diff --git a/crypto/Makefile b/crypto/Makefile
index cb3ebe80f..f51de750e 100644
--- a/crypto/Makefile
+++ b/crypto/Makefile
@@ -64,6 +64,7 @@ SRCS  += nem.c
 SRCS  += segwit_addr.c cash_addr.c
 SRCS  += memzero.c
 SRCS  += shamir.c
+SRCS  += hmac_drbg.c
 
 OBJS   = $(SRCS:.c=.o)
 
diff --git a/crypto/hmac_drbg.c b/crypto/hmac_drbg.c
new file mode 100644
index 000000000..fe53dc7ff
--- /dev/null
+++ b/crypto/hmac_drbg.c
@@ -0,0 +1,126 @@
+/**
+ * Copyright (c) 2019 Andrew R. Kozlik
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included
+ * in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
+ * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES
+ * OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
+ * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
+ * OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+#include <string.h>
+#include "hmac_drbg.h"
+#include "memzero.h"
+#include "sha2.h"
+
+static void update_k(HMAC_DRBG_CTX *ctx, uint8_t domain, const uint8_t *data,
+                     size_t len) {
+  // Computes K = HMAC(K, V || domain || data).
+
+  // First hash operation of HMAC.
+  uint32_t h[SHA256_BLOCK_LENGTH / sizeof(uint32_t)] = {0};
+  if (data == NULL) {
+    ctx->v[8] = 0x00800000;
+    ctx->v[15] = (SHA256_BLOCK_LENGTH + SHA256_DIGEST_LENGTH + 1) * 8;
+    sha256_Transform(ctx->idig, ctx->v, h);
+    ctx->v[8] = 0x80000000;
+    ctx->v[15] = (SHA256_BLOCK_LENGTH + SHA256_DIGEST_LENGTH) * 8;
+  } else {
+    SHA256_CTX sha_ctx;
+    memcpy(sha_ctx.state, ctx->idig, SHA256_DIGEST_LENGTH);
+    for (size_t i = 0; i < SHA256_DIGEST_LENGTH / sizeof(uint32_t); i++) {
+#if BYTE_ORDER == LITTLE_ENDIAN
+      REVERSE32(ctx->v[i], sha_ctx.buffer[i]);
+#else
+      sha_ctx.buffer[i] = ctx->v[i];
+#endif
+    }
+    ((uint8_t *)sha_ctx.buffer)[SHA256_DIGEST_LENGTH] = domain;
+    sha_ctx.bitcount = (SHA256_BLOCK_LENGTH + SHA256_DIGEST_LENGTH + 1) * 8;
+    sha256_Update(&sha_ctx, data, len);
+    sha256_Final(&sha_ctx, (uint8_t *)h);
+#if BYTE_ORDER == LITTLE_ENDIAN
+    for (size_t i = 0; i < SHA256_DIGEST_LENGTH / sizeof(uint32_t); i++)
+      REVERSE32(h[i], h[i]);
+#endif
+  }
+
+  // Second hash operation of HMAC.
+  h[8] = 0x80000000;
+  h[15] = (SHA256_BLOCK_LENGTH + SHA256_DIGEST_LENGTH) * 8;
+  sha256_Transform(ctx->odig, h, h);
+
+  // Precompute the inner digest and outer digest of K.
+  h[8] = 0;
+  h[15] = 0;
+  for (size_t i = 0; i < SHA256_BLOCK_LENGTH / sizeof(uint32_t); i++) {
+    h[i] ^= 0x36363636;
+  }
+  sha256_Transform(sha256_initial_hash_value, h, ctx->idig);
+
+  for (size_t i = 0; i < SHA256_BLOCK_LENGTH / sizeof(uint32_t); i++) {
+    h[i] = h[i] ^ 0x36363636 ^ 0x5c5c5c5c;
+  }
+  sha256_Transform(sha256_initial_hash_value, h, ctx->odig);
+  memzero(h, sizeof(h));
+}
+
+static void update_v(HMAC_DRBG_CTX *ctx) {
+  sha256_Transform(ctx->idig, ctx->v, ctx->v);
+  sha256_Transform(ctx->odig, ctx->v, ctx->v);
+}
+
+void hmac_drbg_init(HMAC_DRBG_CTX *ctx, const uint8_t *entropy, size_t len) {
+  uint32_t h[SHA256_BLOCK_LENGTH / sizeof(uint32_t)];
+
+  // Precompute the inner digest and outer digest of K = 0x00 ... 0x00.
+  memset(h, 0x36, sizeof(h));
+  sha256_Transform(sha256_initial_hash_value, h, ctx->idig);
+  memset(h, 0x5c, sizeof(h));
+  sha256_Transform(sha256_initial_hash_value, h, ctx->odig);
+
+  // Let V = 0x01 ... 0x01.
+  memset(ctx->v, 1, SHA256_DIGEST_LENGTH);
+  for (size_t i = 9; i < 15; i++) ctx->v[i] = 0;
+  ctx->v[8] = 0x80000000;
+  ctx->v[15] = (SHA256_BLOCK_LENGTH + SHA256_DIGEST_LENGTH) * 8;
+
+  hmac_drbg_reseed(ctx, entropy, len);
+
+  memzero(h, sizeof(h));
+}
+
+void hmac_drbg_reseed(HMAC_DRBG_CTX *ctx, const uint8_t *entropy, size_t len) {
+  update_k(ctx, 0, entropy, len);
+  update_v(ctx);
+  if (len == 0) return;
+  update_k(ctx, 1, entropy, len);
+  update_v(ctx);
+}
+
+void hmac_drbg_generate(HMAC_DRBG_CTX *ctx, uint8_t *buf, size_t len) {
+  size_t i = 0;
+  while (i < len) {
+    update_v(ctx);
+    for (size_t j = 0; j < 8; j++) {
+      uint32_t r = ctx->v[j];
+      for (int k = 24; k >= 0; k -= 8) {
+        buf[i++] = (r >> k) & 0xFF;
+      }
+    }
+  }
+  update_k(ctx, 0, NULL, 0);
+  update_v(ctx);
+}
diff --git a/crypto/hmac_drbg.h b/crypto/hmac_drbg.h
new file mode 100644
index 000000000..0bba18901
--- /dev/null
+++ b/crypto/hmac_drbg.h
@@ -0,0 +1,41 @@
+/**
+ * Copyright (c) 2019 Andrew R. Kozlik
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included
+ * in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
+ * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES
+ * OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
+ * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
+ * OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+#ifndef __HMAC_DRBG_H__
+#define __HMAC_DRBG_H__
+
+#include <sha2.h>
+#include <stdint.h>
+
+// HMAC based Deterministic Random Bit Generator with SHA-256
+
+typedef struct _HMAC_DRBG_CTX {
+  uint32_t odig[SHA256_DIGEST_LENGTH / sizeof(uint32_t)];
+  uint32_t idig[SHA256_DIGEST_LENGTH / sizeof(uint32_t)];
+  uint32_t v[SHA256_BLOCK_LENGTH / sizeof(uint32_t)];
+} HMAC_DRBG_CTX;
+
+void hmac_drbg_init(HMAC_DRBG_CTX *ctx, const uint8_t *buf, size_t len);
+void hmac_drbg_reseed(HMAC_DRBG_CTX *ctx, const uint8_t *buf, size_t len);
+void hmac_drbg_generate(HMAC_DRBG_CTX *ctx, uint8_t *buf, size_t len);
+
+#endif
diff --git a/crypto/tests/test_check.c b/crypto/tests/test_check.c
index 9a007bed6..85f106cc8 100644
--- a/crypto/tests/test_check.c
+++ b/crypto/tests/test_check.c
@@ -53,6 +53,7 @@
 #include "ed25519-donna/ed25519-donna.h"
 #include "ed25519-donna/ed25519-keccak.h"
 #include "ed25519-donna/ed25519.h"
+#include "hmac_drbg.h"
 #include "memzero.h"
 #include "monero/monero.h"
 #include "nem.h"
@@ -4624,6 +4625,34 @@ START_TEST(test_pbkdf2_hmac_sha512) {
 }
 END_TEST
 
