agent/pksign.c

   1 /* pksign.c - public key signing (well, actually using a secret key)
   2  * Copyright (C) 2001, 2002, 2003, 2004 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 3 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, see <http://www.gnu.org/licenses/>.
  18  */
  19
  20 #include <config.h>
  21 #include <errno.h>
  22 #include <stdio.h>
  23 #include <stdlib.h>
  24 #include <string.h>
  25 #include <ctype.h>
  26 #include <assert.h>
  27 #include <unistd.h>
  28 #include <sys/stat.h>
  29
  30 #include "agent.h"
  31
  32
  33 static int
  34 do_encode_md (const byte * md, size_t mdlen, int algo, gcry_sexp_t * r_hash,
  35               int raw_value)
  36 {
  37   gcry_sexp_t hash;
  38   int rc;
  39
  40   if (!raw_value)
  41     {
  42       const char *s;
  43       char tmp[16+1];
  44       int i;
  45
  46       s = gcry_md_algo_name (algo);
  47       if (s && strlen (s) < 16)
  48         {
  49           for (i=0; i < strlen (s); i++)
  50             tmp[i] = tolower (s[i]);
  51           tmp[i] = '\0';
  52         }
  53
  54       rc = gcry_sexp_build (&hash, NULL,
  55                             "(data (flags pkcs1) (hash %s %b))",
  56                             tmp, (int)mdlen, md);
  57     }
  58   else
  59     {
  60       gcry_mpi_t mpi;
  61
  62       rc = gcry_mpi_scan (&mpi, GCRYMPI_FMT_USG, md, mdlen, NULL);
  63       if (! rc)
  64         {
  65           rc = gcry_sexp_build (&hash, NULL,
  66                                 "(data (flags raw) (value %m))",
  67                                 mpi);
  68           gcry_mpi_release (mpi);
  69         }
  70
  71     }
  72
  73   *r_hash = hash;
  74   return rc;
  75 }
  76
  77
  78 /* Special version of do_encode_md to take care of pkcs#1 padding.
  79    For TLS-MD5SHA1 we need to do the padding ourself as Libgrypt does
  80    not know about this special scheme.  Fixme: We should have a
  81    pkcs1-only-padding flag for Libgcrypt. */
  82 static int
  83 do_encode_raw_pkcs1 (const byte *md, size_t mdlen, unsigned int nbits,
  84                      gcry_sexp_t *r_hash)
  85 {
  86   int rc;
  87   gcry_sexp_t hash;
  88   unsigned char *frame;
  89   size_t i, n, nframe;
  90
  91   nframe = (nbits+7) / 8;
  92   if ( !mdlen || mdlen + 8 + 4 > nframe )
  93     {
  94       /* Can't encode this hash into a frame of size NFRAME. */
  95       return gpg_error (GPG_ERR_TOO_SHORT);
  96     }
  97
  98   frame = xtrymalloc (nframe);
  99   if (!frame)
 100     return gpg_error_from_syserror ();
 101
 102   /* Assemble the pkcs#1 block type 1. */
 103   n = 0;
 104   frame[n++] = 0;
 105   frame[n++] = 1; /* Block type. */
 106   i = nframe - mdlen - 3 ;
 107   assert (i >= 8); /* At least 8 bytes of padding.  */
 108   memset (frame+n, 0xff, i );
 109   n += i;
 110   frame[n++] = 0;
 111   memcpy (frame+n, md, mdlen );
 112   n += mdlen;
 113   assert (n == nframe);
 114
 115   /* Create the S-expression.  */
 116   rc = gcry_sexp_build (&hash, NULL,
 117                         "(data (flags raw) (value %b))",
 118                         (int)nframe, frame);
 119   xfree (frame);
 120
 121   *r_hash = hash;
 122   return rc;
 123 }
 124
 125
 126
 127 /* SIGN whatever information we have accumulated in CTRL and return
 128    the signature S-Expression. */
 129 int
 130 agent_pksign_do (ctrl_t ctrl, const char *desc_text,
 131                  gcry_sexp_t *signature_sexp, cache_mode_t cache_mode)
 132 {
 133   gcry_sexp_t s_skey = NULL, s_sig = NULL;
 134   unsigned char *shadow_info = NULL;
 135   unsigned int rc = 0;          /* FIXME: gpg-error? */
