[gssapi-openssh.git] / openssh / kexgex.c

/*
 * Copyright (c) 2000 Niels Provos.  All rights reserved.
 * Copyright (c) 2001 Markus Friedl.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include "includes.h"
RCSID("$OpenBSD: kexgex.c,v 1.9 2001/09/17 19:27:15 stevesk Exp $");

#include <openssl/bn.h>

#include "xmalloc.h"
#include "buffer.h"
#include "bufaux.h"
#include "key.h"
#include "kex.h"
#include "log.h"
#include "packet.h"
#include "dh.h"
#include "ssh2.h"
#include "compat.h"

static u_char *
kexgex_hash(
    char *client_version_string,
    char *server_version_string,
    char *ckexinit, int ckexinitlen,
    char *skexinit, int skexinitlen,
    u_char *serverhostkeyblob, int sbloblen,
    int min, int wantbits, int max, BIGNUM *prime, BIGNUM *gen,
    BIGNUM *client_dh_pub,
    BIGNUM *server_dh_pub,
    BIGNUM *shared_secret)
{
	Buffer b;
	static u_char digest[EVP_MAX_MD_SIZE];
	EVP_MD *evp_md = EVP_sha1();
	EVP_MD_CTX md;

	buffer_init(&b);
	buffer_put_cstring(&b, client_version_string);
	buffer_put_cstring(&b, server_version_string);

	/* kexinit messages: fake header: len+SSH2_MSG_KEXINIT */
	buffer_put_int(&b, ckexinitlen+1);
	buffer_put_char(&b, SSH2_MSG_KEXINIT);
	buffer_append(&b, ckexinit, ckexinitlen);
	buffer_put_int(&b, skexinitlen+1);
	buffer_put_char(&b, SSH2_MSG_KEXINIT);
	buffer_append(&b, skexinit, skexinitlen);

	buffer_put_string(&b, serverhostkeyblob, sbloblen);
	if (min == -1 || max == -1)
		buffer_put_int(&b, wantbits);
	else {
		buffer_put_int(&b, min);
		buffer_put_int(&b, wantbits);
		buffer_put_int(&b, max);
	}
	buffer_put_bignum2(&b, prime);
	buffer_put_bignum2(&b, gen);
	buffer_put_bignum2(&b, client_dh_pub);
	buffer_put_bignum2(&b, server_dh_pub);
	buffer_put_bignum2(&b, shared_secret);

#ifdef DEBUG_KEXDH
	buffer_dump(&b);
#endif
	EVP_DigestInit(&md, evp_md);
	EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
	EVP_DigestFinal(&md, digest, NULL);

	buffer_free(&b);

#ifdef DEBUG_KEXDH
	dump_digest("hash", digest, evp_md->md_size);
#endif
	return digest;
}

/* client */

static void
kexgex_client(Kex *kex)
{
	BIGNUM *dh_server_pub = NULL, *shared_secret = NULL;
	BIGNUM *p = NULL, *g = NULL;
	Key *server_host_key;
	u_char *kbuf, *hash, *signature = NULL, *server_host_key_blob = NULL;
	u_int klen, kout, slen, sbloblen;
	int dlen, plen, min, max, nbits;
	DH *dh;

	nbits = dh_estimate(kex->we_need * 8);

	if (datafellows & SSH_OLD_DHGEX) {
		debug("SSH2_MSG_KEX_DH_GEX_REQUEST_OLD sent");

		/* Old GEX request */
		packet_start(SSH2_MSG_KEX_DH_GEX_REQUEST_OLD);
		packet_put_int(nbits);
		min = DH_GRP_MIN;
		max = DH_GRP_MAX;
	} else {
		debug("SSH2_MSG_KEX_DH_GEX_REQUEST sent");

