Abstract: Public blockchain characterizes non-centralization and decentration and allows any node to join,and thus possesses the advantages of high efficiency,low cost and high data security.However,that it allows any node to join increases the vulnerability of blockchain network.This paper proposed a Client Puzzle based access control model named CPACM.In this model,new nodes have to make use of computing power to conduct proof of work before joining the network.Only the successful nodes could join the public blockchain network.This model adopts access control when keeping public blockchain decentralizing.Experimental results show that the proposed model can restrict the low computing-power nodes and unfaithful nodes to access with high probability when not affecting the faithful nodes to access and prevent nodes collusion,thus preventing the malicious behaviors and improving the security of public blockchain.

Key words: Access control, Blockchain, Client Puzzle, Proof of work, Public blockchain