Add mbed TLS Hashing example (#3)

* Add mbed TLS benchmark example

Add the mbed TLS benchmark example that runs multiple cryptographic
primitives and reports performance. Also, modified the repository's
structure so that each example is in a different subdirectory.

* Fix benchmark code and documentation

Fix the benchmark code to remove the conditional preprocessor
directives for platform.h. This code is not meant to be portable to
anything other than mbed OS, so these are not required.

Also, update documentation according to feedback.

* Add mbed TLS hashing example

Add the mbed TLS example that demonstrates the use of hashing
functions.

* Modify hashing sample to use mbedtls/platform.h

Author: Andres Amaya Garcia

hashing/README.md

@@ -0,0 +1,20 @@
+# SHA-256 Hash example on mbed OS
+
+This application performs hashing of a buffer with SHA-256 using various APIs. It serves as a tutorial for the basic hashing APIs of mbed TLS.
+
+# Getting started
+
+Set up your environment if you have not done so already. For instructions, refer to the [main readme](../README.md).
+
+## Monitoring the application
+
+The output in the terminal window should be similar to this:
+
+```
+Method 1: 315f5bdb76d078c43b8ac0064e4a0164612b1fce77c869345bfc94c75894edd3
+Method 2: 315f5bdb76d078c43b8ac0064e4a0164612b1fce77c869345bfc94c75894edd3
+Method 3: 315f5bdb76d078c43b8ac0064e4a0164612b1fce77c869345bfc94c75894edd3
+Method 4: 315f5bdb76d078c43b8ac0064e4a0164612b1fce77c869345bfc94c75894edd3
+
+DONE
+```

hashing/main.cpp

@@ -0,0 +1,159 @@
+/*
+ *  Hello world example of using the hashing functions of mbed TLS
+ *
+ *  Copyright (C) 2016, ARM Limited, All Rights Reserved
+ *  SPDX-License-Identifier: Apache-2.0
+ *
+ *  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.
+ */
+
+/*
+ * This program illustrates various ways of hashing a buffer.
+ * You normally need only one of these two includes.
+ */
+#include "mbed.h"
+#include "mbedtls/sha256.h" /* SHA-256 only */
+#include "mbedtls/md.h"     /* generic interface */
+
+#if DEBUG_LEVEL > 0
+#include "mbedtls/debug.h"
+#endif
+
+#include "mbedtls/platform.h"
+
+#include <string.h>
+
+static void print_hex(const char *title, const unsigned char buf[], size_t len)
+{
+    mbedtls_printf("%s: ", title);
+
+    for (size_t i = 0; i < len; i++)
+        mbedtls_printf("%02x", buf[i]);
+
+    mbedtls_printf("\r\n");
+}
+
+static const char hello_str[] = "Hello, world!";
+static const unsigned char *hello_buffer = (const unsigned char *) hello_str;
+static const size_t hello_len = strlen(hello_str);
+
+static int example(void)
+{
+    mbedtls_printf("\r\n\r\n");
+
+    /*
+     * Method 1: use all-in-one function of a specific SHA-xxx module
+     */
+    unsigned char output1[32]; /* SHA-256 outputs 32 bytes */
+
+    /* 0 here means use the full SHA-256, not the SHA-224 variant */
+    mbedtls_sha256(hello_buffer, hello_len, output1, 0);
+
+    print_hex("Method 1", output1, sizeof output1);
+
+
+    /*
+     * Method 2: use the streaming interface of a specific SHA-xxx module
+     * This is useful if we get our input piecewise.
+     */
+    unsigned char output2[32];
+    mbedtls_sha256_context ctx2;
+
+    mbedtls_sha256_init(&ctx2);
+    mbedtls_sha256_starts(&ctx2, 0); /* SHA-256, not 224 */
+
+    /* Simulating multiple fragments */
+    mbedtls_sha256_update(&ctx2, hello_buffer, 1);
+    mbedtls_sha256_update(&ctx2, hello_buffer + 1, 1);
+    mbedtls_sha256_update(&ctx2, hello_buffer + 2, hello_len - 2);
+
+    mbedtls_sha256_finish(&ctx2, output2);
+    print_hex("Method 2", output2, sizeof output2);
+
+    /* Or you could re-use the context by doing mbedtls_sha256_starts() again */
+    mbedtls_sha256_free(&ctx2);
+
+    /*
+     * Method 3: use all-in-one function of the generice interface
+     */
+    unsigned char output3[MBEDTLS_MD_MAX_SIZE]; /* Enough for any hash */
+
+    /* Can easily pick any hash you want, by identifier */
+    const mbedtls_md_info_t *md_info3 = mbedtls_md_info_from_type(MBEDTLS_MD_SHA256);
+
+    if (md_info3 == NULL)
+    {
+        mbedtls_printf("SHA256 not available\r\n");
+        return 1;
+    }
+
+    int ret3 = mbedtls_md(md_info3, hello_buffer, hello_len, output3);
+
+    if (ret3 != 0)
+    {
+        mbedtls_printf("md() returned -0x%04X\r\n", -ret3);
+        return 1;
+    }
+
+    print_hex("Method 3", output3, mbedtls_md_get_size(md_info3));
+
+
+    /*
+     * Method 4: streaming & generic interface
+     */
+    unsigned char output4[MBEDTLS_MD_MAX_SIZE]; /* Enough for any hash */
+
+    const mbedtls_md_info_t *md_info4 = mbedtls_md_info_from_type(MBEDTLS_MD_SHA256);
+
+    if (md_info4 == NULL)
+    {
+        mbedtls_printf("SHA256 not available\r\n");
+        return 1;
+    }
+
+    mbedtls_md_context_t ctx4;
+
+    mbedtls_md_init(&ctx4);
+
+    int ret4 = mbedtls_md_init_ctx(&ctx4, md_info4);
+    if (ret4 != 0)
+    {
+        mbedtls_printf("md_init_ctx() returned -0x%04X\r\n", -ret4);
+        return 1;
+    }
+
+    mbedtls_md_starts(&ctx4);
+
+    /* Simulating multiple fragments */
+    mbedtls_md_update(&ctx4, hello_buffer, 1);
+    mbedtls_md_update(&ctx4, hello_buffer + 1, 1);
+    mbedtls_md_update(&ctx4, hello_buffer + 2, hello_len - 2);
+
+    mbedtls_md_finish(&ctx4, output4);
+    print_hex("Method 4", output4, mbedtls_md_get_size(md_info4));
+
+    /* Or you could re-use the context by doing mbedtls_md_starts() again */
+    mbedtls_md_free(&ctx4);
+
+
+    mbedtls_printf("\r\nDONE\r\n");
+
+    return 0;
+}
+
+int main() {
+    int ret = example();
+    if (ret != 0) {
+        mbedtls_printf("Example failed with error %d\r\n", ret);
+    }
+}

hashing/mbed-os.lib

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+https://github.com/ARMmbed/mbed-os/#b7b6dd2c8769251c66d68911f116ec899c7054f7