From ad6af37d9982e8c774b8739bef8a692552ecf286 Mon Sep 17 00:00:00 2001
From: Kamil Sroka <kamil.sroka@nordicsemi.no>
Date: Mon, 9 Sep 2019 18:23:05 +0200
Subject: [PATCH] [crypto] don't add entropy source if it's done by mbedTLS
 (#4140)

If platform uses MbedTLS feature to add entropy source during context
init (by platform entropy, HAVEGE or MBEDTLS_ENTROPY_HARDWARE_ALT) we
shouldn't add second entropy source. This saves time and power as we
don't have to poll two different entropy sources/poll same entropy
source twice.
---
 src/core/common/random_manager.cpp | 7 +++++++
 src/core/common/random_manager.hpp | 7 +++++++
 src/core/meshcop/dtls.hpp          | 2 --
 3 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/src/core/common/random_manager.cpp b/src/core/common/random_manager.cpp
index c9602bded..d599224d1 100644
--- a/src/core/common/random_manager.cpp
+++ b/src/core/common/random_manager.cpp
@@ -149,8 +149,11 @@ uint32_t RandomManager::NonCryptoPrng::GetNext(void)
 void RandomManager::Entropy::Init(void)
 {
     mbedtls_entropy_init(&mEntropyContext);
+
+#ifndef OT_MBEDTLS_STRONG_DEFAULT_ENTROPY_PRESENT
     mbedtls_entropy_add_source(&mEntropyContext, &RandomManager::Entropy::HandleMbedtlsEntropyPoll, NULL,
                                MBEDTLS_ENTROPY_MIN_HARDWARE, MBEDTLS_ENTROPY_SOURCE_STRONG);
+#endif // OT_MBEDTLS_STRONG_DEFAULT_ENTROPY_PRESENT
 }
 
 void RandomManager::Entropy::Deinit(void)
@@ -158,6 +161,8 @@ void RandomManager::Entropy::Deinit(void)
     mbedtls_entropy_free(&mEntropyContext);
 }
 
+#ifndef OT_MBEDTLS_STRONG_DEFAULT_ENTROPY_PRESENT
+
 int RandomManager::Entropy::HandleMbedtlsEntropyPoll(void *         aData,
                                                      unsigned char *aOutput,
                                                      size_t         aInLen,
@@ -176,6 +181,8 @@ exit:
     return rval;
 }
 
+#endif // OT_MBEDTLS_STRONG_DEFAULT_ENTROPY_PRESENT
+
 //-------------------------------------------------------------------
 // CryptoCtrDrbg
 
diff --git a/src/core/common/random_manager.hpp b/src/core/common/random_manager.hpp
index c2e78a308..b586b9eaf 100644
--- a/src/core/common/random_manager.hpp
+++ b/src/core/common/random_manager.hpp
@@ -45,6 +45,11 @@
 
 #include "utils/wrap_stdint.h"
 
+#if (!defined(MBEDTLS_NO_DEFAULT_ENTROPY_SOURCES) && \
+     (!defined(MBEDTLS_NO_PLATFORM_ENTROPY) || defined(MBEDTLS_HAVEGE_C) || defined(MBEDTLS_ENTROPY_HARDWARE_ALT)))
+#define OT_MBEDTLS_STRONG_DEFAULT_ENTROPY_PRESENT
+#endif
+
 namespace ot {
 
 /**
@@ -123,7 +128,9 @@ private:
         mbedtls_entropy_context *GetContext(void) { return &mEntropyContext; }
 
     private:
+#ifndef OT_MBEDTLS_STRONG_DEFAULT_ENTROPY_PRESENT
         static int HandleMbedtlsEntropyPoll(void *aData, unsigned char *aOutput, size_t aInLen, size_t *aOutLen);
+#endif // OT_MBEDTLS_STRONG_DEFAULT_ENTROPY_PRESENT
 
         mbedtls_entropy_context mEntropyContext;
     };
diff --git a/src/core/meshcop/dtls.hpp b/src/core/meshcop/dtls.hpp
index f133eb038..764a3f28b 100644
--- a/src/core/meshcop/dtls.hpp
+++ b/src/core/meshcop/dtls.hpp
@@ -438,8 +438,6 @@ private:
     static void HandleUdpTransmit(Tasklet &aTasklet);
     void        HandleUdpTransmit(void);
 
-    static int HandleMbedtlsEntropyPoll(void *aData, unsigned char *aOutput, size_t aInLen, size_t *aOutLen);
-
     void Process(void);
 
     State mState;