Blockchain
A blockchain is a growing list of records, called "blocks", that are securely linked together using cryptography. Each block contains a cryptographic hash of the previous block, a timestamp, and transaction data (generally represented as a Merkle tree, where data nodes are represented by leafs). The timestamp proves that the transaction data existed when the block was published to get into its hash. As blocks each contain information about the block previous to it, they form a chain, with each additional block reinforcing the ones before it. Therefore, blockchains are resistant to modification of their data because once 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 network for use as a publicly distributed ledger, where nodes collectively adhere to a protocol to communicate and validate new blocks. Although blockchain records are not unalterable as forks are possible, blockchains may be considered secure by design and exemplify a distributed computing system with high Byzantine fault tolerance. The blockchain was popularized by a person (or group of people) using the name Satoshi Nakamoto in 2008 to serve as the public transaction ledger of  the cryptocurrency bitcoin, based on work by Stuart Haber, W. Scott Stornetta, and Dave Bayer. The identity of Satoshi Nakamoto remains unknown to date. The implementation of the blockchain within bitcoin made it the first digital currency to solve the double-spending problem without the need of a trusted authority or central server. The bitcoin design has inspired other applications and blockchains that are readable by the public and are widely used by cryptocurrencies. The blockchain is considered a type of payment rail. Private blockchains have been proposed for business use. "Computerworld" called the marketing of such privatized blockchains without  a proper security model "snake oil"; however, others have argued that permissioned blockchains, if carefully designed, may be more decentralized and therefore more secure in practice than permissionless ones. History. Cryptographer David Chaum first proposed a blockchain-like protocol in his 1982 dissertation "Computer Systems Established, Maintained, and Trusted by Mutually Suspicious Groups." Further work on a cryptographically secured chain of blocks was described in 1991 by Stuart Haber and W. Scott Stornetta. They wanted to implement a system wherein document timestamps could not be tampered with. In 1992, Haber, Stornetta, and Dave Bayer incorporated Merkle trees into the design , which improved its efficiency by allowing several document certificates to be collected into one block. Under their company Surety, their document certificate hashes have been published in "The New York Times" every week since 1995. 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 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. The design was  implemented the following year by Nakamoto as a core component of the cryptocurrency bitcoin, where it serves as the public ledger for all transactions on the network. In August 2014, the bitcoin blockchain file size, containing records of all transactions that have occurred on the network, reached 20 GB (gigabytes). In January 2015, the size had grown to almost 30 GB, and from January 2016 to January 2017, the bitcoin blockchain grew from 50 GB to 100 GB in size. The ledger size had exceeded 200 GB by early 2020. 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. According to Accenture, an application of the diffusion of innovations theory suggests that blockchains attained a 13.5% adoption rate within financial services in 2016, therefore reaching the early adopters' phase. Industry trade groups joined to create the Global Blockchain Forum in 2016, an initiative of the Chamber of Digital Commerce. In May 2018, Gartner found that only 1% of 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". For the year 2019 Gartner reported 5% of CIOs believed blockchain technology was a 'game-changer' for their business. Structure. A blockchain is a decentralized, distributed, and oftentimes 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. This allows the participants to verify and audit transactions independently and relatively inexpensively. A blockchain database is managed autonomously using a peer-to-peer network and a distributed timestamping server. They are authenticated by mass collaboration  powered by collective self-interests. Such a design facilitates robust workflow where participants' uncertainty regarding data security is marginal. The use of a blockchain removes the characteristic of infinite 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". A blockchain can maintain title rights because, when properly set up to detail the exchange agreement, it provides a record that compels offer and acceptance. Logically, a blockchain can be seen as consisting of several layers: Blocks . Blocks hold batches of valid transactions that are hashed and encoded into a Merkle tree. Each block includes the cryptographic hash of the prior block in the blockchain, linking the two. The linked blocks form a chain. This iterative process confirms the integrity of the previous block, all the way back to the initial block, which is known as the genesis block. To assure the integrity of a block and the data contained in it, the block is usually digitally signed. Sometimes separate blocks can be produced concurrently, creating a temporary fork. In addition to a secure 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. 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 as more blocks are built on top of it, eventually becoming very low. For example, bitcoin uses a 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. Within a blockchain the computation is carried out redundantly rather than in the traditional segregated and parallel manner. Block time. The "block time" is the average time it takes for the network to generate one extra block in the blockchain. Some blockchains create a new block as frequently as every five seconds. 