1 /* $OpenBSD: kex.c,v 1.181 2023/08/28 03:28:43 djm Exp $ */
3 * Copyright (c) 2000, 2001 Markus Friedl. All rights reserved.
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
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.
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.
28 #include <sys/types.h>
41 #include <openssl/crypto.h>
42 #include <openssl/dh.h>
60 #include "myproposal.h"
68 static int kex_choose_conf(struct ssh *);
69 static int kex_input_newkeys(int, u_int32_t, struct ssh *);
71 static const char * const proposal_names[PROPOSAL_MAX] = {
73 "host key algorithms",
90 static const struct kexalg kexalgs[] = {
92 { KEX_DH1, KEX_DH_GRP1_SHA1, 0, SSH_DIGEST_SHA1 },
93 { KEX_DH14_SHA1, KEX_DH_GRP14_SHA1, 0, SSH_DIGEST_SHA1 },
94 { KEX_DH14_SHA256, KEX_DH_GRP14_SHA256, 0, SSH_DIGEST_SHA256 },
95 { KEX_DH16_SHA512, KEX_DH_GRP16_SHA512, 0, SSH_DIGEST_SHA512 },
96 { KEX_DH18_SHA512, KEX_DH_GRP18_SHA512, 0, SSH_DIGEST_SHA512 },
97 { KEX_DHGEX_SHA1, KEX_DH_GEX_SHA1, 0, SSH_DIGEST_SHA1 },
98 #ifdef HAVE_EVP_SHA256
99 { KEX_DHGEX_SHA256, KEX_DH_GEX_SHA256, 0, SSH_DIGEST_SHA256 },
100 #endif /* HAVE_EVP_SHA256 */
101 #ifdef OPENSSL_HAS_ECC
102 { KEX_ECDH_SHA2_NISTP256, KEX_ECDH_SHA2,
103 NID_X9_62_prime256v1, SSH_DIGEST_SHA256 },
104 { KEX_ECDH_SHA2_NISTP384, KEX_ECDH_SHA2, NID_secp384r1,
106 # ifdef OPENSSL_HAS_NISTP521
107 { KEX_ECDH_SHA2_NISTP521, KEX_ECDH_SHA2, NID_secp521r1,
109 # endif /* OPENSSL_HAS_NISTP521 */
110 #endif /* OPENSSL_HAS_ECC */
111 #endif /* WITH_OPENSSL */
112 #if defined(HAVE_EVP_SHA256) || !defined(WITH_OPENSSL)
113 { KEX_CURVE25519_SHA256, KEX_C25519_SHA256, 0, SSH_DIGEST_SHA256 },
114 { KEX_CURVE25519_SHA256_OLD, KEX_C25519_SHA256, 0, SSH_DIGEST_SHA256 },
115 #ifdef USE_SNTRUP761X25519
116 { KEX_SNTRUP761X25519_SHA512, KEX_KEM_SNTRUP761X25519_SHA512, 0,
119 #endif /* HAVE_EVP_SHA256 || !WITH_OPENSSL */
124 kex_alg_list(char sep)
126 char *ret = NULL, *tmp;
127 size_t nlen, rlen = 0;
128 const struct kexalg *k;
130 for (k = kexalgs; k->name != NULL; k++) {
133 nlen = strlen(k->name);
134 if ((tmp = realloc(ret, rlen + nlen + 2)) == NULL) {
139 memcpy(ret + rlen, k->name, nlen + 1);
145 static const struct kexalg *
146 kex_alg_by_name(const char *name)
148 const struct kexalg *k;
150 for (k = kexalgs; k->name != NULL; k++) {
151 if (strcmp(k->name, name) == 0)
157 /* Validate KEX method name list */
159 kex_names_valid(const char *names)
163 if (names == NULL || strcmp(names, "") == 0)
165 if ((s = cp = strdup(names)) == NULL)
167 for ((p = strsep(&cp, ",")); p && *p != '\0';
168 (p = strsep(&cp, ","))) {
169 if (kex_alg_by_name(p) == NULL) {
170 error("Unsupported KEX algorithm \"%.100s\"", p);
175 debug3("kex names ok: [%s]", names);
181 * Concatenate algorithm names, avoiding duplicates in the process.
182 * Caller must free returned string.
185 kex_names_cat(const char *a, const char *b)
187 char *ret = NULL, *tmp = NULL, *cp, *p, *m;
190 if (a == NULL || *a == '\0')
192 if (b == NULL || *b == '\0')
194 if (strlen(b) > 1024*1024)
196 len = strlen(a) + strlen(b) + 2;
197 if ((tmp = cp = strdup(b)) == NULL ||
198 (ret = calloc(1, len)) == NULL) {
202 strlcpy(ret, a, len);
203 for ((p = strsep(&cp, ",")); p && *p != '\0'; (p = strsep(&cp, ","))) {
204 if ((m = match_list(ret, p, NULL)) != NULL) {
206 continue; /* Algorithm already present */
208 if (strlcat(ret, ",", len) >= len ||
209 strlcat(ret, p, len) >= len) {
212 return NULL; /* Shouldn't happen */
220 * Assemble a list of algorithms from a default list and a string from a
221 * configuration file. The user-provided string may begin with '+' to
222 * indicate that it should be appended to the default, '-' that the
223 * specified names should be removed, or '^' that they should be placed
227 kex_assemble_names(char **listp, const char *def, const char *all)
229 char *cp, *tmp, *patterns;
230 char *list = NULL, *ret = NULL, *matching = NULL, *opatterns = NULL;
231 int r = SSH_ERR_INTERNAL_ERROR;
233 if (listp == NULL || def == NULL || all == NULL)
234 return SSH_ERR_INVALID_ARGUMENT;
236 if (*listp == NULL || **listp == '\0') {
237 if ((*listp = strdup(def)) == NULL)
238 return SSH_ERR_ALLOC_FAIL;
245 /* Append names to default list */
246 if ((tmp = kex_names_cat(def, list + 1)) == NULL) {
247 r = SSH_ERR_ALLOC_FAIL;
252 } else if (*list == '-') {
253 /* Remove names from default list */
254 if ((*listp = match_filter_denylist(def, list + 1)) == NULL) {
255 r = SSH_ERR_ALLOC_FAIL;
259 /* filtering has already been done */
261 } else if (*list == '^') {
262 /* Place names at head of default list */
263 if ((tmp = kex_names_cat(list + 1, def)) == NULL) {
264 r = SSH_ERR_ALLOC_FAIL;
270 /* Explicit list, overrides default - just use "list" as is */
274 * The supplied names may be a pattern-list. For the -list case,
275 * the patterns are applied above. For the +list and explicit list
276 * cases we need to do it now.
