kex.c - security/openssh-library - Rivoreo Source Code Repositories

 /*
  * Copyright (c) 2000 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: kex.c,v 1.25 2001/03/29 21:17:39 markus Exp $");

 #include <openssl/crypto.h>
 #include <openssl/bio.h>
 #include <openssl/bn.h>
 #include <openssl/pem.h>

 #include "ssh2.h"
 #include "xmalloc.h"
 #include "buffer.h"
 #include "bufaux.h"
 #include "packet.h"
 #include "compat.h"
 #include "cipher.h"
 #include "kex.h"
 #include "key.h"
 #include "log.h"
 #include "mac.h"
 #include "match.h"

 #define KEX_COOKIE_LEN	16

 Buffer *
 kex_init(char *myproposal[PROPOSAL_MAX])
 {
 	int first_kex_packet_follows = 0;
 	u_char cookie[KEX_COOKIE_LEN];
 	u_int32_t rand = 0;
 	int i;
 	Buffer *ki = xmalloc(sizeof(*ki));
 	for (i = 0; i < KEX_COOKIE_LEN; i++) {
 		if (i % 4 == 0)
 			rand = arc4random();
 		cookie[i] = rand & 0xff;
 		rand >>= 8;
 	}
 	buffer_init(ki);
 	buffer_append(ki, (char *)cookie, sizeof cookie);
 	for (i = 0; i < PROPOSAL_MAX; i++)
 		buffer_put_cstring(ki, myproposal[i]);
 	buffer_put_char(ki, first_kex_packet_follows);
 	buffer_put_int(ki, 0);				/* uint32 reserved */
 	return ki;
 }

 /* send kexinit, parse and save reply */
 void
 kex_exchange_kexinit(
     Buffer *my_kexinit, Buffer *peer_kexint,
     char *peer_proposal[PROPOSAL_MAX])
 {
 	int i;
 	char *ptr;
 	int plen;

 	debug("send KEXINIT");
 	packet_start(SSH2_MSG_KEXINIT);
 	packet_put_raw(buffer_ptr(my_kexinit), buffer_len(my_kexinit));
 	packet_send();
 	packet_write_wait();
 	debug("done");

 	/*
 	 * read and save raw KEXINIT payload in buffer. this is used during
 	 * computation of the session_id and the session keys.
 	 */
 	debug("wait KEXINIT");
 	packet_read_expect(&plen, SSH2_MSG_KEXINIT);
 	ptr = packet_get_raw(&plen);
 	buffer_append(peer_kexint, ptr, plen);

 	/* parse packet and save algorithm proposal */
 	/* skip cookie */
 	for (i = 0; i < KEX_COOKIE_LEN; i++)
 		packet_get_char();
 	/* extract kex init proposal strings */
 	for (i = 0; i < PROPOSAL_MAX; i++) {
 		peer_proposal[i] = packet_get_string(NULL);
 		debug("got kexinit: %s", peer_proposal[i]);
 	}
 	/* first kex follow / reserved */
 	i = packet_get_char();
 	debug("first kex follow: %d ", i);
 	i = packet_get_int();
 	debug("reserved: %d ", i);
 	packet_done();
 	debug("done");
 }

 #ifdef DEBUG_KEX
 void
 dump_digest(u_char *digest, int len)
 {
 	int i;
 	for (i = 0; i< len; i++){
 		fprintf(stderr, "%02x", digest[i]);
 		if(i%2!=0)
 			fprintf(stderr, " ");
 	}
 	fprintf(stderr, "\n");
 }
 #endif

 u_char *
 kex_hash(
     char *client_version_string,
     char *server_version_string,
     char *ckexinit, int ckexinitlen,
     char *skexinit, int skexinitlen,
     char *serverhostkeyblob, int sbloblen,
     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_string(&b, client_version_string, strlen(client_version_string));
 	buffer_put_string(&b, server_version_string, strlen(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);
 	buffer_put_bignum2(&b, client_dh_pub);
 	buffer_put_bignum2(&b, server_dh_pub);
 	buffer_put_bignum2(&b, shared_secret);

