What is Hash Function?

A hash function maps input data of any size to a fixed-size string (the hash or digest). Good cryptographic hashes are deterministic, fast, and one-way — you cannot feasibly reverse the digest back to the input.

Hashes are used for integrity checks, deduplication, and (with salting) password storage. Common algorithms include SHA-256 and SHA-512; MD5 and SHA-1 are now considered insecure for cryptographic use.