Abstract: A user receives a message via a network service platform at their mobile handset. The user is required to input a PIN, password or other authentication data, before the received message is displayed. The service platform generates a partial encryption key and embeds this within a message which is subsequently encrypted and transmitted to the receiving device. The receiving device or handset receives the message and decrypts it using a previously stored pseudo-random seed, combined with a user entered PIN. The receiving device or handset extracts the partial key delivered with the message and uses this key data to generate a new pseudo-random seed which, in turn, is used to generate a sequence of characters in apparently random order. This sequence of characters or numbers is presented in a text-only form with a cursor or other highlighting method selecting the first character in the pseudo-random sequence. The user is then able enter their PIN by using cursor control keys, such as the right/left keys.