gnupg/g10/encrypt.c

/* encrypt.c - Main encryption driver
 * Copyright (C) 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005,
 *               2006, 2009 Free Software Foundation, Inc.
 * Copyright (C) 2016 g10 Code GmbH
 *
 * 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 <errno.h>

#include "gpg.h"
#include "options.h"
#include "packet.h"
#include "../common/status.h"
#include "../common/iobuf.h"
#include "keydb.h"
#include "../common/util.h"
#include "main.h"
#include "filter.h"
#include "trustdb.h"
#include "../common/i18n.h"
#include "../common/status.h"
#include "pkglue.h"
#include "../common/compliance.h"


static int encrypt_simple( const char *filename, int mode, int use_seskey );
static int write_pubkey_enc_from_list (ctrl_t ctrl,
                                       PK_LIST pk_list, DEK *dek, iobuf_t out);

/****************
 * Encrypt FILENAME with only the symmetric cipher.  Take input from
 * stdin if FILENAME is NULL.  If --force-aead is used we use an SKESK.
 */
int
encrypt_symmetric (const char *filename)
{
  return encrypt_simple( filename, 1, opt.force_aead);
}


/****************
 * Encrypt FILENAME as a literal data packet only. Take input from
 * stdin if FILENAME is NULL.
 */
int
encrypt_store (const char *filename)
{
  return encrypt_simple( filename, 0, 0 );
}


/* Encrypt a session key using DEK and store a pointer to the result
 * at R_ENCKEY and its length at R_ENCKEYLEN.
 *
 * R_SESKEY points to the unencrypted session key (.KEY, .KEYLEN) and
 * the algorithm that will be used to encrypt the contents of the
 * SKESK packet (.ALGO).  If R_SESKEY points to NULL, then a random
 * session key that is appropriate for DEK->ALGO is generated and
 * stored at R_SESKEY.  If AEAD_ALGO is not 0 the given AEAD algorithm
 * is used for encryption.
 */
gpg_error_t
encrypt_seskey (DEK *dek, aead_algo_t aead_algo,
                DEK **r_seskey, void **r_enckey, size_t *r_enckeylen)
{
  gpg_error_t err;
  gcry_cipher_hd_t hd = NULL;
  byte *buf = NULL;
  DEK *seskey;

  *r_enckey = NULL;
  *r_enckeylen = 0;

  if (*r_seskey)
    seskey = *r_seskey;
  else
    {
      seskey = xtrycalloc (1, sizeof(DEK));
      if (!seskey)
        {
          err = gpg_error_from_syserror ();
          goto leave;
        }
      seskey->algo = dek->algo;
      make_session_key (seskey);
      /*log_hexdump( "thekey", c->key, c->keylen );*/
    }


  if (aead_algo)
    {
      unsigned int noncelen;
      enum gcry_cipher_modes ciphermode;
      byte ad[4];

      err = openpgp_aead_algo_info (aead_algo, &ciphermode, &noncelen);
      if (err)
        goto leave;

      /* Allocate space for the nonce, the key, and the authentication
       * tag (16).  */
      buf = xtrymalloc_secure (noncelen + seskey->keylen + 16);
      if (!buf)
        {
          err = gpg_error_from_syserror ();
          goto leave;
        }

      gcry_randomize (buf, noncelen, GCRY_STRONG_RANDOM);

      err = openpgp_cipher_open (&hd, dek->algo,
                                 ciphermode, GCRY_CIPHER_SECURE);
      if (!err)
        err = gcry_cipher_setkey (hd, dek->key, dek->keylen);
      if (!err)
        err = gcry_cipher_setiv (hd, buf, noncelen);
      if (err)
        goto leave;

      ad[0] = (0xc0 | PKT_SYMKEY_ENC);
      ad[1] = 5;
      ad[2] = dek->algo;
      ad[3] = aead_algo;
      err = gcry_cipher_authenticate (hd, ad, 4);
      if (err)
        goto leave;

      memcpy (buf + noncelen, seskey->key, seskey->keylen);
      gcry_cipher_final (hd);
      err = gcry_cipher_encrypt (hd, buf + noncelen, seskey->keylen, NULL,0);
      if (err)
        goto leave;
      err = gcry_cipher_gettag (hd, buf + noncelen + seskey->keylen, 16);
      if (err)
        goto leave;
      *r_enckeylen = noncelen + seskey->keylen + 16;
      *r_enckey = buf;
      buf = NULL;
    }
  else
    {
      /* In the old version 4 SKESK the encrypted session key is
       * prefixed with a one-octet algorithm id.  */
      buf = xtrymalloc_secure (1 + seskey->keylen);
      if (!buf)
        {
          err = gpg_error_from_syserror ();
          goto leave;
        }
      buf[0] = seskey->algo;
      memcpy (buf + 1, seskey->key, seskey->keylen);

      err = openpgp_cipher_open (&hd, dek->algo, GCRY_CIPHER_MODE_CFB, 1);
      if (!err)
        err = gcry_cipher_setkey (hd, dek->key, dek->keylen);
      if (!err)
        err = gcry_cipher_setiv (hd, NULL, 0);
      if (!err)
        err = gcry_cipher_encrypt (hd, buf, seskey->keylen + 1, NULL, 0);
      if (err)
        goto leave;
      *r_enckeylen = seskey->keylen + 1;
      *r_enckey = buf;
      buf = NULL;
    }

