4 files changed, 719 insertions, 3 deletions

diff --git a/ChangeLog b/ChangeLog
index 4b3c1f3d6..bc6879865 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -25,6 +25,7 @@
         (1) force rekeying with ~R, or
         (2) if the server requests rekeying.
      works against ssh-2.0.12/2.0.13/2.1.0/2.2.0/2.3.0/2.3.1/2.4.0
+ - (bal) Oops.. Missed including kexdh.c and kexgex.c in OpenBSD sync.
 
 20010403
  - OpenBSD CVS Sync
@@ -4835,4 +4836,4 @@
  - Wrote replacements for strlcpy and mkdtemp
  - Released 1.0pre1
 
-$Id: ChangeLog,v 1.1053 2001/04/04 02:03:04 mouring Exp $
+$Id: ChangeLog,v 1.1054 2001/04/04 17:39:19 mouring Exp $
diff --git a/Makefile.in b/Makefile.in
index 98d9a46c9..c1f197e40 100644
--- a/Makefile.in
+++ b/Makefile.in
@@ -1,4 +1,4 @@
-# $Id: Makefile.in,v 1.164 2001/03/30 00:55:20 djm Exp $
+# $Id: Makefile.in,v 1.165 2001/04/04 17:39:20 mouring Exp $
 
 prefix=@prefix@
 exec_prefix=@exec_prefix@
@@ -44,7 +44,7 @@ INSTALL_SSH_PRNG_CMDS=@INSTALL_SSH_PRNG_CMDS@
 
 TARGETS=ssh$(EXEEXT) sshd$(EXEEXT) ssh-add$(EXEEXT) ssh-keygen$(EXEEXT) ssh-keyscan${EXEEXT} ssh-agent$(EXEEXT) scp$(EXEEXT) $(SFTP_PROGS)
 
-LIBSSH_OBJS=atomicio.o authfd.o authfile.o bufaux.o buffer.o canohost.o channels.o cipher.o cli.o compat.o compress.o crc32.o deattack.o dh.o dispatch.o mac.o hostfile.o key.o kex.o log.o match.o misc.o mpaux.o nchan.o packet.o radix.o rijndael.o entropy.o readpass.o rsa.o ssh-dss.o ssh-rsa.o tildexpand.o ttymodes.o uidswap.o uuencode.o xmalloc.o 
+LIBSSH_OBJS=atomicio.o authfd.o authfile.o bufaux.o buffer.o canohost.o channels.o cipher.o cli.o compat.o compress.o crc32.o deattack.o dh.o dispatch.o mac.o hostfile.o key.o kex.o kexdh.o kexgex.o log.o match.o misc.o mpaux.o nchan.o packet.o radix.o rijndael.o entropy.o readpass.o rsa.o ssh-dss.o ssh-rsa.o tildexpand.o ttymodes.o uidswap.o uuencode.o xmalloc.o 
 
 SSHOBJS= ssh.o sshconnect.o sshconnect1.o sshconnect2.o readconf.o clientloop.o
 
diff --git a/kexdh.c b/kexdh.c
new file mode 100644
index 000000000..8449ec06a
--- /dev/null
+++ b/kexdh.c
@@ -0,0 +1,304 @@
+/*
+ * 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: kexdh.c,v 1.2 2001/04/03 23:32:12 markus Exp $");
+
+#include <openssl/crypto.h>
+#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"
+
+u_char *
+kex_dh_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("hash", digest, evp_md->md_size);
+#endif
+        return digest;
+}
+
+/* client */
+
+void
+kexdh_client(Kex *kex)
+{
+        BIGNUM *dh_server_pub = NULL, *shared_secret = NULL;
+        DH *dh;
+        Key *server_host_key;
+        char *server_host_key_blob = NULL, *signature = NULL;
+        u_char *kbuf, *hash;
+        u_int klen, kout, slen, sbloblen;
+        int dlen, plen;
+
+        /* generate and send 'e', client DH public key */
+        dh = dh_new_group1();
+        dh_gen_key(dh, kex->we_need * 8);
+        packet_start(SSH2_MSG_KEXDH_INIT);
+        packet_put_bignum2(dh->pub_key);
+        packet_send();
+
+        debug("sending SSH2_MSG_KEXDH_INIT");
+#ifdef DEBUG_KEXDH
+        DHparams_print_fp(stderr, dh);
+        fprintf(stderr, "pub= ");
+        BN_print_fp(stderr, dh->pub_key);
+        fprintf(stderr, "\n");
+#endif
+
+        debug("expecting SSH2_MSG_KEXDH_REPLY");
+        packet_read_expect(&plen, SSH2_MSG_KEXDH_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);
+
+        /* calc and verify H */
+        hash = kex_dh_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,
+            dh->pub_key,
+            dh_server_pub,
+            shared_secret
+        );
+        xfree(server_host_key_blob);
+        DH_free(dh);
+        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();
+}
+
+/* server */
+
+void
+kexdh_server(Kex *kex)
+{
+        BIGNUM *shared_secret = NULL, *dh_client_pub = NULL;
+        DH *dh;
+        Key *server_host_key;
+        u_char *kbuf, *hash, *signature = NULL, *server_host_key_blob = NULL;
+        u_int sbloblen, klen, kout;
+        int dlen, slen, plen;
+
+        /* generate server DH public key */
+        dh = dh_new_group1();
+        dh_gen_key(dh, kex->we_need * 8);
+
+        debug("expecting SSH2_MSG_KEXDH_INIT");
+        packet_read_expect(&plen, SSH2_MSG_KEXDH_INIT);
+
+        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);
+
+        /* 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);
+
+        /* calc H */
+        hash = kex_dh_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,
+            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 */
+        packet_start(SSH2_MSG_KEXDH_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
+kexdh(Kex *kex)
+{
+        if (kex->server)
+                kexdh_server(kex);
+        else
+                kexdh_client(kex);
+}
diff --git a/kexgex.c b/kexgex.c
new file mode 100644
index 000000000..6e8be78b5
--- /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);
+}