Blockchain

The blockchain is a <a href="/facts/Distributed_ledger/msw7wpVC">distributed ledger</a> with growing lists of <a href="/facts/Record_(computer_science)/1fvSgenB">records</a> (blocks) that are securely linked together via <a href="/facts/Cryptographic_hash_function/cuxkgbST">cryptographic hashes</a>. Each block contains a cryptographic hash of the previous block, a <a href="/facts/Trusted_timestamping/eRjuYGTM">timestamp</a>, and transaction data (generally represented as a <a href="/facts/Merkle_tree/uGFY5mNA">Merkle tree</a>, where <a href="/facts/Node_(computer_science)/eYlvVE0z">data nodes</a> are represented by leaves). Since each block contains information about the previous block, they effectively form a chain (compare <a href="/facts/Linked_list/Ik4JTgJW">linked list</a> data structure), with each additional block linking to the ones before it. Consequently, blockchain transactions are resistant to alteration because, once recorded, the data in any given block cannot be changed retroactively without altering all subsequent blocks and obtaining network consensus to accept these changes.
Blockchains are typically managed by a <a href="/facts/Peer-to-peer/wCCdPb0H">peer-to-peer (P2P)</a> computer network for use as a public <a href="/facts/Distributed_ledger/msw7wpVC">distributed ledger</a>, where nodes collectively adhere to a <a href="/facts/Consensus_algorithm/rC0eH88V">consensus algorithm</a> <a href="/facts/Communication_protocol/5uady7cB">protocol</a> to add and validate new transaction blocks. Although blockchain records are not unalterable, since <a href="/facts/Fork_(blockchain)/5KUtGrbC">blockchain forks</a> are possible, blockchains may be considered <a href="/facts/Secure_by_design/Bf9qyAfv">secure by design</a> and exemplify a distributed computing system with high <a href="/facts/Byzantine_fault_tolerance/hucMXMBV">Byzantine fault tolerance</a>.
A blockchain was created by a person (or group of people) using the name (or <a href="/facts/Pseudonym/A5EjmWxQ">pseudonym</a>) <a href="/facts/Satoshi_Nakamoto/jP9akWPY">Satoshi Nakamoto</a> in 2008 to serve as the public <a href="/facts/Distributed_ledger/msw7wpVC">distributed ledger</a> for <a href="/facts/Bitcoin/UJvqfray">bitcoin</a> <a href="/facts/Cryptocurrency/Rg6JAS8y">cryptocurrency</a> transactions, based on previous work by <a href="/facts/Stuart_Haber/qAx1NzR3">Stuart Haber</a>, <a href="/facts/W._Scott_Stornetta/c7pb6KUW">W. Scott Stornetta</a>, and <a href="/facts/Dave_Bayer/qYyL7nIh">Dave Bayer</a>. The implementation of the blockchain within bitcoin made it the first digital currency to solve the <a href="/facts/Double-spending/meFaByPL">double-spending</a> problem without the need for a trusted authority or central <a href="/facts/Server_(computing)/dEaYFD7r">server</a>. The <a href="/facts/Bitcoin/UJvqfray">bitcoin</a> design has inspired other applications and blockchains that are readable by the public and are widely used by <a href="/facts/Cryptocurrencies/Rg6JAS8y">cryptocurrencies</a>. The blockchain may be considered a type of <a href="/facts/Payment_rail/H7d7686K">payment rail</a>.
Private blockchains have been proposed for business use. Computerworld called the marketing of such privatized blockchains without a proper security model "<a href="/facts/Snake_oil/mGozkeMX">snake oil</a>"; however, others have argued that permissioned blockchains, if carefully designed, may be more decentralized and therefore more secure in practice than permissionless ones.

Blockchain open-in-new

Blockchain