  /* Return the session key in case we allocated it.  */
  *r_seskey = seskey;
  seskey = NULL;

 leave:
  gcry_cipher_close (hd);
  if (seskey != *r_seskey)
    xfree (seskey);
  xfree (buf);
  return err;
}


/* Return the AEAD algo if we shall use AEAD mode.  Returns 0 if AEAD
 * shall not be used.  */
aead_algo_t
use_aead (pk_list_t pk_list, int algo)
{
  int can_use;

  if (!opt.flags.rfc4880bis)
    {
      if (opt.force_aead)
        log_info ("Warning: Option %s currently requires option '%s'\n",
                  "--force-aead", "--rfc4880bis");
      return 0;
    }

  can_use = openpgp_cipher_get_algo_blklen (algo) == 16;

  /* With --force-aead we want AEAD.  */
  if (opt.force_aead)
    {
      if (!can_use)
        {
          log_info ("Warning: request to use AEAD ignored for cipher '%s'\n",
                    openpgp_cipher_algo_name (algo));
          return 0;
        }
      return default_aead_algo ();
    }

  /* AEAD does only work with 128 bit cipher blocklength.  */
  if (!can_use)
    return 0;

  /* Note the user which keys have no AEAD feature flag set.  */
  if (opt.verbose)
    warn_missing_aead_from_pklist (pk_list);

  /* If all keys support AEAD we can use it.  */
  return select_aead_from_pklist (pk_list);
}


/* Shall we use the MDC?  Yes - unless rfc-2440 compatibility is
 * requested. */
int
use_mdc (pk_list_t pk_list,int algo)
{
  (void)pk_list;
  (void)algo;

  /* RFC-2440 don't has MDC - this is the only way to create a legacy
   * non-MDC encryption packet.  */
  if (RFC2440)
    return 0;

  return 1; /* In all other cases we use the MDC */
}


/* We don't want to use use_seskey yet because older gnupg versions
   can't handle it, and there isn't really any point unless we're
   making a message that can be decrypted by a public key or
   passphrase. */
static int
encrypt_simple (const char *filename, int mode, int use_seskey)
{
  iobuf_t inp, out;
  PACKET pkt;
  PKT_plaintext *pt = NULL;
  STRING2KEY *s2k = NULL;
  void *enckey = NULL;
  size_t enckeylen = 0;
  int rc = 0;
  u32 filesize;
  cipher_filter_context_t cfx;
  armor_filter_context_t  *afx = NULL;
  compress_filter_context_t zfx;
  text_filter_context_t tfx;
  progress_filter_context_t *pfx;
  int do_compress = !!default_compress_algo();

  if (!gnupg_rng_is_compliant (opt.compliance))
    {
      rc = gpg_error (GPG_ERR_FORBIDDEN);
      log_error (_("%s is not compliant with %s mode\n"),
                 "RNG",
                 gnupg_compliance_option_string (opt.compliance));
      write_status_error ("random-compliance", rc);
      return rc;
    }

  pfx = new_progress_context ();
  memset( &cfx, 0, sizeof cfx);
  memset( &zfx, 0, sizeof zfx);
  memset( &tfx, 0, sizeof tfx);
  init_packet(&pkt);

  /* Prepare iobufs. */
  inp = iobuf_open(filename);
  if (inp)
    iobuf_ioctl (inp, IOBUF_IOCTL_NO_CACHE, 1, NULL);
  if (inp && is_secured_file (iobuf_get_fd (inp)))
    {
      iobuf_close (inp);
      inp = NULL;
      gpg_err_set_errno (EPERM);
    }
  if (!inp)
    {
      rc = gpg_error_from_syserror ();
      log_error(_("can't open '%s': %s\n"), filename? filename: "[stdin]",
                strerror(errno) );
      release_progress_context (pfx);
      return rc;
    }

  handle_progress (pfx, inp, filename);

  if (opt.textmode)
    iobuf_push_filter( inp, text_filter, &tfx );

  cfx.dek = NULL;
  if ( mode )
    {
      aead_algo_t aead_algo;

      rc = setup_symkey (&s2k, &cfx.dek);
      if (rc)
        {
          iobuf_close (inp);
          if (gpg_err_code (rc) == GPG_ERR_CIPHER_ALGO
              || gpg_err_code (rc) == GPG_ERR_DIGEST_ALGO)
            ; /* Error has already been printed.  */
          else
            log_error (_("error creating passphrase: %s\n"), gpg_strerror (rc));
          release_progress_context (pfx);
          return rc;
        }
      if (use_seskey && s2k->mode != 1 && s2k->mode != 3)
        {
          use_seskey = 0;
          log_info (_("can't use a symmetric ESK packet "
                      "due to the S2K mode\n"));
        }

