the method according to an embodiment of the present invention involves three security elements , i . e ., two entities a and b and a trusted third party tp . through the online trusted third party tp , the entities a and b perform authentication with each other , and obtain the valid public key or the status of the public key certificate of their counterparts . the entity a can communicate directly with the trusted third party tp , while the entity b can communicate with the trusted third party tp only through the entity a . for an entity x with x being either a or b , rx denotes the random number generated by the entity x ; cert x is the public key certificate of the entity x ; id x is the identity identifier of the entity x , and is represented by the certificate cert x or the entity distinguisher x ; reqx denotes the request generated by the entity x , and is used to request information such as the valid public key or the status of the public key certificate of the counterpart ; reqxt denotes the request generated or forwarded by the entity x to the trusted third party tp ; repx denotes the response sent to the entity x against reqx , i . e ., to respond to the entity x with information such as the valid public key or the status of the public key certificate of the entity that is requested by the entity x ; reptx denotes the response generated by the trusted third party tp against reqxt , i . e ., the trusted third party tp responds to the entity x with information such as the valid public key or the status of the public key certificate of the entity that is requested directly by the entity x or requested in a request forwarded by the entity x ; token is a field for the token ; text is an optional text field ; and ss x denotes the signature signed by the entity x . the form and definition of reqb , reqat , repta and repb may be determined according to a particular public key verification or distribution protocol that is used , and the online public key verification or distribution protocol may include certificate status protocol ( see gb / t 19713 ), server based certificate verification protocol ( see ietf rfc5055 ) and other public key verification or distribution protocols . as shown in fig2 , the method for entity public key obtaining , certificate verification and authentication with an online trusted third party according to an embodiment of the present invention includes the following steps : 1 ) sending , by an entity b , a message 1 to an entity a , the message 1 including a random number r b , an identity identifier id b , a request reqb and optional text text1 , wherein the request reqb indicates that the entity b requests a valid public key or the status of a public key certificate of its counterpart ( i . e ., the entity a ); 2 ) sending , by the entity a on receipt of the message 1 , a message 2 to a trusted third party tp , the message 2 including a request reqat and optional text text2 , wherein the request reqat includes the content of the request reqb , and the request reqat indicates that the entity a requests a valid public key or the status of a public key certificate of the entity b , and that the entity b requests a valid public key or the status of a public key certificate of the entity a ; 3 ) checking , by the trusted third party tp on receipt of the message 2 , the validity of public key certificates cert a and cert b , according to identity identifiers id a and id b of the entity a and the entity b ; or searching , by the trusted third party tp on receipt of the message 2 , for valid public keys of the entity a and the entity b through entity distinguishers a and b , and determining , by the trusted third party tp , a response repta , wherein the response repta includes the content of a response repb , and the response repta indicates the valid public key or the status of the public key certificate of the entity a as well as the valid public key or the status of the public key certificate of the entity b determined by the trusted third party tp ; 4 ) returning , by the trusted third party tp , a message 3 to the entity a , the message 3 including the response repta and optional text text3 ; 5 ) returning , by the entity a on receipt of the message 3 , a message 4 to the entity b , the message 4 including a random number r a , an identity identifier id a , a token tokenab , the response repb and optional text text5 , wherein tokenab = ss a ( repb ∥ r a ∥ r b ∥ b ∥ a ∥ text4 ), and the response repb indicates the valid public key or the status of the public key certificate of the entity a determined by the trusted third party tp ; 6 ) performing , by the entity b , the following steps on receipt of the message 4 : 6 . 1 ) verifying the response repb according to a public key verification protocol or distribution protocol that is used , and performing step 6 . 2 ) if the verification is passed ; 6 . 2 ) obtaining the public key or the status of the public key certificate of the entity a , verifying whether the signature signed by the entity a in the token tokenab is correct and checking whether a distinguisher of the entity b is consistent with an entity distinguisher ( b ) included in signature data of the entity a in the token tokenab , and if so , checking whether the random number r b generated by the entity b in the message 1 is consistent with the random number r b included in the signature data of the entity a in the token tokenab , and if so , determining the authentication of the entity a by the entity b is passed and performing step 7 ); 7 ) sending , by the entity b , a message 5 to the entity a , the message 5 including a token tokenba and optional text text7 , wherein tokenba = ss b ( r a ∥ a ∥ text6 ); 8 ) performing , by the entity a , the following steps on receipt of the message 5 : 8 . 1 ) verifying the response repta in the message 3 according to a public key verification protocol or distribution protocol that is used , and performing step 8 . 2 ) if the verification is passed ; 8 . 2 ) obtaining the public key or the status of the public key certificate of the entity b , verifying whether the signature signed by the entity b in the token tokenba is correct and checking whether a distinguisher a of the entity a is consistent with an entity distinguisher ( a ) included in signature data of the entity b in the token tokenba , and if so , checking whether the random number r a generated by the entity a in the message 4 is consistent with the random number r a included in the signature data of the entity b in the token tokenba , and if so , determining the authentication of the entity b by the entity a is passed . in the above embodiment , step 8 . 1 ) may be advanced to be within step 5 ), i . e ., on receipt of the message 3 , the entity a performs firstly the step 8 . 1 ), and then sends the message 4 to the entity b . and a time stamp or a serial number may be used in place of the random numbers r a and r b . in a practical application using the authentication system , generally the entity b may reside on a user communication terminal , and the entity a may reside on a network access point . by the method for two - way authentication between the entity b and the entity a according to the embodiment above , two - way verification of validity between the user and the network access point can be realized , thus ensuring a legitimate user to access a legitimate network . in a practical application , sometimes it only needs to ensure the network for the user to access is legitimate . in this case , the method according to the above embodiment may be modified , i . e ., to cancel the message 5 , simplify the content of the messages 1 to 4 , and omit the steps 7 ) and 8 ), thus realizing one - way authentication of the entity a by the entity b . as shown in fig3 , a detailed process includes the following steps . 