1 /*        $NetBSD: kexgen.c,v 1.8 2024/09/24 21:32:18 christos Exp $  */
2 /* $OpenBSD: kexgen.c,v 1.10 2024/09/09 02:39:57 djm Exp $ */
3 
4 /*
5  * Copyright (c) 2019 Markus Friedl.  All rights reserved.
6  *
7  * Redistribution and use in source and binary forms, with or without
8  * modification, are permitted provided that the following conditions
9  * are met:
10  * 1. Redistributions of source code must retain the above copyright
11  *    notice, this list of conditions and the following disclaimer.
12  * 2. Redistributions in binary form must reproduce the above copyright
13  *    notice, this list of conditions and the following disclaimer in the
14  *    documentation and/or other materials provided with the distribution.
15  *
16  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
17  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
18  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
19  * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
20  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
21  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
22  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
23  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
24  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
25  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
26  */
27 #include "includes.h"
28 __RCSID("$NetBSD");
29 
30 #include <sys/types.h>
31 
32 #include <stdio.h>
33 #include <string.h>
34 #include <signal.h>
35 
36 #include "sshkey.h"
37 #include "kex.h"
38 #include "log.h"
39 #include "packet.h"
40 #include "ssh2.h"
41 #include "sshbuf.h"
42 #include "digest.h"
43 #include "ssherr.h"
44 
45 static int input_kex_gen_init(int, u_int32_t, struct ssh *);
46 static int input_kex_gen_reply(int type, u_int32_t seq, struct ssh *ssh);
47 
48 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)49 kex_gen_hash(
50     int hash_alg,
51     const struct sshbuf *client_version,
52     const struct sshbuf *server_version,
53     const struct sshbuf *client_kexinit,
54     const struct sshbuf *server_kexinit,
55     const struct sshbuf *server_host_key_blob,
56     const struct sshbuf *client_pub,
57     const struct sshbuf *server_pub,
58     const struct sshbuf *shared_secret,
59     u_char *hash, size_t *hashlen)
60 {
61           struct sshbuf *b;
62           int r;
63 
64           if (*hashlen < ssh_digest_bytes(hash_alg))
65                     return SSH_ERR_INVALID_ARGUMENT;
66           if ((b = sshbuf_new()) == NULL)
67                     return SSH_ERR_ALLOC_FAIL;
68           if ((r = sshbuf_put_stringb(b, client_version)) != 0 ||
69               (r = sshbuf_put_stringb(b, server_version)) != 0 ||
70               /* kexinit messages: fake header: len+SSH2_MSG_KEXINIT */
71               (r = sshbuf_put_u32(b, sshbuf_len(client_kexinit) + 1)) != 0 ||
72               (r = sshbuf_put_u8(b, SSH2_MSG_KEXINIT)) != 0 ||
73               (r = sshbuf_putb(b, client_kexinit)) != 0 ||
74               (r = sshbuf_put_u32(b, sshbuf_len(server_kexinit) + 1)) != 0 ||
75               (r = sshbuf_put_u8(b, SSH2_MSG_KEXINIT)) != 0 ||
76               (r = sshbuf_putb(b, server_kexinit)) != 0 ||
77               (r = sshbuf_put_stringb(b, server_host_key_blob)) != 0 ||
78               (r = sshbuf_put_stringb(b, client_pub)) != 0 ||
79               (r = sshbuf_put_stringb(b, server_pub)) != 0 ||
80               (r = sshbuf_putb(b, shared_secret)) != 0) {
81                     sshbuf_free(b);
82                     return r;
83           }
84 #ifdef DEBUG_KEX
85           sshbuf_dump(b, stderr);
86 #endif
87           if (ssh_digest_buffer(hash_alg, b, hash, *hashlen) != 0) {
88                     sshbuf_free(b);
89                     return SSH_ERR_LIBCRYPTO_ERROR;
90           }
91           sshbuf_free(b);
92           *hashlen = ssh_digest_bytes(hash_alg);
93 #ifdef DEBUG_KEX
94           dump_digest("hash", hash, *hashlen);
95 #endif
96           return 0;
97 }
98 
