Hash
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In Brief
A hash is a fixed-length string of characters produced by running data through a cryptographic hash function; in blockchain, hashes uniquely fingerprint blocks and transactions and secure the chain against tampering.
What Is a Hash?
A hash is the output of a cryptographic hash function — an algorithm that takes any input (text, a file, a block of transactions) and produces a fixed-length string of characters. The same input always produces the same hash, but even the tiniest change to the input produces a completely different output.
In blockchain, hashes act like unique digital fingerprints for data. They link blocks together, secure transactions, and make tampering immediately detectable. Bitcoin, for example, uses the SHA-256 hash function.
How Does Hashing Work?
Data is fed into a hash function such as SHA-256.
The function processes the data and outputs a fixed-length hash (e.g. 64 hexadecimal characters for SHA-256).
The same input always yields the same hash — it is deterministic.
The process is one-way: you cannot reverse a hash back into the original data.
Changing even one character of the input produces a totally different, unpredictable hash (the "avalanche effect").
Key Properties of Cryptographic Hashes
| Property | What It Means |
|---|---|
| Deterministic | Same input always gives the same output |
| Fixed length | Output size is constant regardless of input size |
| One-way | Cannot reverse the hash to recover the input |
| Avalanche effect | A tiny input change drastically changes the output |
| Collision resistant | Extremely hard to find two inputs with the same hash |
How Are Hashes Used in Blockchain?
Linking blocks — each block stores the hash of the previous block, forming the chain. Altering an old block would change its hash and break every block after it.
Transaction integrity — transactions are hashed so any change is instantly detectable.
Proof of Work mining — miners search for a block hash below a target value to validate the block.
Addresses — wallet addresses are often derived from hashes of public keys.
Why Hashes Make Blockchains Tamper-Proof
Because each block's hash depends on its contents and the previous block's hash, the blocks form an unbreakable chain. To alter a past transaction, an attacker would have to recompute the hashes of that block and every subsequent block faster than the rest of the network — practically impossible on a large network.
Hashes and Trust Wallet
Every transaction you make in Trust Wallet is identified by a unique transaction hash (TXID), which you can use to look up its status on a block explorer. As a non-custodial wallet, Trust Wallet relies on the same cryptographic principles — hashing and digital signatures — to keep your funds secure across 100+ blockchains, with only you in control of your private keys.