 #ifdef DEBUG_KEX
 	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_KEX
 	dump_digest(digest, evp_md->md_size);
 #endif
 	return digest;
 }

 u_char *
 kex_hash_gex(
     char *client_version_string,
     char *server_version_string,
     char *ckexinit, int ckexinitlen,
     char *skexinit, int skexinitlen,
     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_string(&b, client_version_string, strlen(client_version_string));
 	buffer_put_string(&b, server_version_string, strlen(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_KEX
 	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_KEX
 	dump_digest(digest, evp_md->md_size);
 #endif
 	return digest;
 }

 u_char *
 derive_key(int id, int need, u_char *hash, BIGNUM *shared_secret)
 {
 	Buffer b;
 	EVP_MD *evp_md = EVP_sha1();
 	EVP_MD_CTX md;
 	char c = id;
 	int have;
 	int mdsz = evp_md->md_size;
 	u_char *digest = xmalloc(((need+mdsz-1)/mdsz)*mdsz);

 	buffer_init(&b);
 	buffer_put_bignum2(&b, shared_secret);

 	EVP_DigestInit(&md, evp_md);
 	EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));	/* shared_secret K */
 	EVP_DigestUpdate(&md, hash, mdsz);		/* transport-06 */
 	EVP_DigestUpdate(&md, &c, 1);			/* key id */
 	EVP_DigestUpdate(&md, hash, mdsz);		/* session id */
 	EVP_DigestFinal(&md, digest, NULL);

 	/* expand */
 	for (have = mdsz; need > have; have += mdsz) {
 		EVP_DigestInit(&md, evp_md);
 		EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
 		EVP_DigestUpdate(&md, hash, mdsz);
 		EVP_DigestUpdate(&md, digest, have);
 		EVP_DigestFinal(&md, digest + have, NULL);
 	}
 	buffer_free(&b);
 #ifdef DEBUG_KEX
 	fprintf(stderr, "Digest '%c'== ", c);
 	dump_digest(digest, need);
 #endif
 	return digest;
 }

 void
 choose_enc(Enc *enc, char *client, char *server)
 {
 	char *name = match_list(client, server, NULL);
 	if (name == NULL)
 		fatal("no matching cipher found: client %s server %s", client, server);
 	enc->cipher = cipher_by_name(name);
 	if (enc->cipher == NULL)
 		fatal("matching cipher is not supported: %s", name);
 	enc->name = name;
 	enc->enabled = 0;
 	enc->iv = NULL;
 	enc->key = NULL;
 }
 void
 choose_mac(Mac *mac, char *client, char *server)
 {
 	char *name = match_list(client, server, NULL);
 	if (name == NULL)
 		fatal("no matching mac found: client %s server %s", client, server);
 	if (mac_init(mac, name) < 0)
 		fatal("unsupported mac %s", name);
 	/* truncate the key */
 	if (datafellows & SSH_BUG_HMAC)
 		mac->key_len = 16;
 	mac->name = name;
 	mac->key = NULL;
 	mac->enabled = 0;
 }
 void
 choose_comp(Comp *comp, char *client, char *server)
 {
 	char *name = match_list(client, server, NULL);
 	if (name == NULL)
 		fatal("no matching comp found: client %s server %s", client, server);
 	if (strcmp(name, "zlib") == 0) {
 		comp->type = 1;
 	} else if (strcmp(name, "none") == 0) {
 		comp->type = 0;
 	} else {
 		fatal("unsupported comp %s", name);
 	}
 	comp->name = name;
 }
 void
 choose_kex(Kex *k, char *client, char *server)
 {
 	k->name = match_list(client, server, NULL);
 	if (k->name == NULL)
 		fatal("no kex alg");
 	if (strcmp(k->name, KEX_DH1) == 0) {
 		k->kex_type = DH_GRP1_SHA1;
 	} else if (strcmp(k->name, KEX_DHGEX) == 0) {
 		k->kex_type = DH_GEX_SHA1;
 	} else
 		fatal("bad kex alg %s", k->name);
 }
 void
 choose_hostkeyalg(Kex *k, char *client, char *server)
 {
 	char *hostkeyalg = match_list(client, server, NULL);
 	if (hostkeyalg == NULL)
 		fatal("no hostkey alg");
 	k->hostkey_type = key_type_from_name(hostkeyalg);
 	if (k->hostkey_type == KEY_UNSPEC)
 		fatal("bad hostkey alg '%s'", hostkeyalg);
 	xfree(hostkeyalg);
 }