279 if ((patterns = opatterns = strdup(list)) == NULL) {
280 r = SSH_ERR_ALLOC_FAIL;
283 /* Apply positive (i.e. non-negated) patterns from the list */
284 while ((cp = strsep(&patterns, ",")) != NULL) {
286 /* negated matches are not supported here */
287 r = SSH_ERR_INVALID_ARGUMENT;
291 if ((matching = match_filter_allowlist(all, cp)) == NULL) {
292 r = SSH_ERR_ALLOC_FAIL;
295 if ((tmp = kex_names_cat(ret, matching)) == NULL) {
296 r = SSH_ERR_ALLOC_FAIL;
302 if (ret == NULL || *ret == '\0') {
303 /* An empty name-list is an error */
304 /* XXX better error code? */
305 r = SSH_ERR_INVALID_ARGUMENT;
323 * Fill out a proposal array with dynamically allocated values, which may
324 * be modified as required for compatibility reasons.
325 * Any of the options may be NULL, in which case the default is used.
326 * Array contents must be freed by calling kex_proposal_free_entries.
329 kex_proposal_populate_entries(struct ssh *ssh, char *prop[PROPOSAL_MAX],
330 const char *kexalgos, const char *ciphers, const char *macs,
331 const char *comp, const char *hkalgs)
333 const char *defpropserver[PROPOSAL_MAX] = { KEX_SERVER };
334 const char *defpropclient[PROPOSAL_MAX] = { KEX_CLIENT };
335 const char **defprop = ssh->kex->server ? defpropserver : defpropclient;
339 fatal_f("proposal missing");
341 for (i = 0; i < PROPOSAL_MAX; i++) {
343 case PROPOSAL_KEX_ALGS:
344 prop[i] = compat_kex_proposal(ssh,
345 kexalgos ? kexalgos : defprop[i]);
347 case PROPOSAL_ENC_ALGS_CTOS:
348 case PROPOSAL_ENC_ALGS_STOC:
349 prop[i] = xstrdup(ciphers ? ciphers : defprop[i]);
351 case PROPOSAL_MAC_ALGS_CTOS:
352 case PROPOSAL_MAC_ALGS_STOC:
353 prop[i] = xstrdup(macs ? macs : defprop[i]);
355 case PROPOSAL_COMP_ALGS_CTOS:
356 case PROPOSAL_COMP_ALGS_STOC:
357 prop[i] = xstrdup(comp ? comp : defprop[i]);
359 case PROPOSAL_SERVER_HOST_KEY_ALGS:
360 prop[i] = xstrdup(hkalgs ? hkalgs : defprop[i]);
363 prop[i] = xstrdup(defprop[i]);
369 kex_proposal_free_entries(char *prop[PROPOSAL_MAX])
373 for (i = 0; i < PROPOSAL_MAX; i++)
377 /* put algorithm proposal into buffer */
379 kex_prop2buf(struct sshbuf *b, char *proposal[PROPOSAL_MAX])
387 * add a dummy cookie, the cookie will be overwritten by
388 * kex_send_kexinit(), each time a kexinit is set
390 for (i = 0; i < KEX_COOKIE_LEN; i++) {
391 if ((r = sshbuf_put_u8(b, 0)) != 0)
394 for (i = 0; i < PROPOSAL_MAX; i++) {
395 if ((r = sshbuf_put_cstring(b, proposal[i])) != 0)
398 if ((r = sshbuf_put_u8(b, 0)) != 0 || /* first_kex_packet_follows */
399 (r = sshbuf_put_u32(b, 0)) != 0) /* uint32 reserved */
404 /* parse buffer and return algorithm proposal */
406 kex_buf2prop(struct sshbuf *raw, int *first_kex_follows, char ***propp)
408 struct sshbuf *b = NULL;
411 char **proposal = NULL;
415 if ((proposal = calloc(PROPOSAL_MAX, sizeof(char *))) == NULL)
416 return SSH_ERR_ALLOC_FAIL;
417 if ((b = sshbuf_fromb(raw)) == NULL) {
418 r = SSH_ERR_ALLOC_FAIL;
421 if ((r = sshbuf_consume(b, KEX_COOKIE_LEN)) != 0) { /* skip cookie */
422 error_fr(r, "consume cookie");
425 /* extract kex init proposal strings */
426 for (i = 0; i < PROPOSAL_MAX; i++) {
427 if ((r = sshbuf_get_cstring(b, &(proposal[i]), NULL)) != 0) {
428 error_fr(r, "parse proposal %u", i);
431 debug2("%s: %s", proposal_names[i], proposal[i]);
433 /* first kex follows / reserved */
434 if ((r = sshbuf_get_u8(b, &v)) != 0 || /* first_kex_follows */
435 (r = sshbuf_get_u32(b, &i)) != 0) { /* reserved */
436 error_fr(r, "parse");
439 if (first_kex_follows != NULL)
440 *first_kex_follows = v;
441 debug2("first_kex_follows %d ", v);
442 debug2("reserved %u ", i);
446 if (r != 0 && proposal != NULL)
447 kex_prop_free(proposal);
453 kex_prop_free(char **proposal)
457 if (proposal == NULL)
459 for (i = 0; i < PROPOSAL_MAX; i++)
465 kex_protocol_error(int type, u_int32_t seq, struct ssh *ssh)
469 error("kex protocol error: type %d seq %u", type, seq);
470 if ((r = sshpkt_start(ssh, SSH2_MSG_UNIMPLEMENTED)) != 0 ||
471 (r = sshpkt_put_u32(ssh, seq)) != 0 ||
472 (r = sshpkt_send(ssh)) != 0)
