In order to support randomly moving users

a THC（two-hop cover） algorithm and a two-hop cover-based ac-cess control scheme were proposed.The proposed algorithm made two-hop nodes be able to retrieve access control in-formation of user’s in time through diffusing the information periodically.The scheme based on THC algorithm

the se-curity mechanisms of Merkle hash tree and one way chain

as well as distributed access control mode

its main contribu-tion was it supports randomly moving users for the first time.The analyses and experiments have shown that the pro-posed scheme can be applied to both mobile and stationary user and have several advantages over the current access con-trol methods of low cost in computation

communication and storage

and resistance to node capture

query replay and DoS attacks.