library/psa_crypto_ecp.c

/*
 *  PSA ECP 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_ecp.h"
#include "psa_crypto_random_impl.h"
#include "md_psa.h"

#include <stdlib.h>
#include <string.h>
#include "mbedtls/platform.h"

#include <mbedtls/ecdsa.h>
#include <mbedtls/ecdh.h>
#include <mbedtls/ecp.h>
#include <mbedtls/error.h>

#if defined(MBEDTLS_PSA_BUILTIN_KEY_TYPE_ECC_KEY_PAIR_BASIC) || \
    defined(MBEDTLS_PSA_BUILTIN_KEY_TYPE_ECC_KEY_PAIR_IMPORT) || \
    defined(MBEDTLS_PSA_BUILTIN_KEY_TYPE_ECC_KEY_PAIR_EXPORT) || \
    defined(MBEDTLS_PSA_BUILTIN_KEY_TYPE_ECC_PUBLIC_KEY) || \
    defined(MBEDTLS_PSA_BUILTIN_ALG_ECDSA) || \
    defined(MBEDTLS_PSA_BUILTIN_ALG_DETERMINISTIC_ECDSA) || \
    defined(MBEDTLS_PSA_BUILTIN_ALG_ECDH)
psa_status_t mbedtls_psa_ecp_load_representation(
    psa_key_type_t type, size_t curve_bits,
    const uint8_t *data, size_t data_length,
    mbedtls_ecp_keypair **p_ecp)
{
    mbedtls_ecp_group_id grp_id = MBEDTLS_ECP_DP_NONE;
    psa_status_t status;
    mbedtls_ecp_keypair *ecp = NULL;
    size_t curve_bytes = data_length;
    int explicit_bits = (curve_bits != 0);

    if (PSA_KEY_TYPE_IS_PUBLIC_KEY(type) &&
        PSA_KEY_TYPE_ECC_GET_FAMILY(type) != PSA_ECC_FAMILY_MONTGOMERY) {
        /* A Weierstrass public key is represented as:
         * - The byte 0x04;
         * - `x_P` as a `ceiling(m/8)`-byte string, big-endian;
         * - `y_P` as a `ceiling(m/8)`-byte string, big-endian.
         * So its data length is 2m+1 where m is the curve size in bits.
         */
        if ((data_length & 1) == 0) {
            return PSA_ERROR_INVALID_ARGUMENT;
        }
        curve_bytes = data_length / 2;

        /* Montgomery public keys are represented in compressed format, meaning
         * their curve_bytes is equal to the amount of input. */

        /* Private keys are represented in uncompressed private random integer
         * format, meaning their curve_bytes is equal to the amount of input. */
    }

    if (explicit_bits) {
        /* With an explicit bit-size, the data must have the matching length. */
        if (curve_bytes != PSA_BITS_TO_BYTES(curve_bits)) {
            return PSA_ERROR_INVALID_ARGUMENT;
        }
    } else {
        /* We need to infer the bit-size from the data. Since the only
         * information we have is the length in bytes, the value of curve_bits
         * at this stage is rounded up to the nearest multiple of 8. */
        curve_bits = PSA_BYTES_TO_BITS(curve_bytes);
    }

    /* Allocate and initialize a key representation. */
    ecp = mbedtls_calloc(1, sizeof(mbedtls_ecp_keypair));
    if (ecp == NULL) {
        return PSA_ERROR_INSUFFICIENT_MEMORY;
    }
    mbedtls_ecp_keypair_init(ecp);

    /* Load the group. */
    grp_id = mbedtls_ecc_group_of_psa(PSA_KEY_TYPE_ECC_GET_FAMILY(type),
                                      curve_bits, !explicit_bits);
    if (grp_id == MBEDTLS_ECP_DP_NONE) {
        /* We can't distinguish between a nonsensical family/size combination
         * (which would warrant PSA_ERROR_INVALID_ARGUMENT) and a
         * well-regarded curve that Mbed TLS just doesn't know about (which
         * would warrant PSA_ERROR_NOT_SUPPORTED). For uniformity with how
         * curves that Mbed TLS knows about but for which support is disabled
         * at build time, return NOT_SUPPORTED. */
        status = PSA_ERROR_NOT_SUPPORTED;
        goto exit;
    }

    status = mbedtls_to_psa_error(
        mbedtls_ecp_group_load(&ecp->grp, grp_id));
    if (status != PSA_SUCCESS) {
        goto exit;
    }

