978-0-241-23785-4 |location=London |oclc=971395169}}
* {{Cite conference |last1=Saito |first1=Kenji |last2=Yamada |first2=Hiroyuki |date=June 2016 |title=What's So Different about Blockchain? Blockchain is a Probabilistic State Machine |conference=IEEE 36th International Conference on Distributed Computing Systems Workshops |location=Nara, Nara, Japan |publisher=IEEE |pages=168–75 |doi=10.1109/ICDCSW.2016.28 |isbn=978-1-5090-3686-8 |issn=2332-5666 |journal=International Conference on Distributed Computing Systems Workshops (Icdcs)}}
* {{Cite book |last=Raval |first=Siraj |url=http://shop.oreilly.com/product/0636920039334.do?sortby=publicationDate |title=Decentralized Applications: Harnessing Bitcoin's Blockchain Technology |date=2016 |publisher=Oreilly |isbn=9781491924549 }}
* {{Cite book |last=Bashir |first=Imran |title=Mastering Blockchain |date=2017 |publisher=Packt Publishing, Ltd. |isbn=978-1-78712-544-5 |oclc=967373845}}
* {{cite journal|first1=Fabian|last1=Knirsch|first2=Andread|last2=Unterweger|first3=Dominik|last3=Engel|title=Implementing a blockchain from scratch: why, how, and what we learned|journal=EURASIP Journal on Information Security|year=2019|volume=2019|doi=10.1186/s13635-019-0085-3|s2cid=84837476|doi-access=free}}
* D. Puthal, N. Malik, [[Biography:Saraju Mohanty|S. P. Mohanty]], E. Kougianos, and G. Das, "[http://www.smohanty.org/Publications_Journals/2018/Mohanty_IEEE-CEM_2018-Jul_Blockchain.pdf Everything you Wanted to Know about the Blockchain]", ''IEEE Consumer Electronics Magazine'', Volume 7, Issue 4, July 2018, pp.&nbsp;6–14.
* David L. Portilla, David J. Kappos, Minh Van Ngo, Sasha Rosenthal-Larrea, John D. Buretta and Christopher K. Fargo, Cravath, Swaine & Moore LLP, "[https://corpgov.law.harvard.edu/2022/01/28/blockchain-in-the-banking-sector-a-review-of-the-landscape-and-opportunities Blockchain in the Banking Sector: A Review of the Landscape and Opportunities]", ''Harvard Law School of Corporate Governance'', posted on Friday, January 28, 2022
{{Refend}}

== External links ==
{{Cryptocurrencies|state=expanded}}
{{Bitcoin}}
{{Databases}}

[[Category:Bitcoin]]
[[Category:Blockchains| ]]
[[Category:Cryptocurrencies]]
[[Category:Database models]]
[[Category:Financial metadata]]
[[Category:Information systems]]

{{Sourceattribution|Blockchain}}