A cryptographic function which takes an input (or 'message') and returns a fixed-size alphanumeric string, which is called the hash value (sometimes called a message digest, a digital fingerprint, a digest or a checksum). A hash function (or hash algorithm) is a process by which a document (i.e. a piece of data or file) is processed into a small piece of data (usually 32 bytes) which looks completely random, and from which no meaningful data can be recovered about the document, but which has the important property that the result of hashing one particular document is always the same. Additionally, it is crucially important that it is computationally infeasible to find two documents that have the same hash. Generally, changing even one letter in a document will completely randomize the hash; for example, the SHA3 hash of "Saturday" is
c38bbc8e93c09f6ed3fe39b5135da91ad1a99d397ef16948606cdcbd14929f9d, whereas the SHA3 hash of "Caturday" is
b4013c0eed56d5a0b448b02ec1d10dd18c1b3832068fbbdc65b98fa9b14b6dbf. Hashes are usually used as a way of creating a globally agreed-upon identifier for a particular document that cannot be forged.