[openssh.git] / 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 1.18 2002/02/23 17:59:02 markus 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_size(evp_md));
#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 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(SSH2_MSG_KEX_DH_GEX_GROUP);

	if ((p = BN_new()) == NULL)
		fatal("BN_new");
	packet_get_bignum2(p);
	if ((g = BN_new()) == NULL)
		fatal("BN_new");
	packet_get_bignum2(g);
	packet_check_eom();

	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(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 (server_host_key->type != kex->hostkey_type)
		fatal("type mismatch for decoded 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 */
	if ((dh_server_pub = BN_new()) == NULL)
		fatal("dh_server_pub == NULL");
	packet_get_bignum2(dh_server_pub);

#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_check_eom();

	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
	if ((shared_secret = BN_new()) == NULL)
		fatal("kexgex_client: BN_new failed");
	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_clear_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, 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();
	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_check_eom();

	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(SSH2_MSG_KEX_DH_GEX_INIT);

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

#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
	if ((shared_secret = BN_new()) == NULL)
		fatal("kexgex_server: BN_new failed");
	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_clear_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
0bc35151	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"
b967d870	27	RCSID("$OpenBSD: kexgex.c,v 1.18 2002/02/23 17:59:02 markus Exp $");
0bc35151	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
396c147e	42	static u_char *
0bc35151	43	kexgex_hash(
	44	char *client_version_string,
	45	char *server_version_string,
	46	char *ckexinit, int ckexinitlen,
	47	char *skexinit, int skexinitlen,
cf54363d	48	u_char *serverhostkeyblob, int sbloblen,
0bc35151	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);
449c5ba5	60	buffer_put_cstring(&b, client_version_string);
449c5ba5	61	buffer_put_cstring(&b, server_version_string);
0bc35151	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);
cd332296	72	if (min == -1 \|\| max == -1)
0bc35151	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
a209a158	95	dump_digest("hash", digest, EVP_MD_size(evp_md));
0bc35151	96	#endif
	97	return digest;
	98	}
	99
	100	/* client */
	101
396c147e	102	static void
0bc35151	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;
54a5250f	110	int min, max, nbits;
0bc35151	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");
54a5250f	141	packet_read_expect(SSH2_MSG_KEX_DH_GEX_GROUP);
0bc35151	142
	143	if ((p = BN_new()) == NULL)
	144	fatal("BN_new");
20b279e6	145	packet_get_bignum2(p);
0bc35151	146	if ((g = BN_new()) == NULL)
0bc35151	147	fatal("BN_new");
20b279e6	148	packet_get_bignum2(g);
95500969	149	packet_check_eom();
0bc35151	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");
54a5250f	172	packet_read_expect(SSH2_MSG_KEX_DH_GEX_REPLY);
0bc35151	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");
215ced77	179	if (server_host_key->type != kex->hostkey_type)
215ced77	180	fatal("type mismatch for decoded server_host_key_blob");
