diff --git a/library/hmac_drbg.c b/library/hmac_drbg.c
new file mode 100644
index 0000000..aff2cdb
--- /dev/null
+++ b/library/hmac_drbg.c
@@ -0,0 +1,530 @@
+/*
+ *  HMAC_DRBG implementation (NIST SP 800-90)
+ *
+ *  Copyright (C) 2006-2015, ARM Limited, All Rights Reserved
+ *  SPDX-License-Identifier: Apache-2.0
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License"); you may
+ *  not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *  http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ *  WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ *
+ *  This file is part of Mbed Crypto (https://tls.mbed.org)
+ */
+
+/*
+ *  The NIST SP 800-90A DRBGs are described in the following publication.
+ *  http://csrc.nist.gov/publications/nistpubs/800-90A/SP800-90A.pdf
+ *  References below are based on rev. 1 (January 2012).
+ */
+
+#if !defined(MBEDCRYPTO_CONFIG_FILE)
+#include "mbedcrypto/config.h"
+#else
+#include MBEDCRYPTO_CONFIG_FILE
+#endif
+
+#if defined(MBEDCRYPTO_HMAC_DRBG_C)
+
+#include "mbedcrypto/hmac_drbg.h"
+#include "mbedcrypto/platform_util.h"
+
+#include <string.h>
+
+#if defined(MBEDCRYPTO_FS_IO)
+#include <stdio.h>
+#endif
+
+#if defined(MBEDCRYPTO_SELF_TEST)
+#if defined(MBEDCRYPTO_PLATFORM_C)
+#include "mbedcrypto/platform.h"
+#else
+#include <stdio.h>
+#define mbedcrypto_printf printf
+#endif /* MBEDCRYPTO_SELF_TEST */
+#endif /* MBEDCRYPTO_PLATFORM_C */
+
+/*
+ * HMAC_DRBG context initialization
+ */
+void mbedcrypto_hmac_drbg_init( mbedcrypto_hmac_drbg_context *ctx )
+{
+    memset( ctx, 0, sizeof( mbedcrypto_hmac_drbg_context ) );
+
+#if defined(MBEDCRYPTO_THREADING_C)
+    mbedcrypto_mutex_init( &ctx->mutex );
+#endif
+}
+
+/*
+ * HMAC_DRBG update, using optional additional data (10.1.2.2)
+ */
+void mbedcrypto_hmac_drbg_update( mbedcrypto_hmac_drbg_context *ctx,
+                       const unsigned char *additional, size_t add_len )
+{
+    size_t md_len = mbedcrypto_md_get_size( ctx->md_ctx.md_info );
+    unsigned char rounds = ( additional != NULL && add_len != 0 ) ? 2 : 1;
+    unsigned char sep[1];
+    unsigned char K[MBEDCRYPTO_MD_MAX_SIZE];
+
+    for( sep[0] = 0; sep[0] < rounds; sep[0]++ )
+    {
+        /* Step 1 or 4 */
+        mbedcrypto_md_hmac_reset( &ctx->md_ctx );
+        mbedcrypto_md_hmac_update( &ctx->md_ctx, ctx->V, md_len );
+        mbedcrypto_md_hmac_update( &ctx->md_ctx, sep, 1 );
+        if( rounds == 2 )
+            mbedcrypto_md_hmac_update( &ctx->md_ctx, additional, add_len );
+        mbedcrypto_md_hmac_finish( &ctx->md_ctx, K );
+
+        /* Step 2 or 5 */
+        mbedcrypto_md_hmac_starts( &ctx->md_ctx, K, md_len );
+        mbedcrypto_md_hmac_update( &ctx->md_ctx, ctx->V, md_len );
+        mbedcrypto_md_hmac_finish( &ctx->md_ctx, ctx->V );
+    }
+}
+
+/*
+ * Simplified HMAC_DRBG initialisation (for use with deterministic ECDSA)
+ */
+int mbedcrypto_hmac_drbg_seed_buf( mbedcrypto_hmac_drbg_context *ctx,
+                        const mbedcrypto_md_info_t * md_info,
+                        const unsigned char *data, size_t data_len )
+{
+    int ret;
+
+    if( ( ret = mbedcrypto_md_setup( &ctx->md_ctx, md_info, 1 ) ) != 0 )
+        return( ret );
+
+    /*
+     * Set initial working state.
