Patent Publication Number: US-2018034635-A1

Title: GPRS System Key Enhancement Method, SGSN Device, UE, HLR/HSS, and GPRS System

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of International Application No. PCT/CN2015/076118, filed on Apr. 8, 2015, the disclosure of which is hereby incorporated by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     This application relates to the communication security field, and in particular, to a GPRS system key enhancement method, an SGSN device, UE, an HLR/HSS, and a GPRS system. 
     BACKGROUND 
     To implement a data transmission function, user equipment (UE) generally accesses a mobile communications network such as a general packet radio service (GPRS) network of an operator by using a subscriber identity module (SIM) or a universal subscriber identity module (USIM), so as to communicate with other UE, people, or mobile networks. To ensure security of communication of the UE, before the UE accesses the mobile communications network, authentication between a network side and the UE generally needs to be performed so as to ensure validity of the network side and the UE, and a ciphering key and an integrity key are generated so as to provide ciphering protection and integrity protection for a communication message. However, in the prior art, when UE that uses a SIM accesses the GPRS network, only the network side can perform one-way authentication on the UE and perform ciphering protection on a communication message, whereas the UE cannot perform authentication on the network side and cannot perform integrity protection on a communication message. When UE that uses a USIM accesses the GPRS network, two-way authentication can be implemented between the network side and the UE. However, only ciphering protection can be performed on a communication message, and integrity protection cannot be provided for a communication message. Existent security threats are as follows: In one aspect, if the UE cannot perform authentication on a message from the network side, the UE may suffer an attack from a rogue base station. In another aspect, if integrity protection cannot be provided for a communication message, communication between the UE and the network side may suffer an algorithm degrading attack, and a potential security risk such as eavesdropping or tampering of communication content may even exist. For some UEs that require high-security communication, such as Internet of Things UE and machine to machine communication UE, a method needs to be urgently provided to enhance security of communication of this type of UE in the GPRS network. 
     SUMMARY 
     Embodiments of this application disclose a GPRS system key enhancement method, an SGSN device, UE, an HLR/HSS, and a GPRS system, which can enhance a key in the GPRS system, and enhance security of communication of UE of a first type in a GPRS network. 
     A first aspect of the embodiments of this application discloses a GPRS system key enhancement method. The method may include receiving, by an SGSN, a request message sent by UE; acquiring, by the SGSN, an authentication vector from an HLR/HSS, where the authentication vector includes a first ciphering key and a first integrity key. The method may also include, if the SGSN determines that the UE is UE of a first type, selecting a ciphering algorithm and an integrity algorithm for the UE, and sending the selected ciphering algorithm and the selected integrity algorithm to the UE. The method may also include obtaining, by the SGSN, a second ciphering key and a second integrity key according to the first ciphering key and the first integrity key, where the second ciphering key and the selected ciphering algorithm are used to perform ciphering protection on a message transmitted between the SGSN and the UE, and the second integrity key and the selected integrity algorithm are used to perform integrity protection on a message transmitted between the SGSN and the UE. 
     With reference to the first aspect, in a first possible implementation manner, the request message includes an identifier of the UE, and that the SGSN determines that the UE is UE of a first type includes: sending, by the SGSN, the identifier of the UE to the HLR/HSS, so that the HLR/HSS determines, according to the identifier of the UE, that the UE is UE of the first type, and sends UE type indication information to the SGSN, where the UE type indication information is used to indicate that the UE is UE of the first type; and receiving, by the SGSN, the UE type indication information sent by the HLR/HSS, and determining that the UE is UE of the first type. 
     With reference to the first aspect, in a second possible implementation manner, that the SGSN determines that the UE is UE of a first type includes: if the request message includes UE type indication information, determining, by the SGSN, that the UE is UE of the first type, where the UE type indication information is used to indicate that the UE is UE of the first type. 
     With reference to any one of the first aspect, or the first or the second possible implementation manner of the first aspect, in a third possible implementation manner, the obtaining, by the SGSN, a second ciphering key and a second integrity key according to the first ciphering key and the first integrity key includes: computing, by the SGSN, an intermediate key according to the first ciphering key and the first integrity key, computing, by the SGSN, the second ciphering key according to the intermediate key and a ciphering characteristic string, and computing, by the SGSN, the second integrity key according to the intermediate key and an integrity characteristic string; or computing, by the SGSN, an intermediate key according to the first ciphering key and the first integrity key, computing, by the SGSN, the second ciphering key according to the intermediate key, a first algorithm type indication, and an identifier of the selected ciphering algorithm, and computing, by the SGSN, the second integrity key according to the intermediate key, a second algorithm type indication, and an identifier of the selected integrity algorithm, where values of the first algorithm type indication and the second algorithm type indication are different. 
     With reference to any one of the first aspect, or the first or the second possible implementation manner of the first aspect, in a fourth possible implementation manner, the computing, by the SGSN, a second ciphering key and a second integrity key according to the first ciphering key and the first integrity key in the authentication vector includes: computing, by the SGSN, an intermediate key according to the first ciphering key and the first integrity key; and using, by the SGSN, a first preset bit of the intermediate key as the second ciphering key, and using a second preset bit of the intermediate key as the second integrity key; or computing, by the SGSN, the second ciphering key according to the first ciphering key, a first algorithm type indication, and an identifier of the selected ciphering algorithm, and computing, by the SGSN, the second integrity key according to the first integrity key, a second algorithm type indication, and an identifier of the selected integrity algorithm, where values of the first algorithm type indication and the second algorithm type indication are different; or using, by the SGSN, the first ciphering key or a preset bit of the first ciphering key as the second ciphering key, and using, by the SGSN, the first integrity key or a preset bit of the first integrity key as the second integrity key. 
     With reference to any one of the first aspect, or the third or the fourth possible implementation manner of the first aspect, in a fifth possible implementation manner, the authentication vector is an authentication vector quintet; and the first ciphering key is a ciphering key CK in the authentication vector quintet, and the first integrity key is an integrity key IK in the authentication vector quintet. 
     With reference to the fifth possible implementation manner of the first aspect, in a sixth possible implementation manner, the intermediate key is a 64-bit GPRS ciphering key Kc or a 128-bit ciphering key Kc128. 
     A second aspect of the embodiments of this application discloses a GPRS system key enhancement method. The method may include sending, by UE, a request message to an SGSN; receiving, by the UE, a ciphering algorithm and an integrity algorithm that are sent by the SGSN. The method may also include acquiring, by the UE, a second ciphering key and a second integrity key according to a first ciphering key and a first integrity key, where the second ciphering key and the ciphering algorithm are used to perform ciphering protection on a message transmitted between the SGSN and the UE, and the second integrity key and the integrity algorithm are used to perform integrity protection on a message transmitted between the SGSN and the UE. 
     With reference to the second aspect, in a first possible implementation manner, the request message that is sent by the UE to the SGSN includes UE type indication information, where the UE type indication information is used to indicate that the UE is UE of a first type. 
     With reference to the second aspect or the first possible implementation manner of the second aspect, in a second possible implementation manner, the acquiring, by the UE, a second ciphering key and a second integrity key according to a first ciphering key and a first integrity key includes: computing, by the UE, an intermediate key according to the first ciphering key and the first integrity key, computing, by the UE, the second ciphering key according to the intermediate key and a ciphering characteristic string, and computing, by the UE, the second integrity key according to the intermediate key and an integrity characteristic string; or computing, by the UE, an intermediate key according to the first ciphering key and the first integrity key, computing, by the UE, the second ciphering key according to the intermediate key, a first algorithm type indication, and an identifier of the ciphering algorithm, and computing, by the UE, the second integrity key according to the intermediate key, a second algorithm type indication, and an identifier of the integrity algorithm, where values of the first algorithm type indication and the second algorithm type indication are different. 
     With reference to the second aspect or the first possible implementation manner of the second aspect, in a third possible implementation manner, the computing, by the UE, a second ciphering key and a second integrity key according to a first ciphering key and a first integrity key includes: computing, by the UE, an intermediate key according to the first ciphering key and the first integrity key; and using, by the UE, a first preset bit of the intermediate key as the second ciphering key, and using a second preset bit of the intermediate key as the second integrity key; or computing, by the UE, the second ciphering key according to the first ciphering key, a first algorithm type indication, and an identifier of the ciphering algorithm, and computing, by the UE, the second integrity key according to the first integrity key, a second algorithm type indication, and an identifier of the integrity algorithm, where values of the first algorithm type indication and the second algorithm type indication are different; or using, by the UE, the first ciphering key or a preset bit of the first ciphering key as the second ciphering key, and using, by the UE, the first integrity key or a preset bit of the first integrity key as the second integrity key. 
     With reference to the second or the third possible implementation manner of the second aspect, in a fourth possible implementation manner, the first ciphering key is a ciphering key CK in an authentication vector quintet, and the first integrity key is an integrity key IK in the authentication vector quintet. 
     With reference to the fourth possible implementation manner of the second aspect, in a fifth possible implementation manner, the intermediate key is a 64-bit GPRS ciphering key Kc or a 128-bit ciphering key Kc 128 . 
     A third aspect of this application discloses a GPRS system key enhancement method. The method may include: receiving, by an HLR/HSS, an identifier of user equipment UE that is sent by an SGSN. The method may also include determining, by the HLR/HSS according to the identifier of the UE, that the UE is UE of a first type. The method may also include sending, by the HLR/HSS, UE type indication information to the SGSN, where the UE type indication information is used to indicate that the UE is UE of the first type. 
     A fourth aspect of this application discloses an SGSN device. The device may include a receiving module, configured to receive a request message sent by UE. The device may also include an acquiring module, configured to acquire an authentication vector from an HLR/HSS, where the authentication vector includes a first ciphering key and a first integrity key. The device may also include a selection module, configured to: when the SGSN determines that the UE is UE of a first type, select a ciphering algorithm and an integrity algorithm for the UE, and send the selected ciphering algorithm and the selected integrity algorithm to the UE. The device may also include an obtaining module, configured to obtain a second ciphering key and a second integrity key according to the first ciphering key and the first integrity key, where the second ciphering key and the selected ciphering algorithm are used to perform ciphering protection on a message transmitted between the SGSN and the UE, and the second integrity key and the selected integrity algorithm are used to perform integrity protection on a message transmitted between the SGSN and the UE. 
     With reference to the fourth aspect, in a first possible implementation manner, the request message includes an identifier of the UE, and the SGSN device further includes: a sending module, configured to send the identifier of the UE to the HLR/HSS, so that the HLR/HSS determines, according to the identifier of the UE, whether the UE is UE of the first type, and sends UE type indication information to the SGSN, where the UE type indication information is used to indicate that the UE is UE of the first type; and a first determining module, configured to receive the UE type indication information sent by the HLR/HSS, and determine that the UE is UE of the first type. 
     With reference to the fourth aspect, in a second possible implementation manner, the SGSN device further includes: a second determining module, configured to: when the request message includes UE type indication information, determine that the UE is UE of the first type, where the UE type indication information is used to indicate that the UE is UE of the first type. 
     With reference to any one of the fourth aspect, or the first or the second possible implementation manner of the fourth aspect, in a third possible implementation manner, the obtaining module includes: a first computation unit, a second computation unit, and a third computation unit, where the first computation unit is configured to compute an intermediate key according to the first ciphering key and the first integrity key, the second computation unit is configured to compute the second ciphering key according to the intermediate key and a ciphering characteristic string, and the third computation unit is configured to compute the second integrity key according to the intermediate key and an integrity characteristic string; or the first computation unit is configured to compute an intermediate key according to the first ciphering key and the first integrity key, the second computation unit is configured to compute the second ciphering key according to the intermediate key, a first algorithm type indication, and an identifier of the selected ciphering algorithm, and the third computation unit is configured to compute the second integrity key according to the intermediate key, a second algorithm type indication, and an identifier of the selected integrity algorithm, where values of the first algorithm type indication and the second algorithm type indication are different. 
     With reference to any one of the fourth aspect, or the first or the second possible implementation manner of the fourth aspect, in a fourth possible implementation manner, the obtaining module is specifically configured to compute an intermediate key according to the first ciphering key and the first integrity key; and use a first preset bit of the intermediate key as the second ciphering key, and use a second preset bit of the intermediate key as the second integrity key; or the obtaining module includes: a fourth computation unit, configured to compute the second ciphering key according to the first ciphering key, a first algorithm type indication, and an identifier of the selected ciphering algorithm, and a fifth computation unit, configured to compute the second integrity key according to the first integrity key, a second algorithm type indication, and an identifier of the selected integrity algorithm, where values of the first algorithm type indication and the second algorithm type indication are different; or the obtaining module is specifically configured to use the first ciphering key in the authentication vector or a preset bit of the first ciphering key as the second ciphering key, and use the first integrity key in the authentication vector or a preset bit of the first integrity key as the second integrity key. 
     With reference to the third or the fourth possible implementation manner of the fourth aspect, in a fifth possible implementation manner, the authentication vector is an authentication vector quintet; and the first ciphering key is a ciphering key CK in the authentication vector quintet, and the first integrity key is an integrity key IK in the authentication vector quintet. 
     With reference to the fifth possible implementation manner of the fourth aspect, in a sixth possible implementation manner, the intermediate key is a 64-bit GPRS ciphering key Kc or a 128-bit ciphering key Kc 128 . 
     A fifth aspect of this application discloses a computer storage medium, where the computer storage medium stores a program, and when the program runs, the steps described in any one of the first aspect or the first to the sixth possible implementation manners of the first aspect are performed. 
     A sixth aspect of this application provides an SGSN device. The device may include a receiving apparatus, a sending apparatus, and a processor. The receiving apparatus, the sending apparatus, and the processor are connected by using a bus. The receiving apparatus is configured to receive a request message sent by UE. The processor is configured to: acquire an authentication vector from an HLR/HSS, where the authentication vector includes a first ciphering key and a first integrity key. If the SGSN determines that the UE is UE of a first type, the processor is configured to select a ciphering algorithm and an integrity algorithm for the UE, and obtain a second ciphering key and a second integrity key according to the first ciphering key and the first integrity key. The sending apparatus is configured to send the selected ciphering algorithm and the selected integrity algorithm to the UE, where the second ciphering key and the selected ciphering algorithm are used to perform ciphering protection on a message transmitted between the SGSN and the UE, and the second integrity key and the selected integrity algorithm are used to perform integrity protection on a message transmitted between the SGSN and the UE. 
     With reference to the sixth aspect, in a first possible implementation manner, the request message includes an identifier of the UE; the sending apparatus is further configured to send the identifier of the UE to the HLR/HSS, so that the HLR/HSS determines, according to the identifier of the UE, whether the UE is UE of the first type, and sends UE type indication information to the SGSN, where the UE type indication information is used to indicate that the UE is UE of the first type; and that the processor determines that the UE is UE of a first type includes: receiving, by the processor, the UE type indication information sent by the HLR/HSS, and determining that the UE is UE of the first type. 
     With reference to the sixth aspect, in a second possible implementation manner, that the processor determines that the UE is UE of a first type includes: if the request message includes UE type indication information, determining, by the processor, that the UE is UE of the first type, where the UE type indication information is used to indicate that the UE is UE of the first type. 
     With reference to any one of the sixth aspect, or the first or the second possible implementation manner of the sixth aspect, in a third possible implementation manner, that the processor obtains a second ciphering key and a second integrity key according to the first ciphering key and the first integrity key includes: computing, by the processor, an intermediate key according to the first ciphering key and the first integrity key, computing, by the processor, the second ciphering key according to the intermediate key and a ciphering characteristic string, and computing, by the processor, the second integrity key according to the intermediate key and an integrity characteristic string; or computing, by the processor, an intermediate key according to the first ciphering key and the first integrity key, computing, by the processor, the second ciphering key according to the intermediate key, a first algorithm type indication, and an identifier of the selected ciphering algorithm, and computing, by the processor, the second integrity key according to the intermediate key, a second algorithm type indication, and an identifier of the selected integrity algorithm, where values of the first algorithm type indication and the second algorithm type indication are different. 
     With reference to any one of the sixth aspect, or the first or the second possible implementation manner of the sixth aspect, in a fourth possible implementation manner, that the processor obtains a second ciphering key and a second integrity key according to the first ciphering key and the first integrity key includes: computing, by the processor, an intermediate key according to the first ciphering key and the first integrity key; and using, by the processor, a first preset bit of the intermediate key as the second ciphering key, and using a second preset bit of the intermediate key as the second integrity key; or computing, by the processor, the second ciphering key according to the first ciphering key in the authentication vector, a first algorithm type indication, and an identifier of the selected ciphering algorithm, and computing, by the processor, the second integrity key according to the first integrity key in the authentication vector, a second algorithm type indication, and an identifier of the selected integrity algorithm, where values of the first algorithm type indication and the second algorithm type indication are different; or using, by the processor, the first ciphering key or a preset bit of the first ciphering key as the second ciphering key, and using, by the processor, the first integrity key or a preset bit of the first integrity key as the second integrity key. 
     With reference to the third or the fourth possible implementation manner of the sixth aspect, in a fifth possible implementation manner, the authentication vector is an authentication vector quintet; and the first ciphering key is a ciphering key CK in the authentication vector quintet, and the first integrity key is an integrity key IK in the authentication vector quintet. 
     With reference to the fifth possible implementation manner of the sixth aspect, in a sixth possible implementation manner, the intermediate key is a 64-bit GPRS ciphering key Kc or a 128-bit ciphering key Kc 128 . 
     A seventh aspect of this application discloses UE. The UE may include a sending module, configured to send a request message to an SGSN. The UE may also include a receiving module, configured to receive a ciphering algorithm and an integrity algorithm that are sent by the SGSN. The UE may also include an acquiring module, configured to acquire a second ciphering key and a second integrity key according to a first ciphering key and a first integrity key, where the second ciphering key and the ciphering algorithm are used to perform ciphering protection on a message transmitted between the SGSN and the UE, and the second integrity key and the integrity algorithm are used to perform integrity protection on a message transmitted between the SGSN and the UE. 
     With reference to the seventh aspect, in a first possible implementation manner, the request message that is sent by the UE to the SGSN includes UE type indication information, where the UE type indication information is used to indicate that the UE is UE of a first type. 
     With reference to the seventh aspect or the first possible implementation manner of the seventh aspect, in a second possible implementation manner, the acquiring module includes: a first computation unit, a second computation unit, and a third computation unit, where the first computation unit is configured to compute an intermediate key according to the first ciphering key and the first integrity key, the second computation unit is configured to compute the second ciphering key according to the intermediate key and a ciphering characteristic string, and the third computation unit is configured to compute the second integrity key according to the intermediate key and an integrity characteristic string; or the first computation unit is configured to compute an intermediate key according to the first ciphering key and the first integrity key, the second computation unit is configured to compute the second ciphering key according to the intermediate key, a first algorithm type indication, and an identifier of the ciphering algorithm, and the third computation unit is configured to compute the second integrity key according to the intermediate key, a second algorithm type indication, and an identifier of the integrity algorithm, where values of the first algorithm type indication and the second algorithm type indication are different. 
     With reference to the seventh aspect or the first possible implementation manner of the seventh aspect, in a third possible implementation manner, the acquiring module is specifically configured to compute an intermediate key according to the first ciphering key and the first integrity key; and use a first preset bit of the intermediate key as the second ciphering key, and use a second preset bit of the intermediate key as the second integrity key; or the computation module includes: a fourth computation unit, configured to compute the second ciphering key according to the first ciphering key, a first algorithm type indication, and an identifier of the ciphering algorithm, and a fifth computation unit, configured to compute the second integrity key according to the first integrity key, a second algorithm type indication, and an identifier of the integrity algorithm, where values of the first algorithm type indication and the second algorithm type indication are different; or the acquiring module is specifically configured to use the first ciphering key or a preset bit of the first ciphering key as the second ciphering key, and use the first integrity key or a preset bit of the first integrity key as the second integrity key. 
     With reference to the second or the third possible implementation manner of the seventh aspect, in a fourth possible implementation manner, the first ciphering key is a ciphering key CK in an authentication vector quintet, and the first integrity key is an integrity key IK in the authentication vector quintet. 
     With reference to the fourth possible implementation manner of the seventh aspect, in a fifth possible implementation manner, the intermediate key is a 64-bit GPRS ciphering key Kc or a 128-bit ciphering key Kc 128 . 
     An eighth aspect of this application discloses a computer storage medium, where the computer storage medium stores a program, and when the program runs, the steps described in any one of the second aspect or the first to the fifth possible implementation manners of the second aspect are performed. 
     A ninth aspect of this application discloses UE, where the UE may include a sending apparatus, a receiving apparatus, and a processor. The sending apparatus, the receiving apparatus, and the processor are connected by using a bus. The sending apparatus is configured to send a request message to an SGSN. The receiving apparatus is further configured to receive a ciphering algorithm and an integrity algorithm that are sent by the SGSN. The processor is configured to acquire a second ciphering key and a second integrity key according to a first ciphering key and a first integrity key, where the second ciphering key and the ciphering algorithm are used to perform ciphering protection on a message transmitted between the SGSN and the UE, and the second integrity key and the integrity algorithm are used to perform integrity protection on a message transmitted between the SGSN and the UE. 
     With reference to the ninth aspect, in a first possible implementation manner, the request message that is sent by the sending apparatus to the SGSN includes UE type indication information, where the UE type indication information is used to indicate that the UE is UE of a first type. 
