/*

  *  Copyright (C) 2007-2009 Sourcefire, Inc.

  *

  *  Authors: Tomasz Kojm

  *
  *  This program is free software; you can redistribute it and/or modify

  *  it under the terms of the GNU General Public License version 2 as
  *  published by the Free Software Foundation.

  *
  *  This program 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., 51 Franklin Street, Fifth Floor, Boston,
  *  MA 02110-1301, USA.

  */
 

 #if HAVE_CONFIG_H
 #include "clamav-config.h"
 #endif
 

 #include <stdio.h>
 #include <string.h>
 #include <stdlib.h>
 #include <ctype.h>
 
 #include "clamav.h"
 #include "others.h"

 #include "dsig.h"

 #include "str.h"

 #include "bignum.h"

 #define CLI_NSTR "118640995551645342603070001658453189751527774412027743746599405743243142607464144767361060640655844749760788890022283424922762488917565551002467771109669598189410434699034532232228621591089508178591428456220796841621637175567590476666928698770143328137383952820383197532047771780196576957695822641224262693037"

 #define CLI_ESTR "100001027"
 

 static unsigned char cli_ndecode(unsigned char value)

 {

 	unsigned int i;

 	char ncodec[] = {
 	    'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 
 	    'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 
 	    'y', 'z',
 	    'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 
 	    'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 
 	    'Y', 'Z',
 	    '0', '1', '2', '3', '4', '5', '6', '7', '8', '9',
 	    '+', '/'
 	};
 
 
     for(i = 0; i < 64; i++)
 	if(ncodec[i] == value)
 	    return i;
 
     cli_errmsg("cli_ndecode: value out of range\n");
     return -1;
 }
 

 unsigned char *cli_decodesig(const char *sig, unsigned int plen, mp_int e, mp_int n)

 {

 	int i, slen = strlen(sig), dec;

 	unsigned char *plain;

 	mp_int r, p, c;

     mp_init(&r);
     mp_init(&c);

     for(i = 0; i < slen; i++) {

 	if((dec = cli_ndecode(sig[i])) < 0) {

 	    mp_clear(&r);
 	    mp_clear(&c);

 	    return NULL;

 	}

 	mp_set_int(&r, dec);
 	mp_mul_2d(&r, 6 * i, &r);
 	mp_add(&r, &c, &c);

     }
 

     plain = (unsigned char *) cli_calloc(plen + 1, sizeof(unsigned char));
     if(!plain) {
 	cli_errmsg("cli_decodesig: Can't allocate memory for 'plain'\n");

 	mp_clear(&r);
 	mp_clear(&c);

 	return NULL;
     }

     mp_init(&p);
     mp_exptmod(&c, &e, &n, &p); /* plain = cipher^e mod n */
     mp_clear(&c);
     mp_set_int(&c, 256);

     for(i = plen - 1; i >= 0; i--) { /* reverse */

 	mp_div(&p, &c, &p, &r);
 	plain[i] = mp_get_int(&r);

     }

     mp_clear(&c);
     mp_clear(&p);
     mp_clear(&r);

     return plain;

 }

 
 int cli_versig(const char *md5, const char *dsig)
 {

 	mp_int n, e;

 	char *pt, *pt2;
 

     if(strlen(md5) != 32 || !isalnum(md5[0])) {
 	/* someone is trying to fool us with empty/malformed MD5 ? */
 	cli_errmsg("SECURITY WARNING: MD5 basic test failure.\n");

 	return CL_EVERIFY;

     }
 

     mp_init(&n);
     mp_read_radix(&n, CLI_NSTR, 10);
     mp_init(&e);
     mp_read_radix(&e, CLI_ESTR, 10);

     if(!(pt = (char *) cli_decodesig(dsig, 16, e, n))) {

 	mp_clear(&n);
 	mp_clear(&e);

 	return CL_EVERIFY;

     }

     pt2 = cli_str2hex(pt, 16);

     free(pt);
 

     cli_dbgmsg("cli_versig: Decoded signature: %s\n", pt2);

 
     if(strncmp(md5, pt2, 32)) {

 	cli_dbgmsg("cli_versig: Signature doesn't match.\n");

 	free(pt2);

 	mp_clear(&n);
 	mp_clear(&e);

 	return CL_EVERIFY;

     }
 
     free(pt2);

     mp_clear(&n);
     mp_clear(&e);

     cli_dbgmsg("cli_versig: Digital signature is correct.\n");
     return CL_SUCCESS;

 }