Abstract:
A method for generating an identifier of a key includes that: when a user equipment (UE) transfers from an evolved UMTS terrestrial radio access network (EUTRAN) to a universal terrestrial radio access network (UTRAN) or a global system for mobile communications (GSM), or an enhanced data rate for GSM evolved radio access network (GERAN), an identifier of a system key after transfer is generated by mapping an identifier KSI ASME  for an access security management entity, and a mobile management entity generates an identifier of a ciphering key (CK) and an integrity key (IK) by mapping the KSI ASME , and then sends the generated identifier to a serving GPRS support node (SGSN), when the UE transfers from the EUTRAN to the UTRAN, the SGSN stores the ciphering key, the integrity key and the identifier thereof, and when the UE transfers from the EUTRAN to the GERAN, the SGSN assigns the value of the identifier of the ciphering key and the integrity key to an identifier of a ciphering key of the GERAN.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to the field of mobile communications, and in particular to a method and system for generating an identifier of a key when a user equipment (UE) transfers from an evolved UMTS terrestrial radio access network (EUTRAN) to a universal terrestrial radio access network (UTRAN) or a global system for mobile communications (GSM) or an enhanced data rate for GSM evolution (EDGE) radio access network (GERAN, GSM/EDGE radio access network). 
       BACKGROUND 
       [0002]    A 3rd generation partnership project (3GPP) evolved packet system (EPS) comprises an EUTRAN and an EPS core network (EPC, evolved packet core). 
         [0003]    The EPC comprises a mobility management entity (MME). The MME takes charge of operations related to a control plane, such as mobility management, signaling processing of a non-access stratum (NAS), and management of a user security mode. The MME stores a root key of the EUTRAN, that is, a key of an access security management entity (K ASME ), and uses the K ASME  and an uplink non-access stratum sequence number (NAS SQN) to generate a root key of an access stratum which is used by an evolved Node B (eNB), that is, an eNB key (K eNB ). A key set identifier for access security management entity (KSI ASME ) or a key set identifier for an SGSN (KSI SGSN ) is an identifier of the key K ASME  (or called the key sequence number), which is used for performing identification and retrieval of a key between a UE and a network side and has a length of 3 bits. If the K ASME  is directly generated through an authentication and key association (AKA) of the EPS, the KSI ASME  is used as the identifier of the K ASME ; and if the K ASME  is generated by mapping a key of the UMTS or the GERAN, the KSI SGSN  is used as the identifier of the K ASME . 
         [0004]    When a connection is established between a UE and a network side, the UE or the network side may inform the other party through the KSI ASME  that the other party may use a designated key that is previously stored, so as to establish a security context, thereby avoiding performing the authentication and key association (AKA) for each connection and saving network resources. When a key needs to be deleted due to the expiration of the lifetime or other reasons, the UE sets the KSI ASME  to be ‘111’. 
         [0005]    In the EUTRAN, the base station device is an eNB, which mainly takes charge of wireless communication, wireless communication management and mobility context management. 
         [0006]    In a 3GPP universal mobile telecommunication system (UMTS), the device in charge of the management of packet domain mobility context and/or management of a user security mode is a serving GPRS support node (SGSN). The SGSN further takes charge of the authentication and security management of the UTRAN of the UMTS and stores a key set including an integrity key (IK) and a ciphering key (CK). The identifier of the key set is a key set identifier (KSI), the function and the usage of the KSI are similar to that of the KSI ASME  in the EPS, both are used for performing identification and retrieval of a key between the UE and the network side, besides the KSI also has a length of 3 bits. When the KSI is equal to ‘111’, it means that no keys can be used and the KSI is invalid. When an association is needed between the UE and the SGSN to establish a UMTS secure connection, if the UE has stored a key that can be used, it sends the stored KSI to the SGSN, the SGSN checks whether the KSI stored by itself is the same as that sent by the UE and, if so, the SGSN uses the stored key set to establish a security context through association and sends the KSI back to the UE to confirm the key the SGSN uses. If no keys that can be used are stored in the UE, the UE sets the KSI to be ‘111’ and sends the KSI to the SGSN; after checking that the KSI is ‘111’, the SGSN sends an authentication request message to an HLR/HSS, then the UE and the network side re-performs an AKA to generate a new key set. 
         [0007]    In a GSM/EDGE system, the device in charge of management of the packet domain mobility context and/or management of a user security mode is also an SGSN, the SGSN takes charge of the authentication and security management of a GSM/EDGE radio access network (GERAN), and stores a ciphering key (Kc) of the GERAN; and the identifier of the Kc is a ciphering key sequence number (CKSN), the function and usage of the CKSN are identical to that of the KSI. 
         [0008]    When the UE transfers from the EUTRAN to the UTRAN, the MME generates an IK and a CK for a target network using the K ASME  and sends the generated IK and CK to the SGSN, the UE and the SGSN use the IK and the CK to associate a corresponding security algorithm to establish a UTRAN security context. The transfer includes the following two types: a transfer which is performed when a radio resource control (RRC) is in an active state, and a transfer which is performed when the UE is in an idle state. The transfer in an active state includes a handover and so on, and the transfer in an idle state includes a routing area update, an attachment request and so on. 
         [0009]    When the UE transfers from the EUTRAN to the GERAN, the MME generates a CK and an IK using the K ASME  (with the key generation method that is the same as the method used during the transfer to the UMTS), and then sends the generated IK and CK to the SGSN, and the SGSN uses the IK and the CK to generate the key Kc for the GERAN. 
         [0010]    In existing techniques, the KSI ASME , the KSI and the CKSN are all generated at the network side during an authentication process and then sent to the UE via an authentication request. However, although the MME generates the IK and the CK which are needed by the UTRAN or GERAN for the target network during the transfer from the EUTRAN to the UTRAN or the GERAN, no corresponding identifiers are provided for this pair of keys. Once the transfer is completed, the UE and the SGSN can neither retrieve the generated key during the transfer nor reuse this pair of keys. When the UE and the network side reestablish an RRC or other connections, as the stored keys cannot be used, the UE and the network side have no choice but to perform an AKA first so as to regenerate new keys and then establish a wireless connection. This will undoubtedly increase the signaling overheads of the UE and the network side and delay the time for the normal communication between the UE and the network side, and as a result, the satisfaction level of the user is reduced. 