     With reference to the ninth aspect or the first possible implementation manner of the ninth aspect, in a second possible implementation manner, that the processor acquires a second ciphering key and a second integrity key according to a first ciphering key and a first integrity key includes: computing, by the processor, an intermediate key according to the first ciphering key and the first integrity key, computing, by the processor, the second ciphering key according to the intermediate key and a ciphering characteristic string, and computing, by the processor, the second integrity key according to the intermediate key and an integrity characteristic string; or computing, by the processor, an intermediate key according to the first ciphering key and the first integrity key, computing, by the processor, the second ciphering key according to the intermediate key, a first algorithm type indication, and an identifier of the ciphering algorithm, and computing, by the processor, the second integrity key according to the intermediate key, a second algorithm type indication, and an identifier of the integrity algorithm, where values of the first algorithm type indication and the second algorithm type indication are different. 
     With reference to the ninth aspect or the first possible implementation manner of the ninth aspect, in a third possible implementation manner, that the processor acquires a second ciphering key and a second integrity key according to a first ciphering key and a first integrity key includes: computing, by the processor, an intermediate key according to the first ciphering key and the first integrity key; and using, by the processor, a first preset bit of the intermediate key as the second ciphering key, and using a second preset bit of the intermediate key as the second integrity key; or computing, by the processor, the second ciphering key according to the first ciphering key, a first algorithm type indication, and an identifier of the ciphering algorithm, and computing, by the processor, the second integrity key according to the first integrity key, a second algorithm type indication, and an identifier of the integrity algorithm, where values of the first algorithm type indication and the second algorithm type indication are different; or using, by the processor, the first ciphering key or a preset bit of the first ciphering key as the second ciphering key, and using, by the processor, the first integrity key or a preset bit of the first integrity key as the second integrity key. 
     With reference to the second or the third possible implementation manner of the ninth aspect, in a fourth possible implementation manner, the first ciphering key is a ciphering key CK in an authentication vector quintet, and the first integrity key is an integrity key IK in the authentication vector quintet. 
     With reference to the fourth possible implementation manner of the ninth aspect, in a fifth possible implementation manner, the intermediate key is a 64-bit GPRS ciphering key Kc or a 128-bit ciphering key Kc 128 . 
     A tenth aspect of this application discloses an HLR/HSS. The HLR/HSS may include a receiving module, configured to receive an identifier of user equipment UE that is sent by a serving GPRS support node SGSN. The HLR/HSS may also include a determining module, configured to determine, according to the identifier of the UE, that the UE is UE of a first type. The HLR/HSS may also include a sending module, configured to send UE type indication information to the SGSN, where the UE type indication information is used to indicate that the UE is UE of the first type. 
     An eleventh aspect of this application discloses a computer storage medium, where the computer storage medium stores a program, and when the program runs, the steps described in the third aspect of this application are performed. 
     A twelfth aspect of this application discloses an HLR/HSS, where the HLR/HSS may include a sending apparatus, a receiving apparatus, and a processor, where the sending apparatus, the receiving apparatus, and the processor are connected by using a bus. The receiving apparatus is configured to receive an identifier of user equipment UE that is sent by a serving GPRS support node SGSN. The processor is configured to determine, according to the identifier of the UE, that the UE is UE of a first type. The sending apparatus is configured to send UE type indication information to the SGSN, where the UE type indication information is used to indicate that the UE is UE of the first type. 
     A thirteenth aspect of this application discloses a GPRS system, where the GPRS system includes a serving GPRS support node SGSN device, user equipment UE, and a home location register HLR/home subscription system HSS. The SGSN device is configured to: receive a request message sent by the UE, acquire an authentication vector from the HLR/HSS, where the authentication vector includes a first ciphering key and a first integrity key, if the SGSN determines that the UE is UE of a first type, select a ciphering algorithm and an integrity algorithm for the UE, send the selected ciphering algorithm and the selected integrity algorithm to the UE, and obtain a second ciphering key and a second integrity key according to the first ciphering key and the first integrity key. The UE is configured to: send the request message to the SGSN, receive the ciphering algorithm and the integrity algorithm that are sent by the SGSN, and acquire the second ciphering key and the second integrity key according to the first ciphering key and the first integrity key, where the second ciphering key and the ciphering algorithm are used to perform ciphering protection on a message transmitted between the SGSN and the UE, and the second integrity key and the integrity algorithm are used to perform integrity protection on a message transmitted between the SGSN and the UE. 
     With reference to the thirteenth aspect, in a first possible implementation manner, the HLR/HSS is configured to: receive an identifier of the UE that is sent by the SGSN; determine, according to the identifier of the UE, that the UE is UE of the first type; and send UE type indication information to the SGSN, where the UE type indication information is used to indicate that the UE is UE of the first type. 
     In the embodiments of this application, an SGSN receives a request message sent by UE, after determining that the UE is UE of a first type, selects a ciphering algorithm and an integrity algorithm, acquires an authentication vector from an HLR/HSS, obtains an enhanced second ciphering key and an enhanced second integrity key according to a first ciphering key and a first integrity key that are included in the authentication vector, and sends the selected ciphering algorithm and the selected integrity algorithm to the UE, so that after the UE computes the second ciphering key and the second integrity key, both the SGSN and the UE may perform ciphering protection and integrity protection on a communication message between the SGSN and the UE by using the second ciphering key, the second integrity key, and the ciphering algorithm and the integrity algorithm that are selected by the SGSN. This enhances security of communication of UE of the first type in a GPRS network. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       To describe the technical solutions in this application more clearly, the following briefly describes the accompanying drawings required for describing the embodiments. Apparently, the accompanying drawings in the following description show merely some embodiments of this application, and persons of ordinary skill in the art may still derive other drawings from these accompanying drawings without creative efforts. 
         FIG. 1  is a schematic flowchart of an embodiment of a GPRS system key enhancement method according to this application; 
         FIG. 2  is a schematic flowchart of another embodiment of a GPRS system key enhancement method according to this application; 
         FIG. 3  is a schematic flowchart of still another embodiment of a GPRS system key enhancement method according to this application; 
         FIG. 4  is a schematic flowchart of still another embodiment of a GPRS system key enhancement method according to this application; 
         FIG. 5  is a schematic flowchart of still another embodiment of a GPRS system key enhancement method according to this application; 
         FIG. 6  is a schematic flowchart of still another embodiment of a GPRS system key enhancement method according to this application; 
         FIG. 7  is a schematic flowchart of still another embodiment of a GPRS system key enhancement method according to this application; 
         FIG. 8  is a schematic flowchart of still another embodiment of a GPRS system key enhancement method according to this application; 
         FIG. 9  is a schematic flowchart of still another embodiment of a GPRS system key enhancement method according to this application; 
         FIG. 10  is a schematic flowchart of still another embodiment of a GPRS system key enhancement method according to this application; 
         FIG. 11  is a schematic flowchart of still another embodiment of a GPRS system key enhancement method according to this application; 
         FIG. 12  is a schematic flowchart of still another embodiment of a GPRS system key enhancement method according to this application; 
         FIG. 13  is a schematic structural diagram of an embodiment of an SGSN device according to this application; 
         FIG. 14  is a schematic structural diagram of an embodiment of an obtaining module in an SGSN device according to this application; 
         FIG. 15  is a schematic structural diagram of another embodiment of an obtaining module in an SGSN device according to this application; 
         FIG. 16  is a schematic structural diagram of another embodiment of an SGSN device according to this application; 
         FIG. 17  is a schematic structural diagram of an embodiment of UE according to this application; 
         FIG. 18  is a schematic structural diagram of an embodiment of an acquiring module in UE according to this application; 
         FIG. 19  is a schematic structural diagram of another embodiment of an acquiring module in UE according to this application; 
         FIG. 20  is a schematic structural diagram of another embodiment of UE according to this application; 
         FIG. 21  is a schematic structural diagram of an embodiment of an HLR/HSS according to this application; 
         FIG. 22  is a schematic structural diagram of another embodiment of an HLR/HSS according to this application; and 
         FIG. 23  is a schematic structural diagram of an embodiment of a GPRS system according to this application. 
     
    
    
     DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS 
     The following clearly describes the technical solutions in the embodiments of this application with reference to the accompanying drawings in the embodiments of this application. Apparently, the described embodiments are merely some but not all of the embodiments of this application. All other embodiments obtained by persons of ordinary skill in the art based on the embodiments of this application without creative efforts shall fall within the protection scope of this application. 
     This application provides a GPRS system key enhancement method, an SGSN device, UE, an HLR/HSS, and a GPRS system, which may enhance a key between the SGSN and the UE, and provide ciphering protection and integrity protection for communication between the SGSN and the UE. Descriptions are made in the following with reference to the accompanying drawings. 
     Refer to  FIG. 1 .  FIG. 1  is a schematic flowchart of an embodiment of a GPRS system key enhancement method according to this application. As shown in  FIG. 1 , the method may include the following steps. 
     S 101 . An SGSN receives a request message sent by UE. 
     In specific implementation, the request message that is sent by the UE to the SGSN (Serving GPRS Support Node) may be an attach request message, a route update message, or another message, for example, a service request message. After receiving the request message sent by the UE, the SGSN may acquire an identifier of the UE that sends the request message. If the UE is UE of a first type, the request message may carry UE type indication information. 
     In this embodiment of this application, the UE communicates with a network by using a USIM card, and the identifier of the UE may be an IMSI (International Mobile Subscriber Identification Number) of the USIM card. UE of the first type may be Internet of Things UE, machine to machine (M2M) communication UE, or other high-security UE. The Internet of Things UE refers to user equipment that has an information sensing function and a data transmission function, for example, an audio guide, a personal digital assistant, a barcode collector, a data collection terminal, and a POS terminal that is mainly used for purchase or transfer. The machine to machine communication UE refers to user equipment that has a networking and communication capability and that implements an “intelligence” attribute by using a sensor, a controller, and the like, so as to exchange information with a person, a mobile network, or another machine. 
     S 102 . The SGSN acquires an authentication vector from an HLR/HSS, where the authentication vector includes a first ciphering key and a first integrity key. 
     The home location register (HLR) is a permanent database of a GPRS system, and stores information required for managing communication of many mobile users, including static information such as identity information, service information, and service authorization that are of a registered mobile user, and dynamic information such as location information of a user. The home subscription system HSS (HSS) is evolution and upgrade of the HLR, and is mainly responsible for managing subscription data of a user and location information of a mobile user. Because the HSS and the HLR have a similar function in a network, and much data stored in the HSS is repeatedly stored in the HLR, generally, an HSS and HLR convergence device is presented to the outside. In this embodiment of this application, the HLR/HSS may be an HLR device, an HSS device, or an HLR and HSS convergence device. 
     In this embodiment of this application, the authentication vector acquired by the SGSN from the HLR/HSS is an authentication vector quintet, which includes a random number RAND, an expected response XRES, an authentication token AUTN, a ciphering key CK, and an integrity key IK. 
     In this embodiment of this application, the first ciphering key is the ciphering key CK in the authentication vector quintet, and the first integrity key is the integrity key IK in the authentication vector quintet. 
     S 103 . If determining that the UE is UE of a first type, the SGSN selects a ciphering algorithm and an integrity algorithm for the UE, and sends the selected ciphering algorithm and the selected integrity algorithm to the UE. 
     In some feasible implementation manners, the SGSN may send the identifier of the UE to the HLR/HSS. The HLR/HSS determines, according to the identifier of the UE, whether the UE is UE of the first type. If receiving the UE type indication information sent by the HLR/HSS, the SGSN may determine, according to the UE type indication information, that the UE is UE of the first type. 
     In some other feasible implementation manners, if the request message that is sent by the UE to the SGSN carries the UE type indication information, the SGSN may determine that the UE is UE of the first type. 
     Optionally, the UE type indication information may indicate, according to existence of a specific information element (IE), that the UE is UE of the first type. For example, when the SGSN receives the UE type indication information sent by the HLR/HSS or the UE, if a specific IE exists in the UE type indication information, the SGSN may determine that the UE is UE of the first type, and if the specific IE does not exist in the UE type indication information, the SGSN may determine that the UE is not UE of the first type. Alternatively, the UE type indication information may also indicate, according to a value of a specific IE, that the UE is UE of the first type. For example, when the SGSN receives the UE type indication information sent by the HLR/HSS or the UE, if a value of a specific IE in the UE type indication information is 1, the SGSN may determine that the UE is UE of the first type, and if the value of the specific IE is 0, the SGSN may determine that the UE is not UE of the first type. 
     In specific implementation, the SGSN may first acquire the authentication vector from the HLR/HSS, and then determine that the UE is UE of the first type, or may first determine that the UE is UE of the first type, and then acquire the authentication vector from the HLR/HSS. 
     In specific implementation, the UE and the SGSN are separately configured with some ciphering algorithms and integrity algorithms. When sending the request message to the SGSN, the UE sends a ciphering algorithm and an integrity algorithm that are supported by the UE to the SGSN. When receiving the request message of the UE, the SGSN selects a ciphering algorithm supported by the SGSN and an integrity algorithm supported by the SGSN from the ciphering algorithm and the integrity algorithm that are supported by the UE. 
     In some feasible implementation manners, the ciphering algorithm and the integrity algorithm that are selected by the SGSN may be used along with the first ciphering key and the first integrity key in the authentication vector to compute a second ciphering key and a second integrity key. In addition, ciphering may be performed on a communication message according to the ciphering algorithm selected by the SGSN and the second ciphering key to generate a message ciphertext. A message authentication code MAC may be obtained by means of computation according to the integrity algorithm selected by the SGSN and the second integrity key. The message authentication code MAC may be used to verify integrity of the communication message. 
     Optionally, when a GPRS network requires a 128-bit second ciphering key, the ciphering algorithm selected by the SGSN may be any one of a 128-EEM algorithm, a 128-EEA2 algorithm, or a 128-EEA3 algorithm, and the integrity algorithm selected by the SGSN may be any one of a 128-EIA1 algorithm, a 128-EIA2 algorithm, or a 128-EIA3 algorithm. A SNOW  3 G algorithm is used as a core algorithm of the 128-EEM algorithm and the 128-EIA1 algorithm. An AES algorithm is used as a core algorithm of the 128-EEA2 algorithm and the 128-EIA2 algorithm. A ZUC algorithm (ZUC algorithm) is used as a core algorithm of the 128-EEA3 algorithm and the 128-EIA3 algorithm. 
     In specific implementation, when sending the selected ciphering algorithm and the selected integrity algorithm to the UE, the SGSN may further send the random number RAND and the authentication token AUTN in the authentication vector to the UE. The UE may perform authentication on the SGSN side according to the authentication token AUTN, so that the UE side performs authentication on a network side, and may further compute the first ciphering key CK and the first integrity key IK by using f1 to f5 algorithms according to the received random number RAND and the received authentication token AUTN. 
     To protect a communication message between the SGSN and the UE, both the SGSN and the UE need to use an agreed key (that is, the second ciphering key and the second integrity key) and an agreed algorithm (that is, the ciphering algorithm and the integrity algorithm that are selected by the SGSN) to perform ciphering on the communication message. Therefore, after selecting a ciphering algorithm and an integrity algorithm, the SGSN needs to send the selected ciphering algorithm and the selected integrity algorithm to the UE, so that after computing the second ciphering key and the second integrity key according to the first ciphering key CK and the first integrity key IK, the UE performs ciphering on the communication message by using a ciphering algorithm and an integrity algorithm that are the same as those used by the SGSN, the second ciphering key, and the second integrity key. 
     S 104 . The SGSN obtains a second ciphering key and a second integrity key according to the first ciphering key and the first integrity key. 
     In this embodiment of this application, after selecting the ciphering algorithm and the integrity algorithm, the SGSN may obtain the second ciphering key and the second integrity key according to the first ciphering key and the first integrity key in the authentication vector. The second ciphering key and the second integrity key are enhanced keys on the basis of the first ciphering key and the first integrity key, where the second ciphering key and the ciphering algorithm selected by the SGSN may be used to perform ciphering protection on a message transmitted between the SGSN and the UE, and the second integrity key and the integrity algorithm selected by the SGSN may be used to perform integrity protection on a message transmitted between the SGSN and the UE. 
     Optionally, the SGSN may obtain the second ciphering key and the second integrity key only according to the first ciphering key and the first integrity key, or may obtain the second ciphering key and the second integrity key according to the first ciphering key, the first integrity key, the selected ciphering algorithm, and the selected integrity algorithm. 
     In specific implementation, there is no sequence between step S 103  of sending the ciphering algorithm and the integrity algorithm that are selected by the SGSN to the UE and step S 104  of computing, by the SGSN, the second ciphering key and the second integrity key according to the first ciphering key and the first integrity key in the authentication vector. 
     In this embodiment of this application, an SGSN receives a request message sent by UE, after determining that the UE is UE of a first type, selects a ciphering algorithm and an integrity algorithm, acquires an authentication vector from an HLR/HSS, obtains an enhanced second ciphering key and an enhanced second integrity key according to a first ciphering key and a first integrity key that are included in the authentication vector, and sends the selected ciphering algorithm and the selected integrity algorithm to the UE, so that after the UE computes the second ciphering key and the second integrity key, both the SGSN and the UE may perform ciphering protection and integrity protection on a communication message between the SGSN and the UE by using the second ciphering key, the second integrity key, and the ciphering algorithm and the integrity algorithm that are selected by the SGSN. This enhances security of communication of UE of the first type in a GPRS network. 
     Refer to  FIG. 2 .  FIG. 2  is a schematic flowchart of another embodiment of a GPRS system key enhancement method according to this application. As shown in  FIG. 2 , the method may include the following steps. 
     S 201 . An SGSN receives a request message sent by UE. 
     S 202 . The SGSN acquires an authentication vector from an HLR/HSS, where the authentication vector includes a first ciphering key and a first integrity key. 
     S 203 . If determining that the UE is UE of a first type, the SGSN selects a ciphering algorithm and an integrity algorithm for the UE. 
     S 204 . The SGSN sends the selected ciphering algorithm and the selected integrity algorithm to the UE. 
     In this embodiment of this application, for specific implementation manners of steps S 201  to S 204 , refer to steps S 101  to S 103  in the embodiment shown in  FIG. 1 . Details are not described herein. 
     S 205 . The SGSN computes an intermediate key according to the first ciphering key and the first integrity key. 
     In a feasible implementation manner, an operation may be performed on the first ciphering key and the first integrity key, and then an operation result is used as an input parameter of a key derivation function KDF to compute the intermediate key. For example, the intermediate key may be Km=KDF(CK∥IK), where CK∥IK indicates that a join operation is performed on the first ciphering key CK and the first integrity key IK. 
     In another feasible implementation manner, the intermediate key may directly use an existing 64-bit GPRS ciphering key Kc or an existing 128-bit ciphering key Kc 128 , that is, the existing GPRS ciphering key Kc (64-bit) may be directly used as the intermediate key, or the existing Kc 128  (128-bit) is directly used as the intermediate key. Both Kc and Kc 128  are generated by means of computation according to the CK and the IK. 
     S 206 . The SGSN computes a second ciphering key according to the intermediate key or according to the intermediate key and a ciphering characteristic string. 
     In a feasible implementation manner, the SGSN may use a first preset bit of the intermediate key as the second ciphering key. For example, if a GPRS system requires a 64-bit second ciphering key, the most significant 64 bits of the intermediate key may be directly used as the second ciphering key; if the GPRS system requires a 128-bit second ciphering key, the most significant 128 bits of the intermediate key may be directly used as the second ciphering key. In another optional implementation manner, a required quantity of bits may be randomly selected from the intermediate key as the second ciphering key, which is not limited in this application. 
     In another feasible implementation manner, the SGSN may compute the second ciphering key according to the intermediate key and the ciphering characteristic string ciphering. In specific implementation, the intermediate key and the ciphering characteristic string ciphering may be used as input parameters of a key derivation function KDF to compute the second ciphering key. For example, the second ciphering key may be obtained by means of computation by using K cipher =KDF(Km, “ciphering”), where “ciphering” is a ciphering characteristic string, and may be generated by means of coding. 
     In some feasible implementation manners, a GPRS system requires a 128-bit second ciphering key, and in this case, preset 128 bits (for example, the most significant 128 bits) may be intercepted from the computed intermediate key Km as one of input parameters of a key derivation function KDF, and an output of the KDF is used as the second ciphering key; or the computed intermediate key Km may be directly used as one of input parameters of a key derivation function KDF, and preset 128 bits (for example, the most significant 128 bits) are intercepted from an output of the KDF as the second ciphering key; or the intermediate key Kc 128  is used as one of input parameters of a key derivation function KDF, and an output of the key derivation function KDF is used as the second ciphering key. 
     In some feasible implementation manners, a GPRS system requires a 64-bit second ciphering key, and in this case, preset 64 bits (for example, the most significant 64 bits) may be intercepted from the computed intermediate key Km as one of input parameters of a key derivation function KDF, and an output of the KDF is used as the second ciphering key; or the computed intermediate key Km may be directly used as one of input parameters of a key derivation function KDF, and preset 64 bits (for example, the most significant 64 bits) are intercepted from an output of the KDF as the second ciphering key; or the intermediate key Kc (64-bit) may be used as one of input parameters of a key derivation function KDF, and an output of the key derivation function KDF is used as the second ciphering key. 
