/* $OpenBSD: kexdh.c,v 1.35 2025/10/03 00:08:02 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 <stdio.h>

#include <string.h>

#include <signal.h>

#include "openbsd-compat/openssl-compat.h"

#include <openssl/bn.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:

    kex->dh = dh_new_group1();

    break;

  case KEX_DH_GRP14_SHA1:

  case KEX_DH_GRP14_SHA256:

    kex->dh = dh_new_group14();

    break;

  case KEX_DH_GRP16_SHA512:

    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 */