Patent Publication Number: US-11051171-B2

Title: Communication method, related device, and system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of International Application No. PCT/CN2018/077920, filed on Mar. 2, 2018, which claims priority to Chinese Patent Application No. 201710208884.3, filed on Mar. 31, 2017. The disclosures of the aforementioned applications are hereby incorporated by reference in their entireties. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to the field of communications technologies, and in particular, to a communication method, a related device, and a system. 
     BACKGROUND 
     In an existing long term evolution (LTE) security architecture, user equipment (UE) accesses an operator network by using a base station. Control plane data and user plane data are transmitted between the UE and the base station. Protocol stack formats used when the two types of data are transmitted each include a packet data convergence protocol (PDCP) layer. Information at the PDCP layer may be used for encryption/decryption and integrity protection of data. There are a plurality of PDCP formats, and each format includes a PDCP SN field that is briefly referred to as a sequence number (SN) below.  FIG. 1A  shows a PDCP format. The PDCP format includes a PDCP SN field and a data field. The data field is used to encapsulate user data. The PDCP SN field is used to encapsulate a parameter SN that is at the PDCP layer and that is used for encryption/decryption and/or integrity protection. 
       FIG. 1B  is a schematic diagram of an encryption/decryption scenario. In  FIG. 1B , the left side of a dashed line indicates an encryption procedure, and the right side of the dashed line indicates a decryption procedure. An algorithm used in each of the encryption procedure and the decryption procedure may be represented by using f8. Input of f8 includes: a cipher key (CK), a counter (also referred to as Count-C), a bearer identifier (Bearer), a direction, and a length (e.g., a length identifier). Integrity protection of data is similar to encryption/decryption, and the counter parameter needs to be used for both integrity protection and encryption/decryption. The counter generally includes a hyper frame number (HFN) and a SN. A keystream block, a plaintext block, and a ciphertext block may be further used in a key generation process. Encryption is usually performed by a sender, and decryption is usually performed by a receiver. For example, when the UE is a sender, a radio network controller (RNC) is a receiver; or when an RNC is a receiver, the UE is a sender. The SN in the PDCP SN field needs to be sent by using plaintext, so that the receiver can complete decryption or integrity verification based on the SN. However, the SN sent by using the plaintext is easily intercepted by an attacker. When UE is handed over from one base station to another base station, if the attacker intercepts, near the two base stations, a plaintext SN sent by the UE, a moving status of the UE can be determined, and this is unfavorable for security of the UE. 
     SUMMARY 
     To resolve a technical problem, embodiments of the present invention provide a communication method, a related device, and a system, to improve security performance of UE. 
     According to a first aspect, an embodiment of the present invention provides a communications system, where the system includes a terminal, a first access network node (AN), and a second access network node AN, where the first AN is configured to determine that the terminal meets a condition of being handed over from the first AN to the second AN, where a value of a target parameter used for encryption and/or integrity protection when the terminal and the first AN communicate with each other before the terminal is handed over to the second AN is equal to a first reference value, and the target parameter is a counter or a sequence number (SN); the first AN is configured to send a target message to the second AN, to instruct the second AN to obtain a second reference value; the second AN is configured to obtain the second reference value based on the target message; and the terminal is configured to obtain the second reference value, where the second reference value is used as a value of the target parameter used for encryption and/or integrity protection when the second AN and the terminal communicate with each other. 
     The system is run, so that when the terminal is handed over from the first AN to the second AN for communication, the terminal and the second AN both obtain the second reference value, and encryption and/or integrity protection are/is subsequently performed between the terminal and the second AN by using the second reference value instead of still using the first reference value. In this way, when an attacker intercepts the first reference value used before the terminal is handed over and the second reference value used after the terminal is handed over, because the first reference value is different from the second reference value, the attacker does not deduce that the first reference value and the second reference value come from a same terminal, thereby improving security performance of the terminal. 