     S 207 . The SGSN computes a second integrity key according to the intermediate key or according to the intermediate key and an integrity characteristic string. 
     In a feasible implementation manner, the SGSN may use a second preset bit of the intermediate key as the second integrity key. For example, if a GPRS system requires a 64-bit second integrity key, the least significant 64 bits of the intermediate key may be directly used as the second integrity key; if the GPRS system requires a 128-bit second integrity key, the least significant 128 bits of the intermediate key may be directly used as the second integrity key. In another optional implementation manner, a required quantity of bits may be randomly selected from the intermediate key as the second integrity key, which is not limited in this application. 
     In another feasible implementation manner, the SGSN may compute the second integrity key according to the intermediate key and the integrity characteristic string integrity. In specific implementation, the intermediate key and the integrity characteristic string integrity may be used as input parameters of a key derivation function KDF to compute the second integrity key. For example, the second integrity key may be obtained by means of computation by using K integrity =KDF(Km, “integrity”), where “integrity” is an integrity characteristic string, and may be generated by means of coding. 
     In some feasible implementation manners, a GPRS system requires a 128-bit second integrity key, and in this case, preset 128 bits (for example, the most significant 128 bits) may be intercepted from the computed intermediate key Km as one of input parameters of a key derivation function KDF, and an output of the KDF is used as the second integrity key; or the computed intermediate key Km may be directly used as one of input parameters of a key derivation function KDF, and preset 128 bits (for example, the most significant 128 bits) are intercepted from an output of the KDF as the second integrity key; or the intermediate key Kc 128  may be used as one of input parameters of a key derivation function KDF, and an output of the key derivation function KDF is used as the second integrity key. 
     In some feasible implementation manners, a GPRS system requires a 64-bit second integrity key, and in this case, preset 64 bits (for example, the most significant 64 bits) may be intercepted from the computed intermediate key Km as one of input parameters of a key derivation function KDF, and an output of the KDF is used as the second integrity key; or the computed intermediate key Km may be directly used as one of input parameters of a key derivation function KDF, and preset 64 bits (for example, the most significant 64 bits) are intercepted from an output of the KDF as the second integrity key; or the intermediate key Kc (64-bit) may be used as one of input parameters of a key derivation function KDF, and an output of the key derivation function KDF is used as the second integrity key. 
     In this embodiment of this application, the ciphering characteristic string ciphering and the integrity characteristic string integrity are used to make the computed second ciphering key and the computed second integrity key different for easy distinction. Therefore, the integrity characteristic string integrity may be any string inconsistent with the ciphering characteristic string ciphering. 
     In specific implementation, there is no sequence among step S 204  of sending the ciphering algorithm and the integrity algorithm that are selected by the SGSN to the UE, step S 205  of computing the intermediate key, step S 206  of computing the second ciphering key, and step S 207  of computing the second integrity key. 
     In this embodiment of this application, an SGSN receives a request message sent by UE, after determining that the UE is UE of a first type, selects a ciphering algorithm and an integrity algorithm, acquires an authentication vector from an HLR/HSS, obtains an enhanced second ciphering key and an enhanced second integrity key according to a first ciphering key and a first integrity key that are included in the authentication vector, and sends the selected ciphering algorithm and the selected integrity algorithm to the UE, so that after the UE computes the second ciphering key and the second integrity key, both the SGSN and the UE may perform ciphering protection and integrity protection on a communication message between the SGSN and the UE by using the second ciphering key, the second integrity key, and the ciphering algorithm and the integrity algorithm that are selected by the SGSN. This enhances security of communication of UE of the first type in a GPRS network. 
     Refer to  FIG. 3 .  FIG. 3  is a schematic flowchart of still another embodiment of a GPRS system key enhancement method according to this application. As shown in  FIG. 3 , the method may include the following steps. 
     S 301 . An SGSN receives a request message sent by UE. 
     S 302 . The SGSN acquires an authentication vector from an HLR/HSS, where the authentication vector includes a first ciphering key and a first integrity key. 
     S 303 . If determining that the UE is UE of a first type, the SGSN selects a ciphering algorithm and an integrity algorithm for the UE. 
     S 304 . The SGSN sends the selected ciphering algorithm and the selected integrity algorithm to the UE. 
     S 305 . The SGSN computes an intermediate key according to the first ciphering key and the first integrity key. 
     In this embodiment of this application, for specific implementation manners of steps S 301  to S 305 , refer to steps S 201  to S 205  in the embodiment shown in  FIG. 2 . Details are not described herein. 
     S 306 . The SGSN computes a second ciphering key according to the intermediate key, a first algorithm type indication, and an identifier of the selected ciphering algorithm. 
     In specific implementation, the intermediate key, the first algorithm type indication, and the identifier of the selected ciphering algorithm may be used as input parameters of a key derivation function KDF to compute the second ciphering key. For example, the second ciphering key K cipher  may be obtained by means of computation by using K cipher =KDF(Km, algorithm type distinguisher 1 , ciphering algorithm id), where Km is the intermediate key, algorithm type distinguisher 1  is the first algorithm type indication, and ciphering algorithm id is the identifier of the ciphering algorithm selected by the SGSN. 
     In some feasible implementation manners, a GPRS system requires a 128-bit second ciphering key, and in this case, preset 128 bits (for example, the most significant 128 bits) may be intercepted from the computed intermediate key Km as one of input parameters of a key derivation function KDF, and an output of the KDF is used as the second ciphering key; or the computed intermediate key Km may be directly used as one of input parameters of a key derivation function KDF, and preset 128 bits (for example, the most significant 128 bits) are intercepted from an output of the KDF as the second ciphering key; or the intermediate key Kc 128  is used as one of input parameters of a key derivation function KDF, and an output of the key derivation function KDF is used as the second ciphering key. 
     In some feasible implementation manners, a GPRS system requires a 64-bit second ciphering key, and in this case, preset 64 bits (for example, the most significant 64 bits) may be intercepted from the computed intermediate key Km as one of input parameters of a key derivation function KDF, and an output of the KDF is used as the second ciphering key; or the computed intermediate key Km may be directly used as one of input parameters of a key derivation function KDF, and preset 64 bits (for example, the most significant 64 bits) are intercepted from an output of the KDF as the second ciphering key; or the intermediate key Kc (64-bit) may be used as one of input parameters of a key derivation function KDF, and an output of the key derivation function KDF is used as the second ciphering key. 
     S 307 . The SGSN computes a second integrity key according to the intermediate key, a second algorithm type indication, and an identifier of the selected integrity algorithm. 
     In specific implementation, the intermediate key, the second algorithm type indication, and the identifier of the selected integrity algorithm may be used as input parameters of a key derivation function KDF to compute the second integrity key. For example, the second integrity key K integrity  may be obtained by means of computation by using K integrity =KDF(Km, algorithm type distinguisher 2 , integrity algorithm id), where Km is the intermediate key, algorithm type distinguisher 2  is the second algorithm type indication, and integrity algorithm id is the identifier of the integrity algorithm selected by the SGSN. 
     In some feasible implementation manners, a GPRS system requires a 128-bit second integrity key, and in this case, preset 128 bits (for example, the most significant 128 bits) may be intercepted from the computed intermediate key Km as one of input parameters of a key derivation function KDF, and an output of the KDF is used as the second integrity key; or the computed intermediate key Km may be directly used as one of input parameters of a key derivation function KDF, and preset 128 bits (for example, the most significant 128 bits) are intercepted from an output of the KDF as the second integrity key; or the intermediate key Kc 128  may be used as one of input parameters of a key derivation function KDF, and an output of the key derivation function KDF is used as the second integrity key. 
     In some feasible implementation manners, a GPRS system requires a 64-bit second integrity key, and in this case, preset 64 bits (for example, the most significant 64 bits) may be intercepted from the computed intermediate key Km as one of input parameters of a key derivation function KDF, and an output of the KDF is used as the second integrity key; or the computed intermediate key Km may be directly used as one of input parameters of a key derivation function KDF, and preset 64 bits (for example, the most significant 64 bits) are intercepted from an output of the KDF as the second integrity key; or the intermediate key Kc (64-bit) may be used as one of input parameters of a key derivation function KDF, and an output of the key derivation function KDF is used as the second integrity key. 
     In this embodiment of this application, the first algorithm type indication is used to indicate that an algorithm currently participating in an operation is an algorithm of a ciphering type, and the second algorithm type indication is used to indicate that an algorithm currently participating in an operation is an algorithm of an integrity type. Values of the first algorithm type indication and the second algorithm type indication are different. In some feasible embodiments, the first algorithm type indication and the second algorithm type indication may include a same IE, and the first algorithm type indication and the second algorithm type indication are distinguished by using different values of the IE. For example, the IEs of the first algorithm type indication and the second algorithm type indication are both algorithm type distinguisher. When algorithm type distinguisher=00, it indicates an algorithm of a ciphering type. When algorithm type distinguisher=01, it indicates an algorithm of an integrity type. 
     In some possible cases, the ciphering algorithm and the integrity algorithm may use a same identifier, and in these cases, each algorithm needs to be uniquely distinguished with reference to an algorithm type indication. For example, if both a 128-EEM algorithm and 128-EIA1 algorithm use 1 as an algorithm identifier, when the ciphering algorithm and the integrity algorithm that are selected by the SGSN are the 128-EEM algorithm and the 128-EIAs algorithm respectively, the 128-EEM algorithm and the 128-EIA1 algorithm may be distinguished by using different values of IEs in the first algorithm type indication and the second algorithm type indication. In addition, values of the computed second ciphering key and the computed second integrity key may be made different, so as to distinguish between the second ciphering key and the second integrity key. 
     In specific implementation, there is no sequence among step S 304  of sending the ciphering algorithm and the integrity algorithm that are selected by the SGSN to the UE, step S 305  of computing the intermediate key, step S 306  of computing the second ciphering key, and step S 307  of computing the second integrity key. 
     In this embodiment of this application, an SGSN receives a request message sent by UE, after determining that the UE is UE of a first type, selects a ciphering algorithm and an integrity algorithm, acquires an authentication vector from an HLR/HSS, obtains an enhanced second ciphering key and an enhanced second integrity key according to a first ciphering key and a first integrity key that are included in the authentication vector, and sends the selected ciphering algorithm and the selected integrity algorithm to the UE, so that the UE computes the second ciphering key and the second integrity key, and performs ciphering protection and integrity protection on a communication message between the SGSN and the UE by using the second ciphering key and the second integrity key. This enhances security of communication of UE of the first type in a GPRS network. 
     Refer to  FIG. 4 .  FIG. 4  is a schematic flowchart of still another embodiment of a GPRS system key enhancement method according to this application. As shown in  FIG. 4 , the method may include the following steps. 
     S 401 . An SGSN receives a request message sent by UE. 
     S 402 . The SGSN acquires an authentication vector from an HLR/HSS, where the authentication vector includes a first ciphering key and a first integrity key. 
     In this embodiment of this application, for specific implementation manners of steps S 401  and S 402 , refer to steps S 101  and S 102  in the embodiment shown in  FIG. 1 . Details are not described herein. 
     S 403 . The SGSN determines that the UE is UE of a first type. 
     In some feasible implementation manners, the SGSN may send an identifier of the UE to the HLR/HSS. The HLR/HSS determines, according to the identifier of the UE, whether the UE is UE of the first type. If receiving UE type indication information sent by the HLR/HSS, the SGSN may determine, according to the UE type indication information, that the UE is UE of the first type. 
     In some other feasible implementation manners, if the request message that is sent by the UE to the SGSN carries the UE type indication information, the SGSN may determine that the UE is UE of the first type. 
     Optionally, the SGSN may determine, according to existence or non-existence of a specific information element (IE) in the UE type indication information, whether the UE is UE of the first type. For example, when the UE type indication information includes the foregoing specific IE, the SGSN may determine that the UE is UE of the first type; when the UE type indication information does not include the foregoing specific IE, the SGSN may determine that the UE is not UE of the first type. Alternatively, the SGSN may determine, by using data content of an IE in the UE type indication information, whether the UE is UE of the first type. For example, when the data content of the foregoing IE is 1, the SGSN may determine that the UE is UE of the first type; when the data content of the foregoing IE is 0, the SGSN may determine that the UE is not UE of the first type. 
     In specific implementation, the SGSN may first acquire the authentication vector from the HLR/HSS, and then determine that the UE is UE of the first type, or may first determine that the UE is UE of the first type, and then acquire the authentication vector from the HLR/HSS. 
     S 404 . The SGSN selects a ciphering algorithm and an integrity algorithm for the UE. 
     In specific implementation, the UE and the SGSN are separately configured with some ciphering algorithms and integrity algorithms. When sending the request message to the SGSN, the UE sends a ciphering algorithm and an integrity algorithm that are supported by the UE to the SGSN. When receiving the request message of the UE, the SGSN selects a ciphering algorithm supported by the SGSN and an integrity algorithm supported by the SGSN from the ciphering algorithm and the integrity algorithm that are supported by the UE. 
     In this embodiment of this application, the ciphering algorithm and the integrity algorithm that are selected by the SGSN may be used along with the first ciphering key and the first integrity key in the authentication vector to compute a second ciphering key and a second integrity key. In addition, ciphering may be performed on a communication message according to the ciphering algorithm selected by the SGSN and the generated second ciphering key to generate a message ciphertext. A message authentication code MAC may be obtained by means of computation according to the integrity algorithm selected by the SGSN and the generated second integrity key. The message authentication code MAC may be used to verify integrity of the communication message. 
     Optionally, when a GPRS network requires a 128-bit second ciphering key, the ciphering algorithm selected by the SGSN may be any one of a 128-EEM algorithm, a 128-EEA2 algorithm, or a 128-EEA3 algorithm, and the integrity algorithm selected by the SGSN may be any one of a 128-EIA1 algorithm, a 128-EIA2 algorithm, or a 128-EIA3 algorithm. A SNOW  3 G algorithm is used as a core algorithm of the 128-EEM algorithm and the 128-EIA1 algorithm. An AES algorithm is used as a core algorithm of the 128-EEA2 algorithm and the 128-EIA2 algorithm. A ZUC algorithm is used as a core algorithm of the 128-EEA3 algorithm and the 128-EIA3 algorithm. 
     S 405 . The SGSN computes a second ciphering key according to the first ciphering key, a first algorithm type indication, and an identifier of the selected ciphering algorithm. 
     Specifically, the SGSN may use the first ciphering key, the first algorithm type indication, and the identifier of the selected ciphering algorithm as input parameters of a key derivation function KDF to compute the second ciphering key. For example, K cipher =KDF(CK, algorithm type distinguisher 1 , ciphering algorithm id), where CK is the first ciphering key, algorithm type distinguisher 1  is the first algorithm type indication, and ciphering algorithm id is the identifier of the ciphering algorithm selected by the SGSN. 
     Optionally, if a GPRS system requires a 64-bit second ciphering key, the most significant 64 bits may be selected from computed K cipher  as the second ciphering key; if the GPRS system requires a 128-bit second ciphering key, the most significant 128 bits may be selected from computed K cipher  as the second ciphering key. In another feasible implementation manner, a required quantity of bits may be randomly selected from computed K cipher  as the second ciphering key, which is not limited in this application. 
     S 406 . The SGSN computes a second integrity key according to the first integrity key, a second algorithm type indication, and an identifier of the selected integrity algorithm. 
     Specifically, the SGSN may use the first integrity key IK, the second algorithm type indication algorithm type distinguisher 2 , and the identifier of the selected integrity algorithm integrity algorithm id as input parameters of a key derivation function KDF to compute the second integrity key. For example, K integrity =KDF(IK, algorithm type distinguisher 2 , integrity algorithm id), where IK is the first integrity key, algorithm type distinguisher 2  is the second algorithm type indication, and integrity algorithm id is the identifier of the integrity algorithm selected by the SGSN. 
     Optionally, if a GPRS system requires a 64-bit second integrity key, the most significant 64 bits may be selected from computed K integrity  as the second integrity key; if the GPRS system requires a 128-bit second integrity key, the most significant 128 bits may be selected from computed K integrity  as the second integrity key. In another feasible implementation manner, a required quantity of bits may be randomly selected from computed K integrity  as the second integrity key, which is not limited in this application. 
     In this embodiment of this application, the first algorithm type indication is used to indicate that an algorithm currently participating in an operation is an algorithm of a ciphering type, and the second algorithm type indication is used to indicate that an algorithm currently participating in an operation is an algorithm of an integrity type. Values of the first algorithm type indication and the second algorithm type indication are different. In some feasible embodiments, the first algorithm type indication and the second algorithm type indication may include a same IE, and the first algorithm type indication and the second algorithm type indication are distinguished by using different values of the IE. For example, the IEs of the first algorithm type indication and the second algorithm type indication are both algorithm type distinguisher. When algorithm type distinguisher=00, it indicates an algorithm of a ciphering type. When algorithm type distinguisher=01, it indicates an algorithm of an integrity type. 
     In some possible cases, the ciphering algorithm and the integrity algorithm may use a same identifier, and in these cases, each algorithm needs to be uniquely distinguished with reference to an algorithm type indication. For example, if both a 128-EEM algorithm and 128-EIA1 algorithm use 1 as an algorithm identifier, when the ciphering algorithm and the integrity algorithm that are selected by the SGSN are the 128-EEM algorithm and the 128-EIA1 algorithm respectively, the 128-EEM algorithm and the 128-EIA1 algorithm may be distinguished by using different values of the first algorithm type indication and the second algorithm type indication. In addition, values of the computed second ciphering key and the computed second integrity key may be made different, so as to distinguish between the second ciphering key and the second integrity key. 
     S 407 . The SGSN sends the selected ciphering algorithm and the selected integrity algorithm to the UE. 
     In specific implementation, when sending the selected ciphering algorithm and the selected integrity algorithm to the UE, the SGSN may further send a random number RAND and an authentication token AUTN in the authentication vector to the UE. The UE may perform authentication on the SGSN side according to the authentication token AUTN, that is, the UE side performs authentication on a network side, and may further compute the first ciphering key CK and the first integrity key IK by using f1 to f5 algorithms according to the received random number RAND and the received authentication token AUTN. 
     In specific implementation, there is no sequence among step S 407  of sending the ciphering algorithm and the integrity algorithm that are selected by the SGSN to the UE, step S 405  of computing the second ciphering key, and step S 406  of computing the second integrity key. 
     To protect a communication message between the SGSN and the UE, both the SGSN and the UE need to use an agreed key (that is, the second ciphering key and the second integrity key) and an agreed algorithm (that is, the ciphering algorithm and the integrity algorithm that are selected by the SGSN) to perform ciphering on the communication message. Therefore, after selecting a ciphering algorithm and an integrity algorithm, the SGSN needs to send the selected ciphering algorithm and the selected integrity algorithm to the UE, so that after computing the second ciphering key and the second integrity key according to the first ciphering key CK and the first integrity key IK, the UE performs ciphering on the communication message by using a ciphering algorithm and an integrity algorithm that are the same as those used by the SGSN, the second ciphering key, and the second integrity key. 
     In this embodiment of this application, an SGSN receives a request message sent by UE, after determining that the UE is UE of a first type, selects a ciphering algorithm and an integrity algorithm, acquires an authentication vector from an HLR/HSS, obtains an enhanced second ciphering key and an enhanced second integrity key according to a first ciphering key and a first integrity key that are included in the authentication vector, and sends the selected ciphering algorithm and the selected integrity algorithm to the UE, so that the UE computes the second ciphering key and the second integrity key, and performs ciphering protection and integrity protection on a communication message between the SGSN and the UE by using the second ciphering key and the second integrity key. This enhances security of communication of UE of the first type in a GPRS network. 
     Refer to  FIG. 5 .  FIG. 5  is a schematic flowchart of still another embodiment of a GPRS system key enhancement method according to this application. As shown in  FIG. 5 , the method may include the following steps. 
     S 501 . An SGSN receives a request message sent by UE. 
     S 502 . The SGSN acquires an authentication vector from an HLR/HSS, where the authentication vector includes a first ciphering key and a first integrity key. 
     In this embodiment of this application, for specific implementation manners of steps S 501  and S 502 , refer to steps S 101  and S 102  in the embodiment shown in  FIG. 1 . Details are not described herein. 
     S 503 . The SGSN determines that the UE is UE of a first type. 
     S 504 . The SGSN selects a ciphering algorithm and an integrity algorithm for the UE. 
     In this embodiment of this application, for specific implementation manners of steps S 503  and S 504 , refer to steps S 303  and S 304  in the embodiment shown in  FIG. 3 . Details are not described herein. 
     S 505 . The SGSN uses the first ciphering key or a preset bit of the first ciphering key as a second ciphering key. 
     In some feasible implementation manners, if the first ciphering key is a 128-bit key, and the second ciphering key required by a GPRS system is also a 128-bit key, the first ciphering key may be directly used as the second ciphering key. If the second ciphering key required by the GPRS system is a 64-bit key, 64 preset bits may be selected from the first ciphering key as the second ciphering key. For example, the most significant 64 bits are selected as the second ciphering key. 
     S 506 . The SGSN uses the first integrity key or a preset bit of the first integrity key as a second integrity key. 
     In some feasible implementation manners, if the first integrity key is a 128-bit key, and the second integrity key required by a GPRS system is also a 128-bit key, the first integrity key may be directly used as the second integrity key. If the second integrity key required by the GPRS system is a 64-bit key, 64 preset bits may be selected from the first integrity key as the second integrity key. For example, the most significant 64 bits are selected as the second integrity key. 