+     * Use the V memory location, which is currently all 0, to initialize the
+     * MD context with an all-zero key. Then set V to its initial value.
+     */
+    mbedcrypto_md_hmac_starts( &ctx->md_ctx, ctx->V, mbedcrypto_md_get_size( md_info ) );
+    memset( ctx->V, 0x01, mbedcrypto_md_get_size( md_info ) );
+
+    mbedcrypto_hmac_drbg_update( ctx, data, data_len );
+
+    return( 0 );
+}
+
+/*
+ * HMAC_DRBG reseeding: 10.1.2.4 (arabic) + 9.2 (Roman)
+ */
+int mbedcrypto_hmac_drbg_reseed( mbedcrypto_hmac_drbg_context *ctx,
+                      const unsigned char *additional, size_t len )
+{
+    unsigned char seed[MBEDCRYPTO_HMAC_DRBG_MAX_SEED_INPUT];
+    size_t seedlen;
+
+    /* III. Check input length */
+    if( len > MBEDCRYPTO_HMAC_DRBG_MAX_INPUT ||
+        ctx->entropy_len + len > MBEDCRYPTO_HMAC_DRBG_MAX_SEED_INPUT )
+    {
+        return( MBEDCRYPTO_ERR_HMAC_DRBG_INPUT_TOO_BIG );
+    }
+
+    memset( seed, 0, MBEDCRYPTO_HMAC_DRBG_MAX_SEED_INPUT );
+
+    /* IV. Gather entropy_len bytes of entropy for the seed */
+    if( ctx->f_entropy( ctx->p_entropy, seed, ctx->entropy_len ) != 0 )
+        return( MBEDCRYPTO_ERR_HMAC_DRBG_ENTROPY_SOURCE_FAILED );
+
+    seedlen = ctx->entropy_len;
+
+    /* 1. Concatenate entropy and additional data if any */
+    if( additional != NULL && len != 0 )
+    {
+        memcpy( seed + seedlen, additional, len );
+        seedlen += len;
+    }
+
+    /* 2. Update state */
+    mbedcrypto_hmac_drbg_update( ctx, seed, seedlen );
+
+    /* 3. Reset reseed_counter */
+    ctx->reseed_counter = 1;
+
+    /* 4. Done */
+    return( 0 );
+}
+
+/*
+ * HMAC_DRBG initialisation (10.1.2.3 + 9.1)
+ */
+int mbedcrypto_hmac_drbg_seed( mbedcrypto_hmac_drbg_context *ctx,
+                    const mbedcrypto_md_info_t * md_info,
+                    int (*f_entropy)(void *, unsigned char *, size_t),
+                    void *p_entropy,
+                    const unsigned char *custom,
+                    size_t len )
+{
+    int ret;
+    size_t entropy_len, md_size;
+
+    if( ( ret = mbedcrypto_md_setup( &ctx->md_ctx, md_info, 1 ) ) != 0 )
+        return( ret );
+
+    md_size = mbedcrypto_md_get_size( md_info );
+
+    /*
+     * Set initial working state.
+     * Use the V memory location, which is currently all 0, to initialize the
+     * MD context with an all-zero key. Then set V to its initial value.
+     */
+    mbedcrypto_md_hmac_starts( &ctx->md_ctx, ctx->V, md_size );
+    memset( ctx->V, 0x01, md_size );
+
+    ctx->f_entropy = f_entropy;
+    ctx->p_entropy = p_entropy;
+
+    ctx->reseed_interval = MBEDCRYPTO_HMAC_DRBG_RESEED_INTERVAL;
+
+    /*
+     * See SP800-57 5.6.1 (p. 65-66) for the security strength provided by
+     * each hash function, then according to SP800-90A rev1 10.1 table 2,
+     * min_entropy_len (in bits) is security_strength.