    /* Load the key material. */
    if (PSA_KEY_TYPE_IS_PUBLIC_KEY(type)) {
        /* Load the public value. */
        status = mbedtls_to_psa_error(
            mbedtls_ecp_point_read_binary(&ecp->grp, &ecp->Q,
                                          data,
                                          data_length));
        if (status != PSA_SUCCESS) {
            goto exit;
        }

        /* Check that the point is on the curve. */
        status = mbedtls_to_psa_error(
            mbedtls_ecp_check_pubkey(&ecp->grp, &ecp->Q));
        if (status != PSA_SUCCESS) {
            goto exit;
        }
    } else {
        /* Load and validate the secret value. */
        status = mbedtls_to_psa_error(
            mbedtls_ecp_read_key(ecp->grp.id,
                                 ecp,
                                 data,
                                 data_length));
        if (status != PSA_SUCCESS) {
            goto exit;
        }
    }

    *p_ecp = ecp;
exit:
    if (status != PSA_SUCCESS) {
        mbedtls_ecp_keypair_free(ecp);
        mbedtls_free(ecp);
    }

    return status;
}
#endif /* defined(MBEDTLS_PSA_BUILTIN_KEY_TYPE_ECC_KEY_PAIR_BASIC) ||
        * defined(MBEDTLS_PSA_BUILTIN_KEY_TYPE_ECC_KEY_PAIR_IMPORT) ||
        * defined(MBEDTLS_PSA_BUILTIN_KEY_TYPE_ECC_KEY_PAIR_EXPORT) ||
        * defined(MBEDTLS_PSA_BUILTIN_KEY_TYPE_ECC_PUBLIC_KEY) ||
        * defined(MBEDTLS_PSA_BUILTIN_ALG_ECDSA) ||
        * defined(MBEDTLS_PSA_BUILTIN_ALG_DETERMINISTIC_ECDSA) ||
        * defined(MBEDTLS_PSA_BUILTIN_ALG_ECDH) */

#if defined(MBEDTLS_PSA_BUILTIN_KEY_TYPE_ECC_KEY_PAIR_IMPORT) || \
    defined(MBEDTLS_PSA_BUILTIN_KEY_TYPE_ECC_KEY_PAIR_EXPORT) || \
    defined(MBEDTLS_PSA_BUILTIN_KEY_TYPE_ECC_PUBLIC_KEY)

psa_status_t mbedtls_psa_ecp_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)
{
    psa_status_t status;
    mbedtls_ecp_keypair *ecp = NULL;

    /* Parse input */
    status = mbedtls_psa_ecp_load_representation(attributes->core.type,
                                                 attributes->core.bits,
                                                 data,
                                                 data_length,
                                                 &ecp);
    if (status != PSA_SUCCESS) {
        goto exit;
    }

    if (PSA_KEY_TYPE_ECC_GET_FAMILY(attributes->core.type) ==
        PSA_ECC_FAMILY_MONTGOMERY) {
        *bits = ecp->grp.nbits + 1;
    } else {
        *bits = ecp->grp.nbits;
    }

    /* Re-export the data to PSA export format. There is currently no support
     * for other input formats then the export format, so this is a 1-1
     * copy operation. */
    status = mbedtls_psa_ecp_export_key(attributes->core.type,
                                        ecp,
                                        key_buffer,
                                        key_buffer_size,
                                        key_buffer_length);
exit:
    /* Always free the PK object (will also free contained ECP context) */
    mbedtls_ecp_keypair_free(ecp);
    mbedtls_free(ecp);

    return status;
}

psa_status_t mbedtls_psa_ecp_export_key(psa_key_type_t type,
                                        mbedtls_ecp_keypair *ecp,
                                        uint8_t *data,
                                        size_t data_size,
                                        size_t *data_length)
{
    psa_status_t status;

    if (PSA_KEY_TYPE_IS_PUBLIC_KEY(type)) {
        /* Check whether the public part is loaded */
        if (mbedtls_ecp_is_zero(&ecp->Q)) {
            /* Calculate the public key */
            status = mbedtls_to_psa_error(
                mbedtls_ecp_mul(&ecp->grp, &ecp->Q, &ecp->d, &ecp->grp.G,
                                mbedtls_psa_get_random,
                                MBEDTLS_PSA_RANDOM_STATE));
            if (status != PSA_SUCCESS) {
                return status;
            }
        }

