text: /* $OpenBSD: kexdh.c,v 1.34 2020/12/04 02:29:25 djm Exp $ */
  /*
   * Copyright (c) 2019 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 <sys/types.h>
  
  #include <signal.h>
  #include <stdio.h>
  #include <string.h>
  
  #include "openbsd-compat/openssl-compat.h"
  #include <openssl/dh.h>
  
  #include "sshkey.h"
  #include "kex.h"
  #include "sshbuf.h"
  #include "digest.h"
  #include "ssherr.h"
  #include "dh.h"
  #include "log.h"
  
  int
  kex_dh_keygen(struct kex *kex)
  {
  	switch (kex->kex_type) {
  	case KEX_DH_GRP1_SHA1:
  #ifdef GSSAPI
  	case KEX_GSS_GRP1_SHA1:
  #endif
  		kex->dh = dh_new_group1();
  		break;
  	case KEX_DH_GRP14_SHA1:
  	case KEX_DH_GRP14_SHA256:
  #ifdef GSSAPI
  	case KEX_GSS_GRP14_SHA1:
  	case KEX_GSS_GRP14_SHA256:
  #endif
  		kex->dh = dh_new_group14();
  		break;
  	case KEX_DH_GRP16_SHA512:
  #ifdef GSSAPI
  	case KEX_GSS_GRP16_SHA512:
  #endif
  		kex->dh = dh_new_group16();
  		break;
  	case KEX_DH_GRP18_SHA512:
  		kex->dh = dh_new_group18();
  		break;
  	default:
  		return SSH_ERR_INVALID_ARGUMENT;
  	}
  	if (kex->dh == NULL)
  		return SSH_ERR_ALLOC_FAIL;
  	return (dh_gen_key(kex->dh, kex->we_need * 8));
  }
  
  int
  kex_dh_compute_key(struct kex *kex, BIGNUM *dh_pub, struct sshbuf *out)
  {
  	BIGNUM *shared_secret = NULL;
  	u_char *kbuf = NULL;
  	size_t klen = 0;
  	int kout, r;
  
  #ifdef DEBUG_KEXDH
  	fprintf(stderr, "dh_pub= ");
  	BN_print_fp(stderr, dh_pub);
  	fprintf(stderr, "\n");
  	debug("bits %d", BN_num_bits(dh_pub));
  	DHparams_print_fp(stderr, kex->dh);
  	fprintf(stderr, "\n");
  #endif
  
  	if (!dh_pub_is_valid(kex->dh, dh_pub)) {
  		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_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
  	r = sshbuf_put_bignum2(out, shared_secret);
   out:
  	freezero(kbuf, klen);
  	BN_clear_free(shared_secret);
  	return r;
  }
  
  int
  kex_dh_keypair(struct kex *kex)
  {
  	const BIGNUM *pub_key;
  	struct sshbuf *buf = NULL;
  	int r;
  
  	if ((r = kex_dh_keygen(kex)) != 0)
  		return r;
  	DH_get0_key(kex->dh, &pub_key, NULL);
  	if ((buf = sshbuf_new()) == NULL)
  		return SSH_ERR_ALLOC_FAIL;
  	if ((r = sshbuf_put_bignum2(buf, pub_key)) != 0 ||
  	    (r = sshbuf_get_u32(buf, NULL)) != 0)
  		goto out;
  #ifdef DEBUG_KEXDH
  	DHparams_print_fp(stderr, kex->dh);
  	fprintf(stderr, "pub= ");
  	BN_print_fp(stderr, pub_key);
  	fprintf(stderr, "\n");
  #endif
  	kex->client_pub = buf;
  	buf = NULL;
   out:
  	sshbuf_free(buf);
  	return r;
  }
  
  int
  kex_dh_enc(struct kex *kex, const struct sshbuf *client_blob,
      struct sshbuf **server_blobp, struct sshbuf **shared_secretp)
  {
  	const BIGNUM *pub_key;
  	struct sshbuf *server_blob = NULL;
  	int r;
  
  	*server_blobp = NULL;
  	*shared_secretp = NULL;
  
  	if ((r = kex_dh_keygen(kex)) != 0)
  		goto out;
  	DH_get0_key(kex->dh, &pub_key, NULL);
  	if ((server_blob = sshbuf_new()) == NULL) {
  		r = SSH_ERR_ALLOC_FAIL;
  		goto out;
  	}
  	if ((r = sshbuf_put_bignum2(server_blob, pub_key)) != 0 ||
  	    (r = sshbuf_get_u32(server_blob, NULL)) != 0)
  		goto out;
  	if ((r = kex_dh_dec(kex, client_blob, shared_secretp)) != 0)
  		goto out;
  	*server_blobp = server_blob;
  	server_blob = NULL;
   out:
  	DH_free(kex->dh);
  	kex->dh = NULL;
  	sshbuf_free(server_blob);
  	return r;
  }
  
  int
  kex_dh_dec(struct kex *kex, const struct sshbuf *dh_blob,
      struct sshbuf **shared_secretp)
  {
  	struct sshbuf *buf = NULL;
  	BIGNUM *dh_pub = NULL;
  	int r;
  
  	*shared_secretp = NULL;
  
  	if ((buf = sshbuf_new()) == NULL) {
  		r = SSH_ERR_ALLOC_FAIL;
  		goto out;
  	}
  	if ((r = sshbuf_put_stringb(buf, dh_blob)) != 0 ||
  	    (r = sshbuf_get_bignum2(buf, &dh_pub)) != 0)
  		goto out;
  	sshbuf_reset(buf);
  	if ((r = kex_dh_compute_key(kex, dh_pub, buf)) != 0)
  		goto out;
  	*shared_secretp = buf;
  	buf = NULL;
   out:
  	BN_free(dh_pub);
  	DH_free(kex->dh);
  	kex->dh = NULL;
  	sshbuf_free(buf);
  	return r;
  }
  #endif /* WITH_OPENSSL */
  