Irreversible protection algorithm for establishing a unique digital fingerprint of a string of characters of variable length (can be a document, an audio file, a public key, etc). Two perfectly identical documents have the same hash as a result of applying the same hash function. However, if they differ, even minimally, the hashes of the two documents will be noticeably different. This makes it possible to determine the integrity of considerable amounts of data without having to look at them.