摘要： 条件接收是实现PPV 业务的重要技术，而其中的密钥分发效率和安全性又是影响条件接收系统性能的关键因素。文章在基于四层密钥分配方案的基础上，提出了平衡树分层模型及相应密钥分发方法，该方法具有最优的密钥分发效率。

关键词: 条件接收；按节目收费；密钥分配；平衡树

Abstract: Conditional access is the important technology to realize PPV service, as the efficiency and security of key distribution are the main factors which influence the performance of condition access system. This paper proposes a balance-tree key distribution model on the basis of four-level key distribution scheme, and proves that this scheme has optimal distribution efficiency

Key words: Condition access; Pay per view (PPV); Key distribution; Balance tree