gnupg/sm/sign.c

/* sign.c - Sign a message
 * Copyright (C) 2001, 2002, 2003, 2008,
 *               2010 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 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/>.
 */

#include <config.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <unistd.h>
#include <time.h>
#include <assert.h>

#include "gpgsm.h"
#include <gcrypt.h>
#include <ksba.h>

#include "keydb.h"
#include "../common/i18n.h"


/* Hash the data and return if something was hashed.  Return -1 on error.  */
static int
hash_data (int fd, gcry_md_hd_t md)
{
  estream_t fp;
  char buffer[4096];
  int nread;
  int rc = 0;

  fp = es_fdopen_nc (fd, "rb");
  if (!fp)
    {
      log_error ("fdopen(%d) failed: %s\n", fd, strerror (errno));
      return -1;
    }

  do
    {
      nread = es_fread (buffer, 1, DIM(buffer), fp);
      gcry_md_write (md, buffer, nread);
    }
  while (nread);
  if (es_ferror (fp))
    {
      log_error ("read error on fd %d: %s\n", fd, strerror (errno));
      rc = -1;
    }
  es_fclose (fp);
  return rc;
}


static int
hash_and_copy_data (int fd, gcry_md_hd_t md, ksba_writer_t writer)
{
  gpg_error_t err;
  estream_t fp;
  char buffer[4096];
  int nread;
  int rc = 0;
  int any = 0;

  fp = es_fdopen_nc (fd, "rb");
  if (!fp)
    {
      gpg_error_t tmperr = gpg_error_from_syserror ();
      log_error ("fdopen(%d) failed: %s\n", fd, strerror (errno));
      return tmperr;
    }

  do
    {
      nread = es_fread (buffer, 1, DIM(buffer), fp);
      if (nread)
        {
          any = 1;
          gcry_md_write (md, buffer, nread);
          err = ksba_writer_write_octet_string (writer, buffer, nread, 0);
          if (err)
            {
              log_error ("write failed: %s\n", gpg_strerror (err));
              rc = err;
            }
        }
    }
  while (nread && !rc);
  if (es_ferror (fp))
    {
      rc = gpg_error_from_syserror ();
      log_error ("read error on fd %d: %s\n", fd, strerror (errno));
    }
  es_fclose (fp);
  if (!any)
    {
      /* We can't allow signing an empty message because it does not
         make much sense and more seriously, ksba_cms_build has
         already written the tag for data and now expects an octet
         string and an octet string of size 0 is illegal.  */
      log_error ("cannot sign an empty message\n");
      rc = gpg_error (GPG_ERR_NO_DATA);
    }
  if (!rc)
    {
      err = ksba_writer_write_octet_string (writer, NULL, 0, 1);
      if (err)
        {
          log_error ("write failed: %s\n", gpg_strerror (err));
          rc = err;
        }
    }

  return rc;
}


/* Get the default certificate which is defined as the first
   certificate capable of signing returned by the keyDB and has a
   secret key available. */
int
gpgsm_get_default_cert (ctrl_t ctrl, ksba_cert_t *r_cert)
{
  KEYDB_HANDLE hd;
  ksba_cert_t cert = NULL;
  int rc;
  char *p;

  hd = keydb_new ();
  if (!hd)
    return gpg_error (GPG_ERR_GENERAL);
  rc = keydb_search_first (ctrl, hd);
  if (rc)
    {
      keydb_release (hd);
      return rc;
    }

  do
    {
      rc = keydb_get_cert (hd, &cert);
      if (rc)
        {
          log_error ("keydb_get_cert failed: %s\n", gpg_strerror (rc));
          keydb_release (hd);
          return rc;
        }

      if (!gpgsm_cert_use_sign_p (cert))
        {
          p = gpgsm_get_keygrip_hexstring (cert);
          if (p)
            {
              if (!gpgsm_agent_havekey (ctrl, p))
                {
                  xfree (p);
                  keydb_release (hd);
                  *r_cert = cert;
                  return 0; /* got it */
                }
              xfree (p);
            }
        }