      /* See whether we want to use AEAD.  */
      aead_algo = use_aead (NULL, cfx.dek->algo);

      if ( use_seskey )
        {
          DEK *dek = NULL;

          rc = encrypt_seskey (cfx.dek, aead_algo, &dek, &enckey, &enckeylen);
          if (rc)
            {
              xfree (cfx.dek);
              xfree (s2k);
              iobuf_close (inp);
              release_progress_context (pfx);
              return rc;
            }
          /* Replace key in DEK.  */
          xfree (cfx.dek);
          cfx.dek = dek;
        }

      if (aead_algo)
        cfx.dek->use_aead = aead_algo;
      else
        cfx.dek->use_mdc = !!use_mdc (NULL, cfx.dek->algo);

      if (opt.verbose)
        log_info(_("using cipher %s.%s\n"),
                 openpgp_cipher_algo_name (cfx.dek->algo),
                 cfx.dek->use_aead? openpgp_aead_algo_name (cfx.dek->use_aead)
                 /**/             : "CFB");
    }

  if (do_compress
      && cfx.dek
      && (cfx.dek->use_mdc || cfx.dek->use_aead)
      && is_file_compressed(filename, &rc))
    {
      if (opt.verbose)
        log_info(_("'%s' already compressed\n"), filename);
      do_compress = 0;
    }

  if ( rc || (rc = open_outfile (-1, filename, opt.armor? 1:0, 0, &out )))
    {
      iobuf_cancel (inp);
      xfree (cfx.dek);
      xfree (s2k);
      release_progress_context (pfx);
      return rc;
    }

  if ( opt.armor )
    {
      afx = new_armor_context ();
      push_armor_filter (afx, out);
    }

  if ( s2k )
    {
      /* Fixme: This is quite similar to write_symkey_enc.  */
      PKT_symkey_enc *enc = xmalloc_clear (sizeof *enc + enckeylen);
      enc->version = cfx.dek->use_aead ? 5 : 4;
      enc->cipher_algo = cfx.dek->algo;
      enc->aead_algo = cfx.dek->use_aead;
      enc->s2k = *s2k;
      if (enckeylen)
        {
          enc->seskeylen = enckeylen;
          memcpy (enc->seskey, enckey, enckeylen);
        }
      pkt.pkttype = PKT_SYMKEY_ENC;
      pkt.pkt.symkey_enc = enc;
      if ((rc = build_packet( out, &pkt )))
        log_error("build symkey packet failed: %s\n", gpg_strerror (rc) );
      xfree (enc);
      xfree (enckey);
      enckey = NULL;
    }

  if (!opt.no_literal)
    pt = setup_plaintext_name (filename, inp);

  /* Note that PGP 5 has problems decrypting symmetrically encrypted
     data if the file length is in the inner packet. It works when
     only partial length headers are use.  In the past, we always used
     partial body length here, but since PGP 2, PGP 6, and PGP 7 need
     the file length, and nobody should be using PGP 5 nowadays
     anyway, this is now set to the file length.  Note also that this
     only applies to the RFC-1991 style symmetric messages, and not
     the RFC-2440 style.  PGP 6 and 7 work with either partial length
     or fixed length with the new style messages. */

  if ( !iobuf_is_pipe_filename (filename) && *filename && !opt.textmode )
    {
      off_t tmpsize;
      int overflow;

      if ( !(tmpsize = iobuf_get_filelength(inp, &overflow))
           && !overflow && opt.verbose)
        log_info(_("WARNING: '%s' is an empty file\n"), filename );
      /* We can't encode the length of very large files because
         OpenPGP uses only 32 bit for file sizes.  So if the
         size of a file is larger than 2^32 minus some bytes for
         packet headers, we switch to partial length encoding. */
      if ( tmpsize < (IOBUF_FILELENGTH_LIMIT - 65536) )
        filesize = tmpsize;
      else
        filesize = 0;
    }
  else
    filesize = opt.set_filesize ? opt.set_filesize : 0; /* stdin */

  if (!opt.no_literal)
    {
      /* Note that PT has been initialized above in !no_literal mode.  */
      pt->timestamp = make_timestamp();
      pt->mode = opt.mimemode? 'm' : opt.textmode? 't' : 'b';
      pt->len = filesize;
      pt->new_ctb = !pt->len;
      pt->buf = inp;
      pkt.pkttype = PKT_PLAINTEXT;
      pkt.pkt.plaintext = pt;
      cfx.datalen = filesize && !do_compress ? calc_packet_length( &pkt ) : 0;
    }
  else
    {
      cfx.datalen = filesize && !do_compress ? filesize : 0;
      pkt.pkttype = 0;
      pkt.pkt.generic = NULL;
    }

  /* Register the cipher filter. */
  if (mode)
    iobuf_push_filter (out,
                       cfx.dek->use_aead? cipher_filter_aead
                       /**/             : cipher_filter_cfb,
                       &cfx );

  /* Register the compress filter. */
  if ( do_compress )
    {
      if (cfx.dek && (cfx.dek->use_mdc || cfx.dek->use_aead))
        zfx.new_ctb = 1;
      push_compress_filter (out, &zfx, default_compress_algo());
    }

  /* Do the work. */
  if (!opt.no_literal)
    {
      if ( (rc = build_packet( out, &pkt )) )
        log_error("build_packet failed: %s\n", gpg_strerror (rc) );
    }
  else
    {
      /* User requested not to create a literal packet, so we copy the
         plain data.  */
    byte copy_buffer[4096];
    int  bytes_copied;
    while ((bytes_copied = iobuf_read(inp, copy_buffer, 4096)) != -1)
      if ( (rc=iobuf_write(out, copy_buffer, bytes_copied)) ) {
        log_error ("copying input to output failed: %s\n",
                   gpg_strerror (rc) );
        break;
      }
    wipememory (copy_buffer, 4096); /* burn buffer */
    }

