Updated: May 29, 2020
A blockchain is a growing list of records; each record is called blocks, the blocks are linked using cryptography. Each block contains a cryptographic hash of the previous block, a timestamp, and transaction data represented as a Merkle tree.
By design, a blockchain is resistant to modification of its data. It is an open, distributed ledger that can record transactions between two parties efficiently and in a verifiable and permanent way. For use as a distributed ledger, a blockchain is typically managed by a peer-to-peer network collectively adhering to a protocol for inter-node communication and validating new blocks. Once recorded, the data in any given block cannot be altered retrospectively without alteration of all subsequent blocks, which requires the majority consensus of the network. As blockchain records are not unalterable, blockchain is considered secure and exemplifies a distributed computing system with high Byzantine fault tolerance. Decentralized consensus has therefore been claimed.
Blockchain was invented by a person or a group of people using the name Satoshi Nakamoto in 2008 to serve as the public transaction ledger of the cryptocurrency bitcoin. The identity of Satoshi Nakamoto is unknown. The invention of the blockchain for bitcoin made it the first digital currency to solve the double-spending problem without the need for a trusted authority like a bank or central server. The bitcoin design has inspired other applications, and blockchains that are readable by the public are widely used by cryptocurrencies. Blockchain is considered a type of payment rail. Private blockchains have been proposed for business use. Sources such as Computerworld called the marketing of such blockchains without a proper security model "snake oil".
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