99 int
kex_gen_client(struct ssh * ssh)100 kex_gen_client(struct ssh *ssh)
101 {
102           struct kex *kex = ssh->kex;
103           int r;
104 
105           switch (kex->kex_type) {
106 #ifdef WITH_OPENSSL
107           case KEX_DH_GRP1_SHA1:
108           case KEX_DH_GRP14_SHA1:
109           case KEX_DH_GRP14_SHA256:
110           case KEX_DH_GRP16_SHA512:
111           case KEX_DH_GRP18_SHA512:
112                     r = kex_dh_keypair(kex);
113                     break;
114           case KEX_ECDH_SHA2:
115                     r = kex_ecdh_keypair(kex);
116                     break;
117 #endif /* WITH_OPENSSL */
118           case KEX_C25519_SHA256:
119                     r = kex_c25519_keypair(kex);
120                     break;
121           case KEX_KEM_SNTRUP761X25519_SHA512:
122                     r = kex_kem_sntrup761x25519_keypair(kex);
123                     break;
124           case KEX_KEM_MLKEM768X25519_SHA256:
125                     r = kex_kem_mlkem768x25519_keypair(kex);
126                     break;
127           default:
128                     r = SSH_ERR_INVALID_ARGUMENT;
129                     break;
130           }
131           if (r != 0)
132                     return r;
133           if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_ECDH_INIT)) != 0 ||
134               (r = sshpkt_put_stringb(ssh, kex->client_pub)) != 0 ||
135               (r = sshpkt_send(ssh)) != 0)
136                     return r;
137           debug("expecting SSH2_MSG_KEX_ECDH_REPLY");
138           ssh_dispatch_set(ssh, SSH2_MSG_KEX_ECDH_REPLY, &input_kex_gen_reply);
139           return 0;
140 }
141 
142 static int
input_kex_gen_reply(int type,u_int32_t seq,struct ssh * ssh)143 input_kex_gen_reply(int type, u_int32_t seq, struct ssh *ssh)
144 {
145           struct kex *kex = ssh->kex;
146           struct sshkey *server_host_key = NULL;
147           struct sshbuf *shared_secret = NULL;
148           struct sshbuf *server_blob = NULL;
149           struct sshbuf *tmp = NULL, *server_host_key_blob = NULL;
150           u_char *signature = NULL;
151           u_char hash[SSH_DIGEST_MAX_LENGTH];
152           size_t slen, hashlen;
153           int r;
154 
155           debug("SSH2_MSG_KEX_ECDH_REPLY received");
156           ssh_dispatch_set(ssh, SSH2_MSG_KEX_ECDH_REPLY, &kex_protocol_error);
157 
158           /* hostkey */
159           if ((r = sshpkt_getb_froms(ssh, &server_host_key_blob)) != 0)
160                     goto out;
161           /* sshkey_fromb() consumes its buffer, so make a copy */
162           if ((tmp = sshbuf_fromb(server_host_key_blob)) == NULL) {
163                     r = SSH_ERR_ALLOC_FAIL;
164                     goto out;
165           }
166           if ((r = sshkey_fromb(tmp, &server_host_key)) != 0)
167                     goto out;
168           if ((r = kex_verify_host_key(ssh, server_host_key)) != 0)
169                     goto out;
170 
171           /* Q_S, server public key */
172           /* signed H */
173           if ((r = sshpkt_getb_froms(ssh, &server_blob)) != 0 ||
174               (r = sshpkt_get_string(ssh, &signature, &slen)) != 0 ||
175               (r = sshpkt_get_end(ssh)) != 0)
176                     goto out;
177 
178           /* compute shared secret */
179           switch (kex->kex_type) {
180 #ifdef WITH_OPENSSL
181           case KEX_DH_GRP1_SHA1:
182           case KEX_DH_GRP14_SHA1:
183           case KEX_DH_GRP14_SHA256:
184           case KEX_DH_GRP16_SHA512:
185           case KEX_DH_GRP18_SHA512:
186                     r = kex_dh_dec(kex, server_blob, &shared_secret);
187                     break;
188           case KEX_ECDH_SHA2:
189                     r = kex_ecdh_dec(kex, server_blob, &shared_secret);
190                     break;
191 #endif /* WITH_OPENSSL */
192           case KEX_C25519_SHA256:
193                     r = kex_c25519_dec(kex, server_blob, &shared_secret);
194                     break;