  /* Finish the stuff.  */
  iobuf_close (inp);
  if (rc)
    iobuf_cancel(out);
  else
    {
      iobuf_close (out); /* fixme: check returncode */
      if (mode)
        write_status ( STATUS_END_ENCRYPTION );
    }
  if (pt)
    pt->buf = NULL;
  free_packet (&pkt, NULL);
  xfree (enckey);
  xfree (cfx.dek);
  xfree (s2k);
  release_armor_context (afx);
  release_progress_context (pfx);
  return rc;
}


gpg_error_t
setup_symkey (STRING2KEY **symkey_s2k, DEK **symkey_dek)
{
  int canceled;
  int defcipher;
  int s2kdigest;

  defcipher = default_cipher_algo ();
  if (openpgp_cipher_blocklen (defcipher) < 16
      && !opt.flags.allow_old_cipher_algos)
    {
      log_error (_("cipher algorithm '%s' may not be used for encryption\n"),
		 openpgp_cipher_algo_name (defcipher));
      if (!opt.quiet)
        log_info (_("(use option \"%s\" to override)\n"),
                  "--allow-old-cipher-algos");
      return gpg_error (GPG_ERR_CIPHER_ALGO);
    }

  if (!gnupg_cipher_is_allowed (opt.compliance, 1, defcipher,
                                GCRY_CIPHER_MODE_CFB))
    {
      log_error (_("cipher algorithm '%s' may not be used in %s mode\n"),
		 openpgp_cipher_algo_name (defcipher),
		 gnupg_compliance_option_string (opt.compliance));
      return gpg_error (GPG_ERR_CIPHER_ALGO);
    }

  s2kdigest = S2K_DIGEST_ALGO;
  if (!gnupg_digest_is_allowed (opt.compliance, 1, s2kdigest))
    {
      log_error (_("digest algorithm '%s' may not be used in %s mode\n"),
		 gcry_md_algo_name (s2kdigest),
		 gnupg_compliance_option_string (opt.compliance));
      return gpg_error (GPG_ERR_DIGEST_ALGO);
    }

  *symkey_s2k = xmalloc_clear (sizeof **symkey_s2k);
  (*symkey_s2k)->mode = opt.s2k_mode;
  (*symkey_s2k)->hash_algo = s2kdigest;

  *symkey_dek = passphrase_to_dek (defcipher,
                                   *symkey_s2k, 1, 0, NULL, 0, &canceled);
  if (!*symkey_dek || !(*symkey_dek)->keylen)
    {
      xfree(*symkey_dek);
      xfree(*symkey_s2k);
      return gpg_error (canceled?GPG_ERR_CANCELED:GPG_ERR_INV_PASSPHRASE);
    }

  return 0;
}


static int
write_symkey_enc (STRING2KEY *symkey_s2k, aead_algo_t aead_algo,
                  DEK *symkey_dek, DEK *dek, iobuf_t out)
{
  int rc;
  void *enckey;
  size_t enckeylen;
  PKT_symkey_enc *enc;
  PACKET pkt;

  rc = encrypt_seskey (symkey_dek, aead_algo, &dek, &enckey, &enckeylen);
  if (rc)
    return rc;
  enc = xtrycalloc (1, sizeof (PKT_symkey_enc) + enckeylen);
  if (!enc)
    {
      rc = gpg_error_from_syserror ();
      xfree (enckey);
      return rc;
    }

  enc->version = aead_algo? 5 : 4;
  enc->cipher_algo = opt.s2k_cipher_algo;
  enc->aead_algo = aead_algo;
  enc->s2k = *symkey_s2k;
  enc->seskeylen = enckeylen;
  memcpy (enc->seskey, enckey, enckeylen);
  xfree (enckey);

  pkt.pkttype = PKT_SYMKEY_ENC;
  pkt.pkt.symkey_enc = enc;

  if ((rc=build_packet(out,&pkt)))
    log_error("build symkey_enc packet failed: %s\n",gpg_strerror (rc));

  xfree (enc);
  return rc;
}


/*
 * Encrypt the file with the given userids (or ask if none is
 * supplied).  Either FILENAME or FILEFD must be given, but not both.
 * The caller may provide a checked list of public keys in
 * PROVIDED_PKS; if not the function builds a list of keys on its own.
 *
 * Note that FILEFD is currently only used by cmd_encrypt in the
 * not yet finished server.c.
 */
int
encrypt_crypt (ctrl_t ctrl, int filefd, const char *filename,
               strlist_t remusr, int use_symkey, pk_list_t provided_keys,
               int outputfd)
{
  iobuf_t inp = NULL;
  iobuf_t out = NULL;
  PACKET pkt;
  PKT_plaintext *pt = NULL;
  DEK *symkey_dek = NULL;
  STRING2KEY *symkey_s2k = NULL;
  int rc = 0, rc2 = 0;
  u32 filesize;
  cipher_filter_context_t cfx;
  armor_filter_context_t *afx = NULL;
  compress_filter_context_t zfx;
  text_filter_context_t tfx;
  progress_filter_context_t *pfx;
  PK_LIST pk_list;
  int do_compress;
  int compliant;

