/* pubkey-enc.c - Process a public key encoded packet.

 * Copyright (C) 1998, 1999, 2000, 2001, 2002, 2006, 2009,

 *               2010 Free Software Foundation, Inc.

 *

 * This file is part of GnuPG.

 *

 * GnuPG is free software; you can redistribute it and/or modify

 * it under the terms of the GNU General Public License as published by

 * the Free Software Foundation; either version 3 of the License, or

 * (at your option) any later version.

 *

 * GnuPG 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 General Public License for more details.

 *

 * You should have received a copy of the GNU General Public License

 * along with this program; if not, see <https://www.gnu.org/licenses/>.

 */

#include <config.h>

#include <stdio.h>

#include <stdlib.h>

#include <string.h>

#include "gpg.h"

#include "../common/util.h"

#include "packet.h"

#include "keydb.h"

#include "trustdb.h"

#include "../common/status.h"

#include "options.h"

#include "main.h"

#include "../common/i18n.h"

#include "pkglue.h"

#include "call-agent.h"

#include "../common/host2net.h"

#include "../common/compliance.h"

static gpg_error_t get_it (ctrl_t ctrl, struct pubkey_enc_list *k,

                           DEK *dek, PKT_public_key *sk, u32 *keyid);

/* Check that the given algo is mentioned in one of the valid user-ids. */

static int

is_algo_in_prefs (kbnode_t keyblock, preftype_t type, int algo)

{

  kbnode_t k;

  for (k = keyblock; k; k = k->next)

    {

      if (k->pkt->pkttype == PKT_USER_ID)

        {

          PKT_user_id *uid = k->pkt->pkt.user_id;

          prefitem_t *prefs = uid->prefs;

          if (uid->created && prefs && !uid->flags.revoked && !uid->flags.expired)

            {

              for (; prefs->type; prefs++)

                if (prefs->type == type && prefs->value == algo)

                  return 1;

            }

        }

    }

  return 0;

}

/*

 * Get the session key from a pubkey enc packet and return it in DEK,

 * which should have been allocated in secure memory by the caller.

 */

gpg_error_t

get_session_key (ctrl_t ctrl, struct pubkey_enc_list *list, DEK *dek)

{

  PKT_public_key *sk = NULL;

  gpg_error_t err;

  void *enum_context = NULL;

  u32 keyid[2];

  int search_for_secret_keys = 1;

  struct pubkey_enc_list *k;

  if (DBG_CLOCK)

    log_clock ("get_session_key enter");

  while (search_for_secret_keys)

    {

      sk = xmalloc_clear (sizeof *sk);

      err = enum_secret_keys (ctrl, &enum_context, sk);

      if (err)

        break;

      /* Check compliance.  */

      if (! gnupg_pk_is_allowed (opt.compliance, PK_USE_DECRYPTION,

                                 sk->pubkey_algo, 0,

                                 sk->pkey, nbits_from_pk (sk), NULL))

        {

          log_info (_("key %s is not suitable for decryption"

                      " in %s mode\n"),

                    keystr_from_pk (sk),

                    gnupg_compliance_option_string (opt.compliance));

          continue;

        }

      /* FIXME: The list needs to be sorted so that we try the keys in

       * an appropriate order.  For example:

       * - On-disk keys w/o protection

       * - On-disk keys with a cached passphrase

       * - On-card keys of an active card

       * - On-disk keys with protection

       * - On-card keys from cards which are not plugged it.  Here a

       *   cancel-all button should stop asking for other cards.

       * Without any anonymous keys the sorting can be skipped.