     With reference to the first aspect, in a first possible embodiment of the first aspect, the system includes mobility management (MM); the first AN is configured to send a target request to the MM, to request the MM to generate the second reference value, and receive the second reference value sent by the MM, where the target message includes the second reference value; and the MM is configured to receive the target request, generate the second reference value based on the target request, and send the generated second reference value to the first AN. 
     With reference to the first aspect or any one of the foregoing possible embodiment of the first aspect, in a second possible embodiment of the first aspect, the first AN is configured to randomly generate the second reference value by using a randomized algorithm, or derive the second reference value according to a preset rule, where the target message includes the second reference value; and that the second AN is configured to obtain the second reference value based on the target message includes: the second AN is configured to parse out the second reference value from the target message. 
     With reference to the first aspect or either of the foregoing possible embodiments of the first aspect, in a third possible embodiment of the first aspect, the first AN is configured to send the second reference value to the terminal; and that the terminal is configured to obtain the second reference value includes: the terminal is configured to receive the second reference value sent by the first AN. 
     With reference to the first aspect or any one of the foregoing possible embodiments of the first aspect, in a fourth possible embodiment of the first aspect, that the second AN is configured to obtain the second reference value based on the target message includes: the second AN is configured to randomly generate the second reference value based on the target message by using a randomized algorithm, or derive the second reference value based on the target message according to a preset rule. 
     With reference to the first aspect or any one of the foregoing possible embodiments of the first aspect, in a fifth possible embodiment of the first aspect, the system includes mobility management (MM); that the second AN is configured to obtain the second reference value based on the target message includes: the second AN is configured to send a target request to the MM based on the target message, to request the MM to generate the second reference value, and receive the second reference value sent by the MM; and the MM is configured to receive the target request, generate the second reference value based on the target request, and send the generated second reference value to the second AN. 
     With reference to the first aspect or any one of the foregoing possible embodiments of the first aspect, in a sixth possible embodiment of the first aspect, the second AN is configured to send the second reference value to the first AN; and the first AN is configured to send the second reference value to the terminal. 
     With reference to the first aspect or any one of the foregoing possible embodiments of the first aspect, in a seventh possible embodiment of the first aspect, the second AN is configured to send the second reference value to the terminal. 
     With reference to the first aspect or any one of the foregoing possible embodiments of the first aspect, in an eighth possible embodiment of the first aspect, the first AN is configured to send a parameter generation request to the terminal; and that the terminal is configured to obtain the second reference value includes: the terminal is configured to randomly generate the second reference value based on the parameter generation request by using the randomized algorithm, or derive the second reference value based on the parameter generation request according to the preset rule. 
     According to a second aspect, an embodiment of the present invention provides an access network node (AN), where the AN is a first AN, the first AN includes a processor, a memory, and a transceiver, the memory is configured to store a program, and the processor invokes the program in the memory to perform the following operations: determining that a terminal accessing the first AN meets a condition of being handed over from the first AN to a second AN, where a value of a target parameter used for encryption and/or integrity protection when the terminal and the first AN communicate with each other before the terminal is handed over to the second AN is equal to a first reference value, and the target parameter is a counter or a sequence number SN; and sending a target message to the second AN by using the transceiver, to instruct the second AN to obtain a second reference value, where the second reference value is used as a value of the target parameter used for encryption and/or integrity protection when the second AN and the terminal communicate with each other. 
     The foregoing operations are performed, so that when the terminal is handed over from the first AN to the second AN for communication, the terminal and the second AN both obtain the second reference value, and encryption and/or integrity protection are/is subsequently performed between the terminal and the second AN by using the second reference value instead of still using the first reference value. In this way, when an attacker intercepts the first reference value used before the terminal is handed over and the second reference value used after the terminal is handed over, because the first reference value is different from the second reference value, the attacker does not deduce that the first reference value and the second reference value come from a same terminal, thereby improving security performance of the terminal. 