       SUMMARY 
       [0011]    The present invention aims to provide a method and system for generating an identifier of a key when a UE transfers between different access systems, which solve the problem in existing techniques that a generated key which a K ASME  is mapped into during the transferring process cannot be reused for not being provided with an identifier after a UE transfers from an EUTRAN to a UTRAN or GERAN. 
         [0012]    In order to solve the above technical problem, the present invention provides a method for generating an identifier of a key, which comprises that: when a user equipment (UE) transfers from an evolved UMTS terrestrial radio access network (EUTRAN) to a universal terrestrial radio access network (UTRAN), a mobility management entity (MME) and the UE generate a key set identifier of a UTRAN system by mapping a key set identifier for an access security management entity; and the MME sends a serving GPRS support node (SGSN) the key set identifier of the UTRAN system, along with a ciphering key and an integrity key of the system. 
         [0013]    Further, the generation mode of the mapping may be as follows: the UE and the MME may directly assign the value of the key set identifier of the UTRAN system to be that of the key set identifier of the access security management entity, or to be the sum of the value of the key set identifier of the access security management entity and a constant which is appointed by the UE and a network side. 
         [0014]    Further, when the UE transfers from the EUTRAN to the UTRAN in an idle state, after receiving a user information extraction request message sent by the SGSN, the MME may generate an integrity key and a ciphering key using the key of the access security management entity, generate an identifier of the integrity key and the ciphering key, that is, a key set identifier, by mapping the key set identifier of the access security management entity, and send the integrity key, the ciphering key and the key set identifier to the SGSN via a user information extraction response message; and the SGSN may store the ciphering key, the integrity key and the key set identifier. 
         [0015]    Preferably, the request message sent by the UE to the SGSN for transferring to the UTRAN in an idle state may be a routing area update request message; correspondingly, the user information extraction request message may be a context request message, and the user information extraction response message may be a context response. 
         [0016]    Preferably, the request message sent by the UE to the SGSN for transferring to the UTRAN in an idle state may be an attachment request message; correspondingly, the user information extraction request message may be an identification request message, and the user information extraction response message may be an identification response. 
         [0017]    Further, after determining to transfer to the UTRAN in an idle state and before correspondingly sending the SGSN a message indicative of the completion of the transfer to the UTRAN in an idle state, the UE may generate a key set identifier by mapping the key set identifier of the access security management entity, and store the key set identifier, along with the integrity key and the ciphering key which are generated from the key of the access security management entity. 
         [0018]    Preferably, the message sent by the UE to the SGSN for indicating the completion of the transfer to the UTRAN in an idle state may be a routing area update completion message or an attachment completion message. 
         [0019]    Further, when the UE transfers from the EUTRAN to the UTRAN under the condition that a radio source control (RRC) is in an active state, after receiving a handover request, the MME may generate an integrity key and a ciphering key using the key of the access security management entity, generate an identifier of the integrity key and the ciphering key, that is, a key set identifier, by mapping the key set identifier of the access security management entity, and send the integrity key, the ciphering key and the key set identifier to the SGSN via a forward redirecting request message; the SGSN may store the ciphering key, the integrity key and the key set identifier; and after receiving a handover command sent by the network side, the UE may generate a key set identifier by mapping the key set identifier of the access security management entity and store the key set identifier, along with the integrity key and the ciphering key which are generated from the key of the access security management entity. 
         [0020]    Further, if a key is associated by the network side and the UE before the UE transfers, and if the identifier of the key associated before the transfer is the same as that of the system key which is generated by mapping the key set identifier of the access security management entity during the transferring process, then the key stored in the SGSN and the UE before the transfer may be deleted. 
         [0021]    The present invention also provides a method for generating an identifier of a key, which comprises that: when a UE transfers from an EUTRAN to a global system for mobile communications (GSM) or an enhanced data rate for GSM evolution radio access network (GERAN), 
         [0022]    an MME generates an identifier of a ciphering key and an integrity key by mapping a key set identifier for an access security management entity, and sends the ciphering key, the integrity key and the identifier thereof to an SGSN; 
         [0023]    the SGSN assigns the value of the identifier of the ciphering key and the integrity key to an identifier of a ciphering key of the GSM or GERAN, that is, the sequence number of the ciphering key; and 
         [0024]    the UE generates the identifier of the ciphering key of the GSM or GERAN by mapping the key set identifier of the access security management entity. 
         [0025]    Further, the generation mode of the mapping may be as follows: the MME may directly assign the value of the identifier of the ciphering key and the integrity key to be that of the key set identifier of the access security management entity, or to be the sum of the value of the key set identifier of the access security management entity and a constant which is appointed by the UE and a network side; and the UE may directly assign the value of the identifier of the ciphering key of the GSM or GERAN to be that of the key set identifier of the access security management entity, or to be the sum of the value of the key set identifier of the access security management entity and a constant which is appointed by the UE and the network side. 
         [0026]    Further, when the UE transfers from the EUTRAN to the GSM or GERAN in an idle state, after receiving a user information extraction request message, the MME may generate an integrity key, a ciphering key and an identifier thereof, and send the integrity key, the ciphering key and the identifier thereof to the SGSN via a user information extraction response message. 
         [0027]    Preferably, the request message sent by the UE to the SGSN for transferring to the GSM or GERAN in an idle state may be a routing area update request message; correspondingly, the user information extraction request message may be a context request message, and the user information extraction response message may be a context response. 
         [0028]    Preferably, the request message sent by the UE to the SGSN for transferring to the GSM or GERAN in an idle state may be an attachment request message; correspondingly, the user information extraction request message may be an identification request message, and the user information extraction response message may be an identification response. 
         [0029]    Further, after determining to transfer to the GSM or GERAN in an idle state and before correspondingly sending the SGSN a message indicative of the completion of the transfer to the GSM or GERAN in an idle state, the UE may generate an identifier of a ciphering key of the GSM or GERAN by mapping the key set identifier of the access security management entity, and store the identifier of the ciphering key of the GSM or GERAN, along with the ciphering key of the GSM or GERAN which is generated from the key of the access security management entity. 
