text: /* $OpenBSD: kexgexs.c,v 1.30 2016/09/12 01:22:38 deraadt 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 "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, void *);
  static int input_kex_dh_gex_init(int, u_int32_t, void *);
  
  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, void *ctxt)
  {
  	struct ssh *ssh = ctxt;
  	struct kex *kex = ssh->kex;
  	int r;
  	u_int min = 0, max = 0, nbits = 0;
  
  	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");
  	if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_DH_GEX_GROUP)) != 0 ||
  	    (r = sshpkt_put_bignum2(ssh, kex->dh->p)) != 0 ||
  	    (r = sshpkt_put_bignum2(ssh, kex->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, void *ctxt)
  {
  	struct ssh *ssh = ctxt;
  	struct kex *kex = ssh->kex;
  	BIGNUM *shared_secret = NULL, *dh_client_pub = NULL;
  	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;
  
  #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, kex->dh);
  	fprintf(stderr, "pub= ");
  	BN_print_fp(stderr, kex->dh->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,
  	    kex->dh->p, kex->dh->g,
  	    dh_client_pub,
  	    kex->dh->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 singed 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, kex->dh->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:
  	DH_free(kex->dh);
  	kex->dh = NULL;
  	if (dh_client_pub)
  		BN_clear_free(dh_client_pub);
  	if (kbuf) {
  		explicit_bzero(kbuf, klen);
  		free(kbuf);
  	}
  	if (shared_secret)
  		BN_clear_free(shared_secret);
  	free(server_host_key_blob);
  	free(signature);
  	return r;
  }
  #endif /* WITH_OPENSSL */
  