diff --git a/include/polarssl/hmac_drbg.h b/include/polarssl/hmac_drbg.h
new file mode 100644
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+++ b/include/polarssl/hmac_drbg.h
@@ -0,0 +1,112 @@
+/**
+ * \file hmac_drbg.h
+ *
+ * \brief HMAC_DRBG (NIST SP 800-90A)
+ *
+ *  Copyright (C) 2014, Brainspark B.V.
+ *
+ *  This file is part of PolarSSL (http://www.polarssl.org)
+ *  Lead Maintainer: Paul Bakker <polarssl_maintainer at polarssl.org>
+ *
+ *  All rights reserved.
+ *
+ *  This program is free software; you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation; either version 2 of the License, or
+ *  (at your option) any later version.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License along
+ *  with this program; if not, write to the Free Software Foundation, Inc.,
+ *  51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+#ifndef POLARSSL_HMAC_DRBG_H
+#define POLARSSL_HMAC_DRBG_H
+
+#include "md.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/*
+ * Simplified HMAC_DRBG context.
+ * No reseed counter, no prediction resistance flag.
+ */
+typedef struct
+{
+    md_context_t md_ctx;
+    unsigned char V[POLARSSL_MD_MAX_SIZE];
+    unsigned char K[POLARSSL_MD_MAX_SIZE];
+} hmac_drbg_context;
+
+/**
+ * \brief               HMAC_DRBG initialisation
+ *
+ * \param ctx           HMAC_DRBG context to be initialised
+ * \param md_info       MD algorithm to use for HMAC_DRBG
+ * \param data          Concatenation of entropy string and additional data
+ * \param data_len      Length of data in bytes
+ *
+ * \todo                Use entropy callback rather than buffer.
+ *
+ * \return              0 if successful, or
+ *                      POLARSSL_ERR_MD_BAD_INPUT_DATA, or
+ *                      POLARSSL_ERR_MD_ALLOC_FAILED
+ */
+int hmac_drbg_init( hmac_drbg_context *ctx,
+                    const md_info_t * md_info,
+                    const unsigned char *data, size_t data_len );
+
+/**
+ * \brief               HMAC_DRBG update state
+ *
+ * \param ctx           HMAC_DRBG context
+ * \param additional    Additional data to update state with, or NULL
+ * \param add_len       Length of additional data, or 0
+ *
+ * \note                Additional data is optional, pass NULL and 0 as second
+ *                      third argument if no additional data is being used.
+ */
+void hmac_drbg_update( hmac_drbg_context *ctx,
+                       const unsigned char *additional, size_t add_len );
+
+/**
+ * \brief               HMAC_DRBG generate random
+ *
+ * Note: Automatically reseeds if reseed_counter is reached. (TODO)
+ *
+ * \param p_rng         HMAC_DRBG context
+ * \param output        Buffer to fill
+ * \param output_len    Length of the buffer
+ *
+ * \return              0 if successful.
+ */
+int hmac_drbg_random( void *p_rng, unsigned char *output, size_t out_len );
+
+/**
+ * \brief               Free an HMAC_DRBG context
+ *
+ * \param ctx           HMAC_DRBG context to free.
+ */
+void hmac_drbg_free( hmac_drbg_context *ctx );
+
+
+#if defined(POLARSSL_SELF_TEST)
+/**
+ * \brief               Checkup routine
+ *
+ * \return              0 if successful, or 1 if the test failed
+ */
+int hmac_drbg_self_test( int verbose );
+#endif
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* hmac_drbg.h */