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diff --git a/g10/cipher.c b/g10/cipher.c
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+/* cipher.c - En-/De-ciphering filter
+ * 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");
+ }
+
+ write_status_printf (STATUS_BEGIN_ENCRYPTION, "%d %d",
+ ed.mdc_method, cfx->dek->algo);
+
+ 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 (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", *ret_len);
+ }
+
+ return rc;
+}