What cryptographic hash function is used in Bitcoin mining?

Bitcoin mining uses SHA-256, applied twice in the network’s proof-of-work calculation.

Miners assemble candidate blocks containing transactions, a timestamp, a reference to the previous block, and a variable nonce. They repeatedly change the nonce and hash the block header until the resulting number is below Bitcoin’s difficulty target. The winning hash is easy for other nodes to verify, but finding it requires enormous trial-and-error computation.

The “twice” detail is a common source of confusion. SHA-256 is the underlying function, while SHA-256d means double SHA-256. Bitcoin uses double hashing for block headers and several other protocol operations; the quiz’s answer is therefore correctly stated at the algorithm-family level.

Bitcoin’s difficulty adjusts every 2,016 blocks, targeting an average block interval of about 10 minutes. Modern miners use application-specific integrated circuits (ASICs), which are vastly faster and more efficient at SHA-256 calculations than general-purpose computers.