195           case KEX_KEM_SNTRUP761X25519_SHA512:
196                     r = kex_kem_sntrup761x25519_dec(kex, server_blob,
197                         &shared_secret);
198                     break;
199           case KEX_KEM_MLKEM768X25519_SHA256:
200                     r = kex_kem_mlkem768x25519_dec(kex, server_blob,
201                         &shared_secret);
202                     break;
203           default:
204                     r = SSH_ERR_INVALID_ARGUMENT;
205                     break;
206           }
207           if (r !=0 )
208                     goto out;
209 
210           /* calc and verify H */
211           hashlen = sizeof(hash);
212           if ((r = kex_gen_hash(
213               kex->hash_alg,
214               kex->client_version,
215               kex->server_version,
216               kex->my,
217               kex->peer,
218               server_host_key_blob,
219               kex->client_pub,
220               server_blob,
221               shared_secret,
222               hash, &hashlen)) != 0)
223                     goto out;
224 
225           if ((r = sshkey_verify(server_host_key, signature, slen, hash, hashlen,
226               kex->hostkey_alg, ssh->compat, NULL)) != 0)
227                     goto out;
228 
229           if ((r = kex_derive_keys(ssh, hash, hashlen, shared_secret)) != 0 ||
230               (r = kex_send_newkeys(ssh)) != 0)
231                     goto out;
232 
233           /* save initial signature and hostkey */
234           if ((kex->flags & KEX_INITIAL) != 0) {
235                     if (kex->initial_hostkey != NULL || kex->initial_sig != NULL) {
236                               r = SSH_ERR_INTERNAL_ERROR;
237                               goto out;
238                     }
239                     if ((kex->initial_sig = sshbuf_new()) == NULL) {
240                               r = SSH_ERR_ALLOC_FAIL;
241                               goto out;
242                     }
243                     if ((r = sshbuf_put(kex->initial_sig, signature, slen)) != 0)
244                               goto out;
245                     kex->initial_hostkey = server_host_key;
246                     server_host_key = NULL;
247           }
248           /* success */
249 out:
250           explicit_bzero(hash, sizeof(hash));
251           explicit_bzero(kex->c25519_client_key, sizeof(kex->c25519_client_key));
252           explicit_bzero(kex->sntrup761_client_key,
253               sizeof(kex->sntrup761_client_key));
254           explicit_bzero(kex->mlkem768_client_key,
255               sizeof(kex->mlkem768_client_key));
256           sshbuf_free(server_host_key_blob);
257           free(signature);
258           sshbuf_free(tmp);
259           sshkey_free(server_host_key);
260           sshbuf_free(server_blob);
261           sshbuf_free(shared_secret);
262           sshbuf_free(kex->client_pub);
263           kex->client_pub = NULL;
264           return r;
265 }
266 
267 int
kex_gen_server(struct ssh * ssh)268 kex_gen_server(struct ssh *ssh)
269 {
270           debug("expecting SSH2_MSG_KEX_ECDH_INIT");
271           ssh_dispatch_set(ssh, SSH2_MSG_KEX_ECDH_INIT, &input_kex_gen_init);
272           return 0;
273 }
274 
275 static int
input_kex_gen_init(int type,u_int32_t seq,struct ssh * ssh)276 input_kex_gen_init(int type, u_int32_t seq, struct ssh *ssh)
277 {
278           struct kex *kex = ssh->kex;
279           struct sshkey *server_host_private, *server_host_public;
280           struct sshbuf *shared_secret = NULL;
281           struct sshbuf *server_pubkey = NULL;
282           struct sshbuf *client_pubkey = NULL;
283           struct sshbuf *server_host_key_blob = NULL;
284           u_char *signature = NULL, hash[SSH_DIGEST_MAX_LENGTH];
285           size_t slen, hashlen;
286           int r;
287 
288           debug("SSH2_MSG_KEX_ECDH_INIT received");
289           ssh_dispatch_set(ssh, SSH2_MSG_KEX_ECDH_INIT, &kex_protocol_error);
290 
