Abstract:
An entity bidirectional-identification method for supporting fast handoff involves three security elements, which includes two identification elements A and B and a trusted third party (TP). All identification entities of a same element share a public key certification or own a same public key. When any identification entity in identification element A and any identification entity in identification element B need to identify each other, if identification protocol has never been operated between the two identification elements that they belong to respectively, the whole identification protocol process will be operated; otherwise, interaction of identification protocol will be acted only between the two identification entities. Application of the present invention not only centralizes management of public key and simplifies protocol operation condition, but also utilizes the concept of security domain so as to reduce management complexity of public key, shorten identification time and satisfy fast handoff requirements on the premises of guaranteeing security characteristics such as one key for every pair of identification entities, one secret key for every identification and forward secrecy.

Description:
This application claims a priority to Chinese Patent Application No. 200810018333.1 filed with the Chinese Patent Office on May 29, 2008 and entitled “Mutual Entity Authentication Method Supporting Rapid Handoff”, which is hereby incorporated by reference in its entirety. 
     FIELD OF THE INVENTION 
     The present invention relates to the technical field of network security, and in particular to a mutual entity authentication method supporting rapid handoff. 
     BACKGROUND OF THE INVENTION 
     Entity authentication methods adopting an asymmetric cryptographic technique are categorized into two kinds: unilateral authentication and mutual authentication. Uniqueness or timeliness of authentication is controlled by time variant parameters such as timestamps, sequence numbers, and random numbers. If the timestamps or sequence numbers are used as time variant parameters, the unilateral authentication can be completed by only one pass authentication, and the mutual authentication between entities can be completed by two pass authentication; or if random number are used as time variant parameters, the unilateral authentication can be completed by two pass authentication, and the mutual authentication can be completed by three pass authentication or four pass authentication (i.e., two parallel two pass authentication). 
     Before or during operation of whatever authentication mechanism, a verifier shall be provided with a public key of a claimant, otherwise the authentication might be endangered or fail. A three pass mutual authentication is described here as an example. 
     Referring to  FIG. 1 , an authentication entity A transmits a token TokenAB=R A ∥R B ∥B∥Text3∥sS A (R A ∥R B ∥B∥Text2) to an authentication entity B, and the authentication entity B transmits a token TokenBA=R B ∥R A ∥A∥Text5∥sS B (R B ∥R A ∥A∥Text4) to the authentication entity A, where X denotes an authentication entity distinguishing identifier, and the authentication system includes the two authentication entities A and B; Cert X  denotes a certificate of an entity X; sS X  denotes a signature of the entity X; R X  denotes a random number generated by the entity X; and Text denotes an optional text field. 
     A process of operating the three pass authentication mechanism is described in detail below: 
     1) The entity B transmits a random number R B  and an optional text field Text1 to the entity A; 
     2) The entity A transmits a token TokenAB and an optional certificate field Cert A  to the entity B; 
     3) The entity B performs the following steps upon reception of the message transmitted from the entity A: 
     3.1) Guaranteeing to obtain a valid public key of the entity A either by verifying the certificate of the entity A or by some other means; and 
     3.2) After obtaining the public key of the entity A, verifying the signature of the entity A contained in the token TokenAB in the step 2), checking the correctness of the distinguishing identifier B, and checking that the random number R B  transmitted in step 1) is consistent with the random number R B  contained in the token TokenAB received in the step 2), and the entity A is therefore authenticated by the entity B; 
     4) The entity B transmits a token TokenBA and an optional certificate field Cert B  to the entity A; and 
     5) The entity A performs the following steps upon reception of the message including TokenBA transmitted from the entity B: 
     5.1) Guaranteeing to obtain a valid public key of the entity B either by verifying the certificate of the entity B or by some other means; and 
     5.2) After obtaining the valid public key of the entity B, verifying the signature of the entity B contained in the token TokenBA in the step 4), checking the correctness of the distinguishing identifier A, and checking that the random number R A  transmitted in the step 2) is consistent with the random number R A  contained in the token TokenBA received in the step 4) and that the random number R B  received in the step 1) is consistent with the random number R B  contained in the token TokenBA received in the step 4), the entity B is therefore authenticated by the entity A. 
     As can be apparent, successful operation of the three pass authentication mechanism is guaranteed under the condition that the entity A and the entity B possess respectively the valid public keys of each other, but the protocol does not involve how to obtain the valid public keys and the validity thereof. However, this guaranteeing condition can not be satisfied in many application scenarios at present. For example, a user access control function is typically realized by the entity authentication mechanism over a communication network, and thus an access of a user to the network is prohibited before a successful operation of the authentication mechanism, and consequently it is impossible or difficult for the user to access a certificate authority and even impossible to obtain the public key of an opposite entity, i.e., a network access point, and the validity thereof prior to the authentication. 
     At present, mutual authentication typically has to be performed between the user and the network access point over the communication network to guarantee that the user accessing the network is legal, and thus if it is not necessary for a network entity to be aware of the valid public key of the opposite entity but instead the public key of the opposite entity is checked during authentication, then the traditional entity authentication mechanisms can both be improved and gain good feasibility and easy-to-use in practical applications. Moreover, in any of the foregoing authentication mechanisms, a device where an authentication entity resides has to perform the entire authentication protocol each time it is associated to another different device, which may give rise to the issue of whether a demand for rapid handoff can be satisfied over the communication network; and each authentication entity has to be configured with a pair of public and private keys, which may significantly complicate the management of public keys for a large network. Therefore, the protocol has to be designed to reduce the complexity of network management as much as possible while guaranteeing the authentication function to satisfy the demand for rapid handoff. 
     SUMMARY OF THE INVENTION 
     The present invention proposes a mutual entity authentication method supporting rapid handoff to address the foregoing technical problems in the prior art. 
     A technical solution of the present invention lies in that: the present invention provides a mutual entity authentication method supporting rapid handoff, the method involving three security elements comprising two authentication elements A and B and a Trusted third Party TP, wherein the trusted third party TP is a trusted third party of the authentication elements A and B; the authentication element A comprises n authentication entities A 1 , A 2 , . . . , An, and the authentication element B comprises m authentication entities B 1 , B 2 , . . . , Bm, among which synchronization information is provided; and all of the authentication entities in the same authentication element share one public key certificate or possess one public key, and for any pair of authentication entities Ai (i=1, 2, . . . , n) and Bj (j=1, 2, . . . , m), the authentication method comprises the steps of: 
     1) transmitting, by the authentication entity Bj, an authentication activation message INI Bj  to the authentication entity Ai, wherein 
     INI Bj =R Bj ∥ID B ∥Text1, wherein R Bj  denotes a random number generated by the authentication entity Bj, ID B  denotes an identifier of the authentication element B, and Text1 denotes a first optional text; 
     2) transmitting, by the authentication entity Ai, an access authentication request message AREQ Ai  to the authentication entity Bj upon reception of the authentication activation message INI Bj , wherein
 