+     *
+     * (This also matches the sizes used in the NIST test vectors.)
+     */
+    entropy_len = md_size <= 20 ? 16 : /* 160-bits hash -> 128 bits */
+                  md_size <= 28 ? 24 : /* 224-bits hash -> 192 bits */
+                                  32;  /* better (256+) -> 256 bits */
+
+    /*
+     * For initialisation, use more entropy to emulate a nonce
+     * (Again, matches test vectors.)
+     */
+    ctx->entropy_len = entropy_len * 3 / 2;
+
+    if( ( ret = mbedcrypto_hmac_drbg_reseed( ctx, custom, len ) ) != 0 )
+        return( ret );
+
+    ctx->entropy_len = entropy_len;
+
+    return( 0 );
+}
+
+/*
+ * Set prediction resistance
+ */
+void mbedcrypto_hmac_drbg_set_prediction_resistance( mbedcrypto_hmac_drbg_context *ctx,
+                                          int resistance )
+{
+    ctx->prediction_resistance = resistance;
+}
+
+/*
+ * Set entropy length grabbed for reseeds
+ */
+void mbedcrypto_hmac_drbg_set_entropy_len( mbedcrypto_hmac_drbg_context *ctx, size_t len )
+{
+    ctx->entropy_len = len;
+}
+
+/*
+ * Set reseed interval
+ */
+void mbedcrypto_hmac_drbg_set_reseed_interval( mbedcrypto_hmac_drbg_context *ctx, int interval )
+{
+    ctx->reseed_interval = interval;
+}
+
+/*
+ * HMAC_DRBG random function with optional additional data:
+ * 10.1.2.5 (arabic) + 9.3 (Roman)
+ */
+int mbedcrypto_hmac_drbg_random_with_add( void *p_rng,
+                               unsigned char *output, size_t out_len,
+                               const unsigned char *additional, size_t add_len )
+{
+    int ret;
+    mbedcrypto_hmac_drbg_context *ctx = (mbedcrypto_hmac_drbg_context *) p_rng;
+    size_t md_len = mbedcrypto_md_get_size( ctx->md_ctx.md_info );
+    size_t left = out_len;
+    unsigned char *out = output;
+
+    /* II. Check request length */
+    if( out_len > MBEDCRYPTO_HMAC_DRBG_MAX_REQUEST )
+        return( MBEDCRYPTO_ERR_HMAC_DRBG_REQUEST_TOO_BIG );
+
+    /* III. Check input length */
+    if( add_len > MBEDCRYPTO_HMAC_DRBG_MAX_INPUT )
+        return( MBEDCRYPTO_ERR_HMAC_DRBG_INPUT_TOO_BIG );
+
+    /* 1. (aka VII and IX) Check reseed counter and PR */
+    if( ctx->f_entropy != NULL && /* For no-reseeding instances */
+        ( ctx->prediction_resistance == MBEDCRYPTO_HMAC_DRBG_PR_ON ||
+          ctx->reseed_counter > ctx->reseed_interval ) )
+    {
+        if( ( ret = mbedcrypto_hmac_drbg_reseed( ctx, additional, add_len ) ) != 0 )
+            return( ret );
+
+        add_len = 0; /* VII.4 */
+    }
+
+    /* 2. Use additional data if any */
+    if( additional != NULL && add_len != 0 )
+        mbedcrypto_hmac_drbg_update( ctx, additional, add_len );
+
+    /* 3, 4, 5. Generate bytes */