       */

      for (k = list; k; k = k->next)

        {

          if (!(k->pubkey_algo == PUBKEY_ALGO_ELGAMAL_E

                || k->pubkey_algo == PUBKEY_ALGO_ECDH

                || k->pubkey_algo == PUBKEY_ALGO_RSA

                || k->pubkey_algo == PUBKEY_ALGO_RSA_E

                || k->pubkey_algo == PUBKEY_ALGO_ELGAMAL))

            continue;

          if (openpgp_pk_test_algo2 (k->pubkey_algo, PUBKEY_USAGE_ENC))

            continue;

          if (sk->pubkey_algo != k->pubkey_algo)

            continue;

          keyid_from_pk (sk, keyid);

          if (!k->keyid[0] && !k->keyid[1])

            {

              if (opt.skip_hidden_recipients)

                continue;

              if (!opt.quiet)

                log_info (_("anonymous recipient; trying secret key %s ...\n"),

                          keystr (keyid));

            }

          else if (opt.try_all_secrets

                   || (k->keyid[0] == keyid[0] && k->keyid[1] == keyid[1]))

            {

              if (!opt.quiet && !(sk->pubkey_usage & PUBKEY_USAGE_ENC))

                log_info (_("used key is not marked for encryption use.\n"));

            }

          else

            continue;

          err = get_it (ctrl, k, dek, sk, keyid);

          k->result = err;

          if (!err)

            {

              if (!opt.quiet && !k->keyid[0] && !k->keyid[1])

                {

                  log_info (_("okay, we are the anonymous recipient.\n"));

                  if (!(sk->pubkey_usage & PUBKEY_USAGE_ENC))

                    log_info (_("used key is not marked for encryption use.\n")

                              );

                }

              search_for_secret_keys = 0;

              break;

            }

          else if (gpg_err_code (err) == GPG_ERR_FULLY_CANCELED)

            {

              search_for_secret_keys = 0;

              break; /* Don't try any more secret keys.  */

            }

        }

    }

  enum_secret_keys (ctrl, &enum_context, NULL);  /* free context */

  if (gpg_err_code (err) == GPG_ERR_EOF)

    {

      err = gpg_error (GPG_ERR_NO_SECKEY);

      /* Return the last specific error, if any.  */

      for (k = list; k; k = k->next)

        if (k->result != -1)

          err = k->result;

    }

  if (DBG_CLOCK)

    log_clock ("get_session_key leave");

  return err;

}

static gpg_error_t

get_it (ctrl_t ctrl,

        struct pubkey_enc_list *enc, DEK *dek, PKT_public_key *sk, u32 *keyid)

{

  gpg_error_t err;

  byte *frame = NULL;

  unsigned int n;

  size_t nframe;

  u16 csum, csum2;

  int padding;

  gcry_sexp_t s_data;

  char *desc;

  char *keygrip;

  byte fp[MAX_FINGERPRINT_LEN];

  if (DBG_CLOCK)

    log_clock ("decryption start");

  /* Get the keygrip.  */

  err = hexkeygrip_from_pk (sk, &keygrip);

  if (err)

    goto leave;

  /* Convert the data to an S-expression.  */

  if (sk->pubkey_algo == PUBKEY_ALGO_ELGAMAL

      || sk->pubkey_algo == PUBKEY_ALGO_ELGAMAL_E)

    {

      if (!enc->data[0] || !enc->data[1])

        err = gpg_error (GPG_ERR_BAD_MPI);

      else

        err = gcry_sexp_build (&s_data, NULL, "(enc-val(elg(a%m)(b%m)))",

                               enc->data[0], enc->data[1]);

    }

  else if (sk->pubkey_algo == PUBKEY_ALGO_RSA

           || sk->pubkey_algo == PUBKEY_ALGO_RSA_E)

    {

      if (!enc->data[0])

        err = gpg_error (GPG_ERR_BAD_MPI);

      else

        err = gcry_sexp_build (&s_data, NULL, "(enc-val(rsa(a%m)))",

                               enc->data[0]);

    }

  else if (sk->pubkey_algo == PUBKEY_ALGO_ECDH)

    {

      if (!enc->data[0] || !enc->data[1])

        err = gpg_error (GPG_ERR_BAD_MPI);

      else

        err = gcry_sexp_build (&s_data, NULL, "(enc-val(ecdh(s%m)(e%m)))",

                               enc->data[1], enc->data[0]);

    }

  else

    err = gpg_error (GPG_ERR_BUG);

  if (err)

    goto leave;

  if (sk->pubkey_algo == PUBKEY_ALGO_ECDH)

    fingerprint_from_pk (sk, fp, NULL);