     With reference to the second aspect, in a first possible embodiment of the second aspect, before the processor sends the target message to the second AN by using the transceiver, to instruct the second AN to obtain the second reference value, the processor is further configured to send a target request to an MM by using the transceiver, to request the MM to generate the second reference value, and receive, by using the transceiver, the second reference value that is generated by the MM based on the target request and that is sent by the MM, where the target message includes the second reference value. 
     With reference to the second aspect or any one of the foregoing possible embodiment of the second aspect, in a second possible embodiment of the second aspect, before the processor sends the target message to the second AN by using the transceiver, to instruct the second AN to obtain the second reference value, the processor is further configured to randomly generate the second reference value by using a randomized algorithm, or derive the second reference value according to a preset rule, where the target message includes the second reference value. 
     With reference to the second aspect or either of the foregoing possible embodiments of the second aspect, in a third possible embodiment of the second aspect, the processor is further configured to send the second reference value to the terminal by using the transceiver. 
     With reference to the second aspect or either of the foregoing possible embodiments of the second aspect, in a fourth possible embodiment of the second aspect, the processor is further configured to send a parameter generation request to the terminal by using the transceiver, so that the terminal randomly generates the second reference value based on the parameter generation request by using the randomized algorithm, or derives the second reference value based on the parameter generation request according to the preset rule. 
     According to a third aspect, an embodiment of the present invention provides an access network node (AN), where the AN is a second AN, the second AN includes a processor, a memory, and a transceiver, the memory is configured to store a program, and the processor invokes the program in the memory to perform the following operations: receiving, by using the transceiver, a target message sent by a first AN, where the target message is a message sent by the first AN when the first AN determines that the terminal meets a condition of being handed over from the first AN to the second AN, a value of a target parameter used for encryption and/or integrity protection when the terminal and the first AN communicate with each other before the terminal is handed over to the second AN is equal to a first reference value, and the target parameter is a counter or a sequence number SN; and obtaining a second reference value based on the target message, where the second reference value is used as a value of the target parameter used for encryption and/or integrity protection when the second AN and the terminal communicate with each other. 
     The foregoing operations are performed, so that when the terminal is handed over from the first AN to the second AN for communication, the terminal and the second AN both obtain the second reference value, and encryption and/or integrity protection are/is subsequently performed between the terminal and the second AN by using the second reference value instead of still using the first reference value. In this way, when an attacker intercepts the first reference value used before the terminal is handed over and the second reference value used after the terminal is handed over, because the first reference value is different from the second reference value, the attacker does not deduce that the first reference value and the second reference value come from a same terminal, thereby improving security performance of the terminal. 
     With reference to the third aspect, in a first possible embodiment of the third aspect, the target message includes the second reference value, and that the processor obtains a second reference value based on the target message is specifically: parsing out the second reference value from the target message. 
     With reference to the third aspect or any one of the foregoing possible embodiment of the third aspect, in a second possible embodiment of the third aspect, that the processor obtains a second reference value based on the target message is specifically: randomly generating the second reference value based on the target message by using a randomized algorithm, or deriving the second reference value based on the target message according to a preset rule. 
     With reference to the third aspect or either of the foregoing possible embodiments of the third aspect, in a third possible embodiment of the third aspect, that the processor obtains a second reference value based on the target message is specifically: sending a target request to an MM based on the target message by using the transceiver, to request the MM to generate the second reference value; and receiving, by using the transceiver, the second reference value sent by the MM. 
     With reference to the third aspect or any one of the foregoing possible embodiments of the third aspect, in a fourth possible embodiment of the third aspect, after the processor is configured to obtain the second reference value based on the target message, the processor is further configured to send the second reference value to the first AN by using the transceiver, so that the first AN sends the second reference value to the terminal. 
     With reference to the third aspect or any one of the foregoing possible embodiments of the third aspect, in a fifth possible embodiment of the third aspect, after the processor is configured to obtain the second reference value based on the target message, the processor is further configured to send the second reference value to the terminal by using the transceiver. 
