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gnupg/sm/encrypt.c
2008-06-23 14:43:14 +00:00

526 lines
13 KiB
C
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/* encrypt.c - Encrypt a message
* Copyright (C) 2001, 2003, 2004, 2007, 2008 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 <http://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 "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 encryption key (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);
}
/* Extra check for algorithms we consider to be too weak for
encryption, although we support them for decryption. Note that
there is another check below discriminating on the key length. */
switch (dek->algo)
{
case GCRY_CIPHER_DES:
case GCRY_CIPHER_RFC2268_40:
log_error ("cipher algorithm `%s' not allowed: too weak\n",
gcry_cipher_algo_name (dek->algo));
return gpg_error (GPG_ERR_UNSUPPORTED_ALGORITHM);
default:
break;
}
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);
/* Make sure we don't use weak keys. */
if (dek->keylen < 100/8)
{
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_create_nonce (dek->iv, dek->ivlen);
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;
}
static int
encode_session_key (DEK dek, gcry_sexp_t * r_data)
{
gcry_sexp_t data;
char *p;
int rc;
p = xtrymalloc (64 + 2 * dek->keylen);
if (!p)
return gpg_error_from_syserror ();
strcpy (p, "(data\n (flags pkcs1)\n (value #");
bin2hex (dek->key, dek->keylen, p + strlen (p));
strcat (p, "#))\n");
rc = gcry_sexp_sscan (&data, NULL, p, strlen (p));
xfree (p);
*r_data = data;
return rc;
}
/* 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, ksba_cert_t cert, unsigned char **encval)
{
gcry_sexp_t s_ciph, s_data, s_pkey;
int rc;
ksba_sexp_t 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, (char*)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. */
s_data = NULL; /* (avoid compiler warning) */
rc = encode_session_key (dek, &s_data);
if (rc)
{
log_error ("encode_session_key failed: %s\n", gpg_strerror (rc));
return rc;
}
/* 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 ();
gcry_sexp_release (s_ciph);
return tmperr;
}
len = gcry_sexp_sprint (s_ciph, GCRYSEXP_FMT_CANON, (char*)buf, len);
assert (len);
gcry_sexp_release (s_ciph);
*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_t ctrl, certlist_t recplist, int data_fd, FILE *out_fp)
{
int rc = 0;
Base64Context b64writer = NULL;
gpg_error_t err;
ksba_writer_t writer;
ksba_reader_t reader = NULL;
ksba_cms_t cms = NULL;
ksba_stop_reason_t stopreason;
KEYDB_HANDLE kh = NULL;
struct encrypt_cb_parm_s encparm;
DEK dek = NULL;
int recpno;
FILE *data_fp = NULL;
certlist_t cl;
int count;
memset (&encparm, 0, sizeof encparm);
audit_set_type (ctrl->audit, AUDIT_TYPE_ENCRYPT);
/* Check that the certificate list is not empty and that at least
one certificate is not flagged as encrypt_to; i.e. is a real
recipient. */
for (cl = recplist; cl; cl = cl->next)
if (!cl->is_encrypt_to)
break;
if (!cl)
{
log_error(_("no valid recipients given\n"));
gpgsm_status (ctrl, STATUS_NO_RECP, "0");
audit_log_i (ctrl->audit, AUDIT_GOT_RECIPIENTS, 0);
rc = gpg_error (GPG_ERR_NO_PUBKEY);
goto leave;
}
for (count = 0, cl = recplist; cl; cl = cl->next)
count++;
audit_log_i (ctrl->audit, AUDIT_GOT_RECIPIENTS, count);
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;
}
err = ksba_reader_new (&reader);
if (err)
rc = err;
if (!rc)
rc = ksba_reader_set_cb (reader, encrypt_cb, &encparm);
if (rc)
goto leave;
encparm.fp = data_fp;
ctrl->pem_name = "ENCRYPTED MESSAGE";
rc = gpgsm_create_writer (&b64writer, ctrl, out_fp, NULL, &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, reader, writer);
if (err)
{
log_debug ("ksba_cms_set_reader_writer failed: %s\n",
gpg_strerror (err));
rc = err;
goto leave;
}
audit_log (ctrl->audit, AUDIT_GOT_DATA);
/* 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",
gpg_strerror (err));
rc = err;
goto leave;
}
/* Create a session key */
dek = xtrycalloc_secure (1, sizeof *dek);
if (!dek)
rc = out_of_core ();
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",
gpg_strerror (err));
rc = 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 ();
goto leave;
}
audit_log_s (ctrl->audit, AUDIT_SESSION_KEY, dek->algoid);
/* 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)
{
unsigned char *encval;
rc = encrypt_dek (dek, cl->cert, &encval);
if (rc)
{
audit_log_cert (ctrl->audit, AUDIT_ENCRYPTED_TO, cl->cert, 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)
{
audit_log_cert (ctrl->audit, AUDIT_ENCRYPTED_TO, cl->cert, err);
log_error ("ksba_cms_add_recipient failed: %s\n",
gpg_strerror (err));
rc = err;
xfree (encval);
goto leave;
}
err = ksba_cms_set_enc_val (cms, recpno, encval);
xfree (encval);
audit_log_cert (ctrl->audit, AUDIT_ENCRYPTED_TO, cl->cert, err);
if (err)
{
log_error ("ksba_cms_set_enc_val failed: %s\n",
gpg_strerror (err));
rc = 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", gpg_strerror (err));
rc = 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;
}
audit_log (ctrl->audit, AUDIT_ENCRYPTION_DONE);
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;
}