1 /*
2  *  Diffie-Hellman-Merkle key exchange (server 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_PORT "11999"
32 #define PLAINTEXT "==Hello there!=="
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 listen_fd, client_fd;
58 
59     unsigned char buf[2048];
60     unsigned char hash[32];
61     unsigned char buf2[2];
62     const char *pers = "dh_server";
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_mpi N, P, Q, D, E;
71 
72     mbedtls_net_init(&listen_fd);
73     mbedtls_net_init(&client_fd);
74     mbedtls_dhm_init(&dhm);
75     mbedtls_aes_init(&aes);
76     mbedtls_ctr_drbg_init(&ctr_drbg);
77 
78     mbedtls_mpi_init(&N); mbedtls_mpi_init(&P); mbedtls_mpi_init(&Q);
79     mbedtls_mpi_init(&D); mbedtls_mpi_init(&E);
80 
81     /*
82      * 1. Setup the RNG
83      */
84     mbedtls_printf("\n  . Seeding the random number generator");
85     fflush(stdout);
86 
87     mbedtls_entropy_init(&entropy);
88     if ((ret = mbedtls_ctr_drbg_seed(&ctr_drbg, mbedtls_entropy_func, &entropy,
89                                      (const unsigned char *) pers,
90                                      strlen(pers))) != 0) {
91         mbedtls_printf(" failed\n  ! mbedtls_ctr_drbg_seed returned %d\n", ret);
92         goto exit;
93     }
94 
95     /*
96      * 2a. Read the server's private RSA key
97      */
98     mbedtls_printf("\n  . Reading private key from rsa_priv.txt");
99     fflush(stdout);
100 
101     if ((f = fopen("rsa_priv.txt", "rb")) == NULL) {
102         mbedtls_printf(" failed\n  ! Could not open rsa_priv.txt\n" \
103                        "  ! Please run rsa_genkey first\n\n");
104         goto exit;
105     }
106 
107     mbedtls_rsa_init(&rsa);
108 
109     if ((ret = mbedtls_mpi_read_file(&N, 16, f)) != 0 ||
110         (ret = mbedtls_mpi_read_file(&E, 16, f)) != 0 ||
111         (ret = mbedtls_mpi_read_file(&D, 16, f)) != 0 ||
112         (ret = mbedtls_mpi_read_file(&P, 16, f)) != 0 ||
113         (ret = mbedtls_mpi_read_file(&Q, 16, f)) != 0) {
114         mbedtls_printf(" failed\n  ! mbedtls_mpi_read_file returned %d\n\n",
115                        ret);
116         fclose(f);
117         goto exit;
118     }
119     fclose(f);
120 
121     if ((ret = mbedtls_rsa_import(&rsa, &N, &P, &Q, &D, &E)) != 0) {
122         mbedtls_printf(" failed\n  ! mbedtls_rsa_import returned %d\n\n",
123                        ret);
124         goto exit;
125     }
126 
127     if ((ret = mbedtls_rsa_complete(&rsa)) != 0) {
128         mbedtls_printf(" failed\n  ! mbedtls_rsa_complete returned %d\n\n",
129                        ret);
130         goto exit;
131     }
132 
133     /*
134      * 2b. Get the DHM modulus and generator
135      */
136     mbedtls_printf("\n  . Reading DH parameters from dh_prime.txt");
137     fflush(stdout);
138 
139     if ((f = fopen("dh_prime.txt", "rb")) == NULL) {
140         mbedtls_printf(" failed\n  ! Could not open dh_prime.txt\n" \
141                        "  ! Please run dh_genprime first\n\n");
142         goto exit;
143     }
144 
145     if (mbedtls_mpi_read_file(&dhm.MBEDTLS_PRIVATE(P), 16, f) != 0 ||
146         mbedtls_mpi_read_file(&dhm.MBEDTLS_PRIVATE(G), 16, f) != 0) {
147         mbedtls_printf(" failed\n  ! Invalid DH parameter file\n\n");
148         fclose(f);
149         goto exit;
150     }
151 
152     fclose(f);
153 
154     /*
155      * 3. Wait for a client to connect
156      */
157     mbedtls_printf("\n  . Waiting for a remote connection");
158     fflush(stdout);
159 
160     if ((ret = mbedtls_net_bind(&listen_fd, NULL, SERVER_PORT, MBEDTLS_NET_PROTO_TCP)) != 0) {
161         mbedtls_printf(" failed\n  ! mbedtls_net_bind returned %d\n\n", ret);
162         goto exit;
163     }
164 
165     if ((ret = mbedtls_net_accept(&listen_fd, &client_fd,
166                                   NULL, 0, NULL)) != 0) {
167         mbedtls_printf(" failed\n  ! mbedtls_net_accept returned %d\n\n", ret);
168         goto exit;
169     }
170 
171     /*
172      * 4. Setup the DH parameters (P,G,Ys)
173      */
174     mbedtls_printf("\n  . Sending the server's DH parameters");
175     fflush(stdout);
176 
177     memset(buf, 0, sizeof(buf));
178 