478 kex_reset_dispatch(struct ssh *ssh)
480 ssh_dispatch_range(ssh, SSH2_MSG_TRANSPORT_MIN,
481 SSH2_MSG_TRANSPORT_MAX, &kex_protocol_error);
485 kex_send_ext_info(struct ssh *ssh)
490 debug("Sending SSH2_MSG_EXT_INFO");
491 if ((algs = sshkey_alg_list(0, 1, 1, ',')) == NULL)
492 return SSH_ERR_ALLOC_FAIL;
493 /* XXX filter algs list by allowed pubkey/hostbased types */
494 if ((r = sshpkt_start(ssh, SSH2_MSG_EXT_INFO)) != 0 ||
495 (r = sshpkt_put_u32(ssh, 3)) != 0 ||
496 (r = sshpkt_put_cstring(ssh, "server-sig-algs")) != 0 ||
497 (r = sshpkt_put_cstring(ssh, algs)) != 0 ||
498 (r = sshpkt_put_cstring(ssh,
499 "publickey-hostbound@openssh.com")) != 0 ||
500 (r = sshpkt_put_cstring(ssh, "0")) != 0 ||
501 (r = sshpkt_put_cstring(ssh, "ping@openssh.com")) != 0 ||
502 (r = sshpkt_put_cstring(ssh, "0")) != 0 ||
503 (r = sshpkt_send(ssh)) != 0) {
504 error_fr(r, "compose");
515 kex_send_newkeys(struct ssh *ssh)
519 kex_reset_dispatch(ssh);
520 if ((r = sshpkt_start(ssh, SSH2_MSG_NEWKEYS)) != 0 ||
521 (r = sshpkt_send(ssh)) != 0)
523 debug("SSH2_MSG_NEWKEYS sent");
524 ssh_dispatch_set(ssh, SSH2_MSG_NEWKEYS, &kex_input_newkeys);
525 if (ssh->kex->ext_info_c && (ssh->kex->flags & KEX_INITIAL) != 0)
526 if ((r = kex_send_ext_info(ssh)) != 0)
528 debug("expecting SSH2_MSG_NEWKEYS");
532 /* Check whether an ext_info value contains the expected version string */
534 kex_ext_info_check_ver(struct kex *kex, const char *name,
535 const u_char *val, size_t len, const char *want_ver, u_int flag)
537 if (memchr(val, '\0', len) != NULL) {
538 error("SSH2_MSG_EXT_INFO: %s value contains nul byte", name);
539 return SSH_ERR_INVALID_FORMAT;
541 debug_f("%s=<%s>", name, val);
542 if (strcmp(val, want_ver) == 0)
545 debug_f("unsupported version of %s extension", name);
550 kex_input_ext_info(int type, u_int32_t seq, struct ssh *ssh)
552 struct kex *kex = ssh->kex;
559 debug("SSH2_MSG_EXT_INFO received");
560 ssh_dispatch_set(ssh, SSH2_MSG_EXT_INFO, &kex_protocol_error);
561 if ((r = sshpkt_get_u32(ssh, &ninfo)) != 0)
564 error("SSH2_MSG_EXT_INFO with too many entries, expected "
565 "<=1024, received %u", ninfo);
566 return SSH_ERR_INVALID_FORMAT;
568 for (i = 0; i < ninfo; i++) {
569 if ((r = sshpkt_get_cstring(ssh, &name, NULL)) != 0)
571 if ((r = sshpkt_get_string(ssh, &val, &vlen)) != 0) {
575 if (strcmp(name, "server-sig-algs") == 0) {
576 /* Ensure no \0 lurking in value */
577 if (memchr(val, '\0', vlen) != NULL) {
578 error_f("nul byte in %s", name);
581 return SSH_ERR_INVALID_FORMAT;
583 debug_f("%s=<%s>", name, val);
584 kex->server_sig_algs = val;
586 } else if (strcmp(name,
587 "publickey-hostbound@openssh.com") == 0) {
588 if ((r = kex_ext_info_check_ver(kex, name, val, vlen,
589 "0", KEX_HAS_PUBKEY_HOSTBOUND)) != 0) {
594 } else if (strcmp(name, "ping@openssh.com") == 0) {
595 if ((r = kex_ext_info_check_ver(kex, name, val, vlen,
596 "0", KEX_HAS_PING)) != 0) {
602 debug_f("%s (unrecognised)", name);
606 return sshpkt_get_end(ssh);
610 kex_input_newkeys(int type, u_int32_t seq, struct ssh *ssh)
612 struct kex *kex = ssh->kex;
615 debug("SSH2_MSG_NEWKEYS received");
616 ssh_dispatch_set(ssh, SSH2_MSG_NEWKEYS, &kex_protocol_error);
617 ssh_dispatch_set(ssh, SSH2_MSG_KEXINIT, &kex_input_kexinit);
618 if ((r = sshpkt_get_end(ssh)) != 0)
620 if ((r = ssh_set_newkeys(ssh, MODE_IN)) != 0)
623 kex->flags &= ~KEX_INITIAL;
624 sshbuf_reset(kex->peer);
625 /* sshbuf_reset(kex->my); */
626 kex->flags &= ~KEX_INIT_SENT;
633 kex_send_kexinit(struct ssh *ssh)
636 struct kex *kex = ssh->kex;
641 return SSH_ERR_INTERNAL_ERROR;
643 if (kex->flags & KEX_INIT_SENT)
647 /* generate a random cookie */
648 if (sshbuf_len(kex->my) < KEX_COOKIE_LEN) {
649 error_f("bad kex length: %zu < %d",
650 sshbuf_len(kex->my), KEX_COOKIE_LEN);
651 return SSH_ERR_INVALID_FORMAT;
653 if ((cookie = sshbuf_mutable_ptr(kex->my)) == NULL) {
654 error_f("buffer error");
655 return SSH_ERR_INTERNAL_ERROR;
657 arc4random_buf(cookie, KEX_COOKIE_LEN);
659 if ((r = sshpkt_start(ssh, SSH2_MSG_KEXINIT)) != 0 ||
