library/ccm.c

/*
 *  NIST SP800-38C compliant CCM implementation
 *
 *  Copyright The Mbed TLS Contributors
 *  SPDX-License-Identifier: Apache-2.0 OR GPL-2.0-or-later
 */

/*
 * Definition of CCM:
 * http://csrc.nist.gov/publications/nistpubs/800-38C/SP800-38C_updated-July20_2007.pdf
 * RFC 3610 "Counter with CBC-MAC (CCM)"
 *
 * Related:
 * RFC 5116 "An Interface and Algorithms for Authenticated Encryption"
 */

#include "common.h"

#if defined(MBEDTLS_CCM_C)

#include "mbedtls/ccm.h"
#include "mbedtls/platform_util.h"
#include "mbedtls/error.h"
#include "mbedtls/constant_time.h"

#include <string.h>

#include "mbedtls/platform.h"

#if !defined(MBEDTLS_CCM_ALT)

#define CCM_VALIDATE_RET(cond) \
    MBEDTLS_INTERNAL_VALIDATE_RET(cond, MBEDTLS_ERR_CCM_BAD_INPUT)
#define CCM_VALIDATE(cond) \
    MBEDTLS_INTERNAL_VALIDATE(cond)

#define CCM_ENCRYPT 0
#define CCM_DECRYPT 1

/*
 * Initialize context
 */
void mbedtls_ccm_init(mbedtls_ccm_context *ctx)
{
    CCM_VALIDATE(ctx != NULL);
    memset(ctx, 0, sizeof(mbedtls_ccm_context));
}

int mbedtls_ccm_setkey(mbedtls_ccm_context *ctx,
                       mbedtls_cipher_id_t cipher,
                       const unsigned char *key,
                       unsigned int keybits)
{
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
    const mbedtls_cipher_info_t *cipher_info;

    CCM_VALIDATE_RET(ctx != NULL);
    CCM_VALIDATE_RET(key != NULL);

    cipher_info = mbedtls_cipher_info_from_values(cipher, keybits,
                                                  MBEDTLS_MODE_ECB);
    if (cipher_info == NULL) {
        return MBEDTLS_ERR_CCM_BAD_INPUT;
    }

    if (cipher_info->block_size != 16) {
        return MBEDTLS_ERR_CCM_BAD_INPUT;
    }

    mbedtls_cipher_free(&ctx->cipher_ctx);

    if ((ret = mbedtls_cipher_setup(&ctx->cipher_ctx, cipher_info)) != 0) {
        return ret;
    }

    if ((ret = mbedtls_cipher_setkey(&ctx->cipher_ctx, key, keybits,
                                     MBEDTLS_ENCRYPT)) != 0) {
        return ret;
    }

    return 0;
}

/*
 * Free context
 */
void mbedtls_ccm_free(mbedtls_ccm_context *ctx)
{
    if (ctx == NULL) {
        return;
    }
    mbedtls_cipher_free(&ctx->cipher_ctx);
    mbedtls_platform_zeroize(ctx, sizeof(mbedtls_ccm_context));
}

/*
 * Macros for common operations.
 * Results in smaller compiled code than static inline functions.
 */

/*
 * Update the CBC-MAC state in y using a block in b
 * (Always using b as the source helps the compiler optimise a bit better.)
 */
#define UPDATE_CBC_MAC                                                      \
    for (i = 0; i < 16; i++)                                               \
    y[i] ^= b[i];                                                       \
                                                                            \
    if ((ret = mbedtls_cipher_update(&ctx->cipher_ctx, y, 16, y, &olen)) != 0) \
    return ret;

/*
 * Encrypt or decrypt a partial block with CTR
 * Warning: using b for temporary storage! src and dst must not be b!
 * This avoids allocating one more 16 bytes buffer while allowing src == dst.
 */
#define CTR_CRYPT(dst, src, len)                                            \
    do                                                                  \
    {                                                                   \
        if ((ret = mbedtls_cipher_update(&ctx->cipher_ctx, ctr,       \
                                         16, b, &olen)) != 0)      \
        {                                                               \
            return ret;                                              \
        }                                                               \
                                                                      \
        for (i = 0; i < (len); i++)                                    \
        (dst)[i] = (src)[i] ^ b[i];                                 \
    } while (0)

/*
 * Authenticated encryption or decryption
 */
static int ccm_auth_crypt(mbedtls_ccm_context *ctx, int mode, size_t length,
                          const unsigned char *iv, size_t iv_len,
                          const unsigned char *add, size_t add_len,
                          const unsigned char *input, unsigned char *output,
                          unsigned char *tag, size_t tag_len)
{
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
    unsigned char i;
    unsigned char q;
    size_t len_left, olen;
    unsigned char b[16];
    unsigned char y[16];
    unsigned char ctr[16];
    const unsigned char *src;
    unsigned char *dst;

