Summary

A hash_function maps an input to a fixed_size_output called a hash or digest. It is deterministic: the same input yields the same output. Good hashes show the avalanche_effect, where small input changes produce very different outputs. Security goals include preimage_resistance and collision_resistance, making reversal and duplicate outputs impractical. Uses include hash_table indexing, file checksum and data_integrity checks, and cryptographic_hash for signatures and passwords. Remember: fast computation, uniform distribution, and treating the hash as a short fingerprint of data.