+    while( left != 0 )
+    {
+        size_t use_len = left > md_len ? md_len : left;
+
+        mbedcrypto_md_hmac_reset( &ctx->md_ctx );
+        mbedcrypto_md_hmac_update( &ctx->md_ctx, ctx->V, md_len );
+        mbedcrypto_md_hmac_finish( &ctx->md_ctx, ctx->V );
+
+        memcpy( out, ctx->V, use_len );
+        out += use_len;
+        left -= use_len;
+    }
+
+    /* 6. Update */
+    mbedcrypto_hmac_drbg_update( ctx, additional, add_len );
+
+    /* 7. Update reseed counter */
+    ctx->reseed_counter++;
+
+    /* 8. Done */
+    return( 0 );
+}
+
+/*
+ * HMAC_DRBG random function
+ */
+int mbedcrypto_hmac_drbg_random( void *p_rng, unsigned char *output, size_t out_len )
+{
+    int ret;
+    mbedcrypto_hmac_drbg_context *ctx = (mbedcrypto_hmac_drbg_context *) p_rng;
+
+#if defined(MBEDCRYPTO_THREADING_C)
+    if( ( ret = mbedcrypto_mutex_lock( &ctx->mutex ) ) != 0 )
+        return( ret );
+#endif
+
+    ret = mbedcrypto_hmac_drbg_random_with_add( ctx, output, out_len, NULL, 0 );
+
+#if defined(MBEDCRYPTO_THREADING_C)
+    if( mbedcrypto_mutex_unlock( &ctx->mutex ) != 0 )
+        return( MBEDCRYPTO_ERR_THREADING_MUTEX_ERROR );
+#endif
+
+    return( ret );
+}
+
+/*
+ * Free an HMAC_DRBG context
+ */
+void mbedcrypto_hmac_drbg_free( mbedcrypto_hmac_drbg_context *ctx )
+{
+    if( ctx == NULL )
+        return;
+
+#if defined(MBEDCRYPTO_THREADING_C)
+    mbedcrypto_mutex_free( &ctx->mutex );
+#endif
+    mbedcrypto_md_free( &ctx->md_ctx );
+    mbedcrypto_platform_zeroize( ctx, sizeof( mbedcrypto_hmac_drbg_context ) );
+}
+
+#if defined(MBEDCRYPTO_FS_IO)
+int mbedcrypto_hmac_drbg_write_seed_file( mbedcrypto_hmac_drbg_context *ctx, const char *path )
+{
+    int ret;
+    FILE *f;
+    unsigned char buf[ MBEDCRYPTO_HMAC_DRBG_MAX_INPUT ];
+
+    if( ( f = fopen( path, "wb" ) ) == NULL )
+        return( MBEDCRYPTO_ERR_HMAC_DRBG_FILE_IO_ERROR );
+
+    if( ( ret = mbedcrypto_hmac_drbg_random( ctx, buf, sizeof( buf ) ) ) != 0 )
+        goto exit;
+
+    if( fwrite( buf, 1, sizeof( buf ), f ) != sizeof( buf ) )
+    {
+        ret = MBEDCRYPTO_ERR_HMAC_DRBG_FILE_IO_ERROR;
+        goto exit;
+    }
+
+    ret = 0;
+
+exit:
+    fclose( f );
+    mbedcrypto_platform_zeroize( buf, sizeof( buf ) );
+
+    return( ret );
+}
+
+int mbedcrypto_hmac_drbg_update_seed_file( mbedcrypto_hmac_drbg_context *ctx, const char *path )
+{
+    int ret = 0;
+    FILE *f;
+    size_t n;
+    unsigned char buf[ MBEDCRYPTO_HMAC_DRBG_MAX_INPUT ];
+
+    if( ( f = fopen( path, "rb" ) ) == NULL )
+        return( MBEDCRYPTO_ERR_HMAC_DRBG_FILE_IO_ERROR );
+
+    fseek( f, 0, SEEK_END );
+    n = (size_t) ftell( f );
+    fseek( f, 0, SEEK_SET );
