1 /*
2 * Diffie-Hellman-Merkle key exchange (client side)
3 *
4 * Copyright The Mbed TLS Contributors
5 * SPDX-License-Identifier: Apache-2.0 OR GPL-2.0-or-later
6 */
7
8 #include "mbedtls/build_info.h"
9
10 #include "mbedtls/platform.h"
11 /* md.h is included this early since MD_CAN_XXX macros are defined there. */
12 #include "mbedtls/md.h"
13
14 #if defined(MBEDTLS_AES_C) && defined(MBEDTLS_DHM_C) && \
15 defined(MBEDTLS_ENTROPY_C) && defined(MBEDTLS_NET_C) && \
16 defined(MBEDTLS_RSA_C) && defined(MBEDTLS_MD_CAN_SHA256) && \
17 defined(MBEDTLS_FS_IO) && defined(MBEDTLS_CTR_DRBG_C) && \
18 defined(MBEDTLS_MD_CAN_SHA1)
19 #include "mbedtls/net_sockets.h"
20 #include "mbedtls/aes.h"
21 #include "mbedtls/dhm.h"
22 #include "mbedtls/rsa.h"
23 #include "mbedtls/sha1.h"
24 #include "mbedtls/entropy.h"
25 #include "mbedtls/ctr_drbg.h"
26
27 #include <stdio.h>
28 #include <string.h>
29 #endif
30
31 #define SERVER_NAME "localhost"
32 #define SERVER_PORT "11999"
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_MD_CAN_SHA256) || \
37 !defined(MBEDTLS_FS_IO) || !defined(MBEDTLS_CTR_DRBG_C) || \
38 !defined(MBEDTLS_SHA1_C)
main(void)39 int main(void)
40 {
41 mbedtls_printf("MBEDTLS_AES_C and/or MBEDTLS_DHM_C and/or MBEDTLS_ENTROPY_C "
42 "and/or MBEDTLS_NET_C and/or MBEDTLS_RSA_C and/or "
43 "MBEDTLS_MD_CAN_SHA256 and/or MBEDTLS_FS_IO and/or "
44 "MBEDTLS_CTR_DRBG_C and/or MBEDTLS_SHA1_C not defined.\n");
45 mbedtls_exit(0);
46 }
47 #else
48
49
main(void)50 int main(void)
51 {
52 FILE *f;
53
54 int ret = 1;
55 int exit_code = MBEDTLS_EXIT_FAILURE;
56 size_t n, buflen;
57 mbedtls_net_context server_fd;
58
59 unsigned char *p, *end;
60 unsigned char buf[2048];
61 unsigned char hash[32];
62 const char *pers = "dh_client";
63
64 mbedtls_entropy_context entropy;
65 mbedtls_ctr_drbg_context ctr_drbg;
66 mbedtls_rsa_context rsa;
67 mbedtls_dhm_context dhm;
68 mbedtls_aes_context aes;
69
70 mbedtls_net_init(&server_fd);
71 mbedtls_dhm_init(&dhm);
72 mbedtls_aes_init(&aes);
73 mbedtls_ctr_drbg_init(&ctr_drbg);
74
75 /*
76 * 1. Setup the RNG
77 */
78 mbedtls_printf("\n . Seeding the random number generator");
79 fflush(stdout);
80
81 mbedtls_entropy_init(&entropy);
82 if ((ret = mbedtls_ctr_drbg_seed(&ctr_drbg, mbedtls_entropy_func, &entropy,
83 (const unsigned char *) pers,
84 strlen(pers))) != 0) {
85 mbedtls_printf(" failed\n ! mbedtls_ctr_drbg_seed returned %d\n", ret);
86 goto exit;
87 }
88
89 /*
90 * 2. Read the server's public RSA key
91 */
92 mbedtls_printf("\n . Reading public key from rsa_pub.txt");
93 fflush(stdout);
94
95 if ((f = fopen("rsa_pub.txt", "rb")) == NULL) {
96 mbedtls_printf(" failed\n ! Could not open rsa_pub.txt\n" \
97 " ! Please run rsa_genkey first\n\n");
98 goto exit;
99 }
100
101 mbedtls_rsa_init(&rsa);
102
103 if ((ret = mbedtls_mpi_read_file(&rsa.MBEDTLS_PRIVATE(N), 16, f)) != 0 ||
104 (ret = mbedtls_mpi_read_file(&rsa.MBEDTLS_PRIVATE(E), 16, f)) != 0) {
105 mbedtls_printf(" failed\n ! mbedtls_mpi_read_file returned %d\n\n", ret);
106 fclose(f);
107 goto exit;
108 }
109
110 rsa.MBEDTLS_PRIVATE(len) = (mbedtls_mpi_bitlen(&rsa.MBEDTLS_PRIVATE(N)) + 7) >> 3;
111
112 fclose(f);
113
114 /*
115 * 3. Initiate the connection
116 */
117 mbedtls_printf("\n . Connecting to tcp/%s/%s", SERVER_NAME,
118 SERVER_PORT);
119 fflush(stdout);
120
121 if ((ret = mbedtls_net_connect(&server_fd, SERVER_NAME,
122 SERVER_PORT, MBEDTLS_NET_PROTO_TCP)) != 0) {
123 mbedtls_printf(" failed\n ! mbedtls_net_connect returned %d\n\n", ret);
124 goto exit;
125 }
126
127 /*
128 * 4a. First get the buffer length
129 */
130 mbedtls_printf("\n . Receiving the server's DH parameters");
131 fflush(stdout);
132
133 memset(buf, 0, sizeof(buf));
134
135 if ((ret = mbedtls_net_recv(&server_fd, buf, 2)) != 2) {
136 mbedtls_printf(" failed\n ! mbedtls_net_recv returned %d\n\n", ret);
137 goto exit;
138 }
139