660 (r = sshpkt_putb(ssh, kex->my)) != 0 ||
661 (r = sshpkt_send(ssh)) != 0) {
662 error_fr(r, "compose reply");
665 debug("SSH2_MSG_KEXINIT sent");
666 kex->flags |= KEX_INIT_SENT;
671 kex_input_kexinit(int type, u_int32_t seq, struct ssh *ssh)
673 struct kex *kex = ssh->kex;
679 debug("SSH2_MSG_KEXINIT received");
682 return SSH_ERR_INTERNAL_ERROR;
684 ssh_dispatch_set(ssh, SSH2_MSG_KEXINIT, NULL);
685 ptr = sshpkt_ptr(ssh, &dlen);
686 if ((r = sshbuf_put(kex->peer, ptr, dlen)) != 0)
690 for (i = 0; i < KEX_COOKIE_LEN; i++) {
691 if ((r = sshpkt_get_u8(ssh, NULL)) != 0) {
692 error_fr(r, "discard cookie");
696 for (i = 0; i < PROPOSAL_MAX; i++) {
697 if ((r = sshpkt_get_string(ssh, NULL, NULL)) != 0) {
698 error_fr(r, "discard proposal");
703 * XXX RFC4253 sec 7: "each side MAY guess" - currently no supported
704 * KEX method has the server move first, but a server might be using
705 * a custom method or one that we otherwise don't support. We should
706 * be prepared to remember first_kex_follows here so we can eat a
708 * XXX2 - RFC4253 is kind of ambiguous on what first_kex_follows means
709 * for cases where the server *doesn't* go first. I guess we should
710 * ignore it when it is set for these cases, which is what we do now.
712 if ((r = sshpkt_get_u8(ssh, NULL)) != 0 || /* first_kex_follows */
713 (r = sshpkt_get_u32(ssh, NULL)) != 0 || /* reserved */
714 (r = sshpkt_get_end(ssh)) != 0)
717 if (!(kex->flags & KEX_INIT_SENT))
718 if ((r = kex_send_kexinit(ssh)) != 0)
720 if ((r = kex_choose_conf(ssh)) != 0)
723 if (kex->kex_type < KEX_MAX && kex->kex[kex->kex_type] != NULL)
724 return (kex->kex[kex->kex_type])(ssh);
726 error_f("unknown kex type %u", kex->kex_type);
727 return SSH_ERR_INTERNAL_ERROR;
735 if ((kex = calloc(1, sizeof(*kex))) == NULL ||
736 (kex->peer = sshbuf_new()) == NULL ||
737 (kex->my = sshbuf_new()) == NULL ||
738 (kex->client_version = sshbuf_new()) == NULL ||
739 (kex->server_version = sshbuf_new()) == NULL ||
740 (kex->session_id = sshbuf_new()) == NULL) {
748 kex_free_newkeys(struct newkeys *newkeys)
752 if (newkeys->enc.key) {
753 explicit_bzero(newkeys->enc.key, newkeys->enc.key_len);
754 free(newkeys->enc.key);
755 newkeys->enc.key = NULL;
757 if (newkeys->enc.iv) {
758 explicit_bzero(newkeys->enc.iv, newkeys->enc.iv_len);
759 free(newkeys->enc.iv);
760 newkeys->enc.iv = NULL;
762 free(newkeys->enc.name);
763 explicit_bzero(&newkeys->enc, sizeof(newkeys->enc));
764 free(newkeys->comp.name);
765 explicit_bzero(&newkeys->comp, sizeof(newkeys->comp));
766 mac_clear(&newkeys->mac);
767 if (newkeys->mac.key) {
768 explicit_bzero(newkeys->mac.key, newkeys->mac.key_len);
769 free(newkeys->mac.key);
770 newkeys->mac.key = NULL;
772 free(newkeys->mac.name);
773 explicit_bzero(&newkeys->mac, sizeof(newkeys->mac));
774 freezero(newkeys, sizeof(*newkeys));
778 kex_free(struct kex *kex)
787 #ifdef OPENSSL_HAS_ECC
788 EC_KEY_free(kex->ec_client_key);
789 #endif /* OPENSSL_HAS_ECC */
790 #endif /* WITH_OPENSSL */
791 for (mode = 0; mode < MODE_MAX; mode++) {
792 kex_free_newkeys(kex->newkeys[mode]);
793 kex->newkeys[mode] = NULL;
795 sshbuf_free(kex->peer);
796 sshbuf_free(kex->my);
797 sshbuf_free(kex->client_version);
798 sshbuf_free(kex->server_version);
799 sshbuf_free(kex->client_pub);
800 sshbuf_free(kex->session_id);
801 sshbuf_free(kex->initial_sig);
802 sshkey_free(kex->initial_hostkey);
803 free(kex->failed_choice);
804 free(kex->hostkey_alg);
810 kex_ready(struct ssh *ssh, char *proposal[PROPOSAL_MAX])
814 if ((r = kex_prop2buf(ssh->kex->my, proposal)) != 0)
816 ssh->kex->flags = KEX_INITIAL;
817 kex_reset_dispatch(ssh);
818 ssh_dispatch_set(ssh, SSH2_MSG_KEXINIT, &kex_input_kexinit);
823 kex_setup(struct ssh *ssh, char *proposal[PROPOSAL_MAX])
827 if ((r = kex_ready(ssh, proposal)) != 0)
829 if ((r = kex_send_kexinit(ssh)) != 0) { /* we start */
838 * Request key re-exchange, returns 0 on success or a ssherr.h error
839 * code otherwise. Must not be called if KEX is incomplete or in-progress.