+
+    if( n > MBEDCRYPTO_HMAC_DRBG_MAX_INPUT )
+    {
+        fclose( f );
+        return( MBEDCRYPTO_ERR_HMAC_DRBG_INPUT_TOO_BIG );
+    }
+
+    if( fread( buf, 1, n, f ) != n )
+        ret = MBEDCRYPTO_ERR_HMAC_DRBG_FILE_IO_ERROR;
+    else
+        mbedcrypto_hmac_drbg_update( ctx, buf, n );
+
+    fclose( f );
+
+    mbedcrypto_platform_zeroize( buf, sizeof( buf ) );
+
+    if( ret != 0 )
+        return( ret );
+
+    return( mbedcrypto_hmac_drbg_write_seed_file( ctx, path ) );
+}
+#endif /* MBEDCRYPTO_FS_IO */
+
+
+#if defined(MBEDCRYPTO_SELF_TEST)
+
+#if !defined(MBEDCRYPTO_SHA1_C)
+/* Dummy checkup routine */
+int mbedcrypto_hmac_drbg_self_test( int verbose )
+{
+    (void) verbose;
+    return( 0 );
+}
+#else
+
+#define OUTPUT_LEN  80
+
+/* From a NIST PR=true test vector */
+static const unsigned char entropy_pr[] = {
+    0xa0, 0xc9, 0xab, 0x58, 0xf1, 0xe2, 0xe5, 0xa4, 0xde, 0x3e, 0xbd, 0x4f,
+    0xf7, 0x3e, 0x9c, 0x5b, 0x64, 0xef, 0xd8, 0xca, 0x02, 0x8c, 0xf8, 0x11,
+    0x48, 0xa5, 0x84, 0xfe, 0x69, 0xab, 0x5a, 0xee, 0x42, 0xaa, 0x4d, 0x42,
+    0x17, 0x60, 0x99, 0xd4, 0x5e, 0x13, 0x97, 0xdc, 0x40, 0x4d, 0x86, 0xa3,
+    0x7b, 0xf5, 0x59, 0x54, 0x75, 0x69, 0x51, 0xe4 };
+static const unsigned char result_pr[OUTPUT_LEN] = {
+    0x9a, 0x00, 0xa2, 0xd0, 0x0e, 0xd5, 0x9b, 0xfe, 0x31, 0xec, 0xb1, 0x39,
+    0x9b, 0x60, 0x81, 0x48, 0xd1, 0x96, 0x9d, 0x25, 0x0d, 0x3c, 0x1e, 0x94,
+    0x10, 0x10, 0x98, 0x12, 0x93, 0x25, 0xca, 0xb8, 0xfc, 0xcc, 0x2d, 0x54,
+    0x73, 0x19, 0x70, 0xc0, 0x10, 0x7a, 0xa4, 0x89, 0x25, 0x19, 0x95, 0x5e,
+    0x4b, 0xc6, 0x00, 0x1d, 0x7f, 0x4e, 0x6a, 0x2b, 0xf8, 0xa3, 0x01, 0xab,
+    0x46, 0x05, 0x5c, 0x09, 0xa6, 0x71, 0x88, 0xf1, 0xa7, 0x40, 0xee, 0xf3,
+    0xe1, 0x5c, 0x02, 0x9b, 0x44, 0xaf, 0x03, 0x44 };
+
+/* From a NIST PR=false test vector */
+static const unsigned char entropy_nopr[] = {
+    0x79, 0x34, 0x9b, 0xbf, 0x7c, 0xdd, 0xa5, 0x79, 0x95, 0x57, 0x86, 0x66,
+    0x21, 0xc9, 0x13, 0x83, 0x11, 0x46, 0x73, 0x3a, 0xbf, 0x8c, 0x35, 0xc8,
+    0xc7, 0x21, 0x5b, 0x5b, 0x96, 0xc4, 0x8e, 0x9b, 0x33, 0x8c, 0x74, 0xe3,
+    0xe9, 0x9d, 0xfe, 0xdf };
+static const unsigned char result_nopr[OUTPUT_LEN] = {
+    0xc6, 0xa1, 0x6a, 0xb8, 0xd4, 0x20, 0x70, 0x6f, 0x0f, 0x34, 0xab, 0x7f,
+    0xec, 0x5a, 0xdc, 0xa9, 0xd8, 0xca, 0x3a, 0x13, 0x3e, 0x15, 0x9c, 0xa6,
+    0xac, 0x43, 0xc6, 0xf8, 0xa2, 0xbe, 0x22, 0x83, 0x4a, 0x4c, 0x0a, 0x0a,
+    0xff, 0xb1, 0x0d, 0x71, 0x94, 0xf1, 0xc1, 0xa5, 0xcf, 0x73, 0x22, 0xec,
+    0x1a, 0xe0, 0x96, 0x4e, 0xd4, 0xbf, 0x12, 0x27, 0x46, 0xe0, 0x87, 0xfd,
+    0xb5, 0xb3, 0xe9, 0x1b, 0x34, 0x93, 0xd5, 0xbb, 0x98, 0xfa, 0xed, 0x49,