    /*
     * Check length requirements: SP800-38C A.1
     * Additional requirement: a < 2^16 - 2^8 to simplify the code.
     * 'length' checked later (when writing it to the first block)
     *
     * Also, loosen the requirements to enable support for CCM* (IEEE 802.15.4).
     */
    if (tag_len == 2 || tag_len > 16 || tag_len % 2 != 0) {
        return MBEDTLS_ERR_CCM_BAD_INPUT;
    }

    /* Also implies q is within bounds */
    if (iv_len < 7 || iv_len > 13) {
        return MBEDTLS_ERR_CCM_BAD_INPUT;
    }

    if (add_len >= 0xFF00) {
        return MBEDTLS_ERR_CCM_BAD_INPUT;
    }

    q = 16 - 1 - (unsigned char) iv_len;

    /*
     * First block B_0:
     * 0        .. 0        flags
     * 1        .. iv_len   nonce (aka iv)
     * iv_len+1 .. 15       length
     *
     * With flags as (bits):
     * 7        0
     * 6        add present?
     * 5 .. 3   (t - 2) / 2
     * 2 .. 0   q - 1
     */
    b[0] = 0;
    b[0] |= (add_len > 0) << 6;
    b[0] |= ((tag_len - 2) / 2) << 3;
    b[0] |= q - 1;

    memcpy(b + 1, iv, iv_len);

    for (i = 0, len_left = length; i < q; i++, len_left >>= 8) {
        b[15-i] = MBEDTLS_BYTE_0(len_left);
    }

    if (len_left > 0) {
        return MBEDTLS_ERR_CCM_BAD_INPUT;
    }


    /* Start CBC-MAC with first block */
    memset(y, 0, 16);
    UPDATE_CBC_MAC;

    /*
     * If there is additional data, update CBC-MAC with
     * add_len, add, 0 (padding to a block boundary)
     */
    if (add_len > 0) {
        size_t use_len;
        len_left = add_len;
        src = add;

        memset(b, 0, 16);
        MBEDTLS_PUT_UINT16_BE(add_len, b, 0);

        use_len = len_left < 16 - 2 ? len_left : 16 - 2;
        memcpy(b + 2, src, use_len);
        len_left -= use_len;
        src += use_len;

        UPDATE_CBC_MAC;

        while (len_left > 0) {
            use_len = len_left > 16 ? 16 : len_left;

            memset(b, 0, 16);
            memcpy(b, src, use_len);
            UPDATE_CBC_MAC;

            len_left -= use_len;
            src += use_len;
        }
    }

    /*
     * Prepare counter block for encryption:
     * 0        .. 0        flags
     * 1        .. iv_len   nonce (aka iv)
     * iv_len+1 .. 15       counter (initially 1)
     *
     * With flags as (bits):
     * 7 .. 3   0
     * 2 .. 0   q - 1
     */
    ctr[0] = q - 1;
    memcpy(ctr + 1, iv, iv_len);
    memset(ctr + 1 + iv_len, 0, q);
    ctr[15] = 1;

    /*
     * Authenticate and {en,de}crypt the message.
     *
     * The only difference between encryption and decryption is
     * the respective order of authentication and {en,de}cryption.
     */
    len_left = length;
    src = input;
    dst = output;

    while (len_left > 0) {
        size_t use_len = len_left > 16 ? 16 : len_left;

        if (mode == CCM_ENCRYPT) {
            memset(b, 0, 16);
            memcpy(b, src, use_len);
            UPDATE_CBC_MAC;
        }

        CTR_CRYPT(dst, src, use_len);

        if (mode == CCM_DECRYPT) {
            memset(b, 0, 16);
            memcpy(b, dst, use_len);
            UPDATE_CBC_MAC;
        }

        dst += use_len;
        src += use_len;
        len_left -= use_len;

        /*
         * Increment counter.
         * No need to check for overflow thanks to the length check above.
         */
        for (i = 0; i < q; i++) {
            if (++ctr[15-i] != 0) {
                break;
            }
        }
    }

    /*
     * Authentication: reset counter and crypt/mask internal tag
     */
    for (i = 0; i < q; i++) {
        ctr[15-i] = 0;
    }

