dh_server.c

/*
 *  Diffie-Hellman-Merkle key exchange (server side)
 *
 *  Copyright The Mbed TLS Contributors
 *  SPDX-License-Identifier: Apache-2.0 OR GPL-2.0-or-later
 */

#include "mbedtls/build_info.h"

#include "mbedtls/platform.h"
/* md.h is included this early since MD_CAN_XXX macros are defined there. */
#include "mbedtls/md.h"

#if defined(MBEDTLS_AES_C) && defined(MBEDTLS_DHM_C) && \
    defined(MBEDTLS_ENTROPY_C) && defined(MBEDTLS_NET_C) && \
    defined(MBEDTLS_RSA_C) && defined(MBEDTLS_SHA256_C) && \
    defined(MBEDTLS_FS_IO) && defined(MBEDTLS_CTR_DRBG_C)
#include "mbedtls/net_sockets.h"
#include "mbedtls/aes.h"
#include "mbedtls/dhm.h"
#include "mbedtls/rsa.h"
#include "mbedtls/sha256.h"
#include "mbedtls/entropy.h"
#include "mbedtls/ctr_drbg.h"

#include <stdio.h>
#include <string.h>
#endif

#define SERVER_PORT "11999"
#define PLAINTEXT "==Hello there!=="

#if !defined(MBEDTLS_AES_C) || !defined(MBEDTLS_DHM_C) ||     \
    !defined(MBEDTLS_ENTROPY_C) || !defined(MBEDTLS_NET_C) ||  \
    !defined(MBEDTLS_RSA_C) || !defined(MBEDTLS_SHA256_C) ||    \
    !defined(MBEDTLS_FS_IO) || !defined(MBEDTLS_CTR_DRBG_C)
int main(void)
{
    mbedtls_printf("MBEDTLS_AES_C and/or MBEDTLS_DHM_C and/or MBEDTLS_ENTROPY_C "
                   "and/or MBEDTLS_NET_C and/or MBEDTLS_RSA_C and/or "
                   "PSA_WANT_ALG_SHA_256 and/or MBEDTLS_FS_IO and/or "
                   "MBEDTLS_CTR_DRBG_C and/or MBEDTLS_SHA1_C not defined.\n");
    mbedtls_exit(0);
}
#else


int main(void)
{
    FILE *f;

    int ret = 1;
    int exit_code = MBEDTLS_EXIT_FAILURE;
    unsigned int mdlen;
    size_t n, buflen;
    mbedtls_net_context listen_fd, client_fd;

    unsigned char buf[2048];
    unsigned char hash[MBEDTLS_MD_MAX_SIZE];
    unsigned char buf2[2];
    const char *pers = "dh_server";

    mbedtls_entropy_context entropy;
    mbedtls_ctr_drbg_context ctr_drbg;
    mbedtls_rsa_context rsa;
    mbedtls_dhm_context dhm;
    mbedtls_aes_context aes;

    mbedtls_mpi N, P, Q, D, E, dhm_P, dhm_G;

    mbedtls_net_init(&listen_fd);
    mbedtls_net_init(&client_fd);
    mbedtls_dhm_init(&dhm);
    mbedtls_aes_init(&aes);
    mbedtls_ctr_drbg_init(&ctr_drbg);

    mbedtls_mpi_init(&N); mbedtls_mpi_init(&P); mbedtls_mpi_init(&Q);
    mbedtls_mpi_init(&D); mbedtls_mpi_init(&E); mbedtls_mpi_init(&dhm_P);
    mbedtls_mpi_init(&dhm_G);
    /*
     * 1. Setup the RNG
     */
    mbedtls_printf("\n  . 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,
                                     strlen(pers))) != 0) {
        mbedtls_printf(" failed\n  ! mbedtls_ctr_drbg_seed returned %d\n", ret);
        goto exit;
    }

