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 #if defined(MBEDTLS_PLATFORM_C)
23 #include "mbedtls/platform.h"
24 #else
25 #include <stdio.h>
26 #include <stdlib.h>
27 #define mbedtls_printf printf
28 #define mbedtls_time_t time_t
29 #define mbedtls_exit exit
30 #define MBEDTLS_EXIT_SUCCESS EXIT_SUCCESS
31 #define MBEDTLS_EXIT_FAILURE EXIT_FAILURE
32 #endif /* MBEDTLS_PLATFORM_C */
33
34 #if defined(MBEDTLS_AES_C) && defined(MBEDTLS_DHM_C) && \
35 defined(MBEDTLS_ENTROPY_C) && defined(MBEDTLS_NET_C) && \
36 defined(MBEDTLS_RSA_C) && defined(MBEDTLS_SHA256_C) && \
37 defined(MBEDTLS_FS_IO) && defined(MBEDTLS_CTR_DRBG_C) && \
38 defined(MBEDTLS_SHA1_C)
39 #include "mbedtls/net_sockets.h"
40 #include "mbedtls/aes.h"
41 #include "mbedtls/dhm.h"
42 #include "mbedtls/rsa.h"
43 #include "mbedtls/sha1.h"
44 #include "mbedtls/entropy.h"
45 #include "mbedtls/ctr_drbg.h"
46
47 #include <stdio.h>
48 #include <string.h>
49 #endif
50
51 #define SERVER_NAME "localhost"
52 #define SERVER_PORT "11999"
53
54 #if !defined(MBEDTLS_AES_C) || !defined(MBEDTLS_DHM_C) || \
55 !defined(MBEDTLS_ENTROPY_C) || !defined(MBEDTLS_NET_C) || \
56 !defined(MBEDTLS_RSA_C) || !defined(MBEDTLS_SHA256_C) || \
57 !defined(MBEDTLS_FS_IO) || !defined(MBEDTLS_CTR_DRBG_C) || \
58 !defined(MBEDTLS_SHA1_C)
main(void)59 int main( void )
60 {
61 mbedtls_printf("MBEDTLS_AES_C and/or MBEDTLS_DHM_C and/or MBEDTLS_ENTROPY_C "
62 "and/or MBEDTLS_NET_C and/or MBEDTLS_RSA_C and/or "
63 "MBEDTLS_SHA256_C and/or MBEDTLS_FS_IO and/or "
64 "MBEDTLS_CTR_DRBG_C not defined.\n");
65 mbedtls_exit( 0 );
66 }
67 #else
68
69
main(void)70 int main( void )
71 {
72 FILE *f;
73
74 int ret = 1;
75 int exit_code = MBEDTLS_EXIT_FAILURE;
76 size_t n, buflen;
77 mbedtls_net_context server_fd;
78
79 unsigned char *p, *end;
80 unsigned char buf[2048];
81 unsigned char hash[32];
82 const char *pers = "dh_client";
83
84 mbedtls_entropy_context entropy;
85 mbedtls_ctr_drbg_context ctr_drbg;
86 mbedtls_rsa_context rsa;
87 mbedtls_dhm_context dhm;
88 mbedtls_aes_context aes;
89
90 mbedtls_net_init( &server_fd );
91 mbedtls_dhm_init( &dhm );
92 mbedtls_aes_init( &aes );
93 mbedtls_ctr_drbg_init( &ctr_drbg );
94
95 /*
96 * 1. Setup the RNG
97 */
98 mbedtls_printf( "\n . Seeding the random number generator" );
99 fflush( stdout );
100
101 mbedtls_entropy_init( &entropy );
102 if( ( ret = mbedtls_ctr_drbg_seed( &ctr_drbg, mbedtls_entropy_func, &entropy,
103 (const unsigned char *) pers,
104 strlen( pers ) ) ) != 0 )
105 {
106 mbedtls_printf( " failed\n ! mbedtls_ctr_drbg_seed returned %d\n", ret );
107 goto exit;
108 }
109
110 /*
111 * 2. Read the server's public RSA key
112 */
113 mbedtls_printf( "\n . Reading public key from rsa_pub.txt" );
114 fflush( stdout );
115
