programs/cipher/cipher_aead_demo.c

/**
 * Cipher API multi-part AEAD demonstration.
 *
 * This program AEAD-encrypts a message, using the algorithm and key size
 * specified on the command line, using the multi-part API.
 *
 * It comes with a companion program psa/aead_demo.c, which does the same
 * operations with the PSA Crypto API. The goal is that comparing the two
 * programs will help people migrating to the PSA Crypto API.
 *
 * When used with multi-part AEAD operations, the `mbedtls_cipher_context`
 * serves a triple purpose (1) hold the key, (2) store the algorithm when no
 * operation is active, and (3) save progress information for the current
 * operation. With PSA those roles are held by disinct objects: (1) a
 * psa_key_id_t to hold the key, a (2) psa_algorithm_t to represent the
 * algorithm, and (3) a psa_operation_t for multi-part progress.
 *
 * On the other hand, with PSA, the algorithms encodes the desired tag length;
 * with Cipher the desired tag length needs to be tracked separately.
 *
 * This program and its companion psa/aead_demo.c illustrate this by doing the
 * same sequence of multi-part AEAD computation with both APIs; looking at the
 * two side by side should make the differences and similarities clear.
 */

/*
 *  Copyright The Mbed TLS Contributors
 *  SPDX-License-Identifier: Apache-2.0 OR GPL-2.0-or-later
 */

/* First include Mbed TLS headers to get the Mbed TLS configuration and
 * platform definitions that we'll use in this program. Also include
 * standard C headers for functions we'll use here. */
#include "mbedtls/build_info.h"

#include "mbedtls/cipher.h"

#include <stdlib.h>
#include <stdio.h>
#include <string.h>

/* If the build options we need are not enabled, compile a placeholder. */
#if !defined(MBEDTLS_CIPHER_C) || \
    !defined(MBEDTLS_AES_C) || !defined(MBEDTLS_GCM_C) || \
    !defined(MBEDTLS_CHACHAPOLY_C)
int main(void)
{
    printf("MBEDTLS_MD_C and/or "
           "MBEDTLS_AES_C and/or MBEDTLS_GCM_C and/or "
           "MBEDTLS_CHACHAPOLY_C not defined\r\n");
    return 0;
}
#else

/* The real program starts here. */

const char usage[] =
    "Usage: cipher_aead_demo [aes128-gcm|aes256-gcm|aes128-gcm_8|chachapoly]";

/* Dummy data for encryption: IV/nonce, additional data, 2-part message */
const unsigned char iv1[12] = { 0x00 };
const unsigned char add_data1[] = { 0x01, 0x02 };
const unsigned char msg1_part1[] = { 0x03, 0x04 };
const unsigned char msg1_part2[] = { 0x05, 0x06, 0x07 };

/* Dummy data (2nd message) */
const unsigned char iv2[12] = { 0x10 };
const unsigned char add_data2[] = { 0x11, 0x12 };
const unsigned char msg2_part1[] = { 0x13, 0x14 };
const unsigned char msg2_part2[] = { 0x15, 0x16, 0x17 };

/* Maximum total size of the messages */
#define MSG1_SIZE (sizeof(msg1_part1) + sizeof(msg1_part2))
#define MSG2_SIZE (sizeof(msg2_part1) + sizeof(msg2_part2))
#define MSG_MAX_SIZE (MSG1_SIZE > MSG2_SIZE ? MSG1_SIZE : MSG2_SIZE)

/* Dummy key material - never do this in production!
 * 32-byte is enough to all the key size supported by this program. */
const unsigned char key_bytes[32] = { 0x2a };

/* Print the contents of a buffer in hex */
void print_buf(const char *title, unsigned char *buf, size_t len)
{
    printf("%s:", title);
    for (size_t i = 0; i < len; i++) {
        printf(" %02x", buf[i]);
    }
    printf("\n");
}

/* Run an Mbed TLS function and bail out if it fails.
 * A string description of the error code can be recovered with:
 * programs/util/strerror <value> */
#define CHK(expr)                                             \
    do                                                          \
    {                                                           \
        ret = (expr);                                         \
        if (ret != 0)                                          \
        {                                                       \
            printf("Error %d at line %d: %s\n",                \
                   ret,                                        \
                   __LINE__,                                   \
                   #expr);                                    \
            goto exit;                                          \
        }                                                       \
    } while (0)

/*
 * Prepare encryption material:
 * - interpret command-line argument
 * - set up key
 * - outputs: context and tag length, which together hold all the information
 */
static int aead_prepare(const char *info,
                        mbedtls_cipher_context_t *ctx,
                        size_t *tag_len)
{
    int ret;