         [0030]    Preferably, the message sent by the UE to the SGSN for indicating the completion of the transfer to the GSM or GERAN in an idle state may be a routing area update completion message or an attachment completion message. 
         [0031]    Further, when the UE transfers from the EUTRAN to a UTRAN under the condition that a radio resource control (RRC) is in an active state, after receiving a handover request, the MME may generate a ciphering key, an integrity key and an identifier thereof, and send the integrity key, the ciphering key and the identifier thereof to the SGSN via a forward redirecting request message; and after receiving a handover command sent by the network side, the UE may generate a ciphering key of the GSM or GERAN and an identifier thereof. 
         [0032]    Further, if a key is associated by the network side and the UE before the UE transfers, and if the identifier of the key associated before the transfer is the same as that of the ciphering key of the GSM or GERAN which is generated through mapping during the transferring process, then the key stored in the SGSN and the UE before the transfer may be deleted. 
         [0033]    The present invention provides a system for generating an identifier of a key, which comprises a UE, a mobility management entity (MME) and a serving GPRS support node (SGSN), wherein 
         [0034]    the UE is configured to map a key set identifier for an access security management entity into a key set identifier of a UTRAN system when the UE transfers from an EUTRAN to a UTRAN; 
         [0035]    the MME is configured to map a key set identifier of the access security management entity into a key set identifier of the UTRAN system when the UE transfers from the EUTRAN to the UTRAN, and to send the obtained identifier to the SGSN; 
         [0036]    the mapping mode is as follows: the UE and the MME directly assign the value of the key set identifier of the UTRAN system key set to be a value of the key set identifier of the access security management entity, or to be a sum of the value of the key set identifier of the access security management entity and a constant which is appointed by the UE and a network side; 
         [0037]    Further, the UE may comprise: 
         [0038]    a first key set identifier mapping unit configured to generate an identifier of an integrity key and a ciphering key through mapping, and to map the value of an identifier of a key of a root key access security management entity of the EUTRAN to the identifier of the integrity key and the ciphering key, or to map the value of the identifier of the key of the root key access security management entity of the EUTRAN plus an appointed constant to the identifier of the integrity key and the ciphering key; 
         [0039]    a first key and identifier thereof storing unit storing configured to store the ciphering key, the integrity key and the identifier of the ciphering key and the integrity key that is generated by the first key set identifier mapping unit; 
         [0040]    the MME may comprise: 
         [0041]    a second key set identifier mapping unit configured to generate an identifier of an integrity key and a ciphering key, and to map the value of an identifier of a key of a root key access security management entity of the EUTRAN to the identifier of the integrity key and the ciphering key, or to map the value of the identifier of the key of the root key access security management entity of the EUTRAN plus an appointed constant to the identifier of the integrity key and the ciphering key; 
         [0042]    a security parameter sending unit configured to send the SGSN the ciphering key, the integrity key, and the identifier of the ciphering key and integrity key which is generated by the second key set identifier mapping unit; 
         [0043]    the SGSN may comprise: 
         [0044]    a security parameter receiving unit configured to receive the ciphering key, the integrity key and the identifier thereof which are sent by the MME; 
         [0045]    a third key and identifier thereof storing unit configured to store the received ciphering key and integrity key and the identifier thereof. 
         [0046]    The present invention also provides a system for generating an identifier of a key, which comprises a UE, a mobility management entity (MME) and a serving GPRS support node (SGSN), wherein 
         [0047]    the UE is configured to generate an identifier of a ciphering key of a GSM or GERAN by mapping a key set identifier for an access security management entity when transferring from an EUTRAN to the GSM or GERAN; 
         [0048]    the MME is configured to generate an identifier of a ciphering key and an integrity key by mapping a key set identifier of the access security management entity when the UE transfers from the EUTRAN to the GSM or GERAN, and to send the ciphering key, the integrity key and the identifier thereof to the SGSN; 
         [0049]    the SGSN is configured to receive the ciphering key, the integrity key and the identifier thereof which are sent by the MME, and to assign the value of the identifier of the ciphering key and the integrity key to the identifier of the ciphering key of the GSM or GERAN; 
         [0050]    the mapping generation mode is as follows: the MME directly assigns the value of the identifier of the ciphering key and the integrity key to be that of the key set identifier of the access security management entity, or to be the sum of the value of the key set identifier of the access security management entity and a constant which is appointed by the UE and a network side, and the UE directly assigns the value of the identifier of the ciphering key of the GSM or GERAN to be that of the key set identifier of the access security management entity, or to be the sum of the value of the identifier of the key of the access security management entity and a constant which is appointed by the UE and the network side. 
         [0051]    Further, the UE may comprise: 
         [0052]    a first key set identifier mapping unit configured to map the value of an identifier of a key of a root key access security management entity of the EUTRAN to the identifier of the ciphering key of the GSM or GERAN, or to map the value of the identifier of the key of the root key access security management entity of the EUTRAN plus a constant to the identifier of the ciphering key of the GSM or GERAN; 
         [0053]    a first key and identifier thereof storing unit configured to store the ciphering key of the GSM or GERAN and the identifier thereof; 
         [0054]    the MME may comprise: 
         [0055]    a second key set identifier mapping unit configured to generate an identifier of the integrity key and the ciphering key, and to map the value of the key set identifier of the access security management entity to the identifier of the integrity key and the ciphering key, or to map the value of the key set identifier of the access security management entity plus a constant, to the identifier of the integrity key and the ciphering key; 
         [0056]    a security parameter sending unit configured to send the SGSN the ciphering key, the integrity key, and the identifier of the ciphering key and the integrity key that is generated by the second key set identifier mapping unit; 
         [0057]    the SGSN may comprise: 
         [0058]    a security parameter receiving unit configured to receive the ciphering key, the integrity key and the identifier thereof which are sent by the MME; 
         [0059]    a third key set identifier mapping unit configured to assign the value of the ciphering key, the integrity key and the identifier thereof to the identifier of the ciphering key of the GSM or GERAN; 
         [0060]    a third key and identifier thereof storing unit configured to store the ciphering key of the GSM or GERAN and the identifier thereof. 
