/* $OpenBSD: kexecdh.c,v 1.11 2025/10/03 00:08:02 djm Exp $ */

/*

 * Copyright (c) 2010 Damien Miller.  All rights reserved.

 * 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"

#if defined(WITH_OPENSSL) && defined(OPENSSL_HAS_ECC)

#include <sys/types.h>

#include <stdio.h>

#include <string.h>

#include <signal.h>

#include <openssl/bn.h>

#include <openssl/ecdh.h>

#include "sshkey.h"

#include "kex.h"

#include "sshbuf.h"

#include "digest.h"

#include "ssherr.h"

static int

kex_ecdh_dec_key_group(struct kex *, const struct sshbuf *, EC_KEY *key,

    const EC_GROUP *, struct sshbuf **);

int

kex_ecdh_keypair(struct kex *kex)

{

  EC_KEY *client_key = NULL;

  const EC_GROUP *group;

  const EC_POINT *public_key;

  struct sshbuf *buf = NULL;

  int r;

  if ((client_key = EC_KEY_new_by_curve_name(kex->ec_nid)) == NULL) {

    r = SSH_ERR_ALLOC_FAIL;

    goto out;

  }

  if (EC_KEY_generate_key(client_key) != 1) {

    r = SSH_ERR_LIBCRYPTO_ERROR;

    goto out;

  }

  group = EC_KEY_get0_group(client_key);

  public_key = EC_KEY_get0_public_key(client_key);

  if ((buf = sshbuf_new()) == NULL) {

    r = SSH_ERR_ALLOC_FAIL;

    goto out;

  }

  if ((r = sshbuf_put_ec(buf, public_key, group)) != 0 ||

      (r = sshbuf_get_u32(buf, NULL)) != 0)

    goto out;

#ifdef DEBUG_KEXECDH

  fputs("client private key:\n", stderr);

  sshkey_dump_ec_key(client_key);

#endif

  kex->ec_client_key = client_key;

  kex->ec_group = group;

  client_key = NULL; /* owned by the kex */

  kex->client_pub = buf;

  buf = NULL;

 out:

  EC_KEY_free(client_key);

  sshbuf_free(buf);

  return r;

}

int

kex_ecdh_enc(struct kex *kex, const struct sshbuf *client_blob,

    struct sshbuf **server_blobp, struct sshbuf **shared_secretp)

{

  const EC_GROUP *group;

  const EC_POINT *pub_key;

  EC_KEY *server_key = NULL;

  struct sshbuf *server_blob = NULL;

  int r;

  *server_blobp = NULL;

  *shared_secretp = NULL;

  if ((server_key = EC_KEY_new_by_curve_name(kex->ec_nid)) == NULL) {

    r = SSH_ERR_ALLOC_FAIL;

    goto out;

  }

  if (EC_KEY_generate_key(server_key) != 1) {

    r = SSH_ERR_LIBCRYPTO_ERROR;

    goto out;

  }

  group = EC_KEY_get0_group(server_key);

#ifdef DEBUG_KEXECDH

  fputs("server private key:\n", stderr);

  sshkey_dump_ec_key(server_key);

#endif

  pub_key = EC_KEY_get0_public_key(server_key);

  if ((server_blob = sshbuf_new()) == NULL) {

    r = SSH_ERR_ALLOC_FAIL;

    goto out;

  }

  if ((r = sshbuf_put_ec(server_blob, pub_key, group)) != 0 ||

      (r = sshbuf_get_u32(server_blob, NULL)) != 0)

    goto out;

  if ((r = kex_ecdh_dec_key_group(kex, client_blob, server_key, group,

      shared_secretp)) != 0)

    goto out;

  *server_blobp = server_blob;

  server_blob = NULL;

 out:

  EC_KEY_free(server_key);

  sshbuf_free(server_blob);

  return r;

}

static int

kex_ecdh_dec_key_group(struct kex *kex, const struct sshbuf *ec_blob,

    EC_KEY *key, const EC_GROUP *group, struct sshbuf **shared_secretp)

{

  struct sshbuf *buf = NULL;

  BIGNUM *shared_secret = NULL;

  EC_POINT *dh_pub = NULL;

  u_char *kbuf = NULL;

  size_t klen = 0;

  int r;

  *shared_secretp = NULL;

  if ((buf = sshbuf_new()) == NULL) {

    r = SSH_ERR_ALLOC_FAIL;

    goto out;

  }

  if ((r = sshbuf_put_stringb(buf, ec_blob)) != 0)

    goto out;

  if ((dh_pub = EC_POINT_new(group)) == NULL) {

    r = SSH_ERR_ALLOC_FAIL;

    goto out;

  }

  if ((r = sshbuf_get_ec(buf, dh_pub, group)) != 0) {

    goto out;

  }

  sshbuf_reset(buf);

#ifdef DEBUG_KEXECDH

  fputs("public key:\n", stderr);

  sshkey_dump_ec_point(group, dh_pub);

#endif

  if (sshkey_ec_validate_public(group, dh_pub) != 0) {

    r = SSH_ERR_MESSAGE_INCOMPLETE;

    goto out;

  }

  klen = (EC_GROUP_get_degree(group) + 7) / 8;

  if ((kbuf = malloc(klen)) == NULL ||

      (shared_secret = BN_new()) == NULL) {

    r = SSH_ERR_ALLOC_FAIL;

    goto out;

  }

  if (ECDH_compute_key(kbuf, klen, dh_pub, key, NULL) != (int)klen ||

      BN_bin2bn(kbuf, klen, shared_secret) == NULL) {

    r = SSH_ERR_LIBCRYPTO_ERROR;

    goto out;

  }

#ifdef DEBUG_KEXECDH

  dump_digest("shared secret", kbuf, klen);

#endif

  if ((r = sshbuf_put_bignum2(buf, shared_secret)) != 0)

    goto out;

  *shared_secretp = buf;

  buf = NULL;

 out:

  EC_POINT_clear_free(dh_pub);

  BN_clear_free(shared_secret);

  freezero(kbuf, klen);

  sshbuf_free(buf);

  return r;

}

int

kex_ecdh_dec(struct kex *kex, const struct sshbuf *server_blob,

    struct sshbuf **shared_secretp)

{

  int r;

  r = kex_ecdh_dec_key_group(kex, server_blob, kex->ec_client_key,

      kex->ec_group, shared_secretp);

  EC_KEY_free(kex->ec_client_key);

  kex->ec_client_key = NULL;

  return r;

}

#else

#include "ssherr.h"

struct kex;

struct sshbuf;

struct sshkey;

int

kex_ecdh_keypair(struct kex *kex)

{

  return SSH_ERR_SIGN_ALG_UNSUPPORTED;

}

int

kex_ecdh_enc(struct kex *kex, const struct sshbuf *client_blob,

    struct sshbuf **server_blobp, struct sshbuf **shared_secretp)

{

  return SSH_ERR_SIGN_ALG_UNSUPPORTED;

}

int

kex_ecdh_dec(struct kex *kex, const struct sshbuf *server_blob,

    struct sshbuf **shared_secretp)

{

  return SSH_ERR_SIGN_ALG_UNSUPPORTED;

}

#endif /* defined(WITH_OPENSSL) && defined(OPENSSL_HAS_ECC) */