 AREQ   Ai   =R   Bj   ∥R   Ai   ∥ID   A ∥Text2∥Token AB  
 
     TokenAB=sS A (R Bj ∥R Ai   ∥ID   A ∥Text2), wherein R Ai  denotes a random number generated by the authentication entity Ai, ID A  denotes an identifier of the authentication element A, Text2 denotes a second optional text, TokenAB denotes a token transmitted from the authentication entity Ai to the authentication entity Bj, and sS A  denotes a signature of the authentication element A; 
     3) on receiving the access authentication request message AREQ Ai , verifying, by the authentication entity Bj, R Bj  in AREQ Ai  and R Bj  in INI Bj  for consistency, and if R Bj  in AREQ Ai  is consistent with R Bj  in INI Bj , searching, by the authentication entity Bj, for a locally stored authentication result of the authentication element A; if there is stored an authentication result of the authentication element A, going to step 4); 
     4) transmitting, by the authentication entity Bj, an access authentication response message ARES Bj  to the authentication entity Ai, and calculating a shared master key between the authentication entities Ai and Bj, wherein
 
 ARES   Bj   =IRES   TP   ∥R   Ai ∥Text5∥Token BA  
 
     TokenBA=sS B (TokenAB∥R Bj ∥R Ai ∥Text5), wherein Text5 denotes a fifth optional text, IRES TP  denotes a locally stored identity authentication response message which comprises the authentication result of the authentication element A, TokenBA denotes a token transmitted from the authentication entity Bj to the authentication entity Ai, and sS B  denotes a signature of the authentication element B; and 
     5) verifying, by the authentication entity Ai, the access authentication response message ARES Bj  upon reception thereof. 
     In the step 3), the authentication entity Bj verifies R Bj  in AREQ Ai  and R Bj  in INI Bj  for consistency upon reception of the access authentication request message AREQ Ai , and if in case of consistency, if the authentication entity Bj fails to find a locally stored authentication result of the authentication element A, the method further comprises: 
     6) transmitting, by the authentication entity Bj, an identity authentication request message IREQ Bj  to the trusted third party TP, wherein 
     IREQ Bj =R Ai ∥T Bj ∥ID A ∥ID B ∥Text3, wherein Text3 denotes a third optional text, and T Bj  denotes the synchronization information generated by the authentication entity; 
     7) verifying, by the trusted third party TP, the authentication element A and the authentication element B for legality upon reception of the identity authentication request message IREQ Bj ; 
     8) returning, by the trusted third party TP, an identity authentication response message IRES TP  to the authentication entity Bj after verifying the authentication elements A and B for legality, wherein
 
