rule : 0. only 0-9 a-f A-F withe space (32) and return (10, 13) are allowed. 1. 2 char to form 1 byte, so there are alway 2 char w/o space. 2. if there is a space between the 1st char and the 2nd char, then it should be it in all string, and vice and versa 3. All the white space (32) \n(10) and \r(13) will be ignored.