C. VERNAM CIPHER (ONE-TIME PAD) The Vernam Cipher, also called one-time pad, is also implemented using a random set of non repeating characters as the input cipher text. The Vernam Cipher is used one-time pad, which is discarded after a single use, and therefore suitable only for short messages. Example of Vernam Cipher is shown in fig. 8. The plain text is HELLO is converted into UGMEN cipher text by applying one-time pad NCBTZ. The Vernam Cipher was first implemented at AT&T with the help of the a device called Vernam machine.