decode.h

static char base64[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

static int pos(char c)
{
  char *p;
  for(p = base64; *p; p++)
    if(*p == c)
      return p - base64;
  return -1;
}

int base64_decode(const char *str, char **data)
{
  const char *s, *p;
  unsigned char *q;
  int c;
  int x;
  int done = 0;
  int len;
  s = (const char *)malloc(strlen(str));
  q = (unsigned char *)s;
  for(p=str; *p && !done; p+=4){
	  x = pos(p[0]);
	  if(x >= 0)
		  c = x;
	  else{
		  done = 3;
		  break;
	  }
	  c*=64;
	  
	  x = pos(p[1]);
	  if(x >= 0)
		  c += x;
	  else
		  return -1;
	  c*=64;
	  
	  if(p[2] == '=')
		  done++;
	  else{
		  x = pos(p[2]);
		  if(x >= 0)
			  c += x;
		  else
			  return -1;
	  }
	  c*=64;
	  
	  if(p[3] == '=')
		  done++;
	  else{
		  if(done)
			  return -1;
		  x = pos(p[3]);
		  if(x >= 0)
			  c += x;
		  else
			  return -1;
	  }
	  if(done < 3)
		  *q++=(c&0x00ff0000)>>16;
	  
	  if(done < 2)
		  *q++=(c&0x0000ff00)>>8;
	  if(done < 1)
		  *q++=(c&0x000000ff)>>0;
  }

  len = q - (unsigned char*)(s);

  *data = (char*)realloc((void *)s, len);

  return len;
}

char* MyDecode(char *str)
{
	int		i, len;
	char	*data = NULL;
	len = base64_decode(str, &data);
	
	for (i = 0; i < len; i++)
	{
		data[i] -= 0x26;
		data[i] ^= 0x29;
	}
	return data;
}