         [0061]    By mapping the KSI ASME  into the KSI or CKSN, the above method and system for generating a key set identifier, simultaneously guarantee that there are no repeated codes in the value of the KSI/CKSN and the values of previously-stored key set identifiers, and therefore solve the problem in existing techniques that the key obtained through mapping cannot be reused for not being provided with an identifier when the UE transfers from the EUTRAN to the UTRAN/GERAN. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0062]      FIG. 1  is a schematic diagram illustrating the specific implementation of a method for generating a key set identifier during the transfer from an EUTRAN to a UTRAN according to the present invention; 
           [0063]      FIG. 2  is a flowchart illustrating the signaling implementation of a first embodiment according to the method of the present invention; 
           [0064]      FIG. 3  is a flowchart illustrating the signaling implementation of a second embodiment according to the method of the present invention; 
           [0065]      FIG. 4  is a flowchart illustrating the signaling implementation of a third embodiment according to the method of the present invention; 
           [0066]      FIG. 5  is a schematic diagram illustrating the specific implementation of a method for generating a key set identifier during the transfer from an EUTRAN to a GERAN according to the present invention; 
           [0067]      FIG. 6  is a flowchart illustrating the implementation of a fourth embodiment according to the method of the present invention; 
           [0068]      FIG. 7  is a flowchart illustrating the signaling implementation of a fifth embodiment according to the method of the present invention; 
           [0069]      FIG. 8  is a flowchart illustrating the signaling implementation of a sixth embodiment according to the method of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0070]    In order to reuse the key generated by a K ASME  and reduce the signaling interaction between a UE and a network side, it is required to generate an identifier for a key during transferring process. For this reason, the present invention provides a method and system for generating a key set identifier when a UE transfers from an EUTRAN to a UTRAN/GERAN. 
         [0071]    The present invention is illustrated below in detail by reference to the accompanying drawings in combination with the embodiments. 
         [0072]      FIG. 1  is a schematic diagram illustrating the specific implementation of a method for generating a key set identifier when a UE transfers from an EUTRAN to a UTRAN according to the present invention. The method comprises the following steps: 
         [0073]    A 1 , after receiving a request message, a source MME maps a KSI ASME  into a KSI, that is, assigns the value of the KSI ASME  to the KSI to make KSI=KSI ASME , and then sends a target SGSN the KSI, along with an IK and CK which are generated by the K ASME  via an interaction message of the source MME and the target SGSN; 
         [0074]    A 2 , after receiving the KSI, the IK and the CK which are sent by the source MME, the target SGSN stores the KSI, the IK and the CK and sends the UE a message indicative of the completion of KSI mapping; 
         [0075]    A 3 , the UE maps the KSI ASME  into the KSI, that is, assigns the value of the KSI ASME  to the KSI to make KSI=KSI ASME , and stores the KSI, along with the IK and CK which are generated by the K ASME . 
         [0076]    Herein, the source MME and the UE may also make the value of the KSI equal to the sum of the value of the KSI ASME  and a constant. The constant is determined by the UE and a network side together. The sum of the value of the KSI ASME  and the constant should not be ‘111’, and if the sum of the value of the KSI ASME  and the constant is just ‘111’, the UE and the network side are required to determine the sum of the value of the KSI ASME  and the constant to be another value, such as, a next value ‘000’ or other values. 
         [0077]    If a key is associated by the UE and the SGSN at the network side before the transfer, and if the value of the KSI associated before the transfer is the same as that of the generated KSI which the KSI ASME  is mapped into during the transferring process, then the keys stored in the UE and the target SGSN before the transfer are deleted. 
         [0078]      FIG. 2  illustrates a first embodiment of the method according to the present invention, which depicts a flow of the method for generating an identifier of a key when a UE transfers from an EUTRAN to a UTRAN in an idle state. The method comprises the following steps: 
         [0079]    S 201 , the UE determines to transfer to the UTRAN in an idle state and sends a target SGSN a request message for requesting transfer to the UTRAN in an idle state; 
         [0080]    herein, the request message for requesting transfer to the UTRAN in an idle state may be a routing area update request or an attachment request; 
         [0081]    S 202 , after receiving the request message sent by the UE for requesting transfer to the UTRAN in an idle state, the target SGSN sends a source MME a user information extraction request message corresponding to the request message for requesting transfer to the UTRAN in an idle state; 
         [0082]    herein, the ‘corresponding’ refers to a type correspondence between the user information extraction request message sent by the target SGSN to the source MME and the request message received by the target SGSN for requesting transfer to the UTRAN in an idle state; 
         [0083]    for example, if in step S 201  the request message sent by the UE to the target SGSN is a routing area update request, then the user information extraction request message is a context request message in this step; 
         [0084]    for another example, if in step S 201  the request message sent by the UE to the target SGSN is an attachment request, then the user information extraction request message is an identification request message in this step; 
         [0085]    S 203 , after receiving the user information extraction request message sent by the target SGSN, the source MME assigns the value of the KSI ASME  to the KSI, that is, makes KSI=KSI ASME , and generates an IK and a CK using the KSI ASME ; 
         [0086]    S 204 , the source MME sends the target SGSN a user information extraction response message including the KSI, the IK and the CK, wherein: 
         [0087]    if in step S 203  the source MME receives a context request message from the target SGSN, then the user information extraction response message is a context response message in this step; 
         [0088]    if in step S 203  the source MME receives an identification request message from the target SGSN, then the user information extraction response message is an identification response message in this step; 
         [0089]    S 205 , after receiving the KSI, the IK and the CK which are sent by the source MME, the target SGSN stores the KSI, the IK and the CK; 
         [0090]    S 206 , the target SGSN sends the UE a message indicative of accepting the transfer to the UTRAN in an idle state, so as to inform the UE of the successful mapping of the identifier of a key of a network side, wherein: 
         [0091]    if in step S 201  the request message sent by the UE to the target SGSN is a routing area update request, then the message indicative of accepting the transfer to the UTRAN in an idle state is a routing area update accept message in this step; 
         [0092]    if in step S 201  the request message sent by the UE to the target SGSN is an attachment request, then the message indicative of accepting the transfer to the UTRAN in an idle state is an attachment accept message in this step; 
         [0093]    S 207 , the UE assigns the value of the KSI ASME  to the KSI, that is, makes KSI ASME =KSI, and stores the KSI, along with the IK and CK which are generated by the K ASME ; and 
         [0094]    S 208 , the UE sends the target SGSN a message indicative of the completion of the transfer to the UTRAN in an idle state, wherein 
         [0095]    if in step S 201  the request message sent by the UE to the target SGSN is a routing area update request, then the message indicative of the completion of the transfer to the UTRAN in an idle state is a routing area update completion message in this step; 
         [0096]    if in step S 201  the request message sent by the UE to the target SGSN is an attachment request, then the message indicative of the completion of the transfer to the UTRAN in an idle state is an attachment completion message in this step. 
