1 /*
2  *  Diffie-Hellman-Merkle key exchange (client side)
3  *
4  *  Copyright The Mbed TLS Contributors
5  *  SPDX-License-Identifier: Apache-2.0
6  *
7  *  Licensed under the Apache License, Version 2.0 (the "License"); you may
8  *  not use this file except in compliance with the License.
9  *  You may obtain a copy of the License at
10  *
11  *  http://www.apache.org/licenses/LICENSE-2.0
12  *
13  *  Unless required by applicable law or agreed to in writing, software
14  *  distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
15  *  WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
16  *  See the License for the specific language governing permissions and
17  *  limitations under the License.
18  */
19 
20 #include "mbedtls/build_info.h"
21 
22 #include "mbedtls/platform.h"
23 
24 #if defined(MBEDTLS_AES_C) && defined(MBEDTLS_DHM_C) && \
25     defined(MBEDTLS_ENTROPY_C) && defined(MBEDTLS_NET_C) && \
26     defined(MBEDTLS_RSA_C) && defined(MBEDTLS_SHA256_C) && \
27     defined(MBEDTLS_FS_IO) && defined(MBEDTLS_CTR_DRBG_C) && \
28     defined(MBEDTLS_SHA1_C)
29 #include "mbedtls/net_sockets.h"
30 #include "mbedtls/aes.h"
31 #include "mbedtls/dhm.h"
32 #include "mbedtls/rsa.h"
33 #include "mbedtls/sha1.h"
34 #include "mbedtls/entropy.h"
35 #include "mbedtls/ctr_drbg.h"
36 
37 #include <stdio.h>
38 #include <string.h>
39 #endif
40 
41 #define SERVER_NAME "localhost"
42 #define SERVER_PORT "11999"
43 
44 #if !defined(MBEDTLS_AES_C) || !defined(MBEDTLS_DHM_C) ||     \
45     !defined(MBEDTLS_ENTROPY_C) || !defined(MBEDTLS_NET_C) ||  \
46     !defined(MBEDTLS_RSA_C) || !defined(MBEDTLS_SHA256_C) ||    \
47     !defined(MBEDTLS_FS_IO) || !defined(MBEDTLS_CTR_DRBG_C) || \
48     !defined(MBEDTLS_SHA1_C)
main(void)49 int main( void )
50 {
51     mbedtls_printf("MBEDTLS_AES_C and/or MBEDTLS_DHM_C and/or MBEDTLS_ENTROPY_C "
52            "and/or MBEDTLS_NET_C and/or MBEDTLS_RSA_C and/or "
53            "MBEDTLS_SHA256_C and/or MBEDTLS_FS_IO and/or "
54            "MBEDTLS_CTR_DRBG_C not defined.\n");
55     mbedtls_exit( 0 );
56 }
57 #else
58 
59 
main(void)60 int main( void )
61 {
62     FILE *f;
63 
64     int ret = 1;
65     int exit_code = MBEDTLS_EXIT_FAILURE;
66     size_t n, buflen;
67     mbedtls_net_context server_fd;
68 
69     unsigned char *p, *end;
70     unsigned char buf[2048];
71     unsigned char hash[32];
72     const char *pers = "dh_client";
73 
74     mbedtls_entropy_context entropy;
75     mbedtls_ctr_drbg_context ctr_drbg;
76     mbedtls_rsa_context rsa;
77     mbedtls_dhm_context dhm;
78     mbedtls_aes_context aes;
79 
80     mbedtls_net_init( &server_fd );
81     mbedtls_dhm_init( &dhm );
82     mbedtls_aes_init( &aes );
83     mbedtls_ctr_drbg_init( &ctr_drbg );
84 
85     /*
86      * 1. Setup the RNG
87      */
88     mbedtls_printf( "\n  . Seeding the random number generator" );
89     fflush( stdout );
90 
91     mbedtls_entropy_init( &entropy );
92     if( ( ret = mbedtls_ctr_drbg_seed( &ctr_drbg, mbedtls_entropy_func, &entropy,
93                                (const unsigned char *) pers,
94                                strlen( pers ) ) ) != 0 )
95     {
96         mbedtls_printf( " failed\n  ! mbedtls_ctr_drbg_seed returned %d\n", ret );
97         goto exit;
98     }
99 
100     /*
