Mobile phone offer tamper prevention by hiding encrypted, encoded user/offer data in offer page and checking its integrity in received reply

摘要

An HTML or WML offer sent to a mobile phone user (eg. 100 texts for $10) could be altered (eg. increasing the text quantity or reducing the price) because the user can identify the important items in the encoded page. To avoid this a number of offer and user specific variables are encoded to numerical values, and these numerical values compressed into four bit nibbles by means of look up tables. Timestamps and checksums may also be added to the data. The exact choice of which data to encode is dependent upon the handset capabilities and the bandwidth of its network connection. The encoded data is then encrypted (eg with tripe DES or AES) and placed into the offer page. Upon receipt of a user reply the data is decrypted, decoded and compared to the original stored version of the data to detect modification.