 Kex *
 kex_choose_conf(char *cprop[PROPOSAL_MAX], char *sprop[PROPOSAL_MAX], int server)
 {
 	int mode;
 	int ctos;				/* direction: if true client-to-server */
 	int need;
 	Kex *k;

 	k = xmalloc(sizeof(*k));
 	memset(k, 0, sizeof(*k));
 	k->server = server;

 	for (mode = 0; mode < MODE_MAX; mode++) {
 		int nenc, nmac, ncomp;
 		ctos = (!k->server && mode == MODE_OUT) || (k->server && mode == MODE_IN);
 		nenc  = ctos ? PROPOSAL_ENC_ALGS_CTOS  : PROPOSAL_ENC_ALGS_STOC;
 		nmac  = ctos ? PROPOSAL_MAC_ALGS_CTOS  : PROPOSAL_MAC_ALGS_STOC;
 		ncomp = ctos ? PROPOSAL_COMP_ALGS_CTOS : PROPOSAL_COMP_ALGS_STOC;
 		choose_enc (&k->enc [mode], cprop[nenc],  sprop[nenc]);
 		choose_mac (&k->mac [mode], cprop[nmac],  sprop[nmac]);
 		choose_comp(&k->comp[mode], cprop[ncomp], sprop[ncomp]);
 		debug("kex: %s %s %s %s",
 		    ctos ? "client->server" : "server->client",
 		    k->enc[mode].name,
 		    k->mac[mode].name,
 		    k->comp[mode].name);
 	}
 	choose_kex(k, cprop[PROPOSAL_KEX_ALGS], sprop[PROPOSAL_KEX_ALGS]);
 	choose_hostkeyalg(k, cprop[PROPOSAL_SERVER_HOST_KEY_ALGS],
 	    sprop[PROPOSAL_SERVER_HOST_KEY_ALGS]);
 	need = 0;
 	for (mode = 0; mode < MODE_MAX; mode++) {
 	    if (need < k->enc[mode].cipher->key_len)
 		    need = k->enc[mode].cipher->key_len;
 	    if (need < k->enc[mode].cipher->block_size)
 		    need = k->enc[mode].cipher->block_size;
 	    if (need < k->mac[mode].key_len)
 		    need = k->mac[mode].key_len;
 	}
 	/* XXX need runden? */
 	k->we_need = need;
 	return k;
 }

 #define NKEYS	6
 int
 kex_derive_keys(Kex *k, u_char *hash, BIGNUM *shared_secret)
 {
 	int i;
 	int mode;
 	int ctos;
 	u_char *keys[NKEYS];

 	for (i = 0; i < NKEYS; i++)
 		keys[i] = derive_key('A'+i, k->we_need, hash, shared_secret);

 	for (mode = 0; mode < MODE_MAX; mode++) {
 		ctos = (!k->server && mode == MODE_OUT) || (k->server && mode == MODE_IN);
 		k->enc[mode].iv  = keys[ctos ? 0 : 1];
 		k->enc[mode].key = keys[ctos ? 2 : 3];
 		k->mac[mode].key = keys[ctos ? 4 : 5];
 	}
 	return 0;
 }
	/*
	* Copyright (c) 2000 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: kex.c,v 1.25 2001/03/29 21:17:39 markus Exp $");

	#include <openssl/crypto.h>
	#include <openssl/bio.h>
	#include <openssl/bn.h>
	#include <openssl/pem.h>

	#include "ssh2.h"
	#include "xmalloc.h"
	#include "buffer.h"
	#include "bufaux.h"
	#include "packet.h"
	#include "compat.h"
	#include "cipher.h"
	#include "kex.h"
	#include "key.h"
	#include "log.h"
	#include "mac.h"
	#include "match.h"

	#define KEX_COOKIE_LEN 16

	Buffer *
	kex_init(char *myproposal[PROPOSAL_MAX])
	{
	int first_kex_packet_follows = 0;
	u_char cookie[KEX_COOKIE_LEN];
	u_int32_t rand = 0;
	int i;
	Buffer ki = xmalloc(sizeof(ki));
	for (i = 0; i < KEX_COOKIE_LEN; i++) {
	if (i % 4 == 0)
	rand = arc4random();
	cookie[i] = rand & 0xff;
	rand >>= 8;
	}
	buffer_init(ki);
	buffer_append(ki, (char *)cookie, sizeof cookie);
	for (i = 0; i < PROPOSAL_MAX; i++)
	buffer_put_cstring(ki, myproposal[i]);
	buffer_put_char(ki, first_kex_packet_follows);
	buffer_put_int(ki, 0); /* uint32 reserved */
	return ki;
	}

	/* send kexinit, parse and save reply */
	void
	kex_exchange_kexinit(
	Buffer my_kexinit, Buffer peer_kexint,
	char *peer_proposal[PROPOSAL_MAX])
	{
	int i;
	char *ptr;
	int plen;

	debug("send KEXINIT");
	packet_start(SSH2_MSG_KEXINIT);
	packet_put_raw(buffer_ptr(my_kexinit), buffer_len(my_kexinit));
	packet_send();
	packet_write_wait();
	debug("done");

