key derivation function

In cryptography, a key derivation function (or KDF) derives one or more secret keys from a secret value such as a master key, a password, or a passphrase using a pseudo-random function. KDFs can be used to stretch keys into longer keys or to obtain keys of a required format, such as converting a group element that is the result of a Diffie–Hellman key exchange into a symmetric key for use with AES. Keyed cryptographic hash functions are popular examples of pseudo-random functions used for key derivation.