         [0097]      FIG. 3  illustrates a second embodiment of the method according to the present invention, which depicts a flow of the method for generating an identifier of a key when a UE transfers from an EUTRAN to a UTRAN in an idle state, the method comprises the following steps: 
         [0098]    S 301 , the UE determines to transfer to the UTRAN in an idle state, assigns the value of a KSI ASME  to a KSI, that is, makes KSI=KSI ASME , and stores the KSI, along with an IK and CK which are generated by the K ASME ; 
         [0099]    S 302 , the UE sends a target SGSN a request message for requesting transfer to the UTRAN in an idle state; 
         [0100]    herein, the request message for requesting transfer to the UTRAN in an idle state is a routing area update request or an attachment request; 
         [0101]    S 303 , after receiving the request message sent by the UE for requesting transfer to the UTRAN in an idle state, the target SGSN sends a source MME a user information extraction request message corresponding to the request message for requesting transfer to the UTRAN in an idle state, wherein 
         [0102]    if in step S 302  the request message sent by the UE to the target SGSN is a routing area update request, then the user information extraction request message is a context request message in this step; 
         [0103]    and if in step S 302  the request message sent by the UE to the target SGSN is an attachment request, then the user information extraction request message is an identification request message in this step; 
         [0104]    S 304 , after receiving the user information extraction request message sent by the target SGSN, the source MME assigns the value of the KSI ASME  to the KSI, that is, makes KSI=KSI ASME , and generates an IK and a CK using the K ASME ; 
         [0105]    S 305 , the source MME sends the target SGSN a user information extraction response message including the KSI, the IK and the CK, wherein: 
         [0106]    if in step S 304  the source MME receives a context request message from the target SGSN, then the user information extraction response message is a context response message in this step; 
         [0107]    if in step S 304  the source MME receives an identification request message from the target SGSN, then the user information extraction response message is an identification response message in this step; 
         [0108]    S 306 , after receiving the KSI, the IK and the CK which are sent by the source MME, the target SGSN stores the KSI along with the IK and the CK; 
         [0109]    S 307 , the target SGSN sends the UE a message indicative of accepting the transfer to the UTRAN in an idle state, so as to inform the UE of the successful mapping of the identifier of a key of a network side, wherein: 
         [0110]    if in step  302  the request message sent by the UE to the target SGSN is a routing area update request, then the message indicative of accepting the transfer to the UTRAN in an idle state is a routing area update accept message in this step; 
         [0111]    if in step S 302  the request message sent by the UE to the target SGSN is an attachment request, then the message indicative of accepting the transfer to the UTRAN in an idle state is an attachment accept message in this step; and 
         [0112]    S 308 , the UE sends the target SGSN a message indicative of the completion of the transfer to the UTRAN in an idle state, wherein 
         [0113]    if in step S 302  the request message sent by the UE to the target SGSN is a routing area update request, then the message indicative of the completion of the transfer to the UTRAN in an idle state is a routing area update completion message in this step; 
         [0114]    if in step S 302  the request message sent by the UE to the target SGSN is an attachment request, then the message indicative of the completion of the transfer to the UTRAN in an idle state is an attachment completion message in this step. 
         [0115]      FIG. 4  illustrates a third embodiment of the method according to the present invention, which refers to the transfer when an RRC is in an active state, that is, a flow of the method for generating an identifier of a key during the transfer from an EUTRAN to a UTRAN, the method comprises the following steps: 
         [0116]    S 401 , a source eNB determines to initiate a handover; 
         [0117]    herein, the determining of the source eNB on the initiation of a handover may be triggered based on a measurement report sent by a UE to the eNB, or the eNB determines to initiate the transfer based on other reasons; 
         [0118]    S 402 , the source eNB sends a handover request to a source MME; 
         [0119]    S 403 , after receiving the handover request, the source MME assigns the value of a KSI ASME  to a KSI, that is, makes KSI=KSI ASME , and generates an IK and a CK using the K ASME ; 
         [0120]    S 404 , the source MME sends a target SGSN a forward redirecting request including the KSI, the IK and the CK; 
         [0121]    S 405 , the target SGSN stores the KSI along with the IK and the CK; 
         [0122]    S 406 , the target SGSN sends the source MME a forward redirecting response message, so as to inform the source MME that the target network is ready for a handover; 
         [0123]    S 407 , the source MME sends a handover command to the source eNB; 
         [0124]    S 408 , the source eNB sends an EUTRAN handover command to the UE; 
         [0125]    S 409 , after receiving the handover command, the UE assigns the value of the KSI ASME  to the KSI, that is, makes KSI=KSI ASME , generates an IK and a CK using the K ASME , and stores the KSI along with the IK and the CK; and 
         [0126]    S 410 , the UE sends a handover success message to a target radio network controller (RNC) to inform the RNC of the successful generation of the KSI of a network side. 
