path: root/lib/auth/rsa_psk.c

/*
 * Copyright (C) 2000, 2001, 2002, 2003, 2004, 2005, 2007, 2009, 2010
 * Free Software Foundation, Inc.
 *
 * Copyright (C) 2011
 * Bardenheuer GmbH, Munich and Bundesdruckerei GmbH, Berlin
 *
 * Copyright (C) 2013 Frank Morgner
 * Copyright (C) 2013 Nikos Mavrogiannopoulos
 *
 * This file is part of GnuTLS.
 *
 * The GnuTLS is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public License
 * as published by the Free Software Foundation; either version 2.1 of
 * the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301,
 * USA
 *
 */

#include <gnutls_int.h>

#ifdef ENABLE_PSK

#include "gnutls_auth.h"
#include "gnutls_dh.h"
#include "gnutls_errors.h"
#include "gnutls_mpi.h"
#include "gnutls_num.h"
#include "gnutls_int.h"
#include "gnutls_pk.h"
#include "random.h"
#include <abstract_int.h>
#include <algorithms.h>
#include <auth/dh_common.h>
#include <auth/psk.h>
#include <auth/psk_passwd.h>
#include <auth/rsa_common.h>
#include <cert.h>
#include <gnutls_datum.h>
#include <gnutls_state.h>

static int _gnutls_gen_rsa_psk_client_kx (gnutls_session_t session,
                                          gnutls_buffer_st * data);
static int _gnutls_proc_rsa_psk_client_kx (gnutls_session_t, uint8_t *,
                                           size_t);

const mod_auth_st rsa_psk_auth_struct = {
  "RSA PSK",
  _gnutls_gen_cert_server_crt,
  NULL,                         /* generate_client_certificate */
  _gnutls_gen_psk_server_kx,
  _gnutls_gen_rsa_psk_client_kx,
  NULL,                         /* generate_client_cert_vrfy */
  NULL,                         /* generate_server_certificate_request */
  _gnutls_proc_crt,
  NULL,                         /* process_client_certificate */
  _gnutls_proc_psk_server_kx,
  _gnutls_proc_rsa_psk_client_kx,
  NULL,                         /* process_client_cert_vrfy */
  NULL                          /* process_server_certificate_reuqest */
};

/* Set the PSK premaster secret.
 */
static int
set_rsa_psk_session_key (gnutls_session_t session,
                         gnutls_datum_t *ppsk, gnutls_datum_t * rsa_secret)
{
  unsigned char *p;
  size_t rsa_secret_size;
  int ret;


  rsa_secret_size = rsa_secret->size;

  /* set the session key
   */
  session->key.key.size = 2 + rsa_secret_size + 2 + ppsk->size;
  session->key.key.data = gnutls_malloc (session->key.key.size);
  if (session->key.key.data == NULL)
    {
      gnutls_assert ();
      ret = GNUTLS_E_MEMORY_ERROR;
      goto error;
    }

  /* format of the premaster secret:
   * (uint16_t) other_secret size (48)
   * other_secret: 2 byte version + 46 byte random
   * (uint16_t) psk_size
   * the psk
   */
  _gnutls_write_uint16 (rsa_secret_size, session->key.key.data);
  memcpy (&session->key.key.data[2], rsa_secret->data, rsa_secret->size);
  p = &session->key.key.data[rsa_secret_size + 2];
  _gnutls_write_uint16 (ppsk->size, p);
  if (ppsk->data != NULL)
    memcpy (p + 2, ppsk->data, ppsk->size);

  ret = 0;

error:
  return ret;
}

/* Generate client key exchange message
 *
 *
 * struct {
 *    select (KeyExchangeAlgorithm) {
 *       uint8_t psk_identity<0..2^16-1>;
 *       EncryptedPreMasterSecret;
 *    } exchange_keys;
 * } ClientKeyExchange;
 */
static int
_gnutls_gen_rsa_psk_client_kx (gnutls_session_t session,
                               gnutls_buffer_st * data)
{
  cert_auth_info_t auth = session->key.auth_info;
  gnutls_datum_t sdata;         /* data to send */
  gnutls_pk_params_st params;
  gnutls_psk_client_credentials_t cred;
  gnutls_datum_t username, key;
  int ret, free;