		/* New GEX request */
		min = DH_GRP_MIN;
		max = DH_GRP_MAX;
		packet_start(SSH2_MSG_KEX_DH_GEX_REQUEST);
		packet_put_int(min);
		packet_put_int(nbits);
		packet_put_int(max);
	}
#ifdef DEBUG_KEXDH
	fprintf(stderr, "\nmin = %d, nbits = %d, max = %d\n",
	    min, nbits, max);
#endif
	packet_send();

	debug("expecting SSH2_MSG_KEX_DH_GEX_GROUP");
	packet_read_expect(&plen, SSH2_MSG_KEX_DH_GEX_GROUP);

	if ((p = BN_new()) == NULL)
		fatal("BN_new");
	packet_get_bignum2(p, &dlen);
	if ((g = BN_new()) == NULL)
		fatal("BN_new");
	packet_get_bignum2(g, &dlen);
	packet_done();

	if (BN_num_bits(p) < min || BN_num_bits(p) > max)
		fatal("DH_GEX group out of range: %d !< %d !< %d",
		    min, BN_num_bits(p), max);

	dh = dh_new_group(g, p);
	dh_gen_key(dh, kex->we_need * 8);

#ifdef DEBUG_KEXDH
	DHparams_print_fp(stderr, dh);
	fprintf(stderr, "pub= ");
	BN_print_fp(stderr, dh->pub_key);
	fprintf(stderr, "\n");
#endif

	debug("SSH2_MSG_KEX_DH_GEX_INIT sent");
	/* generate and send 'e', client DH public key */
	packet_start(SSH2_MSG_KEX_DH_GEX_INIT);
	packet_put_bignum2(dh->pub_key);
	packet_send();

	debug("expecting SSH2_MSG_KEX_DH_GEX_REPLY");
	packet_read_expect(&plen, SSH2_MSG_KEX_DH_GEX_REPLY);

	/* key, cert */
	server_host_key_blob = packet_get_string(&sbloblen);
	server_host_key = key_from_blob(server_host_key_blob, sbloblen);
	if (server_host_key == NULL)
		fatal("cannot decode server_host_key_blob");

	if (kex->verify_host_key == NULL)
		fatal("cannot verify server_host_key");
	if (kex->verify_host_key(server_host_key) == -1)
		fatal("server_host_key verification failed");

	/* DH paramter f, server public DH key */
	dh_server_pub = BN_new();
	if (dh_server_pub == NULL)
		fatal("dh_server_pub == NULL");
	packet_get_bignum2(dh_server_pub, &dlen);

#ifdef DEBUG_KEXDH
	fprintf(stderr, "dh_server_pub= ");
	BN_print_fp(stderr, dh_server_pub);
	fprintf(stderr, "\n");
	debug("bits %d", BN_num_bits(dh_server_pub));
#endif

	/* signed H */
	signature = packet_get_string(&slen);
	packet_done();

	if (!dh_pub_is_valid(dh, dh_server_pub))
		packet_disconnect("bad server public DH value");

	klen = DH_size(dh);
	kbuf = xmalloc(klen);
	kout = DH_compute_key(kbuf, dh_server_pub, dh);
#ifdef DEBUG_KEXDH
	dump_digest("shared secret", kbuf, kout);
#endif
	shared_secret = BN_new();
	BN_bin2bn(kbuf, kout, shared_secret);
	memset(kbuf, 0, klen);
	xfree(kbuf);

	if (datafellows & SSH_OLD_DHGEX)
		min = max = -1;

	/* calc and verify H */
	hash = kexgex_hash(
	    kex->client_version_string,
	    kex->server_version_string,
	    buffer_ptr(&kex->my), buffer_len(&kex->my),
	    buffer_ptr(&kex->peer), buffer_len(&kex->peer),
	    server_host_key_blob, sbloblen,
	    min, nbits, max,
	    dh->p, dh->g,
	    dh->pub_key,
	    dh_server_pub,
	    shared_secret
	);
	/* have keys, free DH */
	DH_free(dh);
	xfree(server_host_key_blob);
	BN_free(dh_server_pub);

	if (key_verify(server_host_key, signature, slen, hash, 20) != 1)
		fatal("key_verify failed for server_host_key");
	key_free(server_host_key);
	xfree(signature);

