/* encrypt.c - Encrypt a message
* Copyright (C) 2001, 2003 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 <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 "i18n.h"
struct dek_s {
const char *algoid;
int algo;
gcry_cipher_hd_t chd;
char key[32];
int keylen;
char iv[32];
int ivlen;
};
typedef struct dek_s *DEK;
struct encrypt_cb_parm_s {
FILE *fp;
DEK dek;
int eof_seen;
int ready;
int readerror;
int bufsize;
unsigned char *buffer;
int buflen;
};
/* initialize the data encryptionkey (session key) */
static int
init_dek (DEK dek)
{
int rc=0, mode, i;
dek->algo = gcry_cipher_map_name (dek->algoid);
mode = gcry_cipher_mode_from_oid (dek->algoid);
if (!dek->algo || !mode)
{
log_error ("unsupported algorithm `%s'\n", dek->algoid);
return gpg_error (GPG_ERR_UNSUPPORTED_ALGORITHM);
}
dek->keylen = gcry_cipher_get_algo_keylen (dek->algo);
if (!dek->keylen || dek->keylen > sizeof (dek->key))
return gpg_error (GPG_ERR_BUG);
dek->ivlen = gcry_cipher_get_algo_blklen (dek->algo);
if (!dek->ivlen || dek->ivlen > sizeof (dek->iv))
return gpg_error (GPG_ERR_BUG);
if (dek->keylen < 100/8)
{ /* make sure we don't use weak keys */
log_error ("key length of `%s' too small\n", dek->algoid);
return gpg_error (GPG_ERR_UNSUPPORTED_ALGORITHM);
}
rc = gcry_cipher_open (&dek->chd, dek->algo, mode, GCRY_CIPHER_SECURE);
if (rc)
{
log_error ("failed to create cipher context: %s\n", gpg_strerror (rc));
return rc;
}
for (i=0; i < 8; i++)
{
gcry_randomize (dek->key, dek->keylen, GCRY_STRONG_RANDOM );
rc = gcry_cipher_setkey (dek->chd, dek->key, dek->keylen);
if (gpg_err_code (rc) != GPG_ERR_WEAK_KEY)
break;
log_info(_("weak key created - retrying\n") );
}
if (rc)
{
log_error ("failed to set the key: %s\n", gpg_strerror (rc));
gcry_cipher_close (dek->chd);
dek->chd = NULL;
return rc;
}
gcry_randomize (dek->iv, dek->ivlen, GCRY_STRONG_RANDOM);
rc = gcry_cipher_setiv (dek->chd, dek->iv, dek->ivlen);
if (rc)
{
log_error ("failed to set the IV: %s\n", gpg_strerror (rc));
gcry_cipher_close (dek->chd);
dek->chd = NULL;
return rc;
}
return 0;
}
/* Encode the session key. NBITS is the number of bits which should be
used for packing the session key. returns: An mpi with the session
key (caller must free) */
static gcry_mpi_t
encode_session_key (DEK dek, unsigned int nbits)
{
int nframe = (nbits+7) / 8;
byte *p;
byte *frame;
int i,n;
gcry_mpi_t a;
if (dek->keylen + 7 > nframe || !nframe)
log_bug ("can't encode a %d bit key in a %d bits frame\n",
dek->keylen*8, nbits );
/* We encode the session key in this way:
*
* 0 2 RND(n bytes) 0 KEY(k bytes)
*
* (But how can we store the leading 0 - the external representaion
* of MPIs doesn't allow leading zeroes =:-)
*
* RND are non-zero random bytes.