  /* Decrypt. */

  desc = gpg_format_keydesc (ctrl, sk, FORMAT_KEYDESC_NORMAL, 1);

  err = agent_pkdecrypt (NULL, keygrip,

                         desc, sk->keyid, sk->main_keyid, sk->pubkey_algo,

                         s_data, &frame, &nframe, &padding);

  xfree (desc);

  gcry_sexp_release (s_data);

  if (err)

    goto leave;

  /* Now get the DEK (data encryption key) from the frame

   *

   * Old versions encode the DEK in this format (msb is left):

   *

   *     0  1  DEK(16 bytes)  CSUM(2 bytes)  0  RND(n bytes) 2

   *

   * Later versions encode the DEK like this:

   *

   *     0  2  RND(n bytes)  0  A  DEK(k bytes)  CSUM(2 bytes)

   *

   * (mpi_get_buffer already removed the leading zero).

   *

   * RND are non-zero randow bytes.

   * A   is the cipher algorithm

   * DEK is the encryption key (session key) with length k

   * CSUM

   */

  if (DBG_CRYPTO)

    log_printhex (frame, nframe, "DEK frame:");

  n = 0;

  if (sk->pubkey_algo == PUBKEY_ALGO_ECDH)

    {

      gcry_mpi_t decoded;

      /* At the beginning the frame are the bytes of shared point MPI.  */

      err = pk_ecdh_decrypt (&decoded, fp, enc->data[1]/*encr data as an MPI*/,

                             frame, nframe, sk->pkey);

      if(err)

        goto leave;

      xfree (frame);

      err = gcry_mpi_aprint (GCRYMPI_FMT_USG, &frame, &nframe, decoded);

      mpi_release (decoded);

      if (err)

        goto leave;

      /* Now the frame are the bytes decrypted but padded session key.  */

      if (!nframe || nframe <= 8

          || frame[nframe-1] > nframe)

        {

          err = gpg_error (GPG_ERR_WRONG_SECKEY);

          goto leave;

        }

      nframe -= frame[nframe-1]; /* Remove padding.  */

      log_assert (!n); /* (used just below) */

    }

  else

    {

      if (padding)

        {

          if (n + 7 > nframe)

            {

              err = gpg_error (GPG_ERR_WRONG_SECKEY);

              goto leave;

            }

          /* FIXME: Actually the leading zero is required but due to

           * the way we encode the output in libgcrypt as an MPI we

           * are not able to encode that leading zero.  However, when

           * using a Smartcard we are doing it the right way and

           * therefore we have to skip the zero.  This should be fixed

           * in gpg-agent of course. */

          if (!frame[n])

            n++;

          if (frame[n] == 1 && frame[nframe - 1] == 2)

            {

              log_info (_("old encoding of the DEK is not supported\n"));

              err = gpg_error (GPG_ERR_CIPHER_ALGO);

              goto leave;

            }

          if (frame[n] != 2) /* Something went wrong.  */

            {

              err = gpg_error (GPG_ERR_WRONG_SECKEY);

              goto leave;

            }

          for (n++; n < nframe && frame[n]; n++) /* Skip the random bytes.  */

            ;

          n++; /* Skip the zero byte.  */

        }

    }

  if (n + 4 > nframe)

    {

      err = gpg_error (GPG_ERR_WRONG_SECKEY);

      goto leave;

    }

  dek->keylen = nframe - (n + 1) - 2;

  dek->algo = frame[n++];

  err = openpgp_cipher_test_algo (dek->algo);

  if (err)

    {

      if (!opt.quiet && gpg_err_code (err) == GPG_ERR_CIPHER_ALGO)

        {

          log_info (_("cipher algorithm %d%s is unknown or disabled\n"),

                    dek->algo,

                    dek->algo == CIPHER_ALGO_IDEA ? " (IDEA)" : "");

        }

      dek->algo = 0;

      goto leave;

    }

  if (dek->keylen != openpgp_cipher_get_algo_keylen (dek->algo))

    {

      err = gpg_error (GPG_ERR_WRONG_SECKEY);

      goto leave;

    }

  /* Copy the key to DEK and compare the checksum.  */

  csum = buf16_to_u16 (frame+nframe-2);

  memcpy (dek->key, frame + n, dek->keylen);

  for (csum2 = 0, n = 0; n < dek->keylen; n++)

    csum2 += dek->key[n];

  if (csum != csum2)

