Update Devicekey.md

Update content as in PR #785

Author: Amanda Butler

docs/api/drivers/Devicekey.md

@@ -23,7 +23,7 @@ The root of trust is generated at the first use of DeviceKey if the true random
 
 ### Key derivation API
 
-`generate_derived_key`: This API generates a new key based on an array of data ([salt](https://en.wikipedia.org/wiki/Salt_(cryptography)) the caller provides. A single salt value always generates the same key, so if you need a new key, you must use a new salt value. The salt can be have any value - array, string and so on. 
+`generate_derived_key`: This API generates a new key based on an array of data ([salt](https://en.wikipedia.org/wiki/Salt_(cryptography)) the caller provides. A single salt value always generates the same key, so if you need a new key, you must use a new salt value. The salt can have any value - array, string and so on.
 
 The generated keys can be 128 or 256 bits in length.
 
@@ -55,146 +55,4 @@ Run the DeviceKey functionality test with the `mbed` command as following:
 
 ### DeviceKey example
 
-```
-/*
-* Copyright (c) 2018 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.
-*/
-
-#include "mbed.h"
-#include "DeviceKey.h"
-
-//print a unsigned char buffer in hex format
-void print_buffer(unsigned char *buf, size_t size)
-{
-    for (size_t i = 0; i < size; i++) {
-        printf("%02X", buf[i]);
-    }
-}
-
-//Injection of a dummy key when there is no TRNG
-int inject_rot_key()
-{
-    uint32_t key[DEVICE_KEY_16BYTE / sizeof(uint32_t)];
-
-    memset(key, 0, DEVICE_KEY_16BYTE);
-    memcpy(key, "ABCDEF1234567890", DEVICE_KEY_16BYTE);
-    int size = DEVICE_KEY_16BYTE;
-    DeviceKey& devkey = DeviceKey::get_instance();
-    return devkey.device_inject_root_of_trust(key, size);
-}
-
-// Entry point for the example
-int main()
-{
-    unsigned char derive_key1 [DEVICE_KEY_32BYTE];
-    unsigned char derive_key2 [DEVICE_KEY_32BYTE];
-    unsigned char salt1[] = "SALT1 ----- SALT1 ------ SALT1";
-    unsigned char salt2[] = "SALT2 ----- SALT2 ------ SALT2";
-    int ret = DEVICEKEY_SUCCESS;
-
-    printf("\n--- Mbed OS DeviceKey example ---\n");
-
-    //DeviceKey is a singleton
-    DeviceKey& devkey = DeviceKey::get_instance();
-
-#if not defined(DEVICE_TRNG)
-
-    //If TRNG is not available it is a must to inject the ROT before the first call to derive key method.
-    printf("\n--- No TRNG support for this device. injecting ROT. ---\n");
-    ret = inject_rot_key();
-    if (DEVICEKEY_SUCCESS != ret && DEVICEKEY_ALREADY_EXIST != ret) {
-        printf("\n--- Error, injection of ROT key has failed with status %d ---\n", ret);
-        return -1;
-    }
-
-    if ( DEVICEKEY_ALREADY_EXIST == ret ) {
-        printf("\n--- ROT Key already exists in the persistent memory. ---\n", ret);
-    } else {
-        printf("\n--- ROT Key injected and stored in persistent memory. ---\n", ret);
-    }
-
-#endif
-
-    printf("\n--- Using the following salt for key derivation: %s ---\n", salt1);
-
-    //16 byte key derivation.
-    printf("--- First call to derive key, requesting derived key of 16 byte ---\n");
-    ret = devkey.generate_derived_key(salt1, sizeof(salt1), derive_key1, DEVICE_KEY_16BYTE);
-    if (DEVICEKEY_SUCCESS != ret) {
-        printf("\n--- Error, derive key failed with error code %d ---\n", ret);
-        return -1;
-    }
-
-    printf("--- Derived key1 is: \n");
-    print_buffer(derive_key1, DEVICE_KEY_16BYTE);
-    printf("\n");
-
-    //16 byte key derivation with the same salt should result with the same derived key.
-    printf("\n--- Second call to derive key with the same salt. ---\n");
-    ret = devkey.generate_derived_key(salt1, sizeof(salt1), derive_key2, DEVICE_KEY_16BYTE);
-    if (DEVICEKEY_SUCCESS != ret) {
-        printf("\n--- Error, derive key failed with error code %d ---\n", ret);
-        return -1;
-    }
-
-    printf("--- Derived key2 should be equal to key1 from the first call. key2 is: \n");
-    print_buffer(derive_key2, DEVICE_KEY_16BYTE);
-    printf("\n");
-
-    if (memcmp(derive_key1, derive_key2, DEVICE_KEY_16BYTE) != 0) {
-        printf("--- Error, first key and second key do not match ---\n");
-        return -1;
-    } else {
-        printf("--- Keys match ---\n");
-    }
-
-    printf("\n--- Using the following salt for key derivation %s ---\n", salt2);
-
-    //16 byte key derivation with the different salt should result with new derived key.
-    ret = devkey.generate_derived_key(salt2, sizeof(salt2), derive_key1, DEVICE_KEY_16BYTE);
-    if (DEVICEKEY_SUCCESS != ret) {
-        printf("\n--- Error, derive key failed with error code %d ---\n", ret);
-        return -1;
-    }
-
-    printf("--- Third call to derive key with the different salt should result with a new derived key1: \n");
-    print_buffer(derive_key1, DEVICE_KEY_16BYTE);
-    printf("\n");
-
-    if (memcmp(derive_key1, derive_key2, DEVICE_KEY_16BYTE) == 0) {
-        printf("--- Error, first key and second key do not match ---\n");
-        return -1;
-    } else {
-        printf("--- Keys not match ---\n");
-    }
-
-    //32 byte key derivation.
-    printf("\n--- 32 byte key derivation example. ---\n");
-    ret = devkey.generate_derived_key(salt2, sizeof(salt2), derive_key2, DEVICE_KEY_32BYTE);
-    if (DEVICEKEY_SUCCESS != ret) {
-        printf("\n--- Error, derive key failed with error code %d ---\n", ret);
-        return -1;
-    }
-
-    printf("--- 32 byte derived key is: \n");
-    print_buffer(derive_key2, DEVICE_KEY_32BYTE);
-    printf("\n");
-
-    printf("\n--- Mbed OS DeviceKey example done. ---\n");
-
-    return 0;
-}
-```
-
+[![View Example](https://www.mbed.com/embed/?url=https://github.com/ARMmbed/mbed-os-examples-docs_only/tree/master/DeviceKey)](https://github.com/ARMmbed/mbed-os-examples-docs_only/blob/master/DeviceKey/main.cpp)