A flexible method for masked sharing of group keys

This paper proposes a group key distribution scheme with a user exclusion. The user exclusion is how to distribute an encryption key over a broadcast channel shared by n users so that all but d excluded users can get the grou p key. In the broadcast channel such as Pay-TV, Internet multicast and a mo bile telecommunication for a group, a manager should exclude a dishonest us er or an unauthorized terminal as soon as possible to protect the secrecy o f the group communication. However, it takes a long time for the user exclu sion on a large group, if the distributor distributes the group key to each user except the excluded one. We propose a scheme in which the amount of t ransmission and the key storage of each user do not depend on the number of users of the group. Moreover, our scheme does not require a fixed and priv ileged distributor.