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+/* $OpenBSD: kexgexs.c,v 1.35 2018/10/04 00:04:41 djm Exp $ */
+/*
+ * 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"
+
+#ifdef WITH_OPENSSL
+
+
+#include <stdarg.h>
+#include <stdio.h>
+#include <string.h>
+#include <signal.h>
+
+#include <openssl/dh.h>
+
+#include "openbsd-compat/openssl-compat.h"
+
+#include "sshkey.h"
+#include "cipher.h"
+#include "digest.h"
+#include "kex.h"
+#include "log.h"
+#include "packet.h"
+#include "dh.h"
+#include "ssh2.h"
+#include "compat.h"
+#ifdef GSSAPI
+#include "ssh-gss.h"
+#endif
+#include "monitor_wrap.h"
+#include "dispatch.h"
+#include "ssherr.h"
+#include "sshbuf.h"
+#include "misc.h"
+
+static int input_kex_dh_gex_request(int, u_int32_t, struct ssh *);
+static int input_kex_dh_gex_init(int, u_int32_t, struct ssh *);
+
+int
+kexgex_server(struct ssh *ssh)
+{
+ ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_REQUEST,
+ &input_kex_dh_gex_request);
+ debug("expecting SSH2_MSG_KEX_DH_GEX_REQUEST");
+ return 0;
+}
+
+static int
+input_kex_dh_gex_request(int type, u_int32_t seq, struct ssh *ssh)
+{
+ struct kex *kex = ssh->kex;
+ int r;
+ u_int min = 0, max = 0, nbits = 0;
+ const BIGNUM *dh_p, *dh_g;
+
+ debug("SSH2_MSG_KEX_DH_GEX_REQUEST received");
+ if ((r = sshpkt_get_u32(ssh, &min)) != 0 ||
+ (r = sshpkt_get_u32(ssh, &nbits)) != 0 ||
+ (r = sshpkt_get_u32(ssh, &max)) != 0 ||
+ (r = sshpkt_get_end(ssh)) != 0)
+ goto out;
+ kex->nbits = nbits;
+ kex->min = min;
+ kex->max = max;
+ min = MAXIMUM(DH_GRP_MIN, min);
+ max = MINIMUM(DH_GRP_MAX, max);
+ nbits = MAXIMUM(DH_GRP_MIN, nbits);
+ nbits = MINIMUM(DH_GRP_MAX, nbits);
+
+ if (kex->max < kex->min || kex->nbits < kex->min ||
+ kex->max < kex->nbits || kex->max < DH_GRP_MIN) {
+ r = SSH_ERR_DH_GEX_OUT_OF_RANGE;
+ goto out;
+ }
+
+ /* Contact privileged parent */
+ kex->dh = PRIVSEP(choose_dh(min, nbits, max));
+ if (kex->dh == NULL) {
+ sshpkt_disconnect(ssh, "no matching DH grp found");
+ r = SSH_ERR_ALLOC_FAIL;
+ goto out;
+ }
+ debug("SSH2_MSG_KEX_DH_GEX_GROUP sent");
+ DH_get0_pqg(kex->dh, &dh_p, NULL, &dh_g);
+ if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_DH_GEX_GROUP)) != 0 ||
+ (r = sshpkt_put_bignum2(ssh, dh_p)) != 0 ||
+ (r = sshpkt_put_bignum2(ssh, dh_g)) != 0 ||
+ (r = sshpkt_send(ssh)) != 0)
+ goto out;
+
+ /* Compute our exchange value in parallel with the client */
+ if ((r = dh_gen_key(kex->dh, kex->we_need * 8)) != 0)
+ goto out;
+
+ debug("expecting SSH2_MSG_KEX_DH_GEX_INIT");
+ ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_INIT, &input_kex_dh_gex_init);
+ r = 0;
+ out:
+ return r;
+}
+
+static int
+input_kex_dh_gex_init(int type, u_int32_t seq, struct ssh *ssh)
+{
+ struct kex *kex = ssh->kex;
+ BIGNUM *shared_secret = NULL, *dh_client_pub = NULL;
+ const BIGNUM *pub_key, *dh_p, *dh_g;
+ struct sshkey *server_host_public, *server_host_private;
+ u_char *kbuf = NULL, *signature = NULL, *server_host_key_blob = NULL;
+ u_char hash[SSH_DIGEST_MAX_LENGTH];
+ size_t sbloblen, slen;
+ size_t klen = 0, hashlen;
+ int kout, r;
+
+ if (kex->load_host_public_key == NULL ||