101      * 2. Read the server's public RSA key
102      */
103     mbedtls_printf( "\n  . Reading public key from rsa_pub.txt" );
104     fflush( stdout );
105 
106     if( ( f = fopen( "rsa_pub.txt", "rb" ) ) == NULL )
107     {
108         mbedtls_printf( " failed\n  ! Could not open rsa_pub.txt\n" \
109                 "  ! Please run rsa_genkey first\n\n" );
110         goto exit;
111     }
112 
113     mbedtls_rsa_init( &rsa );
114 
115     if( ( ret = mbedtls_mpi_read_file( &rsa.MBEDTLS_PRIVATE(N), 16, f ) ) != 0 ||
116         ( ret = mbedtls_mpi_read_file( &rsa.MBEDTLS_PRIVATE(E), 16, f ) ) != 0 )
117     {
118         mbedtls_printf( " failed\n  ! mbedtls_mpi_read_file returned %d\n\n", ret );
119         fclose( f );
120         goto exit;
121     }
122 
123     rsa.MBEDTLS_PRIVATE(len) = ( mbedtls_mpi_bitlen( &rsa.MBEDTLS_PRIVATE(N) ) + 7 ) >> 3;
124 
125     fclose( f );
126 
127     /*
128      * 3. Initiate the connection
129      */
130     mbedtls_printf( "\n  . Connecting to tcp/%s/%s", SERVER_NAME,
131                                              SERVER_PORT );
132     fflush( stdout );
133 
134     if( ( ret = mbedtls_net_connect( &server_fd, SERVER_NAME,
135                                          SERVER_PORT, MBEDTLS_NET_PROTO_TCP ) ) != 0 )
136     {
137         mbedtls_printf( " failed\n  ! mbedtls_net_connect returned %d\n\n", ret );
138         goto exit;
139     }
140 
141     /*
142      * 4a. First get the buffer length
143      */
144     mbedtls_printf( "\n  . Receiving the server's DH parameters" );
145     fflush( stdout );
146 
147     memset( buf, 0, sizeof( buf ) );
148 
149     if( ( ret = mbedtls_net_recv( &server_fd, buf, 2 ) ) != 2 )
150     {
151         mbedtls_printf( " failed\n  ! mbedtls_net_recv returned %d\n\n", ret );
152         goto exit;
153     }
154 
155     n = buflen = ( buf[0] << 8 ) | buf[1];
156     if( buflen < 1 || buflen > sizeof( buf ) )
157     {
158         mbedtls_printf( " failed\n  ! Got an invalid buffer length\n\n" );
159         goto exit;
160     }
161 
162     /*
163      * 4b. Get the DHM parameters: P, G and Ys = G^Xs mod P
164      */
165     memset( buf, 0, sizeof( buf ) );
166 
167     if( ( ret = mbedtls_net_recv( &server_fd, buf, n ) ) != (int) n )
168     {
169         mbedtls_printf( " failed\n  ! mbedtls_net_recv returned %d\n\n", ret );
170         goto exit;
171     }
172 
173     p = buf, end = buf + buflen;
174 
175     if( ( ret = mbedtls_dhm_read_params( &dhm, &p, end ) ) != 0 )
176     {
177         mbedtls_printf( " failed\n  ! mbedtls_dhm_read_params returned %d\n\n", ret );
178         goto exit;
179     }
180 
181     n = mbedtls_dhm_get_len( &dhm );
182     if( n < 64 || n > 512 )
183     {
184         mbedtls_printf( " failed\n  ! Invalid DHM modulus size\n\n" );
185         goto exit;
186     }
187 
188     /*
189      * 5. Check that the server's RSA signature matches
190      *    the SHA-256 hash of (P,G,Ys)
191      */
192     mbedtls_printf( "\n  . Verifying the server's RSA signature" );
193     fflush( stdout );
194 
195     p += 2;
196 
197     if( ( n = (size_t) ( end - p ) ) != rsa.MBEDTLS_PRIVATE(len) )
198     {
199         mbedtls_printf( " failed\n  ! Invalid RSA signature size\n\n" );
200         goto exit;