	/* save session id */
	if (kex->session_id == NULL) {
		kex->session_id_len = 20;
		kex->session_id = xmalloc(kex->session_id_len);
		memcpy(kex->session_id, hash, kex->session_id_len);
	}
	kex_derive_keys(kex, hash, shared_secret);
	BN_clear_free(shared_secret);

	kex_finish(kex);
}

/* server */

static void
kexgex_server(Kex *kex)
{
	BIGNUM *shared_secret = NULL, *dh_client_pub = NULL;
	Key *server_host_key;
	DH *dh = dh;
	u_char *kbuf, *hash, *signature = NULL, *server_host_key_blob = NULL;
	u_int sbloblen, klen, kout;
	int min = -1, max = -1, nbits = -1, type, plen, dlen, slen;

	if (kex->load_host_key == NULL)
		fatal("Cannot load hostkey");
	server_host_key = kex->load_host_key(kex->hostkey_type);
	if (server_host_key == NULL)
		fatal("Unsupported hostkey type %d", kex->hostkey_type);

	type = packet_read(&plen);
	switch(type){
	case SSH2_MSG_KEX_DH_GEX_REQUEST:
		debug("SSH2_MSG_KEX_DH_GEX_REQUEST received");
		min = packet_get_int();
		nbits = packet_get_int();
		max = packet_get_int();
		min = MAX(DH_GRP_MIN, min);
		max = MIN(DH_GRP_MAX, max);
		break;
	case SSH2_MSG_KEX_DH_GEX_REQUEST_OLD:
		debug("SSH2_MSG_KEX_DH_GEX_REQUEST_OLD received");
		nbits = packet_get_int();
		min = DH_GRP_MIN;
		max = DH_GRP_MAX;
		/* unused for old GEX */
		break;
	default:
		fatal("protocol error during kex, no DH_GEX_REQUEST: %d", type);
	}
	packet_done();

	if (max < min || nbits < min || max < nbits)
		fatal("DH_GEX_REQUEST, bad parameters: %d !< %d !< %d",
		    min, nbits, max);

	dh = choose_dh(min, nbits, max);
	if (dh == NULL)
		packet_disconnect("Protocol error: no matching DH grp found");

	debug("SSH2_MSG_KEX_DH_GEX_GROUP sent");
	packet_start(SSH2_MSG_KEX_DH_GEX_GROUP);
	packet_put_bignum2(dh->p);
	packet_put_bignum2(dh->g);
	packet_send();

	/* flush */
	packet_write_wait();

	/* Compute our exchange value in parallel with the client */
	dh_gen_key(dh, kex->we_need * 8);

	debug("expecting SSH2_MSG_KEX_DH_GEX_INIT");
	packet_read_expect(&plen, SSH2_MSG_KEX_DH_GEX_INIT);

	/* key, cert */
	dh_client_pub = BN_new();
	if (dh_client_pub == NULL)
		fatal("dh_client_pub == NULL");
	packet_get_bignum2(dh_client_pub, &dlen);

#ifdef DEBUG_KEXDH
	fprintf(stderr, "dh_client_pub= ");
	BN_print_fp(stderr, dh_client_pub);
	fprintf(stderr, "\n");
	debug("bits %d", BN_num_bits(dh_client_pub));
#endif

#ifdef DEBUG_KEXDH
	DHparams_print_fp(stderr, dh);
	fprintf(stderr, "pub= ");
	BN_print_fp(stderr, dh->pub_key);
	fprintf(stderr, "\n");
#endif
	if (!dh_pub_is_valid(dh, dh_client_pub))
		packet_disconnect("bad client public DH value");

	klen = DH_size(dh);
	kbuf = xmalloc(klen);
	kout = DH_compute_key(kbuf, dh_client_pub, dh);
#ifdef DEBUG_KEXDH
	dump_digest("shared secret", kbuf, kout);
#endif
	shared_secret = BN_new();
	BN_bin2bn(kbuf, kout, shared_secret);
	memset(kbuf, 0, klen);
	xfree(kbuf);

	key_to_blob(server_host_key, &server_host_key_blob, &sbloblen);

	if (type == SSH2_MSG_KEX_DH_GEX_REQUEST_OLD)
		min = max = -1;

	/* calc H */			/* XXX depends on 'kex' */
	hash = kexgex_hash(
	    kex->client_version_string,
	    kex->server_version_string,
	    buffer_ptr(&kex->peer), buffer_len(&kex->peer),
	    buffer_ptr(&kex->my), buffer_len(&kex->my),
	    server_host_key_blob, sbloblen,
	    min, nbits, max,
	    dh->p, dh->g,
	    dh_client_pub,
	    dh->pub_key,
	    shared_secret
	);
	BN_free(dh_client_pub);

