Add material for generating yotta module
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Manuel Pégourié-Gonnard
Manuel Pégourié-Gonnard
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70
yotta/data/example-authcrypt/README.md
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yotta/data/example-authcrypt/README.md
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# Authenticated encryption example
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This application performs authenticated encryption and authenticated decryption of a buffer. It serves as a tutorial for the basic authenticated encryption functions of mbed TLS.
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## Pre-requisites
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To build and run this example the requirements below are necessary:
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* A computer with the following software installed:
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* [CMake](http://www.cmake.org/download/).
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* [yotta](https://github.com/ARMmbed/yotta). Please note that **yotta has its own set of dependencies**, listed in the [installation instructions](http://armmbed.github.io/yotta/#installing-on-windows).
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* [Python](https://www.python.org/downloads/).
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* [ARM GCC toolchain](https://launchpad.net/gcc-arm-embedded).
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* A serial terminal emulator (e.g. screen, pySerial, cu).
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* An [FRDM-K64F](http://developer.mbed.org/platforms/FRDM-K64F/) development board, or another board supported by mbed OS (in that case you'll have to substitute frdm-k64f-gcc with the appropriate target below).
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* A micro-USB cable.
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* If your OS is Windows, please follow the installation instructions [for the serial port driver](https://developer.mbed.org/handbook/Windows-serial-configuration).
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## Getting started
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1. Connect the FRDM-K64F to the computer with the micro-USB cable, being careful to use the micro-usb port labeled "OpenSDA".
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2. Navigate to the mbedtls directory supplied with your release and open a terminal.
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3. Set the yotta target:
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```
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yotta target frdm-k64f-gcc
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```
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4. Check that there are no missing dependencies:
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```
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$ yt ls
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```
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If there are, yotta will list them in the terminal. Please install them before proceeding.
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5. Build mbedtls and the examples. This will take a long time if it is the first time:
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```
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$ yt build
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```
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6. Copy `build/frdm-k64f-gcc/test/mbedtls-test-example-authcrypt.bin` to your mbed board and wait until the LED next to the USB port stops blinking.
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7. Start the serial terminal emulator and connect to the virtual serial port presented by FRDM-K64F. For settings, use 9600 baud, 8N1, no flow control.
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8. Press the reset button on the board.
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9. The output in the terminal window should look like:
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```
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{{timeout;10}}
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{{host_test_name;default}}
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{{description;mbed TLS example authcrypt}}
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{{test_id;MBEDTLS_EX_AUTHCRYPT}}
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{{start}}
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plaintext message: 536f6d65207468696e67732061726520626574746572206c65667420756e7265616400
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ciphertext: c57f7afb94f14c7977d785d08682a2596bd62ee9dcf216b8cccd997afee9b402f5de1739e8e6467aa363749ef39392e5c66622b01c7203ec0a3d14
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decrypted: 536f6d65207468696e67732061726520626574746572206c65667420756e7265616400
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DONE
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{{success}}
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{{end}}
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```
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The actual output for the ciphertext line will vary on each run due to the use of a random nonce in the encryption process.
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177
yotta/data/example-authcrypt/main.cpp
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yotta/data/example-authcrypt/main.cpp
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/*
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* Hello world example of using the authenticated encryption with mbed TLS
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*
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* Copyright (C) 2006-2015, ARM Limited, All Rights Reserved
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*
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* This file is part of mbed TLS (https://tls.mbed.org)
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*/
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#include "mbedtls/cipher.h"
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#include "mbedtls/entropy.h"
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#include "mbedtls/ctr_drbg.h"
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#include <stdio.h>
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#include <string.h>
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static void print_hex(const char *title, const unsigned char buf[], size_t len)
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{
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printf("%s: ", title);
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for (size_t i = 0; i < len; i++)
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printf("%02x", buf[i]);
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printf("\r\n");
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}
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/*
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* The pre-shared key. Should be generated randomly and be unique to the
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* device/channel/etc. Just used a fixed on here for simplicity.
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*/
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static const unsigned char secret_key[16] = {
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0xf4, 0x82, 0xc6, 0x70, 0x3c, 0xc7, 0x61, 0x0a,
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0xb9, 0xa0, 0xb8, 0xe9, 0x87, 0xb8, 0xc1, 0x72,
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};
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static int example(void)
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{
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/* message that should be protected */
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const char message[] = "Some things are better left unread";
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/* metadata transmitted in the clear but authenticated */
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const char metadata[] = "eg sequence number, routing info";
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/* ciphertext buffer large enough to hold message + nonce + tag */
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unsigned char ciphertext[128] = { 0 };
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int ret;
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printf("\r\n\r\n");
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print_hex("plaintext message", (unsigned char *) message, sizeof message);
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/*
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* Setup random number generator
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* (Note: later this might be done automatically.)