f49bc4f7	181	if (kex->verify_host_key == NULL)
	182	fatal("cannot verify server_host_key");
	183	if (kex->verify_host_key(server_host_key) == -1)
	184	fatal("server_host_key verification failed");
0bc35151	185
0bc35151	186	/* DH paramter f, server public DH key */
b775c6f2	187	if ((dh_server_pub = BN_new()) == NULL)
0bc35151	188	fatal("dh_server_pub == NULL");
20b279e6	189	packet_get_bignum2(dh_server_pub);
0bc35151	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);
95500969	200	packet_check_eom();
0bc35151	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
cd332296	209	dump_digest("shared secret", kbuf, kout);
0bc35151	210	#endif
b775c6f2	211	if ((shared_secret = BN_new()) == NULL)
b775c6f2	212	fatal("kexgex_client: BN_new failed");
0bc35151	213	BN_bin2bn(kbuf, kout, shared_secret);
	214	memset(kbuf, 0, klen);
	215	xfree(kbuf);
	216
	217	if (datafellows & SSH_OLD_DHGEX)
	218	min = max = -1;
	219
	220	/* calc and verify H */
	221	hash = kexgex_hash(
	222	kex->client_version_string,
	223	kex->server_version_string,
	224	buffer_ptr(&kex->my), buffer_len(&kex->my),
	225	buffer_ptr(&kex->peer), buffer_len(&kex->peer),
	226	server_host_key_blob, sbloblen,
	227	min, nbits, max,
	228	dh->p, dh->g,
	229	dh->pub_key,
	230	dh_server_pub,
	231	shared_secret
	232	);
d8ee838b	233	/* have keys, free DH */
d8ee838b	234	DH_free(dh);
0bc35151	235	xfree(server_host_key_blob);
108d362e	236	BN_clear_free(dh_server_pub);
0bc35151	237
cf54363d	238	if (key_verify(server_host_key, signature, slen, hash, 20) != 1)
0bc35151	239	fatal("key_verify failed for server_host_key");
	240	key_free(server_host_key);
	241	xfree(signature);
	242
	243	/* save session id */
	244	if (kex->session_id == NULL) {
	245	kex->session_id_len = 20;
	246	kex->session_id = xmalloc(kex->session_id_len);
	247	memcpy(kex->session_id, hash, kex->session_id_len);
	248	}
0bc35151	249	kex_derive_keys(kex, hash, shared_secret);
	250	BN_clear_free(shared_secret);
	251
d8ee838b	252	kex_finish(kex);
0bc35151	253	}
	254
	255	/* server */
	256
396c147e	257	static void
0bc35151	258	kexgex_server(Kex *kex)
	259	{
	260	BIGNUM shared_secret = NULL, dh_client_pub = NULL;
	261	Key *server_host_key;
	262	DH *dh = dh;
	263	u_char kbuf, hash, signature = NULL, server_host_key_blob = NULL;
	264	u_int sbloblen, klen, kout;
54a5250f	265	int min = -1, max = -1, nbits = -1, type, slen;
0bc35151	266
	267	if (kex->load_host_key == NULL)
	268	fatal("Cannot load hostkey");
	269	server_host_key = kex->load_host_key(kex->hostkey_type);
	270	if (server_host_key == NULL)
	271	fatal("Unsupported hostkey type %d", kex->hostkey_type);
	272
54a5250f	273	type = packet_read();
6aacefa7	274	switch (type) {
0bc35151	275	case SSH2_MSG_KEX_DH_GEX_REQUEST:
	276	debug("SSH2_MSG_KEX_DH_GEX_REQUEST received");
	277	min = packet_get_int();
	278	nbits = packet_get_int();
	279	max = packet_get_int();
	280	min = MAX(DH_GRP_MIN, min);
	281	max = MIN(DH_GRP_MAX, max);
	282	break;
	283	case SSH2_MSG_KEX_DH_GEX_REQUEST_OLD:
	284	debug("SSH2_MSG_KEX_DH_GEX_REQUEST_OLD received");
	285	nbits = packet_get_int();
	286	min = DH_GRP_MIN;
	287	max = DH_GRP_MAX;
	288	/* unused for old GEX */
	289	break;
	290	default:
bbb4cc1b	291	fatal("protocol error during kex, no DH_GEX_REQUEST: %d", type);
0bc35151	292	}
95500969	293	packet_check_eom();
0bc35151	294
	295	if (max < min \|\| nbits < min \|\| max < nbits)
	296	fatal("DH_GEX_REQUEST, bad parameters: %d !< %d !< %d",
	297	min, nbits, max);
	298
	299	dh = choose_dh(min, nbits, max);