     In this embodiment of this application, ciphering may be performed on a communication message according to the second ciphering key and the ciphering algorithm selected by the SGSN to generate a message ciphertext. A message authentication code MAC may be obtained by means of computation according to the second integrity key and the integrity algorithm selected by the SGSN. The message authentication code MAC may be used to verify integrity of the communication message. 
     S 507 . The SGSN sends the selected ciphering algorithm and the selected integrity algorithm to the UE. 
     In specific implementation, when sending the selected ciphering algorithm and the selected integrity algorithm to the UE, the SGSN may further send a random number RAND and an authentication token AUTN in the authentication vector to the UE. The UE may perform authentication on the SGSN side according to the authentication token AUTN, that is, the UE side performs authentication on a network side, and may further compute the first ciphering key CK and the first integrity key IK by using f1 to f5 algorithms according to the received random number RAND and the received authentication token AUTN. 
     In specific implementation, there is no sequence among step S 507  of sending the ciphering algorithm and the integrity algorithm that are selected by the SGSN to the UE, step S 505 , and step  506 . 
     To protect a communication message between the SGSN and the UE, both the SGSN and the UE need to use an agreed key (that is, the second ciphering key and the second integrity key) and an agreed algorithm (that is, the ciphering algorithm and the integrity algorithm that are selected by the SGSN) to perform ciphering on the communication message. Therefore, after selecting a ciphering algorithm and an integrity algorithm, the SGSN needs to send the selected ciphering algorithm and the selected integrity algorithm to the UE, so that after computing the second ciphering key and the second integrity key according to the first ciphering key CK and the first integrity key IK, the UE performs ciphering on the communication message by using a ciphering algorithm and an integrity algorithm that are the same as those used by the SGSN, the second ciphering key, and the second integrity key. 
     In this embodiment of this application, an SGSN receives a request message sent by UE, after determining that the UE is UE of a first type, selects a ciphering algorithm and an integrity algorithm, acquires an authentication vector from an HLR/HSS, obtains an enhanced second ciphering key and an enhanced second integrity key according to a first ciphering key and a first integrity key that are included in the authentication vector, and sends the selected ciphering algorithm and the selected integrity algorithm to the UE, so that after the UE computes the second ciphering key and the second integrity key, both the SGSN and the UE may perform ciphering protection and integrity protection on a communication message between the SGSN and the UE by using the second ciphering key, the second integrity key, and the ciphering algorithm and the integrity algorithm that are selected by the SGSN. This enhances security of communication of UE of the first type in a GPRS network. 
     Refer to  FIG. 6 .  FIG. 6  is a schematic flowchart of still another embodiment of a GPRS system key enhancement method according to this application. As shown in  FIG. 6 , the method may include the following steps. 
     S 601 . UE sends a request message to an SGSN. 
     In specific implementation, the request message that is sent by the UE to the SGSN may be an attach request message, a route update message, or another message, for example, a service request message. After receiving the request message sent by the UE, the SGSN may acquire an identifier of the UE that sends the request message. If the UE is UE of a first type, the request message may carry UE type indication information. 
     In this embodiment of this application, the UE communicates with a network by using a USIM card, and the identifier of the UE may be an IMSI (International Mobile Subscriber Identification Number) of the USIM card. UE of the first type may include Internet of Things UE, machine to machine (M2M) communication UE, or other high-security UE. The Internet of Things UE refers to user equipment that has an information sensing function and a data transmission function, for example, an audio guide, a personal digital assistant, a barcode collector, a data collection terminal, and a POS terminal that is mainly used for purchase or transfer. The machine to machine communication UE refers to user equipment that has a networking and communication capability and that implements an “intelligence” attribute by using a sensor, a controller, and the like, so as to exchange information with a person, a mobile network, or another machine. 
     In this embodiment of this application, an example in which the UE is UE of the first type is used for description. In some feasible implementation manners, the request message that is sent by the UE to the SGSN may include the UE type indication information, so that the SGSN determines, according to the UE type indication information, that the UE is UE of the first type. 
     Optionally, the UE type indication information may indicate, according to existence of a specific information element (IE), that the UE is UE of the first type. For example, when the SGSN receives the UE type indication information sent by the HLR/HSS or the UE, if a specific IE exists in the UE type indication information, the SGSN may determine that the UE is UE of the first type, and if the specific IE does not exist in the UE type indication information, the SGSN may determine that the UE is not UE of the first type. Alternatively, the UE type indication information may also indicate, according to a value of a specific IE, that the UE is UE of the first type. For example, when the SGSN receives the UE type indication information sent by the HLR/HSS or the UE, if a value of a specific IE in the UE type indication information is 1, the SGSN may determine that the UE is UE of the first type, and if the value of the specific IE is 0, the SGSN may determine that the UE is not UE of the first type. 
     In specific implementation, the UE and the SGSN are separately configured with some ciphering algorithms and integrity algorithms. When sending the request message to the SGSN, the UE sends a ciphering algorithm and an integrity algorithm that are supported by the UE to the SGSN. 
     S 602 . The UE receives a ciphering algorithm and an integrity algorithm that are sent by the SGSN. 
     After the SGSN receives the request message of the UE, if it is determined that the foregoing UE is UE of the first type, the SGSN selects a ciphering algorithm supported by the SGSN and an integrity algorithm supported by the SGSN from the ciphering algorithm and the integrity algorithm that are supported by the UE. The SGSN sends the selected ciphering algorithm and the selected integrity algorithm to the UE, and obtains a second ciphering key and a second integrity key according to a first ciphering key and a first integrity key in an authentication vector. 
     In specific implementation, when sending the selected ciphering algorithm and the selected integrity algorithm to the UE, the SGSN may further send a random number RAND and an authentication token AUTN in the authentication vector to the UE. The UE may perform authentication on the SGSN side according to the authentication token AUTN, so that the UE side performs authentication on a network side. The UE may further compute the first ciphering key and the first integrity key by using f1 to f5 algorithms according to the received random number RAND and the received authentication token AUTN. The first ciphering key and the first integrity key that are computed by the UE are the same as the first ciphering key and the first integrity key in the authentication vector that is acquired by the SGSN from the HLR/HSS. The authentication vector acquired by the SGSN from the HLR/HSS is an authentication vector quintet, which includes a random number RAND, an expected response XRES, an authentication token AUTN, a ciphering key CK, and an integrity key IK. 
     In this embodiment of this application, the first ciphering key is the ciphering key CK in the authentication vector quintet, and the first integrity key is the integrity key IK in the authentication vector quintet. 
     In some feasible implementation manners, the ciphering algorithm and the integrity algorithm that are selected by the SGSN may be used along with the first ciphering key CK and the first integrity key IK to compute the second ciphering key and the second integrity key. In addition, ciphering may be performed on a communication message according to the ciphering algorithm and the generated second ciphering key to generate a message ciphertext. A message authentication code MAC may be obtained by means of computation according to the integrity algorithm and the generated second integrity key. The message authentication code MAC may be used to verify integrity of the communication message. 
     Optionally, when a GPRS network requires a 128-bit second ciphering key, the ciphering algorithm selected by the SGSN may be any one of a 128-EEM algorithm, a 128-EEA2 algorithm, or a 128-EEA3 algorithm, and the integrity algorithm selected by the SGSN may be any one of a 128-EIA1 algorithm, a 128-EIA2 algorithm, or a 128-EIA3 algorithm. A SNOW  3 G algorithm is used as a core algorithm of the 128-EEM algorithm and the 128-EIA1 algorithm. An AES algorithm is used as a core algorithm of the 128-EEA2 algorithm and the 128-EIA2 algorithm. A ZUC algorithm is used as a core algorithm of the 128-EEA3 algorithm and the 128-EIA3 algorithm. 
     S 603 . The UE acquires a second ciphering key and a second integrity key according to a first ciphering key and a first integrity key. 
     In this embodiment of this application, the second ciphering key and the second integrity key are enhanced keys on the basis of the first ciphering key and the first integrity key. The second ciphering key and the ciphering algorithm sent by the SGSN are used to perform ciphering protection on a message transmitted between the SGSN and the UE, and the second integrity key and the integrity algorithm sent by the SGSN are used to perform integrity protection on a message transmitted between the SGSN and the UE. 
     Optionally, the UE may acquire the second ciphering key and the second integrity key only according to the first ciphering key and the first integrity key, or may acquire the second ciphering key and the second integrity key according to the first ciphering key, the first integrity key, and the ciphering algorithm and the integrity algorithm that are sent by the SGSN. 
     After the second ciphering key and the second integrity key are acquired, to protect a communication message between the SGSN and the UE, both the SGSN and the UE need to use an agreed key (that is, the second ciphering key and the second integrity key) and an agreed algorithm (that is, the ciphering algorithm and the integrity algorithm that are sent by the SGSN) to perform ciphering on the communication message. 
     In this embodiment of this application, UE sends a request message to an SGSN, receives a ciphering algorithm and an integrity algorithm that are sent by the SGSN, and computes a second ciphering key and a second integrity key according to a first ciphering key and a first integrity key. Both the SGSN and the UE may perform ciphering protection and integrity protection on a communication message between the UE and the SGSN by using the second ciphering key, the second integrity key, and the ciphering algorithm and the integrity algorithm that are sent by the SGSN to the UE. This enhances security of communication of UE of a first type in a GPRS network. 
     Refer to  FIG. 7 .  FIG. 7  is a schematic flowchart of still another embodiment of a GPRS system key enhancement method according to this application. As shown in  FIG. 7 , the method may include the following steps. 
     S 701 . UE sends a request message to an SGSN. 
     S 702 . The UE receives a ciphering algorithm and an integrity algorithm that are sent by the SGSN. 
     In this embodiment of this application, for specific implementation manners of steps S 701  and S 702 , refer to steps S 601  and S 602  in the embodiment shown in  FIG. 6 . Details are not described herein. 
     S 703 . The UE computes an intermediate key according to a first ciphering key and a first integrity key. 
     When receiving the ciphering algorithm and the integrity algorithm that are sent by the SGSN, the UE further receives a random number RAND and an authentication token AUTN that are sent by the SGSN. Before computing the intermediate key, an expected message authentication code XMAC may be first computed according to the authentication token AUTN and the random number RAND, and authentication is performed on the SGSN side by determining whether the expected message authentication code XMAC is the same as a message authentication code MAC in the authentication token AUTN. After authentication on the SGSN side succeeds, the UE computes the first ciphering key CK and the first integrity key IK according to the random number RAND and the authentication token AUTN that are sent by the SGSN, computes a random number response RES, and sends the random number response RES to the SGSN, so that the SGSN side performs authentication on the UE. 
     In a feasible implementation manner, the UE may perform an operation on the first ciphering key and the first integrity key, and use an operation result as an input parameter of a key derivation function KDF to compute the intermediate key. For example, the intermediate key may be Km=KDF(CK∥IK), where CK∥IK indicates that a join operation is performed on the first ciphering key CK and the first integrity key IK. 
     In another feasible implementation manner, the intermediate key may directly use an existing 64-bit GPRS ciphering key Kc or an existing 128-bit ciphering key Kc 128 , that is, the existing GPRS ciphering key Kc (64-bit) may be directly used as the intermediate key, or the existing Kc 128  (128-bit) is directly used as the intermediate key. Both Kc and Kc 128  are generated by means of computation according to the CK and the IK. 
     S 704 . The UE computes a second ciphering key according to the intermediate key or according to the intermediate key and a ciphering characteristic string. 
     In a feasible implementation manner, the UE may use a first preset bit of the intermediate key as the second ciphering key. For example, if a GPRS system requires a 64-bit second ciphering key, the most significant 64 bits of the intermediate key may be directly used as the second ciphering key; if the GPRS system requires a 128-bit second ciphering key, the most significant 128 bits of the intermediate key may be directly used as the second ciphering key. In another optional implementation manner, a required quantity of bits may be randomly selected from the intermediate key as the second ciphering key, which is not limited in this application. 
     In another feasible implementation manner, the UE may compute the second ciphering key according to the intermediate key and the ciphering characteristic string ciphering. In specific implementation, the intermediate key and the ciphering characteristic string ciphering may be used as input parameters of a key derivation function KDF to compute the second ciphering key. For example, the second ciphering key may be obtained by means of computation by using K cipher =KDF(Km, “ciphering”), where “ciphering” is a ciphering characteristic string, and may be generated by means of coding. 
     In some feasible implementation manners, a GPRS system requires a 128-bit second ciphering key, and in this case, preset 128 bits (for example, the most significant 128 bits) may be intercepted from the computed intermediate key Km as one of input parameters of a key derivation function KDF, and an output of the KDF is used as the second ciphering key; or the computed intermediate key Km may be directly used as one of input parameters of a key derivation function KDF, and preset 128 bits (for example, the most significant 128 bits) are intercepted from an output of the KDF as the second ciphering key; or the intermediate key Kc 128  may be used as one of input parameters of a key derivation function KDF, and an output of the key derivation function KDF is used as the second ciphering key. 
     In some feasible implementation manners, a GPRS system requires a 64-bit second ciphering key, and in this case, preset 64 bits (for example, the most significant 64 bits) may be intercepted from the computed intermediate key Km as one of input parameters of a key derivation function KDF, and an output of the KDF is used as the second ciphering key; or the computed intermediate key Km may be directly used as one of input parameters of a key derivation function KDF, and preset 64 bits (for example, the most significant 64 bits) are intercepted from an output of the KDF as the second ciphering key; or the intermediate key Kc (64-bit) may be used as one of input parameters of a key derivation function KDF, and an output of the key derivation function KDF is used as the second ciphering key. 
     S 705 . The UE computes a second integrity key according to the intermediate key or according to the intermediate key and an integrity characteristic string. 
     In a feasible implementation manner, the UE may use a second preset bit of the intermediate key as the second integrity key. For example, if a GPRS system requires a 64-bit second integrity key, the least significant 64 bits of the intermediate key may be directly used as the second integrity key; if the GPRS system requires a 128-bit second integrity key, the least significant 128 bits of the intermediate key may be directly used as the second integrity key. Optionally, a required quantity of bits may be randomly selected from the intermediate key as the second integrity key, which is not limited in this application. 
     In another optional implementation manner, the UE may compute the second integrity key according to the intermediate key and the integrity characteristic string integrity. In specific implementation, the intermediate key and the integrity characteristic string integrity may be used as input parameters of a key derivation function KDF to compute the second integrity key. For example, the second integrity key may be obtained by means of computation by using K integrity =KDF(Km, “integrity”), where “integrity” is an integrity characteristic string, and may be generated by means of coding. 
     In some feasible implementation manners, a GPRS system requires a 128-bit second integrity key, and in this case, preset 128 bits (for example, the most significant 128 bits) may be intercepted from the computed intermediate key Km as one of input parameters of a key derivation function KDF, and an output of the KDF is used as the second integrity key; or the computed intermediate key Km may be directly used as one of input parameters of a key derivation function KDF, and preset 128 bits (for example, the most significant 128 bits) are intercepted from an output of the KDF as the second integrity key; or the intermediate key Kc 128  may be used as one of input parameters of a key derivation function KDF, and an output of the key derivation function KDF is used as the second integrity key. 
     In some feasible implementation manners, a GPRS system requires a 64-bit second integrity key, and in this case, preset 64 bits (for example, the most significant 64 bits) may be intercepted from the computed intermediate key Km as one of input parameters of a key derivation function KDF, and an output of the KDF is used as the second integrity key; or the computed intermediate key Km may be directly used as one of input parameters of a key derivation function KDF, and preset 64 bits (for example, the most significant 64 bits) are intercepted from an output of the KDF as the second integrity key; or the intermediate key Kc (64-bit) may be used as one of input parameters of a key derivation function KDF, and an output of the key derivation function KDF is used as the second integrity key. 
     In this embodiment of this application, the ciphering characteristic string ciphering and the integrity characteristic string integrity are used to make the computed second ciphering key and the computed second integrity key different for easy distinction. Therefore, the integrity characteristic string integrity may be any string inconsistent with the ciphering characteristic string ciphering. 
     In this embodiment of this application, UE sends a request message to an SGSN, receives a ciphering algorithm and an integrity algorithm that are sent by the SGSN, and computes a second ciphering key and a second integrity key according to a first ciphering key and a first integrity key. Both the SGSN and the UE may perform ciphering protection and integrity protection on a communication message between the UE and the SGSN by using the second ciphering key, the second integrity key, and the ciphering algorithm and the integrity algorithm that are sent by the SGSN to the UE. This enhances security of communication of UE of a first type in a GPRS network. 
     Refer to  FIG. 8 .  FIG. 8  is a schematic flowchart of still another embodiment of a GPRS system key enhancement method according to this application. As shown in  FIG. 8 , the method may include the following steps. 
     S 801 . UE sends a request message to an SGSN. 
     S 802 . The UE receives a ciphering algorithm and an integrity algorithm that are sent by the SGSN. 
     S 803 . The UE computes an intermediate key according to a first ciphering key and a first integrity key. 
     In this embodiment of this application, for specific implementation manners of steps S 801  to S 803 , refer to steps S 701  to S 703  in the embodiment shown in  FIG. 7 . Details are not described herein. 
     S 804 . The UE computes a second ciphering key according to the intermediate key, a first algorithm type indication, and an identifier of the ciphering algorithm. 
     In specific implementation, the intermediate key, the first algorithm type indication, and the identifier of the ciphering algorithm may be used as input parameters of a key derivation function KDF to compute the second ciphering key. For example, the second ciphering key K cipher  may be obtained by means of computation by using K cipher =KDF(Km, algorithm type distinguisher 1 , ciphering algorithm id), where Km is the intermediate key, algorithm type distinguisher 1  is the first algorithm type indication, and ciphering algorithm id is the identifier of the ciphering algorithm selected by the SGSN. 
     In some feasible implementation manners, a GPRS system requires a 128-bit second ciphering key, and in this case, preset 128 bits (for example, the most significant 128 bits) may be intercepted from the computed intermediate key Km as one of input parameters of a key derivation function KDF, and an output of the KDF is used as the second ciphering key; or the computed intermediate key Km may be directly used as one of input parameters of a key derivation function KDF, and preset 128 bits (for example, the most significant 128 bits) are intercepted from an output of the KDF as the second ciphering key; or the intermediate key Kc 128  is used as one of input parameters of a key derivation function KDF, and an output of the key derivation function KDF is used as the second ciphering key. 
     In some feasible implementation manners, a GPRS system requires a 64-bit second ciphering key, and in this case, preset 64 bits (for example, the most significant 64 bits) may be intercepted from the computed intermediate key Km as one of input parameters of a key derivation function KDF, and an output of the KDF is used as the second ciphering key; or the computed intermediate key Km may be directly used as one of input parameters of a key derivation function KDF, and preset 64 bits (for example, the most significant 64 bits) are intercepted from an output of the KDF as the second ciphering key; or the intermediate key Kc (64-bit) may be used as one of input parameters of a key derivation function KDF, and an output of the key derivation function KDF is used as the second ciphering key. 
     S 805 . The UE computes a second integrity key according to the intermediate key, a second algorithm type indication, and an identifier of the integrity algorithm. 
     In specific implementation, the intermediate key, the second algorithm type indication, and the identifier of the integrity algorithm may be used as input parameters of a key derivation function KDF to compute the second integrity key. For example, the second integrity key K integrity  may be obtained by means of computation by using K integrity =KDF(Km, algorithm type distinguisher 2 , integrity algorithm id), where Km is the intermediate key, algorithm type distinguisher 2  is the second algorithm type indication, and integrity algorithm id is the identifier of the integrity algorithm selected by the SGSN. 
     In some feasible implementation manners, a GPRS system requires a 128-bit second integrity key, and in this case, preset 128 bits (for example, the most significant 128 bits) may be intercepted from the computed intermediate key Km as one of input parameters of a key derivation function KDF, and an output of the KDF is used as the second integrity key; or the computed intermediate key Km may be directly used as one of input parameters of a key derivation function KDF, and preset 128 bits (for example, the most significant 128 bits) are intercepted from an output of the KDF as the second integrity key; or the intermediate key Kc 128  may be used as one of input parameters of a key derivation function KDF, and an output of the key derivation function KDF is used as the second integrity key. 
     In some feasible implementation manners, a GPRS system requires a 64-bit second integrity key, and in this case, preset 64 bits (for example, the most significant 64 bits) may be intercepted from the computed intermediate key Km as one of input parameters of a key derivation function KDF, and an output of the KDF is used as the second integrity key; or the computed intermediate key Km may be directly used as one of input parameters of a key derivation function KDF, and preset 64 bits (for example, the most significant 64 bits) are intercepted from an output of the KDF as the second integrity key; or the intermediate key Kc (64-bit) may be used as one of input parameters of a key derivation function KDF, and an output of the key derivation function KDF is used as the second integrity key. 
     In this embodiment of this application, the first algorithm type indication is used to indicate that an algorithm currently participating in an operation is an algorithm of a ciphering type, and the second algorithm type indication is used to indicate that an algorithm currently participating in an operation is an algorithm of an integrity type. Values of the first algorithm type indication and the second algorithm type indication are different. In some feasible embodiments, the first algorithm type indication and the second algorithm type indication may include a same IE, and the first algorithm type indication and the second algorithm type indication are distinguished by using different values of the IE. For example, the IEs of the first algorithm type indication and the second algorithm type indication are both algorithm type distinguisher. When algorithm type distinguisher=00, it indicates an algorithm of a ciphering type. When algorithm type distinguisher=01, it indicates an algorithm of an integrity type. 
