In content-based access control systems

the subject is only allowed or denied to access the object.There are partial orders between different subjects and objects.The traditional access control policy manages these subjects and objects independently

and does not consider the partial orders which may improve the efficiency.By considering the partial orders

a hierarchical key assignment scheme is proposed in this paper

so as to make the assignment of keys to achieve secure communication and access control

improving the efficiency.The objects can be formed into a Directed Acyclic Graph (DAG) using the partial orders between these objects.Then

assign each vertex in the DAG an encryption key based on Diffie-Hellman algorithm

while each vertex may derive the encryption keys of its child vertices by the encryption key of itself.These assigned keys are used to encrypt the resources of the vertices.Thus

the access control of the resources can be achieved by the assignment of the encryption keys.The proposed scheme consists of the phases of system initialization and key updating

and supports user dynamics and topology changes.The security is based on DDH assumptions.It can be used for content-based hierarchical access control.