Blockchain

A blockchain is a distributed ledger with growing lists of records (blocks) that are securely linked together via cryptographic hashes.^[1]^[2]^[3]^[4] 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 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 (P2P) computer network for use as a public distributed ledger, where nodes collectively adhere to a consensus algorithm protocol to add and validate new transaction blocks. Although blockchain records are not unalterable, since blockchain forks are possible, blockchains may be considered secure by design and exemplify a distributed computing system with high Byzantine fault tolerance.^[5]

A blockchain was created by a person (or group of people) using the name (or pseudonym) Satoshi Nakamoto in 2008 to serve as the public distributed ledger for bitcoin cryptocurrency transactions, based on previous work by Stuart Haber, W. Scott Stornetta, and Dave Bayer.^[6] The implementation of the blockchain within bitcoin made it the first digital currency to solve the double-spending problem without the need for a trusted authority or central server. The bitcoin design has inspired other applications^[3]^[2] and blockchains that are readable by the public and are widely used by cryptocurrencies. The blockchain may be considered a type of payment rail.^[7]

Private blockchains have been proposed for business use. Computerworld called the marketing of such privatized blockchains without a proper security model "snake oil";^[8] however, others have argued that permissioned blockchains, if carefully designed, may be more decentralized and therefore more secure in practice than permissionless ones.^[4]^[9]

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^ ^a ^b Narayanan, Arvind; Bonneau, Joseph; Felten, Edward; Miller, Andrew; Goldfeder, Steven (2016). Bitcoin and cryptocurrency technologies: a comprehensive introduction. Princeton, New Jersey: Princeton University Press. ISBN 978-0-691-17169-2.
^ Iansiti, Marco; Lakhani, Karim R. (January 2017). "The Truth About Blockchain". Harvard Business Review. Cambridge, Massachusetts: Harvard University. Archived from the original on 18 January 2017. Retrieved 17 January 2017. 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.
^ Oberhaus, Daniel (27 August 2018). "The World's Oldest Blockchain Has Been Hiding in the New York Times Since 1995". Vice. Retrieved 9 October 2021.
^ Lunn, Bernard (10 February 2018). "Blockchain may finally disrupt payments from Micropayments to credit cards to SWIFT". dailyfintech.com. Archived from the original on 27 September 2018. Retrieved 18 November 2018.
^ Cite error: The named reference cw20160905 was invoked but never defined (see the help page).
^ Bakos, Yannis; Halaburda, Hanna; Mueller-Bloch, Christoph (February 2021). "When Permissioned Blockchains Deliver More Decentralization Than Permissionless". Communications of the ACM. 64 (2): 20–22. doi:10.1145/3442371. S2CID 231704491.

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[cryptocurrencytech-4] Narayanan, Arvind; Bonneau, Joseph; Felten, Edward; Miller, Andrew; Goldfeder, Steven (2016). Bitcoin and cryptocurrency technologies: a comprehensive introduction. Princeton, New Jersey: Princeton University Press. ISBN 978-0-691-17169-2.

[5] Iansiti, Marco; Lakhani, Karim R. (January 2017). "The Truth About Blockchain". Harvard Business Review. Cambridge, Massachusetts: Harvard University. Archived from the original on 18 January 2017. Retrieved 17 January 2017. 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.

[6] Oberhaus, Daniel (27 August 2018). "The World's Oldest Blockchain Has Been Hiding in the New York Times Since 1995". Vice. Retrieved 9 October 2021.

[7] Lunn, Bernard (10 February 2018). "Blockchain may finally disrupt payments from Micropayments to credit cards to SWIFT". dailyfintech.com. Archived from the original on 27 September 2018. Retrieved 18 November 2018.

[cw20160905-8] Cite error: The named reference cw20160905 was invoked but never defined (see the help page).

[auto-9] Bakos, Yannis; Halaburda, Hanna; Mueller-Bloch, Christoph (February 2021). "When Permissioned Blockchains Deliver More Decentralization Than Permissionless". Communications of the ACM. 64 (2): 20–22. doi:10.1145/3442371. S2CID 231704491.

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