/*

  *  Copyright (C) 2013-2019 Cisco Systems, Inc. and/or its affiliates. All rights reserved.
  *  Copyright (C) 2007-2013 Sourcefire, Inc.

  *

  *  Authors: Tomasz Kojm

  * 
  *  Acknowledgements: The idea of number encoding comes from yyyRSA by 
  *                    Erik Thiele.

  *
  *  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 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;
 }
 

 static 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;

 }

 #define HASH_LEN 32
 #define SALT_LEN 32
 #define PAD_LEN (2048 / 8)
 #define BLK_LEN (PAD_LEN - HASH_LEN - 1)

 int cli_versig2(const unsigned char *sha256, const char *dsig_str, const char *n_str, const char *e_str)
 {

     unsigned char *decoded, digest1[HASH_LEN], digest2[HASH_LEN], digest3[HASH_LEN], *salt;
     unsigned char mask[BLK_LEN], data[BLK_LEN], final[8 + 2 * HASH_LEN], c[4];
     unsigned int i, rounds;

     void *ctx;

     mp_int n, e;

 
     mp_init(&e);
     mp_read_radix(&e, e_str, 10);
     mp_init(&n);
     mp_read_radix(&n, n_str, 10);
 
     decoded = cli_decodesig(dsig_str, PAD_LEN, e, n);
     mp_clear(&n);
     mp_clear(&e);

     if (!decoded)
         return CL_EVERIFY;

     if (decoded[PAD_LEN - 1] != 0xbc) {
         free(decoded);
         return CL_EVERIFY;

     }
 
     memcpy(mask, decoded, BLK_LEN);
     memcpy(digest2, &decoded[BLK_LEN], HASH_LEN);
     free(decoded);
 
     c[0] = c[1] = 0;

     rounds      = (BLK_LEN + HASH_LEN - 1) / HASH_LEN;
     for (i = 0; i < rounds; i++) {
         c[2] = (unsigned char)(i / 256);
         c[3] = (unsigned char)i;
 
         ctx = cl_hash_init("sha256");
         if (!(ctx))
             return CL_EMEM;
 
         cl_update_hash(ctx, digest2, HASH_LEN);
         cl_update_hash(ctx, c, 4);
         cl_finish_hash(ctx, digest3);
         if (i + 1 == rounds)

             memcpy(&data[i * 32], digest3, BLK_LEN - i * HASH_LEN);

         else
             memcpy(&data[i * 32], digest3, HASH_LEN);

     }
 

     for (i = 0; i < BLK_LEN; i++)
         data[i] ^= mask[i];

     data[0] &= (0xff >> 1);
 

     if (!(salt = memchr(data, 0x01, BLK_LEN)))
         return CL_EVERIFY;

     salt++;
 

     if (data + BLK_LEN - salt != SALT_LEN)
         return CL_EVERIFY;

 
     memset(final, 0, 8);
     memcpy(&final[8], sha256, HASH_LEN);
     memcpy(&final[8 + HASH_LEN], salt, SALT_LEN);
 

     ctx = cl_hash_init("sha256");

     if (!(ctx))
         return CL_EMEM;
 

     cl_update_hash(ctx, final, sizeof(final));
     cl_finish_hash(ctx, digest1);

 
     return memcmp(digest1, digest2, HASH_LEN) ? CL_EVERIFY : CL_SUCCESS;
 }