    /*
     * 2a. Read the server's private RSA key
     */
    mbedtls_printf("\n  . Reading private key from rsa_priv.txt");
    fflush(stdout);

    if ((f = fopen("rsa_priv.txt", "rb")) == NULL) {
        mbedtls_printf(" failed\n  ! Could not open rsa_priv.txt\n" \
                       "  ! Please run rsa_genkey first\n\n");
        goto exit;
    }

    mbedtls_rsa_init(&rsa);

    if ((ret = mbedtls_mpi_read_file(&N, 16, f)) != 0 ||
        (ret = mbedtls_mpi_read_file(&E, 16, f)) != 0 ||
        (ret = mbedtls_mpi_read_file(&D, 16, f)) != 0 ||
        (ret = mbedtls_mpi_read_file(&P, 16, f)) != 0 ||
        (ret = mbedtls_mpi_read_file(&Q, 16, f)) != 0) {
        mbedtls_printf(" failed\n  ! mbedtls_mpi_read_file returned %d\n\n",
                       ret);
        fclose(f);
        goto exit;
    }
    fclose(f);

    if ((ret = mbedtls_rsa_import(&rsa, &N, &P, &Q, &D, &E)) != 0) {
        mbedtls_printf(" failed\n  ! mbedtls_rsa_import returned %d\n\n",
                       ret);
        goto exit;
    }

    if ((ret = mbedtls_rsa_complete(&rsa)) != 0) {
        mbedtls_printf(" failed\n  ! mbedtls_rsa_complete returned %d\n\n",
                       ret);
        goto exit;
    }

    /*
     * 2b. Get the DHM modulus and generator
     */
    mbedtls_printf("\n  . Reading DH parameters from dh_prime.txt");
    fflush(stdout);

    if ((f = fopen("dh_prime.txt", "rb")) == NULL) {
        mbedtls_printf(" failed\n  ! Could not open dh_prime.txt\n" \
                       "  ! Please run dh_genprime first\n\n");
        goto exit;
    }

    if ((ret = mbedtls_mpi_read_file(&dhm_P, 16, f)) != 0 ||
        (ret = mbedtls_mpi_read_file(&dhm_G, 16, f)) != 0 ||
        (ret = mbedtls_dhm_set_group(&dhm, &dhm_P, &dhm_G) != 0)) {
        mbedtls_printf(" failed\n  ! Invalid DH parameter file\n\n");
        fclose(f);
        goto exit;
    }

    fclose(f);

    /*
     * 3. Wait for a client to connect
     */
    mbedtls_printf("\n  . Waiting for a remote connection");
    fflush(stdout);

    if ((ret = mbedtls_net_bind(&listen_fd, NULL, SERVER_PORT, MBEDTLS_NET_PROTO_TCP)) != 0) {
        mbedtls_printf(" failed\n  ! mbedtls_net_bind returned %d\n\n", ret);
        goto exit;
    }

    if ((ret = mbedtls_net_accept(&listen_fd, &client_fd,
                                  NULL, 0, NULL)) != 0) {
        mbedtls_printf(" failed\n  ! mbedtls_net_accept returned %d\n\n", ret);
        goto exit;
    }

    /*
     * 4. Setup the DH parameters (P,G,Ys)
     */
    mbedtls_printf("\n  . Sending the server's DH parameters");
    fflush(stdout);

    memset(buf, 0, sizeof(buf));

    if ((ret =
             mbedtls_dhm_make_params(&dhm, (int) mbedtls_dhm_get_len(&dhm), buf, &n,
                                     mbedtls_ctr_drbg_random, &ctr_drbg)) != 0) {
        mbedtls_printf(" failed\n  ! mbedtls_dhm_make_params returned %d\n\n", ret);
        goto exit;
    }

    /*
     * 5. Sign the parameters and send them
     */

    mdlen = (unsigned int) mbedtls_md_get_size(mbedtls_md_info_from_type(MBEDTLS_MD_SHA256));
    if (mdlen == 0) {
        mbedtls_printf(" failed\n  ! Invalid digest type\n\n");
        goto exit;
    }

    if ((ret = mbedtls_sha256(buf, n, hash, 0)) != 0) {
        mbedtls_printf(" failed\n  ! mbedtls_sha256 returned %d\n\n", ret);
        goto exit;
    }

    const size_t rsa_key_len = mbedtls_rsa_get_len(&rsa);
    buf[n] = (unsigned char) (rsa_key_len >> 8);
    buf[n + 1] = (unsigned char) (rsa_key_len);

