Improvement on the flexible tree-based key management framework

Matsuzaki et al. had proposed a flexible tree-based key management framework for a terminal to connect with multiple content distribution systems (CDSs) using a public bulletin board. In their scheme, the key management center constructs the public bulletin board by utilizing symmetric cryptosystem to protect terminal node keys. On the other hand, the terminals can obtain its node keys by decrypting the cipher which is posted on the public bulletin board of CDS. However, this method is not efficient for a large group which has a number of terminals. When a terminal changes its membership, the key managerial center needs a large amount of computation to structure the public bulletin, and the terminal cannot efficiently compute its node keys from the large pubic bulletin board. In this paper, we propose an improved scheme to structure a public bulletin board efficiently by the key management center of CDS. The improved scheme is capable of a large group of terminals and ensures that low powered equipment can efficiently obtain their node key.