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 <sys/types.h>
27
28 #include <stdio.h>
29 #include <string.h>
30 #include <signal.h>
31
32 #include "sshkey.h"
33 #include "kex.h"
34 #include "log.h"
35 #include "packet.h"
36 #include "ssh2.h"
37 #include "sshbuf.h"
38 #include "digest.h"
39 #include "ssherr.h"
40
41 static int input_kex_gen_init(int, u_int32_t, struct ssh *);
42 static int input_kex_gen_reply(int type, u_int32_t seq, struct ssh *ssh);
43
44 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)45 kex_gen_hash(
46 int hash_alg,
47 const struct sshbuf *client_version,
48 const struct sshbuf *server_version,
49 const struct sshbuf *client_kexinit,
50 const struct sshbuf *server_kexinit,
51 const struct sshbuf *server_host_key_blob,
52 const struct sshbuf *client_pub,
53 const struct sshbuf *server_pub,
54 const struct sshbuf *shared_secret,
55 u_char *hash, size_t *hashlen)
56 {
57 struct sshbuf *b;
58 int r;
59
60 if (*hashlen < ssh_digest_bytes(hash_alg))
61 return SSH_ERR_INVALID_ARGUMENT;
62 if ((b = sshbuf_new()) == NULL)
63 return SSH_ERR_ALLOC_FAIL;
64 if ((r = sshbuf_put_stringb(b, client_version)) != 0 ||
65 (r = sshbuf_put_stringb(b, server_version)) != 0 ||
66 /* kexinit messages: fake header: len+SSH2_MSG_KEXINIT */
67 (r = sshbuf_put_u32(b, sshbuf_len(client_kexinit) + 1)) != 0 ||
68 (r = sshbuf_put_u8(b, SSH2_MSG_KEXINIT)) != 0 ||
69 (r = sshbuf_putb(b, client_kexinit)) != 0 ||
70 (r = sshbuf_put_u32(b, sshbuf_len(server_kexinit) + 1)) != 0 ||
71 (r = sshbuf_put_u8(b, SSH2_MSG_KEXINIT)) != 0 ||
72 (r = sshbuf_putb(b, server_kexinit)) != 0 ||
73 (r = sshbuf_put_stringb(b, server_host_key_blob)) != 0 ||
74 (r = sshbuf_put_stringb(b, client_pub)) != 0 ||
75 (r = sshbuf_put_stringb(b, server_pub)) != 0 ||
76 (r = sshbuf_putb(b, shared_secret)) != 0) {
77 sshbuf_free(b);
78 return r;
79 }
80 #ifdef DEBUG_KEX
81 sshbuf_dump(b, stderr);
82 #endif
83 if (ssh_digest_buffer(hash_alg, b, hash, *hashlen) != 0) {
84 sshbuf_free(b);
85 return SSH_ERR_LIBCRYPTO_ERROR;
86 }
87 sshbuf_free(b);
88 *hashlen = ssh_digest_bytes(hash_alg);
89 #ifdef DEBUG_KEX
90 dump_digest("hash", hash, *hashlen);
91 #endif
92 return 0;
93 }
94
95 int
kex_gen_client(struct ssh * ssh)96 kex_gen_client(struct ssh *ssh)
97 {
98 struct kex *kex = ssh->kex;
99 int r;
100
101 switch (kex->kex_type) {
102 #ifdef WITH_OPENSSL
103 case KEX_DH_GRP1_SHA1:
104 case KEX_DH_GRP14_SHA1:
105 case KEX_DH_GRP14_SHA256:
106 case KEX_DH_GRP16_SHA512:
107 case KEX_DH_GRP18_SHA512:
108 r = kex_dh_keypair(kex);
109 break;
110 case KEX_ECDH_SHA2:
111 r = kex_ecdh_keypair(kex);
112 break;
113 #endif /* WITH_OPENSSL */
114 case KEX_C25519_SHA256:
115 r = kex_c25519_keypair(kex);
116 break;
117 case KEX_KEM_SNTRUP761X25519_SHA512:
118 r = kex_kem_sntrup761x25519_keypair(kex);
119 break;
120 case KEX_KEM_MLKEM768X25519_SHA256:
121 r = kex_kem_mlkem768x25519_keypair(kex);
122 break;
123 default:
124 r = SSH_ERR_INVALID_ARGUMENT;
125 break;
126 }
127 if (r != 0)
128 return r;
129 if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_ECDH_INIT)) != 0 ||
130 (r = sshpkt_put_stringb(ssh, kex->client_pub)) != 0 ||
131 (r = sshpkt_send(ssh)) != 0)
132 return r;
133 debug("expecting SSH2_MSG_KEX_ECDH_REPLY");
134 ssh_dispatch_set(ssh, SSH2_MSG_KEX_ECDH_REPLY, &input_kex_gen_reply);
135 return 0;
136 }
137
138 static int
input_kex_gen_reply(int type,u_int32_t seq,struct ssh * ssh)139 input_kex_gen_reply(int type, u_int32_t seq, struct ssh *ssh)
140 {
141 struct kex *kex = ssh->kex;
142 struct sshkey *server_host_key = NULL;