         [0127]      FIG. 5  is a schematic diagram illustrating the specific implementation of a method for generating a key set identifier during the transfer from an EUTRAN to a GERAN according to the present invention, the method comprises the following steps: 
         [0128]    B 1 , after receiving a relevant request message, a source MME maps a KSI ASME  into a KSI, that is, assigns the value of the KSI ASME  to the KSI to make KSI=KSI ASME , and then sends a target SGSN the KSI, along with an IK and CK which are generated by the K ASME  via an interaction message of the source MME and the target SGSN; 
         [0129]    B 2 , after receiving the KSI, the IK and the CK which are sent by the source MME, the target SGSN assigns the value of the KSI to a CKSN, that is, makes CKSN=KSI, stores the CKSN, along with a Kc generated by the IK and the CK, and sends a UE a message indicative of the completion of CKSN mapping; 
         [0130]    B 3 , the UE maps the KSI ASME  into the CKSN, that is, assigns the value of the KSI ASME  to the CKSN to make CKSN=KSI ASME , and stores the CKSN, along with a Kc generated by the K ASME . 
         [0131]    Herein, the UE may also make the CKSN equal to the sum of the value of the KSI ASME  and a constant, the source MME may also make the value of the KSI equal to the sum of the value of the KSI ASME  and a constant, wherein the above two constants are determined by the UE and a network side together, and the sum of the value of the KSI ASME  and the constant should not be ‘111’, and if the sum of the value of the KSI ASME  and the constant is just ‘111’, the UE and the network side are required to determine the sum of the value of the KSI ASME  and the constant to be another value, such as, a next value ‘000’ or other values. 
         [0132]    In this method, if a key is associated by the UE and the SGSN at the network side before the transfer, and if the value of the identifier CKSN of the key is the same as that of the CKSN which the KSI ASME  is mapped into during the transferring process, then the keys stored in the UE and the target SGSN before the transfer are deleted. 
         [0133]      FIG. 6  illustrates a fourth embodiment of the method according to the present invention, which depicts a flow of the method for generating an identifier of a key when a UE transfers from an EUTRAN to a GERAN in an idle state, the method comprises the following steps: 
         [0134]    S 601 , the UE determines to transfer to the GERAN in an idle state and sends a target SGSN a request message for requesting transfer to the GERAN in an idle state; 
         [0135]    herein, the request message for requesting transfer to the GERAN in an idle state may be a routing area update request or an attachment request; 
         [0136]    S 602 , after receiving the request message sent by the UE for requesting transfer to the GERAN in an idle state, the target SGSN sends a source MME a user information extraction request message corresponding to the request message for requesting transfer to the GERAN in an idle state, wherein: 
         [0137]    if in step S 601  the request message sent by the UE to the target SGSN is a routing area update request, then the user information extraction request message is a context request message in this step; 
         [0138]    if in step S 601  the request message sent by the UE to the target SGSN is an attachment request, then the user information extraction request message is an identification request message in this step; 
         [0139]    S 603 , after receiving the user information extraction request message sent by the target SGSN, the source MME assigns the value of the KSI ASME  to a KSI, that is, makes KSI=KSI ASME , and generates an IK and a CK using a K ASME ; 
         [0140]    S 604 , the source MME sends the target SGSN a user information extraction response message including the KSI, the IK and the CK, wherein: 
         [0141]    if in step S 603  the source MME receives a context request message from the target SGSN, then the user information extraction response message is a context response message in this step; 
         [0142]    if in step S 603  the source MME receives an identification request message from the target SGSN, then the user information extraction response message is an identification response message in this step; 
         [0143]    S 605 , after receiving the KSI, the IK and the CK which are sent by the source MME, the target SGSN assigns the value of the KSI to a CKSN, and stores the CKSN, along with a Kc generated by the IK and the CK; 
         [0144]    S 606 , the target SGSN sends the UE a message indicative of accepting the transfer to the GERAN in an idle state, so as to inform the UE of the successful mapping of the identifier of a key of a network side, wherein: 
         [0145]    if in step S 601  the request message sent by the UE to the target SGSN is a routing area update request, then the message indicative of accepting the transfer to the GERAN in an idle state is a routing area update accept message in this step; 
         [0146]    if in step S 601  the request message sent by the UE to the target SGSN is an attachment request, then the message indicative of accepting the transfer to the GERAN in an idle state is an attachment accept message in this step; 
         [0147]    S 607 , the UE assigns the value of the KSI ASME  to the CKSN, that is, makes CKSN=KSI ASME , and stores the CKSN, along with a Kc generated by the K ASME ; and 
         [0148]    S 608 , the UE sends the target SGSN a message indicative of the completion of the transfer to the GERAN in an idle state, wherein: 
         [0149]    if in step S 601  the request message sent by the UE to the target SGSN is a routing area update request, then the message indicative of the completion of the transfer to the GERAN in an idle state is a routing area update completion message in this step; 
         [0150]    if in step S 601  the request message sent by the UE to the target SGSN is an attachment request, then the message indicative of the completion of the transfer to the GERAN in an idle state is an attachment completion message in this step. 