 IRES   TP =Token TB;  
 
     TokenTB=R Ai ∥Pub B |T Bj ∥Pub A ∥Text4∥sS TP (R Ai ∥Pub B ∥T Bj ∥Pub A ∥Text4), wherein Text4 denotes a fourth optional text, TokenTB denotes a token transmitted from the trusted third party TP to the authentication entity Bj, sS TP  denotes a signature of the trusted third party TP, Pub A  denotes a verification result of the authentication element A by the trusted third party, and Pub B  denotes a verification result of the authentication element B by the trusted third party, and; 
     9) upon reception of the identity authentication response message IRES TP , verifying, by the authentication entity Bj, the identity authentication response message IRES TP , storing locally the identity authentication response message IRES TP , and forwarding the identity authentication response message IRES TP  to other authentication entities B 1 , B 2 , . . . , Bm (other than Bj) in the authentication element B after the verification is passed; 
     10) verifying and storing, by the authentication entities B 1 , B 2 , . . . , Bm (other than Bj) in the element B, the identity authentication response message IRES TP  upon reception thereof; and 
     going to the step 4) to proceed with the subsequent flow. 
     in the step 7), if the identifiers ID A  and ID B  of the authentication elements A and B in the identity authentication request message IREQ Bj  are certificates, the TP verifies the certificates Cert A  and Cert B  of the authentication elements A and B for validity, and if the certificates Cert A  and Cert B  are invalid, the TP discards directly the identity authentication request message IREQ Bj  or returns the identity authentication response message IRES TP ; or if the certificates Cert A  and Cert B  are valid, the TP returns the identity authentication response message IRES TP  and performs the step 8). 
     In the step 7), if the identifiers ID A  and ID B  of the authentication elements A and B in the identity authentication request message IREQ Bj  are distinguishing identifiers, the TP searches for public keys PublicKey A  and PublicKey B  of the authentication elements A and B and verifies the validities thereof, and if no public key is found or the public keys are invalid, the TP discards directly the identity authentication request message IREQ Bj  or returns the identity authentication response message IRES TP ; or if the public keys PublicKeyA and PublicKeyB are found and valid, the TP returns the identity authentication response message IRES TP  and performs the step 8). 
     In the step 9), the authentication entity Bj verifies the identity authentication response message IRES TP  in the following process: verifying the signature of the trusted third party TP in TokenTB, verifying T Bj  in IRES TP  and T Bj  in IREQ Bj  for consistency, and obtaining a verification result Pub A  of the authentication element A after the verification is passed; and if the authentication element A is invalid, ending the process; or if the authentication element A is valid, obtaining a public key PublicKey A  of the authentication element A, verifying the signature of the authentication element A in TokenAB, and if the signature is incorrect, ending the process; or if the signature is correct, storing locally the identity authentication response message IRES TP  and forwarding the identity authentication response message IRES TP  to other authentication entities in the authentication element B, and going to the step 10). 
     In the step 10), the authentication entities B 1 , B 2 , . . . , Bm (other than Bj) verifies the identity authentication response message IRES TP  in the following process: judging the freshness of the identity authentication response message IRES TP  according to T Bj  and local synchronization information, verifying the signature of the trusted third party TP in TokenTB, and if the signature is correct, obtaining the verification result Pub A  of the authentication element A and storing locally the identity authentication response message IRES TP . 
     In the step 4) the authentication entity Bj performs a Diffie-Hellman calculation from R Bj  and R Ai  and obtains a resultant value as the shared master key between the authentication entities Ai and Bj. 
     In the step 5), the authentication entity Ai verifies the access authentication response message ARES Bj  in the following process: 
     verifying the signature of the trusted third party TP in TokenTB, verifying the signature of the authentication element B in TokenBA, verifying R Ai  in the access authentication response message ARES Bj  and R Ai  in the access authentication request message AREQ Ai  for consistency, and obtaining a verification result Pub B  of the authentication element B after the verification is passed; if the authentication element B is invalid, failing with the authentication; or if the authentication element B is valid, obtaining a public key PublicKey B  of the authentication element B and verifying the signature of the authentication element B in TokenBA, and if the signature is incorrect, failing with authentication; or if the signature is correct, performing a Diffie-Hellman calculation from R Bj  and R Ai  to obtain the shared master key between the authentication entities Ai and Bj, thereby completing the mutual authentication between the authentication entities Ai and Bj. 