143 struct sshbuf *shared_secret = NULL;
144 struct sshbuf *server_blob = NULL;
145 struct sshbuf *tmp = NULL, *server_host_key_blob = NULL;
146 u_char *signature = NULL;
147 u_char hash[SSH_DIGEST_MAX_LENGTH];
148 size_t slen, hashlen;
149 int r;
150
151 debug("SSH2_MSG_KEX_ECDH_REPLY received");
152 ssh_dispatch_set(ssh, SSH2_MSG_KEX_ECDH_REPLY, &kex_protocol_error);
153
154 /* hostkey */
155 if ((r = sshpkt_getb_froms(ssh, &server_host_key_blob)) != 0)
156 goto out;
157 /* sshkey_fromb() consumes its buffer, so make a copy */
158 if ((tmp = sshbuf_fromb(server_host_key_blob)) == NULL) {
159 r = SSH_ERR_ALLOC_FAIL;
160 goto out;
161 }
162 if ((r = sshkey_fromb(tmp, &server_host_key)) != 0)
163 goto out;
164 if ((r = kex_verify_host_key(ssh, server_host_key)) != 0)
165 goto out;
166
167 /* Q_S, server public key */
168 /* signed H */
169 if ((r = sshpkt_getb_froms(ssh, &server_blob)) != 0 ||
170 (r = sshpkt_get_string(ssh, &signature, &slen)) != 0 ||
171 (r = sshpkt_get_end(ssh)) != 0)
172 goto out;
173
174 /* compute shared secret */
175 switch (kex->kex_type) {
176 #ifdef WITH_OPENSSL
177 case KEX_DH_GRP1_SHA1:
178 case KEX_DH_GRP14_SHA1:
179 case KEX_DH_GRP14_SHA256:
180 case KEX_DH_GRP16_SHA512:
181 case KEX_DH_GRP18_SHA512:
182 r = kex_dh_dec(kex, server_blob, &shared_secret);
183 break;
184 case KEX_ECDH_SHA2:
185 r = kex_ecdh_dec(kex, server_blob, &shared_secret);
186 break;
187 #endif /* WITH_OPENSSL */
188 case KEX_C25519_SHA256:
189 r = kex_c25519_dec(kex, server_blob, &shared_secret);
190 break;
191 case KEX_KEM_SNTRUP761X25519_SHA512:
192 r = kex_kem_sntrup761x25519_dec(kex, server_blob,
193 &shared_secret);
194 break;
195 case KEX_KEM_MLKEM768X25519_SHA256:
196 r = kex_kem_mlkem768x25519_dec(kex, server_blob,
197 &shared_secret);
198 break;
199 default:
200 r = SSH_ERR_INVALID_ARGUMENT;
201 break;
202 }
203 if (r !=0 )
204 goto out;
205
206 /* calc and verify H */
207 hashlen = sizeof(hash);
208 if ((r = kex_gen_hash(
209 kex->hash_alg,
210 kex->client_version,
211 kex->server_version,
212 kex->my,
213 kex->peer,
214 server_host_key_blob,
215 kex->client_pub,
216 server_blob,
217 shared_secret,
218 hash, &hashlen)) != 0)
219 goto out;
220
221 if ((r = sshkey_verify(server_host_key, signature, slen, hash, hashlen,
222 kex->hostkey_alg, ssh->compat, NULL)) != 0)
223 goto out;
224
225 if ((r = kex_derive_keys(ssh, hash, hashlen, shared_secret)) != 0 ||
226 (r = kex_send_newkeys(ssh)) != 0)
227 goto out;
228
229 /* save initial signature and hostkey */
230 if ((kex->flags & KEX_INITIAL) != 0) {
231 if (kex->initial_hostkey != NULL || kex->initial_sig != NULL) {
232 r = SSH_ERR_INTERNAL_ERROR;
233 goto out;
234 }
235 if ((kex->initial_sig = sshbuf_new()) == NULL) {
236 r = SSH_ERR_ALLOC_FAIL;
237 goto out;
238 }
239 if ((r = sshbuf_put(kex->initial_sig, signature, slen)) != 0)
240 goto out;
241 kex->initial_hostkey = server_host_key;
242 server_host_key = NULL;
243 }
244 /* success */
245 out:
246 explicit_bzero(hash, sizeof(hash));
247 explicit_bzero(kex->c25519_client_key, sizeof(kex->c25519_client_key));
248 explicit_bzero(kex->sntrup761_client_key,
249 sizeof(kex->sntrup761_client_key));
250 explicit_bzero(kex->mlkem768_client_key,
251 sizeof(kex->mlkem768_client_key));
252 sshbuf_free(server_host_key_blob);
253 free(signature);
254 sshbuf_free(tmp);
255 sshkey_free(server_host_key);
256 sshbuf_free(server_blob);
257 sshbuf_free(shared_secret);
258 sshbuf_free(kex->client_pub);
259 kex->client_pub = NULL;
260 return r;
261 }
262
263 int
kex_gen_server(struct ssh * ssh)264 kex_gen_server(struct ssh *ssh)