116 if( ( f = fopen( "rsa_pub.txt", "rb" ) ) == NULL )
117 {
118 mbedtls_printf( " failed\n ! Could not open rsa_pub.txt\n" \
119 " ! Please run rsa_genkey first\n\n" );
120 goto exit;
121 }
122
123 mbedtls_rsa_init( &rsa );
124
125 if( ( ret = mbedtls_mpi_read_file( &rsa.MBEDTLS_PRIVATE(N), 16, f ) ) != 0 ||
126 ( ret = mbedtls_mpi_read_file( &rsa.MBEDTLS_PRIVATE(E), 16, f ) ) != 0 )
127 {
128 mbedtls_printf( " failed\n ! mbedtls_mpi_read_file returned %d\n\n", ret );
129 fclose( f );
130 goto exit;
131 }
132
133 rsa.MBEDTLS_PRIVATE(len) = ( mbedtls_mpi_bitlen( &rsa.MBEDTLS_PRIVATE(N) ) + 7 ) >> 3;
134
135 fclose( f );
136
137 /*
138 * 3. Initiate the connection
139 */
140 mbedtls_printf( "\n . Connecting to tcp/%s/%s", SERVER_NAME,
141 SERVER_PORT );
142 fflush( stdout );
143
144 if( ( ret = mbedtls_net_connect( &server_fd, SERVER_NAME,
145 SERVER_PORT, MBEDTLS_NET_PROTO_TCP ) ) != 0 )
146 {
147 mbedtls_printf( " failed\n ! mbedtls_net_connect returned %d\n\n", ret );
148 goto exit;
149 }
150
151 /*
152 * 4a. First get the buffer length
153 */
154 mbedtls_printf( "\n . Receiving the server's DH parameters" );
155 fflush( stdout );
156
157 memset( buf, 0, sizeof( buf ) );
158
159 if( ( ret = mbedtls_net_recv( &server_fd, buf, 2 ) ) != 2 )
160 {
161 mbedtls_printf( " failed\n ! mbedtls_net_recv returned %d\n\n", ret );
162 goto exit;
163 }
164
165 n = buflen = ( buf[0] << 8 ) | buf[1];
166 if( buflen < 1 || buflen > sizeof( buf ) )
167 {
168 mbedtls_printf( " failed\n ! Got an invalid buffer length\n\n" );
169 goto exit;
170 }
171
172 /*
173 * 4b. Get the DHM parameters: P, G and Ys = G^Xs mod P
174 */
175 memset( buf, 0, sizeof( buf ) );
176
177 if( ( ret = mbedtls_net_recv( &server_fd, buf, n ) ) != (int) n )
178 {
179 mbedtls_printf( " failed\n ! mbedtls_net_recv returned %d\n\n", ret );
180 goto exit;
181 }
182
183 p = buf, end = buf + buflen;
184
185 if( ( ret = mbedtls_dhm_read_params( &dhm, &p, end ) ) != 0 )
186 {
187 mbedtls_printf( " failed\n ! mbedtls_dhm_read_params returned %d\n\n", ret );
188 goto exit;
189 }
190
191 n = mbedtls_dhm_get_len( &dhm );
192 if( n < 64 || n > 512 )
193 {
194 mbedtls_printf( " failed\n ! Invalid DHM modulus size\n\n" );
195 goto exit;
196 }
197
198 /*
199 * 5. Check that the server's RSA signature matches
200 * the SHA-256 hash of (P,G,Ys)
201 */
202 mbedtls_printf( "\n . Verifying the server's RSA signature" );
203 fflush( stdout );
204
205 p += 2;
206
207 if( ( n = (size_t) ( end - p ) ) != rsa.MBEDTLS_PRIVATE(len) )
208 {
209 mbedtls_printf( " failed\n ! Invalid RSA signature size\n\n" );
210 goto exit;
211 }
212
213 if( ( ret = mbedtls_sha1( buf, (int)( p - 2 - buf ), hash ) ) != 0 )
214 {
215 mbedtls_printf( " failed\n ! mbedtls_sha1 returned %d\n\n", ret );