        status = mbedtls_to_psa_error(
            mbedtls_ecp_point_write_binary(&ecp->grp, &ecp->Q,
                                           MBEDTLS_ECP_PF_UNCOMPRESSED,
                                           data_length,
                                           data,
                                           data_size));
        if (status != PSA_SUCCESS) {
            memset(data, 0, data_size);
        }

        return status;
    } else {
        if (data_size < PSA_BITS_TO_BYTES(ecp->grp.nbits)) {
            return PSA_ERROR_BUFFER_TOO_SMALL;
        }

        status = mbedtls_to_psa_error(
            mbedtls_ecp_write_key(ecp,
                                  data,
                                  PSA_BITS_TO_BYTES(ecp->grp.nbits)));
        if (status == PSA_SUCCESS) {
            *data_length = PSA_BITS_TO_BYTES(ecp->grp.nbits);
        } else {
            memset(data, 0, data_size);
        }

        return status;
    }
}

psa_status_t mbedtls_psa_ecp_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)
{
    psa_status_t status = PSA_ERROR_CORRUPTION_DETECTED;
    mbedtls_ecp_keypair *ecp = NULL;

    status = mbedtls_psa_ecp_load_representation(
        attributes->core.type, attributes->core.bits,
        key_buffer, key_buffer_size, &ecp);
    if (status != PSA_SUCCESS) {
        return status;
    }

    status = mbedtls_psa_ecp_export_key(
        PSA_KEY_TYPE_ECC_PUBLIC_KEY(
            PSA_KEY_TYPE_ECC_GET_FAMILY(attributes->core.type)),
        ecp, data, data_size, data_length);

    mbedtls_ecp_keypair_free(ecp);
    mbedtls_free(ecp);

    return status;
}
#endif /* defined(MBEDTLS_PSA_BUILTIN_KEY_TYPE_ECC_KEY_PAIR_IMPORT) ||
        * defined(MBEDTLS_PSA_BUILTIN_KEY_TYPE_ECC_KEY_PAIR_EXPORT) ||
        * defined(MBEDTLS_PSA_BUILTIN_KEY_TYPE_ECC_PUBLIC_KEY) */

#if defined(MBEDTLS_PSA_BUILTIN_KEY_TYPE_ECC_KEY_PAIR_GENERATE)
psa_status_t mbedtls_psa_ecp_generate_key(
    const psa_key_attributes_t *attributes,
    uint8_t *key_buffer, size_t key_buffer_size, size_t *key_buffer_length)
{
    psa_status_t status = PSA_ERROR_CORRUPTION_DETECTED;
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;

    psa_ecc_family_t curve = PSA_KEY_TYPE_ECC_GET_FAMILY(
        attributes->core.type);
    mbedtls_ecp_group_id grp_id =
        mbedtls_ecc_group_of_psa(curve, attributes->core.bits, 0);

    const mbedtls_ecp_curve_info *curve_info =
        mbedtls_ecp_curve_info_from_grp_id(grp_id);
    mbedtls_ecp_keypair ecp;

    if (attributes->domain_parameters_size != 0) {
        return PSA_ERROR_NOT_SUPPORTED;
    }

    if (grp_id == MBEDTLS_ECP_DP_NONE || curve_info == NULL) {
        return PSA_ERROR_NOT_SUPPORTED;
    }

    mbedtls_ecp_keypair_init(&ecp);
    ret = mbedtls_ecp_gen_key(grp_id, &ecp,
                              mbedtls_psa_get_random,
                              MBEDTLS_PSA_RANDOM_STATE);
    if (ret != 0) {
        mbedtls_ecp_keypair_free(&ecp);
        return mbedtls_to_psa_error(ret);
    }

    status = mbedtls_to_psa_error(
        mbedtls_ecp_write_key(&ecp, key_buffer, key_buffer_size));

    mbedtls_ecp_keypair_free(&ecp);

    if (status == PSA_SUCCESS) {
        *key_buffer_length = key_buffer_size;
    }

    return status;
}
#endif /* MBEDTLS_PSA_BUILTIN_KEY_TYPE_ECC_KEY_PAIR_GENERATE */

/****************************************************************/
/* ECDSA sign/verify */
/****************************************************************/