842 kex_start_rekex(struct ssh *ssh)
844 if (ssh->kex == NULL) {
846 return SSH_ERR_INTERNAL_ERROR;
848 if (ssh->kex->done == 0) {
849 error_f("requested twice");
850 return SSH_ERR_INTERNAL_ERROR;
853 return kex_send_kexinit(ssh);
857 choose_enc(struct sshenc *enc, char *client, char *server)
859 char *name = match_list(client, server, NULL);
862 return SSH_ERR_NO_CIPHER_ALG_MATCH;
863 if ((enc->cipher = cipher_by_name(name)) == NULL) {
864 error_f("unsupported cipher %s", name);
866 return SSH_ERR_INTERNAL_ERROR;
871 enc->iv_len = cipher_ivlen(enc->cipher);
873 enc->key_len = cipher_keylen(enc->cipher);
874 enc->block_size = cipher_blocksize(enc->cipher);
879 choose_mac(struct ssh *ssh, struct sshmac *mac, char *client, char *server)
881 char *name = match_list(client, server, NULL);
884 return SSH_ERR_NO_MAC_ALG_MATCH;
885 if (mac_setup(mac, name) < 0) {
886 error_f("unsupported MAC %s", name);
888 return SSH_ERR_INTERNAL_ERROR;
897 choose_comp(struct sshcomp *comp, char *client, char *server)
899 char *name = match_list(client, server, NULL);
902 return SSH_ERR_NO_COMPRESS_ALG_MATCH;
904 if (strcmp(name, "zlib@openssh.com") == 0) {
905 comp->type = COMP_DELAYED;
906 } else if (strcmp(name, "zlib") == 0) {
907 comp->type = COMP_ZLIB;
909 #endif /* WITH_ZLIB */
910 if (strcmp(name, "none") == 0) {
911 comp->type = COMP_NONE;
913 error_f("unsupported compression scheme %s", name);
915 return SSH_ERR_INTERNAL_ERROR;
922 choose_kex(struct kex *k, char *client, char *server)
924 const struct kexalg *kexalg;
926 k->name = match_list(client, server, NULL);
928 debug("kex: algorithm: %s", k->name ? k->name : "(no match)");
930 return SSH_ERR_NO_KEX_ALG_MATCH;
931 if ((kexalg = kex_alg_by_name(k->name)) == NULL) {
932 error_f("unsupported KEX method %s", k->name);
933 return SSH_ERR_INTERNAL_ERROR;
935 k->kex_type = kexalg->type;
936 k->hash_alg = kexalg->hash_alg;
937 k->ec_nid = kexalg->ec_nid;
942 choose_hostkeyalg(struct kex *k, char *client, char *server)
944 free(k->hostkey_alg);
945 k->hostkey_alg = match_list(client, server, NULL);
947 debug("kex: host key algorithm: %s",
948 k->hostkey_alg ? k->hostkey_alg : "(no match)");
949 if (k->hostkey_alg == NULL)
950 return SSH_ERR_NO_HOSTKEY_ALG_MATCH;
951 k->hostkey_type = sshkey_type_from_name(k->hostkey_alg);
952 if (k->hostkey_type == KEY_UNSPEC) {
953 error_f("unsupported hostkey algorithm %s", k->hostkey_alg);
954 return SSH_ERR_INTERNAL_ERROR;
956 k->hostkey_nid = sshkey_ecdsa_nid_from_name(k->hostkey_alg);
961 proposals_match(char *my[PROPOSAL_MAX], char *peer[PROPOSAL_MAX])
963 static int check[] = {
964 PROPOSAL_KEX_ALGS, PROPOSAL_SERVER_HOST_KEY_ALGS, -1
969 for (idx = &check[0]; *idx != -1; idx++) {
970 if ((p = strchr(my[*idx], ',')) != NULL)
972 if ((p = strchr(peer[*idx], ',')) != NULL)
974 if (strcmp(my[*idx], peer[*idx]) != 0) {
975 debug2("proposal mismatch: my %s peer %s",
976 my[*idx], peer[*idx]);
980 debug2("proposals match");
984 /* returns non-zero if proposal contains any algorithm from algs */
986 has_any_alg(const char *proposal, const char *algs)
990 if ((cp = match_list(proposal, algs, NULL)) == NULL)
997 kex_choose_conf(struct ssh *ssh)
999 struct kex *kex = ssh->kex;
1000 struct newkeys *newkeys;
1001 char **my = NULL, **peer = NULL;
1002 char **cprop, **sprop;
1003 int nenc, nmac, ncomp;
1004 u_int mode, ctos, need, dh_need, authlen;
1005 int r, first_kex_follows;
1007 debug2("local %s KEXINIT proposal", kex->server ? "server" : "client");
1008 if ((r = kex_buf2prop(kex->my, NULL, &my)) != 0)
1010 debug2("peer %s KEXINIT proposal", kex->server ? "client" : "server");
1011 if ((r = kex_buf2prop(kex->peer, &first_kex_follows, &peer)) != 0)
1022 /* Check whether client supports ext_info_c */
1023 if (kex->server && (kex->flags & KEX_INITIAL)) {
1026 ext = match_list("ext-info-c", peer[PROPOSAL_KEX_ALGS], NULL);