    /* Convert arg to type + tag_len */
    mbedtls_cipher_type_t type;
    if (strcmp(info, "aes128-gcm") == 0) {
        type = MBEDTLS_CIPHER_AES_128_GCM;
        *tag_len = 16;
    } else if (strcmp(info, "aes256-gcm") == 0) {
        type = MBEDTLS_CIPHER_AES_256_GCM;
        *tag_len = 16;
    } else if (strcmp(info, "aes128-gcm_8") == 0) {
        type = MBEDTLS_CIPHER_AES_128_GCM;
        *tag_len = 8;
    } else if (strcmp(info, "chachapoly") == 0) {
        type = MBEDTLS_CIPHER_CHACHA20_POLY1305;
        *tag_len = 16;
    } else {
        puts(usage);
        return MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA;
    }

    /* Prepare context for the given type */
    CHK(mbedtls_cipher_setup(ctx,
                             mbedtls_cipher_info_from_type(type)));

    /* Import key */
    int key_len = mbedtls_cipher_get_key_bitlen(ctx);
    CHK(mbedtls_cipher_setkey(ctx, key_bytes, key_len, MBEDTLS_ENCRYPT));

exit:
    return ret;
}

/*
 * Print out some information.
 *
 * All of this information was present in the command line argument, but his
 * function demonstrates how each piece can be recovered from (ctx, tag_len).
 */
static void aead_info(const mbedtls_cipher_context_t *ctx, size_t tag_len)
{
    mbedtls_cipher_type_t type = mbedtls_cipher_get_type(ctx);
    const mbedtls_cipher_info_t *info = mbedtls_cipher_info_from_type(type);
    const char *ciph = mbedtls_cipher_info_get_name(info);
    int key_bits = mbedtls_cipher_get_key_bitlen(ctx);
    mbedtls_cipher_mode_t mode = mbedtls_cipher_get_cipher_mode(ctx);

    const char *mode_str = mode == MBEDTLS_MODE_GCM ? "GCM"
                         : mode == MBEDTLS_MODE_CHACHAPOLY ? "ChachaPoly"
                         : "???";

    printf("%s, %d, %s, %u\n",
           ciph, key_bits, mode_str, (unsigned) tag_len);
}

/*
 * Encrypt a 2-part message.
 */
static int aead_encrypt(mbedtls_cipher_context_t *ctx, size_t tag_len,
                        const unsigned char *iv, size_t iv_len,
                        const unsigned char *ad, size_t ad_len,
                        const unsigned char *part1, size_t part1_len,
                        const unsigned char *part2, size_t part2_len)
{
    int ret;
    size_t olen;
#define MAX_TAG_LENGTH 16
    unsigned char out[MSG_MAX_SIZE + MAX_TAG_LENGTH];
    unsigned char *p = out;

    CHK(mbedtls_cipher_set_iv(ctx, iv, iv_len));
    CHK(mbedtls_cipher_reset(ctx));
    CHK(mbedtls_cipher_update_ad(ctx, ad, ad_len));
    CHK(mbedtls_cipher_update(ctx, part1, part1_len, p, &olen));
    p += olen;
    CHK(mbedtls_cipher_update(ctx, part2, part2_len, p, &olen));
    p += olen;
    CHK(mbedtls_cipher_finish(ctx, p, &olen));
    p += olen;
    CHK(mbedtls_cipher_write_tag(ctx, p, tag_len));
    p += tag_len;

    olen = p - out;
    print_buf("out", out, olen);

exit:
    return ret;
}

/*
 * AEAD demo: set up key/alg, print out info, encrypt messages.
 */
static int aead_demo(const char *info)
{
    int ret = 0;

    mbedtls_cipher_context_t ctx;
    size_t tag_len;

    mbedtls_cipher_init(&ctx);

    CHK(aead_prepare(info, &ctx, &tag_len));

    aead_info(&ctx, tag_len);

    CHK(aead_encrypt(&ctx, tag_len,
                     iv1, sizeof(iv1), add_data1, sizeof(add_data1),
                     msg1_part1, sizeof(msg1_part1),
                     msg1_part2, sizeof(msg1_part2)));
    CHK(aead_encrypt(&ctx, tag_len,
                     iv2, sizeof(iv2), add_data2, sizeof(add_data2),
                     msg2_part1, sizeof(msg2_part1),
                     msg2_part2, sizeof(msg2_part2)));

exit:
    mbedtls_cipher_free(&ctx);

    return ret;
}


/*
 * Main function
 */
int main(int argc, char **argv)
{
    /* Check usage */
    if (argc != 2) {
        puts(usage);
        return 1;
    }

    int ret;

    /* Run the demo */
    CHK(aead_demo(argv[1]));

exit:
    return ret == 0 ? EXIT_SUCCESS : EXIT_FAILURE;
}

#endif