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 Ethereum is set to between  14 and 15 seconds, while for bitcoin it is on average 10 minutes. Decentralization. By storing data across its peer-to-peer network, the blockchain eliminates a number of risks that come with data being held centrally. The decentralized blockchain may use ad hoc message passing and distributed networking. One risk of a lack of decentralization is a so-called "51% attack" where a central entity can gain control of more than half of a network and can manipulate that specific blockchain record at will, allowing double-spending. Peer-to-peer blockchain networks lack centralized points of vulnerability that computer  crackers can exploit; likewise, it has no central point of failure. Blockchain security methods include the use of public-key cryptography. 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. Every node in a decentralized system has a copy of the  blockchain. Data quality is maintained by massive database replication and computational trust. No centralized "official" copy exists and no user is "trusted" more than any other. Transactions are broadcast to the network using the software. Messages are delivered on a best-effort basis. Mining nodes validate transactions, add them to the block they are building, and then broadcast the completed block to other nodes. Blockchains use various time-stamping schemes, such as proof-of-work, to serialize changes. Alternative consensus methods include proof-of-stake. The growth of a decentralized blockchain is accompanied by the risk of centralization because the  computer resources required to process larger amounts of data become more expensive. Openness. Open blockchains are more 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. Proponents of permissioned or private chains argue that the term "blockchain" may be applied to any data structure that batches data into time-stamped blocks . These blockchains serve as a distributed version of multiversion concurrency control (MVCC) in databases. 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. 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. 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." Permissionlessness . An advantage to an open, permissionless, or public, blockchain network is that guarding against bad actors is not required and no access control is needed. This means that applications can be added to the network without the approval or trust of others, using the blockchain as a transport layer . 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 Adam Back , the original idea was first proposed by Cynthia Dwork and Moni Naor and Eli Ponyatovski in their  1992 paper "Pricing via Processing or Combatting Junk Mail". In 2016, venture capital investment for blockchain-related projects was weakening in the USA but increasing in China. Bitcoin and many other cryptocurrencies use open (public) blockchains. , bitcoin has the highest market capitalization. Permissioned (private) blockchain. Permissioned blockchains use an access control layer to govern who has access to the network. In contrast to public blockchain networks, validators on private blockchain networks are vetted by the network owner. They do not rely on anonymous nodes to validate transactions nor do they benefit from the network effect . Permissioned blockchains can also go  by the name of 'consortium' blockchains. 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. Disadvantages of private blockchain. Nikolai Hampton pointed out 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." This has a set of particularly profound adverse implications during a financial crisis or debt crisis like the financial crisis of 2007–08 , where politically powerful actors may make decisions that favor some groups at the expense of others, 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." 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." Blockchain analysis. The Blockchain analysis|analysis of public blockchains has become increasingly important with the popularity of bitcoin , Ethereum , litecoin and other cryptocurrencies . 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. The reason for this is accusations of blockchain-enabled cryptocurrencies enabling illicit Darknet market|dark market  trade of drugs, weapons, money laundering, etc. 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 Fiat money|fiat -crypto exchanges. The development, some argue, has led criminals to prioritise the use of new cryptos such as Monero (cryptocurrency)|Monero . The question is about the public accessibility of blockchain data and the personal privacy of the very same data. It is  a key debate in cryptocurrency and ultimately in the blockchain. Standardisation. In April 2016, Standards Australia submitted a proposal to the 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. 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"></ref> More than 50 countries are  participating in the standardization process together with external liaisons such as the Society for Worldwide Interbank Financial Telecommunication (SWIFT), the European Commission , the International Federation of Surveyors , the International Telecommunication Union (ITU) and the United Nations Economic Commission for Europe (UNECE). Many other national standards bodies and open standards bodies are also working on blockchain standards. These include the National Institute of Standards and Technology (NIST), the European Committee for Electrotechnical Standardization (CENELEC), the Institute of Electrical and Electronics Engineers (IEEE), the Organization for the Advancement of Structured Information Standards ( OASIS (organization)|OASIS ), and some individual participants in the Internet Engineering  Task Force <ref name="An Interoperability Architecture for Blockchain/DLT Gateways draft-hardjono-blockchain-interop-arch-02"></ref> (IETF). Types. Currently, there are at least four types of blockchain networks — public blockchains, private blockchains, consortium blockchains and hybrid blockchains. Public blockchains. A public blockchain has absolutely no access restrictions. Anyone with an Internet connection can send Financial transaction|transactions to it as well as become a validator (i.e., participate in the execution of a Consensus (computer science)|consensus protocol ). Usually, such networks offer Incentive|economic incentives for those who secure them and utilize some type of a Proof-of-stake|Proof of Stake or Proof -of-work system|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. 