library/psa_crypto_ffdh.c

/*
 *  PSA FFDH layer on top of Mbed TLS crypto
 */
/*
 *  Copyright The Mbed TLS Contributors
 *  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 "common.h"

#if defined(MBEDTLS_PSA_CRYPTO_C)

#include <psa/crypto.h>
#include "psa_crypto_core.h"
#include "psa_crypto_ffdh.h"
#include "psa_crypto_random_impl.h"

#if defined(MBEDTLS_PSA_BUILTIN_KEY_TYPE_FFDH_KEY_PAIR) || \
    defined(MBEDTLS_PSA_BUILTIN_KEY_TYPE_FFDH_PUBLIC_KEY)
static psa_status_t mbedtls_psa_ffdh_set_prime_generator(size_t key_size,
                                                         mbedtls_mpi *P,
                                                         mbedtls_mpi *G)
{
    const unsigned char *dhm_P = NULL;
    const unsigned char *dhm_G = NULL;
    size_t dhm_size_P = 0;
    size_t dhm_size_G = 0;
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;

    if (P == NULL && G == NULL) {
        return PSA_ERROR_INVALID_ARGUMENT;
    }

    static const unsigned char dhm_P_2048[] =
        MBEDTLS_DHM_RFC7919_FFDHE2048_P_BIN;
    static const unsigned char dhm_P_3072[] =
        MBEDTLS_DHM_RFC7919_FFDHE3072_P_BIN;
    static const unsigned char dhm_P_4096[] =
        MBEDTLS_DHM_RFC7919_FFDHE4096_P_BIN;
    static const unsigned char dhm_P_6144[] =
        MBEDTLS_DHM_RFC7919_FFDHE6144_P_BIN;
    static const unsigned char dhm_P_8192[] =
        MBEDTLS_DHM_RFC7919_FFDHE8192_P_BIN;
    static const unsigned char dhm_G_2048[] =
        MBEDTLS_DHM_RFC7919_FFDHE2048_G_BIN;
    static const unsigned char dhm_G_3072[] =
        MBEDTLS_DHM_RFC7919_FFDHE3072_G_BIN;
    static const unsigned char dhm_G_4096[] =
        MBEDTLS_DHM_RFC7919_FFDHE4096_G_BIN;
    static const unsigned char dhm_G_6144[] =
        MBEDTLS_DHM_RFC7919_FFDHE6144_G_BIN;
    static const unsigned char dhm_G_8192[] =
        MBEDTLS_DHM_RFC7919_FFDHE8192_G_BIN;

    if (key_size <= 256) {
        dhm_P = dhm_P_2048;
        dhm_G = dhm_G_2048;
        dhm_size_P = sizeof(dhm_P_2048);
        dhm_size_G = sizeof(dhm_G_2048);
    } else if (key_size <= 384) {
        dhm_P = dhm_P_3072;
        dhm_G = dhm_G_3072;
        dhm_size_P = sizeof(dhm_P_3072);
        dhm_size_G = sizeof(dhm_G_3072);
    } else if (key_size <= 512) {
        dhm_P = dhm_P_4096;
        dhm_G = dhm_G_4096;
        dhm_size_P = sizeof(dhm_P_4096);
        dhm_size_G = sizeof(dhm_G_4096);
    } else if (key_size <= 768) {
        dhm_P = dhm_P_6144;
        dhm_G = dhm_G_6144;
        dhm_size_P = sizeof(dhm_P_6144);
        dhm_size_G = sizeof(dhm_G_6144);
    } else if (key_size <= 1024) {
        dhm_P = dhm_P_8192;
        dhm_G = dhm_G_8192;
        dhm_size_P = sizeof(dhm_P_8192);
        dhm_size_G = sizeof(dhm_G_8192);
    } else {
        return PSA_ERROR_INVALID_ARGUMENT;
    }

    if (P != NULL) {
        MBEDTLS_MPI_CHK(mbedtls_mpi_read_binary(P, dhm_P,
                                                dhm_size_P));
    }
    if (G != NULL) {
        MBEDTLS_MPI_CHK(mbedtls_mpi_read_binary(G, dhm_G,
                                                dhm_size_G));
    }

cleanup:
    if (ret != 0) {
        return mbedtls_to_psa_error(ret);
    }

    return PSA_SUCCESS;
}

#if defined(MBEDTLS_PSA_BUILTIN_ALG_FFDH)
psa_status_t mbedtls_psa_key_agreement_ffdh(
    const psa_key_attributes_t *attributes,
    const uint8_t *peer_key,
    size_t peer_key_length,
    const uint8_t *key_buffer,
    size_t key_buffer_size,
    uint8_t *shared_secret,
    size_t shared_secret_size,
    size_t *shared_secret_length)
{
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
    psa_status_t status = PSA_ERROR_CORRUPTION_DETECTED;
    mbedtls_mpi P, G, X, GY, K;
    const size_t calculated_shared_secret_size = peer_key_length;

    if (peer_key_length != key_buffer_size ||
        calculated_shared_secret_size > shared_secret_size) {
        return PSA_ERROR_INVALID_ARGUMENT;
    }

    if (!PSA_KEY_TYPE_IS_DH_KEY_PAIR(psa_get_key_type(attributes))) {
        return PSA_ERROR_INVALID_ARGUMENT;
    }

    mbedtls_mpi_init(&P); mbedtls_mpi_init(&G);
    mbedtls_mpi_init(&X); mbedtls_mpi_init(&GY);
    mbedtls_mpi_init(&K);

    status = mbedtls_psa_ffdh_set_prime_generator(
        PSA_BITS_TO_BYTES(attributes->core.bits), &P, &G);

    if (status == PSA_SUCCESS) {
        MBEDTLS_MPI_CHK(mbedtls_mpi_read_binary(&X, key_buffer,
                                                key_buffer_size));