1 ) sending , by an entity b , a message 1 to an entity a , the message 1 including a random number r b , a request reqb and optional text text1 , wherein the request reqb indicates that the entity b requests a valid public key or the status of a public key certificate of its counterpart ( i . e ., the entity a ); 2 ) sending , by the entity a on receipt of the message 1 , a message 2 to a trusted third party tp , the message 2 including a request reqat and optional text text2 , wherein the request reqat equals to the content of the request reqb , and the request reqat indicates that the entity b requests a valid public key or the status of a public key certificate of the entity a ; 3 ) checking , by the trusted third party tp on receipt of the message 2 , the validity of a public key certificate cert a according to an identity identifier id a of the entity a ; or searching , by the trusted third party tp on receipt of the message 2 , for a valid public key of the entity a through an entity distinguisher a , and determining , by the trusted third party tp , a response repta , wherein the response repta equals to the content of a response repb , and the response repta indicates the valid public key or the status of the public key certificate of the entity a determined by the trusted third party tp ; 4 ) returning , by the trusted third party tp , a message 3 to the entity a , the message 3 including the response repta and optional text text3 ; 5 ) returning , by the entity a on receipt of the message 3 , a message 4 to the entity b , the message 4 including an identity identifier id a , a token tokenab , the response repb and optional text text5 , wherein tokenab = ss a ( repb ∥ r b ∥ a ∥ text4 ); 6 ) performing , by the entity b , the following steps on receipt of the message 4 : 6 . 1 ) verifying the response repb according to a public key verification protocol or distribution protocol that is used , and performing step 6 . 2 ) if the verification is passed ; 6 . 2 ) obtaining the public key or the status of the public key certificate of the entity a , verifying whether the signature signed by the entity a in the token tokenab is correct and checking whether the random number r b generated by the entity b in the message 1 is consistent with the random number r b included in signature data of the entity a in the token tokenab , and if so , determining the authentication of the entity a by the entity b is passed . the present invention also provides a system for entity public key obtaining , certificate verification and authentication with an online trusted third party , and the system includes an entity a , an entity b and the trusted third party . the trusted third party includes a response repta generation unit . the trusted third party generates a response repta and sends it to the entity a through the response repta generation unit . the entity a includes a verification unit for verifying the identity of the entity b . the verification unit for verifying the identity of the entity b verifies the response repta according to a public key verification protocol or distribution protocol that is used ; obtains a public key or the status of a public key certificate of the entity b if the verification is passed ; verifies whether a signature signed by the entity b in a token tokenba is correct and checks whether a distinguisher a of the entity a is consistent with an entity distinguisher ( a ) included in signature data of the entity b in the token tokenba ; and if so , checks whether a random number r a generated by the entity a in a message 4 is consistent with a random number r a included in the signature data of the entity b in the token tokenba ; and if so , determines the verification of the identity of the entity b is passed . the entity b includes a verification unit for verifying the identity of the entity a . the verification unit for verifying the identity of the entity a verifies a response repb according to a public key verification protocol or distribution protocol that is used ; obtains a public key or the status of a public key certificate of the entity a if the verification is passed ; verifies whether a signature signed by the entity a in a token tokenab is correct and checks whether a distinguisher of the entity b is consistent with an entity distinguisher ( b ) included in signature data of the entity a in the token tokenab ; and if so , checks whether a random number r b generated by the entity b in a message 1 is consistent with a random number r b included in the signature data of the entity a in the token tokenab ; and if so , determines the verification of the identity of the entity a is passed . the present invention also provides a system for entity public key obtaining , certificate verification and authentication with an online trusted third party , and the system includes an entity a , an entity b and the trusted third party . the trusted third party includes a response repta generation unit . the trusted third party generates a response repta and sends it to the entity a through the response repta generation unit . the entity b includes a verification unit for verifying the identity of the entity a . the verification unit for verifying the identity of the entity a verifies a response repb according to a public key verification protocol or distribution protocol that is used ; obtains a public key or the status of a public key certificate of the entity a if the verification is passed ; verifies whether a signature signed by the entity a in a token tokenab is correct and checks whether a random number r b generated by the entity b in a message 1 is consistent with a random number r b included in signature data of the entity a in the token tokenab ; and if so , determines the verification of the identity of the entity a is passed . the denotations used in the above embodiments such as entities a and b , random numbers r a and r b , messages 1 to 5 , optional text 1 to 5 , and identity identifiers , requests and responses , are for illustrative purposes only and merely distinguish items with the same property ( e . g ., two entities ), which thus shall not be interpreted as limiting the present invention . the method for entity public key obtaining , certificate verification and authentication with an online trusted third party and a system thereof provided by the present invention are described above . specific embodiments are used in the description of the principle and implementation of the present invention . it is noted that the description of the embodiments are merely for better understanding of the method and its basic idea of the present invention ; and modifications may be made by those skilled in the art to the embodiments and applications of the present invention based on the idea of the present invention . therefore , the content of the description shall not be interpreted as limiting the present invention .