216 goto exit;
217 }
218
219 if( ( ret = mbedtls_rsa_pkcs1_verify( &rsa, MBEDTLS_MD_SHA256,
220 32, hash, p ) ) != 0 )
221 {
222 mbedtls_printf( " failed\n ! mbedtls_rsa_pkcs1_verify returned %d\n\n", ret );
223 goto exit;
224 }
225
226 /*
227 * 6. Send our public value: Yc = G ^ Xc mod P
228 */
229 mbedtls_printf( "\n . Sending own public value to server" );
230 fflush( stdout );
231
232 n = mbedtls_dhm_get_len( &dhm );
233 if( ( ret = mbedtls_dhm_make_public( &dhm, (int) n, buf, n,
234 mbedtls_ctr_drbg_random, &ctr_drbg ) ) != 0 )
235 {
236 mbedtls_printf( " failed\n ! mbedtls_dhm_make_public returned %d\n\n", ret );
237 goto exit;
238 }
239
240 if( ( ret = mbedtls_net_send( &server_fd, buf, n ) ) != (int) n )
241 {
242 mbedtls_printf( " failed\n ! mbedtls_net_send returned %d\n\n", ret );
243 goto exit;
244 }
245
246 /*
247 * 7. Derive the shared secret: K = Ys ^ Xc mod P
248 */
249 mbedtls_printf( "\n . Shared secret: " );
250 fflush( stdout );
251
252 if( ( ret = mbedtls_dhm_calc_secret( &dhm, buf, sizeof( buf ), &n,
253 mbedtls_ctr_drbg_random, &ctr_drbg ) ) != 0 )
254 {
255 mbedtls_printf( " failed\n ! mbedtls_dhm_calc_secret returned %d\n\n", ret );
256 goto exit;
257 }
258
259 for( n = 0; n < 16; n++ )
260 mbedtls_printf( "%02x", buf[n] );
261
262 /*
263 * 8. Setup the AES-256 decryption key
264 *
265 * This is an overly simplified example; best practice is
266 * to hash the shared secret with a random value to derive
267 * the keying material for the encryption/decryption keys,
268 * IVs and MACs.
269 */
270 mbedtls_printf( "...\n . Receiving and decrypting the ciphertext" );
271 fflush( stdout );
272
273 ret = mbedtls_aes_setkey_dec( &aes, buf, 256 );
274 if( ret != 0 )
275 goto exit;
276
277 memset( buf, 0, sizeof( buf ) );
278
279 if( ( ret = mbedtls_net_recv( &server_fd, buf, 16 ) ) != 16 )
280 {
281 mbedtls_printf( " failed\n ! mbedtls_net_recv returned %d\n\n", ret );
282 goto exit;
283 }
284
285 ret = mbedtls_aes_crypt_ecb( &aes, MBEDTLS_AES_DECRYPT, buf, buf );
286 if( ret != 0 )
287 goto exit;
288 buf[16] = '\0';
289 mbedtls_printf( "\n . Plaintext is \"%s\"\n\n", (char *) buf );
290
291 exit_code = MBEDTLS_EXIT_SUCCESS;
292
293 exit:
294
295 mbedtls_net_free( &server_fd );
296
297 mbedtls_aes_free( &aes );
298 mbedtls_rsa_free( &rsa );
299 mbedtls_dhm_free( &dhm );
300 mbedtls_ctr_drbg_free( &ctr_drbg );
301 mbedtls_entropy_free( &entropy );
302
303 #if defined(_WIN32)
304 mbedtls_printf( " + Press Enter to exit this program.\n" );
305 fflush( stdout ); getchar();
306 #endif
307
308 mbedtls_exit( exit_code );
309 }
310 #endif /* MBEDTLS_AES_C && MBEDTLS_DHM_C && MBEDTLS_ENTROPY_C &&
311 MBEDTLS_NET_C && MBEDTLS_RSA_C && MBEDTLS_SHA256_C &&
312 MBEDTLS_FS_IO && MBEDTLS_CTR_DRBG_C */
313