    CTR_CRYPT(y, y, 16);
    memcpy(tag, y, tag_len);

    return 0;
}

/*
 * Authenticated encryption
 */
int mbedtls_ccm_star_encrypt_and_tag(mbedtls_ccm_context *ctx, size_t length,
                                     const unsigned char *iv, size_t iv_len,
                                     const unsigned char *add, size_t add_len,
                                     const unsigned char *input, unsigned char *output,
                                     unsigned char *tag, size_t tag_len)
{
    CCM_VALIDATE_RET(ctx != NULL);
    CCM_VALIDATE_RET(iv != NULL);
    CCM_VALIDATE_RET(add_len == 0 || add != NULL);
    CCM_VALIDATE_RET(length == 0 || input != NULL);
    CCM_VALIDATE_RET(length == 0 || output != NULL);
    CCM_VALIDATE_RET(tag_len == 0 || tag != NULL);
    return ccm_auth_crypt(ctx, CCM_ENCRYPT, length, iv, iv_len,
                          add, add_len, input, output, tag, tag_len);
}

int mbedtls_ccm_encrypt_and_tag(mbedtls_ccm_context *ctx, size_t length,
                                const unsigned char *iv, size_t iv_len,
                                const unsigned char *add, size_t add_len,
                                const unsigned char *input, unsigned char *output,
                                unsigned char *tag, size_t tag_len)
{
    CCM_VALIDATE_RET(ctx != NULL);
    CCM_VALIDATE_RET(iv != NULL);
    CCM_VALIDATE_RET(add_len == 0 || add != NULL);
    CCM_VALIDATE_RET(length == 0 || input != NULL);
    CCM_VALIDATE_RET(length == 0 || output != NULL);
    CCM_VALIDATE_RET(tag_len == 0 || tag != NULL);
    if (tag_len == 0) {
        return MBEDTLS_ERR_CCM_BAD_INPUT;
    }

    return mbedtls_ccm_star_encrypt_and_tag(ctx, length, iv, iv_len, add,
                                            add_len, input, output, tag, tag_len);
}

/*
 * Authenticated decryption
 */
int mbedtls_ccm_star_auth_decrypt(mbedtls_ccm_context *ctx, size_t length,
                                  const unsigned char *iv, size_t iv_len,
                                  const unsigned char *add, size_t add_len,
                                  const unsigned char *input, unsigned char *output,
                                  const unsigned char *tag, size_t tag_len)
{
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
    unsigned char check_tag[16];
    int diff;

    CCM_VALIDATE_RET(ctx != NULL);
    CCM_VALIDATE_RET(iv != NULL);
    CCM_VALIDATE_RET(add_len == 0 || add != NULL);
    CCM_VALIDATE_RET(length == 0 || input != NULL);
    CCM_VALIDATE_RET(length == 0 || output != NULL);
    CCM_VALIDATE_RET(tag_len == 0 || tag != NULL);

    if ((ret = ccm_auth_crypt(ctx, CCM_DECRYPT, length,
                              iv, iv_len, add, add_len,
                              input, output, check_tag, tag_len)) != 0) {
        return ret;
    }

    /* Check tag in "constant-time" */
    diff = mbedtls_ct_memcmp(tag, check_tag, tag_len);

    if (diff != 0) {
        mbedtls_platform_zeroize(output, length);
        return MBEDTLS_ERR_CCM_AUTH_FAILED;
    }

    return 0;
}

int mbedtls_ccm_auth_decrypt(mbedtls_ccm_context *ctx, size_t length,
                             const unsigned char *iv, size_t iv_len,
                             const unsigned char *add, size_t add_len,
                             const unsigned char *input, unsigned char *output,
                             const unsigned char *tag, size_t tag_len)
{
    CCM_VALIDATE_RET(ctx != NULL);
    CCM_VALIDATE_RET(iv != NULL);
    CCM_VALIDATE_RET(add_len == 0 || add != NULL);
    CCM_VALIDATE_RET(length == 0 || input != NULL);
    CCM_VALIDATE_RET(length == 0 || output != NULL);
    CCM_VALIDATE_RET(tag_len == 0 || tag != NULL);

    if (tag_len == 0) {
        return MBEDTLS_ERR_CCM_BAD_INPUT;
    }

    return mbedtls_ccm_star_auth_decrypt(ctx, length, iv, iv_len, add,
                                         add_len, input, output, tag, tag_len);
}
#endif /* !MBEDTLS_CCM_ALT */

#if defined(MBEDTLS_SELF_TEST) && defined(MBEDTLS_AES_C)
/*
 * Examples 1 to 3 from SP800-38C Appendix C
 */