#if defined(MBEDTLS_PSA_BUILTIN_ALG_ECDSA) || \
    defined(MBEDTLS_PSA_BUILTIN_ALG_DETERMINISTIC_ECDSA)
psa_status_t mbedtls_psa_ecdsa_sign_hash(
    const psa_key_attributes_t *attributes,
    const uint8_t *key_buffer, size_t key_buffer_size,
    psa_algorithm_t alg, const uint8_t *hash, size_t hash_length,
    uint8_t *signature, size_t signature_size, size_t *signature_length)
{
    psa_status_t status = PSA_ERROR_CORRUPTION_DETECTED;
    mbedtls_ecp_keypair *ecp = NULL;
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
    size_t curve_bytes;
    mbedtls_mpi r, s;

    status = mbedtls_psa_ecp_load_representation(attributes->core.type,
                                                 attributes->core.bits,
                                                 key_buffer,
                                                 key_buffer_size,
                                                 &ecp);
    if (status != PSA_SUCCESS) {
        return status;
    }

    curve_bytes = PSA_BITS_TO_BYTES(ecp->grp.pbits);
    mbedtls_mpi_init(&r);
    mbedtls_mpi_init(&s);

    if (signature_size < 2 * curve_bytes) {
        ret = MBEDTLS_ERR_ECP_BUFFER_TOO_SMALL;
        goto cleanup;
    }

    if (PSA_ALG_ECDSA_IS_DETERMINISTIC(alg)) {
#if defined(MBEDTLS_PSA_BUILTIN_ALG_DETERMINISTIC_ECDSA)
        psa_algorithm_t hash_alg = PSA_ALG_SIGN_GET_HASH(alg);
        mbedtls_md_type_t md_alg = mbedtls_md_type_from_psa_alg(hash_alg);
        MBEDTLS_MPI_CHK(mbedtls_ecdsa_sign_det_ext(
                            &ecp->grp, &r, &s,
                            &ecp->d, hash,
                            hash_length, md_alg,
                            mbedtls_psa_get_random,
                            MBEDTLS_PSA_RANDOM_STATE));
#else
        ret = MBEDTLS_ERR_ECP_FEATURE_UNAVAILABLE;
        goto cleanup;
#endif /* defined(MBEDTLS_PSA_BUILTIN_ALG_DETERMINISTIC_ECDSA) */
    } else {
        (void) alg;
        MBEDTLS_MPI_CHK(mbedtls_ecdsa_sign(&ecp->grp, &r, &s, &ecp->d,
                                           hash, hash_length,
                                           mbedtls_psa_get_random,
                                           MBEDTLS_PSA_RANDOM_STATE));
    }

    MBEDTLS_MPI_CHK(mbedtls_mpi_write_binary(&r,
                                             signature,
                                             curve_bytes));
    MBEDTLS_MPI_CHK(mbedtls_mpi_write_binary(&s,
                                             signature + curve_bytes,
                                             curve_bytes));
cleanup:
    mbedtls_mpi_free(&r);
    mbedtls_mpi_free(&s);
    if (ret == 0) {
        *signature_length = 2 * curve_bytes;
    }

    mbedtls_ecp_keypair_free(ecp);
    mbedtls_free(ecp);

    return mbedtls_to_psa_error(ret);
}

psa_status_t mbedtls_psa_ecp_load_public_part(mbedtls_ecp_keypair *ecp)
{
    int ret = 0;

    /* Check whether the public part is loaded. If not, load it. */
    if (mbedtls_ecp_is_zero(&ecp->Q)) {
        ret = mbedtls_ecp_mul(&ecp->grp, &ecp->Q,
                              &ecp->d, &ecp->grp.G,
                              mbedtls_psa_get_random,
                              MBEDTLS_PSA_RANDOM_STATE);
    }

    return mbedtls_to_psa_error(ret);
}

psa_status_t mbedtls_psa_ecdsa_verify_hash(
    const psa_key_attributes_t *attributes,
    const uint8_t *key_buffer, size_t key_buffer_size,
    psa_algorithm_t alg, const uint8_t *hash, size_t hash_length,
    const uint8_t *signature, size_t signature_length)
{
    psa_status_t status = PSA_ERROR_CORRUPTION_DETECTED;
    mbedtls_ecp_keypair *ecp = NULL;
    size_t curve_bytes;
    mbedtls_mpi r, s;