     As compared with the traditional authentication mechanisms, the present invention arranges several authentication entities with adjacent spatial locations or with identical movement traces or routes of spatial locations into a security domain and takes each security domain as an authentication element during authentication; and all of the authentication entities in the same security domain share a public key certificate or possess the same public key, and the authentication entities in some security domains are provided with synchronization information. Prior to authentication, each authentication element retrieves a public key or a public key certificate of the trusted third party and retrieves a user public key certificate distributed thereto from the trusted third party or submits its own public key to the trusted third party for deposit. When two authentication entities in different security domains require to be authenticated, if no authentication protocol has ever been performed between the two security domains to which they are subordinated, then a complete authentication protocol process is performed, that is, the trusted third party searches for and verifies respective public keys of the authentication entities and validities thereof, which are then transported automatically to opposite ends desiring for them; and if the authentication protocol has been performed between the two security domains to which they are subordinated, that is, there are authentication entities in the two security domains, which have been authenticated, then the protocol process will not be performed again, that is, protocol data interaction between the authentication entities and the trusted third party can be dispensed with, and authentication will be performed only between the two authentication entities. 
     In contrast to the traditional authentication mechanisms, the present invention not only defines an online retrieval and authentication mechanism of public keys, achieves centralized management thereof and simplifies a condition under which the protocol is performed but also makes use of the concept of a security domain to greatly reduce the complexity of managing the public keys, shorten a period of time for authentication and facilitate satisfying a demand for rapid handoff over the network under the precondition of guaranteeing security features including a key for each pair of authentication entities, a key for each authentication thereof, forward privacy, etc. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic authentication diagram of a three pass authentication mechanism in the prior art; 
         FIG. 2  is a schematic authentication diagram according to an embodiment of the present invention; 
         FIG. 3  is a schematic authentication diagram according to another embodiment of the present invention; and 
         FIG. 4  is a schematic authentication diagram according to a further embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The inventive method involves three security elements, i.e., two authentication elements A and B and a Trusted third Party (TP), where the trusted third party TP is a trusted third party of the authentication elements A and B; and the authentication element A includes n authentication entities A 1 , A 2 , . . . , An, the authentication element B includes m authentication entities B 1 , B 2 , . . . , Bm, and among B 1 , B 2 , . . . , Bm synchronization information is provided. Particularly, the synchronization information may be sequence numbers or timestamps, and here the synchronization information is timestamps by way of an example. Such a system in which peer authentication is performed between the two authentication elements A and B through the trusted third party TP is referred to a Tri-element Peer Authentication (TePA) system. 
     The present invention is further described in detail below in connection with embodiments thereof and with reference to the drawings to make the object, aspects and advantages thereof more apparent. 
     Xi denotes an authentication entity in an authentication element X; R Xi  denotes a random number generated by the authentication entity Xi; and T Xi  denotes synchronization information generated by the authentication entity Xi. 
     Cert X  denotes a public key certificate of the authentication element X; ID X  denotes an identifier of the authentication element X, which is represented as the certificate Cert X  or as a distinguishing identifier X of the authentication element; Valid X  denotes the validity of the certificate Cert X ; PublicKey X  denotes a public key of the authentication element X; and Pub X  denotes a verification result of the authentication element X, which is consisted of the certificate Cert X  and the validity Valid X  thereof or of the authentication element X and the public key PublicKey X  thereof. 
     Token denotes a token field; and Text denotes an optional text field. 
     Referring to  FIG. 2 , an authentication process between any pair of authentication entities Ai (i=1, 2, . . . , n) and Bj (j=1, 2, . . . , m) involves either five messages, i.e., an authentication activation message INI Bi , an access authentication request message AREQ Ai , an identity authentication request message IREQ Bj , an identity authentication response message IRES TP  and an access authentication response message ARES Bj , or only three messages, i.e., an authentication activation message INI Bj , an access authentication request message AREQ Ai  and an access authentication response message ARES Bj . 
     A specific authentication process is as follows: 
     1) The authentication entity Bj transmits an authentication activation message INI Bj  to the authentication entity Ai; 
     Where:
 
