/*

 *  PSA FFDH layer on top of Mbed TLS crypto

 */

/*

 *  Copyright The Mbed TLS Contributors

 *  SPDX-License-Identifier: Apache-2.0 OR GPL-2.0-or-later

 */

#include "common.h"

#if defined(MBEDTLS_PSA_CRYPTO_C)

/* This header is only needed because it defines

 * MBEDTLS_DHM_RFC7919_FFDHEXXXX_[P|G]_BIN symbols that are used in

 * mbedtls_psa_ffdh_set_prime_generator(). Apart from that, this module

 * only uses bignum functions for arithmetic. */

#include <mbedtls/dhm.h>

#include <psa/crypto.h>

#include "psa_crypto_core.h"

#include "psa_crypto_ffdh.h"

#include "psa_crypto_random_impl.h"

#include "mbedtls/platform.h"

#include "mbedtls/error.h"

#if defined(MBEDTLS_PSA_BUILTIN_KEY_TYPE_DH_KEY_PAIR_EXPORT) ||   \

    defined(MBEDTLS_PSA_BUILTIN_KEY_TYPE_DH_KEY_PAIR_GENERATE) ||   \

    defined(MBEDTLS_PSA_BUILTIN_KEY_TYPE_DH_PUBLIC_KEY) || \

    defined(MBEDTLS_PSA_BUILTIN_ALG_FFDH)

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;

    }

#if defined(MBEDTLS_PSA_BUILTIN_DH_RFC7919_2048)

    static const unsigned char dhm_P_2048[] =

        MBEDTLS_DHM_RFC7919_FFDHE2048_P_BIN;

    static const unsigned char dhm_G_2048[] =

        MBEDTLS_DHM_RFC7919_FFDHE2048_G_BIN;

#endif /* MBEDTLS_PSA_BUILTIN_DH_RFC7919_2048 */

#if defined(MBEDTLS_PSA_BUILTIN_DH_RFC7919_3072)

    static const unsigned char dhm_P_3072[] =

        MBEDTLS_DHM_RFC7919_FFDHE3072_P_BIN;

    static const unsigned char dhm_G_3072[] =

        MBEDTLS_DHM_RFC7919_FFDHE3072_G_BIN;

#endif /* MBEDTLS_PSA_BUILTIN_DH_RFC7919_3072 */

#if defined(MBEDTLS_PSA_BUILTIN_DH_RFC7919_4096)

    static const unsigned char dhm_P_4096[] =

        MBEDTLS_DHM_RFC7919_FFDHE4096_P_BIN;

    static const unsigned char dhm_G_4096[] =

        MBEDTLS_DHM_RFC7919_FFDHE4096_G_BIN;

#endif /* MBEDTLS_PSA_BUILTIN_DH_RFC7919_4096 */

#if defined(MBEDTLS_PSA_BUILTIN_DH_RFC7919_6144)

    static const unsigned char dhm_P_6144[] =

        MBEDTLS_DHM_RFC7919_FFDHE6144_P_BIN;

    static const unsigned char dhm_G_6144[] =

        MBEDTLS_DHM_RFC7919_FFDHE6144_G_BIN;

#endif /* MBEDTLS_PSA_BUILTIN_DH_RFC7919_6144 */

#if defined(MBEDTLS_PSA_BUILTIN_DH_RFC7919_8192)

    static const unsigned char dhm_P_8192[] =

        MBEDTLS_DHM_RFC7919_FFDHE8192_P_BIN;

    static const unsigned char dhm_G_8192[] =

        MBEDTLS_DHM_RFC7919_FFDHE8192_G_BIN;

#endif /* MBEDTLS_PSA_BUILTIN_DH_RFC7919_8192 */

    switch (key_size) {

#if defined(MBEDTLS_PSA_BUILTIN_DH_RFC7919_2048)

        case sizeof(dhm_P_2048):

            dhm_P = dhm_P_2048;

            dhm_G = dhm_G_2048;

            dhm_size_P = sizeof(dhm_P_2048);

            dhm_size_G = sizeof(dhm_G_2048);

            break;

#endif /* MBEDTLS_PSA_BUILTIN_DH_RFC7919_2048 */

#if defined(MBEDTLS_PSA_BUILTIN_DH_RFC7919_3072)

        case sizeof(dhm_P_3072):

            dhm_P = dhm_P_3072;

            dhm_G = dhm_G_3072;

            dhm_size_P = sizeof(dhm_P_3072);

            dhm_size_G = sizeof(dhm_G_3072);

            break;

