gnupg/agent/findkey.c

/* findkey.c - locate the secret key
 *	Copyright (C) 2001,02 Free Software Foundation, Inc.
 *
 * 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 2 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, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
 */

#include <config.h>
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#include <fcntl.h>
#include <assert.h>
#include <unistd.h>
#include <sys/stat.h>
#include <assert.h>

#include "agent.h"

/* Helper to pass data to the check callback of the unprotect function. */
struct try_unprotect_arg_s {
  const unsigned char *protected_key;
  unsigned char *unprotected_key;
};



int
agent_write_private_key (const unsigned char *grip,
                         const void *buffer, size_t length, int force)
{
  int i;
  char *fname;
  FILE *fp;
  char hexgrip[40+4+1];
  
  for (i=0; i < 20; i++)
    sprintf (hexgrip+2*i, "%02X", grip[i]);
  strcpy (hexgrip+40, ".key");

  fname = make_filename (opt.homedir, GNUPG_PRIVATE_KEYS_DIR, hexgrip, NULL);
  if (force)
    fp = fopen (fname, "wb");
  else
    {
      int fd;

      if (!access (fname, F_OK))
      {
        log_error ("secret key file `%s' already exists\n", fname);
        xfree (fname);
        return seterr (General_Error);
      }

      /* We would like to create FNAME but only if it does not already
	 exist.  We cannot make this guarantee just using POSIX (GNU
	 provides the "x" opentype for fopen, however, this is not
	 portable).  Thus, we use the more flexible open function and
	 then use fdopen to obtain a stream.

	 The mode parameter to open is what fopen uses.  It will be
	 combined with the process' umask automatically.  */
      fd = open (fname, O_CREAT | O_EXCL | O_RDWR,
		 S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP | S_IROTH | S_IWOTH);
      if (fd < 0)
	fp = 0;
      else
	{
	  fp = fdopen (fd, "wb");
	  if (! fp)
	    close (fd);
	}
    }

  if (!fp) 
    { 
      log_error ("can't create `%s': %s\n", fname, strerror (errno));
      xfree (fname);
      return seterr (File_Create_Error);
    }

  if (fwrite (buffer, length, 1, fp) != 1)
    {
      log_error ("error writing `%s': %s\n", fname, strerror (errno));
      fclose (fp);
      remove (fname);
      xfree (fname);
      return seterr (File_Create_Error);
    }
  if ( fclose (fp) )
    {
      log_error ("error closing `%s': %s\n", fname, strerror (errno));
      remove (fname);
      xfree (fname);
      return seterr (File_Create_Error);
    }

  xfree (fname);
  return 0;
}


/* Callback function to try the unprotection from the passpharse query
   code. */
static int
try_unprotect_cb (struct pin_entry_info_s *pi)
{
  struct try_unprotect_arg_s *arg = pi->check_cb_arg;
  size_t dummy;

  assert (!arg->unprotected_key);
  return agent_unprotect (arg->protected_key, pi->pin,
                          &arg->unprotected_key, &dummy);
}


/* Unprotect the canconical encoded S-expression key in KEYBUF.  GRIP
   should be the hex encoded keygrip of that key to be used with the
   cahing mechanism. */
static int
unprotect (unsigned char **keybuf, const unsigned char *grip, int ignore_cache)
{
  struct pin_entry_info_s *pi;
  struct try_unprotect_arg_s arg;
  int rc, i;
  unsigned char *result;
  size_t resultlen;
  char hexgrip[40+1];
  
  for (i=0; i < 20; i++)
    sprintf (hexgrip+2*i, "%02X", grip[i]);
  hexgrip[40] = 0;

  /* first try to get it from the cache - if there is none or we can't
     unprotect it, we fall back to ask the user */
  if (!ignore_cache)
    {
      void *cache_marker;
      const char *pw = agent_get_cache (hexgrip, &cache_marker);
      if (pw)
        {
          rc = agent_unprotect (*keybuf, pw, &result, &resultlen);
          agent_unlock_cache_entry (&cache_marker);
          if (!rc)
            {
              xfree (*keybuf);
              *keybuf = result;
              return 0;
            }
          rc  = 0;
        }
    }
  
  pi = gcry_calloc_secure (1, sizeof (*pi) + 100);
  pi->max_length = 100;
  pi->min_digits = 0;  /* we want a real passphrase */
  pi->max_digits = 8;
  pi->max_tries = 3;
  pi->check_cb = try_unprotect_cb;
  arg.protected_key = *keybuf;
  arg.unprotected_key = NULL;
  pi->check_cb_arg = &arg;

  rc = agent_askpin (NULL, pi);
  if (!rc)
    {
      assert (arg.unprotected_key);
      agent_put_cache (hexgrip, pi->pin, 0);
      xfree (*keybuf);
      *keybuf = arg.unprotected_key;
    }
  xfree (pi);
  return rc;
}



