More on Master Keys for Group

Two schemes for key distribution in a computer network are presented in [ 11. Given a network of N users, these schemes allow the construction of group keys and master keys for each of the 2N N 1 subgroups of two or more users from only O(N) pieces of secret information. Agrroup key allows the members of a group to communicate among themselves; a master kq allows the holder to compute group keys for all subgroups of the group for which it is the master. In this paper we show that the first of the two schemes presented in [ 11 can be compromised. We present a so!ution to this problem, and then show that our solution leads to a general strategy for constructing schemes that support group keys and master keys.