diff --git a/kexgex.c b/kexgex.c
new file mode 100644
index 0000000..6e8be78
--- /dev/null
+++ b/kexgex.c
@@ -0,0 +1,411 @@
+/*
+ * 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 1.2 2001/04/03 23:32:12 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"
+
+u_char *
+kexgex_hash(
+    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_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 */
+
+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->check_host_key == NULL)
+		fatal("cannot check server_host_key");
+	kex->check_host_key(server_host_key);
+
+	/* 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
+	);
+	xfree(server_host_key_blob);
+	BN_free(dh_server_pub);
+
+	if (key_verify(server_host_key, (u_char *)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_send_newkeys();
+
+	/* have keys, free DH */
+	DH_free(dh);
+}
+
+/* server */
+
+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");
+	}
+	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),
+	    (char *)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((char *)server_host_key_blob, sbloblen);
+	packet_put_bignum2(dh->pub_key);	/* f */
+	packet_put_string((char *)signature, slen);
+	packet_send();
+	xfree(signature);
+	xfree(server_host_key_blob);
+
+	kex_derive_keys(kex, hash, shared_secret);
+	BN_clear_free(shared_secret);
+
+	kex_send_newkeys();
+
+	/* have keys, free DH */
+	DH_free(dh);
+}
+
+void
+kexgex(Kex *kex)
+{
+	if (kex->server)
+		kexgex_server(kex);
+	else
+		kexgex_client(kex);
+}