HMAC_RNG - based on the design described in "On Extract-then-Expand Key Derivation Functions and an HMAC-based KDF" by Hugo Krawczyk (henceforce, 'E-t-E')
Botan is released under the Simplified BSD License (see LICENSE.md)
(C) 2008,2013 Jack Lloyd (C) 2014-2015 Etienne Cimon
HMAC RNG