#define NB_TESTS 3
#define CCM_SELFTEST_PT_MAX_LEN 24
#define CCM_SELFTEST_CT_MAX_LEN 32
/*
 * The data is the same for all tests, only the used length changes
 */
static const unsigned char key_test_data[] = {
    0x40, 0x41, 0x42, 0x43, 0x44, 0x45, 0x46, 0x47,
    0x48, 0x49, 0x4a, 0x4b, 0x4c, 0x4d, 0x4e, 0x4f
};

static const unsigned char iv_test_data[] = {
    0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17,
    0x18, 0x19, 0x1a, 0x1b
};

static const unsigned char ad_test_data[] = {
    0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,
    0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f,
    0x10, 0x11, 0x12, 0x13
};

static const unsigned char msg_test_data[CCM_SELFTEST_PT_MAX_LEN] = {
    0x20, 0x21, 0x22, 0x23, 0x24, 0x25, 0x26, 0x27,
    0x28, 0x29, 0x2a, 0x2b, 0x2c, 0x2d, 0x2e, 0x2f,
    0x30, 0x31, 0x32, 0x33, 0x34, 0x35, 0x36, 0x37,
};

static const size_t iv_len_test_data[NB_TESTS] = { 7, 8,  12 };
static const size_t add_len_test_data[NB_TESTS] = { 8, 16, 20 };
static const size_t msg_len_test_data[NB_TESTS] = { 4, 16, 24 };
static const size_t tag_len_test_data[NB_TESTS] = { 4, 6,  8  };

static const unsigned char res_test_data[NB_TESTS][CCM_SELFTEST_CT_MAX_LEN] = {
    {   0x71, 0x62, 0x01, 0x5b, 0x4d, 0xac, 0x25, 0x5d },
    {   0xd2, 0xa1, 0xf0, 0xe0, 0x51, 0xea, 0x5f, 0x62,
        0x08, 0x1a, 0x77, 0x92, 0x07, 0x3d, 0x59, 0x3d,
        0x1f, 0xc6, 0x4f, 0xbf, 0xac, 0xcd },
    {   0xe3, 0xb2, 0x01, 0xa9, 0xf5, 0xb7, 0x1a, 0x7a,
        0x9b, 0x1c, 0xea, 0xec, 0xcd, 0x97, 0xe7, 0x0b,
        0x61, 0x76, 0xaa, 0xd9, 0xa4, 0x42, 0x8a, 0xa5,
        0x48, 0x43, 0x92, 0xfb, 0xc1, 0xb0, 0x99, 0x51 }
};

int mbedtls_ccm_self_test(int verbose)
{
    mbedtls_ccm_context ctx;
    /*
     * Some hardware accelerators require the input and output buffers
     * would be in RAM, because the flash is not accessible.
     * Use buffers on the stack to hold the test vectors data.
     */
    unsigned char plaintext[CCM_SELFTEST_PT_MAX_LEN];
    unsigned char ciphertext[CCM_SELFTEST_CT_MAX_LEN];
    size_t i;
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;

    mbedtls_ccm_init(&ctx);

    if (mbedtls_ccm_setkey(&ctx, MBEDTLS_CIPHER_ID_AES, key_test_data,
                           8 * sizeof(key_test_data)) != 0) {
        if (verbose != 0) {
            mbedtls_printf("  CCM: setup failed");
        }

        return 1;
    }

    for (i = 0; i < NB_TESTS; i++) {
        if (verbose != 0) {
            mbedtls_printf("  CCM-AES #%u: ", (unsigned int) i + 1);
        }

        memset(plaintext, 0, CCM_SELFTEST_PT_MAX_LEN);
        memset(ciphertext, 0, CCM_SELFTEST_CT_MAX_LEN);
        memcpy(plaintext, msg_test_data, msg_len_test_data[i]);

        ret = mbedtls_ccm_encrypt_and_tag(&ctx, msg_len_test_data[i],
                                          iv_test_data, iv_len_test_data[i],
                                          ad_test_data, add_len_test_data[i],
                                          plaintext, ciphertext,
                                          ciphertext + msg_len_test_data[i],
                                          tag_len_test_data[i]);

        if (ret != 0 ||
            memcmp(ciphertext, res_test_data[i],
                   msg_len_test_data[i] + tag_len_test_data[i]) != 0) {
            if (verbose != 0) {
                mbedtls_printf("failed\n");
            }

            return 1;
        }
        memset(plaintext, 0, CCM_SELFTEST_PT_MAX_LEN);

        ret = mbedtls_ccm_auth_decrypt(&ctx, msg_len_test_data[i],
                                       iv_test_data, iv_len_test_data[i],
                                       ad_test_data, add_len_test_data[i],
                                       ciphertext, plaintext,
                                       ciphertext + msg_len_test_data[i],
                                       tag_len_test_data[i]);

        if (ret != 0 ||
            memcmp(plaintext, msg_test_data, msg_len_test_data[i]) != 0) {
            if (verbose != 0) {
                mbedtls_printf("failed\n");
            }

            return 1;
        }

        if (verbose != 0) {
            mbedtls_printf("passed\n");
        }
    }

    mbedtls_ccm_free(&ctx);

    if (verbose != 0) {
        mbedtls_printf("\n");
    }

    return 0;
}

#endif /* MBEDTLS_SELF_TEST && MBEDTLS_AES_C */

#endif /* MBEDTLS_CCM_C */