libsodium: Use mbedTLS implementations for SHA256 & SHA512

* Adds support for hardware accelerated SHA
* Saves code size (~5.5KB) for SHA256 & SHA512 where libsodium & mbedTLS both used

components/libsodium/port/randombytes_esp32.c

@@ -0,0 +1,45 @@
+// Copyright 2017 Espressif Systems (Shanghai) PTE LTD
+//
+// 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.
+#include "randombytes_default.h"
+#include "esp_system.h"
+
+static void randombytes_esp32_random_buf(void * const buf, const size_t size)
+{
+    uint8_t *p = (uint8_t *)buf;
+    for (size_t i = 0; i < size; i++) {
+        p[i] = esp_random();
+    }
+}
+
+static const char *randombytes_esp32_implementation_name(void)
+{
+    return "esp32";
+}
+
+/*
+  Plug the ESP32 hardware RNG into libsodium's custom RNG support, as per
+  https://download.libsodium.org/doc/advanced/custom_rng.html
+
+  Note that this RNG is selected by default (see randombytes_default.h), so there
+  is no need to call randombytes_set_implementation().
+*/
+const struct randombytes_implementation randombytes_esp32_implementation = {
+    .implementation_name = randombytes_esp32_implementation_name,
+    .random = esp_random,
+    .stir = NULL,
+    .uniform = NULL,
+    .buf = randombytes_esp32_random_buf,
+    .close = NULL,
+};
+