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 #include "iriver.h"
  24
  25 void usage(void)
  26 {
  27     printf("usage: descramble [options] <input file> <output file>\n");
  28     printf("options:\n"
  29            "\t-fm     Archos FM recorder format\n"
  30            "\t-v2     Archos V2 recorder format\n"
  31            "\t-mm=X   Archos Multimedia format (X values: A=JBMM, B=AV1xx, C=AV3xx)\n"
  32            "\t-iriver iRiver format\n"
  33           "\nNo option assumes Archos standard player/recorder format.\n");
  34     exit(1);
  35 }
  36
  37 int main (int argc, char** argv)
  38 {
  39     unsigned long length,i,slen;
  40     unsigned char *inbuf,*outbuf;
  41     unsigned char *iname = argv[1];
  42     unsigned char *oname = argv[2];
  43     unsigned char header[32];
  44     int headerlen = 6;
  45     int descramble = 1;
  46     FILE* file;
  47
  48     if (argc < 3) {
  49         usage();
  50     }
  51
  52     if (!strcmp(argv[1], "-fm") || !strcmp(argv[1], "-v2")) {
  53         headerlen = 24;
  54         iname = argv[2];
  55         oname = argv[3];
  56     }
  57
  58     if (!strcmp(argv[1], "-mm")) {
  59         headerlen = 16;
  60         iname = argv[2];
  61         oname = argv[3];
  62         descramble = 0;
  63     }
  64
  65     if(!strcmp(argv[1], "-iriver")) {
  66         /* iRiver code dealt with in the iriver.c code */
  67         iname = argv[2];
  68         oname = argv[3];
  69         iriver_decode(iname, oname, FALSE, STRIP_NONE);
  70         return 0;
  71     }
  72
  73     /* open file and check size */
  74     file = fopen(iname,"rb");
  75     if (!file) {
  76        perror(oname);
  77        return -1;
  78     }
  79     fseek(file,0,SEEK_END);
  80     length = ftell(file) - headerlen; /* skip header */
  81     fseek(file,0,SEEK_SET);
  82     i = fread(header, 1, headerlen, file);
  83     if ( !i ) {
  84        perror(iname);
  85        return -1;
  86     }
  87
  88     inbuf = malloc(length);
  89     outbuf = malloc(length);
  90     if ( !inbuf || !outbuf ) {
  91        printf("out of memory!\n");
  92        return -1;
  93     }
  94
  95     /* read file */
  96     i=fread(inbuf,1,length,file);
  97     if ( !i ) {
  98        perror(iname);
  99        return -1;
 100     }
 101     fclose(file);
 102
 103     if (descramble) {
 104         /* descramble */
 105         slen = length/4;
 106         for (i = 0; i < length; i++) {
 107             unsigned long addr = ((i % slen) << 2) + i/slen;
 108             unsigned char data = inbuf[i];
 109             data = ~((data >> 1) | ((data << 7) & 0x80)); /* poor man's ROR */
 110             outbuf[addr] = data;
 111         }
 112     }
 113     else {
 114         void* tmpptr;
 115         unsigned int j=0;
 116         int stringlen = 32;
 117         int unpackedsize;
 118         unsigned char xorstring[32];
 119
 120         unpackedsize = header[4] | header[5] << 8;
 121         unpackedsize |= header[6] << 16 | header[7] << 24;
 122
 123         length = header[8] | header[9] << 8;
 124         length |= header[10] << 16 | header[11] << 24;
 125
 126         /* calculate the xor string used */
 127         for (i=0; i<stringlen; i++) {
 128             int top=0, topchar=0, c;
 129             int bytecount[256];
 130             memset(bytecount, 0, sizeof(bytecount));
 131
 132             /* gather byte frequency statistics */
 133             for (c=i; c<length; c+=stringlen)
 134                 bytecount[inbuf[c]]++;
 135
 136             /* find the most frequent byte */
 137             for (c=0; c<256; c++) {
 138                 if (bytecount[c] > top) {
 139                     top = bytecount[c];
 140                     topchar = c;
 141                 }
 142             }
 143             xorstring[i] = topchar;
 144         }
 145         printf("XOR string: %.*s\n", stringlen, xorstring);
 146
 147         /* xor the buffer */
 148         for (i=0; i<length; i++)
 149             outbuf[i] = inbuf[i] ^ xorstring[i & (stringlen-1)];
 150
 151         /* unpack */
 152         tmpptr = realloc(inbuf, unpackedsize);
 153         memset(tmpptr, 0, unpackedsize);
 154         inbuf = outbuf;
 155         outbuf = tmpptr;
 156
 157         for (i=0; i<length;) {
 158             int bit;
 159             int head = inbuf[i++];
 160
 161             for (bit=0; bit<8 && i<length; bit++) {
 162                 if (head & (1 << (bit))) {
 163                     outbuf[j++] = inbuf[i++];
 164                 }
 165                 else {
 166                     int x;
 167                     int byte1 = inbuf[i];
 168                     int byte2 = inbuf[i+1];
 169                     int count = (byte2 & 0x0f) + 3;
 170                     int src =
 171                         (j & 0xfffff000) + (byte1 | ((byte2 & 0xf0)<<4)) + 18;
 172                     if (src > j)
 173                         src -= 0x1000;
 174
 175                     for (x=0; x<count; x++)
 176                         outbuf[j++] = outbuf[src+x];
 177                     i += 2;
 178                 }
 179             }
 180         }
 181         length = j;
 182     }
 183
 184     /* write file */
 185     file = fopen(oname,"wb");
 186     if ( !file ) {
 187        perror(argv[2]);
 188        return -1;
 189     }
 190     if ( !fwrite(outbuf,length,1,file) ) {
 191        perror(argv[2]);
 192        return -1;
 193     }
 194     fclose(file);
 195
 196     free(inbuf);
 197     free(outbuf);
 198
 199     return 0;
 200 }