140 n = buflen = (buf[0] << 8) | buf[1];
141 if (buflen < 1 || buflen > sizeof(buf)) {
142 mbedtls_printf(" failed\n ! Got an invalid buffer length\n\n");
143 goto exit;
144 }
145
146 /*
147 * 4b. Get the DHM parameters: P, G and Ys = G^Xs mod P
148 */
149 memset(buf, 0, sizeof(buf));
150
151 if ((ret = mbedtls_net_recv(&server_fd, buf, n)) != (int) n) {
152 mbedtls_printf(" failed\n ! mbedtls_net_recv returned %d\n\n", ret);
153 goto exit;
154 }
155
156 p = buf, end = buf + buflen;
157
158 if ((ret = mbedtls_dhm_read_params(&dhm, &p, end)) != 0) {
159 mbedtls_printf(" failed\n ! mbedtls_dhm_read_params returned %d\n\n", ret);
160 goto exit;
161 }
162
163 n = mbedtls_dhm_get_len(&dhm);
164 if (n < 64 || n > 512) {
165 mbedtls_printf(" failed\n ! Invalid DHM modulus size\n\n");
166 goto exit;
167 }
168
169 /*
170 * 5. Check that the server's RSA signature matches
171 * the SHA-256 hash of (P,G,Ys)
172 */
173 mbedtls_printf("\n . Verifying the server's RSA signature");
174 fflush(stdout);
175
176 p += 2;
177
178 if ((n = (size_t) (end - p)) != rsa.MBEDTLS_PRIVATE(len)) {
179 mbedtls_printf(" failed\n ! Invalid RSA signature size\n\n");
180 goto exit;
181 }
182
183 if ((ret = mbedtls_sha1(buf, (int) (p - 2 - buf), hash)) != 0) {
184 mbedtls_printf(" failed\n ! mbedtls_sha1 returned %d\n\n", ret);
185 goto exit;
186 }
187
188 if ((ret = mbedtls_rsa_pkcs1_verify(&rsa, MBEDTLS_MD_SHA256,
189 32, hash, p)) != 0) {
190 mbedtls_printf(" failed\n ! mbedtls_rsa_pkcs1_verify returned %d\n\n", ret);
191 goto exit;
192 }
193
194 /*
195 * 6. Send our public value: Yc = G ^ Xc mod P
196 */
197 mbedtls_printf("\n . Sending own public value to server");
198 fflush(stdout);
199
200 n = mbedtls_dhm_get_len(&dhm);
201 if ((ret = mbedtls_dhm_make_public(&dhm, (int) n, buf, n,
202 mbedtls_ctr_drbg_random, &ctr_drbg)) != 0) {
203 mbedtls_printf(" failed\n ! mbedtls_dhm_make_public returned %d\n\n", ret);
204 goto exit;
205 }
206
207 if ((ret = mbedtls_net_send(&server_fd, buf, n)) != (int) n) {
208 mbedtls_printf(" failed\n ! mbedtls_net_send returned %d\n\n", ret);
209 goto exit;
210 }
211
212 /*
213 * 7. Derive the shared secret: K = Ys ^ Xc mod P
214 */
215 mbedtls_printf("\n . Shared secret: ");
216 fflush(stdout);
217
218 if ((ret = mbedtls_dhm_calc_secret(&dhm, buf, sizeof(buf), &n,
219 mbedtls_ctr_drbg_random, &ctr_drbg)) != 0) {
220 mbedtls_printf(" failed\n ! mbedtls_dhm_calc_secret returned %d\n\n", ret);
221 goto exit;
222 }
223
224 for (n = 0; n < 16; n++) {
225 mbedtls_printf("%02x", buf[n]);
226 }
227
228 /*
229 * 8. Setup the AES-256 decryption key
230 *
231 * This is an overly simplified example; best practice is
232 * to hash the shared secret with a random value to derive
233 * the keying material for the encryption/decryption keys,
234 * IVs and MACs.
235 */
236 mbedtls_printf("...\n . Receiving and decrypting the ciphertext");
237 fflush(stdout);
238
239 ret = mbedtls_aes_setkey_dec(&aes, buf, 256);
240 if (ret != 0) {
241 goto exit;
242 }
243
244 memset(buf, 0, sizeof(buf));
245
246 if ((ret = mbedtls_net_recv(&server_fd, buf, 16)) != 16) {
247 mbedtls_printf(" failed\n ! mbedtls_net_recv returned %d\n\n", ret);
248 goto exit;
249 }
250
251 ret = mbedtls_aes_crypt_ecb(&aes, MBEDTLS_AES_DECRYPT, buf, buf);
252 if (ret != 0) {
253 goto exit;
254 }
255 buf[16] = '\0';
256 mbedtls_printf("\n . Plaintext is \"%s\"\n\n", (char *) buf);
257
258 exit_code = MBEDTLS_EXIT_SUCCESS;
259
260 exit:
261
262 mbedtls_net_free(&server_fd);
263
264 mbedtls_aes_free(&aes);
265 mbedtls_rsa_free(&rsa);
266 mbedtls_dhm_free(&dhm);
267 mbedtls_ctr_drbg_free(&ctr_drbg);
268 mbedtls_entropy_free(&entropy);
269
270 mbedtls_exit(exit_code);
271 }
272 #endif /* MBEDTLS_AES_C && MBEDTLS_DHM_C && MBEDTLS_ENTROPY_C &&
273 MBEDTLS_NET_C && MBEDTLS_RSA_C && MBEDTLS_MD_CAN_SHA256 &&
274 MBEDTLS_FS_IO && MBEDTLS_CTR_DRBG_C */
275