1027 kex->ext_info_c = (ext != NULL);
1031 /* Check whether client supports rsa-sha2 algorithms */
1032 if (kex->server && (kex->flags & KEX_INITIAL)) {
1033 if (has_any_alg(peer[PROPOSAL_SERVER_HOST_KEY_ALGS],
1034 "rsa-sha2-256,rsa-sha2-256-cert-v01@openssh.com"))
1035 kex->flags |= KEX_RSA_SHA2_256_SUPPORTED;
1036 if (has_any_alg(peer[PROPOSAL_SERVER_HOST_KEY_ALGS],
1037 "rsa-sha2-512,rsa-sha2-512-cert-v01@openssh.com"))
1038 kex->flags |= KEX_RSA_SHA2_512_SUPPORTED;
1041 /* Algorithm Negotiation */
1042 if ((r = choose_kex(kex, cprop[PROPOSAL_KEX_ALGS],
1043 sprop[PROPOSAL_KEX_ALGS])) != 0) {
1044 kex->failed_choice = peer[PROPOSAL_KEX_ALGS];
1045 peer[PROPOSAL_KEX_ALGS] = NULL;
1048 if ((r = choose_hostkeyalg(kex, cprop[PROPOSAL_SERVER_HOST_KEY_ALGS],
1049 sprop[PROPOSAL_SERVER_HOST_KEY_ALGS])) != 0) {
1050 kex->failed_choice = peer[PROPOSAL_SERVER_HOST_KEY_ALGS];
1051 peer[PROPOSAL_SERVER_HOST_KEY_ALGS] = NULL;
1054 for (mode = 0; mode < MODE_MAX; mode++) {
1055 if ((newkeys = calloc(1, sizeof(*newkeys))) == NULL) {
1056 r = SSH_ERR_ALLOC_FAIL;
1059 kex->newkeys[mode] = newkeys;
1060 ctos = (!kex->server && mode == MODE_OUT) ||
1061 (kex->server && mode == MODE_IN);
1062 nenc = ctos ? PROPOSAL_ENC_ALGS_CTOS : PROPOSAL_ENC_ALGS_STOC;
1063 nmac = ctos ? PROPOSAL_MAC_ALGS_CTOS : PROPOSAL_MAC_ALGS_STOC;
1064 ncomp = ctos ? PROPOSAL_COMP_ALGS_CTOS : PROPOSAL_COMP_ALGS_STOC;
1065 if ((r = choose_enc(&newkeys->enc, cprop[nenc],
1066 sprop[nenc])) != 0) {
1067 kex->failed_choice = peer[nenc];
1071 authlen = cipher_authlen(newkeys->enc.cipher);
1072 /* ignore mac for authenticated encryption */
1074 (r = choose_mac(ssh, &newkeys->mac, cprop[nmac],
1075 sprop[nmac])) != 0) {
1076 kex->failed_choice = peer[nmac];
1080 if ((r = choose_comp(&newkeys->comp, cprop[ncomp],
1081 sprop[ncomp])) != 0) {
1082 kex->failed_choice = peer[ncomp];
1086 debug("kex: %s cipher: %s MAC: %s compression: %s",
1087 ctos ? "client->server" : "server->client",
1089 authlen == 0 ? newkeys->mac.name : "<implicit>",
1090 newkeys->comp.name);
1093 for (mode = 0; mode < MODE_MAX; mode++) {
1094 newkeys = kex->newkeys[mode];
1095 need = MAXIMUM(need, newkeys->enc.key_len);
1096 need = MAXIMUM(need, newkeys->enc.block_size);
1097 need = MAXIMUM(need, newkeys->enc.iv_len);
1098 need = MAXIMUM(need, newkeys->mac.key_len);
1099 dh_need = MAXIMUM(dh_need, cipher_seclen(newkeys->enc.cipher));
1100 dh_need = MAXIMUM(dh_need, newkeys->enc.block_size);
1101 dh_need = MAXIMUM(dh_need, newkeys->enc.iv_len);
1102 dh_need = MAXIMUM(dh_need, newkeys->mac.key_len);
1104 /* XXX need runden? */
1105 kex->we_need = need;
1106 kex->dh_need = dh_need;
1108 /* ignore the next message if the proposals do not match */
1109 if (first_kex_follows && !proposals_match(my, peer))
1110 ssh->dispatch_skip_packets = 1;
1114 kex_prop_free(peer);
1119 derive_key(struct ssh *ssh, int id, u_int need, u_char *hash, u_int hashlen,
1120 const struct sshbuf *shared_secret, u_char **keyp)
1122 struct kex *kex = ssh->kex;
1123 struct ssh_digest_ctx *hashctx = NULL;
1130 if ((mdsz = ssh_digest_bytes(kex->hash_alg)) == 0)
1131 return SSH_ERR_INVALID_ARGUMENT;
1132 if ((digest = calloc(1, ROUNDUP(need, mdsz))) == NULL) {
1133 r = SSH_ERR_ALLOC_FAIL;
1137 /* K1 = HASH(K || H || "A" || session_id) */
1138 if ((hashctx = ssh_digest_start(kex->hash_alg)) == NULL ||
1139 ssh_digest_update_buffer(hashctx, shared_secret) != 0 ||
1140 ssh_digest_update(hashctx, hash, hashlen) != 0 ||
1141 ssh_digest_update(hashctx, &c, 1) != 0 ||
1142 ssh_digest_update_buffer(hashctx, kex->session_id) != 0 ||
1143 ssh_digest_final(hashctx, digest, mdsz) != 0) {
1144 r = SSH_ERR_LIBCRYPTO_ERROR;
1145 error_f("KEX hash failed");
1148 ssh_digest_free(hashctx);
1153 * Kn = HASH(K || H || K1 || K2 || ... || Kn-1)
1154 * Key = K1 || K2 || ... || Kn
