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diff --git a/src/lib/rng/hmac_rng/hmac_rng.h b/src/lib/rng/hmac_rng/hmac_rng.h
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+++ b/src/lib/rng/hmac_rng/hmac_rng.h
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+/*
+* HMAC RNG
+* (C) 2008,2013 Jack Lloyd
+*
+* Distributed under the terms of the Botan license
+*/
+
+#ifndef BOTAN_HMAC_RNG_H__
+#define BOTAN_HMAC_RNG_H__
+
+#include <botan/mac.h>
+#include <botan/rng.h>
+#include <vector>
+
+namespace Botan {
+
+/**
+* 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')
+*
+* However it actually can be parameterized with any two MAC functions,
+* not restricted to HMAC (this variation is also described in
+* Krawczyk's paper), for instance one could use HMAC(SHA-512) as the
+* extractor and CMAC(AES-256) as the PRF.
+*/
+class BOTAN_DLL HMAC_RNG : public RandomNumberGenerator
+   {
+   public:
+      void randomize(byte buf[], size_t len);
+      bool is_seeded() const;
+      void clear();
+      std::string name() const;
+
+      void reseed(size_t poll_bits);
+      void add_entropy(const byte[], size_t);
+
+      /**
+      * @param extractor a MAC used for extracting the entropy
+      * @param prf a MAC used as a PRF using HKDF construction
+      */
+      HMAC_RNG(MessageAuthenticationCode* extractor,
+               MessageAuthenticationCode* prf);
+   private:
+      std::unique_ptr<MessageAuthenticationCode> m_extractor;
+      std::unique_ptr<MessageAuthenticationCode> m_prf;
+
+      size_t m_collected_entropy_estimate = 0;
+      size_t m_output_since_reseed = 0;
+
+      secure_vector<byte> m_K;
+      u32bit m_counter = 0;
+   };
+
+}
+
+#endif