      ksba_cert_release (cert);
      cert = NULL;
    }
  while (!(rc = keydb_search_next (ctrl, hd)));
  if (rc && rc != -1)
    log_error ("keydb_search_next failed: %s\n", gpg_strerror (rc));

  ksba_cert_release (cert);
  keydb_release (hd);
  return rc;
}


static ksba_cert_t
get_default_signer (ctrl_t ctrl)
{
  KEYDB_SEARCH_DESC desc;
  ksba_cert_t cert = NULL;
  KEYDB_HANDLE kh = NULL;
  int rc;

  if (!opt.local_user)
    {
      rc = gpgsm_get_default_cert (ctrl, &cert);
      if (rc)
        {
          if (rc != -1)
            log_debug ("failed to find default certificate: %s\n",
                       gpg_strerror (rc));
          return NULL;
        }
      return cert;
    }

  rc = classify_user_id (opt.local_user, &desc, 0);
  if (rc)
    {
      log_error ("failed to find default signer: %s\n", gpg_strerror (rc));
      return NULL;
    }

  kh = keydb_new ();
  if (!kh)
    return NULL;

  rc = keydb_search (ctrl, kh, &desc, 1);
  if (rc)
    {
      log_debug ("failed to find default certificate: rc=%d\n", rc);
    }
  else
    {
      rc = keydb_get_cert (kh, &cert);
      if (rc)
        {
          log_debug ("failed to get cert: rc=%d\n", rc);
        }
    }

  keydb_release (kh);
  return cert;
}

/* Depending on the options in CTRL add the certificate CERT as well as
   other certificate up in the chain to the Root-CA to the CMS
   object. */
static int
add_certificate_list (ctrl_t ctrl, ksba_cms_t cms, ksba_cert_t cert)
{
  gpg_error_t err;
  int rc = 0;
  ksba_cert_t next = NULL;
  int n;
  int not_root = 0;

  ksba_cert_ref (cert);

  n = ctrl->include_certs;
  log_debug ("adding certificates at level %d\n", n);
  if (n == -2)
    {
      not_root = 1;
      n = -1;
    }
  if (n < 0 || n > 50)
    n = 50; /* We better apply an upper bound */

  /* First add my own certificate unless we don't want any certificate
     included at all. */
  if (n)
    {
      if (not_root && gpgsm_is_root_cert (cert))
        err = 0;
      else
        err = ksba_cms_add_cert (cms, cert);
      if (err)
        goto ksba_failure;
      if (n>0)
        n--;
    }
  /* Walk the chain to include all other certificates.  Note that a -1
     used for N makes sure that there is no limit and all certs get
     included. */
  while ( n-- && !(rc = gpgsm_walk_cert_chain (ctrl, cert, &next)) )
    {
      if (not_root && gpgsm_is_root_cert (next))
        err = 0;
      else
        err = ksba_cms_add_cert (cms, next);
      ksba_cert_release (cert);
      cert = next; next = NULL;
      if (err)
        goto ksba_failure;
    }
  ksba_cert_release (cert);

  return rc == -1? 0: rc;

 ksba_failure:
  ksba_cert_release (cert);
  log_error ("ksba_cms_add_cert failed: %s\n", gpg_strerror (err));
  return err;
}




/* Perform a sign operation.

   Sign the data received on DATA-FD in embedded mode or in detached
   mode when DETACHED is true.  Write the signature to OUT_FP.  The
   keys used to sign are taken from SIGNERLIST or the default one will
   be used if the value of this argument is NULL. */
int
gpgsm_sign (ctrl_t ctrl, certlist_t signerlist,
            int data_fd, int detached, estream_t out_fp)
{
  int i, rc;
  gpg_error_t err;
  gnupg_ksba_io_t b64writer = NULL;
  ksba_writer_t writer;
  ksba_cms_t cms = NULL;
  ksba_stop_reason_t stopreason;
  KEYDB_HANDLE kh = NULL;
  gcry_md_hd_t data_md = NULL;
  int signer;
  const char *algoid;
  int algo;
  ksba_isotime_t signed_at;
  certlist_t cl;
  int release_signerlist = 0;

  audit_set_type (ctrl->audit, AUDIT_TYPE_SIGN);