     According to a fourth aspect, an embodiment of the present invention provides a terminal, where the terminal includes a processor, a memory, and a transceiver, the memory is configured to store a program, and the processor invokes the program in the memory to perform the following operations: if the terminal meets a condition of being handed over from a first AN to a second AN, generating a second reference value, or receiving, by using the transceiver, the second reference value sent by the first AN, or receiving, by using the transceiver, the second reference value sent by the second AN, where the second reference value is used as a value of a target parameter used for encryption and/or integrity protection when the second AN and the terminal communicate with each other, a value of the target parameter used for encryption and/or integrity protection when the terminal and the first AN communicate with each other before the terminal is handed over to the second AN is equal to a first reference value, and the target parameter is a counter or a sequence number (SN). 
     The foregoing operations are performed, so that when the terminal is handed over from the first AN to the second AN for communication, the terminal and the second AN both obtain the second reference value, and encryption and/or integrity protection are/is subsequently performed between the terminal and the second AN by using the second reference value instead of still using the first reference value. In this way, when an attacker intercepts the first reference value used before the terminal is handed over and the second reference value used after the terminal is handed over, because the first reference value is different from the second reference value, the attacker does not deduce that the first reference value and the second reference value come from a same terminal, thereby improving security performance of the terminal. 
     With reference to the fourth aspect, in a first possible embodiment of the fourth aspect, that the processor generates a second reference value is specifically: receiving, by using the transceiver, a parameter generation request sent by the first AN when the first AN determines that the terminal meets the condition of being handed over from the first AN to the second AN; and randomly generating the second reference value based on the parameter generation request by using a randomized algorithm, or deriving the second reference value based on the parameter generation request according to the preset rule. 
     According to a fifth aspect, an embodiment of the present invention provides an access network node (AN), where the AN may be referred to as a first AN, and the first AN includes a determining unit and a first sending unit, where the determining unit is configured to determine that a terminal accessing the first AN meets a condition of being handed over from the first AN to a second AN, where a value of a target parameter used for encryption and/or integrity protection when the terminal and the first AN communicate with each other before the terminal is handed over to the second AN is equal to a first reference value, and the target parameter is a counter or a sequence number (SN); and the first sending unit is configured to send a target message to the second AN, to instruct the second AN to obtain a second reference value, where the second reference value is used as a value of the target parameter used for encryption and/or integrity protection when the second AN and the terminal communicate with each other. 
     The foregoing units are run, so that when the terminal is handed over from the first AN to the second AN for communication, the terminal and the second AN both obtain the second reference value, and encryption and/or integrity protection are/is subsequently performed between the terminal and the second AN by using the second reference value instead of still using the first reference value. In this way, when an attacker intercepts the first reference value used before the terminal is handed over and the second reference value used after the terminal is handed over, because the first reference value is different from the second reference value, the attacker does not deduce that the first reference value and the second reference value come from a same terminal, thereby improving security performance of the terminal. 
     With reference to the fifth aspect, in a first possible embodiment of the fifth aspect, the first AN further includes a second processing unit, where the second processing unit is configured to, before the first sending unit sends the target message to the second AN to instruct the second AN to obtain the second reference value, send a target request to an MM to request the MM to generate the second reference value, and receive the second reference value that is generated by the MM based on the target request and that is sent by the MM, where the target message includes the second reference value. 
     With reference to the fifth aspect or any one of the foregoing possible embodiment of the fifth aspect, in a second possible embodiment of the fifth aspect, the first AN further includes a calculation unit, where the calculation unit is configured to, before the first sending unit sends the target message to the second AN to instruct the second AN to obtain the second reference value, randomly generate the second reference value by using a randomized algorithm, or derive the second reference value according to a preset rule, where the target message includes the second reference value. 
     With reference to the fifth aspect or either of the foregoing possible embodiments of the fifth aspect, in a third possible embodiment of the fifth aspect, the first AN further includes a second sending unit, where the second sending unit is configured to send the second reference value to the terminal. 
