Nonce

A nonce (“number used once”) is a value that is varied to produce a different cryptographic result. In proof-of-work mining it is the number miners repeatedly change while searching for a valid block.

How it works

To mine a block, a miner hashes the block’s contents together with a nonce and checks whether the resulting hash meets the network’s difficulty target. If not, they change the nonce and try again, billions of times per second, until one produces a qualifying hash. The winning nonce is included in the block so anyone can verify the solution instantly.

Why it matters

The nonce search is the “work” in proof of work: it is hard to find but trivial to check, which is what secures the network. A separate kind of nonce is also used in account-based chains to order each address’s transactions and prevent replay.

Example

A miner that finds the right nonce earns the block reward; everyone else immediately verifies their answer and moves on.