Cryptographic hash function

A deterministic function that maps data of any length to a fixed-length digest. It is designed to make finding collisions or recovering an input from its digest computationally infeasible.

Hash function: A function that maps inputs to values in a fixed or variable output space. Cryptographic hashes are the security-focused members of this broader family.
Compression function (cryptography): A fixed-input-length function that produces a shorter fixed-length output in a hash construction. Iterated hash designs repeatedly apply one to message blocks and an internal state.
Message authentication code: A keyed function that authenticates a message's integrity and origin using a shared secret. Unlike an unkeyed hash, a MAC prevents outsiders from forging valid authentication tags.
MD5: A 128-bit cryptographic hash algorithm whose collision resistance is broken. Its practical collisions show why legacy hash functions cannot be trusted for security.
Collision resistance: The computational difficulty of finding distinct inputs that produce the same hash output. This is one of the defining security goals for a cryptographic hash.
Block cipher: A symmetric-key algorithm that transforms fixed-size data blocks under a secret key. Some hash designs adapt block ciphers to build compression functions.
HMAC: A message authentication code built from a cryptographic hash function and a secret key. It uses hashing to authenticate messages without exposing the key.
SHA-1: A 160-bit hash algorithm for which practical collision attacks have been demonstrated. It remains a prominent example of a once-standard hash becoming unsafe.
Preimage resistance: The computational difficulty of finding an input that produces a specified hash output. It captures the intended difficulty of reversing a digest to recover an input.
Sponge function: A construction that absorbs input into an internal state and then squeezes out output. It underlies SHA-3 and supports outputs of varying lengths.

Linked from 29 pages