mbedtls/programs/pkey/ecdh_curve25519.c

/*
 *  Example ECDHE with Curve25519 program
 *
 *  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 "mbedtls/build_info.h"

#if defined(MBEDTLS_PLATFORM_C)
#    include "mbedtls/platform.h"
#else
#    include <stdio.h>
#    include <stdlib.h>
#    define mbedtls_printf       printf
#    define mbedtls_exit         exit
#    define MBEDTLS_EXIT_SUCCESS EXIT_SUCCESS
#    define MBEDTLS_EXIT_FAILURE EXIT_FAILURE
#endif /* MBEDTLS_PLATFORM_C */

#if !defined(MBEDTLS_ECDH_C) || !defined(MBEDTLS_ECDH_LEGACY_CONTEXT) || \
    !defined(MBEDTLS_ECP_DP_CURVE25519_ENABLED) ||                       \
    !defined(MBEDTLS_ENTROPY_C) || !defined(MBEDTLS_CTR_DRBG_C)
int main(void)
{
    mbedtls_printf("MBEDTLS_ECDH_C and/or MBEDTLS_ECDH_LEGACY_CONTEXT and/or "
                   "MBEDTLS_ECP_DP_CURVE25519_ENABLED and/or "
                   "MBEDTLS_ENTROPY_C and/or MBEDTLS_CTR_DRBG_C "
                   "not defined\n");
    mbedtls_exit(0);
}
#else

#    include "mbedtls/entropy.h"
#    include "mbedtls/ctr_drbg.h"
#    include "mbedtls/ecdh.h"

int main(int argc, char *argv[])
{
    int ret = 1;
    int exit_code = MBEDTLS_EXIT_FAILURE;
    mbedtls_ecdh_context ctx_cli, ctx_srv;
    mbedtls_entropy_context entropy;
    mbedtls_ctr_drbg_context ctr_drbg;
    unsigned char cli_to_srv[32], srv_to_cli[32];
    const char pers[] = "ecdh";
    ((void)argc);
    ((void)argv);

    mbedtls_ecdh_init(&ctx_cli);
    mbedtls_ecdh_init(&ctx_srv);
    mbedtls_ctr_drbg_init(&ctr_drbg);

    /*
     * Initialize random number generation
     */
    mbedtls_printf("  . Seeding the random number generator...");
    fflush(stdout);

    mbedtls_entropy_init(&entropy);
    if ((ret = mbedtls_ctr_drbg_seed(&ctr_drbg, mbedtls_entropy_func, &entropy,
                                     (const unsigned char *)pers,
                                     sizeof(pers))) != 0) {
        mbedtls_printf(" failed\n  ! mbedtls_ctr_drbg_seed returned %d\n", ret);
        goto exit;
    }

    mbedtls_printf(" ok\n");

    /*
     * Client: initialize context and generate keypair
     */
    mbedtls_printf("  . Setting up client context...");
    fflush(stdout);

    ret = mbedtls_ecp_group_load(&ctx_cli.MBEDTLS_PRIVATE(grp),
                                 MBEDTLS_ECP_DP_CURVE25519);
    if (ret != 0) {
        mbedtls_printf(" failed\n  ! mbedtls_ecp_group_load returned %d\n",
                       ret);
        goto exit;
    }

    ret = mbedtls_ecdh_gen_public(&ctx_cli.MBEDTLS_PRIVATE(grp),
                                  &ctx_cli.MBEDTLS_PRIVATE(d),
                                  &ctx_cli.MBEDTLS_PRIVATE(Q),
                                  mbedtls_ctr_drbg_random, &ctr_drbg);
    if (ret != 0) {
        mbedtls_printf(" failed\n  ! mbedtls_ecdh_gen_public returned %d\n",
                       ret);
        goto exit;
    }

    ret = mbedtls_mpi_write_binary(
        &ctx_cli.MBEDTLS_PRIVATE(Q).MBEDTLS_PRIVATE(X), cli_to_srv, 32);
    if (ret != 0) {
        mbedtls_printf(" failed\n  ! mbedtls_mpi_write_binary returned %d\n",
                       ret);
        goto exit;
    }

    mbedtls_printf(" ok\n");

    /*
     * Server: initialize context and generate keypair
     */
    mbedtls_printf("  . Setting up server context...");
    fflush(stdout);

    ret = mbedtls_ecp_group_load(&ctx_srv.MBEDTLS_PRIVATE(grp),
                                 MBEDTLS_ECP_DP_CURVE25519);
    if (ret != 0) {
        mbedtls_printf(" failed\n  ! mbedtls_ecp_group_load returned %d\n",
                       ret);
        goto exit;
    }

    ret = mbedtls_ecdh_gen_public(&ctx_srv.MBEDTLS_PRIVATE(grp),
                                  &ctx_srv.MBEDTLS_PRIVATE(d),
                                  &ctx_srv.MBEDTLS_PRIVATE(Q),
                                  mbedtls_ctr_drbg_random, &ctr_drbg);
    if (ret != 0) {
        mbedtls_printf(" failed\n  ! mbedtls_ecdh_gen_public returned %d\n",
                       ret);
        goto exit;
    }

    ret = mbedtls_mpi_write_binary(
        &ctx_srv.MBEDTLS_PRIVATE(Q).MBEDTLS_PRIVATE(X), srv_to_cli, 32);
    if (ret != 0) {
        mbedtls_printf(" failed\n  ! mbedtls_mpi_write_binary returned %d\n",
                       ret);
        goto exit;
    }

    mbedtls_printf(" ok\n");

