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pksign.c
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pksign.c
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/* pksign.c - public key signing (well, acually using a secret key)
* Copyright (C) 2001 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 <assert.h>
#include <unistd.h>
#include <sys/stat.h>
#include "agent.h"
static int
do_encode_md (const unsigned char *digest, size_t digestlen, int algo,
unsigned int nbits, GCRY_MPI *r_val)
{
int nframe = (nbits+7) / 8;
byte *frame;
int i, n;
byte asn[100];
size_t asnlen;
asnlen = DIM(asn);
if (gcry_md_algo_info (algo, GCRYCTL_GET_ASNOID, asn, &asnlen))
{
log_error ("no object identifier for algo %d\n", algo);
return GNUPG_Internal_Error;
}
if (digestlen + asnlen + 4 > nframe )
{
log_error ("can't encode a %d bit MD into a %d bits frame\n",
(int)(digestlen*8), (int)nbits);
return GNUPG_Internal_Error;
}
/* We encode the MD in this way:
*
* 0 1 PAD(n bytes) 0 ASN(asnlen bytes) MD(len bytes)
*
* PAD consists of FF bytes.
*/
frame = xtrymalloc (nframe);
if (!frame)
return GNUPG_Out_Of_Core;
n = 0;
frame[n++] = 0;
frame[n++] = 1; /* block type */
i = nframe - digestlen - asnlen -3 ;
assert ( i > 1 );
memset ( frame+n, 0xff, i ); n += i;
frame[n++] = 0;
memcpy ( frame+n, asn, asnlen ); n += asnlen;
memcpy ( frame+n, digest, digestlen ); n += digestlen;
assert ( n == nframe );
if (DBG_CRYPTO)
log_printhex ("encoded hash:", frame, nframe);
gcry_mpi_scan (r_val, GCRYMPI_FMT_USG, frame, &nframe);
xfree (frame);
return 0;
}
/* SIGN whatever information we have accumulated in CTRL and write it
back to OUTFP. */
int
agent_pksign (CTRL ctrl, FILE *outfp, int ignore_cache)
{
GCRY_SEXP s_skey = NULL, s_hash = NULL, s_sig = NULL;
GCRY_MPI frame = NULL;
unsigned char *shadow_info = NULL;
int rc;
char *buf = NULL;
size_t len;
if (!ctrl->have_keygrip)
return seterr (No_Secret_Key);
s_skey = agent_key_from_file (ctrl->keygrip, &shadow_info, ignore_cache);
if (!s_skey && !shadow_info)
{
log_error ("failed to read the secret key\n");
rc = seterr (No_Secret_Key);
goto leave;
}
if (!s_skey)
{ /* divert operation to the smartcard */
unsigned char *sigbuf;
rc = divert_pksign (ctrl->digest.value,
ctrl->digest.valuelen,
ctrl->digest.algo,
shadow_info, &sigbuf);
if (rc)
{
log_error ("smartcard signing failed: %s\n", gnupg_strerror (rc));
goto leave;
}
len = gcry_sexp_canon_len (sigbuf, 0, NULL, NULL);
assert (len);
buf = sigbuf;
}
else
{ /* no smartcard, but a private key */
/* put the hash into a sexp */
rc = do_encode_md (ctrl->digest.value,
ctrl->digest.valuelen,
ctrl->digest.algo,
gcry_pk_get_nbits (s_skey),
&frame);
if (rc)
goto leave;
if ( gcry_sexp_build (&s_hash, NULL, "%m", frame) )
BUG ();
if (DBG_CRYPTO)
{
log_debug ("skey: ");
gcry_sexp_dump (s_skey);
}
/* sign */
rc = gcry_pk_sign (&s_sig, s_hash, s_skey);
if (rc)
{
log_error ("signing failed: %s\n", gcry_strerror (rc));
rc = map_gcry_err (rc);
goto leave;
}
if (DBG_CRYPTO)
{
log_debug ("result: ");
gcry_sexp_dump (s_sig);
}
len = gcry_sexp_sprint (s_sig, GCRYSEXP_FMT_CANON, NULL, 0);
assert (len);
buf = xmalloc (len);
len = gcry_sexp_sprint (s_sig, GCRYSEXP_FMT_CANON, buf, len);
assert (len);
}
/* FIXME: we must make sure that no buffering takes place or we are
in full control of the buffer memory (easy to do) - should go
into assuan. */
fwrite (buf, 1, len, outfp);
leave:
gcry_sexp_release (s_skey);
gcry_sexp_release (s_hash);
gcry_sexp_release (s_sig);
gcry_mpi_release (frame);
xfree (buf);
xfree (shadow_info);
return rc;
}

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Sun, Feb 15, 3:46 PM (15 h, 30 m)
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