	/* save session id := H */
	/* XXX hashlen depends on KEX */
	if (kex->session_id == NULL) {
		kex->session_id_len = 20;
		kex->session_id = xmalloc(kex->session_id_len);
		memcpy(kex->session_id, hash, kex->session_id_len);
	}

	/* sign H */
	/* XXX hashlen depends on KEX */
	key_sign(server_host_key, &signature, &slen, hash, 20);

	/* destroy_sensitive_data(); */

	/* send server hostkey, DH pubkey 'f' and singed H */
	debug("SSH2_MSG_KEX_DH_GEX_REPLY sent");
	packet_start(SSH2_MSG_KEX_DH_GEX_REPLY);
	packet_put_string(server_host_key_blob, sbloblen);
	packet_put_bignum2(dh->pub_key);	/* f */
	packet_put_string(signature, slen);
	packet_send();
	xfree(signature);
	xfree(server_host_key_blob);
	/* have keys, free DH */
	DH_free(dh);

	kex_derive_keys(kex, hash, shared_secret);
	BN_clear_free(shared_secret);

	kex_finish(kex);
}

void
kexgex(Kex *kex)
{
	if (kex->server)
		kexgex_server(kex);
	else
		kexgex_client(kex);
}
Commit	Line	Data
3c0ef626	1	/*
	2	* Copyright (c) 2000 Niels Provos. All rights reserved.
	3	* Copyright (c) 2001 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	RCSID("$OpenBSD: kexgex.c,v 1.9 2001/09/17 19:27:15 stevesk Exp $");
	28
	29	#include <openssl/bn.h>
	30
	31	#include "xmalloc.h"
	32	#include "buffer.h"
	33	#include "bufaux.h"
	34	#include "key.h"
	35	#include "kex.h"
	36	#include "log.h"
	37	#include "packet.h"
	38	#include "dh.h"
	39	#include "ssh2.h"
	40	#include "compat.h"
	41
	42	static u_char *
	43	kexgex_hash(
	44	char *client_version_string,
	45	char *server_version_string,
	46	char *ckexinit, int ckexinitlen,
	47	char *skexinit, int skexinitlen,
	48	u_char *serverhostkeyblob, int sbloblen,
	49	int min, int wantbits, int max, BIGNUM prime, BIGNUM gen,
	50	BIGNUM *client_dh_pub,
	51	BIGNUM *server_dh_pub,
	52	BIGNUM *shared_secret)
	53	{
	54	Buffer b;
	55	static u_char digest[EVP_MAX_MD_SIZE];
	56	EVP_MD *evp_md = EVP_sha1();
	57	EVP_MD_CTX md;
	58
	59	buffer_init(&b);
	60	buffer_put_cstring(&b, client_version_string);
	61	buffer_put_cstring(&b, server_version_string);
	62
	63	/* kexinit messages: fake header: len+SSH2_MSG_KEXINIT */
	64	buffer_put_int(&b, ckexinitlen+1);
65	buffer_put_char(&b, SSH2_MSG_KEXINIT);
66	buffer_append(&b, ckexinit, ckexinitlen);
67	buffer_put_int(&b, skexinitlen+1);
68	buffer_put_char(&b, SSH2_MSG_KEXINIT);
69	buffer_append(&b, skexinit, skexinitlen);
70
71	buffer_put_string(&b, serverhostkeyblob, sbloblen);
72	if (min == -1 \|\| max == -1)
73	buffer_put_int(&b, wantbits);
74	else {
75	buffer_put_int(&b, min);
76	buffer_put_int(&b, wantbits);
77	buffer_put_int(&b, max);
78	}
79	buffer_put_bignum2(&b, prime);
80	buffer_put_bignum2(&b, gen);
81	buffer_put_bignum2(&b, client_dh_pub);
82	buffer_put_bignum2(&b, server_dh_pub);
83	buffer_put_bignum2(&b, shared_secret);
84
85	#ifdef DEBUG_KEXDH
86	buffer_dump(&b);
87	#endif
88	EVP_DigestInit(&md, evp_md);
89	EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
90	EVP_DigestFinal(&md, digest, NULL);
91
