Cryptographic Hash

A cryptographic hash is a mathematical function that turns any input — a file, a transaction, an entire block — into a fixed-length string of characters called a hash or digest. The same input always produces the same output, the tiniest change produces a completely different result, and there is no practical way to work backwards from a digest to the original data. Blockchains use hash functions such as SHA-256 and Keccak to link blocks together, derive addresses from public keys and prove that stored data has not been altered. A hash is not encryption: it cannot be decrypted, only recomputed and compared, which is exactly what makes it a tamper-evident fingerprint.