	/*
	* read and save raw KEXINIT payload in buffer. this is used during
	* computation of the session_id and the session keys.
	*/
	debug("wait KEXINIT");
	packet_read_expect(&plen, SSH2_MSG_KEXINIT);
	ptr = packet_get_raw(&plen);
	buffer_append(peer_kexint, ptr, plen);

	/* parse packet and save algorithm proposal */
	/* skip cookie */
	for (i = 0; i < KEX_COOKIE_LEN; i++)
	packet_get_char();
	/* extract kex init proposal strings */
	for (i = 0; i < PROPOSAL_MAX; i++) {
	peer_proposal[i] = packet_get_string(NULL);
	debug("got kexinit: %s", peer_proposal[i]);
	}
	/* first kex follow / reserved */
	i = packet_get_char();
	debug("first kex follow: %d ", i);
	i = packet_get_int();
	debug("reserved: %d ", i);
	packet_done();
	debug("done");
	}

	#ifdef DEBUG_KEX
	void
	dump_digest(u_char *digest, int len)
	{
	int i;
	for (i = 0; i< len; i++){
	fprintf(stderr, "%02x", digest[i]);
	if(i%2!=0)
	fprintf(stderr, " ");
	}
	fprintf(stderr, "\n");
	}
	#endif

	u_char *
	kex_hash(
	char *client_version_string,
	char *server_version_string,
	char *ckexinit, int ckexinitlen,
	char *skexinit, int skexinitlen,
	char *serverhostkeyblob, int sbloblen,
	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_string(&b, client_version_string, strlen(client_version_string));
	buffer_put_string(&b, server_version_string, strlen(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);
	buffer_put_bignum2(&b, client_dh_pub);
	buffer_put_bignum2(&b, server_dh_pub);
	buffer_put_bignum2(&b, shared_secret);

	#ifdef DEBUG_KEX
	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_KEX
	dump_digest(digest, evp_md->md_size);
	#endif
	return digest;
	}

	u_char *
	kex_hash_gex(
	char *client_version_string,
	char *server_version_string,
	char *ckexinit, int ckexinitlen,
	char *skexinit, int skexinitlen,
	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_string(&b, client_version_string, strlen(client_version_string));
	buffer_put_string(&b, server_version_string, strlen(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_KEX
	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_KEX
	dump_digest(digest, evp_md->md_size);
	#endif
	return digest;
	}

	u_char *
	derive_key(int id, int need, u_char hash, BIGNUM shared_secret)
	{
	Buffer b;
	EVP_MD *evp_md = EVP_sha1();
	EVP_MD_CTX md;
	char c = id;
	int have;
	int mdsz = evp_md->md_size;
	u_char digest = xmalloc(((need+mdsz-1)/mdsz)mdsz);

	buffer_init(&b);
	buffer_put_bignum2(&b, shared_secret);

	EVP_DigestInit(&md, evp_md);
	EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b)); /* shared_secret K */
	EVP_DigestUpdate(&md, hash, mdsz); /* transport-06 */
	EVP_DigestUpdate(&md, &c, 1); /* key id */
	EVP_DigestUpdate(&md, hash, mdsz); /* session id */
	EVP_DigestFinal(&md, digest, NULL);

	/* expand */
	for (have = mdsz; need > have; have += mdsz) {
	EVP_DigestInit(&md, evp_md);
	EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
	EVP_DigestUpdate(&md, hash, mdsz);
	EVP_DigestUpdate(&md, digest, have);
	EVP_DigestFinal(&md, digest + have, NULL);
	}
	buffer_free(&b);
	#ifdef DEBUG_KEX
	fprintf(stderr, "Digest '%c'== ", c);
	dump_digest(digest, need);
	#endif
	return digest;
	}