  kh = keydb_new ();
  if (!kh)
    {
      log_error (_("failed to allocate keyDB handle\n"));
      rc = gpg_error (GPG_ERR_GENERAL);
      goto leave;
    }

  if (!gnupg_rng_is_compliant (opt.compliance))
    {
      rc = gpg_error (GPG_ERR_FORBIDDEN);
      log_error (_("%s is not compliant with %s mode\n"),
                 "RNG",
                 gnupg_compliance_option_string (opt.compliance));
      gpgsm_status_with_error (ctrl, STATUS_ERROR,
                               "random-compliance", rc);
      goto leave;
    }

  ctrl->pem_name = "SIGNED MESSAGE";
  rc = gnupg_ksba_create_writer
    (&b64writer, ((ctrl->create_pem? GNUPG_KSBA_IO_PEM : 0)
                  | (ctrl->create_base64? GNUPG_KSBA_IO_BASE64 : 0)),
     ctrl->pem_name, out_fp, &writer);
  if (rc)
    {
      log_error ("can't create writer: %s\n", gpg_strerror (rc));
      goto leave;
    }

  err = ksba_cms_new (&cms);
  if (err)
    {
      rc = err;
      goto leave;
    }

  err = ksba_cms_set_reader_writer (cms, NULL, writer);
  if (err)
    {
      log_debug ("ksba_cms_set_reader_writer failed: %s\n",
                 gpg_strerror (err));
      rc = err;
      goto leave;
    }

  /* We are going to create signed data with data as encap. content */
  err = ksba_cms_set_content_type (cms, 0, KSBA_CT_SIGNED_DATA);
  if (!err)
    err = ksba_cms_set_content_type (cms, 1, KSBA_CT_DATA);
  if (err)
    {
      log_debug ("ksba_cms_set_content_type failed: %s\n",
                 gpg_strerror (err));
      rc = err;
      goto leave;
    }

  /* If no list of signers is given, use the default certificate. */
  if (!signerlist)
    {
      ksba_cert_t cert = get_default_signer (ctrl);
      if (!cert)
        {
          log_error ("no default signer found\n");
          gpgsm_status2 (ctrl, STATUS_INV_SGNR,
                         get_inv_recpsgnr_code (GPG_ERR_NO_SECKEY), NULL);
          rc = gpg_error (GPG_ERR_GENERAL);
          goto leave;
        }

      /* Although we don't check for ambiguous specification we will
         check that the signer's certificate is usable and valid.  */
      rc = gpgsm_cert_use_sign_p (cert);
      if (!rc)
        rc = gpgsm_validate_chain (ctrl, cert, "", NULL, 0, NULL, 0, NULL);
      if (rc)
        {
          char *tmpfpr;

          tmpfpr = gpgsm_get_fingerprint_hexstring (cert, 0);
          gpgsm_status2 (ctrl, STATUS_INV_SGNR,
                         get_inv_recpsgnr_code (rc), tmpfpr, NULL);
          xfree (tmpfpr);
          goto leave;
        }

      /* That one is fine - create signerlist. */
      signerlist = xtrycalloc (1, sizeof *signerlist);
      if (!signerlist)
        {
          rc = out_of_core ();
          ksba_cert_release (cert);
          goto leave;
        }
      signerlist->cert = cert;
      release_signerlist = 1;
    }

  /* Figure out the hash algorithm to use. We do not want to use the
     one for the certificate but if possible an OID for the plain
     algorithm.  */
  if (opt.forced_digest_algo && opt.verbose)
    log_info ("user requested hash algorithm %d\n", opt.forced_digest_algo);
  for (i=0, cl=signerlist; cl; cl = cl->next, i++)
    {
      const char *oid;

      if (opt.forced_digest_algo)
        {
          oid = NULL;
          cl->hash_algo = opt.forced_digest_algo;
        }
      else
        {
          oid = ksba_cert_get_digest_algo (cl->cert);
          cl->hash_algo = oid ? gcry_md_map_name (oid) : 0;
        }
      switch (cl->hash_algo)
        {
        case GCRY_MD_SHA1:   oid = "1.3.14.3.2.26"; break;
        case GCRY_MD_RMD160: oid = "1.3.36.3.2.1"; break;
        case GCRY_MD_SHA224: oid = "2.16.840.1.101.3.4.2.4"; break;
        case GCRY_MD_SHA256: oid = "2.16.840.1.101.3.4.2.1"; break;
        case GCRY_MD_SHA384: oid = "2.16.840.1.101.3.4.2.2"; break;
        case GCRY_MD_SHA512: oid = "2.16.840.1.101.3.4.2.3"; break;
/*         case GCRY_MD_WHIRLPOOL: oid = "No OID yet"; break; */

