gnupg/g10/cipher-cfb.c

/* cipher-cfb.c - Enciphering filter for the old CFB mode.
 * Copyright (C) 1998-2003, 2006, 2009 Free Software Foundation, Inc.
 * Copyright (C) 1998-2003, 2006, 2009, 2017 Werner koch
 *
 * 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/>.
 * SPDX-License-Identifier: GPL-3.0+
 */

#include <config.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>

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


#define MIN_PARTIAL_SIZE 512


static void
write_header (cipher_filter_context_t *cfx, iobuf_t a)
{
  gcry_error_t err;
  PACKET pkt;
  PKT_encrypted ed;
  byte temp[18];
  unsigned int blocksize;
  unsigned int nprefix;

  blocksize = openpgp_cipher_get_algo_blklen (cfx->dek->algo);
  if ( blocksize < 8 || blocksize > 16 )
    log_fatal ("unsupported blocksize %u\n", blocksize);

  memset (&ed, 0, sizeof ed);
  ed.len = cfx->datalen;
  ed.extralen = blocksize + 2;
  ed.new_ctb = !ed.len;
  if (cfx->dek->use_mdc)
    {
      ed.mdc_method = DIGEST_ALGO_SHA1;
      gcry_md_open (&cfx->mdc_hash, DIGEST_ALGO_SHA1, 0);
      if (DBG_HASHING)
        gcry_md_debug (cfx->mdc_hash, "creatmdc");
    }
  else
    {
      log_info (_("WARNING: "
                  "encrypting without integrity protection is dangerous\n"));
      log_info (_("Hint: Do not use option %s\n"), "--rfc2440");
    }

  init_packet (&pkt);
  pkt.pkttype = cfx->dek->use_mdc? PKT_ENCRYPTED_MDC : PKT_ENCRYPTED;
  pkt.pkt.encrypted = &ed;
  if (build_packet( a, &pkt))
    log_bug ("build_packet(ENCR_DATA) failed\n");
  nprefix = blocksize;
  gcry_randomize (temp, nprefix, GCRY_STRONG_RANDOM );
  temp[nprefix] = temp[nprefix-2];
  temp[nprefix+1] = temp[nprefix-1];
  print_cipher_algo_note (cfx->dek->algo);
  err = openpgp_cipher_open (&cfx->cipher_hd,
                             cfx->dek->algo,
                             GCRY_CIPHER_MODE_CFB,
                             (GCRY_CIPHER_SECURE
                              | ((cfx->dek->use_mdc || cfx->dek->algo >= 100)?
                                 0 : GCRY_CIPHER_ENABLE_SYNC)));
  if (err)
    {
      /* We should never get an error here cause we already checked,
       * that the algorithm is available.  */
      BUG();
    }

  /* log_hexdump ("thekey", cfx->dek->key, cfx->dek->keylen); */
  gcry_cipher_setkey (cfx->cipher_hd, cfx->dek->key, cfx->dek->keylen);
  gcry_cipher_setiv (cfx->cipher_hd, NULL, 0);
  /* log_hexdump ("prefix", temp, nprefix+2); */
  if (cfx->mdc_hash) /* Hash the "IV". */
    gcry_md_write (cfx->mdc_hash, temp, nprefix+2 );
  gcry_cipher_encrypt (cfx->cipher_hd, temp, nprefix+2, NULL, 0);
  gcry_cipher_sync (cfx->cipher_hd);
  iobuf_write (a, temp, nprefix+2);

  cfx->short_blklen_warn = (blocksize < 16);
  cfx->short_blklen_count = nprefix+2;

  cfx->wrote_header = 1;
}


/*
 * This filter is used to en/de-cipher data with a symmetric algorithm
 */
int
cipher_filter_cfb (void *opaque, int control,
                   iobuf_t a, byte *buf, size_t *ret_len)
{
  cipher_filter_context_t *cfx = opaque;
  size_t size = *ret_len;
  int rc = 0;

  if (control == IOBUFCTRL_UNDERFLOW) /* decrypt */
    {
      rc = -1; /* not yet used */
    }
  else if (control == IOBUFCTRL_FLUSH) /* encrypt */
    {
      log_assert (a);
      if (!cfx->wrote_header)
        write_header (cfx, a);
      if (cfx->mdc_hash)
        gcry_md_write (cfx->mdc_hash, buf, size);
      gcry_cipher_encrypt (cfx->cipher_hd, buf, size, NULL, 0);
      if (cfx->short_blklen_warn)
        {
          cfx->short_blklen_count += size;
          if (cfx->short_blklen_count > (150 * 1024 * 1024))
            {
              log_info ("WARNING: encrypting more than %d MiB with algorithm "
                        "%s should be avoided\n", 150,
                        openpgp_cipher_algo_name (cfx->dek->algo));
              cfx->short_blklen_warn = 0; /* Don't show again.  */
            }
        }

      rc = iobuf_write (a, buf, size);
    }
  else if (control == IOBUFCTRL_FREE)
    {
      if (cfx->mdc_hash)
        {
          byte *hash;
          int hashlen = gcry_md_get_algo_dlen (gcry_md_get_algo(cfx->mdc_hash));
          byte temp[22];

          log_assert (hashlen == 20);
          /* We must hash the prefix of the MDC packet here. */
          temp[0] = 0xd3;
          temp[1] = 0x14;
          gcry_md_putc (cfx->mdc_hash, temp[0]);
          gcry_md_putc (cfx->mdc_hash, temp[1]);

          gcry_md_final (cfx->mdc_hash);
          hash = gcry_md_read (cfx->mdc_hash, 0);
          memcpy(temp+2, hash, 20);
          gcry_cipher_encrypt (cfx->cipher_hd, temp, 22, NULL, 0);
          gcry_md_close (cfx->mdc_hash); cfx->mdc_hash = NULL;
          if (iobuf_write( a, temp, 22))
            log_error ("writing MDC packet failed\n");
	}

      gcry_cipher_close (cfx->cipher_hd);
    }
  else if (control == IOBUFCTRL_DESC)
    {
      mem2str (buf, "cipher_filter_cfb", *ret_len);
    }
  else if (control == IOBUFCTRL_INIT)
    {
      write_status_printf (STATUS_BEGIN_ENCRYPTION, "%d %d",
                           cfx->dek->use_mdc ? DIGEST_ALGO_SHA1 : 0,
                           cfx->dek->algo);
    }

  return rc;
}