     In some possible cases, the ciphering algorithm and the integrity algorithm may use a same identifier, and in these cases, each algorithm needs to be uniquely distinguished with reference to an algorithm type indication. For example, if both a 128-EEM algorithm and 128-EIA1 algorithm use 1 as an algorithm identifier, when the ciphering algorithm and the integrity algorithm that are selected by the SGSN are the 128-EEM algorithm and the 128-EIA1 algorithm respectively, the 128-EEM algorithm and the 128-EIA1 algorithm may be distinguished by using different values of IEs in the first algorithm type indication and the second algorithm type indication. In addition, values of the computed second ciphering key and the computed second integrity key may be made different, so as to distinguish between the second ciphering key and the second integrity key. 
     In this embodiment of this application, UE sends a request message to an SGSN, receives a ciphering algorithm and an integrity algorithm that are sent by the SGSN, and acquires a second ciphering key and a second integrity key according to a first ciphering key and a first integrity key. Both the SGSN and the UE may perform ciphering protection and integrity protection on a communication message between the UE and the SGSN by using the second ciphering key, the second integrity key, and the ciphering algorithm and the integrity algorithm that are sent by the SGSN to the UE. This enhances security of communication of UE of a first type in a GPRS network. 
     Refer to  FIG. 9 .  FIG. 9  is a schematic flowchart of still another embodiment of a GPRS system key enhancement method according to this application. As shown in  FIG. 9 , the method may include the following steps. 
     S 901 . UE sends a request message to an SGSN. 
     S 902 . The UE receives a ciphering algorithm and an integrity algorithm that are sent by the SGSN. 
     In this embodiment of this application, for specific implementation manners of steps S 901  and S 902 , refer to steps S 601  and S 602  in the embodiment shown in  FIG. 6 . Details are not described herein. 
     S 903 . The UE computes a second ciphering key according to a first ciphering key, a first algorithm type indication, and an identifier of the ciphering algorithm. 
     When receiving the ciphering algorithm and the integrity algorithm that are sent by the SGSN, the UE further receives a random number RAND and an authentication token AUTN that are sent by the SGSN. Before computing the second ciphering key or a second integrity key, the UE may first compute an expected message authentication code XMAC according to the authentication token AUTN and the random number RAND, and perform authentication on the SGSN side by determining whether the expected message authentication code XMAC is the same as a message authentication code MAC in the authentication token AUTN. After authentication on the SGSN side succeeds, the UE computes the first ciphering key CK and a first integrity key IK according to the random number RAND and the authentication token AUTN that are sent by the SGSN, computes a random number response RES, and sends the random number response RES to the SGSN, so that the SGSN side performs authentication on the UE. 
     Specifically, the UE may use the first ciphering key, the first algorithm type indication, and the identifier of the selected ciphering algorithm as input parameters of a key derivation function KDF to compute the second ciphering key. For example, K cipher =KDF(CK, algorithm type distinguisher 1 , ciphering algorithm id), where CK is the first ciphering key, algorithm type distinguisher 1  is the first algorithm type indication, and ciphering algorithm id is the identifier of the ciphering algorithm selected by the SGSN. 
     Optionally, if a GPRS system requires a 64-bit second ciphering key, the most significant 64 bits may be selected from computed K cipher  as the second ciphering key; if the GPRS system requires a 128-bit second ciphering key, the most significant 128 bits may be selected from computed K cipher  as the second ciphering key. In another feasible implementation manner, a required quantity of bits may be randomly selected from computed K cipher  as the second ciphering key, which is not limited in this application. 
     S 904 . The UE computes a second integrity key according to a first integrity key, a second algorithm type indication, and an identifier of the integrity algorithm. 
     Specifically, the UE may use the first integrity key IK, the second algorithm type indication algorithm type distinguisher 2 , and the identifier of the selected integrity algorithm integrity algorithm id as input parameters of a key derivation function KDF to compute the second integrity key. For example, K integrity =KDF(IK, algorithm type distinguisher 2 , integrity algorithm id), where IK is the first integrity key, algorithm type distinguisher 2  is the second algorithm type indication, and integrity algorithm id is the identifier of the integrity algorithm selected by the SGSN. 
     Optionally, if a GPRS system requires a 64-bit second integrity key, the most significant 64 bits may be selected from computed K integrity  as the second integrity key; if the GPRS system requires a 128-bit second integrity key, the most significant 128 bits may be selected from computed K integrity  as the second integrity key. In another feasible implementation manner, a required quantity of bits may be randomly selected from computed K integrity  as the second integrity key, which is not limited in this application. 
     In this embodiment of this application, the first algorithm type indication is used to indicate that an algorithm currently participating in an operation is an algorithm of a ciphering type, and the second algorithm type indication is used to indicate that an algorithm currently participating in an operation is an algorithm of an integrity type. Values of the first algorithm type indication and the second algorithm type indication are different. In some feasible embodiments, the first algorithm type indication and the second algorithm type indication may include a same IE, and the first algorithm type indication and the second algorithm type indication are distinguished by using different values of the IE. For example, the IEs of the first algorithm type indication and the second algorithm type indication are both algorithm type distinguisher. When algorithm type distinguisher=00, it indicates an algorithm of a ciphering type. When algorithm type distinguisher=01, it indicates an algorithm of an integrity type. 
     In some possible cases, the ciphering algorithm and the integrity algorithm may use a same identifier, and in these cases, each algorithm needs to be uniquely distinguished with reference to an algorithm type indication. For example, if both a 128-EEM algorithm and 128-EIA1 algorithm use 1 as an algorithm identifier, when the ciphering algorithm and the integrity algorithm that are selected by the SGSN are the 128-EEM algorithm and the 128-EIA1 algorithm respectively, the 128-EEM algorithm and the 128-EIA1 algorithm may be distinguished by using different values of the first algorithm type indication and the second algorithm type indication. In addition, values of the computed second ciphering key and the computed second integrity key may be made different, so as to distinguish between the second ciphering key and the second integrity key. 
     In this embodiment of this application, UE sends a request message to an SGSN, receives a ciphering algorithm and an integrity algorithm that are sent by the SGSN, and computes a second ciphering key and a second integrity key according to a first ciphering key and a first integrity key. Both the SGSN and the UE may perform ciphering protection and integrity protection on a communication message between the UE and the SGSN by using the second ciphering key, the second integrity key, and the ciphering algorithm and the integrity algorithm that are sent by the SGSN to the UE. This enhances security of communication of UE of a first type in a GPRS network. 
     Refer to  FIG. 10 .  FIG. 10  is a schematic flowchart of still another embodiment of a GPRS system key enhancement method according to this application. As shown in  FIG. 10 , the method may include the following steps. 
     S 1001 . UE sends a request message to an SGSN. 
     S 1002 . The UE receives a ciphering algorithm and an integrity algorithm that are sent by the SGSN. 
     In this embodiment of this application, for specific implementation manners of steps S 1001  and S 1002 , refer to steps S 601  and S 602  in the embodiment shown in  FIG. 6 . Details are not described herein. 
     S 1003 . The UE uses a first ciphering key or a preset bit of a first ciphering key as a second ciphering key. 
     When receiving the ciphering algorithm and the integrity algorithm that are sent by the SGSN, the UE further receives a random number RAND and an authentication token AUTN that are sent by the SGSN. Before computing the second ciphering key or a second integrity key, the UE may first compute an expected message authentication code XMAC according to the authentication token AUTN and the random number RAND, and perform authentication on the SGSN side by determining whether the expected message authentication code XMAC is the same as a message authentication code MAC in the authentication token AUTN. After authentication on the SGSN side succeeds, the UE computes the first ciphering key CK and a first integrity key IK according to the random number RAND and the authentication token AUTN that are sent by the SGSN, computes a random number response RES, and sends the random number response RES to the SGSN, so that the SGSN side performs authentication on the UE. 
     In some feasible implementation manners, if the first ciphering key is a 128-bit key, and the second ciphering key required by a GPRS system is also a 128-bit key, the first ciphering key may be directly used as the second ciphering key. If the second ciphering key required by the GPRS system is a 64-bit key, 64 preset bits may be selected from the first ciphering key as the second ciphering key. For example, the most significant 64 bits are selected as the second ciphering key. 
     S 1004 . The UE uses a first integrity key or a preset bit of a first integrity key as a second integrity key. 
     In some feasible implementation manners, if the first integrity key is a 128-bit key, and the second integrity key required by a GPRS system is also a 128-bit key, the first integrity key may be directly used as the second integrity key. If the second integrity key required by the GPRS system is a 64-bit key, 64 preset bits may be selected from the first integrity key as the second integrity key. For example, the most significant 64 bits are selected as the second integrity key. 
     In this embodiment of this application, UE sends a request message to an SGSN, receives a ciphering algorithm and an integrity algorithm that are sent by the SGSN, and computes a second ciphering key and a second integrity key according to a first ciphering key and a first integrity key. Both the SGSN and the UE may perform ciphering protection and integrity protection on a communication message between the UE and the SGSN by using the second ciphering key, the second integrity key, and the ciphering algorithm and the integrity algorithm that are sent by the SGSN to the UE. This enhances security of communication of UE of a first type in a GPRS network. 
     Refer to  FIG. 11 .  FIG. 11  is a schematic flowchart of still another embodiment of a GPRS system key enhancement method according to this application. As shown in  FIG. 11 , the method may include the following steps. 
     S 1101 . An HLR/HSS receives an identifier of UE that is sent by an SGSN. 
     The home location register (HLR) is a permanent database of a GPRS system, and stores information required for managing communication of many mobile users, including static information such as identity information, service information, and service authorization that are of a registered mobile user, and dynamic information such as location information of a user. The home subscription system (HSS) is evolution and upgrade of the HLR, and is mainly responsible for managing subscription data of a user and location information of a mobile user. Because the HSS and the HLR have a similar function in a network, and much data stored in the HSS is repeatedly stored in the HLR, generally, an HSS and HLR convergence device is presented to the outside. In this embodiment of this application, the HLR/HSS may be an HLR device, an HSS device, or an HLR and HSS convergence device. 
     In this embodiment of this application, the UE communicates with a network by using a USIM card, and the identifier of the UE may be an IMSI (International Mobile Subscriber Identification Number) of the USIM card. 
     S 1102 . The HLR/HSS determines, according to the identifier of the UE, that the UE is UE of a first type. 
     In specific implementation, the HLR/HSS stores various information of many UEs. After receiving the identifier of the UE that is sent by the SGSN, the HLR/HSS may query information about the UE, so as to determine whether the UE is UE of the first type. In this embodiment of this application, an example in which the UE is UE of the first type is used for description. 
     In this embodiment of this application, UE of the first type may include Internet of Things UE, machine to machine (M2M) communication UE, or other high-security UE. The Internet of Things UE refers to user equipment that has an information sensing function and a data transmission function, for example, an audio guide, a personal digital assistant, a barcode collector, a data collection terminal, and a POS terminal that is mainly used for purchase or transfer. The machine to machine communication UE refers to user equipment that has a networking and communication capability and that implements an “intelligence” attribute by using a sensor, a controller, and the like, so as to exchange information with a person, a mobile network, or another machine. 
     S 1103 . The HLR/HSS sends UE type indication information to the SGSN, where the UE type indication information is used to indicate that the UE is UE of the first type. 
     Optionally, the UE type indication information may indicate, according to existence of a specific information element (IE), that the UE is UE of the first type. For example, when the SGSN receives the UE type indication information sent by the HLR/HSS or the UE, if a specific IE exists in the UE type indication information, the SGSN may determine that the UE is UE of the first type, and if the specific IE does not exist in the UE type indication information, the SGSN may determine that the UE is not UE of the first type. Alternatively, the UE type indication information may also indicate, according to a value of a specific IE, that the UE is UE of the first type. For example, when the SGSN receives the UE type indication information sent by the HLR/HSS or the UE, if a value of a specific IE in the UE type indication information is 1, the SGSN may determine that the UE is UE of the first type, and if the value of the specific IE is 0, the SGSN may determine that the UE is not UE of the first type. 
     In this embodiment of this application, the HLR/HSS may further send an authentication vector to the SGSN, where the authentication vector includes a first ciphering key and a first integrity key. 
     In some feasible implementation manners, the foregoing authentication vector may be an authentication vector quintet, which includes a random number RAND, an expected response XRES, an authentication token AUTN, a ciphering key CK, and an integrity key IK. The first ciphering key is the ciphering key CK in the authentication vector quintet, and the first integrity key is the integrity key IK in the authentication vector quintet. 
     In this embodiment of this application, an HLR/HSS may receive an identifier of UE that is sent by an SGSN, determine, according to the identifier of the UE, that the UE is UE of a first type, and send UE type indication information to the SGSN so as to indicate that the UE is UE of the first type, so that key enhancement processing for the UE of the first type may be performed between the SGSN and the UE of the first type, and security of communication of the UE of the first type in a GPRS network is enhanced. 
     Refer to  FIG. 12 .  FIG. 12  is a schematic flowchart of still another embodiment of a GPRS system key enhancement method according to this application. As shown in  FIG. 12 , the method may include the following steps. 
     S 1201 . UE sends a request message to an SGSN. 
     S 1202 . The SGSN sends an identifier of the UE to an HLR/HSS. 
     S 1203 . The HLR/HSS determines, according to the identifier of the UE, that the UE is UE of a first type. 
     S 1204 . The HLR/HSS sends UE type indication information and an authentication vector to the SGSN. 
     S 1205 . The SGSN selects a ciphering algorithm and an integrity algorithm according to the UE type indication information and an algorithm supported by the UE, and obtains a second ciphering key and a second integrity key. 
     S 1206 . The SGSN sends an authentication and ciphering request to the UE, which includes the ciphering algorithm and the integrity algorithm that are selected by the SGSN, a random number RAND, and an authentication token AUTN. 
     S 1207 . The UE performs authentication on the SGSN side, and after the authentication succeeds, acquires the second ciphering key and the second integrity key. 
     S 1208 . The UE sends an authentication and ciphering response RES to the SGSN. 
     S 1209 . The SGSN verifies a RES value, and performs authentication on the UE side. 
     In this embodiment of this application, UE sends a request message to an SGSN. After determining that the UE is UE of a first type, the SGSN selects a ciphering algorithm and an integrity algorithm. Both the UE and the SGSN compute an enhanced second ciphering key and an enhanced second integrity key according to a first ciphering key and a first integrity key, and perform ciphering protection and integrity protection on a communication message between the UE and the SGSN by using the second ciphering key, the second integrity key, and the ciphering algorithm and the integrity algorithm that are selected by the SGSN. This enhances security of communication of UE of the first type in a GPRS network. 
     Refer to  FIG. 13 .  FIG. 13  is a schematic structural diagram of an embodiment of an SGSN device according to this application. As shown in  FIG. 13 , the SGSN device may include a receiving module  1301 , an acquiring module  1302 , a selection module  1303 , and an obtaining module  1304 . 
     The receiving module  1301  is configured to receive a request message sent by UE. 
     In specific implementation, the request message that is sent by the UE to the SGSN may be an attach request message, a route update message, or another message, for example, a service request message. After receiving the request message sent by the UE, the SGSN may acquire an identifier of the UE that sends the request message. If the UE is UE of a first type, the request message may carry UE type indication information. 
     In this embodiment of this application, the UE communicates with a network by using a USIM card, and the identifier of the UE may be an IMSI (International Mobile Subscriber Identification Number) of the USIM card. UE of the first type may include Internet of Things UE, machine to machine (M2M) communication UE, or other high-security UE. The Internet of Things UE refers to user equipment that has an information sensing function and a data transmission function, for example, an audio guide, a personal digital assistant, a barcode collector, a data collection terminal, and a POS terminal that is mainly used for purchase or transfer. The machine to machine communication UE refers to user equipment that has a networking and communication capability and that implements an “intelligence” attribute by using a sensor, a controller, and the like, so as to exchange information with a person, a mobile network, or another machine. 
     The acquiring module  1302  is configured to acquire an authentication vector from an HLR/HSS, where the authentication vector includes a first ciphering key and a first integrity key. 
     The home location register (HLR) is a permanent database of a GPRS system, and stores information required for managing communication of many mobile users, including static information such as identity information, service information, and service authorization that are of a registered mobile user, and dynamic information such as location information of a user. The home subscription system (HSS) is evolution and upgrade of the HLR, and is mainly responsible for managing subscription data of a user and location information of a mobile user. Because the HSS and the HLR have a similar function in a network, and much data stored in the HSS is repeatedly stored in the HLR, generally, an HSS and HLR convergence device is presented to the outside. In this embodiment of this application, the HLR/HSS may be an HLR device, an HSS device, or an HLR and HSS convergence device. 
     In this embodiment of this application, the authentication vector acquired by the SGSN from the HLR/HSS is an authentication vector quintet, which includes a random number RAND, an expected response XRES, an authentication token AUTN, a ciphering key CK, and an integrity key IK. 
     In this embodiment of this application, the first ciphering key is the ciphering key CK in the authentication vector quintet, and the first integrity key is the integrity key IK in the authentication vector quintet. 
     The selection module  1303  is configured to: when the SGSN determines that the UE is UE of a first type, select a ciphering algorithm and an integrity algorithm for the UE, and send the selected ciphering algorithm and the selected integrity algorithm to the UE. 
     In some feasible implementation manners, the SGSN device may further include a sending module and a first determining module (not shown in the figure). 
     The sending module may be configured to send the identifier of the UE to the HLR/HSS, so that the HLR/HSS determines, according to the identifier of the UE, whether the UE is UE of the first type, and sends UE type indication information to the SGSN, where the UE type indication information is used to indicate that the UE is UE of the first type. 
     The first determining module may be configured to receive the UE type indication information sent by the HLR/HSS, and determine that the UE is UE of the first type. 
     In some feasible implementation manners, the SGSN device may further include a second determining module (not shown in the figure), and the second determining module may be configured to: when the request message includes the UE type indication information, determine that the UE is UE of the first type, where the UE type indication information is used to indicate that the UE is UE of the first type. 
     In some feasible implementation manners, the SGSN device may also include a sending module, a first determining module, and a second determining module. 
     Optionally, the UE type indication information may indicate, according to existence of a specific information element (IE), that the UE is UE of the first type. For example, when the SGSN receives the UE type indication information sent by the HLR/HSS or the UE, if a specific IE exists in the UE type indication information, the SGSN may determine that the UE is UE of the first type, and if the specific IE does not exist in the UE type indication information, the SGSN may determine that the UE is not UE of the first type. Alternatively, the UE type indication information may also indicate, according to a value of a specific IE, that the UE is UE of the first type. For example, when the SGSN receives the UE type indication information sent by the HLR/HSS or the UE, if a value of a specific IE in the UE type indication information is 1, the SGSN may determine that the UE is UE of the first type, and if the value of the specific IE is 0, the SGSN may determine that the UE is not UE of the first type. 
     In specific implementation, the SGSN may first acquire the authentication vector from the HLR/HSS, and then determine that the UE is UE of the first type, or the SGSN may first determine that the UE is UE of the first type, and then acquire the authentication vector from the HLR/HSS. 
     In specific implementation, the UE and the SGSN are separately configured with some ciphering algorithms and integrity algorithms. When sending the request message to the SGSN, the UE sends a ciphering algorithm and an integrity algorithm that are supported by the UE to the SGSN. When receiving the request message of the UE, the SGSN selects a ciphering algorithm supported by the SGSN and an integrity algorithm supported by the SGSN from the ciphering algorithm and the integrity algorithm that are supported by the UE. 
     In some feasible implementation manners, the ciphering algorithm and the integrity algorithm that are selected by the SGSN may be used along with the first ciphering key and the first integrity key in the authentication vector to compute a second ciphering key and a second integrity key. In addition, ciphering may be performed on a communication message according to the ciphering algorithm selected by the SGSN and the second ciphering key to generate a message ciphertext. A message authentication code MAC may be obtained by means of computation according to the integrity algorithm selected by the SGSN and the second integrity key. The message authentication code MAC may be used to verify integrity of the communication message. 
     Optionally, when a GPRS network requires a 128-bit second ciphering key, the ciphering algorithm selected by the SGSN may be any one of a 128-EEM algorithm, a 128-EEA2 algorithm, or a 128-EEA3 algorithm, and the integrity algorithm selected by the SGSN may be any one of a 128-EIA1 algorithm, a 128-EIA2 algorithm, or a 128-EIA3 algorithm. A SNOW  3 G algorithm is used as a core algorithm of the 128-EEM algorithm and the 128-EIA1 algorithm. An AES algorithm is used as a core algorithm of the 128-EEA2 algorithm and the 128-EIA2 algorithm. A ZUC algorithm is used as a core algorithm of the 128-EEA3 algorithm and the 128-EIA3 algorithm. 
     In specific implementation, when sending the selected ciphering algorithm and the selected integrity algorithm to the UE, the SGSN may further send the random number RAND and the authentication token AUTN in the authentication vector to the UE. The UE may perform authentication on the SGSN side according to the authentication token AUTN, so that the UE side performs authentication on a network side, and may further compute the first ciphering key CK and the first integrity key IK by using f1 to f5 algorithms according to the received random number RAND and the received authentication token AUTN. 
