Hash

A fixed-length fingerprint of arbitrary data. Bitcoin uses SHA-256 hashes for everything from block IDs to addresses.

A hash is the output of a one-way function — a mathematical operation that takes any input (a piece of text, a file, a Bitcoin block) and produces a fixed-length output (a string of letters and numbers). The same input always produces the same hash. Different inputs almost always produce different hashes. And critically: you can't reverse the operation — given a hash, you can't derive the input.

Bitcoin uses SHA-256, a specific hash function with strong cryptographic properties. Every transaction has a hash that uniquely identifies it. Every block has a hash that depends on its contents and on the hash of the previous block — that's what links the chain together.

For mining, hashes are the lottery ticket. Miners try trillions of slight variations of a block hoping to find one whose hash starts with enough leading zeros to satisfy the current difficulty target. The first to find one wins the block reward.

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Mining & nodes

How Bitcoin actually works. Miners, nodes, blocks, and what running your own changes.

Related terms

Glossary

Mining

The process of competing to add new blocks to the Bitcoin blockchain. Miners earn block rewards plus fees.

Glossary

Block

A bundle of Bitcoin transactions added to the blockchain roughly every ten minutes.

Glossary

Blockchain

The public ledger of every Bitcoin transaction, organised into a chain of blocks.

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