1156 for (have = mdsz; need > have; have += mdsz) {
1157 if ((hashctx = ssh_digest_start(kex->hash_alg)) == NULL ||
1158 ssh_digest_update_buffer(hashctx, shared_secret) != 0 ||
1159 ssh_digest_update(hashctx, hash, hashlen) != 0 ||
1160 ssh_digest_update(hashctx, digest, have) != 0 ||
1161 ssh_digest_final(hashctx, digest + have, mdsz) != 0) {
1162 error_f("KDF failed");
1163 r = SSH_ERR_LIBCRYPTO_ERROR;
1166 ssh_digest_free(hashctx);
1170 fprintf(stderr, "key '%c'== ", c);
1171 dump_digest("key", digest, need);
1178 ssh_digest_free(hashctx);
1184 kex_derive_keys(struct ssh *ssh, u_char *hash, u_int hashlen,
1185 const struct sshbuf *shared_secret)
1187 struct kex *kex = ssh->kex;
1188 u_char *keys[NKEYS];
1189 u_int i, j, mode, ctos;
1192 /* save initial hash as session id */
1193 if ((kex->flags & KEX_INITIAL) != 0) {
1194 if (sshbuf_len(kex->session_id) != 0) {
1195 error_f("already have session ID at kex");
1196 return SSH_ERR_INTERNAL_ERROR;
1198 if ((r = sshbuf_put(kex->session_id, hash, hashlen)) != 0)
1200 } else if (sshbuf_len(kex->session_id) == 0) {
1201 error_f("no session ID in rekex");
1202 return SSH_ERR_INTERNAL_ERROR;
1204 for (i = 0; i < NKEYS; i++) {
1205 if ((r = derive_key(ssh, 'A'+i, kex->we_need, hash, hashlen,
1206 shared_secret, &keys[i])) != 0) {
1207 for (j = 0; j < i; j++)
1212 for (mode = 0; mode < MODE_MAX; mode++) {
1213 ctos = (!kex->server && mode == MODE_OUT) ||
1214 (kex->server && mode == MODE_IN);
1215 kex->newkeys[mode]->enc.iv = keys[ctos ? 0 : 1];
1216 kex->newkeys[mode]->enc.key = keys[ctos ? 2 : 3];
1217 kex->newkeys[mode]->mac.key = keys[ctos ? 4 : 5];
1223 kex_load_hostkey(struct ssh *ssh, struct sshkey **prvp, struct sshkey **pubp)
1225 struct kex *kex = ssh->kex;
1229 if (kex->load_host_public_key == NULL ||
1230 kex->load_host_private_key == NULL) {
1231 error_f("missing hostkey loader");
1232 return SSH_ERR_INVALID_ARGUMENT;
1234 *pubp = kex->load_host_public_key(kex->hostkey_type,
1235 kex->hostkey_nid, ssh);
1236 *prvp = kex->load_host_private_key(kex->hostkey_type,
1237 kex->hostkey_nid, ssh);
1239 return SSH_ERR_NO_HOSTKEY_LOADED;
1244 kex_verify_host_key(struct ssh *ssh, struct sshkey *server_host_key)
1246 struct kex *kex = ssh->kex;
1248 if (kex->verify_host_key == NULL) {
1249 error_f("missing hostkey verifier");
1250 return SSH_ERR_INVALID_ARGUMENT;
1252 if (server_host_key->type != kex->hostkey_type ||
1253 (kex->hostkey_type == KEY_ECDSA &&
1254 server_host_key->ecdsa_nid != kex->hostkey_nid))
1255 return SSH_ERR_KEY_TYPE_MISMATCH;
1256 if (kex->verify_host_key(server_host_key, ssh) == -1)
1257 return SSH_ERR_SIGNATURE_INVALID;
1261 #if defined(DEBUG_KEX) || defined(DEBUG_KEXDH) || defined(DEBUG_KEXECDH)
1263 dump_digest(const char *msg, const u_char *digest, int len)
1265 fprintf(stderr, "%s\n", msg);
1266 sshbuf_dump_data(digest, len, stderr);
1271 * Send a plaintext error message to the peer, suffixed by \r\n.
1272 * Only used during banner exchange, and there only for the server.
1275 send_error(struct ssh *ssh, char *msg)
1277 char *crnl = "\r\n";
1279 if (!ssh->kex->server)
1282 if (atomicio(vwrite, ssh_packet_get_connection_out(ssh),
1283 msg, strlen(msg)) != strlen(msg) ||
1284 atomicio(vwrite, ssh_packet_get_connection_out(ssh),
1285 crnl, strlen(crnl)) != strlen(crnl))
1286 error_f("write: %.100s", strerror(errno));
1290 * Sends our identification string and waits for the peer's. Will block for
1291 * up to timeout_ms (or indefinitely if timeout_ms <= 0).
1292 * Returns on 0 success or a ssherr.h code on failure.
1295 kex_exchange_identification(struct ssh *ssh, int timeout_ms,
1296 const char *version_addendum)
1298 int remote_major, remote_minor, mismatch, oerrno = 0;
1302 struct sshbuf *our_version = ssh->kex->server ?
1303 ssh->kex->server_version : ssh->kex->client_version;
1304 struct sshbuf *peer_version = ssh->kex->server ?