        case GCRY_MD_MD5:  /* We don't want to use MD5.  */
        case 0:            /* No algorithm found in cert.  */
        default:           /* Other algorithms.  */
          log_info (_("hash algorithm %d (%s) for signer %d not supported;"
                      " using %s\n"),
                    cl->hash_algo, oid? oid: "?", i,
                    gcry_md_algo_name (GCRY_MD_SHA1));
          cl->hash_algo = GCRY_MD_SHA1;
          oid = "1.3.14.3.2.26";
          break;
        }
      cl->hash_algo_oid = oid;

      /* Check compliance.  */
      if (! gnupg_digest_is_allowed (opt.compliance, 1, cl->hash_algo))
        {
          log_error (_("digest algorithm '%s' may not be used in %s mode\n"),
                     gcry_md_algo_name (cl->hash_algo),
                     gnupg_compliance_option_string (opt.compliance));
          err = gpg_error (GPG_ERR_DIGEST_ALGO);
          goto leave;
        }

      {
        unsigned int nbits;
        int pk_algo = gpgsm_get_key_algo_info (cl->cert, &nbits);

        if (! gnupg_pk_is_allowed (opt.compliance, PK_USE_SIGNING, pk_algo,
                                   NULL, nbits, NULL))
          {
            char  kidstr[10+1];

            snprintf (kidstr, sizeof kidstr, "0x%08lX",
                      gpgsm_get_short_fingerprint (cl->cert, NULL));
            log_error (_("key %s may not be used for signing in %s mode\n"),
                       kidstr,
                       gnupg_compliance_option_string (opt.compliance));
            err = gpg_error (GPG_ERR_PUBKEY_ALGO);
            goto leave;
          }
      }
    }

  if (opt.verbose)
    {
      for (i=0, cl=signerlist; cl; cl = cl->next, i++)
        log_info (_("hash algorithm used for signer %d: %s (%s)\n"),
                  i, gcry_md_algo_name (cl->hash_algo), cl->hash_algo_oid);
    }


  /* Gather certificates of signers and store them in the CMS object. */
  for (cl=signerlist; cl; cl = cl->next)
    {
      rc = gpgsm_cert_use_sign_p (cl->cert);
      if (rc)
        goto leave;

      err = ksba_cms_add_signer (cms, cl->cert);
      if (err)
        {
          log_error ("ksba_cms_add_signer failed: %s\n", gpg_strerror (err));
          rc = err;
          goto leave;
        }
      rc = add_certificate_list (ctrl, cms, cl->cert);
      if (rc)
        {
          log_error ("failed to store list of certificates: %s\n",
                     gpg_strerror(rc));
          goto leave;
        }
      /* Set the hash algorithm we are going to use */
      err = ksba_cms_add_digest_algo (cms, cl->hash_algo_oid);
      if (err)
        {
          log_debug ("ksba_cms_add_digest_algo failed: %s\n",
                     gpg_strerror (err));
          rc = err;
          goto leave;
        }
    }


  /* Check whether one of the certificates is qualified.  Note that we
     already validated the certificate and thus the user data stored
     flag must be available. */
  if (!opt.no_chain_validation)
    {
      for (cl=signerlist; cl; cl = cl->next)
        {
          size_t buflen;
          char buffer[1];

          err = ksba_cert_get_user_data (cl->cert, "is_qualified",
                                         &buffer, sizeof (buffer), &buflen);
          if (err || !buflen)
            {
              log_error (_("checking for qualified certificate failed: %s\n"),
                         gpg_strerror (err));
              rc = err;
              goto leave;
            }
          if (*buffer)
            err = gpgsm_qualified_consent (ctrl, cl->cert);
          else
            err = gpgsm_not_qualified_warning (ctrl, cl->cert);
          if (err)
            {
              rc = err;
              goto leave;
            }
        }
    }

