unsteg.c

/*
 * =====================================================================================
 *
 *       Filename:  unsteg.c
 *
 *    Description:  This tool decrypts the hidden image/message of uncompressed
 *                  bitmap files. This tool has been tested with an image given
 *                  by my GDV2 lecturer.
 *
 *        Version:  1.0
 *        Created:  04/18/07 23:01:59 CEST
 *       Revision:  none
 *       Compiler:  gcc
 *
 *         Author:  Julian Knauer (JPK), jpk@goatpron.de
 *        Company:  
 *
 * =====================================================================================
 */
 
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
 
int main(int argc, char *argv[])
{
  int fp, mod;
  char *fname;
  char *buf;
  int i, s = 0x36, x, r = 0;
 
  fp = open(argv[1], O_RDONLY);
  if (!fp) {
    fprintf(stderr, "Error opening file.\n");
    return -1;
  }
 
  i = strlen(argv[1]);
  fname = (char *)malloc(sizeof(char) * i + 4);
  sprintf(fname, "%s.bmp", argv[1]);
 
  mod = open(fname, O_WRONLY|O_CREAT|0444);
  if (!mod) {
    fprintf(stderr, "Error opening output header file.\n");
    exit(-1);
  }
 
  buf = (char *)malloc(sizeof(char) * 2048);
  while ((i = read(fp, buf, s)) > 0) {
    if (s == 0x36) {
      write(mod, buf, i); // dump header directly to output
      s = 2048; // resize read blocks
    } else {
      for (x = 0; x < i; x++) {
	// Some "fancy" output
	fprintf(stderr, "%4d -> %d", (int)buf[x], (int)(buf[x] & 1));
	if (!(++r % 9))
	  fprintf(stderr, "\n");
	else
	  fprintf(stderr, " | ");
 
	buf[x] = buf[x] & 1;
	if (buf[x] != 0x00) // if LSB is set,
	  buf[x] = 0xff; // than maximize value
      }
      write(mod, buf, i); // write may modified buffer to file
    }
  }
  free(buf);
 
  close(mod);
  close(fp);
 
  return 0;
}