+    0xe8, 0x5f, 0x13, 0x0f, 0xc8, 0xa4, 0x59, 0xb7 };
+
+/* "Entropy" from buffer */
+static size_t test_offset;
+static int hmac_drbg_self_test_entropy( void *data,
+                                        unsigned char *buf, size_t len )
+{
+    const unsigned char *p = data;
+    memcpy( buf, p + test_offset, len );
+    test_offset += len;
+    return( 0 );
+}
+
+#define CHK( c )    if( (c) != 0 )                          \
+                    {                                       \
+                        if( verbose != 0 )                  \
+                            mbedcrypto_printf( "failed\n" );  \
+                        return( 1 );                        \
+                    }
+
+/*
+ * Checkup routine for HMAC_DRBG with SHA-1
+ */
+int mbedcrypto_hmac_drbg_self_test( int verbose )
+{
+    mbedcrypto_hmac_drbg_context ctx;
+    unsigned char buf[OUTPUT_LEN];
+    const mbedcrypto_md_info_t *md_info = mbedcrypto_md_info_from_type( MBEDCRYPTO_MD_SHA1 );
+
+    mbedcrypto_hmac_drbg_init( &ctx );
+
+    /*
+     * PR = True
+     */
+    if( verbose != 0 )
+        mbedcrypto_printf( "  HMAC_DRBG (PR = True) : " );
+
+    test_offset = 0;
+    CHK( mbedcrypto_hmac_drbg_seed( &ctx, md_info,
+                         hmac_drbg_self_test_entropy, (void *) entropy_pr,
+                         NULL, 0 ) );
+    mbedcrypto_hmac_drbg_set_prediction_resistance( &ctx, MBEDCRYPTO_HMAC_DRBG_PR_ON );
+    CHK( mbedcrypto_hmac_drbg_random( &ctx, buf, OUTPUT_LEN ) );
+    CHK( mbedcrypto_hmac_drbg_random( &ctx, buf, OUTPUT_LEN ) );
+    CHK( memcmp( buf, result_pr, OUTPUT_LEN ) );
+    mbedcrypto_hmac_drbg_free( &ctx );
+
+    mbedcrypto_hmac_drbg_free( &ctx );
+
+    if( verbose != 0 )
+        mbedcrypto_printf( "passed\n" );
+
+    /*
+     * PR = False
+     */
+    if( verbose != 0 )
+        mbedcrypto_printf( "  HMAC_DRBG (PR = False) : " );
+
+    mbedcrypto_hmac_drbg_init( &ctx );
+
+    test_offset = 0;
+    CHK( mbedcrypto_hmac_drbg_seed( &ctx, md_info,
+                         hmac_drbg_self_test_entropy, (void *) entropy_nopr,
+                         NULL, 0 ) );
+    CHK( mbedcrypto_hmac_drbg_reseed( &ctx, NULL, 0 ) );
+    CHK( mbedcrypto_hmac_drbg_random( &ctx, buf, OUTPUT_LEN ) );
+    CHK( mbedcrypto_hmac_drbg_random( &ctx, buf, OUTPUT_LEN ) );
+    CHK( memcmp( buf, result_nopr, OUTPUT_LEN ) );
+    mbedcrypto_hmac_drbg_free( &ctx );
+
+    mbedcrypto_hmac_drbg_free( &ctx );
+
+    if( verbose != 0 )
+        mbedcrypto_printf( "passed\n" );
+
+    if( verbose != 0 )
+        mbedcrypto_printf( "\n" );
+
+    return( 0 );
+}
+#endif /* MBEDCRYPTO_SHA1_C */
+#endif /* MBEDCRYPTO_SELF_TEST */
+
+#endif /* MBEDCRYPTO_HMAC_DRBG_C */