  if (filefd != -1 && filename)
    return gpg_error (GPG_ERR_INV_ARG);  /* Both given.  */

  do_compress = !!opt.compress_algo;

  pfx = new_progress_context ();
  memset( &cfx, 0, sizeof cfx);
  memset( &zfx, 0, sizeof zfx);
  memset( &tfx, 0, sizeof tfx);
  init_packet(&pkt);

  if (use_symkey
      && (rc=setup_symkey(&symkey_s2k,&symkey_dek)))
    {
      release_progress_context (pfx);
      return rc;
    }

  if (provided_keys)
    pk_list = provided_keys;
  else
    {
      if ((rc = build_pk_list (ctrl, remusr, &pk_list)))
        {
          release_progress_context (pfx);
          return rc;
        }
    }

  /* Prepare iobufs. */
#ifdef HAVE_W32_SYSTEM
  if (filefd == -1)
    inp = iobuf_open (filename);
  else
    {
      inp = NULL;
      gpg_err_set_errno (ENOSYS);
    }
#else
  if (filefd == GNUPG_INVALID_FD)
    inp = iobuf_open (filename);
  else
    inp = iobuf_fdopen_nc (FD2INT(filefd), "rb");
#endif
  if (inp)
    iobuf_ioctl (inp, IOBUF_IOCTL_NO_CACHE, 1, NULL);
  if (inp && is_secured_file (iobuf_get_fd (inp)))
    {
      iobuf_close (inp);
      inp = NULL;
      gpg_err_set_errno (EPERM);
    }
  if (!inp)
    {
      char xname[64];

      rc = gpg_error_from_syserror ();
      if (filefd != -1)
        snprintf (xname, sizeof xname, "[fd %d]", filefd);
      else if (!filename)
        strcpy (xname, "[stdin]");
      else
        *xname = 0;
      log_error (_("can't open '%s': %s\n"),
                 *xname? xname : filename, gpg_strerror (rc) );
      goto leave;
    }

  if (opt.verbose)
    log_info (_("reading from '%s'\n"), iobuf_get_fname_nonnull (inp));

  handle_progress (pfx, inp, filename);

  if (opt.textmode)
    iobuf_push_filter (inp, text_filter, &tfx);

  rc = open_outfile (outputfd, filename, opt.armor? 1:0, 0, &out);
  if (rc)
    goto leave;

  if (opt.armor)
    {
      afx = new_armor_context ();
      push_armor_filter (afx, out);
    }

  /* Create a session key. */
  cfx.dek = xmalloc_secure_clear (sizeof *cfx.dek);
  if (!opt.def_cipher_algo)
    {
      /* Try to get it from the prefs.  */
      cfx.dek->algo = select_algo_from_prefs (pk_list, PREFTYPE_SYM, -1, NULL);
      /* The only way select_algo_from_prefs can fail here is when
         mixing v3 and v4 keys, as v4 keys have an implicit preference
         entry for 3DES, and the pk_list cannot be empty.  In this
         case, use 3DES anyway as it's the safest choice - perhaps the
         v3 key is being used in an OpenPGP implementation and we know
         that the implementation behind any v4 key can handle 3DES.
         Note that we do not support v3 keys since version 2.2 so the
         above description gives only historical background. */
      if (cfx.dek->algo == -1)
        {
          /* If does not make sense to fallback to the rfc4880
           * required 3DES if we will reject that algo later.  Thus we
           * fallback to AES anticipating RFC4880bis rules.  */
          if (opt.flags.allow_old_cipher_algos)
            cfx.dek->algo = CIPHER_ALGO_3DES;
          else
            cfx.dek->algo = CIPHER_ALGO_AES;
        }

      /* In case 3DES has been selected, print a warning if any key
         does not have a preference for AES.  This should help to
         identify why encrypting to several recipients falls back to
         3DES. */
      if (opt.verbose && cfx.dek->algo == CIPHER_ALGO_3DES)
        warn_missing_aes_from_pklist (pk_list);
    }
  else
    {
      if (!opt.expert
          && (select_algo_from_prefs (pk_list, PREFTYPE_SYM,
                                      opt.def_cipher_algo, NULL)
              != opt.def_cipher_algo))
        {
          log_info(_("WARNING: forcing symmetric cipher %s (%d)"
                     " violates recipient preferences\n"),
                   openpgp_cipher_algo_name (opt.def_cipher_algo),
                   opt.def_cipher_algo);
        }

      cfx.dek->algo = opt.def_cipher_algo;
    }

  if (openpgp_cipher_blocklen (cfx.dek->algo) < 16
      && !opt.flags.allow_old_cipher_algos)
    {
      log_error (_("cipher algorithm '%s' may not be used for encryption\n"),
		 openpgp_cipher_algo_name (cfx.dek->algo));
      if (!opt.quiet)
        log_info (_("(use option \"%s\" to override)\n"),
                  "--allow-old-cipher-algos");
      rc = gpg_error (GPG_ERR_CIPHER_ALGO);
      goto leave;
    }

