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A blockchain is a decentralized, distributed ledger composed of cryptographically linked blocks.
Blockchain is a distributed digital ledger that records transactions in sequentially linked blocks. Each block contains transaction data, a timestamp, and the cryptographic hash of the previous block, creating a tamper-resistant chain. Transactions are maintained across a peer-to-peer network, allowing participants to independently verify records without relying on a central authority. Consensus mechanisms, such as proof of work and proof of stake, are used to validate and add new blocks. The design of blockchain technology helps prevent unauthorized alteration and solves the double-spending problem by ensuring that digital assets cannot be duplicated or transferred more than once. However, records are not absolutely immutable because forks, protocol changes, and attacks such as a 51% attack can affect the accepted chain. Blockchains may be public and permissionless, private and permissioned, consortium-based, or hybrid. Their applications extend beyond cryptocurrencies to areas such as supply chains, digital identity, payments, auditing, and data verification, although concerns remain regarding scalability, energy use, centralization, privacy, and security models.
A blockchain is a decentralized, distributed ledger composed of cryptographically linked blocks.
Each block commonly includes transaction data, a timestamp, and the previous block's hash, making retroactive alteration difficult.
Peer-to-peer networks and consensus algorithms validate transactions and maintain a shared version of the ledger.
Blockchain technology supports independent verification and addresses the digital double-spending problem without requiring a central authority.
Public, private, consortium, and hybrid blockchains differ in their access controls and levels of decentralization.
Blockchain security is strong by design but not absolute; forks, 51% attacks, governance decisions, and centralization risks can affect records.
Important challenges include scalability, transaction finality, energy consumption, privacy, interoperability, and the security of permissioned systems.
A shared database replicated across multiple network participants rather than controlled by a single central authority.
A collection of validated transactions and related metadata that is added to a blockchain.
A fixed-length digital fingerprint used to identify data and detect changes to it.
The first block in a blockchain, to which all subsequent blocks are ultimately linked.
A hierarchical structure of cryptographic hashes that efficiently represents and verifies the integrity of many transactions.
A protocol that enables network participants to agree on which transactions and blocks are valid.
A consensus method in which participants perform computational work to validate blocks and secure the network.
A consensus method in which validators are selected partly according to assets they commit to the network.
A divergence in the blockchain's history or protocol that can produce multiple competing versions of the chain.
The degree of confidence that a confirmed block will not later be reversed or replaced.
A blockchain that allows anyone to participate in transactions and, depending on the protocol, validation.
A blockchain that restricts network access or validation rights to authorized participants.
An attack in which an entity controls more than half of a network's relevant validation power and may manipulate transaction history.
The attempted use of the same digital asset in more than one transaction.
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