What is Hashing?
Applying a one-way function that maps any input to a fixed-size digest, used for integrity checks and password storage.
Definition
A hash function deterministically maps input of any size to a fixed-length digest and cannot be feasibly reversed. Cryptographic hashes like SHA-256 guarantee that finding two inputs with the same digest is computationally infeasible, which underpins file integrity checks, Git commit IDs, and digital signatures. Password storage demands a different class: deliberately slow, memory-hard functions like bcrypt, scrypt, and Argon2 that throttle brute-force attempts — fast hashes like MD5 or plain SHA-256 are dangerously wrong for passwords. Unlike encryption, hashing has no key and no decryption; you verify by hashing again and comparing.