291           if ((r = kex_load_hostkey(ssh, &server_host_private,
292               &server_host_public)) != 0)
293                     goto out;
294 
295           if ((r = sshpkt_getb_froms(ssh, &client_pubkey)) != 0 ||
296               (r = sshpkt_get_end(ssh)) != 0)
297                     goto out;
298 
299           /* compute shared secret */
300           switch (kex->kex_type) {
301 #ifdef WITH_OPENSSL
302           case KEX_DH_GRP1_SHA1:
303           case KEX_DH_GRP14_SHA1:
304           case KEX_DH_GRP14_SHA256:
305           case KEX_DH_GRP16_SHA512:
306           case KEX_DH_GRP18_SHA512:
307                     r = kex_dh_enc(kex, client_pubkey, &server_pubkey,
308                         &shared_secret);
309                     break;
310           case KEX_ECDH_SHA2:
311                     r = kex_ecdh_enc(kex, client_pubkey, &server_pubkey,
312                         &shared_secret);
313                     break;
314 #endif /* WITH_OPENSSL */
315           case KEX_C25519_SHA256:
316                     r = kex_c25519_enc(kex, client_pubkey, &server_pubkey,
317                         &shared_secret);
318                     break;
319           case KEX_KEM_SNTRUP761X25519_SHA512:
320                     r = kex_kem_sntrup761x25519_enc(kex, client_pubkey,
321                         &server_pubkey, &shared_secret);
322                     break;
323           case KEX_KEM_MLKEM768X25519_SHA256:
324                     r = kex_kem_mlkem768x25519_enc(kex, client_pubkey,
325                         &server_pubkey, &shared_secret);
326                     break;
327           default:
328                     r = SSH_ERR_INVALID_ARGUMENT;
329                     break;
330           }
331           if (r !=0 )
332                     goto out;
333 
334           /* calc H */
335           if ((server_host_key_blob = sshbuf_new()) == NULL) {
336                     r = SSH_ERR_ALLOC_FAIL;
337                     goto out;
338           }
339           if ((r = sshkey_putb(server_host_public, server_host_key_blob)) != 0)
340                     goto out;
341           hashlen = sizeof(hash);
342           if ((r = kex_gen_hash(
343               kex->hash_alg,
344               kex->client_version,
345               kex->server_version,
346               kex->peer,
347               kex->my,
348               server_host_key_blob,
349               client_pubkey,
350               server_pubkey,
351               shared_secret,
352               hash, &hashlen)) != 0)
353                     goto out;
354 
355           /* sign H */
356           if ((r = kex->sign(ssh, server_host_private, server_host_public,
357               &signature, &slen, hash, hashlen, kex->hostkey_alg)) != 0)
358                     goto out;
359 
360           /* send server hostkey, ECDH pubkey 'Q_S' and signed H */
361           if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_ECDH_REPLY)) != 0 ||
362               (r = sshpkt_put_stringb(ssh, server_host_key_blob)) != 0 ||
363               (r = sshpkt_put_stringb(ssh, server_pubkey)) != 0 ||
364               (r = sshpkt_put_string(ssh, signature, slen)) != 0 ||
365               (r = sshpkt_send(ssh)) != 0)
366                     goto out;
367 
368           if ((r = kex_derive_keys(ssh, hash, hashlen, shared_secret)) != 0 ||
369               (r = kex_send_newkeys(ssh)) != 0)
370                     goto out;
371           /* retain copy of hostkey used at initial KEX */
372           if (kex->initial_hostkey == NULL &&
373               (r = sshkey_from_private(server_host_public,
374               &kex->initial_hostkey)) != 0)
375                     goto out;
376           /* success */
377 out:
378           explicit_bzero(hash, sizeof(hash));
379           sshbuf_free(server_host_key_blob);
380           free(signature);
381           sshbuf_free(shared_secret);
382           sshbuf_free(client_pubkey);
383           sshbuf_free(server_pubkey);
384           return r;
385 }
386