HMAC-based Extract-and-Expand Key Derivation Function (HKDF)
Description
This module implements the HMAC Key Derivation function, defined at
http://tools.ietf.org/html/draft-krawczyk-hkdf-01. There are two
interfaces: a functional interface, with separate extract and expand
functions as defined in the draft RFC, and a wrapper class for these
functions.
