a method and system for entity public key acquiring , certificate validation and authentication by introducing an online credible third party is disclosed . the method includes the following steps : 1 ) an entity b transmits a message 1 to an entity a ; 2 ) the entity a transmits a message 2 to a credible third party tp after receiving the message 1 ; 3 ) the credible third party tp determines the response repta after receiving the message 2 ; 4 ) the credible third party tp returns a message 3 to the entity a ; 5 ) the entity a returns a message 4 to the entity b after receiving the message 3 ; 6 ) the entity b receives the message 4 ; 7 ) the entity b transmits a message 5 to the entity a ; 8 ) the entity a receives the message 5 . the present invention can achieve public key acquisition , certificate validation and authentication of the entity by integrating them in one protocol , thereby facilitate the execution efficiency and the effect of the protocol and facilitate the combination with various public key acquisition and public key certificate state enquiry protocols . the present invention suits with a “ user - access point - server ” access network structure to meet the authentication requirement of the access network .