From 2f423473fc4b132dd6982a22c65d121767550069 Mon Sep 17 00:00:00 2001
From: Benjamin Valentin <benjamin.valentin@ml-pa.com>
Date: Tue, 7 Jul 2020 15:34:52 +0200
Subject: [PATCH 1/2] sys/random: add option to use HWRNG as source of
 randomness

Add the `prng_hwrng` module to enable the HWRNG as source of all randomness, not just
for seeding a PRNG.

saves ~260 bytes compared to using tinymt32.
---
 Makefile.dep         |  4 ++++
 sys/include/random.h |  3 +++
 sys/random/hwrng.c   | 38 ++++++++++++++++++++++++++++++++++++++
 3 files changed, 45 insertions(+)
 create mode 100644 sys/random/hwrng.c

diff --git a/Makefile.dep b/Makefile.dep
index 783119f4d3..eb4e8a138d 100644
--- a/Makefile.dep
+++ b/Makefile.dep
@@ -786,6 +786,10 @@ ifneq (,$(filter random,$(USEMODULE)))
     USEMODULE += hashes
   endif
 
+  ifneq (,$(filter prng_hwrng,$(USEMODULE)))
+    FEATURES_REQUIRED += periph_hwrng
+  endif
+
   ifeq (,$(filter puf_sram,$(USEMODULE)))
     FEATURES_OPTIONAL += periph_hwrng
   endif
diff --git a/sys/include/random.h b/sys/include/random.h
index 252a8379cf..dfd35a15fa 100644
--- a/sys/include/random.h
+++ b/sys/include/random.h
@@ -22,6 +22,9 @@
  *  - Simple Park-Miller PRNG
  *  - Musl C PRNG
  *  - Fortuna (CS)PRNG
+ *  - Hardware Random Number Generator (non-seedable)
+ *    HWRNG differ in how they generate random numbers and may not use a PRNG internally.
+ *    Refer to the manual of your MCU for details.
  */
 
 #ifndef RANDOM_H
diff --git a/sys/random/hwrng.c b/sys/random/hwrng.c
new file mode 100644
index 0000000000..8bde81b68c
--- /dev/null
+++ b/sys/random/hwrng.c
@@ -0,0 +1,38 @@
+/**
+ * Copyright (C) 2020 ML!PA Consulting GmbH
+ *
+ * This file is subject to the terms and conditions of the GNU Lesser
+ * General Public License v2.1. See the file LICENSE in the top level
+ * directory for more details.
+ */
+
+ /**
+ * @ingroup sys_random
+ * @{
+ * @file
+ *
+ * @brief   Use the HWRNG as source of randomness
+ *
+ * @author  Benjamin Valentin <benjamin.valentin@ml-pa.com>
+ * @}
+ */
+
+#include "kernel_defines.h"
+#include "periph/hwrng.h"
+#include "random.h"
+
+uint32_t random_uint32(void)
+{
+    uint32_t rnd;
+    hwrng_read(&rnd, sizeof(rnd));
+    return rnd;
+}
+
+void random_init(uint32_t val)
+{
+    (void) val;
+
+    if (!IS_ACTIVE(MODULE_PERIPH_INIT_HWRNG)) {
+        hwrng_init();
+    }
+}

From 04f3a9798c2dc9b07f7f7699a7d46a23292e2472 Mon Sep 17 00:00:00 2001
From: Benjamin Valentin <benpicco@googlemail.com>
Date: Wed, 8 Jul 2020 18:27:00 +0200
Subject: [PATCH 2/2] tests/rng: print when HWRNG is uses as system RNG

---
 tests/rng/test.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/tests/rng/test.c b/tests/rng/test.c
index 41bf6f229e..29521c715a 100644
--- a/tests/rng/test.c
+++ b/tests/rng/test.c
@@ -65,6 +65,8 @@ static void test_init(char *name)
         puts("Tiny Mersenne Twister PRNG.\n");
 #elif MODULE_PRNG_XORSHIFT
         puts("XOR Shift PRNG.\n");
+#elif MODULE_PRNG_HWRNG
+        puts("Hardware RNG.\n");
 #else
         puts("unknown PRNG.\n");
 #endif