* KEY is the encryption key (session key)
*/
frame = gcry_xmalloc_secure (nframe);
n = 0;
frame[n++] = 0;
frame[n++] = 2;
i = nframe - 3 - dek->keylen;
assert (i > 0);
p = gcry_random_bytes_secure (i, GCRY_STRONG_RANDOM);
/* replace zero bytes by new values */
for (;;)
{
int j, k;
byte *pp;
/* count the zero bytes */
for(j=k=0; j < i; j++ )
{
if( !p[j] )
k++;
}
if( !k )
break; /* okay: no zero bytes */
k += k/128; /* better get some more */
pp = gcry_random_bytes_secure (k, GCRY_STRONG_RANDOM);
for (j=0; j < i && k; j++)
{
if( !p[j] )
p[j] = pp[--k];
}
xfree (pp);
}
memcpy (frame+n, p, i);
xfree (p);
n += i;
frame[n++] = 0;
memcpy (frame+n, dek->key, dek->keylen);
n += dek->keylen;
assert (n == nframe);
if (gcry_mpi_scan (&a, GCRYMPI_FMT_USG, frame, n, &nframe) )
BUG ();
gcry_free(frame);
return a;
}
/* encrypt the DEK under the key contained in CERT and return it as a
canonical S-Exp in encval */
static int
encrypt_dek (const DEK dek, KsbaCert cert, char **encval)
{
gcry_sexp_t s_ciph, s_data, s_pkey;
int rc;
KsbaSexp buf;
size_t len;
*encval = NULL;
/* get the key from the cert */
buf = ksba_cert_get_public_key (cert);
if (!buf)
{
log_error ("no public key for recipient\n");
return gpg_error (GPG_ERR_NO_PUBKEY);
}
len = gcry_sexp_canon_len (buf, 0, NULL, NULL);
if (!len)
{
log_error ("libksba did not return a proper S-Exp\n");
return gpg_error (GPG_ERR_BUG);
}
rc = gcry_sexp_sscan (&s_pkey, NULL, buf, len);
xfree (buf); buf = NULL;
if (rc)
{
log_error ("gcry_sexp_scan failed: %s\n", gpg_strerror (rc));
return rc;
}
/* put the encoded cleartext into a simple list */
{
/* fixme: actually the pkcs-1 encoding should go into libgcrypt */
gcry_mpi_t data = encode_session_key (dek, gcry_pk_get_nbits (s_pkey));
if (!data)
{
gcry_mpi_release (data);
return gpg_error (GPG_ERR_GENERAL);
}
if (gcry_sexp_build (&s_data, NULL, "%m", data))
BUG ();
gcry_mpi_release (data);
}
/* pass it to libgcrypt */
rc = gcry_pk_encrypt (&s_ciph, s_data, s_pkey);
gcry_sexp_release (s_data);
gcry_sexp_release (s_pkey);
/* reformat it */
len = gcry_sexp_sprint (s_ciph, GCRYSEXP_FMT_CANON, NULL, 0);
assert (len);
buf = xtrymalloc (len);
if (!buf)
{
gpg_error_t tmperr = OUT_OF_CORE (errno);
gcry_sexp_release (s_ciph);
return tmperr;
}
len = gcry_sexp_sprint (s_ciph, GCRYSEXP_FMT_CANON, buf, len);
assert (len);
*encval = buf;
return 0;
}
/* do the actual encryption */
static int
encrypt_cb (void *cb_value, char *buffer, size_t count, size_t *nread)
{
struct encrypt_cb_parm_s *parm = cb_value;
int blklen = parm->dek->ivlen;
unsigned char *p;
size_t n;
*nread = 0;
if (!buffer)
return -1; /* not supported */
if (parm->ready)
return -1;
if (count < blklen)
BUG ();
if (!parm->eof_seen)
{ /* fillup the buffer */
p = parm->buffer;
for (n=parm->buflen; n < parm->bufsize; n++)
{
int c = getc (parm->fp);
if (c == EOF)
{
if (ferror (parm->fp))
{
parm->readerror = errno;
return -1;
}
parm->eof_seen = 1;
break;
}
p[n] = c;
}
parm->buflen = n;
}
n = parm->buflen < count? parm->buflen : count;
n = n/blklen * blklen;
if (n)
{ /* encrypt the stuff */
gcry_cipher_encrypt (parm->dek->chd, buffer, n, parm->buffer, n);
*nread = n;
/* Who cares about cycles, take the easy way and shift the buffer */
parm->buflen -= n;
memmove (parm->buffer, parm->buffer+n, parm->buflen);
}
else if (parm->eof_seen)
{ /* no complete block but eof: add padding */
/* fixme: we should try to do this also in the above code path */
int i, npad = blklen - (parm->buflen % blklen);
p = parm->buffer;
for (n=parm->buflen, i=0; n < parm->bufsize && i < npad; n++, i++)
p[n] = npad;
gcry_cipher_encrypt (parm->dek->chd, buffer, n, parm->buffer, n);
*nread = n;
parm->ready = 1;
}
return 0;
}
/* Perform an encrypt operation.
