tools/descramble.c

   1 /***************************************************************************
   2  *             __________               __   ___.
   3  *   Open      \______   \ ____   ____ |  | _\_ |__   _______  ___
   4  *   Source     |       _//  _ \_/ ___\|  |/ /| __ \ /  _ \  \/  /
   5  *   Jukebox    |    |   (  <_> )  \___|    < | \_\ (  <_> > <  <
   6  *   Firmware   |____|_  /\____/ \___  >__|_ \|___  /\____/__/\_ \
   7  *                     \/            \/     \/    \/            \/
   8  * $Id$
   9  *
  10  * Copyright (C) 2002 by Björn Stenberg
  11  *
  12  * All files in this archive are subject to the GNU General Public License.
  13  * See the file COPYING in the source tree root for full license agreement.
  14  *
  15  * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
  16  * KIND, either express or implied.
  17  *
  18  ****************************************************************************/
  19
  20 #include <stdio.h>
  21 #include <stdlib.h>
  22
  23 int main (int argc, char** argv)
  24 {
  25     unsigned long length,i,slen;
  26     unsigned char *inbuf,*outbuf;
  27     unsigned char *iname = argv[1];
  28     unsigned char *oname = argv[2];
  29     unsigned char header[32];
  30     int headerlen = 6;
  31     int descramble = 1;
  32     FILE* file;
  33
  34     if (argc < 3) {
  35        printf("usage: %s [-fm] [-v2] [-mm] <input file> <output file>\n",
  36               argv[0]);
  37        return -1;
  38     }
  39
  40     if (!strcmp(argv[1], "-fm") || !strcmp(argv[1], "-v2")) {
  41         headerlen = 24;
  42         iname = argv[2];
  43         oname = argv[3];
  44     }
  45
  46     if (!strcmp(argv[1], "-mm")) {
  47         headerlen = 16;
  48         iname = argv[2];
  49         oname = argv[3];
  50         descramble = 0;
  51     }
  52
  53     /* open file and check size */
  54     file = fopen(iname,"rb");
  55     if (!file) {
  56        perror(oname);
  57        return -1;
  58     }
  59     fseek(file,0,SEEK_END);
  60     length = ftell(file) - headerlen; /* skip header */
  61     fseek(file,0,SEEK_SET);
  62     i = fread(header, 1, headerlen, file);
  63     if ( !i ) {
  64        perror(iname);
  65        return -1;
  66     }
  67
  68     inbuf = malloc(length);
  69     outbuf = malloc(length);
  70     if ( !inbuf || !outbuf ) {
  71        printf("out of memory!\n");
  72        return -1;
  73     }
  74
  75     /* read file */
  76     i=fread(inbuf,1,length,file);
  77     if ( !i ) {
  78        perror(iname);
  79        return -1;
  80     }
  81     fclose(file);
  82
  83     if (descramble) {
  84         /* descramble */
  85         slen = length/4;
  86         for (i = 0; i < length; i++) {
  87             unsigned long addr = ((i % slen) << 2) + i/slen;
  88             unsigned char data = inbuf[i];
  89             data = ~((data >> 1) | ((data << 7) & 0x80)); /* poor man's ROR */
  90             outbuf[addr] = data;
  91         }
  92     }
  93     else {
  94         void* tmpptr;
  95         unsigned int j=0;
  96         int stringlen = 32;
  97         int unpackedsize;
  98         unsigned char xorstring[32];
  99
 100         unpackedsize = header[4] | header[5] << 8;
 101         unpackedsize |= header[6] << 16 | header[7] << 24;
 102
 103         length = header[8] | header[9] << 8;
 104         length |= header[10] << 16 | header[11] << 24;
 105
 106         /* calculate the xor string used */
 107         for (i=0; i<stringlen; i++) {
 108             int top=0, topchar=0, c;
 109             int bytecount[256];
 110             memset(bytecount, 0, sizeof(bytecount));
 111
 112             /* gather byte frequency statistics */
 113             for (c=i; c<length; c+=stringlen)
 114                 bytecount[inbuf[c]]++;
 115
 116             /* find the most frequent byte */
 117             for (c=0; c<256; c++) {
 118                 if (bytecount[c] > top) {
 119                     top = bytecount[c];
 120                     topchar = c;
 121                 }
 122             }
 123             xorstring[i] = topchar;
 124         }
 125         printf("XOR string: %.*s\n", stringlen, xorstring);
 126
 127         /* xor the buffer */
 128         for (i=0; i<length; i++)
 129             outbuf[i] = inbuf[i] ^ xorstring[i & (stringlen-1)];
 130
 131         /* unpack */
 132         tmpptr = realloc(inbuf, unpackedsize);
 133         memset(tmpptr, 0, unpackedsize);
 134         inbuf = outbuf;
 135         outbuf = tmpptr;
 136
 137         for (i=0; i<length;) {
 138             int bit;
 139             int head = inbuf[i++];
 140
 141             for (bit=0; bit<8 && i<length; bit++) {
 142                 if (head & (1 << (bit))) {
 143                     outbuf[j++] = inbuf[i++];
 144                 }
 145                 else {
 146                     int x;
 147                     int byte1 = inbuf[i];
 148                     int byte2 = inbuf[i+1];
 149                     int count = (byte2 & 0x0f) + 3;
 150                     int src =
 151                         (j & 0xfffff000) + (byte1 | ((byte2 & 0xf0)<<4)) + 18;
 152                     if (src > j)
 153                         src -= 0x1000;
 154
 155                     for (x=0; x<count; x++)
 156                         outbuf[j++] = outbuf[src+x];
 157                     i += 2;
 158                 }
 159             }
 160         }
 161         length = j;
 162     }
 163
 164     /* write file */
 165     file = fopen(oname,"wb");
 166     if ( !file ) {
 167        perror(argv[2]);
 168        return -1;
 169     }
 170     if ( !fwrite(outbuf,length,1,file) ) {
 171        perror(argv[2]);
 172        return -1;
 173     }
 174     fclose(file);
 175
 176     free(inbuf);
 177     free(outbuf);
 178
 179     return 0;
 180 }