    (void) alg;

    status = mbedtls_psa_ecp_load_representation(attributes->core.type,
                                                 attributes->core.bits,
                                                 key_buffer,
                                                 key_buffer_size,
                                                 &ecp);
    if (status != PSA_SUCCESS) {
        return status;
    }

    curve_bytes = PSA_BITS_TO_BYTES(ecp->grp.pbits);
    mbedtls_mpi_init(&r);
    mbedtls_mpi_init(&s);

    if (signature_length != 2 * curve_bytes) {
        status = PSA_ERROR_INVALID_SIGNATURE;
        goto cleanup;
    }

    status = mbedtls_to_psa_error(mbedtls_mpi_read_binary(&r,
                                                          signature,
                                                          curve_bytes));
    if (status != PSA_SUCCESS) {
        goto cleanup;
    }

    status = mbedtls_to_psa_error(mbedtls_mpi_read_binary(&s,
                                                          signature + curve_bytes,
                                                          curve_bytes));
    if (status != PSA_SUCCESS) {
        goto cleanup;
    }

    status = mbedtls_psa_ecp_load_public_part(ecp);
    if (status != PSA_SUCCESS) {
        goto cleanup;
    }

    status = mbedtls_to_psa_error(mbedtls_ecdsa_verify(&ecp->grp, hash,
                                                       hash_length, &ecp->Q,
                                                       &r, &s));
cleanup:
    mbedtls_mpi_free(&r);
    mbedtls_mpi_free(&s);
    mbedtls_ecp_keypair_free(ecp);
    mbedtls_free(ecp);

    return status;
}

#endif /* defined(MBEDTLS_PSA_BUILTIN_ALG_ECDSA) || \
        * defined(MBEDTLS_PSA_BUILTIN_ALG_DETERMINISTIC_ECDSA) */

/****************************************************************/
/* ECDH Key Agreement */
/****************************************************************/

#if defined(MBEDTLS_PSA_BUILTIN_ALG_ECDH)
psa_status_t mbedtls_psa_key_agreement_ecdh(
    const psa_key_attributes_t *attributes,
    const uint8_t *key_buffer, size_t key_buffer_size,
    psa_algorithm_t alg, const uint8_t *peer_key, size_t peer_key_length,
    uint8_t *shared_secret, size_t shared_secret_size,
    size_t *shared_secret_length)
{
    psa_status_t status;
    if (!PSA_KEY_TYPE_IS_ECC_KEY_PAIR(attributes->core.type) ||
        !PSA_ALG_IS_ECDH(alg)) {
        return PSA_ERROR_INVALID_ARGUMENT;
    }
    mbedtls_ecp_keypair *ecp = NULL;
    status = mbedtls_psa_ecp_load_representation(
        attributes->core.type,
        attributes->core.bits,
        key_buffer,
        key_buffer_size,
        &ecp);
    if (status != PSA_SUCCESS) {
        return status;
    }
    mbedtls_ecp_keypair *their_key = NULL;
    mbedtls_ecdh_context ecdh;
    size_t bits = 0;
    psa_ecc_family_t curve = mbedtls_ecc_group_to_psa(ecp->grp.id, &bits);
    mbedtls_ecdh_init(&ecdh);

    status = mbedtls_psa_ecp_load_representation(
        PSA_KEY_TYPE_ECC_PUBLIC_KEY(curve),
        bits,
        peer_key,
        peer_key_length,
        &their_key);
    if (status != PSA_SUCCESS) {
        goto exit;
    }

    status = mbedtls_to_psa_error(
        mbedtls_ecdh_get_params(&ecdh, their_key, MBEDTLS_ECDH_THEIRS));
    if (status != PSA_SUCCESS) {
        goto exit;
    }
    status = mbedtls_to_psa_error(
        mbedtls_ecdh_get_params(&ecdh, ecp, MBEDTLS_ECDH_OURS));
    if (status != PSA_SUCCESS) {
        goto exit;
    }

    status = mbedtls_to_psa_error(
        mbedtls_ecdh_calc_secret(&ecdh,
                                 shared_secret_length,
                                 shared_secret, shared_secret_size,
                                 mbedtls_psa_get_random,
                                 MBEDTLS_PSA_RANDOM_STATE));
    if (status != PSA_SUCCESS) {
        goto exit;
    }
    if (PSA_BITS_TO_BYTES(bits) != *shared_secret_length) {
        status = PSA_ERROR_CORRUPTION_DETECTED;
    }
exit:
    if (status != PSA_SUCCESS) {
        mbedtls_platform_zeroize(shared_secret, shared_secret_size);
    }
    mbedtls_ecdh_free(&ecdh);
    mbedtls_ecp_keypair_free(their_key);
    mbedtls_free(their_key);
    mbedtls_ecp_keypair_free(ecp);
    mbedtls_free(ecp);
    return status;
}
#endif /* MBEDTLS_PSA_BUILTIN_ALG_ECDH */


#endif /* MBEDTLS_PSA_CRYPTO_C */