     With reference to the fifth aspect or either of the foregoing possible embodiments of the fifth aspect, in a fourth possible embodiment of the fifth aspect, the first AN further includes a third sending unit, where the third sending unit is configured to send a parameter generation request to the terminal, so that the terminal randomly generates the second reference value based on the parameter generation request by using the randomized algorithm, or derives the second reference value based on the parameter generation request according to the preset rule. 
     According to a sixth aspect, an embodiment of the present invention provides an AN, where the AN is a second AN, and the second AN includes a first receiving unit and an obtaining unit, where the first receiving unit is configured to receive a target message sent by a first AN, where the target message is a message sent by the first AN when the first AN determines that the terminal meets a condition of being handed over from the first AN to the second AN, a value of a target parameter used for encryption and/or integrity protection when the terminal and the first AN communicate with each other before the terminal is handed over to the second AN is equal to a first reference value, and the target parameter is a counter or a sequence number (SN); and the obtaining unit is configured to obtain a second reference value based on the target message, where the second reference value is used as a value of the target parameter used for encryption and/or integrity protection when the second AN and the terminal communicate with each other. 
     The foregoing units are run, so that when the terminal is handed over from the first AN to the second AN for communication, the terminal and the second AN both obtain the second reference value, and encryption and/or integrity protection are/is subsequently performed between the terminal and the second AN by using the second reference value instead of still using the first reference value. In this way, when an attacker intercepts the first reference value used before the terminal is handed over and the second reference value used after the terminal is handed over, because the first reference value is different from the second reference value, the attacker does not deduce that the first reference value and the second reference value come from a same terminal, thereby improving security performance of the terminal. 
     With reference to the sixth aspect, in a first possible embodiment of the sixth aspect, the target message includes the second reference value, and that the obtaining unit obtains a second reference value based on the target message is specifically: parsing out the second reference value from the target message. 
     With reference to the sixth aspect or any one of the foregoing possible embodiment of the sixth aspect, in a second possible embodiment of the sixth aspect, that the obtaining unit obtains a second reference value based on the target message is specifically: randomly generating the second reference value based on the target message by using a randomized algorithm, or deriving the second reference value based on the target message according to a preset rule. 
     With reference to the sixth aspect or either of the foregoing possible embodiments of the sixth aspect, in a third possible embodiment of the sixth aspect, that the obtaining unit obtains a second reference value based on the target message is specifically: sending a target request to an MM based on the target message, to request the MM to generate the second reference value; and receiving the second reference value sent by the MM. 
     With reference to the sixth aspect or any one of the foregoing possible embodiments of the sixth aspect, in a fourth possible embodiment of the sixth aspect, the second AN further includes a fourth sending unit, where the fourth sending unit is configured to, after the obtaining unit obtains the second reference value based on the target message, send the second reference value to the first AN, so that the first AN sends the second reference value to the terminal. 
     With reference to the sixth aspect or any one of the foregoing possible embodiments of the sixth aspect, in a fifth possible embodiment of the sixth aspect, the second AN further includes a fifth sending unit, where the fifth sending unit is configured to, after the second AN obtains the second reference value based on the target message, send the second reference value to the terminal. 
     According to a seventh aspect, an embodiment of the present invention provides a terminal, where the terminal includes a processing unit, where the processing unit is configured to, when the terminal meets a condition of being handed over from a first AN to a second AN, generate a second reference value, or receive the second reference value sent by the first AN, or receive the second reference value sent by the second AN, where the second reference value is used as a value of a target parameter used for encryption and/or integrity protection when the second AN and the terminal communicate with each other, a value of the target parameter used for encryption and/or integrity protection when the terminal and the first AN communicate with each other before the terminal is handed over to the second AN is equal to a first reference value, and the target parameter is a counter or a sequence number SN. 
     The foregoing unit is run, so that when the terminal is handed over from the first AN to the second AN for communication, the terminal and the second AN both obtain the second reference value, and encryption and/or integrity protection are/is subsequently performed between the terminal and the second AN by using the second reference value instead of still using the first reference value. In this way, when an attacker intercepts the first reference value used before the terminal is handed over and the second reference value used after the terminal is handed over, because the first reference value is different from the second reference value, the attacker does not deduce that the first reference value and the second reference value come from a same terminal, thereby improving security performance of the terminal. 