    /*
     * Server: read peer's key and generate shared secret
     */
    mbedtls_printf("  . Server reading client key and computing secret...");
    fflush(stdout);

    ret = mbedtls_mpi_lset(&ctx_srv.MBEDTLS_PRIVATE(Qp).MBEDTLS_PRIVATE(Z), 1);
    if (ret != 0) {
        mbedtls_printf(" failed\n  ! mbedtls_mpi_lset returned %d\n", ret);
        goto exit;
    }

    ret = mbedtls_mpi_read_binary(
        &ctx_srv.MBEDTLS_PRIVATE(Qp).MBEDTLS_PRIVATE(X), cli_to_srv, 32);
    if (ret != 0) {
        mbedtls_printf(" failed\n  ! mbedtls_mpi_read_binary returned %d\n",
                       ret);
        goto exit;
    }

    ret = mbedtls_ecdh_compute_shared(&ctx_srv.MBEDTLS_PRIVATE(grp),
                                      &ctx_srv.MBEDTLS_PRIVATE(z),
                                      &ctx_srv.MBEDTLS_PRIVATE(Qp),
                                      &ctx_srv.MBEDTLS_PRIVATE(d),
                                      mbedtls_ctr_drbg_random, &ctr_drbg);
    if (ret != 0) {
        mbedtls_printf(" failed\n  ! mbedtls_ecdh_compute_shared returned %d\n",
                       ret);
        goto exit;
    }

    mbedtls_printf(" ok\n");

    /*
     * Client: read peer's key and generate shared secret
     */
    mbedtls_printf("  . Client reading server key and computing secret...");
    fflush(stdout);

    ret = mbedtls_mpi_lset(&ctx_cli.MBEDTLS_PRIVATE(Qp).MBEDTLS_PRIVATE(Z), 1);
    if (ret != 0) {
        mbedtls_printf(" failed\n  ! mbedtls_mpi_lset returned %d\n", ret);
        goto exit;
    }

    ret = mbedtls_mpi_read_binary(
        &ctx_cli.MBEDTLS_PRIVATE(Qp).MBEDTLS_PRIVATE(X), srv_to_cli, 32);
    if (ret != 0) {
        mbedtls_printf(" failed\n  ! mbedtls_mpi_read_binary returned %d\n",
                       ret);
        goto exit;
    }

    ret = mbedtls_ecdh_compute_shared(&ctx_cli.MBEDTLS_PRIVATE(grp),
                                      &ctx_cli.MBEDTLS_PRIVATE(z),
                                      &ctx_cli.MBEDTLS_PRIVATE(Qp),
                                      &ctx_cli.MBEDTLS_PRIVATE(d),
                                      mbedtls_ctr_drbg_random, &ctr_drbg);
    if (ret != 0) {
        mbedtls_printf(" failed\n  ! mbedtls_ecdh_compute_shared returned %d\n",
                       ret);
        goto exit;
    }

    mbedtls_printf(" ok\n");

    /*
     * Verification: are the computed secrets equal?
     */
    mbedtls_printf("  . Checking if both computed secrets are equal...");
    fflush(stdout);

    ret = mbedtls_mpi_cmp_mpi(&ctx_cli.MBEDTLS_PRIVATE(z),
                              &ctx_srv.MBEDTLS_PRIVATE(z));
    if (ret != 0) {
        mbedtls_printf(" failed\n  ! mbedtls_ecdh_compute_shared returned %d\n",
                       ret);
        goto exit;
    }

    mbedtls_printf(" ok\n");

    exit_code = MBEDTLS_EXIT_SUCCESS;

exit:

#    if defined(_WIN32)
    mbedtls_printf("  + Press Enter to exit this program.\n");
    fflush(stdout);
    getchar();
#    endif

    mbedtls_ecdh_free(&ctx_srv);
    mbedtls_ecdh_free(&ctx_cli);
    mbedtls_ctr_drbg_free(&ctr_drbg);
    mbedtls_entropy_free(&entropy);

    mbedtls_exit(exit_code);
}
#endif /* MBEDTLS_ECDH_C && MBEDTLS_ECP_DP_CURVE25519_ENABLED && \
          MBEDTLS_ENTROPY_C && MBEDTLS_CTR_DRBG_C */