| /* |
| * Hello world example of using the authenticated encryption with mbed TLS |
| * |
| * Copyright (C) 2006-2015, ARM Limited, All Rights Reserved |
| * |
| * This file is part of mbed TLS (https://tls.mbed.org) |
| */ |
| |
| #include "mbedtls/cipher.h" |
| #include "mbedtls/entropy.h" |
| #include "mbedtls/ctr_drbg.h" |
| |
| #include <stdio.h> |
| #include <string.h> |
| |
| static void print_hex(const char *title, const unsigned char buf[], size_t len) |
| { |
| printf("%s: ", title); |
| |
| for (size_t i = 0; i < len; i++) |
| printf("%02x", buf[i]); |
| |
| printf("\r\n"); |
| } |
| |
| /* |
| * The pre-shared key. Should be generated randomly and be unique to the |
| * device/channel/etc. Just used a fixed on here for simplicity. |
| */ |
| static const unsigned char secret_key[16] = { |
| 0xf4, 0x82, 0xc6, 0x70, 0x3c, 0xc7, 0x61, 0x0a, |
| 0xb9, 0xa0, 0xb8, 0xe9, 0x87, 0xb8, 0xc1, 0x72, |
| }; |
| |
| static int example(void) |
| { |
| /* message that should be protected */ |
| const char message[] = "Some things are better left unread"; |
| /* metadata transmitted in the clear but authenticated */ |
| const char metadata[] = "eg sequence number, routing info"; |
| /* ciphertext buffer large enough to hold message + nonce + tag */ |
| unsigned char ciphertext[128] = { 0 }; |
| int ret; |
| |
| printf("\r\n\r\n"); |
| print_hex("plaintext message", (unsigned char *) message, sizeof message); |
| |
| /* |
| * Setup random number generator |
| * (Note: later this might be done automatically.) |
| */ |
| mbedtls_entropy_context entropy; /* entropy pool for seeding PRNG */ |
| mbedtls_ctr_drbg_context drbg; /* pseudo-random generator */ |
| |
| mbedtls_entropy_init(&entropy); |
| mbedtls_ctr_drbg_init(&drbg); |
| |
| /* Seed the PRNG using the entropy pool, and throw in our secret key as an |
| * additional source of randomness. */ |
| ret = mbedtls_ctr_drbg_seed(&drbg, mbedtls_entropy_func, &entropy, |
| secret_key, sizeof (secret_key)); |
| if (ret != 0) { |
| printf("mbedtls_ctr_drbg_init() returned -0x%04X\r\n", -ret); |
| return 1; |
| } |
| |
| /* |
| * Setup AES-CCM contex |
| */ |
| mbedtls_cipher_context_t ctx; |
| |
| mbedtls_cipher_init(&ctx); |
| |
| ret = mbedtls_cipher_setup(&ctx, mbedtls_cipher_info_from_type(MBEDTLS_CIPHER_AES_128_CCM)); |
| if (ret != 0) { |
| printf("mbedtls_cipher_setup() returned -0x%04X\r\n", -ret); |
| return 1; |
| } |
| |
| ret = mbedtls_cipher_setkey(&ctx, secret_key, 8 * sizeof secret_key, MBEDTLS_ENCRYPT); |
| if (ret != 0) { |
| printf("mbedtls_cipher_setkey() returned -0x%04X\r\n", -ret); |
| return 1; |
| } |
| |
| /* |
| * Encrypt-authenticate the message and authenticate additional data |
| * |
| * First generate a random 8-byte nonce. |
| * Put it directly in the output buffer as the recipient will need it. |
| * |
| * Warning: you must never re-use the same (key, nonce) pair. One of the |
| * best ways to ensure this to use a counter for the nonce. However this |
| * means you should save the counter accross rebots, if the key is a |
| * long-term one. The alternative we choose here is to generate the nonce |
| * randomly. However it only works if you have a good source of |
| * randomness. |
| */ |
| const size_t nonce_len = 8; |
| mbedtls_ctr_drbg_random(&drbg, ciphertext, nonce_len); |
| |
| size_t ciphertext_len = 0; |
| /* Go for a conservative 16-byte (128-bit) tag |
| * and append it to the ciphertext */ |
| const size_t tag_len = 16; |
| ret = mbedtls_cipher_auth_encrypt(&ctx, ciphertext, nonce_len, |
| (const unsigned char *) metadata, sizeof metadata, |
| (const unsigned char *) message, sizeof message, |
| ciphertext + nonce_len, &ciphertext_len, |
| ciphertext + nonce_len + sizeof message, tag_len ); |
| if (ret != 0) { |
| printf("mbedtls_cipher_auth_encrypt() returned -0x%04X\r\n", -ret); |
| return 1; |
| } |
| ciphertext_len += nonce_len + tag_len; |
| |
| /* |
| * The following information should now be transmitted: |
| * - first ciphertext_len bytes of ciphertext buffer |
| * - metadata if not already transmitted elsewhere |
| */ |
| print_hex("ciphertext", ciphertext, ciphertext_len); |
| |
| /* |
| * Decrypt-authenticate |
| */ |
| unsigned char decrypted[128] = { 0 }; |
| size_t decrypted_len = 0; |
| |
| ret = mbedtls_cipher_setkey(&ctx, secret_key, 8 * sizeof secret_key, MBEDTLS_DECRYPT); |
| if (ret != 0) { |
| printf("mbedtls_cipher_setkey() returned -0x%04X\r\n", -ret); |
| return 1; |
| } |
| |
| ret = mbedtls_cipher_auth_decrypt(&ctx, |
| ciphertext, nonce_len, |
| (const unsigned char *) metadata, sizeof metadata, |
| ciphertext + nonce_len, ciphertext_len - nonce_len - tag_len, |
| decrypted, &decrypted_len, |
| ciphertext + ciphertext_len - tag_len, tag_len ); |
| /* Checking the return code is CRITICAL for security here */ |
| if (ret == MBEDTLS_ERR_CIPHER_AUTH_FAILED) { |
| printf("Something bad is happening! Data is not authentic!\r\n"); |
| return 1; |
| } |
| if (ret != 0) { |
| printf("mbedtls_cipher_authdecrypt() returned -0x%04X\r\n", -ret); |
| return 1; |
| } |
| |
| print_hex("decrypted", decrypted, decrypted_len); |
| |
| printf("\r\nDONE\r\n"); |
| |
| return 0; |
| } |
| |
| #if defined(TARGET_LIKE_MBED) |
| |
| #include "mbed/test_env.h" |
| |
| int main() { |
| /* Use 115200 bps for consistency with other examples */ |
| Serial pc(USBTX, USBRX); |
| pc.baud(115200); |
| |
| MBED_HOSTTEST_TIMEOUT(10); |
| MBED_HOSTTEST_SELECT(default); |
| MBED_HOSTTEST_DESCRIPTION(mbed TLS example authcrypt); |
| MBED_HOSTTEST_START("MBEDTLS_EX_AUTHCRYPT"); |
| MBED_HOSTTEST_RESULT(example() == 0); |
| } |
| |
| #else |
| |
| int main() { |
| return example(); |
| } |
| |
| #endif |