dh_client.c

/*
 *  Diffie-Hellman-Merkle key exchange (client side)
 *
 *  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"

#include "mbedtls/platform.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) && \
    defined(MBEDTLS_SHA1_C)
#include "mbedtls/net_sockets.h"
#include "mbedtls/aes.h"
#include "mbedtls/dhm.h"
#include "mbedtls/rsa.h"
#include "mbedtls/sha1.h"
#include "mbedtls/entropy.h"
#include "mbedtls/ctr_drbg.h"

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

#define SERVER_NAME "localhost"
#define SERVER_PORT "11999"

#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) || \
    !defined(MBEDTLS_SHA1_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 "
           "MBEDTLS_SHA256_C and/or MBEDTLS_FS_IO and/or "
           "MBEDTLS_CTR_DRBG_C not defined.\n");
    mbedtls_exit( 0 );
}
#else


int main( void )
{
    FILE *f;

    int ret = 1;
    int exit_code = MBEDTLS_EXIT_FAILURE;
    size_t n, buflen;
    mbedtls_net_context server_fd;

    unsigned char *p, *end;
    unsigned char buf[2048];
    unsigned char hash[32];
    const char *pers = "dh_client";

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

    mbedtls_net_init( &server_fd );
    mbedtls_dhm_init( &dhm );
    mbedtls_aes_init( &aes );
    mbedtls_ctr_drbg_init( &ctr_drbg );

    /*
     * 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;
    }

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

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

    mbedtls_rsa_init( &rsa );

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

    rsa.MBEDTLS_PRIVATE(len) = ( mbedtls_mpi_bitlen( &rsa.MBEDTLS_PRIVATE(N) ) + 7 ) >> 3;

    fclose( f );

    /*
     * 3. Initiate the connection
     */
    mbedtls_printf( "\n  . Connecting to tcp/%s/%s", SERVER_NAME,
                                             SERVER_PORT );
    fflush( stdout );

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

    /*
     * 4a. First get the buffer length
     */
    mbedtls_printf( "\n  . Receiving the server's DH parameters" );
    fflush( stdout );

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

    if( ( ret = mbedtls_net_recv( &server_fd, buf, 2 ) ) != 2 )
    {
        mbedtls_printf( " failed\n  ! mbedtls_net_recv returned %d\n\n", ret );
        goto exit;
    }

    n = buflen = ( buf[0] << 8 ) | buf[1];
    if( buflen < 1 || buflen > sizeof( buf ) )
    {
        mbedtls_printf( " failed\n  ! Got an invalid buffer length\n\n" );
        goto exit;
    }

    /*
     * 4b. Get the DHM parameters: P, G and Ys = G^Xs mod P
     */
    memset( buf, 0, sizeof( buf ) );

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

    p = buf, end = buf + buflen;

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

    n = mbedtls_dhm_get_len( &dhm );
    if( n < 64 || n > 512 )
    {
        mbedtls_printf( " failed\n  ! Invalid DHM modulus size\n\n" );
        goto exit;
    }

    /*
     * 5. Check that the server's RSA signature matches
     *    the SHA-256 hash of (P,G,Ys)
     */
    mbedtls_printf( "\n  . Verifying the server's RSA signature" );
    fflush( stdout );

    p += 2;

    if( ( n = (size_t) ( end - p ) ) != rsa.MBEDTLS_PRIVATE(len) )
    {
        mbedtls_printf( " failed\n  ! Invalid RSA signature size\n\n" );
        goto exit;
    }

    if( ( ret = mbedtls_sha1( buf, (int)( p - 2 - buf ), hash ) ) != 0 )
    {
        mbedtls_printf( " failed\n  ! mbedtls_sha1 returned %d\n\n", ret );
        goto exit;
    }

    if( ( ret = mbedtls_rsa_pkcs1_verify( &rsa, MBEDTLS_MD_SHA256,
                                          32, hash, p ) ) != 0 )
    {
        mbedtls_printf( " failed\n  ! mbedtls_rsa_pkcs1_verify returned %d\n\n", ret );
        goto exit;
    }

    /*
     * 6. Send our public value: Yc = G ^ Xc mod P
     */
    mbedtls_printf( "\n  . Sending own public value to server" );
    fflush( stdout );

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

    if( ( ret = mbedtls_net_send( &server_fd, buf, n ) ) != (int) n )
    {
        mbedtls_printf( " failed\n  ! mbedtls_net_send 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 decryption 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,
     * IVs and MACs.
     */
    mbedtls_printf( "...\n  . Receiving and decrypting the ciphertext" );
    fflush( stdout );

    ret = mbedtls_aes_setkey_dec( &aes, buf, 256 );
    if( ret != 0 )
        goto exit;

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

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

    ret = mbedtls_aes_crypt_ecb( &aes, MBEDTLS_AES_DECRYPT, buf, buf );
    if( ret != 0 )
        goto exit;
    buf[16] = '\0';
    mbedtls_printf( "\n  . Plaintext is \"%s\"\n\n", (char *) buf );

    exit_code = MBEDTLS_EXIT_SUCCESS;

exit:

    mbedtls_net_free( &server_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 && MBEDTLS_SHA256_C &&
          MBEDTLS_FS_IO && MBEDTLS_CTR_DRBG_C */