  /* Check compliance.  */
  if (! gnupg_cipher_is_allowed (opt.compliance, 1, cfx.dek->algo,
                                 GCRY_CIPHER_MODE_CFB))
    {
      log_error (_("cipher algorithm '%s' may not be used in %s mode\n"),
		 openpgp_cipher_algo_name (cfx.dek->algo),
		 gnupg_compliance_option_string (opt.compliance));
      rc = gpg_error (GPG_ERR_CIPHER_ALGO);
      goto leave;
    }

  if (!gnupg_rng_is_compliant (opt.compliance))
    {
      rc = gpg_error (GPG_ERR_FORBIDDEN);
      log_error (_("%s is not compliant with %s mode\n"),
                 "RNG",
                 gnupg_compliance_option_string (opt.compliance));
      write_status_error ("random-compliance", rc);
      goto leave;
    }

  compliant = gnupg_cipher_is_compliant (CO_DE_VS, cfx.dek->algo,
                                         GCRY_CIPHER_MODE_CFB);

  {
    pk_list_t pkr;

    for (pkr = pk_list; pkr; pkr = pkr->next)
      {
        PKT_public_key *pk = pkr->pk;
        unsigned int nbits = nbits_from_pk (pk);

        if (!gnupg_pk_is_compliant (opt.compliance, pk->pubkey_algo, 0,
                                    pk->pkey, nbits, NULL))
          log_info (_("WARNING: key %s is not suitable for encryption"
                      " in %s mode\n"),
                    keystr_from_pk (pk),
                    gnupg_compliance_option_string (opt.compliance));

        if (compliant
            && !gnupg_pk_is_compliant (CO_DE_VS, pk->pubkey_algo, 0, pk->pkey,
                                       nbits, NULL))
          compliant = 0;
      }

  }

  if (compliant)
    write_status_strings (STATUS_ENCRYPTION_COMPLIANCE_MODE,
                          gnupg_status_compliance_flag (CO_DE_VS),
                          NULL);

  cfx.dek->use_aead = use_aead (pk_list, cfx.dek->algo);
  if (!cfx.dek->use_aead)
    cfx.dek->use_mdc = !!use_mdc (pk_list, cfx.dek->algo);

  /* Only do the is-file-already-compressed check if we are using a
   * MDC or AEAD.  This forces compressed files to be re-compressed if
   * we do not have a MDC to give some protection against chosen
   * ciphertext attacks. */
  if (do_compress
      && (cfx.dek->use_mdc || cfx.dek->use_aead)
      && is_file_compressed (filename, &rc2))
    {
      if (opt.verbose)
        log_info(_("'%s' already compressed\n"), filename);
      do_compress = 0;
    }
  if (rc2)
    {
      rc = rc2;
      goto leave;
    }

  make_session_key (cfx.dek);
  if (DBG_CRYPTO)
    log_printhex (cfx.dek->key, cfx.dek->keylen, "DEK is: ");

  rc = write_pubkey_enc_from_list (ctrl, pk_list, cfx.dek, out);
  if (rc)
    goto leave;

  /* We put the passphrase (if any) after any public keys as this
   * seems to be the most useful on the recipient side - there is no
   * point in prompting a user for a passphrase if they have the
   * secret key needed to decrypt.  */
  if (use_symkey && (rc = write_symkey_enc (symkey_s2k, cfx.dek->use_aead,
                                            symkey_dek, cfx.dek, out)))
    goto leave;

  if (!opt.no_literal)
    pt = setup_plaintext_name (filename, inp);

  /* Get the size of the file if possible, i.e., if it is a real file.  */
  if (filename && *filename
      && !iobuf_is_pipe_filename (filename) && !opt.textmode )
    {
      off_t tmpsize;
      int overflow;

      if ( !(tmpsize = iobuf_get_filelength(inp, &overflow))
           && !overflow && opt.verbose)
        log_info(_("WARNING: '%s' is an empty file\n"), filename );
      /* We can't encode the length of very large files because
         OpenPGP uses only 32 bit for file sizes.  So if the size
         of a file is larger than 2^32 minus some bytes for packet
         headers, we switch to partial length encoding. */
      if (tmpsize < (IOBUF_FILELENGTH_LIMIT - 65536) )
        filesize = tmpsize;
      else
        filesize = 0;
    }
  else
    filesize = opt.set_filesize ? opt.set_filesize : 0; /* stdin */

  if (!opt.no_literal)
    {
      pt->timestamp = make_timestamp();
      pt->mode = opt.mimemode? 'm' : opt.textmode ? 't' : 'b';
      pt->len = filesize;
      pt->new_ctb = !pt->len;
      pt->buf = inp;
      pkt.pkttype = PKT_PLAINTEXT;
      pkt.pkt.plaintext = pt;
      cfx.datalen = filesize && !do_compress? calc_packet_length( &pkt ) : 0;
    }
  else
    cfx.datalen = filesize && !do_compress ? filesize : 0;

  /* Register the cipher filter. */
  iobuf_push_filter (out,
                     cfx.dek->use_aead? cipher_filter_aead
                     /**/             : cipher_filter_cfb,
                     &cfx);

