Blockchain

A blockchain is a distributed digital ledger in which records are grouped into cryptographically linked blocks and replicated across a network. Its participants use a shared protocol to agree on the ledger’s history.

Cryptographic hash function: A function that maps data to a fixed-length value, designed to make collisions and recovery of the input computationally difficult. Each block’s hash links it to earlier data, so changes disrupt the chain.
Distributed ledger: A database whose records are shared and synchronized across multiple computers or organizations. Blockchain is one way to structure and synchronize a distributed ledger.
Bitcoin: A peer-to-peer cryptocurrency system introduced in 2009, using proof of work to order transactions in a public blockchain. Bitcoin is the first widely adopted blockchain-based cryptocurrency.
Relational database: A database that organizes data into tables of rows and columns linked through defined relationships. A conventional database usually relies on an administrator rather than distributed consensus to authorize updates.
Decentralization: The distribution of authority, control, or decision-making across multiple participants rather than a central body. Blockchain aims to reduce reliance on a single recordkeeping authority, though control can still concentrate.
Merkle tree: A tree of hashes that summarizes a collection of data and supports efficient proofs about individual entries. Blockchains use Merkle roots to summarize transactions compactly.
Digital signature: A cryptographic value that verifies a message’s origin and integrity using a private key and corresponding public key. Signatures let nodes verify who authorized a transaction without revealing private keys.
Ethereum: A blockchain platform that supports programmable smart contracts and its native cryptocurrency, ether. Ethereum extends blockchain use from transfers to general-purpose on-chain programs.
Centralized database: A database controlled and maintained by a central authority or server. Blockchain distributes recordkeeping among network participants instead of assigning it to one operator.
Byzantine fault tolerance: The ability of a distributed system to reach agreement despite some participants behaving arbitrarily or maliciously. Blockchain consensus protocols address agreement among nodes that may fail or act adversarially.

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