  if (auth == NULL)
    {
      /* this shouldn't have happened. The proc_certificate
       * function should have detected that.
       */
      gnutls_assert ();
      return GNUTLS_E_INSUFFICIENT_CREDENTIALS;
    }

  gnutls_datum_t premaster_secret;
  premaster_secret.size = GNUTLS_MASTER_SIZE;
  premaster_secret.data = gnutls_secure_malloc (premaster_secret.size);

  if (premaster_secret.data == NULL)
    {
      gnutls_assert ();
      return GNUTLS_E_MEMORY_ERROR;
    }

  /* Generate random */
  ret = _gnutls_rnd (GNUTLS_RND_RANDOM, premaster_secret.data,
                     premaster_secret.size);
  if (ret < 0)
    {
      gnutls_assert ();
      return ret;
    }

  /* Set version */
  if (session->internals.rsa_pms_version[0] == 0)
    {
      premaster_secret.data[0] = _gnutls_get_adv_version_major (session);
      premaster_secret.data[1] = _gnutls_get_adv_version_minor (session);
    }
  else
    {                           /* use the version provided */
      premaster_secret.data[0] = session->internals.rsa_pms_version[0];
      premaster_secret.data[1] = session->internals.rsa_pms_version[1];
    }

  /* move RSA parameters to key (session).
   */
  if ((ret = _gnutls_get_public_rsa_params (session, &params)) < 0)
    {
      gnutls_assert ();
      return ret;
    }

  /* Encrypt premaster secret */
  if ((ret =
       _gnutls_pk_encrypt (GNUTLS_PK_RSA, &sdata, &premaster_secret,
                           &params)) < 0)
    {
      gnutls_assert ();
      return ret;
    }

  gnutls_pk_params_release (&params);

  cred = (gnutls_psk_client_credentials_t)
    _gnutls_get_cred (session, GNUTLS_CRD_PSK, NULL);

  if (cred == NULL)
    {
      gnutls_assert ();
      return GNUTLS_E_INSUFFICIENT_CREDENTIALS;
    }

  ret = _gnutls_find_psk_key( session, cred, &username, &key, &free);
  if (ret < 0)
    return gnutls_assert_val(ret);

  /* Here we set the PSK key */
  ret = set_rsa_psk_session_key (session, &key, &premaster_secret);
  if (ret < 0)
    {
      gnutls_assert ();
      goto cleanup;
    }

  /* Create message for client key exchange
   *
   * struct {
   *   uint8_t psk_identity<0..2^16-1>;
   *   EncryptedPreMasterSecret;
   * }
   */

  /* Write psk_identity and EncryptedPreMasterSecret into data stream
   */
  ret = _gnutls_buffer_append_data_prefix (data, 16, cred->username.data,
                                           cred->username.size);
  if (ret < 0)
    {
      gnutls_assert();
      goto cleanup;
    }

  ret = _gnutls_buffer_append_data_prefix (data, 16, sdata.data, sdata.size);
  if (ret < 0)
    {
      gnutls_assert();
      goto cleanup;
    }

  ret = 0;

cleanup:
  _gnutls_free_datum (&sdata);
  _gnutls_free_datum (&premaster_secret);
  if (free)
    {
      gnutls_free(key.data);
      gnutls_free(username.data);
    }

  return data->length;
}

/*
  Process the client key exchange message
*/
static int
_gnutls_proc_rsa_psk_client_kx (gnutls_session_t session, uint8_t * data,
                                size_t _data_size)
{
  gnutls_datum_t username;
  psk_auth_info_t info;
  gnutls_datum_t plaintext;
  gnutls_datum_t ciphertext;
  gnutls_datum_t pwd_psk = {NULL, 0};
  int ret, dsize;
  int randomize_key = 0;
  ssize_t data_size = _data_size;
  gnutls_psk_server_credentials_t cred;
  gnutls_datum_t premaster_secret = {NULL, 0};

  cred = (gnutls_psk_server_credentials_t)
    _gnutls_get_cred (session, GNUTLS_CRD_PSK, NULL);

  if (cred == NULL)
    {
      gnutls_assert ();
      return GNUTLS_E_INSUFFICIENT_CREDENTIALS;
    }

  ret = _gnutls_auth_info_set (session, GNUTLS_CRD_PSK,
                               sizeof (psk_auth_info_st), 1);
  if (ret < 0)
    {
      gnutls_assert ();
      return ret;
    }