     With reference to the seventh aspect, in a first possible embodiment of the seventh aspect, that the terminal generates a second reference value is specifically: receiving a parameter generation request sent by the first AN when the first AN determines that the terminal meets the condition of being handed over from the first AN to the second AN; and randomly generating the second reference value based on the parameter generation request by using a randomized algorithm, or deriving the second reference value based on the parameter generation request according to the preset rule. 
     According to an eighth aspect, an embodiment of the present invention provides a communication method, where the communication method includes: determining, by a first AN, that a terminal accessing the first AN meets a condition of being handed over from the first AN to a second AN, where a value of a target parameter used for encryption and/or integrity protection when the terminal and the first AN communicate with each other before the terminal is handed over to the second AN is equal to a first reference value, and the target parameter is a counter or a sequence number (SN); and sending, by the first AN, a target message to the second AN, to instruct the second AN to obtain a second reference value, where the second reference value is used as a value of the target parameter used for encryption and/or integrity protection when the second AN and the terminal communicate with each other. 
     The foregoing steps are performed, so that when the terminal is handed over from the first AN to the second AN for communication, the terminal and the second AN both obtain the second reference value, and encryption and/or integrity protection are/is subsequently performed between the terminal and the second AN by using the second reference value instead of still using the first reference value. In this way, when an attacker intercepts the first reference value used before the terminal is handed over and the second reference value used after the terminal is handed over, because the first reference value is different from the second reference value, the attacker does not deduce that the first reference value and the second reference value come from a same terminal, thereby improving security performance of the terminal. 
     With reference to the eighth aspect, in a first possible embodiment of the eighth aspect, before the sending, by the first AN, a target message to the second AN, to instruct the second AN to obtain a second reference value, the method further includes: sending, by the first AN, a target request to the MM, to request the MM to generate the second reference value, and receiving the second reference value that is generated by the MM based on the target request and that is sent by the MM, where the target message includes the second reference value. 
     With reference to the eighth aspect or any one of the foregoing possible embodiment of the eighth aspect, in a second possible embodiment of the eighth aspect, before the sending, by the first AN, a target message to the second AN, to instruct the second AN to obtain a second reference value, the method further includes: randomly generating, by the first AN, the second reference value by using a randomized algorithm, or deriving the second reference value according to a preset rule, where the target message includes the second reference value. 
     With reference to the eighth aspect or either of the foregoing possible embodiments of the eighth aspect, in a third possible embodiment of the eighth aspect, the method further includes: sending, by the first AN, the second reference value to the terminal. 
     With reference to the eighth aspect or either of the foregoing possible embodiments of the eighth aspect, in a fourth possible embodiment of the eighth aspect, the method further includes: sending, by the first AN, a parameter generation request to the terminal, so that the terminal randomly generates the second reference value based on the parameter generation request by using the randomized algorithm, or derives the second reference value based on the parameter generation request according to the preset rule. 
     According to a ninth aspect, an embodiment of the present invention provides a communication method, where the communication method includes: receiving, by a second AN, a target message sent by a first AN, where the target message is a message sent by the first AN when the first AN determines that the terminal meets a condition of being handed over from the first AN to the second AN, a value of a target parameter used for encryption and/or integrity protection when the terminal and the first AN communicate with each other before the terminal is handed over to the second AN is equal to a first reference value, and the target parameter is a counter or a sequence number (SN); and obtaining, by the second AN, a second reference value based on the target message, where the second reference value is used as a value of the target parameter used for encryption and/or integrity protection when the second AN and the terminal communicate with each other. 
