Bitcoin protocol

The Bitcoin protocol is the rule system that coordinates the Bitcoin network and defines how transactions, blocks, ownership, issuance, and consensus operate. It is not a company, exchange, payment processor, or centrally managed commercial brand. Instead, it is an open, decentralized communications and accounting protocol implemented by independently operated network nodes, mining systems, wallet software, and other related tools. Bitcoin transactions are created and signed with public-key cryptography. A wallet constructs a transaction that transfers control of bitcoin from one set of cryptographic keys to another, and broadcasts it to the peer-to-peer network. Nodes relay transactions on a best-effort basis and independently check whether they follow the protocol's rules, including whether the inputs are valid and have not already been spent. Nodes may leave and rejoin the network; after reconnecting, they can obtain and verify blocks needed to update their local copy of the ledger. The protocol's central record is the blockchain, a public, ordered history of transactions grouped into blocks. Mining nodes compete to produce a valid proof-of-work by finding a block hash that satisfies a dynamically adjusted difficulty target. The successful block is proposed to the network, and nodes accept it only if it conforms to the protocol. When competing histories exist, the chain representing the greatest cumulative proof-of-work is treated as authoritative. This mechanism allows participants without a central administrator to converge on a shared transaction history, while making retrospective alteration increasingly difficult as additional blocks are added. Mining also provides the original method for issuing new bitcoin. The first transaction in a valid block can pay a block subsidy to the miner, together with applicable transaction fees. The subsidy is periodically reduced by half after each 210,000-block interval. The reward began at 50 bitcoin per block, was reduced to 25 in 2012, 12.5 in 2016, 6.25 in 2020, and 3.125 at the April 2024 halving. The programmed issuance schedule is intended to end new coin creation after the permitted sequence of halvings, although the network's monetary rules can only change if sufficient participants adopt compatible software and consensus is achieved. The protocol includes defenses against unauthorized spending, forgery, and double spending. A user who receives bitcoin generally controls it through a private key, and another party cannot create a valid spending signature without that key. The public ledger allows nodes to identify attempts to spend the same inputs more than once. Transaction recipients can wait for additional blocks, called confirmations, to reduce the probability that a transaction is reversed by a competing chain. Simplified payment verification allows some users to verify payments using block headers and Merkle proofs rather than maintaining the entire transaction history. Bitcoin's architecture has also created important limitations and debates. Proof-of-work requires substantial computational resources and has encouraged specialized ASIC hardware and mining pools. Transaction throughput, confirmation time, fees, privacy, and the geographic and organizational concentration of mining have all been subjects of technical and policy discussion. The protocol is pseudonymous rather than inherently anonymous: transaction-graph analysis and network metadata can sometimes associate addresses with users. Its elliptic-curve signatures and hash-based proof-of-work were designed for conventional computing and may require future adaptation if sufficiently capable quantum computers become available. Protocol changes require coordination among users, node operators, miners, developers, businesses, and other participants. As a result, Bitcoin has no formal central owner or executive leadership structure. Its design has nevertheless influenced numerous other cryptocurrencies, distrib…

Bitcoin protocol history begins with the publication of the Bitcoin design and the emergence of a peer-to-peer network intended to transfer digital value without a central intermediary. The protocol combined several previously studied ideas—cryptographic signatures, a public transaction record, hash-linked data, proof-of-work, and network consensus—into an operating system for digital cash. Rather than relying on a company or central clearinghouse, it gave independently operated nodes the ability to validate transactions and reject records that violated shared rules. The blockchain became the protocol's core accounting mechanism. Transactions are broadcast across an ad hoc network and collected by miners into blocks. Each block references earlier history and includes proof-of-work, creating a cumulative record whose alteration requires repeating the computational work for the affected block and all later blocks. Nodes select the valid chain with the greatest accumulated work when competing histories arise. This approach addresses the double-spending problem by making one public transaction history the basis for determining which transfers are accepted. Mining initially could be performed with general-purpose computer processors. As participation and competition increased, miners adopted graphics processors, field-programmable gate arrays, and eventually application-specific integrated circuits. Mining pools developed because pooling computing power reduces the income variance faced by individual operators. The changing hardware landscape and the protocol's periodic difficulty adjustment helped preserve an average block interval of roughly ten minutes despite fluctuations in total network computing power. Bitcoin's issuance rules were designed into the protocol. A miner may claim a block subsidy through the first transaction in a block, and that subsidy is reduced by half every 210,000 blocks. The reward fell from 50 bitcoin to 25 in 2012, 12.5 in 2016, 6.25 in 2020, and 3.125 in April 2024. The schedule made monetary issuance predictable and progressively reduced, while transaction fees can provide an increasing component of miner compensation as subsidy issuance declines. The protocol's development has been shaped by distributed consensus rather than executive decision-making. Changes require compatible software and sufficient agreement among relevant participants. This governance model can make upgrades difficult, but it also limits the ability of any single organization to alter the ledger or monetary rules unilaterally. Disagreements can result in temporary or persistent blockchain forks when participants run incompatible rules. Over time, the protocol became the reference design for a broad class of cryptocurrencies and blockchain systems. It also generated continuing debate over transaction capacity, fee markets, energy consumption, mining-pool concentration, privacy, regulatory treatment, and the practical security of digital ownership. Bitcoin addresses are pseudonymous, and transaction histories can sometimes be linked through graph analysis or network information. The protocol's cryptographic assumptions are secure against ordinary current computing techniques but may require future changes in response to cryptographically relevant quantum computers. Its continuing operation depends on voluntary participation by nodes, miners, wallet users, developers, merchants, and other network actors rather than on a formal corporate hierarchy.

