Secure group key distribution schemes for broadcast encryption

Abstract

Broadcast encryption schemes provide efficient solutions for protecting the contents in the contents broadcasting environment. In the broadcast encryption, contents are enciphered with a group key and a contents provider distributes this group key to members in the privileged class through a encrypted key message or other secure channels. After receiving the encrypted key message and encrypted contents data, the privileged members can get the group key by deciphering the key message with their private key received from the contents provider in the member-join step, and then they decipher the contents data. There are many problems to be solved in the broadcast encryption. Among those problems, we investigate to solve the two problems in this thesis. One is a rekeying problem of the group key upon the membership change and another is an authentication problem of the broadcast sender. Self-healing key distribution is an efficient rekeying method in the broadcast encryption. It provides an efficient key distribution for stateless receivers in a large dynamic group. It can recover the lost group keys. There have been several self-healing key distribution schemes in the past decade. However, previous schemes just considered m sessions. That is, after m sessions have expired, rekeying of users` private keys is necessary before distributing a new group key. It is called a life-time extension problem. In this thesis, we propose a new self-healing key distribution scheme. The proposed scheme solves the life-time extension problem. Furthermore, we present a new definition for the self-healing key distribution. The proposed definition describes the concept of self-healing key distribution with unlimited sessions. For the sender authentication problem, a malicious member in the group can disturb the broadcast encryption system by impersonating the broadcast sender. They can mount garbage messages or illegal group keys to other members by modifying the broadcast message. He...