     To protect a communication message between the SGSN and the UE, both the SGSN and the UE need to use an agreed key (that is, the second ciphering key and the second integrity key) and an agreed algorithm (that is, the ciphering algorithm and the integrity algorithm that are selected by the SGSN) to perform ciphering on the communication message. Therefore, after selecting a ciphering algorithm and an integrity algorithm, the SGSN needs to send the selected ciphering algorithm and the selected integrity algorithm to the UE, so that after computing the second ciphering key and the second integrity key according to the first ciphering key CK and the first integrity key IK, the UE performs ciphering on the communication message by using a ciphering algorithm and an integrity algorithm that are the same as those used by the SGSN, the second ciphering key, and the second integrity key. 
     The obtaining module  1304  is configured to obtain the second ciphering key and the second integrity key according to the first ciphering key and the first integrity key. 
     In this embodiment of this application, after selecting the ciphering algorithm and the integrity algorithm, the SGSN computes the second ciphering key and the second integrity key according to the first ciphering key and the first integrity key in the authentication vector, where the first ciphering key is the ciphering key CK in the authentication vector quintet, and the first integrity key is the integrity key IK in the authentication vector quintet. The second ciphering key and the second integrity key are enhanced keys on the basis of the first ciphering key and the first integrity key, where the second ciphering key and the ciphering algorithm selected by the SGSN may be used to perform ciphering protection on a message transmitted between the SGSN and the UE, and the second integrity key and the integrity algorithm selected by the SGSN may be used to perform integrity protection on a message transmitted between the SGSN and the UE. 
     Optionally, the SGSN may compute the second ciphering key and the second integrity key only according to the first ciphering key and the first integrity key, or may compute the second ciphering key and the second integrity key according to the first ciphering key, the first integrity key, the selected ciphering algorithm, and the selected integrity algorithm. 
     In specific implementation, there may be no sequence between the sending, by the selection module  1303 , the ciphering algorithm and the integrity algorithm that are selected by the SGSN to the UE and the obtaining, by the obtaining module  1304 , the second ciphering key and the second integrity key according to the first ciphering key and the first integrity key in the authentication vector. 
     In this embodiment of this application, an SGSN receives a request message sent by UE, after determining that the UE is UE of a first type, selects a ciphering algorithm and an integrity algorithm, acquires an authentication vector from an HLR/HSS, obtains an enhanced second ciphering key and an enhanced second integrity key according to a first ciphering key and a first integrity key that are included in the authentication vector, and sends the selected ciphering algorithm and the selected integrity algorithm to the UE, so that after the UE computes the second ciphering key and the second integrity key, both the SGSN and the UE may perform ciphering protection and integrity protection on a communication message between the SGSN and the UE by using the second ciphering key, the second integrity key, and the ciphering algorithm and the integrity algorithm that are selected by the SGSN. This enhances security of communication of UE of the first type in a GPRS network. 
     The following describes, in detail, a structure and a function of the obtaining module  1304  shown in  FIG. 13  with reference to  FIG. 14  and  FIG. 15 . 
     In some feasible implementation manners, as shown in  FIG. 14 , the obtaining module  1304  may include a first computation unit  13041 , a second computation unit  13042 , and a third computation unit  13043 . 
     The first computation unit  13041  is configured to compute an intermediate key according to the first ciphering key and the first integrity key. 
     In a feasible implementation manner, the first computation unit  13041  may perform an operation on the first ciphering key and the first integrity key, and then use an operation result as an input parameter of a key derivation function KDF to compute the intermediate key. For example, the intermediate key may be Km=KDF(CK∥IK), where CK∥IK indicates that a join operation is performed on the first ciphering key CK and the first integrity key IK. 
     In another feasible implementation manner, the intermediate key may directly use an existing 64-bit GPRS ciphering key Kc or an existing 128-bit ciphering key Kc 128 , that is, the first computation unit  13041  may directly use the existing GPRS ciphering key Kc (64-bit) as the intermediate key, or directly use the existing Kc 128  (128-bit) as the intermediate key. Both Kc and Kc 128  are generated by means of computation according to the CK and the IK. 
     The second computation unit  13042  is configured to compute the second ciphering key according to the intermediate key and a ciphering characteristic string. 
     In specific implementation, the intermediate key and the ciphering characteristic string ciphering may be used as input parameters of a key derivation function KDF to compute the second ciphering key. For example, the second ciphering key may be obtained by means of computation by using K cipher =KDF(Km, “ciphering”), where “ciphering” is a ciphering characteristic string, and may be generated by means of coding. 
     In some feasible implementation manners, a GPRS system requires a 128-bit second ciphering key, and in this case, preset 128 bits (for example, the most significant 128 bits) may be intercepted from the computed intermediate key Km as one of input parameters of a key derivation function KDF, and an output of the KDF is used as the second ciphering key; or the computed intermediate key Km may be directly used as one of input parameters of a key derivation function KDF, and preset 128 bits (for example, the most significant 128 bits) are intercepted from an output of the KDF as the second ciphering key; or the intermediate key Kc 128  is used as one of input parameters of a key derivation function KDF, and an output of the key derivation function KDF is used as the second ciphering key. 
     In some feasible implementation manners, a GPRS system requires a 64-bit second ciphering key, and in this case, preset 64 bits (for example, the most significant 64 bits) may be intercepted from the computed intermediate key Km as one of input parameters of a key derivation function KDF, and an output of the KDF is used as the second ciphering key; or the computed intermediate key Km may be directly used as one of input parameters of a key derivation function KDF, and preset 64 bits (for example, the most significant 64 bits) are intercepted from an output of the KDF as the second ciphering key; or the intermediate key Kc (64-bit) may be used as one of input parameters of a key derivation function KDF, and an output of the key derivation function KDF is used as the second ciphering key. 
     The third computation unit  13043  is configured to compute the second integrity key according to the intermediate key and an integrity characteristic string. 
     In specific implementation, the intermediate key and the integrity characteristic string integrity may be used as input parameters of a key derivation function KDF to compute the second integrity key. For example, the second integrity key may be obtained by means of computation by using K integrity =KDF(Km, “integrity”), where “integrity” is an integrity characteristic string, and may be generated by means of coding. 
     In some feasible implementation manners, a GPRS system requires a 128-bit second integrity key, and in this case, preset 128 bits (for example, the most significant 128 bits) may be intercepted from the computed intermediate key Km as one of input parameters of a key derivation function KDF and K integrity  obtained by means of computation according to the preset 128 bits of the Km is used as the second integrity key; or the computed intermediate key Km may be directly used as one of input parameters of a key derivation function KDF, and preset 128 bits (for example, the most significant 128 bits) are intercepted from computed K integrity  as the second integrity key; or the intermediate key Kc 128  may be used as one of input parameters of a key derivation function KDF, and an output of the key derivation function KDF is used as the second integrity key. 
     In some feasible implementation manners, a GPRS system requires a 64-bit second integrity key, and in this case, preset 64 bits (for example, the most significant 64 bits) may be intercepted from the computed intermediate key Km as one of input parameters of a key derivation function KDF, and an output of the KDF is used as the second integrity key; or the computed intermediate key Km may be directly used as one of input parameters of a key derivation function KDF, and preset 64 bits (for example, the most significant 64 bits) are intercepted from an output of the KDF as the second integrity key; or the intermediate key Kc (64-bit) may be used as one of input parameters of a key derivation function KDF, and an output of the key derivation function KDF is used as the second integrity key. 
     In this embodiment of this application, the ciphering characteristic string ciphering and the integrity characteristic string integrity are used to make the computed second ciphering key and the computed second integrity key different for easy distinction. Therefore, the integrity characteristic string integrity may be any string inconsistent with the ciphering characteristic string ciphering. 
     In some feasible implementation manners, as shown in  FIG. 14 , the obtaining module  1304  may include a first computation unit  13041 , a second computation unit  13042 , and a third computation unit  13043 . 
     The first computation unit  13041  is configured to compute an intermediate key according to the first ciphering key and the first integrity key. 
     In a feasible implementation manner, the first computation unit  13041  may perform an operation on the first ciphering key and the first integrity key, and then use an operation result as an input parameter of a key derivation function KDF to compute the intermediate key. For example, the intermediate key may be Km=KDF(CK∥IK), where CK∥IK indicates that a join operation is performed on the first ciphering key CK and the first integrity key IK. 
     In another feasible implementation manner, the first computation unit  13041  may directly use an existing GPRS ciphering key Kc (64-bit) as the intermediate key, or directly use an existing Kc 128  (128-bit) as the intermediate key. Both Kc and Kc 128  are generated by means of computation according to the CK and the IK. 
     The second computation unit  13042  is configured to compute the second ciphering key according to the intermediate key, a first algorithm type indication, and an identifier of the selected ciphering algorithm. 
     In specific implementation, the second computation unit  13042  may use the intermediate key, the first algorithm type indication, and the identifier of the selected ciphering algorithm as input parameters of a key derivation function KDF to compute the second ciphering key. For example, the second ciphering key K cipher  may be obtained by means of computation by using K cipher =KDF(Km, algorithm type distinguisher 1 , ciphering algorithm id), where Km is the intermediate key, algorithm type distinguisher 1  is the first algorithm type indication, and ciphering algorithm id is the identifier of the ciphering algorithm selected by the SGSN. 
     In some feasible implementation manners, a GPRS system requires a 128-bit second ciphering key, and in this case, preset 128 bits (for example, the most significant 128 bits) may be intercepted from the computed intermediate key Km as one of input parameters of a key derivation function KDF, and an output of the KDF is used as the second ciphering key; or the computed intermediate key Km may be directly used as one of input parameters of a key derivation function KDF, and preset 128 bits (for example, the most significant 128 bits) are intercepted from an output of the KDF as the second ciphering key; or the intermediate key Kc 128  is used as one of input parameters of a key derivation function KDF, and an output of the key derivation function KDF is used as the second ciphering key. 
     In some feasible implementation manners, a GPRS system requires a 64-bit second ciphering key, and in this case, preset 64 bits (for example, the most significant 64 bits) may be intercepted from the computed intermediate key Km as one of input parameters of a key derivation function KDF, and an output of the KDF is used as the second ciphering key; or the computed intermediate key Km may be directly used as one of input parameters of a key derivation function KDF, and preset 64 bits (for example, the most significant 64 bits) are intercepted from an output of the KDF as the second ciphering key; or the intermediate key Kc (64-bit) may be used as one of input parameters of a key derivation function KDF, and an output of the key derivation function KDF is used as the second ciphering key. 
     The third computation unit  13043  is configured to compute the second integrity key according to the intermediate key, a second algorithm type indication, and an identifier of the selected integrity algorithm, where values of the first algorithm type indication and the second algorithm type indication are different. 
     In specific implementation, the third computation unit  13043  may use the intermediate key, the second algorithm type indication, and the identifier of the selected integrity algorithm as input parameters of a key derivation function KDF to compute the second integrity key. For example, the second integrity key K integrity  may be obtained by means of computation by using K integrity =KDF(Km, algorithm type distinguisher 2 , integrity algorithm id), where Km is the intermediate key, algorithm type distinguisher 2  is the second algorithm type indication, and integrity algorithm id is the identifier of the integrity algorithm selected by the SGSN. 
     In some feasible implementation manners, a GPRS system requires a 128-bit second integrity key, and in this case, preset 128 bits (for example, the most significant 128 bits) may be intercepted from the computed intermediate key Km as one of input parameters of a key derivation function KDF, and an output of the KDF is used as the second integrity key; or the computed intermediate key Km may be directly used as one of input parameters of a key derivation function KDF, and preset 128 bits (for example, the most significant 128 bits) are intercepted from an output of the KDF as the second integrity key; or the intermediate key Kc 128  may be used as one of input parameters of a key derivation function KDF, and an output of the key derivation function KDF is used as the second integrity key. 
     In some feasible implementation manners, a GPRS system requires a 64-bit second integrity key, and in this case, preset 64 bits (for example, the most significant 64 bits) may be intercepted from the computed intermediate key Km as one of input parameters of a key derivation function KDF, and an output of the KDF is used as the second integrity key; or the computed intermediate key Km may be directly used as one of input parameters of a key derivation function KDF, and preset 64 bits (for example, the most significant 64 bits) are intercepted from an output of the KDF as the second integrity key; or the intermediate key Kc (64-bit) may be used as one of input parameters of a key derivation function KDF, and an output of the key derivation function KDF is used as the second integrity key. 
     In this embodiment of this application, the first algorithm type indication is used to indicate that an algorithm currently participating in an operation is an algorithm of a ciphering type, and the second algorithm type indication is used to indicate that an algorithm currently participating in an operation is an algorithm of an integrity type. In some feasible embodiments, the first algorithm type indication and the second algorithm type indication may include a same IE, and the first algorithm type indication and the second algorithm type indication are distinguished by using different values of the IE. For example, the IEs of the first algorithm type indication and the second algorithm type indication are both algorithm type distinguisher. When algorithm type distinguisher=00, it indicates an algorithm of a ciphering type. When algorithm type distinguisher=01, it indicates an algorithm of an integrity type. 
     In some possible cases, the ciphering algorithm and the integrity algorithm may use a same identifier, and in these cases, each algorithm needs to be uniquely distinguished with reference to an algorithm type indication. For example, if both a 128-EEM algorithm and 128-EIA1 algorithm use 1 as an algorithm identifier, when the ciphering algorithm and the integrity algorithm that are selected by the SGSN are the 128-EEM algorithm and the 128-EIA1 algorithm respectively, the 128-EEM algorithm and the 128-EIA1 algorithm may be distinguished by using different values of IEs in the first algorithm type indication and the second algorithm type indication. In addition, values of the computed second ciphering key and the computed second integrity key may be made different, so as to distinguish between the second ciphering key and the second integrity key. 
     In some feasible implementation manners, as shown in  FIG. 15 , the obtaining module  1304  may include a fourth computation unit  13044  and a fifth computation unit  13045 . 
     The fourth computation unit  13044  is configured to compute the second ciphering key according to the first ciphering key, a first algorithm type indication, and an identifier of the selected ciphering algorithm. 
     Specifically, the fourth computation unit  13044  may use the first ciphering key, the first algorithm type indication, and the identifier of the selected ciphering algorithm as input parameters of a key derivation function KDF to compute the second ciphering key. For example, K cipher =KDF(CK, algorithm type distinguisher 1 , ciphering algorithm id), where CK is the first ciphering key, algorithm type distinguisher 1  is the first algorithm type indication, and ciphering algorithm id is the identifier of the ciphering algorithm selected by the SGSN. 
     Optionally, if a GPRS system requires a 64-bit second ciphering key, the most significant 64 bits may be selected from computed K cipher  as the second ciphering key; if the GPRS system requires a 128-bit second ciphering key, the most significant 128 bits may be selected from computed K cipher  as the second ciphering key. In another feasible implementation manner, a required quantity of bits may be randomly selected from computed K cipher  as the second ciphering key, which is not limited in this application. 
     The fifth computation unit  13045  computes the second integrity key according to the first integrity key in the authentication vector, a second algorithm type indication, and an identifier of the selected integrity algorithm. 
     Specifically, the fifth computation unit  13045  may use the first integrity key, the second algorithm type indication, and the identifier of the selected integrity algorithm as input parameters of a key derivation function KDF to compute the second integrity key. For example, K integrity =KDF(IK, algorithm type distinguisher 2 , integrity algorithm id), where IK is the first integrity key, algorithm type distinguisher 2  is the second algorithm type indication, and integrity algorithm id is the identifier of the integrity algorithm selected by the SGSN. 
     Optionally, if a GPRS system requires a 64-bit second integrity key, the most significant 64 bits may be selected from computed K integrity  as the second integrity key; if the GPRS system requires a 128-bit second integrity key, the most significant 128 bits may be selected from computed K integrity  as the second integrity key. In another feasible implementation manner, a required quantity of bits may be randomly selected from computed K integrity  as the second integrity key, which is not limited in this application. 
     In this embodiment of this application, the first algorithm type indication is used to indicate that an algorithm currently participating in an operation is an algorithm of a ciphering type, and the second algorithm type indication is used to indicate that an algorithm currently participating in an operation is an algorithm of an integrity type. Values of the first algorithm type indication and the second algorithm type indication are different. In some feasible embodiments, the first algorithm type indication and the second algorithm type indication may include a same IE, and the first algorithm type indication and the second algorithm type indication are distinguished by using different values of the IE. For example, the IEs of the first algorithm type indication and the second algorithm type indication are both algorithm type distinguisher. When algorithm type distinguisher=00, it indicates an algorithm of a ciphering type. When algorithm type distinguisher=01, it indicates an algorithm of an integrity type. 
     In some possible cases, the ciphering algorithm and the integrity algorithm may use a same identifier, and in these cases, each algorithm needs to be uniquely distinguished with reference to an algorithm type indication. For example, if both a 128-EEM algorithm and 128-EIA1 algorithm use 1 as an algorithm identifier, when the ciphering algorithm and the integrity algorithm that are selected by the SGSN are the 128-EEM algorithm and the 128-EIA1 algorithm respectively, the 128-EEM algorithm and the 128-EIA1 algorithm may be distinguished by using different values of the first algorithm type indication and the second algorithm type indication. In addition, values of the computed second ciphering key and the computed second integrity key may be made different, so as to distinguish between the second ciphering key and the second integrity key. 
     In some feasible implementation manners, the obtaining module  1304  may be specifically configured to: compute an intermediate key according to the first ciphering key and the first integrity key; and use a first preset bit of the intermediate key as the second ciphering key, and use a second preset bit of the intermediate key as the second integrity key. 
     In a feasible implementation manner, the obtaining module  1304  may perform an operation on the first ciphering key and the first integrity key, and then use an operation result as an input parameter of a key derivation function KDF to compute the intermediate key. For example, the intermediate key may be Km=KDF(CK∥IK), where CK∥IK indicates that a join operation is performed on the first ciphering key CK and the first integrity key IK. 
     In another feasible implementation manner, the obtaining module  1304  may directly use an existing GPRS ciphering key Kc (64-bit) as the intermediate key, or directly use an existing Kc 128  (128-bit) as the intermediate key. Both Kc and Kc 128  are generated by means of computation according to the CK and the IK. 
     In a feasible implementation manner, the obtaining module  1304  may use a first preset bit of the intermediate key as the second ciphering key. For example, if a GPRS system requires a 64-bit second ciphering key, the most significant 64 bits of the intermediate key may be directly used as the second ciphering key; if the GPRS system requires a 128-bit second ciphering key, the most significant 128 bits of the intermediate key may be directly used as the second ciphering key. In another optional implementation manner, a required quantity of bits may be randomly selected from the intermediate key as the second ciphering key, which is not limited in this application. 
     In a feasible implementation manner, the obtaining module  1304  may use a second preset bit of the intermediate key as the second integrity key. For example, if a GPRS system requires a 64-bit second integrity key, the least significant 64 bits of the intermediate key may be directly used as the second integrity key; if the GPRS system requires a 128-bit second integrity key, the least significant 128 bits of the intermediate key may be directly used as the second integrity key. In another optional implementation manner, a required quantity of bits may be randomly selected from the intermediate key as the second integrity key, which is not limited in this application. 
     In some feasible implementation manners, the obtaining module  1304  may be specifically configured to: use the first ciphering key or a preset bit of the first ciphering key as the second ciphering key, and use the first integrity key or a preset bit of the first integrity key as the second integrity key. 
     In some feasible implementation manners, if the first ciphering key is a 128-bit key, and the second ciphering key required by a GPRS system is also a 128-bit key, the first ciphering key may be directly used as the second ciphering key. If the second ciphering key required by the GPRS system is a 64-bit key, 64 preset bits may be selected from the first ciphering key as the second ciphering key. For example, the most significant 64 bits are selected as the second ciphering key. 
     In some feasible implementation manners, if the first integrity key is a 128-bit key, and the second integrity key required by a GPRS system is also a 128-bit key, the first integrity key may be directly used as the second integrity key. If the second integrity key required by the GPRS system is a 64-bit key, 64 preset bits may be selected from the first integrity key as the second integrity key. For example, the most significant 64 bits are selected as the second integrity key. 
     In this embodiment of this application, an SGSN receives a request message sent by UE, after determining that the UE is UE of a first type, selects a ciphering algorithm and an integrity algorithm, acquires an authentication vector from an HLR/HSS, obtains an enhanced second ciphering key and an enhanced second integrity key according to a first ciphering key and a first integrity key that are included in the authentication vector, and sends the selected ciphering algorithm and the selected integrity algorithm to the UE, so that the UE computes the second ciphering key and the second integrity key, and performs ciphering protection and integrity protection on a communication message between the SGSN and the UE by using the second ciphering key and the second integrity key. This enhances security of communication of UE of the first type in a GPRS network. 
     Refer to  FIG. 16 .  FIG. 16  is a schematic structural diagram of another embodiment of an SGSN device according to this application. As shown in  FIG. 16 , the SGSN device may include a receiving apparatus  1601 , a sending apparatus  1602 , and a processor  1603 , where the receiving apparatus  1601 , the sending apparatus  1602 , and the processor  1603  are connected by using a bus. 
     The receiving apparatus  1601  is configured to receive a request message sent by UE. 
