A hash is a short string of characters calculated from data by a hash functionHash functionA mathematical function that turns data of any size into a short fingerprint of fixed length, called a hash.. It works like a fingerprint: the same data always gives the same hash, but the smallest change to the data gives a completely different one.
What does a hash look like?
Bitcoin uses the SHA-256 hash function, which always returns a 64-character string, however much data you put in. See how one small letter changes everything:
- "Hello" gives
185f8db32271fe25f561a6fc938b2e264306ec304eda518007d1764826381969 - "hello" gives
2cf24dba5fb0a30e26e83b2ac5b9e29e1b161e5c1fa7425e73043362938b9824
A hash function only works one way. It takes a computer a fraction of a second to calculate a hash, but it is impossible to work back from the hash to the data.
What are hashes used for?
- Linking blocks together. Each BlockBlockA batch of transactions added to a blockchain in one go, together with a reference to the block before it. contains the hash of the block before it. If someone changed an old transaction, the hash would change and the chain would break. That is what makes the BlockchainBlockchainA public ledger where transactions are grouped into blocks, each linked to the one before, so past records can't be altered without it showing. practically unchangeable.
- Mining. In MiningMiningThe process in which computers compete to solve a puzzle so they can add the next block to the blockchain and earn new bitcoin and fees., computers calculate hashes over and over, looking for one that meets the network's target. The number of attempts per second is called the HashrateHashrateThe total number of guesses a network's mining computers make each second, and a measure of how well the network is protected from attack..
- Identifying transactions and addresses. Every transaction gets a hash as its ID, and wallet addresses are also derived using hash functions.
Hashing is part of CryptographyCryptographyMathematical methods that protect information and prove who sent it, forming the basis of security in crypto., but it doesn't hide information. It proves that the information hasn't changed.
Everything in Myntkaup Learn is written and regularly reviewed by the Myntkaup editorial team. It is for education and is not investment advice. Editorial policy. Updated 18 October 2026.