xref: /freebsd/crypto/openssh/kexgexs.c (revision 195ebc7e9e4b129de810833791a19dfb4349d6a9)
1 /* $OpenBSD: kexgexs.c,v 1.11 2009/01/01 21:17:36 djm Exp $ */
2 /*
3  * Copyright (c) 2000 Niels Provos.  All rights reserved.
4  * Copyright (c) 2001 Markus Friedl.  All rights reserved.
5  *
6  * Redistribution and use in source and binary forms, with or without
7  * modification, are permitted provided that the following conditions
8  * are met:
9  * 1. Redistributions of source code must retain the above copyright
10  *    notice, this list of conditions and the following disclaimer.
11  * 2. Redistributions in binary form must reproduce the above copyright
12  *    notice, this list of conditions and the following disclaimer in the
13  *    documentation and/or other materials provided with the distribution.
14  *
15  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
16  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
17  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
18  * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
19  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
20  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
21  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
22  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
23  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
24  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
25  */
26 
27 #include "includes.h"
28 
29 #include <sys/param.h>
30 
31 #include <stdarg.h>
32 #include <stdio.h>
33 #include <string.h>
34 #include <signal.h>
35 
36 #include "xmalloc.h"
37 #include "buffer.h"
38 #include "key.h"
39 #include "cipher.h"
40 #include "kex.h"
41 #include "log.h"
42 #include "packet.h"
43 #include "dh.h"
44 #include "ssh2.h"
45 #include "compat.h"
46 #ifdef GSSAPI
47 #include "ssh-gss.h"
48 #endif
49 #include "monitor_wrap.h"
50 
51 void
52 kexgex_server(Kex *kex)
53 {
54 	BIGNUM *shared_secret = NULL, *dh_client_pub = NULL;
55 	Key *server_host_key;
56 	DH *dh;
57 	u_char *kbuf, *hash, *signature = NULL, *server_host_key_blob = NULL;
58 	u_int sbloblen, klen, slen, hashlen;
59 	int omin = -1, min = -1, omax = -1, max = -1, onbits = -1, nbits = -1;
60 	int type, kout;
61 
62 	if (kex->load_host_key == NULL)
63 		fatal("Cannot load hostkey");
64 	server_host_key = kex->load_host_key(kex->hostkey_type);
65 	if (server_host_key == NULL)
66 		fatal("Unsupported hostkey type %d", kex->hostkey_type);
67 
68 	type = packet_read();
69 	switch (type) {
70 	case SSH2_MSG_KEX_DH_GEX_REQUEST:
71 		debug("SSH2_MSG_KEX_DH_GEX_REQUEST received");
72 		omin = min = packet_get_int();
73 		onbits = nbits = packet_get_int();
74 		omax = max = packet_get_int();
75 		min = MAX(DH_GRP_MIN, min);
76 		max = MIN(DH_GRP_MAX, max);
77 		nbits = MAX(DH_GRP_MIN, nbits);
78 		nbits = MIN(DH_GRP_MAX, nbits);
79 		break;
80 	case SSH2_MSG_KEX_DH_GEX_REQUEST_OLD:
81 		debug("SSH2_MSG_KEX_DH_GEX_REQUEST_OLD received");
82 		onbits = nbits = packet_get_int();
83 		/* unused for old GEX */
84 		omin = min = DH_GRP_MIN;
85 		omax = max = DH_GRP_MAX;
86 		break;
87 	default:
88 		fatal("protocol error during kex, no DH_GEX_REQUEST: %d", type);
89 	}
90 	packet_check_eom();
91 
92 	if (omax < omin || onbits < omin || omax < onbits)
93 		fatal("DH_GEX_REQUEST, bad parameters: %d !< %d !< %d",