1305 ssh->kex->client_version : ssh->kex->server_version;
1306 char *our_version_string = NULL, *peer_version_string = NULL;
1307 char *cp, *remote_version = NULL;
1309 /* Prepare and send our banner */
1310 sshbuf_reset(our_version);
1311 if (version_addendum != NULL && *version_addendum == '\0')
1312 version_addendum = NULL;
1313 if ((r = sshbuf_putf(our_version, "SSH-%d.%d-%.100s%s%s\r\n",
1314 PROTOCOL_MAJOR_2, PROTOCOL_MINOR_2, SSH_VERSION,
1315 version_addendum == NULL ? "" : " ",
1316 version_addendum == NULL ? "" : version_addendum)) != 0) {
1318 error_fr(r, "sshbuf_putf");
1322 if (atomicio(vwrite, ssh_packet_get_connection_out(ssh),
1323 sshbuf_mutable_ptr(our_version),
1324 sshbuf_len(our_version)) != sshbuf_len(our_version)) {
1326 debug_f("write: %.100s", strerror(errno));
1327 r = SSH_ERR_SYSTEM_ERROR;
1330 if ((r = sshbuf_consume_end(our_version, 2)) != 0) { /* trim \r\n */
1332 error_fr(r, "sshbuf_consume_end");
1335 our_version_string = sshbuf_dup_string(our_version);
1336 if (our_version_string == NULL) {
1337 error_f("sshbuf_dup_string failed");
1338 r = SSH_ERR_ALLOC_FAIL;
1341 debug("Local version string %.100s", our_version_string);
1343 /* Read other side's version identification. */
1344 for (n = 0; ; n++) {
1345 if (n >= SSH_MAX_PRE_BANNER_LINES) {
1346 send_error(ssh, "No SSH identification string "
1348 error_f("No SSH version received in first %u lines "
1349 "from server", SSH_MAX_PRE_BANNER_LINES);
1350 r = SSH_ERR_INVALID_FORMAT;
1353 sshbuf_reset(peer_version);
1356 if (timeout_ms > 0) {
1357 r = waitrfd(ssh_packet_get_connection_in(ssh),
1359 if (r == -1 && errno == ETIMEDOUT) {
1360 send_error(ssh, "Timed out waiting "
1361 "for SSH identification string.");
1362 error("Connection timed out during "
1364 r = SSH_ERR_CONN_TIMEOUT;
1366 } else if (r == -1) {
1368 error_f("%s", strerror(errno));
1369 r = SSH_ERR_SYSTEM_ERROR;
1374 len = atomicio(read, ssh_packet_get_connection_in(ssh),
1376 if (len != 1 && errno == EPIPE) {
1377 verbose_f("Connection closed by remote host");
1378 r = SSH_ERR_CONN_CLOSED;
1380 } else if (len != 1) {
1382 error_f("read: %.100s", strerror(errno));
1383 r = SSH_ERR_SYSTEM_ERROR;
1392 if (c == '\0' || expect_nl) {
1393 verbose_f("banner line contains invalid "
1397 if ((r = sshbuf_put_u8(peer_version, c)) != 0) {
1399 error_fr(r, "sshbuf_put");
1402 if (sshbuf_len(peer_version) > SSH_MAX_BANNER_LEN) {
1403 verbose_f("banner line too long");
1407 /* Is this an actual protocol banner? */
1408 if (sshbuf_len(peer_version) > 4 &&
1409 memcmp(sshbuf_ptr(peer_version), "SSH-", 4) == 0)
1411 /* If not, then just log the line and continue */
1412 if ((cp = sshbuf_dup_string(peer_version)) == NULL) {
1413 error_f("sshbuf_dup_string failed");
1414 r = SSH_ERR_ALLOC_FAIL;
1417 /* Do not accept lines before the SSH ident from a client */
1418 if (ssh->kex->server) {
1419 verbose_f("client sent invalid protocol identifier "
1424 debug_f("banner line %zu: %s", n, cp);
1427 peer_version_string = sshbuf_dup_string(peer_version);
1428 if (peer_version_string == NULL)
1429 fatal_f("sshbuf_dup_string failed");
1430 /* XXX must be same size for sscanf */
1431 if ((remote_version = calloc(1, sshbuf_len(peer_version))) == NULL) {
1432 error_f("calloc failed");
1433 r = SSH_ERR_ALLOC_FAIL;
1438 * Check that the versions match. In future this might accept
1439 * several versions and set appropriate flags to handle them.
1441 if (sscanf(peer_version_string, "SSH-%d.%d-%[^\n]\n",
1442 &remote_major, &remote_minor, remote_version) != 3) {
1443 error("Bad remote protocol version identification: '%.100s'",
1444 peer_version_string);
1446 send_error(ssh, "Invalid SSH identification string.");
1447 r = SSH_ERR_INVALID_FORMAT;
1450 debug("Remote protocol version %d.%d, remote software version %.100s",
1451 remote_major, remote_minor, remote_version);
1452 compat_banner(ssh, remote_version);
1455 switch (remote_major) {
1459 if (remote_minor != 99)
1467 error("Protocol major versions differ: %d vs. %d",
1468 PROTOCOL_MAJOR_2, remote_major);
1469 send_error(ssh, "Protocol major versions differ.");
1470 r = SSH_ERR_NO_PROTOCOL_VERSION;
1474 if (ssh->kex->server && (ssh->compat & SSH_BUG_PROBE) != 0) {
1475 logit("probed from %s port %d with %s. Don't panic.",
1476 ssh_remote_ipaddr(ssh), ssh_remote_port(ssh),
1477 peer_version_string);
1478 r = SSH_ERR_CONN_CLOSED; /* XXX */
1481 if (ssh->kex->server && (ssh->compat & SSH_BUG_SCANNER) != 0) {
1482 logit("scanned from %s port %d with %s. Don't panic.",
1483 ssh_remote_ipaddr(ssh), ssh_remote_port(ssh),
1484 peer_version_string);
1485 r = SSH_ERR_CONN_CLOSED; /* XXX */
1491 free(our_version_string);
1492 free(peer_version_string);
1493 free(remote_version);
1494 if (r == SSH_ERR_SYSTEM_ERROR)