    {

      err = gpg_error (GPG_ERR_WRONG_SECKEY);

      goto leave;

    }

  if (DBG_CLOCK)

    log_clock ("decryption ready");

  if (DBG_CRYPTO)

    log_printhex (dek->key, dek->keylen, "DEK is:");

  /* Check that the algo is in the preferences and whether it has

   * expired.  Also print a status line with the key's fingerprint.  */

  {

    PKT_public_key *pk = NULL;

    PKT_public_key *mainpk = NULL;

    KBNODE pkb = get_pubkeyblock (ctrl, keyid);

    if (!pkb)

      {

        err = -1;

        log_error ("oops: public key not found for preference check\n");

      }

    else if (pkb->pkt->pkt.public_key->selfsigversion > 3

             && dek->algo != CIPHER_ALGO_3DES

             && !opt.quiet

             && !is_algo_in_prefs (pkb, PREFTYPE_SYM, dek->algo))

      log_info (_("WARNING: cipher algorithm %s not found in recipient"

                  " preferences\n"), openpgp_cipher_algo_name (dek->algo));

    if (!err)

      {

        kbnode_t k;

        int first = 1;

        for (k = pkb; k; k = k->next)

          {

            if (k->pkt->pkttype == PKT_PUBLIC_KEY

                || k->pkt->pkttype == PKT_PUBLIC_SUBKEY)

              {

                u32 aki[2];

                if (first)

                  {

                    first = 0;

                    mainpk = k->pkt->pkt.public_key;

                  }

                keyid_from_pk (k->pkt->pkt.public_key, aki);

                if (aki[0] == keyid[0] && aki[1] == keyid[1])

                  {

                    pk = k->pkt->pkt.public_key;

                    break;

                  }

              }

          }

        if (!pk)

          BUG ();

        if (pk->expiredate && pk->expiredate <= make_timestamp ())

          {

            log_info (_("Note: secret key %s expired at %s\n"),

                      keystr (keyid), asctimestamp (pk->expiredate));

          }

      }

    if (pk && pk->flags.revoked)

      {

        log_info (_("Note: key has been revoked"));

        log_printf ("\n");

        show_revocation_reason (ctrl, pk, 1);

      }

    if (is_status_enabled () && pk && mainpk)

      {

        char pkhex[MAX_FINGERPRINT_LEN*2+1];

        char mainpkhex[MAX_FINGERPRINT_LEN*2+1];

        hexfingerprint (pk, pkhex, sizeof pkhex);

        hexfingerprint (mainpk, mainpkhex, sizeof mainpkhex);

        /* Note that we do not want to create a trustdb just for

         * getting the ownertrust: If there is no trustdb there can't

         * be ulitmately trusted key anyway and thus the ownertrust

         * value is irrelevant.  */

        write_status_printf (STATUS_DECRYPTION_KEY, "%s %s %c",

                             pkhex, mainpkhex,

                             get_ownertrust_info (ctrl, mainpk, 1));

      }

    release_kbnode (pkb);

    err = 0;

  }

 leave:

  xfree (frame);

  xfree (keygrip);

  return err;

}

/*

 * Get the session key from the given string.

 * String is supposed to be formatted as this:

 *  <algo-id>:<even-number-of-hex-digits>

 */

gpg_error_t

get_override_session_key (DEK *dek, const char *string)

{

  const char *s;

  int i;

  if (!string)

    return GPG_ERR_BAD_KEY;

  dek->algo = atoi (string);

  if (dek->algo < 1)

    return GPG_ERR_BAD_KEY;

  if (!(s = strchr (string, ':')))

    return GPG_ERR_BAD_KEY;

  s++;

  for (i = 0; i < DIM (dek->key) && *s; i++, s += 2)

    {

      int c = hextobyte (s);

      if (c == -1)

        return GPG_ERR_BAD_KEY;

      dek->key[i] = c;

    }

  if (*s)

    return GPG_ERR_BAD_KEY;

  dek->keylen = i;

  return 0;

}