 136
 137   if (! ctrl->have_keygrip)
 138     return gpg_error (GPG_ERR_NO_SECKEY);
 139
 140   rc = agent_key_from_file (ctrl, desc_text, ctrl->keygrip,
 141                             &shadow_info, cache_mode, &s_skey);
 142   if (rc)
 143     {
 144       log_error ("failed to read the secret key\n");
 145       goto leave;
 146     }
 147
 148   if (!s_skey)
 149     {
 150       /* Divert operation to the smartcard */
 151
 152       unsigned char *buf = NULL;
 153       size_t len = 0;
 154
 155       rc = divert_pksign (ctrl,
 156                           ctrl->digest.value,
 157                           ctrl->digest.valuelen,
 158                           ctrl->digest.algo,
 159                           shadow_info, &buf);
 160       if (rc)
 161         {
 162           log_error ("smartcard signing failed: %s\n", gpg_strerror (rc));
 163           goto leave;
 164         }
 165       len = gcry_sexp_canon_len (buf, 0, NULL, NULL);
 166       assert (len);
 167
 168       rc = gcry_sexp_sscan (&s_sig, NULL, (char*)buf, len);
 169       xfree (buf);
 170       if (rc)
 171         {
 172           log_error ("failed to convert sigbuf returned by divert_pksign "
 173                      "into S-Exp: %s", gpg_strerror (rc));
 174           goto leave;
 175         }
 176     }
 177   else
 178     {
 179       /* No smartcard, but a private key */
 180
 181       gcry_sexp_t s_hash = NULL;
 182
 183       /* Put the hash into a sexp */
 184       if (ctrl->digest.algo == MD_USER_TLS_MD5SHA1)
 185         rc = do_encode_raw_pkcs1 (ctrl->digest.value,
 186                                   ctrl->digest.valuelen,
 187                                   gcry_pk_get_nbits (s_skey),
 188                                   &s_hash);
 189       else
 190         rc = do_encode_md (ctrl->digest.value,
 191                            ctrl->digest.valuelen,
 192                            ctrl->digest.algo,
 193                            &s_hash,
 194                            ctrl->digest.raw_value);
 195       if (rc)
 196         goto leave;
 197
 198       if (DBG_CRYPTO)
 199         {
 200           log_debug ("skey: ");
 201           gcry_sexp_dump (s_skey);
 202         }
 203
 204       /* sign */
 205       rc = gcry_pk_sign (&s_sig, s_hash, s_skey);
 206       gcry_sexp_release (s_hash);
 207       if (rc)
 208         {
 209           log_error ("signing failed: %s\n", gpg_strerror (rc));
 210           goto leave;
 211         }
 212
 213       if (DBG_CRYPTO)
 214         {
 215           log_debug ("result: ");
 216           gcry_sexp_dump (s_sig);
 217         }
 218     }
 219
 220  leave:
 221
 222   *signature_sexp = s_sig;
 223
 224   gcry_sexp_release (s_skey);
 225   xfree (shadow_info);
 226
 227   return rc;
 228 }
 229
 230 /* SIGN whatever information we have accumulated in CTRL and write it
 231    back to OUTFP. */
 232 int
 233 agent_pksign (ctrl_t ctrl, const char *desc_text,
 234               membuf_t *outbuf, cache_mode_t cache_mode)
 235 {
 236   gcry_sexp_t s_sig = NULL;
 237   char *buf = NULL;
 238   size_t len = 0;
 239   int rc = 0;
 240
 241   rc = agent_pksign_do (ctrl, desc_text, &s_sig, cache_mode);
 242   if (rc)
 243     goto leave;
 244
 245   len = gcry_sexp_sprint (s_sig, GCRYSEXP_FMT_CANON, NULL, 0);
 246   assert (len);
 247   buf = xmalloc (len);
 248   len = gcry_sexp_sprint (s_sig, GCRYSEXP_FMT_CANON, buf, len);
 249   assert (len);
 250
 251   put_membuf (outbuf, buf, len);
 252
 253  leave:
 254   gcry_sexp_release (s_sig);
 255   xfree (buf);
 256
 257   return rc;
 258 }