 INI   Bj   =R   Bj   ∥ID   B ∥Text1
 
     2) The authentication entity Ai transmits the access authentication request message AREQ Ai  to the authentication entity Bj upon reception of the authentication activation message INI Bj ; 
     Where:
 
 AREQ   Ai   =R   Bj   ∥R   Ai   ∥ID   A ∥Text2∥Token AB  
 
Token AB=sS   A ( R   Bj   ∥R   Ai   ∥ID   A ∥Text2)
 
     3) The authentication entity Bj receives the access authentication request message AREQ Ai  and verifies the access authentication request message AREQ Ai , then transmits an identity authentication request message IREQ Bj  to the trusted third party TP, and the process goes to the step 4); or, the authentication entity Bj performs the step 8) directly; 
     Where:
 
 IREQ   Bj   =R   Ai   ∥T   Bj   ∥ID   A   ∥ID   B ∥Text3;
 
     The authentication entity Bj verifies the access authentication request message AREQ Ai  in the following process: verifying R Bj  in AREQ Ai  and R Bj  in INI Bj  for consistency, and if the R Bj  in AREQ Ai  and the R Bj  in INI Bj  are inconsistent, directly discarding AREQ Ai ; if the R Bj  in AREQ Ai  and the R Bj  in INI Bj  are consistent, searching for a locally stored authentication result of the authentication element A, and if there is no stored authentication result of the authentication element A, transmitting the identity authentication request message IREQ Bj  to the trusted third party TP, and going to the step 4); if there is a stored authentication result of the authentication element A, going to the step 8) directly; 
     4) The trusted third party TP verifies the authentication element A and the authentication element B for legality upon reception of the identity authentication request message IREQ Bj ; 
     Where: 
     If the identifiers ID A  and ID B  of the authentication elements A and B in the identity authentication request message IREQ Bj  are certificates, the trusted third party TP verifies the certificates Cert A  and Cert B  of the authentication elements A and B for validity, and if the certificates Cert A  and Cert B  are invalid, the trusted third party TP discards directly the identity authentication request message IREQ Bj  or returns an identity authentication response message IRES TP ; or if the certificates Cert A  and Cert B  are valid, the trusted third party TP returns an identity authentication response message IRES TP  and goes to the step 5); 
     If the identifiers ID A  and ID B  of the authentication elements A and B in the identity authentication request message IREQ Bj  are distinguishing identifiers, the trusted third party TP searches for public keys PublicKey A  and PublicKey B  of the authentication elements A and B and verifies the validities of the public keys PublicKey A  and PublicKey B ; and if no public key is found or the public keys are invalid, the trusted third party TP discards directly the identity authentication request message IREQ Bj  or returns an identity authentication response message IRES TP ; or if the public keys PublicKey A  and PublicKey B  are found and valid, the trusted third party TP returns an identity authentication response message IRES TP  and goes to the step 5); 
     5) The trusted third party TP returns the identity authentication response message IRES TP  to the authentication entity Bj after verifying the authentication entities Ai and Bj for legality; 
     Where:
 
 IRES   TP =Token TB  
 
Token TB=R   Ai ∥Pub B   ∥T   Bj ∥Pub A ∥Text4
 
∥ sS   TP ( R   Ai ∥Pub B   ∥T   Bj ∥Pub A ∥Text4)
 
     6) The authentication entity Bj receives the identity authentication response message IRES TP  and verifies the identity authentication response message IRES TP , then stores locally the identity authentication response message IRES TP  while forwarding the identity authentication response message IRES TP  to other authentication entities B 1 , B 2 , . . . , Bm (other than Bj) in the authentication element B after a verification thereof is passed; 
     Where: 
     The authentication entity Bj verifies the identity authentication response message IRES TP  in the following process: (1) verifying the signature of the trusted third party TP in TokenTB, then verifying T Bj  in IRES TP  and T Bj  in IREQ Bj  for consistency, and thus obtaining a verification result Pub A  of the authentication element A after the verification is passed; (2) If the authentication element A is invalid, ending the process; if the authentication element A is valid, retrieving the public key PublicKey A  of the authentication element A, verifying the signature of the authentication element A in TokenAB, and if the signature is incorrect, ending the process; if the signature is correct, storing locally the identity authentication response message IRES TP , forwarding the identity authentication response message IRES TP  to other authentication entities in the authentication element B, and going to the step 7); 
     7) Other authentication entities B 1 , B 2 , . . . , Bm (other than Bj) in the authentication element B receive the identity authentication response message IRES TP , verify the identity authentication response message IRES TP , and then store locally the identity authentication response message IRES TP  after a verification thereof is passed; 
     Where: 
     The authentication entities B 1 , B 2 , . . . , Bm (other than Bj) verify the identity authentication response message IRES TP  in the following process: judging the freshness of the identity authentication response message IRES TP  according to T Bj  and local synchronization information (a timestamp) and verifying the signature of the trusted third party TP in TokenTB, and if the signature is correct, obtaining the verification result Pub A  of the authentication element A and storing locally the identity authentication response message IRES TP ; 
     8) The authentication entity Bj transmits an access authentication response message ARES Bj  to the authentication entity Ai and calculates a shared master key between the authentication entities Ai and Bj; 
     Where:
 