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. 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. Entries from the primary blockchain (where said entries typically represent digital asset s) 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.). Uses. |thumb|220x220px| 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 for cryptocurrency|cryptocurrencies such as bitcoin ; there were also a few other operational products that had matured from proof of concept by late 2016. 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 back office . 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 . Furthermore, According to 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 indicts a significant demand and interest in blockchain technology. Individual use of blockchain technology has also greatly increased since 2016. According to statistics in 2020, there were more than 40 million blockchain  wallets in 2020 in comparison to around 10 million blockchain wallets in 2016. Cryptocurrencies. Most cryptocurrencies use blockchain technology to record transactions. For example, the bitcoin network and Ethereum network are both based on blockchain. On 8 May 2018 Facebook confirmed that it would open a new blockchain group which would be headed by David A. Marcus|David Marcus , who previously was in charge of Facebook Messenger|Messenger . Facebook's planned cryptocurrency platform, Libra (cryptocurrency)|Libra (now known as Diem), was formally announced on June 18, 2019. The criminal enterprise Silk Road (marketplace)|Silk Road , which operated on Tor (anonymity network)|Tor , utilized cryptocurrency for  payments, some of which the US federal government has seized through research on the blockchain and Forfeiture (law)|forfeiture. 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 Central bank digital currency|national digital currency which launched in 2020. To strengthen their respective currencies, Western governments including the European Union and the United States have initiated similar projects. Smart contracts. Blockchain-based smart contract s are proposed contracts that can be partially or fully executed or enforced without human interaction. One of  the main objectives of a smart contract is automation|automated 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. An International Monetary Fund|IMF staff discussion from 2018 reported that smart contracts based on blockchain technology might reduce 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. Financial services. According to " Reason (magazine)|Reason ", many banks have expressed interest in implementing distributed ledger s for use in banking and are cooperating with companies creating private blockchains, and according to a September 2016 IBM study, this is occurring faster than expected. Banks are interested in this technology not least because it has the potential to speed up back office settlement systems. 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. Bank s such as 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. 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. The blockchain has also given rise to 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). 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, art, or individual products. A number of companies are active in this space providing services for compliant tokenization, private STOs, and public STOs. Games. Blockchain technology, such as cryptocurrencies and non-fungible token s (NFTs), has been used in video games for 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 , and thus publishers typically have shied away from allowing players to earn real-world funds from games. Blockchain games typically allow players to trade these in-game items for cryptocurrency, which can  then be exchanged for money. The first known game to use blockchain technologies was " CryptoKitties ", launched in November 2017, where the player would purchase NFTs with Ethereum cryptocurrency, each NFT consisting of a virtual pet that the player could breed with others to create offspring with combined traits as new NFTs. The game made headlines in December 2017 when one virtual pet sold for more than United States dollar|US$ 100,000. "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 being for  the game. 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. 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. Several major publishers, including Ubisoft , Electronic Arts , and Take Two Interactive , have stated that blockchain and NFT-based games are under serious consideration for their companies in the future. In October 2021, Valve Corporation banned blockchain games, including those using cryptocurrency and NFTs, from being hosted on its 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 , was speculated  to be a factor in the decision to ban blockchain games. 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, 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. Supply chain. There have been several different efforts to employ blockchains in supply chain management . Domain names. There are several different efforts to offer 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. Namecoin is a cryptocurrency that supports the ".bit" top-level domain (TLD). Namecoin was forked from bitcoin in 2011. The .bit TLD is not sanctioned by ICANN , instead requiring an alternative DNS root . As of 2015, it was used by 28 websites, out of 120,000 registered names. Namecoin was dropped by OpenNIC in 2019, due to malware and potential other legal issues. Other blockchain alternatives to ICANN  include The Handshake Network, EmerDNS, and Unstoppable Domains. 