Hash

A hash is a fixed-length string of characters produced by running data through a cryptographic hash function. It acts as a unique digital fingerprint of that data.

How it works

A hash function takes an input of any size and returns an output of fixed length. The same input always yields the same hash, but even a tiny change to the input produces a completely different result, and the process cannot practically be reversed to recover the original data. These properties make hashes ideal for verifying integrity.

Why it matters

Hashes are fundamental to blockchains: each block is identified by its hash and references the previous block’s hash, which is what makes the chain tamper-evident. Proof-of-work mining is essentially a race to find an input that produces a hash meeting a target.

Example

Changing a single character in a block’s data would change its hash entirely, instantly signalling that the data was altered.