1 /* $OpenBSD: kexgen.c,v 1.10 2024/09/09 02:39:57 djm Exp $ */
2 /*
3 * Copyright (c) 2019 Markus Friedl. All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
8 * 1. Redistributions of source code must retain the above copyright
9 * notice, this list of conditions and the following disclaimer.
10 * 2. Redistributions in binary form must reproduce the above copyright
11 * notice, this list of conditions and the following disclaimer in the
12 * documentation and/or other materials provided with the distribution.
13 *
14 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
15 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
16 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
17 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
18 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
19 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
20 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
21 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
22 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
23 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
24 */
25
26 #include "includes.h"
27
28 #include <sys/types.h>
29
30 #include <stdarg.h>
31 #include <stdio.h>
32 #include <string.h>
33 #include <signal.h>
34
35 #include "sshkey.h"
36 #include "kex.h"
37 #include "log.h"
38 #include "packet.h"
39 #include "ssh2.h"
40 #include "sshbuf.h"
41 #include "digest.h"
42 #include "ssherr.h"
43
44 static int input_kex_gen_init(int, u_int32_t, struct ssh *);
45 static int input_kex_gen_reply(int type, u_int32_t seq, struct ssh *ssh);
46
47 static int
kex_gen_hash(int hash_alg,const struct sshbuf * client_version,const struct sshbuf * server_version,const struct sshbuf * client_kexinit,const struct sshbuf * server_kexinit,const struct sshbuf * server_host_key_blob,const struct sshbuf * client_pub,const struct sshbuf * server_pub,const struct sshbuf * shared_secret,u_char * hash,size_t * hashlen)48 kex_gen_hash(
49 int hash_alg,
50 const struct sshbuf *client_version,
51 const struct sshbuf *server_version,
52 const struct sshbuf *client_kexinit,
53 const struct sshbuf *server_kexinit,
54 const struct sshbuf *server_host_key_blob,
55 const struct sshbuf *client_pub,
56 const struct sshbuf *server_pub,
57 const struct sshbuf *shared_secret,
58 u_char *hash, size_t *hashlen)
59 {
60 struct sshbuf *b;
61 int r;
62
63 if (*hashlen < ssh_digest_bytes(hash_alg))
64 return SSH_ERR_INVALID_ARGUMENT;
65 if ((b = sshbuf_new()) == NULL)
66 return SSH_ERR_ALLOC_FAIL;
67 if ((r = sshbuf_put_stringb(b, client_version)) != 0 ||
68 (r = sshbuf_put_stringb(b, server_version)) != 0 ||
69 /* kexinit messages: fake header: len+SSH2_MSG_KEXINIT */
70 (r = sshbuf_put_u32(b, sshbuf_len(client_kexinit) + 1)) != 0 ||
71 (r = sshbuf_put_u8(b, SSH2_MSG_KEXINIT)) != 0 ||
72 (r = sshbuf_putb(b, client_kexinit)) != 0 ||
73 (r = sshbuf_put_u32(b, sshbuf_len(server_kexinit) + 1)) != 0 ||
74 (r = sshbuf_put_u8(b, SSH2_MSG_KEXINIT)) != 0 ||
75 (r = sshbuf_putb(b, server_kexinit)) != 0 ||
