g10/encr-data.c

   1 /* encr-data.c -  process an encrypted data packet
   2  * Copyright (C) 1998, 1999, 2000, 2001, 2003 Free Software Foundation, Inc.
   3  *
   4  * This file is part of GnuPG.
   5  *
   6  * GnuPG is free software; you can redistribute it and/or modify
   7  * it under the terms of the GNU General Public License as published by
   8  * the Free Software Foundation; either version 2 of the License, or
   9  * (at your option) any later version.
  10  *
  11  * GnuPG is distributed in the hope that it will be useful,
  12  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14  * GNU General Public License for more details.
  15  *
  16  * You should have received a copy of the GNU General Public License
  17  * along with this program; if not, write to the Free Software
  18  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
  19  */
  20
  21 #include <config.h>
  22 #include <stdio.h>
  23 #include <stdlib.h>
  24 #include <string.h>
  25 #include <assert.h>
  26
  27 #include "gpg.h"
  28 #include "util.h"
  29 #include "memory.h"
  30 #include "packet.h"
  31 #include "mpi.h"
  32 #include "cipher.h"
  33 #include "options.h"
  34 #include "i18n.h"
  35
  36
  37 static int mdc_decode_filter( void *opaque, int control, iobuf_t a,
  38                                               byte *buf, size_t *ret_len);
  39 static int decode_filter( void *opaque, int control, iobuf_t a,
  40                                         byte *buf, size_t *ret_len);
  41
  42 typedef struct {
  43     CIPHER_HANDLE cipher_hd;
  44     MD_HANDLE mdc_hash;
  45     char defer[20];
  46     int  defer_filled;
  47     int  eof_seen;
  48 } decode_filter_ctx_t;
  49
  50
  51 /****************
  52  * Decrypt the data, specified by ED with the key DEK.
  53  */
  54 int
  55 decrypt_data( void *procctx, PKT_encrypted *ed, DEK *dek )
  56 {
  57     decode_filter_ctx_t dfx;
  58     byte *p;
  59     int rc=0, c, i;
  60     byte temp[32];
  61     unsigned blocksize;
  62     unsigned nprefix;
  63
  64     memset( &dfx, 0, sizeof dfx );
  65     if( opt.verbose && !dek->algo_info_printed ) {
  66         const char *s = gcry_cipher_algo_name (dek->algo);
  67         if (s && *s)
  68             log_info(_("%s encrypted data\n"), s );
  69         else
  70             log_info(_("encrypted with unknown algorithm %d\n"), dek->algo );
  71         dek->algo_info_printed = 1;
  72     }
  73     if( (rc=openpgp_cipher_test_algo(dek->algo)) )
  74         goto leave;
  75     blocksize = gcry_cipher_get_algo_blklen (dek->algo);
  76     if( !blocksize || blocksize > 16 )
  77         log_fatal("unsupported blocksize %u\n", blocksize );
  78     nprefix = blocksize;
  79     if( ed->len && ed->len < (nprefix+2) )
  80         BUG();
  81
  82     if( ed->mdc_method ) {
  83         gcry_md_open (&dfx.mdc_hash, ed->mdc_method, 0 );
  84         if ( DBG_HASHING )
  85             gcry_md_start_debug (dfx.mdc_hash, "checkmdc");
  86     }
  87     rc = gcry_cipher_open (&dfx.cipher_hd, dek->algo,
  88                            GCRY_CIPHER_MODE_CFB,
  89                            GCRY_CIPHER_SECURE
  90                            | ((ed->mdc_method || dek->algo >= 100)?
  91                               0 : GCRY_CIPHER_ENABLE_SYNC) );
  92      if (rc)
  93        {
  94          /* we should never get an error here cause we already
  95           * checked, that the algorithm is available. What about a
  96           * flag to let the function die in this case? */
  97         BUG();
  98        }
  99     /* log_hexdump( "thekey", dek->key, dek->keylen );*/
 100     rc = gcry_cipher_setkey (dfx.cipher_hd, dek->key, dek->keylen);
 101     if( gpg_err_code (rc) == GPG_ERR_WEAK_KEY )
 102         log_info(_("WARNING: message was encrypted with "
 103                     "a weak key in the symmetric cipher.\n"));
 104     else if( rc ) {
 105         log_error("key setup failed: %s\n", gpg_strerror (rc) );
 106         goto leave;
 107     }
 108     if (!ed->buf) {
 109         log_error(_("problem handling encrypted packet\n"));
 110         goto leave;
 111     }
 112
 113     gcry_cipher_setiv (dfx.cipher_hd, NULL, 0);
 114
 115     if (ed->len) {
 116         for(i=0; i < (nprefix+2) && ed->len; i++, ed->len-- ) {
 117             if( (c=iobuf_get(ed->buf)) == -1 )
 118                 break;
 119             else
 120                 temp[i] = c;
 121         }
 122     }
 123     else {
 124         for(i=0; i < (nprefix+2); i++ )
 125             if( (c=iobuf_get(ed->buf)) == -1 )
 126                 break;
 127             else
 128                 temp[i] = c;
 129     }
 130     gcry_cipher_decrypt( dfx.cipher_hd, temp, nprefix+2, NULL, 0);
 131     gcry_cipher_sync( dfx.cipher_hd );
 132     p = temp;
