mirror of git://git.gnupg.org/gnupg.git
365 lines
9.8 KiB
C
365 lines
9.8 KiB
C
/* encr-data.c - process an encrypted data packet
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* Copyright (C) 1998, 1999, 2000, 2001, 2005,
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* 2006 Free Software Foundation, Inc.
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*
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* This file is part of GnuPG.
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*
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* GnuPG is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 3 of the License, or
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* (at your option) any later version.
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*
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* GnuPG is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, see <http://www.gnu.org/licenses/>.
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*/
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#include <config.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <assert.h>
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#include "gpg.h"
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#include "util.h"
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#include "packet.h"
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#include "cipher.h"
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#include "options.h"
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#include "i18n.h"
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static int mdc_decode_filter ( void *opaque, int control, IOBUF a,
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byte *buf, size_t *ret_len);
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static int decode_filter ( void *opaque, int control, IOBUF a,
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byte *buf, size_t *ret_len);
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typedef struct decode_filter_context_s
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{
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gcry_cipher_hd_t cipher_hd;
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gcry_md_hd_t mdc_hash;
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char defer[22];
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int defer_filled;
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int eof_seen;
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int refcount;
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} *decode_filter_ctx_t;
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/* Helper to release the decode context. */
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static void
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release_dfx_context (decode_filter_ctx_t dfx)
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{
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if (!dfx)
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return;
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assert (dfx->refcount);
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if ( !--dfx->refcount )
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{
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gcry_cipher_close (dfx->cipher_hd);
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dfx->cipher_hd = NULL;
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gcry_md_close (dfx->mdc_hash);
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dfx->mdc_hash = NULL;
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xfree (dfx);
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}
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}
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/****************
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* Decrypt the data, specified by ED with the key DEK.
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*/
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int
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decrypt_data( void *procctx, PKT_encrypted *ed, DEK *dek )
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{
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decode_filter_ctx_t dfx;
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byte *p;
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int rc=0, c, i;
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byte temp[32];
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unsigned blocksize;
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unsigned nprefix;
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dfx = xtrycalloc (1, sizeof *dfx);
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if (!dfx)
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return gpg_error_from_syserror ();
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dfx->refcount = 1;
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if ( opt.verbose && !dek->algo_info_printed )
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{
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if (!openpgp_cipher_test_algo (dek->algo))
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log_info (_("%s encrypted data\n"),
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openpgp_cipher_algo_name (dek->algo));
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else
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log_info (_("encrypted with unknown algorithm %d\n"), dek->algo );
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dek->algo_info_printed = 1;
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}
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rc = openpgp_cipher_test_algo (dek->algo);
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if (rc)
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goto leave;
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blocksize = gcry_cipher_get_algo_blklen (dek->algo);
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if ( !blocksize || blocksize > 16 )
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log_fatal ("unsupported blocksize %u\n", blocksize );
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nprefix = blocksize;
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if ( ed->len && ed->len < (nprefix+2) )
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BUG();
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if ( ed->mdc_method )
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{
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if (gcry_md_open (&dfx->mdc_hash, ed->mdc_method, 0 ))
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BUG ();
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if ( DBG_HASHING )
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gcry_md_start_debug (dfx->mdc_hash, "checkmdc");
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}
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rc = gcry_cipher_open (&dfx->cipher_hd, dek->algo,
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GCRY_CIPHER_MODE_CFB,
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(GCRY_CIPHER_SECURE
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| ((ed->mdc_method || dek->algo >= 100)?
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0 : GCRY_CIPHER_ENABLE_SYNC)));
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if (rc)
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{
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/* We should never get an error here cause we already checked
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* that the algorithm is available. */
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BUG();
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}
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/* log_hexdump( "thekey", dek->key, dek->keylen );*/
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rc = gcry_cipher_setkey (dfx->cipher_hd, dek->key, dek->keylen);
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if ( gpg_err_code (rc) == GPG_ERR_WEAK_KEY )
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{
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log_info(_("WARNING: message was encrypted with"
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" a weak key in the symmetric cipher.\n"));
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rc=0;
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}
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else if( rc )
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{
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log_error("key setup failed: %s\n", g10_errstr(rc) );
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goto leave;
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}
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if (!ed->buf)
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{
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log_error(_("problem handling encrypted packet\n"));
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goto leave;
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}
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gcry_cipher_setiv (dfx->cipher_hd, NULL, 0);
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if ( ed->len )
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{
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for (i=0; i < (nprefix+2) && ed->len; i++, ed->len-- )
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{
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if ( (c=iobuf_get(ed->buf)) == -1 )
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break;
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else
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temp[i] = c;
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}
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}
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else
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{
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for (i=0; i < (nprefix+2); i++ )
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if ( (c=iobuf_get(ed->buf)) == -1 )
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break;
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else
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temp[i] = c;
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}
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gcry_cipher_decrypt (dfx->cipher_hd, temp, nprefix+2, NULL, 0);
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gcry_cipher_sync (dfx->cipher_hd);
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p = temp;
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/* log_hexdump( "prefix", temp, nprefix+2 ); */
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if (dek->symmetric
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&& (p[nprefix-2] != p[nprefix] || p[nprefix-1] != p[nprefix+1]) )
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{
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rc = gpg_error (GPG_ERR_BAD_KEY);
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goto leave;
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}
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if ( dfx->mdc_hash )
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gcry_md_write (dfx->mdc_hash, temp, nprefix+2);
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dfx->refcount++;
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if ( ed->mdc_method )
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iobuf_push_filter ( ed->buf, mdc_decode_filter, dfx );
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else
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iobuf_push_filter ( ed->buf, decode_filter, dfx );
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proc_packets ( procctx, ed->buf );
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ed->buf = NULL;
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if ( ed->mdc_method && dfx->eof_seen == 2 )