1. 2024Fourth block-subsidy halving

   At block 840,000 on 20 April 2024, the block subsidy fell from 6.25 bitcoin to 3.125 bitcoin.

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2. 2021China prohibited Bitcoin mining

   Regulatory action in China led to a major relocation and reorganization of mining activity.

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3. 2020Third block-subsidy halving

   The mining reward declined from 12.5 bitcoin to 6.25 bitcoin per block.

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4. 2016Second block-subsidy halving

   The programmed reward declined from 25 bitcoin to 12.5 bitcoin per block.

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5. 2012First scheduled block-subsidy halving

   The mining subsidy decreased from 50 bitcoin to 25 bitcoin per block after the network reached the first 210,000-block interval.

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6. 2009Peer-to-peer Bitcoin network established

   The Bitcoin protocol began operating as a decentralized network in which nodes could broadcast transactions, validate blocks, and maintain a shared blockchain without central oversight.

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Decentralized digital-currency and peer-to-peer payment protocol

• Bitcoin blockchainDistributed ledger

  The blockchain is the protocol's public, append-only transaction history. Transactions are grouped into blocks, and each block is linked to earlier blocks through cryptographic hashes. Nodes independently download and verify this history, using consensus rules and cumulative proof-of-work to determine which valid chain represents the accepted ledger.

• Bitcoin proof-of-work miningConsensus and issuance

  Mining is the competitive process through which specialized nodes assemble transactions into blocks and search for a valid double-SHA-256 hash. Successful miners may receive the block subsidy and transaction fees. Difficulty is adjusted approximately every two weeks to moderate changes in network computing power and preserve an average block interval of about ten minutes.

• Bitcoin transactionsPayment protocol

  Transactions are cryptographically signed messages that propose changes to ownership recorded by the ledger. Network nodes validate their signatures and spending conditions, relay acceptable transactions, and reject attempts that conflict with the protocol, including attempts to spend the same inputs more than once.

• Simplified payment verificationVerification method

  Simplified payment verification allows a client to verify a transaction without storing the complete blockchain. It uses block headers and Merkle-tree proofs to establish that a transaction is included in a block on the chain with the greatest accumulated proof-of-work, subject to the security assumptions of the method.

• 2024Scheduled reduction of block subsidyStrategy

  The protocol reduces new bitcoin issuance after every 210,000 blocks as part of its predetermined monetary design.

  What changed. The subsidy was reduced from 6.25 bitcoin to 3.125 bitcoin at block 840,000.

  Aftermath. Miners continued to receive transaction fees in addition to the lower subsidy, while the next scheduled reduction is expected after another 210,000 blocks.

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• 2024Bitcoin block subsidy reduced to 3.125 bitcoin

  At block 840,000, the protocol's programmed halving reduced the mining subsidy from 6.25 bitcoin to 3.125 bitcoin per block.

  OtherProduct generation
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• 2022Bitcoin mining's environmental impact remained a subject of research

  Research cited in the protocol article revisited estimates of Bitcoin's carbon footprint and contributed to continuing debate about the energy use of proof-of-work mining.

  OtherRegulation
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• 2021China's mining ban reshaped the geographic distribution of Bitcoin mining

  The reference material describes China's ban on Bitcoin mining as a major factor in the subsequent distribution of mining activity, with the United States holding the largest share of mining pools at the time described.

  RegulationOther
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1. Bitcoin protocol
2. Revisiting Bitcoin's carbon footprint