76 (r = sshbuf_put_stringb(b, server_host_key_blob)) != 0 ||
77 (r = sshbuf_put_stringb(b, client_pub)) != 0 ||
78 (r = sshbuf_put_stringb(b, server_pub)) != 0 ||
79 (r = sshbuf_putb(b, shared_secret)) != 0) {
80 sshbuf_free(b);
81 return r;
82 }
83 #ifdef DEBUG_KEX
84 sshbuf_dump(b, stderr);
85 #endif
86 if (ssh_digest_buffer(hash_alg, b, hash, *hashlen) != 0) {
87 sshbuf_free(b);
88 return SSH_ERR_LIBCRYPTO_ERROR;
89 }
90 sshbuf_free(b);
91 *hashlen = ssh_digest_bytes(hash_alg);
92 #ifdef DEBUG_KEX
93 dump_digest("hash", hash, *hashlen);
94 #endif
95 return 0;
96 }
97
98 int
kex_gen_client(struct ssh * ssh)99 kex_gen_client(struct ssh *ssh)
100 {
101 struct kex *kex = ssh->kex;
102 int r;
103
104 switch (kex->kex_type) {
105 #ifdef WITH_OPENSSL
106 case KEX_DH_GRP1_SHA1:
107 case KEX_DH_GRP14_SHA1:
108 case KEX_DH_GRP14_SHA256:
109 case KEX_DH_GRP16_SHA512:
110 case KEX_DH_GRP18_SHA512:
111 r = kex_dh_keypair(kex);
112 break;
113 case KEX_ECDH_SHA2:
114 r = kex_ecdh_keypair(kex);
115 break;
116 #endif
117 case KEX_C25519_SHA256:
118 r = kex_c25519_keypair(kex);
119 break;
120 case KEX_KEM_SNTRUP761X25519_SHA512:
121 r = kex_kem_sntrup761x25519_keypair(kex);
122 break;
123 case KEX_KEM_MLKEM768X25519_SHA256:
124 r = kex_kem_mlkem768x25519_keypair(kex);
125 break;
126 default:
127 r = SSH_ERR_INVALID_ARGUMENT;
128 break;
129 }
130 if (r != 0)
131 return r;
132 if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_ECDH_INIT)) != 0 ||
133 (r = sshpkt_put_stringb(ssh, kex->client_pub)) != 0 ||
134 (r = sshpkt_send(ssh)) != 0)
135 return r;
136 debug("expecting SSH2_MSG_KEX_ECDH_REPLY");
137 ssh_dispatch_set(ssh, SSH2_MSG_KEX_ECDH_REPLY, &input_kex_gen_reply);
138 return 0;
139 }
140
141 static int
input_kex_gen_reply(int type,u_int32_t seq,struct ssh * ssh)142 input_kex_gen_reply(int type, u_int32_t seq, struct ssh *ssh)
143 {
144 struct kex *kex = ssh->kex;
145 struct sshkey *server_host_key = NULL;
146 struct sshbuf *shared_secret = NULL;
147 struct sshbuf *server_blob = NULL;
148 struct sshbuf *tmp = NULL, *server_host_key_blob = NULL;
149 u_char *signature = NULL;
150 u_char hash[SSH_DIGEST_MAX_LENGTH];
151 size_t slen, hashlen;
152 int r;
153
154 debug("SSH2_MSG_KEX_ECDH_REPLY received");
155 ssh_dispatch_set(ssh, SSH2_MSG_KEX_ECDH_REPLY, &kex_protocol_error);
156
157 /* hostkey */
158 if ((r = sshpkt_getb_froms(ssh, &server_host_key_blob)) != 0)
159 goto out;
160 /* sshkey_fromb() consumes its buffer, so make a copy */
161 if ((tmp = sshbuf_fromb(server_host_key_blob)) == NULL) {
162 r = SSH_ERR_ALLOC_FAIL;
163 goto out;
164 }
165 if ((r = sshkey_fromb(tmp, &server_host_key)) != 0)
166 goto out;
167 if ((r = kex_verify_host_key(ssh, server_host_key)) != 0)
168 goto out;
169
170 /* Q_S, server public key */
171 /* signed H */
172 if ((r = sshpkt_getb_froms(ssh, &server_blob)) != 0 ||
173 (r = sshpkt_get_string(ssh, &signature, &slen)) != 0 ||
174 (r = sshpkt_get_end(ssh)) != 0)
175 goto out;
176
177 /* compute shared secret */
178 switch (kex->kex_type) {