     The foregoing steps are performed, so that when the terminal is handed over from the first AN to the second AN for communication, the terminal and the second AN both obtain the second reference value, and encryption and/or integrity protection are/is subsequently performed between the terminal and the second AN by using the second reference value instead of still using the first reference value. In this way, when an attacker intercepts the first reference value used before the terminal is handed over and the second reference value used after the terminal is handed over, because the first reference value is different from the second reference value, the attacker does not deduce that the first reference value and the second reference value come from a same terminal, thereby improving security performance of the terminal. 
     With reference to the ninth aspect, in a first possible embodiment of the ninth aspect, the target message includes the second reference value, and the obtaining, by the second AN, a second reference value based on the target message includes: parsing out the second reference value from the target message. 
     With reference to the ninth aspect or any one of the foregoing possible embodiment of the ninth aspect, in a second possible embodiment of the ninth aspect, the obtaining, by the second AN, a second reference value based on the target message includes: randomly generating the second reference value based on the target message by using a randomized algorithm, or deriving the second reference value based on the target message according to a preset rule. 
     With reference to the ninth aspect or either of the foregoing possible embodiments of the ninth aspect, in a third possible embodiment of the ninth aspect, the obtaining, by the second AN, a second reference value based on the target message includes: sending a target request to an MM based on the target message, to request the MM to generate the second reference value; and receiving the second reference value sent by the MM. 
     With reference to the ninth aspect or any one of the foregoing possible embodiments of the ninth aspect, in a fourth possible embodiment of the ninth aspect, after the obtaining, by the second AN, a second reference value based on the target message, the method further includes: sending, by the second AN, the second reference value to the first AN, so that the first AN sends the second reference value to the terminal. 
     With reference to the ninth aspect or any one of the foregoing possible embodiments of the ninth aspect, in a fifth possible embodiment of the ninth aspect, after the obtaining, by the second AN, a second reference value based on the target message, the method further includes: sending, by the second AN, the second reference value to the terminal. 
     According to a tenth aspect, an embodiment of the present invention provides a communication method, where the method includes: if a terminal meets a condition of being handed over from a first AN to a second AN, generating, by the terminal, a second reference value, or receiving the second reference value sent by the first AN, or receiving the second reference value sent by the second AN, where the second reference value is used as a value of a target parameter used for encryption and/or integrity protection when the second AN and the terminal communicate with each other, a value of the target parameter used for encryption and/or integrity protection when the terminal and the first AN communicate with each other before the terminal is handed over to the second AN is equal to a first reference value, and the target parameter is a counter or a sequence number (SN). 
     The foregoing steps are performed, so that when the terminal is handed over from the first AN to the second AN for communication, the terminal and the second AN both obtain the second reference value, and encryption and/or integrity protection are/is subsequently performed between the terminal and the second AN by using the second reference value instead of still using the first reference value. In this way, when an attacker intercepts the first reference value used before the terminal is handed over and the second reference value used after the terminal is handed over, because the first reference value is different from the second reference value, the attacker does not deduce that the first reference value and the second reference value come from a same terminal, thereby improving security performance of the terminal. 
     With reference to the tenth aspect, in a first possible embodiment of the tenth aspect, the generating, by the terminal, a second reference value includes: receiving a parameter generation request sent by the first AN when the first AN determines that the terminal meets the condition of being handed over from the first AN to the second AN; and randomly generating the second reference value based on the parameter generation request by using a randomized algorithm, or deriving the second reference value based on the parameter generation request according to the preset rule. 
     According to an eleventh aspect, an embodiment of the present invention provides a communication method, where the method includes: receiving, by a mobility management node (MM), a target message, where the target message is sent by a first access network node (AN) or a second access network node (AN) to the MM when a terminal meets a condition of being handed over from the first AN to the second AN; generating, by the MM, a second reference value based on the target message; and sending, by the MM, the second reference value to the second AN, where the second reference value is used as a value of a target parameter used for encryption and/or integrity protection when the second AN and the terminal communicate with each other, a value of the target parameter used for encryption and/or integrity protection when the terminal and the first AN communicate with each other before the terminal is handed over to the second AN is equal to a first reference value, and the target parameter is a counter or a sequence number (SN). 