  /* Prepare hashing (actually we are figuring out what we have set
     above). */
  rc = gcry_md_open (&data_md, 0, 0);
  if (rc)
    {
      log_error ("md_open failed: %s\n", gpg_strerror (rc));
      goto leave;
    }
  if (DBG_HASHING)
    gcry_md_debug (data_md, "sign.data");

  for (i=0; (algoid=ksba_cms_get_digest_algo_list (cms, i)); i++)
    {
      algo = gcry_md_map_name (algoid);
      if (!algo)
        {
          log_error ("unknown hash algorithm '%s'\n", algoid? algoid:"?");
          rc = gpg_error (GPG_ERR_BUG);
          goto leave;
        }
      gcry_md_enable (data_md, algo);
      audit_log_i (ctrl->audit, AUDIT_DATA_HASH_ALGO, algo);
    }

  audit_log (ctrl->audit, AUDIT_SETUP_READY);

  if (detached)
    { /* We hash the data right now so that we can store the message
         digest.  ksba_cms_build() takes this as an flag that detached
         data is expected. */
      unsigned char *digest;
      size_t digest_len;

      if (!hash_data (data_fd, data_md))
        audit_log (ctrl->audit, AUDIT_GOT_DATA);
      for (cl=signerlist,signer=0; cl; cl = cl->next, signer++)
        {
          digest = gcry_md_read (data_md, cl->hash_algo);
          digest_len = gcry_md_get_algo_dlen (cl->hash_algo);
          if ( !digest || !digest_len )
            {
              log_error ("problem getting the hash of the data\n");
              rc = gpg_error (GPG_ERR_BUG);
              goto leave;
            }
          err = ksba_cms_set_message_digest (cms, signer, digest, digest_len);
          if (err)
            {
              log_error ("ksba_cms_set_message_digest failed: %s\n",
                         gpg_strerror (err));
              rc = err;
              goto leave;
            }
        }
    }

  gnupg_get_isotime (signed_at);
  for (cl=signerlist,signer=0; cl; cl = cl->next, signer++)
    {
      err = ksba_cms_set_signing_time (cms, signer, signed_at);
      if (err)
        {
          log_error ("ksba_cms_set_signing_time failed: %s\n",
                     gpg_strerror (err));
          rc = err;
          goto leave;
        }
    }

  /* We need to write at least a minimal list of our capabilities to
     try to convince some MUAs to use 3DES and not the crippled
     RC2. Our list is:

        aes128-CBC
        des-EDE3-CBC
  */
  err = ksba_cms_add_smime_capability (cms, "2.16.840.1.101.3.4.1.2", NULL, 0);
  if (!err)
    err = ksba_cms_add_smime_capability (cms, "1.2.840.113549.3.7", NULL, 0);
  if (err)
    {
      log_error ("ksba_cms_add_smime_capability failed: %s\n",
                 gpg_strerror (err));
      goto leave;
    }


  /* Main building loop. */
  do
    {
      err = ksba_cms_build (cms, &stopreason);
      if (err)
        {
          log_debug ("ksba_cms_build failed: %s\n", gpg_strerror (err));
          rc = err;
          goto leave;
        }

      if (stopreason == KSBA_SR_BEGIN_DATA)
        {
          /* Hash the data and store the message digest. */
          unsigned char *digest;
          size_t digest_len;

          assert (!detached);

          rc = hash_and_copy_data (data_fd, data_md, writer);
          if (rc)
            goto leave;
          audit_log (ctrl->audit, AUDIT_GOT_DATA);
          for (cl=signerlist,signer=0; cl; cl = cl->next, signer++)
            {
              digest = gcry_md_read (data_md, cl->hash_algo);
              digest_len = gcry_md_get_algo_dlen (cl->hash_algo);
              if ( !digest || !digest_len )
                {
                  log_error ("problem getting the hash of the data\n");
                  rc = gpg_error (GPG_ERR_BUG);
                  goto leave;
                }
              err = ksba_cms_set_message_digest (cms, signer,
                                                 digest, digest_len);
              if (err)
                {
                  log_error ("ksba_cms_set_message_digest failed: %s\n",
                             gpg_strerror (err));
                  rc = err;
                  goto leave;
                }
            }
        }
      else if (stopreason == KSBA_SR_NEED_SIG)
        {
          /* Compute the signature for all signers.  */
          gcry_md_hd_t md;