         [0151]      FIG. 7  illustrates a fifth embodiment of the method according to the present invention, which depicts a flow of the method for generating an identifier of a key when a UE transfers from an EUTRAN to a GERAN in an idle state, the method comprises the following steps: 
         [0152]    S 701 , the UE determines to transfer to the GERAN in an idle state, assigns the value of a KSI ASME  to a CKSN, that is, makes CKSN=KSI ASME , and stores the CKSN, along with a Kc generated by the K ASME ; 
         [0153]    S 702 , the UE sends a target SGSN a request message for requesting transfer to the GERAN in an idle state; 
         [0154]    herein, the request message for requesting transfer to the GERAN in an idle state is a routing area update request or an attachment request; 
         [0155]    S 703 , after receiving the request message sent by the UE for requesting transfer to the GERAN in an idle state, the target SGSN sends a source MME a user information extraction request message corresponding to the request message for requesting transfer to the GERAN in an idle state, wherein: 
         [0156]    if in step S 702  the request message sent by the UE to the target SGSN is a routing area update request, then the user information extraction request message is a context request message in this step; 
         [0157]    if in step S 702  the request message sent by the UE to the target SGSN is an attachment request, then the user information extraction request message is an identification request message in this step; 
         [0158]    S 704 , after receiving the user information extraction request message sent by the target SGSN, the source MME assigns the value of the KSI ASME  to a KSI, that is, makes KSI=KSI ASME , and generates an IK and a CK using the K ASME ; 
         [0159]    S 705 , the source MME sends the target SGSN a user information extraction response message including the KSI, the IK and the CK, wherein: 
         [0160]    if in step S 704  the source MME receives a context request message from the target SGSN, then the user information extraction response message is a context response message in this step; 
         [0161]    if in step S 704  the source MME receives an identification request message from the target SGSN, then the user information extraction response message is an identification response message in this step; 
         [0162]    S 706 , after receiving the KSI, the IK and the CK which are sent by the source MME, the target SGSN assigns the value of the KSI to the CKSN, and stores the CKSN, along with a Kc generated by the IK and the CK; 
         [0163]    S 707 , the target SGSN sends the UE a message indicative of accepting the transfer to the GERAN in an idle state, so as to inform the UE of the successful mapping of the identifier of a key of a network side, wherein: 
         [0164]    if in step S 702  the request message sent by the UE to the target SGSN is a routing area update request, then the message indicative of accepting the transfer to the GERAN in an idle state is a routing area update accept message in this step; 
         [0165]    if in step S 702  the request message sent by the UE to the target SGSN is an attachment request, then the message indicative of accepting the transfer to the GERAN in an idle state is an attachment accept message in this step; and 
         [0166]    S 708 , the UE sends the target SGSN a message indicative of the completion of the transfer to the GERAN in an idle state, wherein: 
         [0167]    if in step S 702  the request message sent by the UE to the target SGSN is a routing area update request, then the message indicative of the completion of the transfer to the GERAN in an idle state is a routing area update completion message in this step; 
         [0168]    if in step S 702  the request message sent by the UE to the target SGSN is an attachment request, then the message indicative of the completion of the transfer to the GERAN in an idle state is an attachment completion message in this step. 
         [0169]      FIG. 8  illustrates a sixth embodiment of the method according to the present invention, which depicts a flow of the method for generating an identifier of a key during mobility from an EUTRAN to a GERAN when an RRC is in an active state, the method comprises the following steps: 
         [0170]    S 801 , a source eNB determines to initiate a handover; 
         [0171]    herein, the determining of the source eNB on the initiation of a handover may be triggered based on a measurement report sent by a UE to the eNB, or the eNB determines to initiate the transfer based on other reasons; 
         [0172]    S 802 , the source eNB sends a handover request to a source MME; 
         [0173]    S 803 , after receiving the handover request, the source MME assigns the value of a KSI ASME  to a KSI, that is, makes KSI=KSI ASME , and generates an IK and a CK using the K ASME ; 
         [0174]    S 804 , the source MME sends a target SGSN a forward redirecting request including the KSI, the IK and the CK; 
         [0175]    S 805 , the target SGSN assigns the value of the KSI to a CKSN, that is, makes CKSN=KSI, and stores the CKSN, along with a Kc generated by the IK and the CK; 
         [0176]    S 806 , the target SGSN sends the source MME a forward redirecting response message, so as to inform the source MME that the target network is ready for a handover; 
         [0177]    S 807 , the source MME sends a handover command to the source eNB; 
         [0178]    S 808 , the source eNB sends an EUTRAN handover command to the UE; 
         [0179]    S 809 , after receiving the handover command, the UE assigns the value of the KSI ASME  to the CKSN, that is, makes CKSN=KSI ASME , generates a Kc using the K ASME , and stores the generated CKSN and Kc; and 
         [0180]    S 810 , the UE sends a handover success message to a target RNC or BSS to inform the target RNC or BSS of the successful mapping of the CKSN of a network side. 
         [0181]    In the above six embodiments, the source MME and the UE may also make the value of the identifier of a key of the target system equal to the sum of the value of the KSI ASME  and a constant, wherein the constant is determined by the UE and the network side together, and the sum of the value of the KSI ASME  and the constant should not be ‘111’, and if the sum of the value of the KSI ASME  and the constant is just ‘111’, the UE and the network side are required to determine the sum of the value of the KSI ASME  and the constant to be another value, such as, a next value ‘000’ or other values. 
         [0182]    The KSI ASME  and the KSI SGSN  have been introduced in above descriptions, the format of the KSI ASME  is the same as that of the KSI SGSN , only the KSI ASME  is taken as an example for description in the above embodiments, the processing method of the KSI SGSN  is the same as that of the KSI ASME , therefore description relating to the KSI SGSN  is not repeated in the present invention. 
         [0183]    The present invention provides a system for generating an identifier of a key, which is suitable for generating an identifier of a key when a UE transfers from an EUTRAN to a UTRAN, the system comprises: a UE, a mobility management entity (MME) and a serving GPRS support node (SGSN), wherein: 
         [0184]    the UE is configured to map a KSI ASME  of the EUTRAN into an identifier of a system key of the UTRAN; 
         [0185]    the MME is configured to map the KSI ASME  into an identifier of a system key of the UTRAN, and to send the identifier to the target SGSN; 
         [0186]    the SGSN is configured to receive and store the identifier of the system key and the ciphering key and the integrity key which are sent by the MME; 
         [0187]    the mapping mode is as follows: the MME and the UE directly make the value of the identifier of the system key equal to that of the KSI ASME , or equal to the sum of the value of the KSI ASME  and a constant which is determined by the UE and a network side together. 
         [0188]    Further, the UE comprises: 
         [0189]    a first key set identifier mapping unit configured to generate an identifier KSI of an IK and a CK, and to map the value of the identifier KSI ASME  of a key of a root key access security management entity of the EUTRAN to the KSI, or to map the value of the identifier KSI ASME  plus an appointed constant to the KSI; 
         [0190]    a first key and identifier thereof storing unit configured to store the system keys of the UTRAN, that is, the IK and CK, and the identifier KSI of the system keys generated by the first key set identifier mapping unit; 
         [0191]    a message receiving unit configured to receive a key set identifier mapping success message sent from the network side; and 
         [0192]    a message sending unit configured to send a request message to the network side. 