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rc = gpg_error (GPG_ERR_INV_PACKET);
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else if ( ed->mdc_method )
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{
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/* We used to let parse-packet.c handle the MDC packet but this
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turned out to be a problem with compressed packets: With old
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style packets there is no length information available and
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the decompressor uses an implicit end. However we can't know
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this implicit end beforehand (:-) and thus may feed the
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decompressor with more bytes than actually needed. It would
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be possible to unread the extra bytes but due to our weird
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iobuf system any unread is non reliable due to filters
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already popped off. The easy and sane solution is to care
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about the MDC packet only here and never pass it to the
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packet parser. Fortunatley the OpenPGP spec requires a
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strict format for the MDC packet so that we know that 22
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bytes are appended. */
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int datalen = gcry_md_get_algo_dlen (ed->mdc_method);
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assert (dfx->cipher_hd);
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assert (dfx->mdc_hash);
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gcry_cipher_decrypt (dfx->cipher_hd, dfx->defer, 22, NULL, 0);
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gcry_md_write (dfx->mdc_hash, dfx->defer, 2);
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gcry_md_final (dfx->mdc_hash);
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if (dfx->defer[0] != '\xd3' || dfx->defer[1] != '\x14' )
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{
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log_error("mdc_packet with invalid encoding\n");
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rc = gpg_error (GPG_ERR_INV_PACKET);
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}
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else if (datalen != 20
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|| memcmp (gcry_md_read (dfx->mdc_hash, 0),
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dfx->defer+2,datalen ))
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rc = gpg_error (GPG_ERR_BAD_SIGNATURE);
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/* log_printhex("MDC message:", dfx->defer, 22); */
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/* log_printhex("MDC calc:", gcry_md_read (dfx->mdc_hash,0), datalen); */
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}
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leave:
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release_dfx_context (dfx);
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return rc;
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}
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/* I think we should merge this with cipher_filter */
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static int
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mdc_decode_filter (void *opaque, int control, IOBUF a,
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byte *buf, size_t *ret_len)
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{
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decode_filter_ctx_t dfx = opaque;
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size_t n, size = *ret_len;
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int rc = 0;
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int c;
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if ( control == IOBUFCTRL_UNDERFLOW && dfx->eof_seen )
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{
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*ret_len = 0;
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rc = -1;
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}
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else if( control == IOBUFCTRL_UNDERFLOW )
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{
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assert (a);
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assert ( size > 44 );
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/* Get at least 22 bytes and put it somewhere ahead in the buffer. */
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for (n=22; n < 44 ; n++ )
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{
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if( (c = iobuf_get(a)) == -1 )
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break;
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buf[n] = c;
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}
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if ( n == 44 )
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{
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/* We have enough stuff - flush the deferred stuff. */
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/* (we asserted that the buffer is large enough) */
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if ( !dfx->defer_filled ) /* First time. */
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{
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memcpy (buf, buf+22, 22 );
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n = 22;
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}
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else
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{
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memcpy (buf, dfx->defer, 22 );
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}
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/* Now fill up. */
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for (; n < size; n++ )
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{
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if ( (c = iobuf_get(a)) == -1 )
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break;
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buf[n] = c;
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}
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/* Move the last 22 bytes back to the defer buffer. */
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/* (right, we are wasting 22 bytes of the supplied buffer.) */
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n -= 22;
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memcpy (dfx->defer, buf+n, 22 );
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dfx->defer_filled = 1;
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}
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else if ( !dfx->defer_filled ) /* EOF seen but empty defer buffer. */
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{
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/* This is bad because it means an incomplete hash. */
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n -= 22;
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memcpy (buf, buf+22, n );
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dfx->eof_seen = 2; /* EOF with incomplete hash. */
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}
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else /* EOF seen (i.e. read less than 22 bytes). */
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{
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memcpy (buf, dfx->defer, 22 );
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n -= 22;
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memcpy (dfx->defer, buf+n, 22 );
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dfx->eof_seen = 1; /* Normal EOF. */
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}
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if ( n )
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{
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if ( dfx->cipher_hd )
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gcry_cipher_decrypt (dfx->cipher_hd, buf, n, NULL, 0);
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if ( dfx->mdc_hash )
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gcry_md_write (dfx->mdc_hash, buf, n);
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}
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else
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{
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assert ( dfx->eof_seen );
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rc = -1; /* eof */
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}
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*ret_len = n;
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}
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else if ( control == IOBUFCTRL_FREE )
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{
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release_dfx_context (dfx);
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}
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else if ( control == IOBUFCTRL_DESC )
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{
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*(char**)buf = "mdc_decode_filter";
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}
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return rc;
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}
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static int
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decode_filter( void *opaque, int control, IOBUF a, byte *buf, size_t *ret_len)
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{
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decode_filter_ctx_t fc = opaque;
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size_t n, size = *ret_len;
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int rc = 0;
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if ( control == IOBUFCTRL_UNDERFLOW )
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{
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assert(a);
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n = iobuf_read ( a, buf, size );
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if ( n == -1 )
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n = 0;
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if ( n )
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{
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if (fc->cipher_hd)
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gcry_cipher_decrypt (fc->cipher_hd, buf, n, NULL, 0);
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}
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else
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rc = -1; /* EOF */
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*ret_len = n;
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}
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else if ( control == IOBUFCTRL_FREE )
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{
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release_dfx_context (fc);
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}
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else if ( control == IOBUFCTRL_DESC )
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{
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*(char**)buf = "decode_filter";
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}
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return rc;
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}
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