Broadcast encryption (BE) is a cryptographic primitive which sends encrypted message to the users securely. The BE scheme proposed by Naor, Naor, and Lotspiech (NNL) in 2001 is a popular BE scheme which uses a binary tree. The advanced access content system standard suggested to use it for digital right management in Blue-ray and DVD-discs. This paper puts forward an efficient broadcast encryption in public key setting employing ternary tree subset difference method for revocation. Our approach utilizes composite order bilinear group setting to achieve the tree based construction in public key setting. Our second construction is an extension of our first construction and provides outsider-anonymity by disabling the revoked users from getting any information of message and concealing the set of subscribed users from the revoked users. The construction of Fazio and Perera is the closest one to that of our second scheme (as both of these construction are in public key setting and provides outsider-anonymity). We have reduced the ciphertext size from \(r\log N/r\) to min\(\{N/3,N-r,2r-1\}.\) Thus reduces the communication bandwidth. We have also reduced the public key size. Our constructions enjoy the revocation property. Both of our constructions achieve selective semantic security in the standard model under reasonable assumptions and new users can join without updating the pre-existing setup.

广播加密（BE）是一种加密原语，可以安全地将加密的消息发送给用户。Naor，Naor和Lotspiech（NNL）在2001年提出的BE方案是使用二叉树的流行BE方案。先进的访问内容系统标准建议将其用于蓝光和DVD光盘中的数字版权管理。提出了一种利用三叉树子集差分方法撤销公钥的有效广播加密方法。我们的方法利用复合顺序双线性组设置在公共密钥设置中实现基于树的构造。我们的第二个构造是我们第一个构造的扩展，并提供了外部匿名性通过禁止被撤消的用户获取任何消息信息，并向被撤消的用户隐藏订阅的用户集。Fazio和Perera的构建与我们第二个方案的构建最接近（因为这两个构建都是在公共密钥环境中进行的，并且提供了外部匿名性）。我们将密文大小从\（r \ log N / r \）减小到最小\（\ {N / 3，Nr，2r-1 \}。\），从而减少了通信带宽。我们还减小了公共密钥的大小。我们的建筑享有撤销权。我们的两种构造都可以在合理的假设下在标准模型中实现选择性语义安全性，并且新用户可以加入而无需更新现有设置。