What consensus mechanism does Bitcoin use?

Bitcoin uses proof of work as its consensus mechanism, allowing a distributed network to agree on which transactions and blockchain history to accept.

In Bitcoin mining, specialized computers repeatedly vary a number called a nonce while hashing a candidate block. A valid block must produce a hash below the network’s current difficulty target. Finding that result requires substantial computation, but other participants can verify it quickly. The winning miner broadcasts the block, and nodes accept it if its transactions and proof satisfy the protocol’s rules.

Proof of work helps protect Bitcoin from fraudulent history changes and double-spending. To rewrite confirmed blocks, an attacker would need to redo the computational work and catch up with the honest chain, an increasingly difficult task as more blocks are added. Bitcoin adjusts mining difficulty every 2,016 blocks so blocks arrive roughly every ten minutes despite changes in total computing power.

Proof of work is sometimes confused with proof of stake, used by other blockchain networks. Bitcoin has never switched to proof of stake. Its security model depends on energy-intensive computation, which is why mining’s electricity use remains a major subject of debate.