A cryptographic key assignment scheme in a hierarchy for access control

Access control is one of the mechanisms for data protection in a computer system. Many literatures based on cryptography have been proposed to solve the problem of access control in hierarchic structures. Recently, Liaw and Lei proposed an optimal heuristic algorithm for multilevel data security. But, their heuristic algorithm can only be used in a tree structure, which it is a special case of a partially-ordered hierarchy. In this article, we present a modification of their algorithm that enables the algorithm to be used in a partially-ordered structure.