/* Return the secret key as an S-Exp after locating it using the grip.
   Returns NULL if key is not available or the operation should be
   diverted to a token.  In the latter case shadow_info will point to
   an allocated S-Expression with the shadow_info part from the file.
   With IGNORE_CACHE passed as true the passphrase is not taken from
   the cache.*/
GCRY_SEXP
agent_key_from_file (const unsigned char *grip, unsigned char **shadow_info,
                     int ignore_cache)
{
  int i, rc;
  char *fname;
  FILE *fp;
  struct stat st;
  unsigned char *buf;
  size_t len, buflen, erroff;
  GCRY_SEXP s_skey;
  char hexgrip[40+4+1];
  
  if (shadow_info)
      *shadow_info = NULL;

  for (i=0; i < 20; i++)
    sprintf (hexgrip+2*i, "%02X", grip[i]);
  strcpy (hexgrip+40, ".key");

  fname = make_filename (opt.homedir, GNUPG_PRIVATE_KEYS_DIR, hexgrip, NULL);
  fp = fopen (fname, "rb");
  if (!fp)
    {
      log_error ("can't open `%s': %s\n", fname, strerror (errno));
      xfree (fname);
      return NULL;
    }
  
  if (fstat (fileno(fp), &st))
    {
      log_error ("can't stat `%s': %s\n", fname, strerror (errno));
      xfree (fname);
      fclose (fp);
      return NULL;
    }

  buflen = st.st_size;
  buf = xmalloc (buflen+1);
  if (fread (buf, buflen, 1, fp) != 1)
    {
      log_error ("error reading `%s': %s\n", fname, strerror (errno));
      xfree (fname);
      fclose (fp);
      xfree (buf);
      return NULL;
    }

  rc = gcry_sexp_sscan (&s_skey, &erroff, buf, buflen);
  xfree (fname);
  fclose (fp);
  xfree (buf);
  if (rc)
    {
      log_error ("failed to build S-Exp (off=%u): %s\n",
                 (unsigned int)erroff, gcry_strerror (rc));
      return NULL;
    }
  len = gcry_sexp_sprint (s_skey, GCRYSEXP_FMT_CANON, NULL, 0);
  assert (len);
  buf = xtrymalloc (len);
  if (!buf)
    {
      gcry_sexp_release (s_skey);
      return NULL;
    }
  len = gcry_sexp_sprint (s_skey, GCRYSEXP_FMT_CANON, buf, len);
  assert (len);
  gcry_sexp_release (s_skey);

  switch (agent_private_key_type (buf))
    {
    case PRIVATE_KEY_CLEAR:
      break; /* no unprotection needed */
    case PRIVATE_KEY_PROTECTED:
      rc = unprotect (&buf, grip, ignore_cache);
      if (rc)
        log_error ("failed to unprotect the secret key: %s\n",
                   gnupg_strerror (rc));
      break;
    case PRIVATE_KEY_SHADOWED:
      if (shadow_info)
        {
          const unsigned char *s;
          size_t n;

          rc = agent_get_shadow_info (buf, &s);
          if (!rc)
            {
              n = gcry_sexp_canon_len (s, 0, NULL,NULL);
              assert (n);
              *shadow_info = xtrymalloc (n);
              if (!*shadow_info)
                rc = GNUPG_Out_Of_Core;
              else
                {
                  memcpy (*shadow_info, s, n);
                  rc = 0;
                }
            }
          if (rc)
            log_error ("get_shadow_info failed: %s\n", gnupg_strerror (rc));
        }
      rc = -1; /* ugly interface: we return an error but keep a value
                  in shadow_info.  */
      break;
    default:
      log_error ("invalid private key format\n");
      rc = GNUPG_Bad_Secret_Key;
      break;
    }
  if (rc)
    {
      xfree (buf);
      return NULL;
    }

  /* arggg FIXME: does scan support secure memory? */
  rc = gcry_sexp_sscan (&s_skey, &erroff,
                        buf, gcry_sexp_canon_len (buf, 0, NULL, NULL));
  xfree (buf);
  if (rc)
    {
      log_error ("failed to build S-Exp (off=%u): %s\n",
                 (unsigned int)erroff, gcry_strerror (rc));
      return NULL;
    }

  return s_skey;
}

/* Return the secret key as an S-Exp after locating it using the grip.
   Returns NULL if key is not available. 0 = key is available */
int
agent_key_available (const unsigned char *grip)
{
  int i;
  char *fname;
  char hexgrip[40+4+1];
  
  for (i=0; i < 20; i++)
    sprintf (hexgrip+2*i, "%02X", grip[i]);
  strcpy (hexgrip+40, ".key");

  fname = make_filename (opt.homedir, GNUPG_PRIVATE_KEYS_DIR, hexgrip, NULL);
  i = !access (fname, R_OK)? 0 : -1;
  xfree (fname);
  return i;
}