265 {
266 debug("expecting SSH2_MSG_KEX_ECDH_INIT");
267 ssh_dispatch_set(ssh, SSH2_MSG_KEX_ECDH_INIT, &input_kex_gen_init);
268 return 0;
269 }
270
271 static int
input_kex_gen_init(int type,u_int32_t seq,struct ssh * ssh)272 input_kex_gen_init(int type, u_int32_t seq, struct ssh *ssh)
273 {
274 struct kex *kex = ssh->kex;
275 struct sshkey *server_host_private, *server_host_public;
276 struct sshbuf *shared_secret = NULL;
277 struct sshbuf *server_pubkey = NULL;
278 struct sshbuf *client_pubkey = NULL;
279 struct sshbuf *server_host_key_blob = NULL;
280 u_char *signature = NULL, hash[SSH_DIGEST_MAX_LENGTH];
281 size_t slen, hashlen;
282 int r;
283
284 debug("SSH2_MSG_KEX_ECDH_INIT received");
285 ssh_dispatch_set(ssh, SSH2_MSG_KEX_ECDH_INIT, &kex_protocol_error);
286
287 if ((r = kex_load_hostkey(ssh, &server_host_private,
288 &server_host_public)) != 0)
289 goto out;
290
291 if ((r = sshpkt_getb_froms(ssh, &client_pubkey)) != 0 ||
292 (r = sshpkt_get_end(ssh)) != 0)
293 goto out;
294
295 /* compute shared secret */
296 switch (kex->kex_type) {
297 #ifdef WITH_OPENSSL
298 case KEX_DH_GRP1_SHA1:
299 case KEX_DH_GRP14_SHA1:
300 case KEX_DH_GRP14_SHA256:
301 case KEX_DH_GRP16_SHA512:
302 case KEX_DH_GRP18_SHA512:
303 r = kex_dh_enc(kex, client_pubkey, &server_pubkey,
304 &shared_secret);
305 break;
306 case KEX_ECDH_SHA2:
307 r = kex_ecdh_enc(kex, client_pubkey, &server_pubkey,
308 &shared_secret);
309 break;
310 #endif /* WITH_OPENSSL */
311 case KEX_C25519_SHA256:
312 r = kex_c25519_enc(kex, client_pubkey, &server_pubkey,
313 &shared_secret);
314 break;
315 case KEX_KEM_SNTRUP761X25519_SHA512:
316 r = kex_kem_sntrup761x25519_enc(kex, client_pubkey,
317 &server_pubkey, &shared_secret);
318 break;
319 case KEX_KEM_MLKEM768X25519_SHA256:
320 r = kex_kem_mlkem768x25519_enc(kex, client_pubkey,
321 &server_pubkey, &shared_secret);
322 break;
323 default:
324 r = SSH_ERR_INVALID_ARGUMENT;
325 break;
326 }
327 if (r !=0 )
328 goto out;
329
330 /* calc H */
331 if ((server_host_key_blob = sshbuf_new()) == NULL) {
332 r = SSH_ERR_ALLOC_FAIL;
333 goto out;
334 }
335 if ((r = sshkey_putb(server_host_public, server_host_key_blob)) != 0)
336 goto out;
337 hashlen = sizeof(hash);
338 if ((r = kex_gen_hash(
339 kex->hash_alg,
340 kex->client_version,
341 kex->server_version,
342 kex->peer,
343 kex->my,
344 server_host_key_blob,
345 client_pubkey,
346 server_pubkey,
347 shared_secret,
348 hash, &hashlen)) != 0)
349 goto out;
350
351 /* sign H */
352 if ((r = kex->sign(ssh, server_host_private, server_host_public,
353 &signature, &slen, hash, hashlen, kex->hostkey_alg)) != 0)
354 goto out;
355
356 /* send server hostkey, ECDH pubkey 'Q_S' and signed H */
357 if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_ECDH_REPLY)) != 0 ||
358 (r = sshpkt_put_stringb(ssh, server_host_key_blob)) != 0 ||
359 (r = sshpkt_put_stringb(ssh, server_pubkey)) != 0 ||
360 (r = sshpkt_put_string(ssh, signature, slen)) != 0 ||
361 (r = sshpkt_send(ssh)) != 0)
362 goto out;
363
364 if ((r = kex_derive_keys(ssh, hash, hashlen, shared_secret)) != 0 ||
365 (r = kex_send_newkeys(ssh)) != 0)
366 goto out;
367 /* retain copy of hostkey used at initial KEX */
368 if (kex->initial_hostkey == NULL &&
369 (r = sshkey_from_private(server_host_public,
370 &kex->initial_hostkey)) != 0)
371 goto out;
372 /* success */
373 out:
374 explicit_bzero(hash, sizeof(hash));
375 sshbuf_free(server_host_key_blob);
376 free(signature);
377 sshbuf_free(shared_secret);
378 sshbuf_free(client_pubkey);
379 sshbuf_free(server_pubkey);
380 return r;
381 }
382