 133 /* log_hexdump( "prefix", temp, nprefix+2 ); */
 134     if( p[nprefix-2] != p[nprefix] || p[nprefix-1] != p[nprefix+1] ) {
 135         rc = GPG_ERR_BAD_KEY;
 136         goto leave;
 137     }
 138
 139     if( dfx.mdc_hash )
 140         gcry_md_write( dfx.mdc_hash, temp, nprefix+2 );
 141
 142     if( ed->mdc_method )
 143         iobuf_push_filter( ed->buf, mdc_decode_filter, &dfx );
 144     else
 145         iobuf_push_filter( ed->buf, decode_filter, &dfx );
 146
 147     proc_packets( procctx, ed->buf );
 148     ed->buf = NULL;
 149     if( ed->mdc_method && dfx.eof_seen == 2 )
 150         rc = gpg_error (GPG_ERR_INV_PACKET);
 151     else if( ed->mdc_method ) { /* check the mdc */
 152         int datalen = gcry_md_get_algo_dlen (ed->mdc_method);
 153
 154         gcry_cipher_decrypt (dfx.cipher_hd, dfx.defer, 20, NULL, 0);
 155         gcry_md_final ( dfx.mdc_hash );
 156         if( datalen != 20
 157             || memcmp(gcry_md_read ( dfx.mdc_hash, 0 ), dfx.defer, datalen) )
 158             rc = gpg_error (GPG_ERR_BAD_SIGNATURE);
 159         /*log_hexdump("MDC calculated:", gcry_md_read ( dfx.mdc_hash, 0), datalen);*/
 160         /*log_hexdump("MDC message   :", dfx.defer, 20);*/
 161     }
 162
 163
 164   leave:
 165     gcry_cipher_close(dfx.cipher_hd);
 166     gcry_md_close ( dfx.mdc_hash );
 167     return rc;
 168 }
 169
 170
 171
 172 /* I think we should merge this with cipher_filter */
 173 static int
 174 mdc_decode_filter( void *opaque, int control, iobuf_t a,
 175                                               byte *buf, size_t *ret_len)
 176 {
 177     decode_filter_ctx_t *dfx = opaque;
 178     size_t n, size = *ret_len;
 179     int rc = 0;
 180     int c;
 181
 182     if( control == IOBUFCTRL_UNDERFLOW && dfx->eof_seen ) {
 183         *ret_len = 0;
 184         rc = -1;
 185     }
 186     else if( control == IOBUFCTRL_UNDERFLOW ) {
 187         assert(a);
 188         assert( size > 40 );
 189
 190         /* get at least 20 bytes and put it somewhere ahead in the buffer */
 191         for(n=20; n < 40 ; n++ ) {
 192             if( (c = iobuf_get(a)) == -1 )
 193                 break;
 194             buf[n] = c;
 195         }
 196         if( n == 40 ) {
 197             /* we have enough stuff - flush the deferred stuff */
 198             /* (we have asserted that the buffer is large enough) */
 199             if( !dfx->defer_filled ) { /* the first time */
 200                 memcpy(buf, buf+20, 20 );
 201                 n = 20;
 202             }
 203             else {
 204                 memcpy(buf, dfx->defer, 20 );
 205             }
 206             /* now fill up */
 207             for(; n < size; n++ ) {
 208                 if( (c = iobuf_get(a)) == -1 )
 209                     break;
 210                 buf[n] = c;
 211             }
 212             /* move the last 20 bytes back to the defer buffer */
 213             /* (okay, we are wasting 20 bytes of supplied buffer) */
 214             n -= 20;
 215             memcpy( dfx->defer, buf+n, 20 );
 216             dfx->defer_filled = 1;
 217         }
 218         else if( !dfx->defer_filled ) { /* eof seen buf empty defer */
 219             /* this is bad because there is an incomplete hash */
 220             n -= 20;
 221             memcpy(buf, buf+20, n );
 222             dfx->eof_seen = 2; /* eof with incomplete hash */
 223         }
 224         else { /* eof seen */
 225             memcpy(buf, dfx->defer, 20 );
 226             n -= 20;
 227             memcpy( dfx->defer, buf+n, 20 );
 228             dfx->eof_seen = 1; /* normal eof */
 229         }
 230
 231         if( n ) {
 232             gcry_cipher_decrypt( dfx->cipher_hd, buf, n, NULL, 0);
 233             gcry_md_write( dfx->mdc_hash, buf, n );
 234         }
 235         else {
 236             assert( dfx->eof_seen );
 237             rc = -1; /* eof */
 238         }
 239         *ret_len = n;
 240     }
 241     else if( control == IOBUFCTRL_DESC ) {
 242         *(char**)buf = "mdc_decode_filter";
 243     }
 244     return rc;
 245 }
 246
 247 static int
 248 decode_filter( void *opaque, int control, iobuf_t a, byte *buf, size_t *ret_len)
 249 {
 250     decode_filter_ctx_t *fc = opaque;
 251     size_t n, size = *ret_len;
 252     int rc = 0;
 253
 254     if( control == IOBUFCTRL_UNDERFLOW ) {
 255         assert(a);
 256         n = iobuf_read( a, buf, size );
 257         if( n == -1 ) n = 0;
 258         if( n )
 259             gcry_cipher_decrypt( fc->cipher_hd, buf, n, NULL, 0);
 260         else
 261             rc = -1; /* eof */
 262         *ret_len = n;
 263     }
 264     else if( control == IOBUFCTRL_DESC ) {
 265         *(char**)buf = "decode_filter";
 266     }
 267     return rc;
 268 }
 269