        MBEDTLS_MPI_CHK(mbedtls_mpi_read_binary(&GY, peer_key,
                                                peer_key_length));

        /* Calculate shared secret public key: K = G^(XY) mod P = GY^X mod P */
        MBEDTLS_MPI_CHK(mbedtls_mpi_exp_mod(&K, &GY, &X, &P, NULL));

        MBEDTLS_MPI_CHK(mbedtls_mpi_write_binary(&K, shared_secret,
                                                 calculated_shared_secret_size));

        *shared_secret_length = calculated_shared_secret_size;
    }
cleanup:
    mbedtls_mpi_free(&P); mbedtls_mpi_free(&G);
    mbedtls_mpi_free(&X); mbedtls_mpi_free(&GY);
    mbedtls_mpi_free(&K);

    if (status == PSA_SUCCESS && ret != 0) {
        return mbedtls_to_psa_error(ret);
    }

    return PSA_SUCCESS;
}
#endif /* MBEDTLS_PSA_BUILTIN_ALG_FFDH */

psa_status_t mbedtls_psa_export_ffdh_public_key(
    const psa_key_attributes_t *attributes,
    const uint8_t *key_buffer,
    size_t key_buffer_size,
    uint8_t *data,
    size_t data_size,
    size_t *data_length)
{
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
    psa_status_t status = PSA_ERROR_CORRUPTION_DETECTED;
    mbedtls_mpi GX, G, X, P;

    mbedtls_mpi_init(&GX); mbedtls_mpi_init(&G);
    mbedtls_mpi_init(&X); mbedtls_mpi_init(&P);

    status = mbedtls_psa_ffdh_set_prime_generator(
        PSA_BITS_TO_BYTES(attributes->core.bits), &P, &G);

    if (status == PSA_SUCCESS) {
        MBEDTLS_MPI_CHK(mbedtls_mpi_read_binary(&X, key_buffer,
                                                key_buffer_size));

        MBEDTLS_MPI_CHK(mbedtls_mpi_exp_mod(&GX, &G, &X, &P, NULL));
        MBEDTLS_MPI_CHK(mbedtls_mpi_write_binary(&GX, data, data_size));

        *data_length = mbedtls_mpi_size(&GX);
    }
cleanup:
    mbedtls_mpi_free(&P); mbedtls_mpi_free(&G);
    mbedtls_mpi_free(&X); mbedtls_mpi_free(&GX);

    if (status == PSA_SUCCESS && ret != 0) {
        return mbedtls_to_psa_error(ret);
    }

    return status;
}

psa_status_t mbedtls_psa_ffdh_generate_key(
    const psa_key_attributes_t *attributes,
    uint8_t *key_buffer, size_t key_buffer_size, size_t *key_buffer_length)
{
    mbedtls_mpi X, P;
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
    psa_status_t status = PSA_ERROR_CORRUPTION_DETECTED;
    mbedtls_mpi_init(&P); mbedtls_mpi_init(&X);

    status = mbedtls_psa_ffdh_set_prime_generator(
        PSA_BITS_TO_BYTES(attributes->core.bits), &P, NULL);

    if (status == PSA_SUCCESS) {
        /* RFC7919: Traditional finite field Diffie-Hellman has each peer choose their
           secret exponent from the range [2, P-2].
           Select random value in range [4, P] and decrease it by 2. */
        MBEDTLS_MPI_CHK(mbedtls_mpi_random(&X, 4, &P, mbedtls_psa_get_random,
                                           MBEDTLS_PSA_RANDOM_STATE));
        MBEDTLS_MPI_CHK(mbedtls_mpi_sub_int(&X, &X, 2));

        *key_buffer_length = mbedtls_mpi_size(&X);

        MBEDTLS_MPI_CHK(mbedtls_mpi_write_binary(&X, key_buffer,
                                                 key_buffer_size));
    }

cleanup:
    mbedtls_mpi_free(&P); mbedtls_mpi_free(&X);
    if (status == PSA_SUCCESS && ret != 0) {
        return mbedtls_to_psa_error(ret);
    }

    return status;
}
#endif /* MBEDTLS_PSA_BUILTIN_KEY_TYPE_FFDH_KEY_PAIR ||
          MBEDTLS_PSA_BUILTIN_KEY_TYPE_FFDH_PUBLIC_KEY */

#endif /* MBEDTLS_PSA_CRYPTO_C */