What Is a Hash in Crypto?

A hash is a fixed-length string of characters produced by running data through a cryptographic hash function. Blockchains use hashes extensively: every transaction has a transaction hash (also called a TXID) that uniquely identifies it, and each block contains the hash of the previous block, creating the chain.

How Hashing Works

A hash function takes any input (a word, a file, a transaction’s data) and produces a fixed-length output. The same input always produces the same hash, but even a tiny change in the input produces a completely different hash. This property, called determinism and collision resistance, makes hashes useful for verifying data integrity: if the hash of a file matches the expected value, the file has not been tampered with.

Transaction Hashes in Crypto

Every confirmed transaction on a blockchain has a unique hash you can use to look it up on a block explorer. When you send a transaction, the network returns a TXID (transaction ID) in the form of a hash. You can paste this hash into a Solana explorer like Solscan or SolanaFM to see the status, the accounts involved, the amounts transferred, and any errors if the transaction failed.

Block Hashes and the Chain Structure

Each block in the blockchain contains the hash of the previous block in its header. This means changing data in any prior block would change that block’s hash, which would invalidate every subsequent block’s reference to it. This linkage is what makes the blockchain tamper-resistant: you cannot quietly alter old transactions without breaking the entire chain of hashes that follows. Keeping your funds in a non-custodial wallet means only you control the private key that signs transactions whose hashes are recorded permanently on-chain.

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