 ARES   Bj   =IRES   TP   ∥R   Ai ∥Text5∥Token BA  
 
Token BA=sS   B (Token TB∥R   Bj   ∥R   Ai ∥Text5)
 
     The authentication entity Bj performs a Diffie-Hellman calculation from R Bj  and R Ai  and takes a resultant value as the shared master key between the authentication entities Ai and Bj. 
     9) The authentication entity Ai verifies the access authentication response message ARES Bj  upon reception thereof. 
     Where: 
     The authentication entity Ai verifies the access authentication response message ARES Bj  in the following process: verifying the signature of the trusted third party TP in TokenTB, verifying the signature of the authentication element B in TokenBA, and verifying R Ai  in the access authentication response message ARES Bj  and R Ai  in the access authentication request message AREQ Ai  for consistency, thereby obtaining a verification result Pub B  of the authentication element B after all the verifications are passed; if the authentication element B is invalid, failing with the authentication; or if the authentication element B is valid, obtaining the public key PublicKey B  of the authentication element B and verifying the signature of the authentication element B in TokenBA; if the signature of the authentication element B in TokenBA is incorrect, failing with the authentication; or if the signature of the authentication element B in TokenBA is correct, performing a Diffie-Hellman calculation from R Bj  and R Ai  to obtain a shared master key between the authentication entities Ai and Bj, and thereby completing the mutual authentication between the authentication entities Ai and Bj. 
     In the event that both of the authentication elements have been authenticated mutually through the trusted third party, the authentication entities subordinated respectively to the two security domains can further require a complete authentication process to be performed in view of a local policy. If an authentication entity in the authentication element B requires a complete authentication process to be performed, the authentication entity in the authentication element B transmits an identity authentication request message to the trusted third party TP regardless of whether there is a locally stored authentication result upon reception of an access authentication request message transmitted from an opposite authentication entity; or if an authentication entity in the authentication element A requires a complete authentication process to be performed, the requirement can be identified in an optional field of the access authentication request message, and an authentication entity in the authentication element B which is opposite to the authentication entity in the authentication element A transmits an identity authentication request message to the trusted third party TP after identifying the field to perform the complete authentication process. 
     Referring to  FIG. 3  and assuming the authentication entity A 1  requires to be authenticated with the authentication entity B 1 , if no authentication process has ever been performed between the authentication elements A and B to which the authentication entities A 1  and B 1  are subordinated, a specific authentication flow of the entities A 1  and B 1  is as follows: 
     1) The authentication entity B 1  transmits an authentication activation message INI B1  to the authentication entity A 1 ; 
     Where:
 
 INI   B1   =R   B1   ∥ID   B ∥Text1
 
     2) The authentication entity A 1  transmits an access authentication request message AREQ A1  to the authentication entity B 1  upon reception of the authentication activation message INI B1 ; 
     Where:
 
 AREQ   A1   =R   B1   ∥R   A1   ∥ID   A ∥Text2∥Token AB  
 
Token AB=sS   A ( R   B1   ∥R   Ai   ∥ID   A ∥Text2)
 
     3) The authentication entity B 1  receives the access authentication request message AREQ A1  and verifies the access authentication request message AREQ A1 , then transmits an identity authentication request message IREQ B1  to the trusted third party TP; 
     Where:
 
 IREQ   B1   =R   A1   ∥T   B1   ∥ID   A   ∥ID   B ∥Text3;
 
