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/* certcheck.c - check one certificate
* 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 <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <unistd.h>
#include <time.h>
#include <assert.h>
#include <gcrypt.h>
#include <ksba.h>
#include "gpgsm.h"
#include "keydb.h"
#include "i18n.h"
static int
do_encode_md (GCRY_MD_HD md, int algo, size_t len, unsigned nbits,
const byte *asn, size_t asnlen, GCRY_MPI *r_val)
{
int nframe = (nbits+7) / 8;
byte *frame;
int i, n;
if ( len + asnlen + 4 > nframe )
{
log_error ("can't encode a %d bit MD into a %d bits frame\n",
(int)(len*8), (int)nbits);
return GPGSM_Internal_Error;
}
/* We encode the MD in this way:
*
* 0 A PAD(n bytes) 0 ASN(asnlen bytes) MD(len bytes)
*
* PAD consists of FF bytes.
*/
frame = xtrymalloc (nframe);
if (!frame)
return GPGSM_Out_Of_Core;
n = 0;
frame[n++] = 0;
frame[n++] = 1; /* block type */
i = nframe - len - 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, gcry_md_read(md, algo), len ); n += len;
assert ( n == nframe );
gcry_mpi_scan (r_val, GCRYMPI_FMT_USG, frame, &nframe);
xfree (frame);
return 0;
}
/*
Check the signature on CERT using the ISSUER-CERT. This function
does only test the cryptographic signature and nothing else. It is
assumed that the ISSUER_CERT is valid. */
int
gpgsm_check_cert_sig (KsbaCert issuer_cert, KsbaCert cert)
{
/* OID for MD5 as defined in PKCS#1 (rfc2313) */
static byte asn[18] = /* Object ID is 1.2.840.113549.2.5 (md5) */
{ 0x30, 0x20, 0x30, 0x0c, 0x06, 0x08, 0x2a, 0x86, 0x48,
0x86, 0xf7, 0x0d, 0x02, 0x05, 0x05, 0x00, 0x04, 0x10
};
GCRY_MD_HD md;
int rc, algo;
GCRY_MPI frame;
char *p;
GCRY_SEXP s_sig, s_hash, s_pkey;
algo = ksba_cert_get_digest_algo (cert);
md = gcry_md_open (algo, 0);
if (!md)
{
log_error ("md_open failed: %s\n", gcry_strerror (-1));
return GPGSM_General_Error;
}
rc = ksba_cert_hash (cert, 1, HASH_FNC, md);
if (rc)
{
log_error ("ksba_cert_hash failed: %s\n", ksba_strerror (rc));
gcry_md_close (md);
return map_ksba_err (rc);
}
gcry_md_final (md);
p = ksba_cert_get_sig_val (cert); /* fixme: check p*/
if (DBG_X509)
log_debug ("signature: %s\n", p);
rc = gcry_sexp_sscan ( &s_sig, NULL, p, strlen(p));
if (rc)
{
log_error ("gcry_sexp_scan failed: %s\n", gcry_strerror (rc));
return map_gcry_err (rc);
}
/*gcry_sexp_dump (s_sig);*/
/* FIXME: need to map the algo to the ASN OID - we assume a fixed
one for now */
rc = do_encode_md (md, algo, 16, 2048, asn, DIM(asn), &frame);
if (rc)
{
/* fixme: clean up some things */
return rc;
}
/* put hash into the S-Exp s_hash */
if ( gcry_sexp_build (&s_hash, NULL, "%m", frame) )
BUG ();
/*fputs ("hash:\n", stderr); gcry_sexp_dump (s_hash);*/
p = ksba_cert_get_public_key (issuer_cert);
if (DBG_X509)
log_debug ("issuer public key: %s\n", p);
rc = gcry_sexp_sscan ( &s_pkey, NULL, p, strlen(p));
if (rc)
{
log_error ("gcry_sexp_scan failed: %s\n", gcry_strerror (rc));
return map_gcry_err (rc);
}
/*gcry_sexp_dump (s_pkey);*/
rc = gcry_pk_verify (s_sig, s_hash, s_pkey);
if (DBG_CRYPTO)
log_debug ("gcry_pk_verify: %s\n", gcry_strerror (rc));
return map_gcry_err (rc);
}
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