179 #ifdef WITH_OPENSSL
180 case KEX_DH_GRP1_SHA1:
181 case KEX_DH_GRP14_SHA1:
182 case KEX_DH_GRP14_SHA256:
183 case KEX_DH_GRP16_SHA512:
184 case KEX_DH_GRP18_SHA512:
185 r = kex_dh_dec(kex, server_blob, &shared_secret);
186 break;
187 case KEX_ECDH_SHA2:
188 r = kex_ecdh_dec(kex, server_blob, &shared_secret);
189 break;
190 #endif
191 case KEX_C25519_SHA256:
192 r = kex_c25519_dec(kex, server_blob, &shared_secret);
193 break;
194 case KEX_KEM_SNTRUP761X25519_SHA512:
195 r = kex_kem_sntrup761x25519_dec(kex, server_blob,
196 &shared_secret);
197 break;
198 case KEX_KEM_MLKEM768X25519_SHA256:
199 r = kex_kem_mlkem768x25519_dec(kex, server_blob,
200 &shared_secret);
201 break;
202 default:
203 r = SSH_ERR_INVALID_ARGUMENT;
204 break;
205 }
206 if (r !=0 )
207 goto out;
208
209 /* calc and verify H */
210 hashlen = sizeof(hash);
211 if ((r = kex_gen_hash(
212 kex->hash_alg,
213 kex->client_version,
214 kex->server_version,
215 kex->my,
216 kex->peer,
217 server_host_key_blob,
218 kex->client_pub,
219 server_blob,
220 shared_secret,
221 hash, &hashlen)) != 0)
222 goto out;
223
224 if ((r = sshkey_verify(server_host_key, signature, slen, hash, hashlen,
225 kex->hostkey_alg, ssh->compat, NULL)) != 0)
226 goto out;
227
228 if ((r = kex_derive_keys(ssh, hash, hashlen, shared_secret)) != 0 ||
229 (r = kex_send_newkeys(ssh)) != 0)
230 goto out;
231
232 /* save initial signature and hostkey */
233 if ((kex->flags & KEX_INITIAL) != 0) {
234 if (kex->initial_hostkey != NULL || kex->initial_sig != NULL) {
235 r = SSH_ERR_INTERNAL_ERROR;
236 goto out;
237 }
238 if ((kex->initial_sig = sshbuf_new()) == NULL) {
239 r = SSH_ERR_ALLOC_FAIL;
240 goto out;
241 }
242 if ((r = sshbuf_put(kex->initial_sig, signature, slen)) != 0)
243 goto out;
244 kex->initial_hostkey = server_host_key;
245 server_host_key = NULL;
246 }
247 /* success */
248 out:
249 explicit_bzero(hash, sizeof(hash));
250 explicit_bzero(kex->c25519_client_key, sizeof(kex->c25519_client_key));
251 explicit_bzero(kex->sntrup761_client_key,
252 sizeof(kex->sntrup761_client_key));
253 explicit_bzero(kex->mlkem768_client_key,
254 sizeof(kex->mlkem768_client_key));
255 sshbuf_free(server_host_key_blob);
256 free(signature);
257 sshbuf_free(tmp);
258 sshkey_free(server_host_key);
259 sshbuf_free(server_blob);
260 sshbuf_free(shared_secret);
261 sshbuf_free(kex->client_pub);
262 kex->client_pub = NULL;
263 return r;
264 }
265
266 int
kex_gen_server(struct ssh * ssh)267 kex_gen_server(struct ssh *ssh)
268 {
269 debug("expecting SSH2_MSG_KEX_ECDH_INIT");
270 ssh_dispatch_set(ssh, SSH2_MSG_KEX_ECDH_INIT, &input_kex_gen_init);
271 return 0;
272 }
273
274 static int
input_kex_gen_init(int type,u_int32_t seq,struct ssh * ssh)275 input_kex_gen_init(int type, u_int32_t seq, struct ssh *ssh)
276 {
277 struct kex *kex = ssh->kex;
278 struct sshkey *server_host_private, *server_host_public;
279 struct sshbuf *shared_secret = NULL;
280 struct sshbuf *server_pubkey = NULL;
281 struct sshbuf *client_pubkey = NULL;