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*/
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mbedtls_entropy_context entropy; /* entropy pool for seeding PRNG */
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mbedtls_ctr_drbg_context drbg; /* pseudo-random generator */
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mbedtls_entropy_init(&entropy);
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mbedtls_ctr_drbg_init(&drbg);
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/* Seed the PRNG using the entropy pool, and throw in our secret key as an
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* additional source of randomness. */
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ret = mbedtls_ctr_drbg_seed(&drbg, mbedtls_entropy_func, &entropy,
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secret_key, sizeof (secret_key));
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if (ret != 0) {
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printf("mbedtls_ctr_drbg_init() returned -0x%04X\r\n", -ret);
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return 1;
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}
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/*
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* Setup AES-CCM contex
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*/
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mbedtls_cipher_context_t ctx;
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mbedtls_cipher_init(&ctx);
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ret = mbedtls_cipher_setup(&ctx, mbedtls_cipher_info_from_type(MBEDTLS_CIPHER_AES_128_CCM));
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if (ret != 0) {
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printf("mbedtls_cipher_setup() returned -0x%04X\r\n", -ret);
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return 1;
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}
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ret = mbedtls_cipher_setkey(&ctx, secret_key, 8 * sizeof secret_key, MBEDTLS_ENCRYPT);
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if (ret != 0) {
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printf("mbedtls_cipher_setkey() returned -0x%04X\r\n", -ret);
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return 1;
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}
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/*
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* Encrypt-authenticate the message and authenticate additional data
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*
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* First generate a random 8-byte nonce.
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* Put it directly in the output buffer as the recipient will need it.
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*
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* Warning: you must never re-use the same (key, nonce) pair. One of the
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* best ways to ensure this to use a counter for the nonce. However this
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* means you should save the counter accross rebots, if the key is a
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* long-term one. The alternative we choose here is to generate the nonce
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* randomly. However it only works if you have a good source of
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* randomness.
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*/
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const size_t nonce_len = 8;
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mbedtls_ctr_drbg_random(&drbg, ciphertext, nonce_len);
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size_t ciphertext_len = 0;
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/* Go for a conservative 16-byte (128-bit) tag
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* and append it to the ciphertext */
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const size_t tag_len = 16;
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ret = mbedtls_cipher_auth_encrypt(&ctx, ciphertext, nonce_len,
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(const unsigned char *) metadata, sizeof metadata,
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(const unsigned char *) message, sizeof message,
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ciphertext + nonce_len, &ciphertext_len,
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ciphertext + nonce_len + sizeof message, tag_len );
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if (ret != 0) {
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printf("mbedtls_cipher_auth_encrypt() returned -0x%04X\r\n", -ret);
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return 1;
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}
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ciphertext_len += nonce_len + tag_len;
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/*
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* The following information should now be transmitted:
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* - first ciphertext_len bytes of ciphertext buffer
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* - metadata if not already transmitted elsewhere
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*/
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print_hex("ciphertext", ciphertext, ciphertext_len);
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/*
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* Decrypt-authenticate
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*/
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unsigned char decrypted[128] = { 0 };
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size_t decrypted_len = 0;
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ret = mbedtls_cipher_setkey(&ctx, secret_key, 8 * sizeof secret_key, MBEDTLS_DECRYPT);
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if (ret != 0) {
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printf("mbedtls_cipher_setkey() returned -0x%04X\r\n", -ret);
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return 1;
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}
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ret = mbedtls_cipher_auth_decrypt(&ctx,
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ciphertext, nonce_len,
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(const unsigned char *) metadata, sizeof metadata,
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ciphertext + nonce_len, ciphertext_len - nonce_len - tag_len,
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decrypted, &decrypted_len,
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ciphertext + ciphertext_len - tag_len, tag_len );
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/* Checking the return code is CRITICAL for security here */
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if (ret == MBEDTLS_ERR_CIPHER_AUTH_FAILED) {
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printf("Something bad is happening! Data is not authentic!\r\n");
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return 1;
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}
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if (ret != 0) {
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printf("mbedtls_cipher_authdecrypt() returned -0x%04X\r\n", -ret);
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return 1;
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}
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print_hex("decrypted", decrypted, decrypted_len);
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printf("\r\nDONE\r\n");
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return 0;
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}
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#if defined(TARGET_LIKE_MBED)
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#include "mbed/test_env.h"
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int main() {
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MBED_HOSTTEST_TIMEOUT(10);
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MBED_HOSTTEST_SELECT(default);
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MBED_HOSTTEST_DESCRIPTION(mbed TLS example authcrypt);
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MBED_HOSTTEST_START("MBEDTLS_EX_AUTHCRYPT");
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MBED_HOSTTEST_RESULT(example() == 0);
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}
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#else
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int main() {
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return example();
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}
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#endif
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