92	buffer_free(&b);
93
94	#ifdef DEBUG_KEXDH
95	dump_digest("hash", digest, evp_md->md_size);
96	#endif
97	return digest;
98	}
99
100	/* client */
101
102	static void
103	kexgex_client(Kex *kex)
104	{
105	BIGNUM dh_server_pub = NULL, shared_secret = NULL;
106	BIGNUM p = NULL, g = NULL;
107	Key *server_host_key;
108	u_char kbuf, hash, signature = NULL, server_host_key_blob = NULL;
109	u_int klen, kout, slen, sbloblen;
110	int dlen, plen, min, max, nbits;
111	DH *dh;
112
113	nbits = dh_estimate(kex->we_need * 8);
114
115	if (datafellows & SSH_OLD_DHGEX) {
116	debug("SSH2_MSG_KEX_DH_GEX_REQUEST_OLD sent");
117
118	/* Old GEX request */
119	packet_start(SSH2_MSG_KEX_DH_GEX_REQUEST_OLD);
120	packet_put_int(nbits);
121	min = DH_GRP_MIN;
122	max = DH_GRP_MAX;
123	} else {
124	debug("SSH2_MSG_KEX_DH_GEX_REQUEST sent");
125
126	/* New GEX request */
127	min = DH_GRP_MIN;
128	max = DH_GRP_MAX;
129	packet_start(SSH2_MSG_KEX_DH_GEX_REQUEST);
130	packet_put_int(min);
131	packet_put_int(nbits);
132	packet_put_int(max);
133	}
134	#ifdef DEBUG_KEXDH
135	fprintf(stderr, "\nmin = %d, nbits = %d, max = %d\n",
136	min, nbits, max);
137	#endif
138	packet_send();
139
140	debug("expecting SSH2_MSG_KEX_DH_GEX_GROUP");
141	packet_read_expect(&plen, SSH2_MSG_KEX_DH_GEX_GROUP);
142
143	if ((p = BN_new()) == NULL)
144	fatal("BN_new");
145	packet_get_bignum2(p, &dlen);
146	if ((g = BN_new()) == NULL)
147	fatal("BN_new");
148	packet_get_bignum2(g, &dlen);
149	packet_done();
150
151	if (BN_num_bits(p) < min \|\| BN_num_bits(p) > max)
152	fatal("DH_GEX group out of range: %d !< %d !< %d",
153	min, BN_num_bits(p), max);
154
155	dh = dh_new_group(g, p);
156	dh_gen_key(dh, kex->we_need * 8);
157
158	#ifdef DEBUG_KEXDH
159	DHparams_print_fp(stderr, dh);
160	fprintf(stderr, "pub= ");
161	BN_print_fp(stderr, dh->pub_key);
162	fprintf(stderr, "\n");
163	#endif
164
165	debug("SSH2_MSG_KEX_DH_GEX_INIT sent");
166	/* generate and send 'e', client DH public key */
167	packet_start(SSH2_MSG_KEX_DH_GEX_INIT);
168	packet_put_bignum2(dh->pub_key);
169	packet_send();
170
171	debug("expecting SSH2_MSG_KEX_DH_GEX_REPLY");
172	packet_read_expect(&plen, SSH2_MSG_KEX_DH_GEX_REPLY);
173
174	/* key, cert */
175	server_host_key_blob = packet_get_string(&sbloblen);
176	server_host_key = key_from_blob(server_host_key_blob, sbloblen);
177	if (server_host_key == NULL)
178	fatal("cannot decode server_host_key_blob");
179
180	if (kex->verify_host_key == NULL)
181	fatal("cannot verify server_host_key");
182	if (kex->verify_host_key(server_host_key) == -1)
183	fatal("server_host_key verification failed");
184
185	/* DH paramter f, server public DH key */
186	dh_server_pub = BN_new();
187	if (dh_server_pub == NULL)
188	fatal("dh_server_pub == NULL");
189	packet_get_bignum2(dh_server_pub, &dlen);
190
191	#ifdef DEBUG_KEXDH
192	fprintf(stderr, "dh_server_pub= ");
193	BN_print_fp(stderr, dh_server_pub);
194	fprintf(stderr, "\n");
195	debug("bits %d", BN_num_bits(dh_server_pub));