282 struct sshbuf *server_host_key_blob = NULL;
283 u_char *signature = NULL, hash[SSH_DIGEST_MAX_LENGTH];
284 size_t slen, hashlen;
285 int r;
286
287 debug("SSH2_MSG_KEX_ECDH_INIT received");
288 ssh_dispatch_set(ssh, SSH2_MSG_KEX_ECDH_INIT, &kex_protocol_error);
289
290 if ((r = kex_load_hostkey(ssh, &server_host_private,
291 &server_host_public)) != 0)
292 goto out;
293
294 if ((r = sshpkt_getb_froms(ssh, &client_pubkey)) != 0 ||
295 (r = sshpkt_get_end(ssh)) != 0)
296 goto out;
297
298 /* compute shared secret */
299 switch (kex->kex_type) {
300 #ifdef WITH_OPENSSL
301 case KEX_DH_GRP1_SHA1:
302 case KEX_DH_GRP14_SHA1:
303 case KEX_DH_GRP14_SHA256:
304 case KEX_DH_GRP16_SHA512:
305 case KEX_DH_GRP18_SHA512:
306 r = kex_dh_enc(kex, client_pubkey, &server_pubkey,
307 &shared_secret);
308 break;
309 case KEX_ECDH_SHA2:
310 r = kex_ecdh_enc(kex, client_pubkey, &server_pubkey,
311 &shared_secret);
312 break;
313 #endif
314 case KEX_C25519_SHA256:
315 r = kex_c25519_enc(kex, client_pubkey, &server_pubkey,
316 &shared_secret);
317 break;
318 case KEX_KEM_SNTRUP761X25519_SHA512:
319 r = kex_kem_sntrup761x25519_enc(kex, client_pubkey,
320 &server_pubkey, &shared_secret);
321 break;
322 case KEX_KEM_MLKEM768X25519_SHA256:
323 r = kex_kem_mlkem768x25519_enc(kex, client_pubkey,
324 &server_pubkey, &shared_secret);
325 break;
326 default:
327 r = SSH_ERR_INVALID_ARGUMENT;
328 break;
329 }
330 if (r !=0 )
331 goto out;
332
333 /* calc H */
334 if ((server_host_key_blob = sshbuf_new()) == NULL) {
335 r = SSH_ERR_ALLOC_FAIL;
336 goto out;
337 }
338 if ((r = sshkey_putb(server_host_public, server_host_key_blob)) != 0)
339 goto out;
340 hashlen = sizeof(hash);
341 if ((r = kex_gen_hash(
342 kex->hash_alg,
343 kex->client_version,
344 kex->server_version,
345 kex->peer,
346 kex->my,
347 server_host_key_blob,
348 client_pubkey,
349 server_pubkey,
350 shared_secret,
351 hash, &hashlen)) != 0)
352 goto out;
353
354 /* sign H */
355 if ((r = kex->sign(ssh, server_host_private, server_host_public,
356 &signature, &slen, hash, hashlen, kex->hostkey_alg)) != 0)
357 goto out;
358
359 /* send server hostkey, ECDH pubkey 'Q_S' and signed H */
360 if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_ECDH_REPLY)) != 0 ||
361 (r = sshpkt_put_stringb(ssh, server_host_key_blob)) != 0 ||
362 (r = sshpkt_put_stringb(ssh, server_pubkey)) != 0 ||
363 (r = sshpkt_put_string(ssh, signature, slen)) != 0 ||
364 (r = sshpkt_send(ssh)) != 0)
365 goto out;
366
367 if ((r = kex_derive_keys(ssh, hash, hashlen, shared_secret)) != 0 ||
368 (r = kex_send_newkeys(ssh)) != 0)
369 goto out;
370 /* retain copy of hostkey used at initial KEX */
371 if (kex->initial_hostkey == NULL &&
372 (r = sshkey_from_private(server_host_public,
373 &kex->initial_hostkey)) != 0)
374 goto out;
375 /* success */
376 out:
377 explicit_bzero(hash, sizeof(hash));
378 sshbuf_free(server_host_key_blob);
379 free(signature);
380 sshbuf_free(shared_secret);
381 sshbuf_free(client_pubkey);
382 sshbuf_free(server_pubkey);
383 return r;
384 }
385