Two simple schemes for access control

In an open information system, all the information in the system are known by the public. For such a system, the users are responsible for enciphering their own information in a way that they can be accessed by authorized users only. Let U={U₁...,U_n,) be the set of users in the system. Associated with each U_i is an authorization list A_i⊂U such that U_i can access the information of U_j if and only if U_i∈A_j. We propose two simple access control schemes. For the first scheme, for any 1⩽i,j,k⩽n, (U_k∈A_j and U_j∈A_i)≫⇒U_k∈A_i . In other words, if U_k can access the information of U _j and U_j can access the information of U_i , then U_k can access the information of U_i. This is called hierarchical accessibility. For the second scheme, there is no constraint on the authorisation lists. To our knowledge, this is the first scheme in the literature that supports arbitrary accessibility