196	#endif
197
198	/* signed H */
199	signature = packet_get_string(&slen);
200	packet_done();
201
202	if (!dh_pub_is_valid(dh, dh_server_pub))
203	packet_disconnect("bad server public DH value");
204
205	klen = DH_size(dh);
206	kbuf = xmalloc(klen);
207	kout = DH_compute_key(kbuf, dh_server_pub, dh);
208	#ifdef DEBUG_KEXDH
209	dump_digest("shared secret", kbuf, kout);
210	#endif
211	shared_secret = BN_new();
212	BN_bin2bn(kbuf, kout, shared_secret);
213	memset(kbuf, 0, klen);
214	xfree(kbuf);
215
216	if (datafellows & SSH_OLD_DHGEX)
217	min = max = -1;
218
219	/* calc and verify H */
220	hash = kexgex_hash(
221	kex->client_version_string,
222	kex->server_version_string,
223	buffer_ptr(&kex->my), buffer_len(&kex->my),
224	buffer_ptr(&kex->peer), buffer_len(&kex->peer),
225	server_host_key_blob, sbloblen,
226	min, nbits, max,
227	dh->p, dh->g,
228	dh->pub_key,
229	dh_server_pub,
230	shared_secret
231	);
232	/* have keys, free DH */
233	DH_free(dh);
234	xfree(server_host_key_blob);
235	BN_free(dh_server_pub);
236
237	if (key_verify(server_host_key, signature, slen, hash, 20) != 1)
238	fatal("key_verify failed for server_host_key");
239	key_free(server_host_key);
240	xfree(signature);
241
242	/* save session id */
243	if (kex->session_id == NULL) {
244	kex->session_id_len = 20;
245	kex->session_id = xmalloc(kex->session_id_len);
246	memcpy(kex->session_id, hash, kex->session_id_len);
247	}
248	kex_derive_keys(kex, hash, shared_secret);
249	BN_clear_free(shared_secret);
250
251	kex_finish(kex);
252	}
253
254	/* server */
255
256	static void
257	kexgex_server(Kex *kex)
258	{
259	BIGNUM shared_secret = NULL, dh_client_pub = NULL;
260	Key *server_host_key;
261	DH *dh = dh;
262	u_char kbuf, hash, signature = NULL, server_host_key_blob = NULL;
263	u_int sbloblen, klen, kout;
264	int min = -1, max = -1, nbits = -1, type, plen, dlen, slen;
265
266	if (kex->load_host_key == NULL)
267	fatal("Cannot load hostkey");
268	server_host_key = kex->load_host_key(kex->hostkey_type);
269	if (server_host_key == NULL)
270	fatal("Unsupported hostkey type %d", kex->hostkey_type);
271
272	type = packet_read(&plen);
273	switch(type){
274	case SSH2_MSG_KEX_DH_GEX_REQUEST:
275	debug("SSH2_MSG_KEX_DH_GEX_REQUEST received");
276	min = packet_get_int();
277	nbits = packet_get_int();
278	max = packet_get_int();
279	min = MAX(DH_GRP_MIN, min);
280	max = MIN(DH_GRP_MAX, max);
281	break;
282	case SSH2_MSG_KEX_DH_GEX_REQUEST_OLD:
283	debug("SSH2_MSG_KEX_DH_GEX_REQUEST_OLD received");
284	nbits = packet_get_int();
285	min = DH_GRP_MIN;
286	max = DH_GRP_MAX;
287	/* unused for old GEX */
288	break;
289	default:
290	fatal("protocol error during kex, no DH_GEX_REQUEST: %d", type);
291	}
292	packet_done();
293
294	if (max < min \|\| nbits < min \|\| max < nbits)
295	fatal("DH_GEX_REQUEST, bad parameters: %d !< %d !< %d",
296	min, nbits, max);
297
298	dh = choose_dh(min, nbits, max);
299	if (dh == NULL)
300	packet_disconnect("Protocol error: no matching DH grp found");