#endif /* MBEDTLS_PSA_BUILTIN_DH_RFC7919_3072 */

#if defined(MBEDTLS_PSA_BUILTIN_DH_RFC7919_4096)

        case sizeof(dhm_P_4096):

            dhm_P = dhm_P_4096;

            dhm_G = dhm_G_4096;

            dhm_size_P = sizeof(dhm_P_4096);

            dhm_size_G = sizeof(dhm_G_4096);

            break;

#endif /* MBEDTLS_PSA_BUILTIN_DH_RFC7919_4096 */

#if defined(MBEDTLS_PSA_BUILTIN_DH_RFC7919_6144)

        case sizeof(dhm_P_6144):

            dhm_P = dhm_P_6144;

            dhm_G = dhm_G_6144;

            dhm_size_P = sizeof(dhm_P_6144);

            dhm_size_G = sizeof(dhm_G_6144);

            break;

#endif /* MBEDTLS_PSA_BUILTIN_DH_RFC7919_6144 */

#if defined(MBEDTLS_PSA_BUILTIN_DH_RFC7919_8192)

        case sizeof(dhm_P_8192):

            dhm_P = dhm_P_8192;

            dhm_G = dhm_G_8192;

            dhm_size_P = sizeof(dhm_P_8192);

            dhm_size_G = sizeof(dhm_G_8192);

            break;

#endif /* MBEDTLS_PSA_BUILTIN_DH_RFC7919_8192 */

        default:

            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;

}

#endif /* MBEDTLS_PSA_BUILTIN_KEY_TYPE_DH_KEY_PAIR_EXPORT ||

          MBEDTLS_PSA_BUILTIN_KEY_TYPE_DH_KEY_PAIR_GENERATE ||

          MBEDTLS_PSA_BUILTIN_KEY_TYPE_DH_PUBLIC_KEY ||

          MBEDTLS_PSA_BUILTIN_ALG_FFDH */

#if defined(MBEDTLS_PSA_BUILTIN_KEY_TYPE_DH_KEY_PAIR_EXPORT) || \

    defined(MBEDTLS_PSA_BUILTIN_KEY_TYPE_DH_PUBLIC_KEY)

psa_status_t mbedtls_psa_ffdh_export_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;

    psa_key_type_t type = attributes->type;

    if (PSA_KEY_TYPE_IS_PUBLIC_KEY(type)) {

        if (key_buffer_size > data_size) {

            return PSA_ERROR_BUFFER_TOO_SMALL;

        }

        memcpy(data, key_buffer, key_buffer_size);

        memset(data + key_buffer_size, 0,

               data_size - key_buffer_size);

        *data_length = key_buffer_size;

        return PSA_SUCCESS;

    }

    mbedtls_mpi_init(&GX); mbedtls_mpi_init(&G);

    mbedtls_mpi_init(&X); mbedtls_mpi_init(&P);

    size_t key_len = PSA_BITS_TO_BYTES(attributes->bits);

    if (key_len > data_size) {

        status = PSA_ERROR_BUFFER_TOO_SMALL;

        goto cleanup;

    }

    status = mbedtls_psa_ffdh_set_prime_generator(key_len, &P, &G);

    if (status != PSA_SUCCESS) {

        goto cleanup;

    }

    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, key_len));

    *data_length = key_len;

    ret = 0;

cleanup:

    mbedtls_mpi_free(&P); mbedtls_mpi_free(&G);

    mbedtls_mpi_free(&X); mbedtls_mpi_free(&GX);

    if (status == PSA_SUCCESS && ret != 0) {

        status = mbedtls_to_psa_error(ret);

    }

    return status;

}

#endif /* MBEDTLS_PSA_BUILTIN_KEY_TYPE_DH_KEY_PAIR_EXPORT ||

          MBEDTLS_PSA_BUILTIN_KEY_TYPE_DH_PUBLIC_KEY */

#if defined(MBEDTLS_PSA_BUILTIN_KEY_TYPE_DH_KEY_PAIR_GENERATE)

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);

    (void) attributes;

    status = mbedtls_psa_ffdh_set_prime_generator(key_buffer_size, &P, NULL);

    if (status != PSA_SUCCESS) {

        goto cleanup;

    }

    /* RFC7919: Traditional finite field Diffie-Hellman has each peer choose their

        secret exponent from the range [2, P-2].

