Cryptographic Hashing

Hashing involves an algorithm (a “hash function”) generating a fixed output (hash) from a data input of any size. In most blockchains, the hash is an alphanumeric string of fixed length.

Because a hash is dependent on block data, hashes serve as unique identifiers for blocks on the chain. Running the same data through the hash function will produce the same hash no matter how many times you perform the operation.

A change in a block’s data automatically triggers the generation of a new hash. Which is why it’s easy to know if a block containing transactions has been altered.