+ kex->load_host_private_key == NULL) {
+ r = SSH_ERR_INVALID_ARGUMENT;
+ goto out;
+ }
+ server_host_public = kex->load_host_public_key(kex->hostkey_type,
+ kex->hostkey_nid, ssh);
+ server_host_private = kex->load_host_private_key(kex->hostkey_type,
+ kex->hostkey_nid, ssh);
+ if (server_host_public == NULL) {
+ r = SSH_ERR_NO_HOSTKEY_LOADED;
+ goto out;
+ }
+
+ /* key, cert */
+ if ((dh_client_pub = BN_new()) == NULL) {
+ r = SSH_ERR_ALLOC_FAIL;
+ goto out;
+ }
+ if ((r = sshpkt_get_bignum2(ssh, dh_client_pub)) != 0 ||
+ (r = sshpkt_get_end(ssh)) != 0)
+ goto out;
+
+ DH_get0_key(kex->dh, &pub_key, NULL);
+ DH_get0_pqg(kex->dh, &dh_p, NULL, &dh_g);
+
+#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));
+ DHparams_print_fp(stderr, kex->dh);
+ fprintf(stderr, "pub= ");
+ BN_print_fp(stderr, pub_key);
+ fprintf(stderr, "\n");
+#endif
+ if (!dh_pub_is_valid(kex->dh, dh_client_pub)) {
+ sshpkt_disconnect(ssh, "bad client public DH value");
+ r = SSH_ERR_MESSAGE_INCOMPLETE;
+ goto out;
+ }
+
+ klen = DH_size(kex->dh);
+ if ((kbuf = malloc(klen)) == NULL ||
+ (shared_secret = BN_new()) == NULL) {
+ r = SSH_ERR_ALLOC_FAIL;
+ goto out;
+ }
+ if ((kout = DH_compute_key(kbuf, dh_client_pub, kex->dh)) < 0 ||
+ BN_bin2bn(kbuf, kout, shared_secret) == NULL) {
+ r = SSH_ERR_LIBCRYPTO_ERROR;
+ goto out;
+ }
+#ifdef DEBUG_KEXDH
+ dump_digest("shared secret", kbuf, kout);
+#endif
+ if ((r = sshkey_to_blob(server_host_public, &server_host_key_blob,
+ &sbloblen)) != 0)
+ goto out;
+ /* calc H */
+ hashlen = sizeof(hash);
+ if ((r = kexgex_hash(
+ kex->hash_alg,
+ kex->client_version_string,
+ kex->server_version_string,
+ sshbuf_ptr(kex->peer), sshbuf_len(kex->peer),
+ sshbuf_ptr(kex->my), sshbuf_len(kex->my),
+ server_host_key_blob, sbloblen,
+ kex->min, kex->nbits, kex->max,
+ dh_p, dh_g,
+ dh_client_pub,
+ pub_key,
+ shared_secret,
+ hash, &hashlen)) != 0)
+ goto out;
+
+ /* save session id := H */
+ if (kex->session_id == NULL) {
+ kex->session_id_len = hashlen;
+ kex->session_id = malloc(kex->session_id_len);
+ if (kex->session_id == NULL) {
+ r = SSH_ERR_ALLOC_FAIL;
+ goto out;
+ }
+ memcpy(kex->session_id, hash, kex->session_id_len);
+ }
+
+ /* sign H */
+ if ((r = kex->sign(server_host_private, server_host_public, &signature,
+ &slen, hash, hashlen, kex->hostkey_alg, ssh->compat)) < 0)
+ goto out;
+
+ /* destroy_sensitive_data(); */
+
+ /* send server hostkey, DH pubkey 'f' and signed H */
+ if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_DH_GEX_REPLY)) != 0 ||
+ (r = sshpkt_put_string(ssh, server_host_key_blob, sbloblen)) != 0 ||
+ (r = sshpkt_put_bignum2(ssh, pub_key)) != 0 || /* f */
+ (r = sshpkt_put_string(ssh, signature, slen)) != 0 ||
+ (r = sshpkt_send(ssh)) != 0)
+ goto out;
+
+ if ((r = kex_derive_keys_bn(ssh, hash, hashlen, shared_secret)) == 0)
+ r = kex_send_newkeys(ssh);
+ out:
+ explicit_bzero(hash, sizeof(hash));
+ DH_free(kex->dh);
+ kex->dh = NULL;
+ BN_clear_free(dh_client_pub);
+ if (kbuf) {
+ explicit_bzero(kbuf, klen);
+ free(kbuf);
+ }
+ BN_clear_free(shared_secret);
+ free(server_host_key_blob);
+ free(signature);
+ return r;
+}
+#endif /* WITH_OPENSSL */