	300	if (dh == NULL)
	301	packet_disconnect("Protocol error: no matching DH grp found");
	302
	303	debug("SSH2_MSG_KEX_DH_GEX_GROUP sent");
	304	packet_start(SSH2_MSG_KEX_DH_GEX_GROUP);
	305	packet_put_bignum2(dh->p);
	306	packet_put_bignum2(dh->g);
	307	packet_send();
	308
	309	/* flush */
	310	packet_write_wait();
	311
	312	/* Compute our exchange value in parallel with the client */
	313	dh_gen_key(dh, kex->we_need * 8);
	314
	315	debug("expecting SSH2_MSG_KEX_DH_GEX_INIT");
54a5250f	316	packet_read_expect(SSH2_MSG_KEX_DH_GEX_INIT);
0bc35151	317
0bc35151	318	/* key, cert */
b775c6f2	319	if ((dh_client_pub = BN_new()) == NULL)
0bc35151	320	fatal("dh_client_pub == NULL");
20b279e6	321	packet_get_bignum2(dh_client_pub);
b967d870	322	packet_check_eom();
0bc35151	323
	324	#ifdef DEBUG_KEXDH
	325	fprintf(stderr, "dh_client_pub= ");
	326	BN_print_fp(stderr, dh_client_pub);
	327	fprintf(stderr, "\n");
	328	debug("bits %d", BN_num_bits(dh_client_pub));
	329	#endif
	330
	331	#ifdef DEBUG_KEXDH
	332	DHparams_print_fp(stderr, dh);
	333	fprintf(stderr, "pub= ");
	334	BN_print_fp(stderr, dh->pub_key);
	335	fprintf(stderr, "\n");
	336	#endif
	337	if (!dh_pub_is_valid(dh, dh_client_pub))
	338	packet_disconnect("bad client public DH value");
	339
	340	klen = DH_size(dh);
	341	kbuf = xmalloc(klen);
	342	kout = DH_compute_key(kbuf, dh_client_pub, dh);
	343	#ifdef DEBUG_KEXDH
cd332296	344	dump_digest("shared secret", kbuf, kout);
0bc35151	345	#endif
b775c6f2	346	if ((shared_secret = BN_new()) == NULL)
b775c6f2	347	fatal("kexgex_server: BN_new failed");
0bc35151	348	BN_bin2bn(kbuf, kout, shared_secret);
	349	memset(kbuf, 0, klen);
	350	xfree(kbuf);
	351
	352	key_to_blob(server_host_key, &server_host_key_blob, &sbloblen);
	353
	354	if (type == SSH2_MSG_KEX_DH_GEX_REQUEST_OLD)
	355	min = max = -1;
	356
	357	/* calc H / / XXX depends on 'kex' */
	358	hash = kexgex_hash(
	359	kex->client_version_string,
	360	kex->server_version_string,
	361	buffer_ptr(&kex->peer), buffer_len(&kex->peer),
	362	buffer_ptr(&kex->my), buffer_len(&kex->my),
cf54363d	363	server_host_key_blob, sbloblen,
0bc35151	364	min, nbits, max,
	365	dh->p, dh->g,
	366	dh_client_pub,
	367	dh->pub_key,
	368	shared_secret
	369	);
108d362e	370	BN_clear_free(dh_client_pub);
0bc35151	371
	372	/* save session id := H */
	373	/* XXX hashlen depends on KEX */
	374	if (kex->session_id == NULL) {
	375	kex->session_id_len = 20;
	376	kex->session_id = xmalloc(kex->session_id_len);
	377	memcpy(kex->session_id, hash, kex->session_id_len);
	378	}
	379
	380	/* sign H */
	381	/* XXX hashlen depends on KEX */
	382	key_sign(server_host_key, &signature, &slen, hash, 20);
	383
	384	/* destroy_sensitive_data(); */
	385
	386	/* send server hostkey, DH pubkey 'f' and singed H */
	387	debug("SSH2_MSG_KEX_DH_GEX_REPLY sent");
	388	packet_start(SSH2_MSG_KEX_DH_GEX_REPLY);
cf54363d	389	packet_put_string(server_host_key_blob, sbloblen);
0bc35151	390	packet_put_bignum2(dh->pub_key); /* f */
cf54363d	391	packet_put_string(signature, slen);
0bc35151	392	packet_send();
	393	xfree(signature);
	394	xfree(server_host_key_blob);
d8ee838b	395	/* have keys, free DH */
d8ee838b	396	DH_free(dh);
0bc35151	397
	398	kex_derive_keys(kex, hash, shared_secret);
	399	BN_clear_free(shared_secret);
	400
d8ee838b	401	kex_finish(kex);
0bc35151	402	}
	403
	404	void
	405	kexgex(Kex *kex)
	406	{
	407	if (kex->server)
	408	kexgex_server(kex);
	409	else
	410	kexgex_client(kex);
	411	}