模式匹配在条件接收系统中的应用

条件接收系统（Conditional Access System ，CAS）是付费数字电视的核心技术，是对数字电视内容的一种保护手段，保证用户只有在满足一定的条件下才能正常收看特定的内容1]。通过前端条件接收系统，可以向用户发送授权指令、邮件、公告等信息，同时前端条件接收系统还会接受来处营业厅的催缴费信息、加授权或者减授权的指令，即前端系统对外是具有一定的开放性。因此，对邮件、公告信息、催缴费信息等内容建立审查机制是十分必要的，而这些内容大多数为文字，使用模式匹配算法来建立自动审查机制是一个好的选择。本文主要介绍文本过滤在条件接收系统中的重要性、如何将模式匹配算法加入到条件接收系统中。

Application of pattern matching in conditional access system

Conditional access system is the core technology of Digital TV, is a kind of protection means for the digital television content, and is used to ensure that the user can only watch specific content while meeting the certain conditions normally. Through the Conditional access front system, the operator can send Authorized instructions, e-mail, announcements and other information users. At the same time, the Conditional access front system will accept urging payment information, plus authorized instruction or less authorized instruction that all from Business hall, immediately that the Conditional access front system is a certain degree open for the outside door. Therefore, establishing a review mechanism for the e-mail, bulletin information, urging payment information and other content is essential. And most of these elements is text, using pattern matching algorithms to establish an automatic review mechanism is a good choice. This paper describes how important the text transitions is for the conditional access system and how the pattern matching algorithm is added to the conditional access system.This paper mainly introduces the importance of text filtering in conditional access system, how to join the conditional access system pattern matching algorithm.