+START_TEST(test_hmac_drbg) {
+  char entropy[] =
+      "06032cd5eed33f39265f49ecb142c511da9aff2af71203bffaf34a9ca5bd9c0d0e66f71e"
+      "dc43e42a45ad3c6fc6cdc4df";
+  char reseed[] =
+      "01920a4e669ed3a85ae8a33b35a74ad7fb2a6bb4cf395ce00334a9c9a5a5d552";
+  char expected[] =
+      "76fc79fe9b50beccc991a11b5635783a83536add03c157fb30645e611c2898bb2b1bc215"
+      "000209208cd506cb28da2a51bdb03826aaf2bd2335d576d519160842e7158ad0949d1a9e"
+      "c3e66ea1b1a064b005de914eac2e9d4f2d72a8616a80225422918250ff66a41bd2f864a6"
+      "a38cc5b6499dc43f7f2bd09e1e0f8f5885935124";
+  uint8_t result[128];
+
+  HMAC_DRBG_CTX ctx;
+  hmac_drbg_init(&ctx, fromhex(entropy), strlen(entropy) / 2);
+  hmac_drbg_reseed(&ctx, fromhex(reseed), strlen(reseed) / 2);
+  hmac_drbg_generate(&ctx, result, sizeof(result));
+  hmac_drbg_generate(&ctx, result, sizeof(result));
+  ck_assert_mem_eq(result, fromhex(expected), sizeof(result));
+
+  hmac_drbg_init(&ctx, fromhex(entropy), strlen(entropy) / 2);
+  hmac_drbg_reseed(&ctx, fromhex(reseed), strlen(reseed) / 2);
+  hmac_drbg_generate(&ctx, result, sizeof(result) - 13);
+  hmac_drbg_generate(&ctx, result, sizeof(result) - 17);
+  ck_assert_mem_eq(result, fromhex(expected), sizeof(result) - 17);
+}
+END_TEST
+
 START_TEST(test_mnemonic) {
   static const char *vectors[] = {
       "00000000000000000000000000000000",
@@ -8628,6 +8657,10 @@ Suite *test_suite(void) {
   tcase_add_test(tc, test_pbkdf2_hmac_sha512);
   suite_add_tcase(s, tc);
 
+  tc = tcase_create("hmac_drbg");
+  tcase_add_test(tc, test_hmac_drbg);
+  suite_add_tcase(s, tc);
+
   tc = tcase_create("bip39");
   tcase_add_test(tc, test_mnemonic);
   tcase_add_test(tc, test_mnemonic_check);