Hash function
Mining & BlocksThis term is part of the Bitcoin glossary — See all terms
A hash function is a one-way machine turning any data into a fixed-length fingerprint: the same input gives the same output, a tiny change gives a totally different one.
A hash function is like a blender for data: you pour something in, it comes out as a uniform mush of fixed length, and you cannot un-blend it. Feed in the same input twice and you get exactly the same output every time — that determinism lets everyone agree on what a block's fingerprint should be. Change a single character and the output changes completely, as if you had swapped an ingredient in a recipe.
Bitcoin leans on those two habits constantly. Addresses are hashes of public keys; transactions are linked through a Merkle tree of hashes; miners hash block headers trillions of times a second looking for a value below the target. Because hashing is cheap to do but impossible to undo, it underpins both mining and the security of your wallet. You can check any of these fingerprints yourself with this block explorer.