     The processor  1603  is configured to: acquire an authentication vector from an HLR/HSS, where the authentication vector includes a first ciphering key and a first integrity key; if the SGSN determines that the UE is UE of a first type, select a ciphering algorithm and an integrity algorithm for the UE; and obtain a second ciphering key and a second integrity key according to the first ciphering key and the first integrity key. 
     The sending apparatus  1602  is configured to send the selected ciphering algorithm and the selected integrity algorithm to the UE. 
     The second ciphering key and the selected ciphering algorithm are used to perform ciphering protection on a message transmitted between the SGSN and the UE, and the second integrity key and the selected integrity algorithm are used to perform integrity protection on a message transmitted between the SGSN and the UE. 
     In some feasible implementation manners, the request message includes an identifier of the UE. 
     The sending apparatus  1602  is further configured to send the identifier of the UE to the HLR/HSS, so that the HLR/HSS determines, according to the identifier of the UE, that the UE is UE of the first type, and sends UE type indication information to the SGSN, where the UE type indication information is used to indicate that the UE is UE of the first type. 
     That the processor  1603  determines whether the UE is UE of a first type includes: receiving, by the processor  1603 , the UE type indication information sent by the HLR/HSS, and determining that the UE is UE of the first type. 
     In some feasible implementation manners, that the processor  1603  determines that the UE is UE of a first type includes: if the request message includes UE type indication information, determining, by the processor  1603 , that the UE is UE of the first type. 
     In some feasible implementation manners, that the processor  1603  obtains a second ciphering key and a second integrity key according to the first ciphering key and the first integrity key includes: computing, by the processor  1603 , an intermediate key according to the first ciphering key and the first integrity key; computing, by the processor  1603 , the second ciphering key according to the intermediate key and a ciphering characteristic string; and computing, by the processor  1603 , the second integrity key according to the intermediate key and an integrity characteristic string. 
     In some feasible implementation manners, that the processor  1603  obtains a second ciphering key and a second integrity key according to the first ciphering key and the first integrity key includes: computing, by the processor, an intermediate key according to the first ciphering key and the first integrity key; and using, by the processor, a first preset bit of the intermediate key as the second ciphering key, and using a second preset bit of the intermediate key as the second integrity key; or computing, by the processor, the second ciphering key according to the first ciphering key in the authentication vector, a first algorithm type indication, and an identifier of the selected ciphering algorithm, and computing, by the processor, the second integrity key according to the first integrity key in the authentication vector, a second algorithm type indication, and an identifier of the selected integrity algorithm, where values of the first algorithm type indication and the second algorithm type indication are different; or using, by the processor, the first ciphering key or a preset bit of the first ciphering key as the second ciphering key, and using, by the processor, the first integrity key or a preset bit of the first integrity key as the second integrity key. 
     In some feasible implementation manners, the authentication vector is an authentication vector quintet. 
     The first ciphering key is a ciphering key CK in the authentication vector quintet, and the first integrity key is an integrity key IK in the authentication vector quintet. 
     In some feasible implementation manners, the intermediate key is a 64-bit GPRS ciphering key Kc or a 128-bit ciphering key Kc 128 . 
     In this embodiment of this application, an SGSN receives a request message sent by UE, after determining that the UE is UE of a first type, selects a ciphering algorithm and an integrity algorithm, acquires an authentication vector from an HLR/HSS, obtains an enhanced second ciphering key and an enhanced second integrity key according to a first ciphering key and a first integrity key that are included in the authentication vector, and sends the selected ciphering algorithm and the selected integrity algorithm to the UE, so that after the UE computes the second ciphering key and the second integrity key, both the SGSN and the UE may perform ciphering protection and integrity protection on a communication message between the SGSN and the UE by using the second ciphering key, the second integrity key, and the ciphering algorithm and the integrity algorithm that are selected by the SGSN. This enhances security of communication of UE of the first type in a GPRS network. 
     Refer to  FIG. 17 .  FIG. 17  is a schematic structural diagram of an embodiment of UE according to this application. As shown in  FIG. 17 , the UE may include a sending module  1701 , a receiving module  1702 , and an acquiring module  1703 . 
     The sending module  1701  is configured to send a request message to an SGSN. 
     In specific implementation, the request message sent by the sending module  1701  to the SGSN may be an attach request message, a route update message, or another message, for example, a service request message. After receiving the request message sent by the UE, the SGSN may acquire an identifier of the UE that sends the request message. If the UE is UE of a first type, the request message may carry UE type indication information. 
     In this embodiment of this application, the UE communicates with a network by using a USIM card, and the identifier of the UE may be an IMSI (International Mobile Subscriber Identification Number) of the USIM card. Internet of Things UE refers to user equipment that has an information sensing function and a message transmission function, for example, an audio guide, a personal digital assistant, a barcode collector, a data collection terminal, and a POS terminal that is mainly used for purchase or transfer. Machine to machine communication UE refers to user equipment that has a networking and communication capability and that implements an “intelligence” attribute by using a sensor, a controller, and the like, so as to exchange information with a person, a mobile network, or another machine. 
     The UE in this embodiment of this application is UE of the first type. In some feasible implementation manners, the request message that is sent by the sending module  1701  to the SGSN may include the UE type indication information, so that the SGSN determines, according to the UE type indication information, that the UE is UE of the first type. 
     Optionally, the UE type indication information may indicate, according to existence of a specific information element (IE), that the UE is UE of the first type. For example, when the SGSN receives the UE type indication information sent by the HLR/HSS or the UE, if a specific IE exists in the UE type indication information, the SGSN may determine that the UE is UE of the first type, and if the specific IE does not exist in the UE type indication information, the SGSN may determine that the UE is not UE of the first type. Alternatively, the UE type indication information may also indicate, according to a value of a specific IE, that the UE is UE of the first type. For example, when the SGSN receives the UE type indication information sent by the HLR/HSS or the UE, if a value of a specific IE in the UE type indication information is 1, the SGSN may determine that the UE is UE of the first type, and if the value of the specific IE is 0, the SGSN may determine that the UE is not UE of the first type. 
     In specific implementation, the UE and the SGSN are separately configured with some ciphering algorithms and integrity algorithms. When sending the request message to the SGSN, the sending module  1701  sends a ciphering algorithm and an integrity algorithm that are supported by the UE to the SGSN. 
     The receiving module  1702  is configured to receive a ciphering algorithm and an integrity algorithm that are sent by the SGSN. 
     After the SGSN receives the request message of the UE, if it is determined that the foregoing UE is UE of the first type, the SGSN selects a ciphering algorithm supported by the SGSN and an integrity algorithm supported by the SGSN from the ciphering algorithm and the integrity algorithm that are supported by the UE. The SGSN sends the selected ciphering algorithm and the selected integrity algorithm to the UE, and obtains a second ciphering key and a second integrity key according to a first ciphering key and a first integrity key in an authentication vector. 
     In specific implementation, when sending the selected ciphering algorithm and the selected integrity algorithm to the UE, the SGSN may further send a random number RAND and an authentication token AUTN in the authentication vector to the UE. The UE may perform authentication on the SGSN side according to the authentication token AUTN, so that the UE side performs authentication on a network side. The UE may further compute the first ciphering key and the first integrity key by using f1 to f5 algorithms according to the received random number RAND and the received authentication token AUTN. The first ciphering key and the first integrity key that are computed by the UE are the same as the first ciphering key and the first integrity key in the authentication vector that is acquired by the SGSN from the HLR/HSS. The authentication vector acquired by the SGSN from the HLR/HSS is an authentication vector quintet, which includes a random number RAND, an expected response XRES, an authentication token AUTN, a ciphering key CK, and an integrity key IK. 
     In this embodiment of this application, the first ciphering key is the ciphering key CK in the authentication vector quintet, and the first integrity key is the integrity key IK in the authentication vector quintet. 
     In some feasible implementation manners, the ciphering algorithm and the integrity algorithm that are selected by the SGSN may be used along with the first ciphering key CK and the first integrity key IK in the authentication vector to compute a second ciphering key and a second integrity key. In addition, ciphering may be performed on a communication message according to the ciphering algorithm and the generated second ciphering key to generate a message ciphertext. A message authentication code MAC may be obtained by means of computation according to the integrity algorithm and the generated second integrity key. The message authentication code MAC may be used to verify integrity of the communication message. 
     Optionally, when a GPRS network requires a 128-bit second ciphering key, the ciphering algorithm selected by the SGSN may be any one of a 128-EEM algorithm, a 128-EEA2 algorithm, or a 128-EEA3 algorithm, and the integrity algorithm selected by the SGSN may be any one of a 128-EIA1 algorithm, a 128-EIA2 algorithm, or a 128-EIA3 algorithm. A SNOW  3 G algorithm is used as a core algorithm of the 128-EEM algorithm and the 128-EIA1 algorithm. An AES algorithm is used as a core algorithm of the 128-EEA2 algorithm and the 128-EIA2 algorithm. A ZUC algorithm is used as a core algorithm of the 128-EEA3 algorithm and the 128-EIA3 algorithm. 
     The acquiring module  1703  is configured to acquire the second ciphering key and the second integrity key according to the first ciphering key and the first integrity key. 
     In this embodiment of this application, the second ciphering key and the second integrity key are enhanced keys on the basis of the first ciphering key and the first integrity key. The second ciphering key and the ciphering algorithm sent by the SGSN are used to perform ciphering protection on a message transmitted between the SGSN and the UE, and the second integrity key and the integrity algorithm sent by the SGSN are used to perform integrity protection on a message transmitted between the SGSN and the UE. 
     Optionally, the acquiring module  1703  may acquire the second ciphering key and the second integrity key only according to the first ciphering key and the first integrity key, or the acquiring module  1703  may acquire the second ciphering key and the second integrity key according to the first ciphering key, the first integrity key, and the ciphering algorithm and the integrity algorithm that are sent by the SGSN. 
     After the second ciphering key and the second integrity key are acquired, to protect a communication message between the SGSN and the UE, both the SGSN and the UE need to use an agreed key (that is, the second ciphering key and the second integrity key) and an agreed algorithm (that is, the ciphering algorithm and the integrity algorithm that are sent by the SGSN) to perform ciphering on the communication message. 
     In this embodiment of this application, UE sends a request message to an SGSN, receives a ciphering algorithm and an integrity algorithm that are sent by the SGSN, and computes a second ciphering key and a second integrity key according to a first ciphering key and a first integrity key. Both the SGSN and the UE may perform ciphering protection and integrity protection on a communication message between the UE and the SGSN by using the second ciphering key, the second integrity key, and the ciphering algorithm and the integrity algorithm that are sent by the SGSN to the UE. This enhances security of communication of UE of a first type in a GPRS network. 
     The following describes, in detail, a structure and a function of the acquiring module  1703  shown in  FIG. 17  with reference to  FIG. 18  and  FIG. 19 . 
     In some feasible implementation manners, as shown in  FIG. 18 , the acquiring module  1703  may include a first computation unit  17031 , a second computation unit  17032 , and a third computation unit  17033 . 
     The first computation unit  17031  is configured to compute an intermediate key according to the first ciphering key and the first integrity key. 
     In some feasible implementation manners, before the first computation unit  17031  computes the intermediate key, the UE first computes an expected message authentication code XMAC according to the authentication token AUTN and the random number RAND that are sent by the SGSN, and performs authentication on the SGSN side by determining whether the expected message authentication code XMAC is the same as a message authentication code MAC in the authentication token AUTN. After authentication on the SGSN side succeeds, the UE computes the first ciphering key CK and the first integrity key IK according to the random number RAND and the authentication token AUTN that are sent by the SGSN, computes a random number response RES, and sends the random number response RES to the SGSN, so that the SGSN side performs authentication on the UE. 
     In a feasible implementation manner, the first computation unit  17031  may perform an operation on the first ciphering key and the first integrity key, and then use an operation result as an input parameter of a key derivation function KDF to compute the intermediate key. For example, the intermediate key may be Km=KDF(CK∥IK), where CK∥IK indicates that a join operation is performed on the first ciphering key CK and the first integrity key IK. 
     In another feasible implementation manner, the intermediate key may directly use an existing 64-bit GPRS ciphering key Kc or an existing 128-bit ciphering key Kc 128 , that is, the first computation unit  17031  may directly use the existing GPRS ciphering key Kc (64-bit) as the intermediate key, or directly use the existing Kc 128  (128-bit) as the intermediate key. Both Kc and Kc 128  are generated by means of computation according to the CK and the IK. 
     The second computation unit  17032  is configured to compute the second ciphering key according to the intermediate key and a ciphering characteristic string. 
     In specific implementation, the intermediate key and the ciphering characteristic string ciphering may be used as input parameters of a key derivation function KDF to compute the second ciphering key. For example, the second ciphering key may be obtained by means of computation by using K cipher =KDF(Km, “ciphering”), where “ciphering” is a ciphering characteristic string, and may be generated by means of coding. 
     In some feasible implementation manners, a GPRS system requires a 128-bit second ciphering key, and in this case, preset 128 bits (for example, the most significant 128 bits) may be intercepted from the computed intermediate key Km as one of input parameters of a key derivation function KDF, and an output of the KDF is used as the second ciphering key; or the computed intermediate key Km may be directly used as one of input parameters of a key derivation function KDF, and preset 128 bits (for example, the most significant 128 bits) are intercepted from an output of the KDF as the second ciphering key; or the intermediate key Kc 128  may be used as one of input parameters of a key derivation function KDF, and an output of the key derivation function KDF is used as the second ciphering key. 
     In some feasible implementation manners, a GPRS system requires a 64-bit second ciphering key, and in this case, preset 64 bits (for example, the most significant 64 bits) may be intercepted from the computed intermediate key Km as one of input parameters of a key derivation function KDF, and an output of the KDF is used as the second ciphering key; or the computed intermediate key Km may be directly used as one of input parameters of a key derivation function KDF, and preset 64 bits (for example, the most significant 64 bits) are intercepted from an output of the KDF as the second ciphering key; or the intermediate key Kc (64-bit) may be used as one of input parameters of a key derivation function KDF, and an output of the key derivation function KDF is used as the second ciphering key. 
     The third computation unit  17033  is configured to compute the second integrity key according to the intermediate key and an integrity characteristic string. 
     In specific implementation, the intermediate key and the integrity characteristic string integrity may be used as input parameters of a key derivation function KDF to compute the second integrity key. For example, the second integrity key may be obtained by means of computation by using K integrity =KDF(Km, “integrity”), where “integrity” is an integrity characteristic string, and may be generated by means of coding. 
     In some feasible implementation manners, a GPRS system requires a 128-bit second integrity key, and in this case, preset 128 bits (for example, the most significant 128 bits) may be intercepted from the computed intermediate key Km as one of input parameters of a key derivation function KDF, and an output of the KDF is used as the second integrity key; or the computed intermediate key Km may be directly used as one of input parameters of a key derivation function KDF, and preset 128 bits (for example, the most significant 128 bits) are intercepted from an output of the KDF as the second integrity key; or the intermediate key Kc 128  may be used as one of input parameters of a key derivation function KDF, and an output of the key derivation function KDF is used as the second integrity key. 
     In some feasible implementation manners, a GPRS system requires a 64-bit second integrity key, and in this case, preset 64 bits (for example, the most significant 64 bits) may be intercepted from the computed intermediate key Km as one of input parameters of a key derivation function KDF, and an output of the KDF is used as the second integrity key; or the computed intermediate key Km may be directly used as one of input parameters of a key derivation function KDF, and preset 64 bits (for example, the most significant 64 bits) are intercepted from an output of the KDF as the second integrity key; or the intermediate key Kc (64-bit) may be used as one of input parameters of a key derivation function KDF, and an output of the key derivation function KDF is used as the second integrity key. 
     In this embodiment of this application, the ciphering characteristic string ciphering and the integrity characteristic string integrity are used to make the computed second ciphering key and the computed second integrity key different for easy distinction. Therefore, the integrity characteristic string integrity may be any string inconsistent with the ciphering characteristic string ciphering. 
     In some feasible implementation manners, as shown in  FIG. 18 , the acquiring module  1703  may include a first computation unit  17031 , a second computation unit  17032 , and a third computation unit  17033 . 
     The first computation unit  17031  is configured to compute an intermediate key according to the first ciphering key and the first integrity key. 
     In a feasible implementation manner, the first computation unit  17031  may perform an operation on the first ciphering key and the first integrity key, and then use an operation result as an input parameter of a key derivation function KDF to compute the intermediate key. For example, the intermediate key may be Km=KDF(CK∥IK), where CK∥IK indicates that a join operation is performed on the first ciphering key CK and the first integrity key IK. 
     In another feasible implementation manner, the first computation unit  17031  may directly use an existing GPRS ciphering key Kc (64-bit) as the intermediate key, or directly use an existing Kc 128  (128-bit) as the intermediate key. Both Kc and Kc 128  are generated by means of computation according to the CK and the IK. 
     The second computation unit  17032  is configured to compute the second ciphering key according to the intermediate key, a first algorithm type indication, and an identifier of the ciphering algorithm. 
     In specific implementation, the second computation unit  17032  may use the intermediate key, the first algorithm type indication, and the identifier of the ciphering algorithm as input parameters of a key derivation function KDF to compute the second ciphering key. For example, the second ciphering key K cipher  may be obtained by means of computation by using K cipher =KDF(Km, algorithm type distinguisher 1 , ciphering algorithm id), where Km is the intermediate key, algorithm type distinguisher 1  is the first algorithm type indication, and ciphering algorithm id is the identifier of the ciphering algorithm selected by the SGSN. 
     In some feasible implementation manners, a GPRS system requires a 128-bit second ciphering key, and in this case, preset 128 bits (for example, the most significant 128 bits) may be intercepted from the computed intermediate key Km as one of input parameters of a key derivation function KDF, and an output of the KDF is used as the second ciphering key; or the computed intermediate key Km may be directly used as one of input parameters of a key derivation function KDF, and preset 128 bits (for example, the most significant 128 bits) are intercepted from an output of the KDF as the second ciphering key; or the intermediate key Kc 128  is used as one of input parameters of a key derivation function KDF, and an output of the key derivation function KDF is used as the second ciphering key. 
     In some feasible implementation manners, a GPRS system requires a 64-bit second ciphering key, and in this case, preset 64 bits (for example, the most significant 64 bits) may be intercepted from the computed intermediate key Km as one of input parameters of a key derivation function KDF, and an output of the KDF is used as the second ciphering key; or the computed intermediate key Km may be directly used as one of input parameters of a key derivation function KDF, and preset 64 bits (for example, the most significant 64 bits) are intercepted from an output of the KDF as the second ciphering key; or the intermediate key Kc (64-bit) may be used as one of input parameters of a key derivation function KDF, and an output of the key derivation function KDF is used as the second ciphering key. 
     The third computation unit  17033  is configured to compute the second integrity key according to the intermediate key, a second algorithm type indication, and an identifier of the integrity algorithm, where values of the first algorithm type indication and the second algorithm type indication are different. 
     In specific implementation, the third computation unit  17033  may use the intermediate key, the second algorithm type indication, and the identifier of the integrity algorithm as input parameters of a key derivation function KDF to compute the second integrity key. For example, the second integrity key K integrity  may be obtained by means of computation by using K integrity =KDF(Km, algorithm type distinguisher 2 , integrity algorithm id), where Km is the intermediate key, algorithm type distinguisher 2  is the second algorithm type indication, and integrity algorithm id is the identifier of the integrity algorithm selected by the SGSN. 
     In some feasible implementation manners, a GPRS system requires a 128-bit second integrity key, and in this case, preset 128 bits (for example, the most significant 128 bits) may be intercepted from the computed intermediate key Km as one of input parameters of a key derivation function KDF, and an output of the KDF is used as the second integrity key; or the computed intermediate key Km may be directly used as one of input parameters of a key derivation function KDF, and preset 128 bits (for example, the most significant 128 bits) are intercepted from an output of the KDF as the second integrity key; or the intermediate key Kc 128  may be used as one of input parameters of a key derivation function KDF, and an output of the key derivation function KDF is used as the second integrity key. 
     In some feasible implementation manners, a GPRS system requires a 64-bit second integrity key, and in this case, preset 64 bits (for example, the most significant 64 bits) may be intercepted from the computed intermediate key Km as one of input parameters of a key derivation function KDF, and an output of the KDF is used as the second integrity key; or the computed intermediate key Km may be directly used as one of input parameters of a key derivation function KDF, and preset 64 bits (for example, the most significant 64 bits) are intercepted from an output of the KDF as the second integrity key; or the intermediate key Kc (64-bit) may be used as one of input parameters of a key derivation function KDF, and an output of the key derivation function KDF is used as the second integrity key. 
     In this embodiment of this application, the first algorithm type indication is used to indicate that an algorithm currently participating in an operation is an algorithm of a ciphering type, and the second algorithm type indication is used to indicate that an algorithm currently participating in an operation is an algorithm of an integrity type. In some feasible embodiments, the first algorithm type indication and the second algorithm type indication may include a same IE, and the first algorithm type indication and the second algorithm type indication are distinguished by using different values of the IE. For example, the IEs of the first algorithm type indication and the second algorithm type indication are both algorithm type distinguisher. When algorithm type distinguisher=00, it indicates an algorithm of a ciphering type. When algorithm type distinguisher=01, it indicates an algorithm of an integrity type. 
