Patent ID: 8160246

Claim:
A broadcast encryption apparatus comprising: a node key generation device for generating a node key for each node; a header generator for generating header information by selecting a relevant node key among the node keys generated at the node key generator according to group information of users to which data is to be transmitted; a data encryptor for encrypting the data to be delivered to the users; a header inserter for appending the header information generated by the header generator to the encrypted data; and a data transmitter for transmitting the data including the header information to a receiver side, wherein the node key generation device comprises: a node secret generator for managing a user that receives a broadcast data in a tree structure and generating a unique node secret for each node in the tree structure; an instant key generator for temporarily generating an instant key used at all nodes in common in the tree structure; and a node key generator for generating a node key for each node by operating the node secret generated at the node secret generator and the instant key generated at the instant key generator, and wherein the broadcast data is decrypted by a combined value of the node secret and the instant key as they are received by the user which receives the broadcast data, wherein the node key generator generates the node key for each node having a same length by operating the instant key and the node secret of each node that has a same length.