301
302	debug("SSH2_MSG_KEX_DH_GEX_GROUP sent");
303	packet_start(SSH2_MSG_KEX_DH_GEX_GROUP);
304	packet_put_bignum2(dh->p);
305	packet_put_bignum2(dh->g);
306	packet_send();
307
308	/* flush */
309	packet_write_wait();
310
311	/* Compute our exchange value in parallel with the client */
312	dh_gen_key(dh, kex->we_need * 8);
313
314	debug("expecting SSH2_MSG_KEX_DH_GEX_INIT");
315	packet_read_expect(&plen, SSH2_MSG_KEX_DH_GEX_INIT);
316
317	/* key, cert */
318	dh_client_pub = BN_new();
319	if (dh_client_pub == NULL)
320	fatal("dh_client_pub == NULL");
321	packet_get_bignum2(dh_client_pub, &dlen);
322
323	#ifdef DEBUG_KEXDH
324	fprintf(stderr, "dh_client_pub= ");
325	BN_print_fp(stderr, dh_client_pub);
326	fprintf(stderr, "\n");
327	debug("bits %d", BN_num_bits(dh_client_pub));
328	#endif
329
330	#ifdef DEBUG_KEXDH
331	DHparams_print_fp(stderr, dh);
332	fprintf(stderr, "pub= ");
333	BN_print_fp(stderr, dh->pub_key);
334	fprintf(stderr, "\n");
335	#endif
336	if (!dh_pub_is_valid(dh, dh_client_pub))
337	packet_disconnect("bad client public DH value");
338
339	klen = DH_size(dh);
340	kbuf = xmalloc(klen);
341	kout = DH_compute_key(kbuf, dh_client_pub, dh);
342	#ifdef DEBUG_KEXDH
343	dump_digest("shared secret", kbuf, kout);
344	#endif
345	shared_secret = BN_new();
346	BN_bin2bn(kbuf, kout, shared_secret);
347	memset(kbuf, 0, klen);
348	xfree(kbuf);
349
350	key_to_blob(server_host_key, &server_host_key_blob, &sbloblen);
351
352	if (type == SSH2_MSG_KEX_DH_GEX_REQUEST_OLD)
353	min = max = -1;
354
355	/* calc H / / XXX depends on 'kex' */
356	hash = kexgex_hash(
357	kex->client_version_string,
358	kex->server_version_string,
359	buffer_ptr(&kex->peer), buffer_len(&kex->peer),
360	buffer_ptr(&kex->my), buffer_len(&kex->my),
361	server_host_key_blob, sbloblen,
362	min, nbits, max,
363	dh->p, dh->g,
364	dh_client_pub,
365	dh->pub_key,
366	shared_secret
367	);
368	BN_free(dh_client_pub);
369
370	/* save session id := H */
371	/* XXX hashlen depends on KEX */
372	if (kex->session_id == NULL) {
373	kex->session_id_len = 20;
374	kex->session_id = xmalloc(kex->session_id_len);
375	memcpy(kex->session_id, hash, kex->session_id_len);
376	}
377
378	/* sign H */
379	/* XXX hashlen depends on KEX */
380	key_sign(server_host_key, &signature, &slen, hash, 20);
381
382	/* destroy_sensitive_data(); */
383
384	/* send server hostkey, DH pubkey 'f' and singed H */
385	debug("SSH2_MSG_KEX_DH_GEX_REPLY sent");
386	packet_start(SSH2_MSG_KEX_DH_GEX_REPLY);
387	packet_put_string(server_host_key_blob, sbloblen);
388	packet_put_bignum2(dh->pub_key); /* f */
389	packet_put_string(signature, slen);
390	packet_send();
391	xfree(signature);
392	xfree(server_host_key_blob);
393	/* have keys, free DH */
394	DH_free(dh);
395
396	kex_derive_keys(kex, hash, shared_secret);
397	BN_clear_free(shared_secret);
398
399	kex_finish(kex);
400	}
401
402	void
403	kexgex(Kex *kex)
404	{
405	if (kex->server)
406	kexgex_server(kex);
407	else
408	kexgex_client(kex);
409	}