     The authentication entity B 1  verifies the access authentication request message AREQ A1  in the following process: verifying R B1  in AREQ A1  and R B1  in INI B1  for consistency, and if the R B1  in AREQ A1  and the R B1  in INI B1  are consistent, transmitting the identity authentication request message IREQ B1  to the trusted third party TP; if the R B1  in AREQ A1  and the R B1  in INI B1  are inconsistent, discarding AREQ A1  directly; 
     4) The trusted third party TP verifies the authentication elements A and B for legality upon reception of the identity authentication request message IREQ B1 ; 
     Where: 
     If the identifiers ID A  and ID B  of the authentication elements A and B in the identity authentication request message IREQ B1  are certificates, the trusted third party TP verifies the certificates Cert A  and Cert B  of the authentication elements A and B for validity, and if the certificates Cert A  and Cert B  are invalid, the trusted third party TP discards directly the identity authentication request message IREQ B1  or returns an identity authentication response message IRES TP ; or if the certificates Cert A  and Cert B  are valid, the trusted third party TP returns an identity authentication response message IRES TP  and goes to the step 5); 
     If the identifiers ID A  and ID B  of the authentication elements A and B in the identity authentication request message IREQ B1  are distinguishing identifiers, the trusted third party TP searches for public keys PublicKey A  and PublicKey B  of the authentication elements A and B and verifies the validities of the public keys PublicKey A  and PublicKey B , and if no public key is found or the public keys are invalid, the trusted third party TP discards directly the identity authentication request message IREQ B1  or returns an identity authentication response message IRES TP ; or if the public keys PublicKey A  and PublicKey B  are found and valid, the trusted third party TP returns an identity authentication response message IRES TP  and goes to the step 5); 
     5) The trusted third party TP returns the identity authentication response message IRES TP  to the authentication entity B 1  after verifying the authentication elements A and B for legality; 
     Where:
 
 IRES   TP =Token TB  
 
Token TB=R   A1 ∥Pub B   ∥T   B1 ∥Pub A ∥Text4
 
∥ sS   TP ( R   A1 ∥Pub B   ∥T   B1 ∥Pub A ∥Text4)
 
     6) The authentication entity B 1  receives the identity authentication response message IRES TP , verifies the identity authentication response message IRES TP , and then stores locally the identity authentication response message IRES TP  while forwarding the identity authentication response message IRES TP  to other authentication entities B 2 , B 3 , . . . , Bm in the authentication element B after verification thereof is passed; 
     Where: 
     The authentication entity B 1  verifies the identity authentication response message IRES TP  in the following process: (1) verifying the signature of the trusted third party TP in TokenTB, verifying T B1  in IRES TP  and T B1  in IREQ B1  for consistency, and then obtaining a verification result Pub A  of the authentication element A after the verification is passed; (2) if the authentication element A is invalid, ending the process; or if the authentication element A is valid, obtaining the public key PublicKey A  of the authentication element A, and verifying the signature of the authentication element A in TokenAB; if the signature is incorrect, ending the process ends; or if the signature is correct, storing locally the identity authentication response message IRES TP , forwarding the identity authentication response message IRES TP  to other authentication entities in the authentication element B, and going to the step 7); 
     7) Other authentication entities B 2 , B 3 , . . . , Bm in the authentication element B receive the identity authentication response message IRES TP , and verify the identity authentication response message IRES TP , and then store locally the identity authentication response message IRES TP  after a verification thereof is passed; 
     Where: 
     The authentication entities B 2 , B 3 , . . . , Bm verify the identity authentication response message IRES TP  in the following process: judging the freshness of the identity authentication response message IRES TP  according to T B1  and local synchronization information (a timestamp) and verifying the signature of the trusted third party TP in TokenTB; if the verification is passed, obtaining a verification result Pub A  of the authentication element A and storing locally the identity authentication response message IRES TP ; or if the verification is not passed, discarding directly the identity authentication response message IRES TP ; 
     8) The authentication entity B 1  transmits an access authentication response message ARES B1  to the authentication entity A 1  and calculates a shared master key between the authentication entities A 1  and B 1 ; 
     Where:
 
 ARES   B1   =IRES   TP   ∥R   A1 ∥Text5∥Token BA  
 
Token BA=sS   B (Token TB∥R   B1   ∥R   A1 ∥Text5)
 
