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/* 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;
}
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