Encrypt the data received on DATA-FD and write it to OUT_FP. The
recipients are take from the certificate given in recplist; if this
is NULL it will be encrypted for a default recipient */
int
gpgsm_encrypt (CTRL ctrl, CERTLIST recplist, int data_fd, FILE *out_fp)
{
int rc = 0;
Base64Context b64writer = NULL;
KsbaError err;
KsbaWriter writer;
KsbaReader reader = NULL;
KsbaCMS cms = NULL;
KsbaStopReason stopreason;
KEYDB_HANDLE kh = NULL;
struct encrypt_cb_parm_s encparm;
DEK dek = NULL;
int recpno;
FILE *data_fp = NULL;
CERTLIST cl;
memset (&encparm, 0, sizeof encparm);
if (!recplist)
{
log_error(_("no valid recipients given\n"));
gpgsm_status (ctrl, STATUS_NO_RECP, "0");
rc = gpg_error (GPG_ERR_NO_PUBKEY);
goto leave;
}
kh = keydb_new (0);
if (!kh)
{
log_error (_("failed to allocated keyDB handle\n"));
rc = gpg_error (GPG_ERR_GENERAL);
goto leave;
}
data_fp = fdopen ( dup (data_fd), "rb");
if (!data_fp)
{
rc = gpg_error (gpg_err_code_from_errno (errno));
log_error ("fdopen() failed: %s\n", strerror (errno));
goto leave;
}
reader = ksba_reader_new ();
if (!reader)
rc = KSBA_Out_Of_Core;
if (!rc)
rc = ksba_reader_set_cb (reader, encrypt_cb, &encparm);
if (rc)
{
rc = map_ksba_err (rc);
goto leave;
}
encparm.fp = data_fp;
ctrl->pem_name = "ENCRYPTED MESSAGE";
rc = gpgsm_create_writer (&b64writer, ctrl, out_fp, &writer);
if (rc)
{
log_error ("can't create writer: %s\n", gpg_strerror (rc));
goto leave;
}
cms = ksba_cms_new ();
if (!cms)
{
rc = gpg_error (GPG_ERR_ENOMEM);
goto leave;
}
err = ksba_cms_set_reader_writer (cms, reader, writer);
if (err)
{
log_debug ("ksba_cms_set_reader_writer failed: %s\n",
ksba_strerror (err));
rc = map_ksba_err (err);
goto leave;
}
/* We are going to create enveloped data with uninterpreted data as
inner content */
err = ksba_cms_set_content_type (cms, 0, KSBA_CT_ENVELOPED_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",
ksba_strerror (err));
rc = map_ksba_err (err);
goto leave;
}
/* create a session key */
dek = xtrycalloc (1, sizeof *dek); /* hmmm: should we put it into secmem?*/
if (!dek)
rc = OUT_OF_CORE (errno);
else
{
dek->algoid = opt.def_cipher_algoid;
rc = init_dek (dek);
}
if (rc)
{
log_error ("failed to create the session key: %s\n",
gpg_strerror (rc));
goto leave;
}
err = ksba_cms_set_content_enc_algo (cms, dek->algoid, dek->iv, dek->ivlen);
if (err)
{
log_error ("ksba_cms_set_content_enc_algo failed: %s\n",
ksba_strerror (err));
rc = map_ksba_err (err);
goto leave;
}
encparm.dek = dek;
/* Use a ~8k (AES) or ~4k (3DES) buffer */
encparm.bufsize = 500 * dek->ivlen;
encparm.buffer = xtrymalloc (encparm.bufsize);
if (!encparm.buffer)
{
rc = OUT_OF_CORE (errno);
goto leave;
}
/* gather certificates of recipients, encrypt the session key for
each and store them in the CMS object */
for (recpno = 0, cl = recplist; cl; recpno++, cl = cl->next)
{
char *encval;
rc = encrypt_dek (dek, cl->cert, &encval);
if (rc)
{
log_error ("encryption failed for recipient no. %d: %s\n",
recpno, gpg_strerror (rc));
goto leave;
}
err = ksba_cms_add_recipient (cms, cl->cert);
if (err)
{
log_error ("ksba_cms_add_recipient failed: %s\n",
ksba_strerror (err));
rc = map_ksba_err (err);
xfree (encval);
goto leave;
}
err = ksba_cms_set_enc_val (cms, recpno, encval);
xfree (encval);
if (err)
{
log_error ("ksba_cms_set_enc_val failed: %s\n",
ksba_strerror (err));
rc = map_ksba_err (err);
goto leave;
}
}
/* main control loop for encryption */
recpno = 0;
do
{
err = ksba_cms_build (cms, &stopreason);
if (err)
{
log_debug ("ksba_cms_build failed: %s\n", ksba_strerror (err));
rc = map_ksba_err (err);
goto leave;
}
}
while (stopreason != KSBA_SR_READY);
if (encparm.readerror)
{
log_error ("error reading input: %s\n", strerror (encparm.readerror));
rc = gpg_error (gpg_err_code_from_errno (encparm.readerror));
goto leave;
}
rc = gpgsm_finish_writer (b64writer);
if (rc)
{
log_error ("write failed: %s\n", gpg_strerror (rc));
goto leave;
}
log_info ("encrypted data created\n");
leave:
ksba_cms_release (cms);
gpgsm_destroy_writer (b64writer);
ksba_reader_release (reader);
keydb_release (kh);
xfree (dek);
if (data_fp)
fclose (data_fp);
xfree (encparm.buffer);
return rc;
}