     In some possible cases, the ciphering algorithm and the integrity algorithm may use a same identifier, and in these cases, each algorithm needs to be uniquely distinguished with reference to an algorithm type indication. For example, if both a 128-EEM algorithm and 128-EIA1 algorithm use 1 as an algorithm identifier, when the ciphering algorithm and the integrity algorithm that are selected by the SGSN are the 128-EEM algorithm and the 128-EIA1 algorithm respectively, the 128-EEM algorithm and the 128-EIA1 algorithm may be distinguished by using different values of IEs in the first algorithm type indication and the second algorithm type indication. In addition, values of the computed second ciphering key and the computed second integrity key may be made different, so as to distinguish between the second ciphering key and the second integrity key. 
     In some feasible implementation manners, as shown in  FIG. 19 , the acquiring module  1703  may include a fourth computation unit  17034  and a fifth computation unit  17035 . 
     The fourth computation unit  17034  is configured to compute the second ciphering key according to the first ciphering key, a first algorithm type indication, and an identifier of the ciphering algorithm. 
     In some feasible implementation manners, before the fourth computation unit  17034  computes the second ciphering key and the fifth computation unit  17035  computes the second integrity key, the UE first computes an expected message authentication code XMAC according to the authentication token AUTN and the random number RAND that are sent by the SGSN, and performs authentication on the SGSN side by determining whether the expected message authentication code XMAC is the same as a message authentication code MAC in the authentication token AUTN. After authentication on the SGSN side succeeds, the UE computes the first ciphering key CK and the first integrity key IK according to the random number RAND and the authentication token AUTN that are sent by the SGSN, computes a random number response RES, and sends the random number response RES to the SGSN, so that the SGSN side performs authentication on the UE. 
     Specifically, the fourth computation unit  17034  may use the first ciphering key, the first algorithm type indication, and the identifier of the selected ciphering algorithm as input parameters of a key derivation function KDF to compute the second ciphering key. For example, K cipher =KDF(CK, algorithm type distinguisher 1 , ciphering algorithm id), where CK is the first ciphering key, algorithm type distinguisher 1  is the first algorithm type indication, and ciphering algorithm id is the identifier of the ciphering algorithm selected by the SGSN. 
     Optionally, if a GPRS system requires a 64-bit second ciphering key, the most significant 64 bits may be selected from computed K cipher  as the second ciphering key; if the GPRS system requires a 128-bit second ciphering key, the most significant 128 bits may be selected from computed K cipher  as the second ciphering key. In another feasible implementation manner, a required quantity of bits may be randomly selected from computed K cipher  as the second ciphering key, which is not limited in this application. 
     The fifth computation unit  17035  is configured to compute the second integrity key according to the first integrity key, a second algorithm type indication, and an identifier of the integrity algorithm. 
     Specifically, the fifth computation unit  17035  may use the first integrity key, the second algorithm type indication, and the identifier of the selected integrity algorithm as input parameters of a key derivation function KDF to compute the second integrity key. For example, K integrity =KDF(IK, algorithm type distinguisher 2 , integrity algorithm id), where IK is the first integrity key, algorithm type distinguisher 2  is the second algorithm type indication, and integrity algorithm id is the identifier of the integrity algorithm selected by the SGSN. 
     Optionally, if a GPRS system requires a 64-bit second integrity key, the most significant 64 bits may be selected from computed K integrity  as the second integrity key; if the GPRS system requires a 128-bit second integrity key, the most significant 128 bits may be selected from computed K integrity  as the second integrity key. 
     In this embodiment of this application, the first algorithm type indication is used to indicate that an algorithm currently participating in an operation is an algorithm of a ciphering type, and the second algorithm type indication is used to indicate that an algorithm currently participating in an operation is an algorithm of an integrity type. Values of the first algorithm type indication and the second algorithm type indication are different. In some feasible embodiments, the first algorithm type indication and the second algorithm type indication may include a same IE, and the first algorithm type indication and the second algorithm type indication are distinguished by using different values of the IE. For example, the IEs of the first algorithm type indication and the second algorithm type indication are both algorithm type distinguisher. When algorithm type distinguisher=00, it indicates an algorithm of a ciphering type. When algorithm type distinguisher=01, it indicates an algorithm of an integrity type. 
     In some possible cases, the ciphering algorithm and the integrity algorithm may use a same identifier, and in these cases, each algorithm needs to be uniquely distinguished with reference to an algorithm type indication. For example, if both a 128-EEM algorithm and 128-EIA1 algorithm use 1 as an algorithm identifier, when the ciphering algorithm and the integrity algorithm that are selected by the SGSN are the 128-EEM algorithm and the 128-EIA1 algorithm respectively, the 128-EEM algorithm and the 128-EIA1 algorithm may be distinguished by using different values of the first algorithm type indication and the second algorithm type indication. In addition, values of the computed second ciphering key and the computed second integrity key may be made different, so as to distinguish between the second ciphering key and the second integrity key. 
     In some feasible implementation manners, the acquiring module  1703  may be specifically configured to: compute an intermediate key according to the first ciphering key and the first integrity key; and use a first preset bit of the intermediate key as the second ciphering key, and use a second preset bit of the intermediate key as the second integrity key. 
     In some feasible implementation manners, before the acquiring module  1703  computes the intermediate key, the UE first computes an expected message authentication code XMAC according to the authentication token AUTN and the random number RAND that are sent by the SGSN, and performs authentication on the SGSN side by determining whether the expected message authentication code XMAC is the same as a message authentication code MAC in the authentication token AUTN. After authentication on the SGSN side succeeds, the UE computes the first ciphering key CK and the first integrity key IK according to the random number RAND and the authentication token AUTN that are sent by the SGSN, computes a random number response RES, and sends the random number response RES to the SGSN, so that the SGSN side performs authentication on the UE. 
     In a feasible implementation manner, the acquiring module  1703  may perform an operation on the first ciphering key and the first integrity key, and then use an operation result as an input parameter of a key derivation function KDF to compute the intermediate key. For example, the intermediate key may be Km=KDF(CK∥IK), where CK∥IK indicates that a join operation is performed on the first ciphering key CK and the first integrity key IK. 
     In another feasible implementation manner, the intermediate key may directly use an existing 64-bit GPRS ciphering key Kc or an existing 128-bit ciphering key Kc 128 , that is, the acquiring module  1703  may directly use the existing GPRS ciphering key Kc (64-bit) as the intermediate key, or directly use the existing Kc 128  (128-bit) as the intermediate key. Both Kc and Kc 128  are generated by means of computation according to the CK and the IK. 
     In a feasible implementation manner, the acquiring module  1703  may use a first preset bit of the intermediate key as the second ciphering key. For example, if a GPRS system requires a 64-bit second ciphering key, the most significant 64 bits of the intermediate key may be directly used as the second ciphering key; if the GPRS system requires a 128-bit second ciphering key, the most significant 128 bits of the intermediate key may be directly used as the second ciphering key. Optionally, a required quantity of bits may be randomly selected from the intermediate key as the second ciphering key, which is not limited in this application. 
     In a feasible implementation manner, the acquiring module  1703  may use a second preset bit of the intermediate key as the second integrity key. For example, if a GPRS system requires a 64-bit second integrity key, the least significant 64 bits of the intermediate key may be directly used as the second integrity key; if the GPRS system requires a 128-bit second integrity key, the least significant 128 bits of the intermediate key may be directly used as the second integrity key. Optionally, a required quantity of bits may be randomly selected from the intermediate key as the second integrity key, which is not limited in this application. 
     In some feasible implementation manners, the acquiring module  1703  may be specifically configured to: use the first ciphering key or a preset bit of the first ciphering key as the second ciphering key; and use the first integrity key or a preset bit of the first integrity key as the second integrity key. 
     In some feasible implementation manners, before the acquiring module  1703  computes the second ciphering key or the second integrity key, the UE may first compute an expected message authentication code XMAC according to the authentication token AUTN and the random number RAND, and perform authentication on the SGSN side by determining whether the expected message authentication code XMAC is the same as a message authentication code MAC in the authentication token AUTN. After authentication on the SGSN side succeeds, the UE computes the first ciphering key CK and the first integrity key IK according to the random number RAND and the authentication token AUTN that are sent by the SGSN, computes a random number response RES, and sends the random number response RES to the SGSN, so that the SGSN side performs authentication on the UE. 
     In some feasible implementation manners, if the first ciphering key is a 128-bit key, and the second ciphering key required by a GPRS system is also a 128-bit key, the first ciphering key may be directly used as the second ciphering key. If the second ciphering key required by the GPRS system is a 64-bit key, 64 preset bits may be selected from the first ciphering key as the second ciphering key. For example, the most significant 64 bits are selected as the second ciphering key. 
     In some feasible implementation manners, if the first integrity key is a 128-bit key, and the second integrity key required by a GPRS system is also a 128-bit key, the first integrity key may be directly used as the second integrity key. If the second integrity key required by the GPRS system is a 64-bit key, 64 preset bits may be selected from the first integrity key as the second integrity key. For example, the most significant 64 bits are selected as the second integrity key. 
     In this embodiment of this application, UE sends a request message to an SGSN, receives a ciphering algorithm and an integrity algorithm that are sent by the SGSN, and computes a second ciphering key and a second integrity key according to a first ciphering key and a first integrity key. Both the SGSN and the UE may perform ciphering protection and integrity protection on a communication message between the UE and the SGSN by using the second ciphering key, the second integrity key, and the ciphering algorithm and the integrity algorithm that are sent by the SGSN to the UE. This enhances security of communication of UE of a first type in a GPRS network. 
     Refer to  FIG. 20 .  FIG. 20  is a schematic structural diagram of another embodiment of UE according to this application. As shown in  FIG. 20 , the UE may include a sending apparatus  2001 , a receiving apparatus  2002 , and a processor  2003 , where the sending apparatus  2001 , the receiving apparatus  2002 , and the processor  2003  may be connected by using a bus. 
     The sending apparatus  2001  is configured to send a request message to an SGSN. 
     The receiving apparatus  2002  is configured to receive a ciphering algorithm and an integrity algorithm that are sent by the SGSN. 
     The processor  2003  is configured to acquire a second ciphering key and a second integrity key according to a first ciphering key and a first integrity key. 
     The second ciphering key and the ciphering algorithm are used to perform ciphering protection on a message transmitted between the SGSN and the UE, and the second integrity key and the integrity algorithm are used to perform integrity protection on a message transmitted between the SGSN and the UE. 
     In some feasible implementation manners, the request message sent by the sending apparatus  2001  to the SGSN includes UE type indication information, where the UE type indication information is used to indicate that the UE is UE of a first type. 
     In some feasible implementation manners, that the processor  2003  acquires a second ciphering key and a second integrity key according to a first ciphering key and a first integrity key includes: computing, by the processor  2003 , an intermediate key according to the first ciphering key and the first integrity key; computing, by the processor  2003 , the second ciphering key according to the intermediate key and a ciphering characteristic string; and computing, by the processor  2003 , the second integrity key according to the intermediate key and an integrity characteristic string. 
     In some feasible implementation manners, that the processor  2003  acquires a second ciphering key and a second integrity key according to a first ciphering key and a first integrity key includes: computing, by the processor  2003 , an intermediate key according to the first ciphering key and the first integrity key; and using, by the processor  2003 , a first preset bit of the intermediate key as the second ciphering key, and using a second preset bit of the intermediate key as the second integrity key; or computing, by the processor  2003 , the second ciphering key according to the first ciphering key, a first algorithm type indication, and an identifier of the ciphering algorithm, and computing, by the processor  2003 , the second integrity key according to the first integrity key, a second algorithm type indication, and an identifier of the integrity algorithm; or using, by the processor  2003 , the first ciphering key or a preset bit of the first ciphering key as the second ciphering key, and using, by the processor  2003 , the first integrity key or a preset bit of the first integrity key as the second integrity key. 
     In some feasible implementation manners, the first ciphering key is a ciphering key CK in an authentication vector quintet, and the first integrity key is an integrity key IK in the authentication vector quintet. 
     In some feasible implementation manners, the intermediate key is a 64-bit GPRS ciphering key Kc or a 128-bit ciphering key Kc 128 . 
     In this embodiment of this application, UE sends a request message to an SGSN, computes a second ciphering key and a second integrity key according to a ciphering algorithm and an integrity algorithm that are selected by the SGSN, a first ciphering key, and a first integrity key, and performs ciphering protection and integrity protection on a communication message between the UE and the SGSN by using the second ciphering key and the second integrity key. This enhances security of communication of UE of a first type in a GPRS network. 
     Refer to  FIG. 21 .  FIG. 21  is a schematic structural diagram of an embodiment of an HLR/HSS according to an embodiment of this application. As shown in  FIG. 21 , the HLR/HSS may include a receiving module  2101 , a determining module  2102 , and a sending module  2103 . 
     The receiving module  2101  is configured to receive an identifier of user equipment UE that is sent by a serving GPRS support node SGSN. 
     The home location register (HLR) is a permanent database of a GPRS system, and stores information required for managing communication of many mobile users, including static information such as identity information, service information, and service authorization that are of a registered mobile user, and dynamic information such as location information of a user. The home subscription system HSS (Home Subscription System, HSS) is evolution and upgrade of the HLR, and is mainly responsible for managing subscription data of a user and location information of a mobile user. Because the HSS and the HLR have a similar function in a network, and much data stored in the HSS is repeatedly stored in the HLR, generally, an HSS and HLR convergence device is presented to the outside. In this embodiment of this application, the HLR/HSS may be an HLR device, an HSS device, or an HLR and HSS convergence device. 
     In this embodiment of this application, the UE communicates with a network by using a USIM card, and the identifier of the UE may be an IMSI (International Mobile Subscriber Identification Number) of the USIM card. 
     The determining module  2102  is configured to determine, according to the identifier of the UE, that the UE is UE of a first type. 
     In specific implementation, the HLR/HSS stores various information of many UEs. After receiving the identifier of the UE that is sent by the SGSN, the HLR/HSS may query information about the UE, so as to determine whether the UE is UE of the first type. In this embodiment of this application, an example in which the UE is UE of the first type is used for description. 
     In this embodiment of this application, UE of the first type may include Internet of Things UE, machine to machine (M2M) communication UE, or other high-security UE. The Internet of Things UE refers to user equipment that has an information sensing function and a data transmission function, for example, an audio guide, a personal digital assistant, a barcode collector, a data collection terminal, and a POS terminal that is mainly used for purchase or transfer. The machine to machine communication UE refers to user equipment that has a networking and communication capability and that implements an “intelligence” attribute by using a sensor, a controller, and the like, so as to exchange information with a person, a mobile network, or another machine. 
     The sending module  2103  is configured to send UE type indication information to the SGSN, where the UE type indication information is used to indicate that the UE is UE of the first type. 
     Optionally, the UE type indication information may indicate, according to existence of a specific information element (IE), that the UE is UE of the first type. For example, when the SGSN receives the UE type indication information sent by the HLR/HSS or the UE, if a specific IE exists in the UE type indication information, the SGSN may determine that the UE is UE of the first type, and if the specific IE does not exist in the UE type indication information, the SGSN may determine that the UE is not UE of the first type. Alternatively, the UE type indication information may also indicate, according to a value of a specific IE, that the UE is UE of the first type. For example, when the SGSN receives the UE type indication information sent by the HLR/HSS or the UE, if a value of a specific IE in the UE type indication information is 1, the SGSN may determine that the UE is UE of the first type, and if the value of the specific IE is 0, the SGSN may determine that the UE is not UE of the first type. 
     In this embodiment of this application, the HLR/HSS may further send an authentication vector to the SGSN, where the authentication vector includes a first ciphering key and a first integrity key. 
     In some feasible implementation manners, the foregoing authentication vector may be an authentication vector quintet, which includes a random number RAND, an expected response XRES, an authentication token AUTN, a ciphering key CK, and an integrity key IK. The first ciphering key is the ciphering key CK in the authentication vector quintet, and the first integrity key is the integrity key IK in the authentication vector quintet. 
     In this embodiment of this application, an HLR/HSS may receive an identifier of UE that is sent by an SGSN, determine, according to the identifier of the UE, that the UE is UE of a first type, and send UE type indication information to the SGSN so as to indicate that the UE is UE of the first type, so that key enhancement processing for the UE of the first type may be performed between the SGSN and the UE of the first type, and security of communication of the UE of the first type in a GPRS network is enhanced. 
     Refer to  FIG. 22 .  FIG. 22  is a schematic structural diagram of another embodiment of an HLR/HSS according to an embodiment of this application. As shown in  FIG. 22 , the HLR/HSS may include a receiving apparatus  2201 , a sending apparatus  2202 , and a processor  2203 , where the receiving apparatus  2201 , the sending apparatus  2202 , and the processor  2203  are connected by using a bus. 
     The receiving apparatus  2201  is configured to receive an identifier of user equipment UE that is sent by an SGSN. 
     The processor  2203  is configured to determine, according to the identifier of the UE, that the UE is UE of a first type. 
     The sending apparatus  2202  is configured to send UE type indication information to the SGSN, where the UE type indication information is used to indicate that the UE is UE of the first type. 
     In this embodiment of this application, an HLR/HSS may receive an identifier of UE that is sent by an SGSN, determine, according to the identifier of the UE, that the UE is UE of a first type, and send UE type indication information to the SGSN so as to indicate that the UE is UE of the first type, so that key enhancement processing for the UE of the first type may be performed between the SGSN and the UE of the first type, and security of communication of the UE of the first type in a GPRS network is enhanced. 
     Refer to  FIG. 23 .  FIG. 23  is a schematic structural diagram of an embodiment of a GPRS system according to an embodiment of this application. As shown in  FIG. 23 , the GPRS system may include an SGSN device  2301 , UE  2302 , and an HLR/HSS  2303 . 
     The SGSN device is configured to: receive a request message sent by the UE, acquire an authentication vector from the HLR/HSS, where the authentication vector includes a first ciphering key and a first integrity key, if the SGSN determines that the UE is UE of a first type, select a ciphering algorithm and an integrity algorithm for the UE, send the selected ciphering algorithm and the selected integrity algorithm to the UE, and obtain a second ciphering key and a second integrity key according to the first ciphering key and the first integrity key. 
     The UE is configured to: send the request message to the SGSN, receive the ciphering algorithm and the integrity algorithm that are sent by the SGSN, and acquire the second ciphering key and the second integrity key according to the first ciphering key and the first integrity key. 
     The second ciphering key and the ciphering algorithm are used to perform ciphering protection on a message transmitted between the SGSN and the UE, and the second integrity key and the integrity algorithm are used to perform integrity protection on a message transmitted between the SGSN and the UE. 
     In some feasible implementation manners, the HLR/HSS  2303  may be configured to: receive an identifier of the UE that is sent by the SGSN; determine, according to the identifier of the UE, that the UE is UE of the first type; and send UE type indication information to the SGSN, where the UE type indication information is used to indicate that the UE is UE of the first type. 
     In this embodiment of this application, UE sends a request message to an SGSN. After determining that the UE is UE of a first type, the SGSN selects a ciphering algorithm and an integrity algorithm. Both the UE and the SGSN compute an enhanced second ciphering key and an enhanced second integrity key according to a first ciphering key and a first integrity key, and perform ciphering protection and integrity protection on a communication message between the UE and the SGSN by using the second ciphering key, the second integrity key, and the ciphering algorithm and the integrity algorithm that are selected by the SGSN. This enhances security of communication of UE of the first type in a GPRS network. 
     Accordingly, an embodiment of this application further discloses a computer storage medium, where the computer storage medium stores a program, and when the program runs, the embodiments described in any one of  FIG. 1  to  FIG. 5  of this application may be performed. 
     Accordingly, an embodiment of this application further discloses another computer storage medium, where the computer storage medium stores a program, and when the program runs, the embodiments described in any one of  FIG. 6  to  FIG. 10  of this application may be performed. 
     Accordingly, an embodiment of this application further discloses still another computer storage medium, where the computer storage medium stores a program, and when the program runs, the embodiment described in  FIG. 11  of this application may be performed. 
     It should be noted that, for brief description, the foregoing method embodiments are represented as a series of actions. However, persons skilled in the art should appreciate that this application is not limited to the described order of the actions, because according to this application, some steps may be performed in other orders or simultaneously. It should be further appreciated by persons skilled in the art that the embodiments described in this specification all belong to embodiments, and the involved actions and modules are not necessarily required by this application. 
     In the foregoing embodiments, the description of each embodiment has respective focuses. For a part that is not described in detail in an embodiment, reference may be made to related descriptions in other embodiments. 
     Persons of ordinary skill in the art may understand that all or some of the steps of the methods in the embodiments may be implemented by a program instructing relevant hardware. The program may be stored in a computer readable storage medium. The storage medium may include a flash memory, a read-only memory (ROM), a random access memory (RAM), a magnetic disk, and an optical disc. 
     The foregoing describes in detail the GPRS system key enhancement method, the SGSN device, the UE, the HLR/HSS, and the GPRS system provided in the embodiments of this application. Specific examples are used in this specification to describe the principle and implementation manners of this application. The descriptions of the foregoing embodiments are merely intended to facilitate understanding of the method and core idea of this application. In addition, with respect to the specific implementation manners and the application scope, modifications may be made by persons of ordinary skill in the art according to the idea of this application. In conclusion, the content of this specification shall not be understood as a limitation on this application.