94 		    omin, onbits, omax);
95 
96 	/* Contact privileged parent */
97 	dh = PRIVSEP(choose_dh(min, nbits, max));
98 	if (dh == NULL)
99 		packet_disconnect("Protocol error: no matching DH grp found");
100 
101 	debug("SSH2_MSG_KEX_DH_GEX_GROUP sent");
102 	packet_start(SSH2_MSG_KEX_DH_GEX_GROUP);
103 	packet_put_bignum2(dh->p);
104 	packet_put_bignum2(dh->g);
105 	packet_send();
106 
107 	/* flush */
108 	packet_write_wait();
109 
110 	/* Compute our exchange value in parallel with the client */
111 	dh_gen_key(dh, kex->we_need * 8);
112 
113 	debug("expecting SSH2_MSG_KEX_DH_GEX_INIT");
114 	packet_read_expect(SSH2_MSG_KEX_DH_GEX_INIT);
115 
116 	/* key, cert */
117 	if ((dh_client_pub = BN_new()) == NULL)
118 		fatal("dh_client_pub == NULL");
119 	packet_get_bignum2(dh_client_pub);
120 	packet_check_eom();
121 
122 #ifdef DEBUG_KEXDH
123 	fprintf(stderr, "dh_client_pub= ");
124 	BN_print_fp(stderr, dh_client_pub);
125 	fprintf(stderr, "\n");
126 	debug("bits %d", BN_num_bits(dh_client_pub));
127 #endif
128 
129 #ifdef DEBUG_KEXDH
130 	DHparams_print_fp(stderr, dh);
131 	fprintf(stderr, "pub= ");
132 	BN_print_fp(stderr, dh->pub_key);
133 	fprintf(stderr, "\n");
134 #endif
135 	if (!dh_pub_is_valid(dh, dh_client_pub))
136 		packet_disconnect("bad client public DH value");
137 
138 	klen = DH_size(dh);
139 	kbuf = xmalloc(klen);
140 	if ((kout = DH_compute_key(kbuf, dh_client_pub, dh)) < 0)
141 		fatal("DH_compute_key: failed");
142 #ifdef DEBUG_KEXDH
143 	dump_digest("shared secret", kbuf, kout);
144 #endif
145 	if ((shared_secret = BN_new()) == NULL)
146 		fatal("kexgex_server: BN_new failed");
147 	if (BN_bin2bn(kbuf, kout, shared_secret) == NULL)
148 		fatal("kexgex_server: BN_bin2bn failed");
149 	memset(kbuf, 0, klen);
150 	xfree(kbuf);
151 
152 	key_to_blob(server_host_key, &server_host_key_blob, &sbloblen);
153 
154 	if (type == SSH2_MSG_KEX_DH_GEX_REQUEST_OLD)
155 		omin = min = omax = max = -1;
156 
157 	/* calc H */
158 	kexgex_hash(
159 	    kex->evp_md,
160 	    kex->client_version_string,
161 	    kex->server_version_string,
162 	    buffer_ptr(&kex->peer), buffer_len(&kex->peer),
163 	    buffer_ptr(&kex->my), buffer_len(&kex->my),
164 	    server_host_key_blob, sbloblen,
165 	    omin, onbits, omax,
166 	    dh->p, dh->g,
167 	    dh_client_pub,
168 	    dh->pub_key,
169 	    shared_secret,
170 	    &hash, &hashlen
171 	);
172 	BN_clear_free(dh_client_pub);
173 
174 	/* save session id := H */
175 	if (kex->session_id == NULL) {
176 		kex->session_id_len = hashlen;
177 		kex->session_id = xmalloc(kex->session_id_len);
178 		memcpy(kex->session_id, hash, kex->session_id_len);
179 	}
180 
181 	/* sign H */
182 	PRIVSEP(key_sign(server_host_key, &signature, &slen, hash, hashlen));
183 
184 	/* destroy_sensitive_data(); */
185 
186 	/* send server hostkey, DH pubkey 'f' and singed H */
187 	debug("SSH2_MSG_KEX_DH_GEX_REPLY sent");
188 	packet_start(SSH2_MSG_KEX_DH_GEX_REPLY);
189 	packet_put_string(server_host_key_blob, sbloblen);
190 	packet_put_bignum2(dh->pub_key);	/* f */
191 	packet_put_string(signature, slen);
192 	packet_send();
193 
194 	xfree(signature);
195 	xfree(server_host_key_blob);
196 	/* have keys, free DH */
197 	DH_free(dh);
198 
199 	kex_derive_keys(kex, hash, hashlen, shared_secret);
200 	BN_clear_free(shared_secret);
201 
202 	kex_finish(kex);
203 }
204