        Select random value in range [3, P-1] and decrease it by 1. */

    MBEDTLS_MPI_CHK(mbedtls_mpi_random(&X, 3, &P, mbedtls_psa_get_random,

                                       MBEDTLS_PSA_RANDOM_STATE));

    MBEDTLS_MPI_CHK(mbedtls_mpi_sub_int(&X, &X, 1));

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

    *key_buffer_length = 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_DH_KEY_PAIR_GENERATE */

#if defined(MBEDTLS_PSA_BUILTIN_KEY_TYPE_DH_KEY_PAIR_IMPORT)

psa_status_t mbedtls_psa_ffdh_import_key(

    const psa_key_attributes_t *attributes,

    const uint8_t *data, size_t data_length,

    uint8_t *key_buffer, size_t key_buffer_size,

    size_t *key_buffer_length, size_t *bits)

{

    (void) attributes;

    if (key_buffer_size < data_length) {

        return PSA_ERROR_BUFFER_TOO_SMALL;

    }

    memcpy(key_buffer, data, data_length);

    *key_buffer_length = data_length;

    *bits = PSA_BYTES_TO_BITS(data_length);

    return PSA_SUCCESS;

}

#endif /* MBEDTLS_PSA_BUILTIN_KEY_TYPE_DH_KEY_PAIR_IMPORT */

#if defined(MBEDTLS_PSA_BUILTIN_ALG_FFDH)

psa_status_t mbedtls_psa_ffdh_key_agreement(

    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, X, GY, K;

    const size_t calculated_shared_secret_size = key_buffer_size;

    if (!PSA_KEY_TYPE_IS_DH_KEY_PAIR(psa_get_key_type(attributes))) {

        return PSA_ERROR_INVALID_ARGUMENT;

    }

    if (peer_key_length != key_buffer_size) {

        return PSA_ERROR_INVALID_ARGUMENT;

    }

    /* This has been checked by the core, but keep a local check too. */

    if (calculated_shared_secret_size > shared_secret_size) {

        return PSA_ERROR_BUFFER_TOO_SMALL;

    }

    mbedtls_mpi_init(&P);

    mbedtls_mpi_init(&X); mbedtls_mpi_init(&GY);

    mbedtls_mpi_init(&K);

    status = mbedtls_psa_ffdh_set_prime_generator(

        PSA_BITS_TO_BYTES(attributes->bits), &P, NULL);

    if (status != PSA_SUCCESS) {

        goto cleanup;

    }

    MBEDTLS_MPI_CHK(mbedtls_mpi_read_binary(&GY, peer_key,

                                            peer_key_length));

    /* RFC 7919 5.1: validate the peer's public key: 1 < GY < P-1

     *

     * This check is sufficient to ensure GY is not of low order, because we're

     * using a safe prime (that is, q = (p-1) / 2 is also prime), so the only

     * group elements of low order are 1 and p-1. (Obviously we also want to

     * exclude 0 that is not a group element, and values >= p as they are not

     * residues mod p.)

     *

     * Note: we know we're using a safe prime because the only FFDH groups

     * defined by the PSA spec are from RFC 7919 (since version 1.0) and RFC

     * 3525 (since v1.4, not yet supported in tf-psa-crypto as of writing this

     * comment), which both use safe primes.

     *

     * Note: NIST SP 800-56Ar3 5.7.1.1 (2) has the check on the shared secret,

     * but checking before is equivalent (unless our secret key is exactly

     * (p-1)/2, which has negligible probability and can't be influenced by the

     * adversary). Checking before is cleaner in terms of side channel analysis,

     * as we haven't loaded our secret yet, so no worries about branches.

     *

     * Use X as a temporary, since we haven't loaded it yet.

     */

    MBEDTLS_MPI_CHK(mbedtls_mpi_sub_int(&X, &P, 1)); // x = p - 1

    if (mbedtls_mpi_cmp_mpi(&GY, &X) >= 0) {

        status = PSA_ERROR_INVALID_ARGUMENT;

        goto cleanup;

    }

    MBEDTLS_MPI_CHK(mbedtls_mpi_lset(&X, 1)); // x = 1

    if (mbedtls_mpi_cmp_mpi(&GY, &X) <= 0) {

        status = PSA_ERROR_INVALID_ARGUMENT;

        goto cleanup;

    }

    MBEDTLS_MPI_CHK(mbedtls_mpi_read_binary(&X, key_buffer,

                                            key_buffer_size));

    /* 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;

    ret = 0;

cleanup:

    mbedtls_mpi_free(&P);

    mbedtls_mpi_free(&X); mbedtls_mpi_free(&GY);

    mbedtls_mpi_free(&K);

    if (status == PSA_SUCCESS && ret != 0) {

        status = mbedtls_to_psa_error(ret);

    }

    return status;

}

#endif /* MBEDTLS_PSA_BUILTIN_ALG_FFDH */

#endif /* MBEDTLS_PSA_CRYPTO_C */