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 cryptocurrency wallet addresses, as a convenience for transferring cryptocurrency. Other uses. 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 or musicians. 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. In 2017, IBM partnered with ASCAP and PRS for Music to adopt blockchain technology in music distribution. 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." New distribution methods are available for the insurance industry such as peer-to-peer insurance , parametric insurance and microinsurance following the adoption of blockchain. The sharing economy and Internet of Things|IoT are also set to benefit from blockchains because they involve many collaborating  peers. The use of blockchain in libraries is being studied with a grant from the U.S. Institute of Museum and Library Services. Other blockchain designs include Hyperledger , a collaborative effort from the Linux Foundation to support blockchain-based distributed ledgers, with projects under this initiative including Hyperledger Burrow (by Monax) and Hyperledger Fabric (spearheaded by IBM). Another is Quorum, a permissionable private blockchain by JPMorgan Chase with private storage, used for contract applications. Blockchain is also being used in peer-to-peer energy trading . 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. It is however argued that blockchain technology needs to be supplemented with technologies that provide a strong binding between physical objects and blockchain systems. The 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. The Dutch Standardisation organisation NEN uses blockchain together with QR Codes to authenticate certificates. 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 stated that "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. 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. Energy consumption concerns. Blockchain  mining — the peer-to-peer computer computations by which transactions are validated and verified — requires a significant amount of energy. In June 2018 the Bank for International Settlements criticized the use of public proof-of-work blockchains for their high energy consumption. In 2021, a study by 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). According to Digiconomist, one bitcoin transaction required 708 kilowatt-hours of electrical energy, the amount an average U.S. household consumed in 24 days. In February 2021, U.S. Treasury secretary  Janet Yellen called Bitcoin "an extremely inefficient way to conduct transactions", saying "the amount of energy consumed in processing those transactions is staggering." In March 2021, 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." Nicholas Weaver, of the International Computer Science Institute at the University of California, Berkeley , examined blockchain's online security, and the energy efficiency of proof-of-work public blockchains, and in both cases found it grossly inadequate. The 31TWh–45TWh of electricity used for bitcoin in 2018 produced 17–22.9 million  tonnes of CO2. 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. Inside the cryptocurrency industry, concern about high energy consumption has led some companies to consider moving from the proof of work blockchain model to the less energy-intensive proof of stake model. Academics and researchers have estimated that Bitcoin consumes 100,000 times as much energy as proof-of-stake  networks. Academic research. |thumb|Blockchain panel discussion at the first IEEE Computer Society TechIgnite conference In October 2014, the MIT Bitcoin Club, with funding from MIT alumni, provided undergraduate students at the Massachusetts Institute of Technology access to $100 of bitcoin. The adoption rates, as studied by Christian Catalini|Catalini and Catherine Tucker|Tucker (2016), revealed that when people who typically adopt technologies early are given delayed access, they tend to reject the technology. Many universities have founded departments focusing on crypto and blockchain, including Massachusetts Institute of Technology|MIT , in 2017. In the same year, university of Edinburgh|Edinburgh became "one of the  first big European universities to launch a blockchain course", according to the "Financial Times". Adoption decision. Motivations for adopting blockchain technology (an aspect of Diffusion of innovations|innovation adoptation ) have been investigated by researchers. For example, Janssen, et al. provided a framework for analysis, and Koens & Poll pointed out that adoption could be heavily driven by non-technical factors. Based on behavioral models, Li 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. 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. In addition, contrary to the use of relational norms, blockchains do not require a trust or direct connections between collaborators. Blockchain and internal audit. 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. 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. The American Institute of Certified Public Accountants has outlined new roles for auditors as a result of blockchain. 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. The journal covers aspects of mathematics , computer science , engineering , law , economics and philosophy that relate to cryptocurrencies such as bitcoin. 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. External links. Category:Bitcoin Category:Blockchains| Category:Cryptocurrencies Category:Database models Category:Emerging technologies Category:Financial metadata Category:Computer-related introductions in 2009  Category:Information systems Category:Writing systems Category:Mathematical tools Category:Counting instruments Category:Encodings Category:Decentralization Category:21st-century inventions