         [0193]    Further, the MME unit comprises: 
         [0194]    a second key set identifier mapping unit configured to generate an identifier KSI of the IK and the CK, and to map the value of the KSI ASME  to the KS, or to map the value of the KSI ASME  plus an appointed constant to the KSI; 
         [0195]    a security parameter sending unit configured to send the identifier KSI of the system keys generated by the second key set identifier mapping unit and the IK and the CK to the SGSN; and 
         [0196]    a request message receiving unit configured to receive a key set identifier mapping request. 
         [0197]    Further, the SGSN comprises: 
         [0198]    a security parameter receiving unit configured to receive the IK and the CK and the identifier KSI of the IK and CK which are sent by the MME; 
         [0199]    a third key and identifier thereof storing unit configured to store the received identifier KSI, and the IK and the CK; 
         [0200]    a message sending unit configured to inform the UE of a message indicative of the completion of the generation of an identifier of the network side. 
         [0201]    By mapping the value of the KSI ASME  in the EUTRAN into the value of the KSI in the UTRAN, the above method and system for generating a key set identifier, simultaneously guarantee that there are no repeated codes in the KSI and the previously-stored key sequence numbers, and solve the problem in existing techniques that the IK and the CK which are obtained through mapping cannot be reused for not being provided with an identifier when a UE transfers from the EUTRAN to the UTRAN. 
         [0202]    The present invention also provides a system for generating an identifier of a key, which is suitable for generating an identifier of a key when a UE transfers from an EUTRAN to a GERAN, the system comprises a UE, a mobility management entity (MME) and a serving GPRS support node (SGSN), wherein: 
         [0203]    the UE is configured to generate an identifier CKSN of a ciphering key Kc of the GERAN by mapping a key set identifier for an access security management entity; 
         [0204]    the MME is configured to generate an identifier of a ciphering key and an integrity key by mapping a key set identifier of the access security management entity, and to send the ciphering key, the integrity key and the identifier of the ciphering key and integrity key to the SGSN; and 
         [0205]    the SGSN is configured to receive the ciphering key, the integrity key and identifier thereof which are sent by the MME, and assigning the value of the identifier to the identifier CKSN of the ciphering key Kc of the GERAN. 
         [0206]    Further, the UE comprises: 
         [0207]    a first key set identifier mapping unit configured to generate an identifier CKSN of a Kc, and to map a value of a root key of the EUTRAN, that is, a value of a key set identifier of an access security management entity (KSI ASME ) to the CKSN, or to map the value of the identifier KSI ASME  plus an appointed constant to the CKSN; 
         [0208]    a first key and identifier thereof storing unit configured to store the key Kc generated by a first key generating unit and the identifier CKSN of the key generated by the first key set identifier mapping unit; 
         [0209]    a message receiving unit configured to receive a key set identifier mapping completion message sent from a network side; and 
         [0210]    a message sending unit configured to send a request message to inform the network side of performing key set identifier mapping. 
         [0211]    Further, the mobility management comprises: 
         [0212]    a second key set identifier mapping unit configured to generate an identifier KSI of the IK and the CK, and to map the value of the KSI ASME  to the KSI, or to map the value of the KSI ASME  plus an appointed constant to the KSI; 
         [0213]    a security parameter sending unit configured to send the SGSN the IK and the CK, and the identifier KSI of the IK and the CK which is generated by the second key set identifier mapping unit; 
         [0214]    a request message receiving unit configured to receive a key set identifier mapping request. 
         [0215]    Further, the SGSN comprises: 
         [0216]    a security parameter receiving unit configured to receive the keys of IK and CK, and the identifier KSI thereof which are sent by the MME; 
         [0217]    a third key set identifier mapping unit configured to assign the value of the KSI to the CKSN; 
         [0218]    a third key and identifier thereof storing unit configured to store the key Kc and the identifier CKSN of the key Kc; and 
         [0219]    a message sending unit configured to inform the UE of a message indicative of the completion of the generation of an identifier of the network side. 
         [0220]    By mapping the value of the KSI ASME  into the value of the CKSN, the method and system in the above embodiments for generating a key set identifier, simultaneously guarantee that there are no repeated codes in the CKSN and the key sequence number previously stored by the SGSN, and therefore solve the problem in existing techniques that the IK, the CK or the Kc which the K ASME  is mapped into cannot be reused for not being provided with an identifier when the UE transfers from the EUTRAN to the UTRAN or GERAN. By using the method and system, the IK, the CK or the Kc can be reused after the transfer, the interaction signaling is reduced between the UE and the network side, and the satisfaction level of the user on the use of the network is improved. 
         [0221]    Apparently, it should be understood by those skilled in the art that all the modules or steps of the present invention can be realized by universal computing devices, and can be centralized on a single computing device or distributed on a network consisting of multiple computing devices, and optionally can be realized by program codes executable to computing devices, therefore all the modules or steps can be stored in a storage device to be executed by computing devices, or it can be realized by making all the modules or steps into integrated circuit modules respectively, or making multiple modules or steps of them into a single integrated circuit module, thus the present invention is not limited to the combination of any specific hardware and software. 
         [0222]    The above mentioned is only preferred embodiments of the present invention but not to limit the present invention, various modifications and changes can be devised by those skilled in the art, and it should be understood that any modification, equivalent substitution and improvement devised without departing from the spirit and scope of the present invention, shall be within the protection scope of the present invention. 
       INDUSTRIAL APPLICABILITY 
       [0223]    By mapping the value of a KSI ASME  into the value of a CKSN, the above method and system for generating an identifier of a key, simultaneously guarantee that there are no repeated codes in the CKSN and the key sequence number previously stored by an SGSN, and therefore solve the problem in existing techniques that, the IK, the CK or the Kc which a K ASME  is mapped into cannot be reused for not being provided with an identifier when a UE transfers from an EUTRAN to a UTRAN or GERAN; thereby the method and system of the present invention make the IK, the CK or the Kc can be reused after the transfer, reducing the interaction signaling between the UE and a network side, improving the satisfaction level of the user on the use of the network, and therefore has high industrial applicability.