Use Openthread Hardware Entropy Collector (#484)

* create new file named as hardware_entropy.c for mbedtls to use OT hardware entropy source

examples/platforms/posix/random.c

@@ -69,7 +69,7 @@ uint32_t otPlatRandomGet(void)
     return mlcg;
 }
 
-ThreadError otPlatSecureRandomGet(uint16_t aInputLength, uint8_t *aOutput, uint16_t *aOutputLength)
+ThreadError otPlatRandomSecureGet(uint16_t aInputLength, uint8_t *aOutput, uint16_t *aOutputLength)
 {
     ThreadError error = kThreadError_None;
 

third_party/mbedtls/Makefile.am

@@ -42,6 +42,7 @@ libmbedcrypto_a_CPPFLAGS                      = \
     $(NULL)
 
 libmbedcrypto_a_SOURCES                       = \
+    hardware_entropy.c                          \
     repo/library/aes.c                          \
     repo/library/md.c                           \
     repo/library/md_wrap.c                      \

third_party/mbedtls/hardware_entropy.c

@@ -0,0 +1,44 @@
+/*
+ *    Copyright 2016 Nest Labs Inc. All Rights Reserved.
+ *
+ *    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.
+ */
+
+/**
+ * @file
+ *   This file implements to use hardware entropy source.
+ *   uncomment MBEDTLS_ENTROPY_HARDWARE_ALT in mbedtls/mbedtls_config.h to use this.
+ */
+
+#include <stddef.h>
+
+#include <openthread-types.h>
+#include <platform/random.h>
+
+#include "mbedtls/entropy.h"
+
+int mbedtls_hardware_poll(void *data, unsigned char *output, size_t len, size_t *olen)
+{
+    ThreadError error;
+
+    (void)data;
+
+    error = otPlatRandomSecureGet((uint16_t)len, (uint8_t *)output, (uint16_t *)olen);
+
+    if (error != kThreadError_None)
+    {
+        return MBEDTLS_ERR_ENTROPY_SOURCE_FAILED;
+    }
+
+    return 0;
+}

third_party/mbedtls/mbedtls-config.h

@@ -294,7 +294,7 @@
  *
  * Uncomment to use your own hardware entropy collector.
  */
-//#define MBEDTLS_ENTROPY_HARDWARE_ALT
+#define MBEDTLS_ENTROPY_HARDWARE_ALT
 
 /**
  * \def MBEDTLS_AES_ROM_TABLES
@@ -786,7 +786,7 @@
  *
  * Uncomment this macro to disable the built-in platform entropy functions.
  */
-//#define MBEDTLS_NO_PLATFORM_ENTROPY
+#define MBEDTLS_NO_PLATFORM_ENTROPY
 
 /**
  * \def MBEDTLS_ENTROPY_FORCE_SHA256