          rc = gcry_md_open (&md, 0, 0);
          if (rc)
            {
              log_error ("md_open failed: %s\n", gpg_strerror (rc));
              goto leave;
            }
          if (DBG_HASHING)
            gcry_md_debug (md, "sign.attr");
          ksba_cms_set_hash_function (cms, HASH_FNC, md);
          for (cl=signerlist,signer=0; cl; cl = cl->next, signer++)
            {
              unsigned char *sigval = NULL;
              char *buf, *fpr;

              audit_log_i (ctrl->audit, AUDIT_NEW_SIG, signer);
              if (signer)
                gcry_md_reset (md);
              {
                certlist_t cl_tmp;

                for (cl_tmp=signerlist; cl_tmp; cl_tmp = cl_tmp->next)
                  {
                    gcry_md_enable (md, cl_tmp->hash_algo);
                    audit_log_i (ctrl->audit, AUDIT_ATTR_HASH_ALGO,
                                 cl_tmp->hash_algo);
                  }
              }

              rc = ksba_cms_hash_signed_attrs (cms, signer);
              if (rc)
                {
                  log_debug ("hashing signed attrs failed: %s\n",
                             gpg_strerror (rc));
                  gcry_md_close (md);
                  goto leave;
                }

              rc = gpgsm_create_cms_signature (ctrl, cl->cert,
                                               md, cl->hash_algo, &sigval);
              if (rc)
                {
                  audit_log_cert (ctrl->audit, AUDIT_SIGNED_BY, cl->cert, rc);
                  gcry_md_close (md);
                  goto leave;
                }

              err = ksba_cms_set_sig_val (cms, signer, sigval);
              xfree (sigval);
              if (err)
                {
                  audit_log_cert (ctrl->audit, AUDIT_SIGNED_BY, cl->cert, err);
                  log_error ("failed to store the signature: %s\n",
                             gpg_strerror (err));
                  rc = err;
                  gcry_md_close (md);
                  goto leave;
                }

              /* write a status message */
              fpr = gpgsm_get_fingerprint_hexstring (cl->cert, GCRY_MD_SHA1);
              if (!fpr)
                {
                  rc = gpg_error (GPG_ERR_ENOMEM);
                  gcry_md_close (md);
                  goto leave;
                }
              rc = 0;
              {
                int pkalgo = gpgsm_get_key_algo_info (cl->cert, NULL);
                buf = xtryasprintf ("%c %d %d 00 %s %s",
                                    detached? 'D':'S',
                                    pkalgo,
                                    cl->hash_algo,
                                    signed_at,
                                    fpr);
                if (!buf)
                  rc = gpg_error_from_syserror ();
              }
              xfree (fpr);
              if (rc)
                {
                  gcry_md_close (md);
                  goto leave;
                }
              gpgsm_status (ctrl, STATUS_SIG_CREATED, buf);
              xfree (buf);
              audit_log_cert (ctrl->audit, AUDIT_SIGNED_BY, cl->cert, 0);
            }
          gcry_md_close (md);
        }
    }
  while (stopreason != KSBA_SR_READY);

  rc = gnupg_ksba_finish_writer (b64writer);
  if (rc)
    {
      log_error ("write failed: %s\n", gpg_strerror (rc));
      goto leave;
    }

  audit_log (ctrl->audit, AUDIT_SIGNING_DONE);
  log_info ("signature created\n");


 leave:
  if (rc)
    log_error ("error creating signature: %s <%s>\n",
               gpg_strerror (rc), gpg_strsource (rc) );
  if (release_signerlist)
    gpgsm_release_certlist (signerlist);
  ksba_cms_release (cms);
  gnupg_ksba_destroy_writer (b64writer);
  keydb_release (kh);
  gcry_md_close (data_md);
  return rc;
}