179     if ((ret =
180              mbedtls_dhm_make_params(&dhm, (int) mbedtls_mpi_size(&dhm.MBEDTLS_PRIVATE(P)), buf, &n,
181                                      mbedtls_ctr_drbg_random, &ctr_drbg)) != 0) {
182         mbedtls_printf(" failed\n  ! mbedtls_dhm_make_params returned %d\n\n", ret);
183         goto exit;
184     }
185 
186     /*
187      * 5. Sign the parameters and send them
188      */
189     if ((ret = mbedtls_sha1(buf, n, hash)) != 0) {
190         mbedtls_printf(" failed\n  ! mbedtls_sha1 returned %d\n\n", ret);
191         goto exit;
192     }
193 
194     buf[n] = (unsigned char) (rsa.MBEDTLS_PRIVATE(len) >> 8);
195     buf[n + 1] = (unsigned char) (rsa.MBEDTLS_PRIVATE(len));
196 
197     if ((ret = mbedtls_rsa_pkcs1_sign(&rsa, NULL, NULL, MBEDTLS_MD_SHA256,
198                                       32, hash, buf + n + 2)) != 0) {
199         mbedtls_printf(" failed\n  ! mbedtls_rsa_pkcs1_sign returned %d\n\n", ret);
200         goto exit;
201     }
202 
203     buflen = n + 2 + rsa.MBEDTLS_PRIVATE(len);
204     buf2[0] = (unsigned char) (buflen >> 8);
205     buf2[1] = (unsigned char) (buflen);
206 
207     if ((ret = mbedtls_net_send(&client_fd, buf2, 2)) != 2 ||
208         (ret = mbedtls_net_send(&client_fd, buf, buflen)) != (int) buflen) {
209         mbedtls_printf(" failed\n  ! mbedtls_net_send returned %d\n\n", ret);
210         goto exit;
211     }
212 
213     /*
214      * 6. Get the client's public value: Yc = G ^ Xc mod P
215      */
216     mbedtls_printf("\n  . Receiving the client's public value");
217     fflush(stdout);
218 
219     memset(buf, 0, sizeof(buf));
220 
221     n = mbedtls_dhm_get_len(&dhm);
222     if ((ret = mbedtls_net_recv(&client_fd, buf, n)) != (int) n) {
223         mbedtls_printf(" failed\n  ! mbedtls_net_recv returned %d\n\n", ret);
224         goto exit;
225     }
226 
227     if ((ret = mbedtls_dhm_read_public(&dhm, buf, n)) != 0) {
228         mbedtls_printf(" failed\n  ! mbedtls_dhm_read_public returned %d\n\n", ret);
229         goto exit;
230     }
231 
232     /*
233      * 7. Derive the shared secret: K = Ys ^ Xc mod P
234      */
235     mbedtls_printf("\n  . Shared secret: ");
236     fflush(stdout);
237 
238     if ((ret = mbedtls_dhm_calc_secret(&dhm, buf, sizeof(buf), &n,
239                                        mbedtls_ctr_drbg_random, &ctr_drbg)) != 0) {
240         mbedtls_printf(" failed\n  ! mbedtls_dhm_calc_secret returned %d\n\n", ret);
241         goto exit;
242     }
243 
244     for (n = 0; n < 16; n++) {
245         mbedtls_printf("%02x", buf[n]);
246     }
247 
248     /*
249      * 8. Setup the AES-256 encryption key
250      *
251      * This is an overly simplified example; best practice is
252      * to hash the shared secret with a random value to derive
253      * the keying material for the encryption/decryption keys
254      * and MACs.
255      */
256     mbedtls_printf("...\n  . Encrypting and sending the ciphertext");
257     fflush(stdout);
258 
259     ret = mbedtls_aes_setkey_enc(&aes, buf, 256);
260     if (ret != 0) {
261         goto exit;
262     }
263     memcpy(buf, PLAINTEXT, 16);
264     ret = mbedtls_aes_crypt_ecb(&aes, MBEDTLS_AES_ENCRYPT, buf, buf);
265     if (ret != 0) {
266         goto exit;
267     }
268 
269     if ((ret = mbedtls_net_send(&client_fd, buf, 16)) != 16) {
270         mbedtls_printf(" failed\n  ! mbedtls_net_send returned %d\n\n", ret);
271         goto exit;
272     }
273 
274     mbedtls_printf("\n\n");
275 
276     exit_code = MBEDTLS_EXIT_SUCCESS;
277 
278 exit:
279 
280     mbedtls_mpi_free(&N); mbedtls_mpi_free(&P); mbedtls_mpi_free(&Q);
281     mbedtls_mpi_free(&D); mbedtls_mpi_free(&E);
282 
283     mbedtls_net_free(&client_fd);
284     mbedtls_net_free(&listen_fd);
285 
286     mbedtls_aes_free(&aes);
287     mbedtls_rsa_free(&rsa);
288     mbedtls_dhm_free(&dhm);
289     mbedtls_ctr_drbg_free(&ctr_drbg);
290     mbedtls_entropy_free(&entropy);
291 
292     mbedtls_exit(exit_code);
293 }
294 #endif /* MBEDTLS_AES_C && MBEDTLS_DHM_C && MBEDTLS_ENTROPY_C &&
295           MBEDTLS_NET_C && MBEDTLS_RSA_C && MBEDTLS_MD_CAN_SHA256 &&
296           MBEDTLS_FS_IO && MBEDTLS_CTR_DRBG_C */
297