Cryptographic Hash Function
A one-way function that maps arbitrary input to a fixed-size output, designed to be collision-resistant and irreversible.
A cryptographic hash function takes input of any length and produces a fixed-length digest (e.g. 256 bits for SHA-256). It must be one-way (no efficient way to recover input from the digest), second-preimage resistant (hard to find a different input with the same digest), and collision-resistant (hard to find any two inputs that hash to the same digest). Hashes underpin password storage (with a slow KDF wrapper), digital signatures, TLS certificate fingerprints, Git commit IDs, blockchain proofs, and DNSSEC NSEC3 hashing. MD5 and SHA-1 are broken for collision resistance and should not be used in new security contexts.