     The authentication entity B 1  performs a Diffie-Hellman calculation from R B1  and R A1  and takes a resultant value as the shared master key between the authentication entities A 1  and B 1 . 
     9) The authentication entity A 1  verifies the access authentication response message ARES B1  upon reception thereof. 
     Where: 
     The authentication entity A 1  verifies the access authentication response message ARES B1  in the following process: verifying the signature of the trusted third party TP in TokenTB, verifying the signature of the authentication element B in TokenBA, and verifying R A1  in the access authentication response message ARES B1  and R A1  in the access authentication request message AREQ A1  for consistency, and thereby obtaining a verification result Pub B  of the authentication element B after the verification is passed; if the authentication element B is invalid, failing with the authentication; or if the authentication element B is valid, the public key PublicKey B  of the authentication element B and verifying the signature of the authentication element B in TokenBA, and if the signature is incorrect, failing with the authentication; or if the signature is correct, performing a Diffie-Hellman calculation from R B1  and R A1  to obtain a shared master key between the authentication entities A 1  and B 1 , thereby completing the mutual authentication between the authentication entities A 1  and B 1 . 
     Referring to  FIG. 4 , an authentication is required between another pair of entities after the authentication of authentication entities A 1  and B 1 , and if a mutual authentication between the authentication entity A 2  and the authentication entity B needs to be performed, a specific authentication flow thereof is as follows: 
     1) The authentication entity B 2  transmits an authentication activation message INI B2  to the authentication entity A 2 ; 
     Where:
 
 INI   B2   =R   B2   ∥ID   B ∥Text1
 
     2) The authentication entity A 2  transmits an access authentication request message AREQ A2  to the authentication entity B 2  upon reception of the authentication activation message INI B2 ; 
     Where:
 
 AREQ   A2   =R   B2   ∥R   A2   ∥ID   A ∥Text2∥Token AB  
 
Token AB=sS   A ( R   B2   ∥R   A2   ∥ID   A ∥Text2)
 
     3) The authentication entity B 2  receives the access authentication request message AREQ A2 , verifies the access authentication request message AREQ A2  in connection with a locally stored authentication result of the authentication element A, transmits an access authentication response message ARES B2  to the authentication entity A 2 , and calculates a shared master key between the authentication entities A 2  and B 2 ; 
     Where: 
     The authentication entity B 2  verifies the access authentication request message AREQ A2  in the following process: (1) verifying R B2  in AREQ A2  and R B2  in INI B2  for consistency; and (2) if the authentication entity B 2  locally stores the authentication result of the authentication element A indicating legal validity, verifying the signature of the authentication element A in TokenAB for correctness according to the public key PublicKeyA of the authentication element A;
 
 ARES   B2   =IRES   TP   ∥R   A2 ∥Text5∥Token BA  
 
Token BA=sS   B (Token TB∥R   B2   ∥R   A2 ∥Text5)
 
     IRES TP  denotes an identity authentication response message stored locally at the authentication entity B 2 , which includes the authentication result of the authentication element A. 
     The authentication entity B 2  performs a Diffie-Hellman calculation from R B2  and R A2  and takes a resultant value as the shared master key between the authentication entities A 2  and B 2 ; 
     4) The authentication entity A 2  verifies the access authentication response message ARES B2  upon reception thereof. 
     Where: 
     The authentication entity A 2  verifies the access authentication response message ARES B2  in the following process: verifying the signature of the trusted third party TP in TokenTB, verifying the signature of the authentication element B in TokenBA, and verifying R A2  in the access authentication response message ARES B2  and R A2  in the access authentication request message AREQ A2  for consistency, and thereby obtaining a verification result Pub B  of the authentication element B after the verification is passed; if the authentication element B is invalid, failing with the authentication; or if the authentication element B is valid, obtaining the public key PublicKey B  of the authentication element B and verifying the signature of the authentication element B in TokenBA, and if the signature is incorrect, failing with the authentication; or if the signature is correct, performing a Diffie-Hellman calculation from R B2  and R A2  to obtain a shared master key between the authentication entities A 2  and B 2 , thereby completing the mutual authentication between the authentication entities A 2  and B 2 . 
     The inventive method not only accomplishes mutual identity authentication between authentication entities but also guarantees the uniqueness and freshness of a master key which each pair of entities negotiate each time, and the master key is forward private. For the two security domains A and B, as in a traditional method, a public key certificate or a public key is distributed to each authentication entity, and a trusted third party TP manages n×m user certificates or public keys; if the authentication between each authentication entity in the security domain A and each authentication entity in the security domain B needs to be performed, 5×n×m messages have to be exchanged. With the inventive method, the trusted third party TP manages only two user certificates or public keys, and a minimum number of 3×n×m+2 messages need to be exchanged for authentication between respective two ones. As can be apparent, the present invention can significantly reduce the complexity of network management, improve the efficiency of performing the protocol and satisfy a handoff demand under the precondition of guaranteeing security. 
     The foregoing description is merely of the preferred embodiments of the present invention, and it shall be noted that those ordinarily skilled in the art can further make various modifications and variations without departing the principle of the present invention and that these modifications and variations shall also be deemed falling into the scope of the present invention.