201     }
202 
203     if( ( ret = mbedtls_sha1( buf, (int)( p - 2 - buf ), hash ) ) != 0 )
204     {
205         mbedtls_printf( " failed\n  ! mbedtls_sha1 returned %d\n\n", ret );
206         goto exit;
207     }
208 
209     if( ( ret = mbedtls_rsa_pkcs1_verify( &rsa, MBEDTLS_MD_SHA256,
210                                           32, hash, p ) ) != 0 )
211     {
212         mbedtls_printf( " failed\n  ! mbedtls_rsa_pkcs1_verify returned %d\n\n", ret );
213         goto exit;
214     }
215 
216     /*
217      * 6. Send our public value: Yc = G ^ Xc mod P
218      */
219     mbedtls_printf( "\n  . Sending own public value to server" );
220     fflush( stdout );
221 
222     n = mbedtls_dhm_get_len( &dhm );
223     if( ( ret = mbedtls_dhm_make_public( &dhm, (int) n, buf, n,
224                                  mbedtls_ctr_drbg_random, &ctr_drbg ) ) != 0 )
225     {
226         mbedtls_printf( " failed\n  ! mbedtls_dhm_make_public returned %d\n\n", ret );
227         goto exit;
228     }
229 
230     if( ( ret = mbedtls_net_send( &server_fd, buf, n ) ) != (int) n )
231     {
232         mbedtls_printf( " failed\n  ! mbedtls_net_send returned %d\n\n", ret );
233         goto exit;
234     }
235 
236     /*
237      * 7. Derive the shared secret: K = Ys ^ Xc mod P
238      */
239     mbedtls_printf( "\n  . Shared secret: " );
240     fflush( stdout );
241 
242     if( ( ret = mbedtls_dhm_calc_secret( &dhm, buf, sizeof( buf ), &n,
243                                  mbedtls_ctr_drbg_random, &ctr_drbg ) ) != 0 )
244     {
245         mbedtls_printf( " failed\n  ! mbedtls_dhm_calc_secret returned %d\n\n", ret );
246         goto exit;
247     }
248 
249     for( n = 0; n < 16; n++ )
250         mbedtls_printf( "%02x", buf[n] );
251 
252     /*
253      * 8. Setup the AES-256 decryption key
254      *
255      * This is an overly simplified example; best practice is
256      * to hash the shared secret with a random value to derive
257      * the keying material for the encryption/decryption keys,
258      * IVs and MACs.
259      */
260     mbedtls_printf( "...\n  . Receiving and decrypting the ciphertext" );
261     fflush( stdout );
262 
263     ret = mbedtls_aes_setkey_dec( &aes, buf, 256 );
264     if( ret != 0 )
265         goto exit;
266 
267     memset( buf, 0, sizeof( buf ) );
268 
269     if( ( ret = mbedtls_net_recv( &server_fd, buf, 16 ) ) != 16 )
270     {
271         mbedtls_printf( " failed\n  ! mbedtls_net_recv returned %d\n\n", ret );
272         goto exit;
273     }
274 
275     ret = mbedtls_aes_crypt_ecb( &aes, MBEDTLS_AES_DECRYPT, buf, buf );
276     if( ret != 0 )
277         goto exit;
278     buf[16] = '\0';
279     mbedtls_printf( "\n  . Plaintext is \"%s\"\n\n", (char *) buf );
280 
281     exit_code = MBEDTLS_EXIT_SUCCESS;
282 
283 exit:
284 
285     mbedtls_net_free( &server_fd );
286 
287     mbedtls_aes_free( &aes );
288     mbedtls_rsa_free( &rsa );
289     mbedtls_dhm_free( &dhm );
290     mbedtls_ctr_drbg_free( &ctr_drbg );
291     mbedtls_entropy_free( &entropy );
292 
293     mbedtls_exit( exit_code );
294 }
295 #endif /* MBEDTLS_AES_C && MBEDTLS_DHM_C && MBEDTLS_ENTROPY_C &&
296           MBEDTLS_NET_C && MBEDTLS_RSA_C && MBEDTLS_SHA256_C &&
297           MBEDTLS_FS_IO && MBEDTLS_CTR_DRBG_C */
298