  /* Register the compress filter. */
  if (do_compress)
    {
      int compr_algo = opt.compress_algo;

      if (compr_algo == -1)
        {
          compr_algo = select_algo_from_prefs (pk_list, PREFTYPE_ZIP, -1, NULL);
          if (compr_algo == -1)
            compr_algo = DEFAULT_COMPRESS_ALGO;
          /* Theoretically impossible to get here since uncompressed
             is implicit.  */
        }
      else if (!opt.expert
               && select_algo_from_prefs(pk_list, PREFTYPE_ZIP,
                                         compr_algo, NULL) != compr_algo)
        {
          log_info (_("WARNING: forcing compression algorithm %s (%d)"
                      " violates recipient preferences\n"),
                    compress_algo_to_string(compr_algo), compr_algo);
        }

      /* Algo 0 means no compression. */
      if (compr_algo)
        {
          if (cfx.dek && (cfx.dek->use_mdc || cfx.dek->use_aead))
            zfx.new_ctb = 1;
          push_compress_filter (out,&zfx,compr_algo);
        }
    }

  /* Do the work. */
  if (!opt.no_literal)
    {
      if ((rc = build_packet( out, &pkt )))
        log_error ("build_packet failed: %s\n", gpg_strerror (rc));
    }
  else
    {
      /* User requested not to create a literal packet, so we copy the
         plain data. */
      byte copy_buffer[4096];
      int  bytes_copied;
      while ((bytes_copied = iobuf_read (inp, copy_buffer, 4096)) != -1)
        {
          rc = iobuf_write (out, copy_buffer, bytes_copied);
          if (rc)
            {
              log_error ("copying input to output failed: %s\n",
                         gpg_strerror (rc));
              break;
            }
        }
      wipememory (copy_buffer, 4096); /* Burn the buffer. */
    }

  /* Finish the stuff. */
 leave:
  iobuf_close (inp);
  if (rc)
    iobuf_cancel (out);
  else
    {
      iobuf_close (out); /* fixme: check returncode */
      write_status (STATUS_END_ENCRYPTION);
    }
  if (pt)
    pt->buf = NULL;
  free_packet (&pkt, NULL);
  xfree (cfx.dek);
  xfree (symkey_dek);
  xfree (symkey_s2k);
  if (!provided_keys)
    release_pk_list (pk_list);
  release_armor_context (afx);
  release_progress_context (pfx);
  return rc;
}


/*
 * Filter to do a complete public key encryption.
 */
int
encrypt_filter (void *opaque, int control,
                iobuf_t a, byte *buf, size_t *ret_len)
{
  size_t size = *ret_len;
  encrypt_filter_context_t *efx = opaque;
  int rc = 0;

  if (control == IOBUFCTRL_UNDERFLOW) /* decrypt */
    {
      BUG(); /* not used */
    }
  else if ( control == IOBUFCTRL_FLUSH ) /* encrypt */
    {
      if ( !efx->header_okay )
        {
          efx->cfx.dek = xmalloc_secure_clear ( sizeof *efx->cfx.dek );
          if ( !opt.def_cipher_algo  )
            {
              /* Try to get it from the prefs. */
              efx->cfx.dek->algo =
                select_algo_from_prefs (efx->pk_list, PREFTYPE_SYM, -1, NULL);
              if (efx->cfx.dek->algo == -1 )
                {
                  /* Because 3DES is implicitly in the prefs, this can
                     only happen if we do not have any public keys in
                     the list.  */
                  efx->cfx.dek->algo = DEFAULT_CIPHER_ALGO;
                }

              /* In case 3DES has been selected, print a warning if
                 any key does not have a preference for AES.  This
                 should help to identify why encrypting to several
                 recipients falls back to 3DES. */
              if (opt.verbose
                  && efx->cfx.dek->algo == CIPHER_ALGO_3DES)
                warn_missing_aes_from_pklist (efx->pk_list);
	    }
          else
            {
	      if (!opt.expert
                  && select_algo_from_prefs (efx->pk_list,PREFTYPE_SYM,
                                             opt.def_cipher_algo,
                                             NULL) != opt.def_cipher_algo)
		log_info(_("forcing symmetric cipher %s (%d) "
			   "violates recipient preferences\n"),
			 openpgp_cipher_algo_name (opt.def_cipher_algo),
			 opt.def_cipher_algo);

	      efx->cfx.dek->algo = opt.def_cipher_algo;
	    }

          efx->cfx.dek->use_aead = use_aead (efx->pk_list, efx->cfx.dek->algo);
          if (!efx->cfx.dek->use_aead)
            efx->cfx.dek->use_mdc = !!use_mdc (efx->pk_list,efx->cfx.dek->algo);

          make_session_key ( efx->cfx.dek );
          if (DBG_CRYPTO)
            log_printhex (efx->cfx.dek->key, efx->cfx.dek->keylen, "DEK is: ");

          rc = write_pubkey_enc_from_list (efx->ctrl,
                                           efx->pk_list, efx->cfx.dek, a);
          if (rc)
            return rc;

          if(efx->symkey_s2k && efx->symkey_dek)
            {
              rc = write_symkey_enc (efx->symkey_s2k, efx->cfx.dek->use_aead,
                                     efx->symkey_dek, efx->cfx.dek, a);
              if (rc)
                return rc;
            }

          iobuf_push_filter (a,
                             efx->cfx.dek->use_aead? cipher_filter_aead
                             /**/                  : cipher_filter_cfb,
                             &efx->cfx);

          efx->header_okay = 1;
        }
      rc = iobuf_write (a, buf, size);