    if ((ret = mbedtls_rsa_pkcs1_sign(&rsa, mbedtls_ctr_drbg_random, &ctr_drbg,
                                      MBEDTLS_MD_SHA256, mdlen,
                                      hash, buf + n + 2)) != 0) {
        mbedtls_printf(" failed\n  ! mbedtls_rsa_pkcs1_sign returned %d\n\n", ret);
        goto exit;
    }

    buflen = n + 2 + rsa_key_len;
    buf2[0] = (unsigned char) (buflen >> 8);
    buf2[1] = (unsigned char) (buflen);

    if ((ret = mbedtls_net_send(&client_fd, buf2, 2)) != 2 ||
        (ret = mbedtls_net_send(&client_fd, buf, buflen)) != (int) buflen) {
        mbedtls_printf(" failed\n  ! mbedtls_net_send returned %d\n\n", ret);
        goto exit;
    }

    /*
     * 6. Get the client's public value: Yc = G ^ Xc mod P
     */
    mbedtls_printf("\n  . Receiving the client's public value");
    fflush(stdout);

    memset(buf, 0, sizeof(buf));

    n = mbedtls_dhm_get_len(&dhm);
    if ((ret = mbedtls_net_recv(&client_fd, buf, n)) != (int) n) {
        mbedtls_printf(" failed\n  ! mbedtls_net_recv returned %d\n\n", ret);
        goto exit;
    }

    if ((ret = mbedtls_dhm_read_public(&dhm, buf, n)) != 0) {
        mbedtls_printf(" failed\n  ! mbedtls_dhm_read_public returned %d\n\n", ret);
        goto exit;
    }

    /*
     * 7. Derive the shared secret: K = Ys ^ Xc mod P
     */
    mbedtls_printf("\n  . Shared secret: ");
    fflush(stdout);

    if ((ret = mbedtls_dhm_calc_secret(&dhm, buf, sizeof(buf), &n,
                                       mbedtls_ctr_drbg_random, &ctr_drbg)) != 0) {
        mbedtls_printf(" failed\n  ! mbedtls_dhm_calc_secret returned %d\n\n", ret);
        goto exit;
    }

    for (n = 0; n < 16; n++) {
        mbedtls_printf("%02x", buf[n]);
    }

    /*
     * 8. Setup the AES-256 encryption key
     *
     * This is an overly simplified example; best practice is
     * to hash the shared secret with a random value to derive
     * the keying material for the encryption/decryption keys
     * and MACs.
     */
    mbedtls_printf("...\n  . Encrypting and sending the ciphertext");
    fflush(stdout);

    ret = mbedtls_aes_setkey_enc(&aes, buf, 256);
    if (ret != 0) {
        goto exit;
    }
    memcpy(buf, PLAINTEXT, 16);
    ret = mbedtls_aes_crypt_ecb(&aes, MBEDTLS_AES_ENCRYPT, buf, buf);
    if (ret != 0) {
        goto exit;
    }

    if ((ret = mbedtls_net_send(&client_fd, buf, 16)) != 16) {
        mbedtls_printf(" failed\n  ! mbedtls_net_send returned %d\n\n", ret);
        goto exit;
    }

    mbedtls_printf("\n\n");

    exit_code = MBEDTLS_EXIT_SUCCESS;

exit:

    mbedtls_mpi_free(&N); mbedtls_mpi_free(&P); mbedtls_mpi_free(&Q);
    mbedtls_mpi_free(&D); mbedtls_mpi_free(&E); mbedtls_mpi_free(&dhm_P);
    mbedtls_mpi_free(&dhm_G);

    mbedtls_net_free(&client_fd);
    mbedtls_net_free(&listen_fd);

    mbedtls_aes_free(&aes);
    mbedtls_rsa_free(&rsa);
    mbedtls_dhm_free(&dhm);
    mbedtls_ctr_drbg_free(&ctr_drbg);
    mbedtls_entropy_free(&entropy);

    mbedtls_exit(exit_code);
}
#endif /* MBEDTLS_AES_C && MBEDTLS_DHM_C && MBEDTLS_ENTROPY_C &&
          MBEDTLS_NET_C && MBEDTLS_RSA_C && PSA_WANT_ALG_SHA_256 &&
          MBEDTLS_FS_IO && MBEDTLS_CTR_DRBG_C */