Abstract: Alphabets consisting of letters (‘A’-‘Z’) minus ‘O’ and digits (‘0’-‘9’) are used to form a sequential code where all the codewords are unique. A sequential codeword is used to generate another unique pseudo-random codeword with larger code length using the Time Reversal Transformation (TRT). A TRT codeword is divided into a number of equal-sized sub-codewords which are used to authenticate a group of users to play Internet-based hand-held video games. A sub-codeword has the format that every two alphabets are followed by a digit to avoid the possibility of the occurrence of any obscene words.