Hash
A hash is a short, fixed-length fingerprint of data made by a hash function. Change one character of the data and the hash changes completely, and you cannot rebuild the data from it.
How it works
A hash function takes any input, a word, a file or a block of transactions, and outputs a string of the same length. SHA-256, used by bitcoin, always outputs 256 bits, which is 64 hexadecimal characters. The same input always gives the same hash.
A good hash function works one way: you cannot work out the input from the hash, and it is practically impossible to find two different inputs with the same hash. That makes a hash a way to check integrity: compare fingerprints and you know whether anything changed.
Hashes are everywhere in crypto. Each block contains the previous block's hash, which is what makes the chain tamper-evident. PoW mining is guessing numbers until the block's hash falls below a target. Wallet addresses are derived from public keys by hashing, and every transaction has its own hash, its ID (TxID).
The SHA-256 hash of "hello" starts with 2cf24dba…, while the hash of "Hello" starts with 185f8db3…. One capital letter changes the whole result, yet both are 64 characters long.
Beginners confuse hashing with encryption and think a hash can be "decrypted". A hash is not a cipher and has no key. If someone asks for your transaction hash to check a payment, that is safe to share, but never send your private key or seed phrase to anyone for any reason.
Questions and answers
What is a hash in simple terms?
It is a digital fingerprint of data. It is short, always the same length and changes completely if the data changes even slightly.
What is a transaction hash (TxID)?
It is the unique ID of a transfer. You can paste it into a block explorer to find the transaction and check its status.
Can you get the original data from a hash?
No. Hash functions are one-way, so the only way back is guessing, which is practically impossible for anything but very short inputs.
Related terms
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Updated: 2026-10-19