  /*** 1. Extract user psk_identity ***/

  DECR_LEN (data_size, 2);
  username.size = _gnutls_read_uint16 (&data[0]);

  DECR_LEN (data_size, username.size);

  username.data = &data[2];

  /* copy the username to the auth info structures
   */
  info = _gnutls_get_auth_info (session);

  if (username.size > MAX_USERNAME_SIZE)
    {
      gnutls_assert ();
      return GNUTLS_E_ILLEGAL_SRP_USERNAME;
    }

  memcpy (info->username, username.data, username.size);
  info->username[username.size] = 0;

  /* Adjust data so it points to EncryptedPreMasterSecret */
  data += username.size + 2;

  /*** 2. Decrypt and extract EncryptedPreMasterSecret ***/

  DECR_LEN (data_size, 2);
  ciphertext.data = &data[2];
  dsize = _gnutls_read_uint16 (data);

  if (dsize != data_size)
    {
      gnutls_assert ();
      return GNUTLS_E_UNEXPECTED_PACKET_LENGTH;
    }
  ciphertext.size = dsize;

  ret = gnutls_privkey_decrypt_data (session->internals.selected_key, 0,
                                     &ciphertext, &plaintext);
  if (ret < 0 || plaintext.size != GNUTLS_MASTER_SIZE)
    {
      /* In case decryption fails then don't inform
       * the peer. Just use a random key. (in order to avoid
       * attack against pkcs-1 formating).
       */
      gnutls_assert ();
      _gnutls_debug_log ("auth_rsa_psk: Possible PKCS #1 format attack\n");
      randomize_key = 1;
    }
  else
    {
      /* If the secret was properly formatted, then
       * check the version number.
       */
      if (_gnutls_get_adv_version_major (session) != plaintext.data[0] ||
          (session->internals.priorities.allow_wrong_pms == 0 &&
           _gnutls_get_adv_version_minor (session) != plaintext.data[1]))
        {
          /* No error is returned here, if the version number check
           * fails. We proceed normally.
           * That is to defend against the attack described in the paper
           * "Attacking RSA-based sessions in SSL/TLS" by Vlastimil Klima,
           * Ondej Pokorny and Tomas Rosa.
           */
          gnutls_assert ();
          _gnutls_debug_log
            ("auth_rsa: Possible PKCS #1 version check format attack\n");
        }
    }


  if (randomize_key != 0)
    {
      premaster_secret.size = GNUTLS_MASTER_SIZE;
      premaster_secret.data = gnutls_malloc (premaster_secret.size);
      if (premaster_secret.data == NULL)
        {
          gnutls_assert ();
          return GNUTLS_E_MEMORY_ERROR;
        }

      /* we do not need strong random numbers here.
       */
      ret = _gnutls_rnd (GNUTLS_RND_NONCE, premaster_secret.data,
                         premaster_secret.size);
      if (ret < 0)
        {
          gnutls_assert ();
          goto cleanup;
        }
    }
  else
    {
      premaster_secret.data = plaintext.data;
      premaster_secret.size = plaintext.size;
    }

  /* This is here to avoid the version check attack
   * discussed above.
   */

  premaster_secret.data[0] = _gnutls_get_adv_version_major (session);
  premaster_secret.data[1] = _gnutls_get_adv_version_minor (session);

  /* find the key of this username
   */
  ret = _gnutls_psk_pwd_find_entry (session, info->username, &pwd_psk);
  if (ret < 0)
    {
      gnutls_assert();
      goto cleanup;
    }

  ret = set_rsa_psk_session_key (session, &pwd_psk, &premaster_secret);
  if (ret < 0)
    {
      gnutls_assert ();
      goto cleanup;
    }

  ret = 0;
cleanup:
  _gnutls_free_datum (&pwd_psk);
  _gnutls_free_datum (&premaster_secret);

  return ret;
}

#endif /* ENABLE_PSK */