	void
	choose_enc(Enc enc, char client, char *server)
	{
	char *name = match_list(client, server, NULL);
	if (name == NULL)
	fatal("no matching cipher found: client %s server %s", client, server);
	enc->cipher = cipher_by_name(name);
	if (enc->cipher == NULL)
	fatal("matching cipher is not supported: %s", name);
	enc->name = name;
	enc->enabled = 0;
	enc->iv = NULL;
	enc->key = NULL;
	}
	void
	choose_mac(Mac mac, char client, char *server)
	{
	char *name = match_list(client, server, NULL);
	if (name == NULL)
	fatal("no matching mac found: client %s server %s", client, server);
	if (mac_init(mac, name) < 0)
	fatal("unsupported mac %s", name);
	/* truncate the key */
	if (datafellows & SSH_BUG_HMAC)
	mac->key_len = 16;
	mac->name = name;
	mac->key = NULL;
	mac->enabled = 0;
	}
	void
	choose_comp(Comp comp, char client, char *server)
	{
	char *name = match_list(client, server, NULL);
	if (name == NULL)
	fatal("no matching comp found: client %s server %s", client, server);
	if (strcmp(name, "zlib") == 0) {
	comp->type = 1;
	} else if (strcmp(name, "none") == 0) {
	comp->type = 0;
	} else {
	fatal("unsupported comp %s", name);
	}
	comp->name = name;
	}
	void
	choose_kex(Kex k, char client, char *server)
	{
	k->name = match_list(client, server, NULL);
	if (k->name == NULL)
	fatal("no kex alg");
	if (strcmp(k->name, KEX_DH1) == 0) {
	k->kex_type = DH_GRP1_SHA1;
	} else if (strcmp(k->name, KEX_DHGEX) == 0) {
	k->kex_type = DH_GEX_SHA1;
	} else
	fatal("bad kex alg %s", k->name);
	}
	void
	choose_hostkeyalg(Kex k, char client, char *server)
	{
	char *hostkeyalg = match_list(client, server, NULL);
	if (hostkeyalg == NULL)
	fatal("no hostkey alg");
	k->hostkey_type = key_type_from_name(hostkeyalg);
	if (k->hostkey_type == KEY_UNSPEC)
	fatal("bad hostkey alg '%s'", hostkeyalg);
	xfree(hostkeyalg);
	}

	Kex *
	kex_choose_conf(char cprop[PROPOSAL_MAX], char sprop[PROPOSAL_MAX], int server)
	{
	int mode;
	int ctos; /* direction: if true client-to-server */
	int need;
	Kex *k;

	k = xmalloc(sizeof(*k));
	memset(k, 0, sizeof(*k));
	k->server = server;

	for (mode = 0; mode < MODE_MAX; mode++) {
	int nenc, nmac, ncomp;
	ctos = (!k->server && mode == MODE_OUT) \|\| (k->server && mode == MODE_IN);
	nenc = ctos ? PROPOSAL_ENC_ALGS_CTOS : PROPOSAL_ENC_ALGS_STOC;
	nmac = ctos ? PROPOSAL_MAC_ALGS_CTOS : PROPOSAL_MAC_ALGS_STOC;
	ncomp = ctos ? PROPOSAL_COMP_ALGS_CTOS : PROPOSAL_COMP_ALGS_STOC;
	choose_enc (&k->enc [mode], cprop[nenc], sprop[nenc]);
	choose_mac (&k->mac [mode], cprop[nmac], sprop[nmac]);
	choose_comp(&k->comp[mode], cprop[ncomp], sprop[ncomp]);
	debug("kex: %s %s %s %s",
	ctos ? "client->server" : "server->client",
	k->enc[mode].name,
	k->mac[mode].name,
	k->comp[mode].name);
	}
	choose_kex(k, cprop[PROPOSAL_KEX_ALGS], sprop[PROPOSAL_KEX_ALGS]);
	choose_hostkeyalg(k, cprop[PROPOSAL_SERVER_HOST_KEY_ALGS],
	sprop[PROPOSAL_SERVER_HOST_KEY_ALGS]);
	need = 0;
	for (mode = 0; mode < MODE_MAX; mode++) {
	if (need < k->enc[mode].cipher->key_len)
	need = k->enc[mode].cipher->key_len;
	if (need < k->enc[mode].cipher->block_size)
	need = k->enc[mode].cipher->block_size;
	if (need < k->mac[mode].key_len)
	need = k->mac[mode].key_len;
	}
	/* XXX need runden? */
	k->we_need = need;
	return k;
	}

	#define NKEYS 6
	int
	kex_derive_keys(Kex k, u_char hash, BIGNUM *shared_secret)
	{
	int i;
	int mode;
	int ctos;
	u_char *keys[NKEYS];

	for (i = 0; i < NKEYS; i++)
	keys[i] = derive_key('A'+i, k->we_need, hash, shared_secret);

	for (mode = 0; mode < MODE_MAX; mode++) {
	ctos = (!k->server && mode == MODE_OUT) \|\| (k->server && mode == MODE_IN);
	k->enc[mode].iv = keys[ctos ? 0 : 1];
	k->enc[mode].key = keys[ctos ? 2 : 3];
	k->mac[mode].key = keys[ctos ? 4 : 5];
	}
	return 0;
	}