    }
  else if (control == IOBUFCTRL_FREE)
    {
      xfree (efx->symkey_dek);
      xfree (efx->symkey_s2k);
    }
  else if ( control == IOBUFCTRL_DESC )
    {
      mem2str (buf, "encrypt_filter", *ret_len);
    }
  return rc;
}


/*
 * Write a pubkey-enc packet for the public key PK to OUT.
 */
int
write_pubkey_enc (ctrl_t ctrl,
                  PKT_public_key *pk, int throw_keyid, DEK *dek, iobuf_t out)
{
  PACKET pkt;
  PKT_pubkey_enc *enc;
  int rc;
  gcry_mpi_t frame;

  print_pubkey_algo_note ( pk->pubkey_algo );
  enc = xmalloc_clear ( sizeof *enc );
  enc->pubkey_algo = pk->pubkey_algo;
  keyid_from_pk( pk, enc->keyid );
  enc->throw_keyid = throw_keyid;

  /* Okay, what's going on: We have the session key somewhere in
   * the structure DEK and want to encode this session key in an
   * integer value of n bits. pubkey_nbits gives us the number of
   * bits we have to use.  We then encode the session key in some
   * way and we get it back in the big intger value FRAME.  Then
   * we use FRAME, the public key PK->PKEY and the algorithm
   * number PK->PUBKEY_ALGO and pass it to pubkey_encrypt which
   * returns the encrypted value in the array ENC->DATA.  This
   * array has a size which depends on the used algorithm (e.g. 2
   * for Elgamal).  We don't need frame anymore because we have
   * everything now in enc->data which is the passed to
   * build_packet().  */
  frame = encode_session_key (pk->pubkey_algo, dek,
                              pubkey_nbits (pk->pubkey_algo, pk->pkey));
  rc = pk_encrypt (pk->pubkey_algo, enc->data, frame, pk, pk->pkey);
  gcry_mpi_release (frame);
  if (rc)
    log_error ("pubkey_encrypt failed: %s\n", gpg_strerror (rc) );
  else
    {
      if ( opt.verbose )
        {
          char *ustr = get_user_id_string_native (ctrl, enc->keyid);
          log_info (_("%s/%s.%s encrypted for: \"%s\"\n"),
                    openpgp_pk_algo_name (enc->pubkey_algo),
                    openpgp_cipher_algo_name (dek->algo),
                    dek->use_aead? openpgp_aead_algo_name (dek->use_aead)
                    /**/         : "CFB",
                    ustr );
          xfree (ustr);
        }
      /* And write it. */
      init_packet (&pkt);
      pkt.pkttype = PKT_PUBKEY_ENC;
      pkt.pkt.pubkey_enc = enc;
      rc = build_packet (out, &pkt);
      if (rc)
        log_error ("build_packet(pubkey_enc) failed: %s\n",
                   gpg_strerror (rc));
    }
  free_pubkey_enc(enc);
  return rc;
}


/*
 * Write pubkey-enc packets from the list of PKs to OUT.
 */
static int
write_pubkey_enc_from_list (ctrl_t ctrl, PK_LIST pk_list, DEK *dek, iobuf_t out)
{
  if (opt.throw_keyids && (PGP7 || PGP8))
    {
      log_info(_("option '%s' may not be used in %s mode\n"),
               "--throw-keyids",
               gnupg_compliance_option_string (opt.compliance));
      compliance_failure();
    }

  for ( ; pk_list; pk_list = pk_list->next )
    {
      PKT_public_key *pk = pk_list->pk;
      int throw_keyid = (opt.throw_keyids || (pk_list->flags&1));
      int rc = write_pubkey_enc (ctrl, pk, throw_keyid, dek, out);
      if (rc)
        return rc;
    }

  return 0;
}

void
encrypt_crypt_files (ctrl_t ctrl, int nfiles, char **files, strlist_t remusr)
{
  int rc = 0;

  if (opt.outfile)
    {
      log_error(_("--output doesn't work for this command\n"));
      return;
    }

  if (!nfiles)
    {
      char line[2048];
      unsigned int lno = 0;
      while ( fgets(line, DIM(line), stdin) )
        {
          lno++;
          if (!*line || line[strlen(line)-1] != '\n')
            {
              log_error("input line %u too long or missing LF\n", lno);
              return;
            }
          line[strlen(line)-1] = '\0';
          print_file_status(STATUS_FILE_START, line, 2);
          rc = encrypt_crypt (ctrl, -1, line, remusr, 0, NULL, -1);
          if (rc)
            log_error ("encryption of '%s' failed: %s\n",
                       print_fname_stdin(line), gpg_strerror (rc) );
          write_status( STATUS_FILE_DONE );
        }
    }
  else
    {
      while (nfiles--)
        {
          print_file_status(STATUS_FILE_START, *files, 2);
          if ( (rc = encrypt_crypt (ctrl, -1, *files, remusr, 0, NULL, -1)) )
            log_error("encryption of '%s' failed: %s\n",
                      print_fname_stdin(*files), gpg_strerror (rc) );
          write_status( STATUS_FILE_DONE );
          files++;
        }
    }
}