     The foregoing steps are performed, so that when the terminal is handed over from the first AN to the second AN for communication, the terminal and the second AN both obtain the second reference value, and encryption and/or integrity protection are/is subsequently performed between the terminal and the second AN by using the second reference value instead of still using the first reference value. In this way, when an attacker intercepts the first reference value used before the terminal is handed over and the second reference value used after the terminal is handed over, because the first reference value is different from the second reference value, the attacker does not deduce that the first reference value and the second reference value come from a same terminal, thereby improving security performance of the terminal. 
     With reference to the eleventh aspect, in a first possible embodiment of the eleventh aspect, the sending, by the MM, the second reference value to the second AN includes: sending, by the MM, the second reference value to the first AN, so that the first AN sends the second reference value to the second AN. 
     According to a twelfth aspect, an embodiment of the present invention provides a mobility management node (MM), where the MM includes a processor, a memory, and a transceiver, the memory is configured to store a program, and the processor invokes the program in the memory to perform the following operations: receiving a target message by using the transceiver, where the target message is sent by a first access network node (AN) or a second access network node (AN) to the MM when a terminal meets a condition of being handed over from the first AN to the second AN; generating a second reference value based on the target message; and sending the second reference value to the second AN by using the transceiver, where the second reference value is used as a value of a target parameter used for encryption and/or integrity protection when the second AN and the terminal communicate with each other, a value of the target parameter used for encryption and/or integrity protection when the terminal and the first AN communicate with each other before the terminal is handed over to the second AN is equal to a first reference value, and the target parameter is a counter or a sequence number (SN). 
     The foregoing operations are performed, so that when the terminal is handed over from the first AN to the second AN for communication, the terminal and the second AN both obtain the second reference value, and encryption and/or integrity protection are/is subsequently performed between the terminal and the second AN by using the second reference value instead of still using the first reference value. In this way, when an attacker intercepts the first reference value used before the terminal is handed over and the second reference value used after the terminal is handed over, because the first reference value is different from the second reference value, the attacker does not deduce that the first reference value and the second reference value come from a same terminal, thereby improving security performance of the terminal. 
     With reference to the twelfth aspect, in a first possible embodiment of the twelfth aspect, that the processor sends the second reference value to the second AN by using the transceiver is specifically: sending the second reference value to the first AN by using the transceiver, so that the first AN sends the second reference value to the second AN. 
     According to a thirteenth aspect, an embodiment of the present invention provides a mobility management node (MM), where the MM includes a receiving unit, a generation unit, and a sending unit, where the receiving unit is configured to receive a target message, where the target message is sent by a first access network node (AN) or a second access network node AN to the MM when a terminal meets a condition of being handed over from the first AN to the second AN; the generation unit is configured to generate a second reference value based on the target message; and the sending unit is configured to send the second reference value to the second AN, where the second reference value is used as a value of a target parameter used for encryption and/or integrity protection when the second AN and the terminal communicate with each other, a value of the target parameter used for encryption and/or integrity protection when the terminal and the first AN communicate with each other before the terminal is handed over to the second AN is equal to a first reference value, and the target parameter is a counter or a sequence number (SN). 
     The foregoing steps are performed, so that when the terminal is handed over from the first AN to the second AN for communication, the terminal and the second AN both obtain the second reference value, and encryption and/or integrity protection are/is subsequently performed between the terminal and the second AN by using the second reference value instead of still using the first reference value. In this way, when an attacker intercepts the first reference value used before the terminal is handed over and the second reference value used after the terminal is handed over, because the first reference value is different from the second reference value, the attacker does not deduce that the first reference value and the second reference value come from a same terminal, thereby improving security performance of the terminal. 
     With reference to the thirteenth aspect, in a first possible embodiment of the thirteenth aspect, that the sending unit sends the second reference value to the second AN is specifically: sending the second reference value to the first AN, so that the first AN sends the second reference value to the second AN. 
     According to a fourteenth aspect, an embodiment of the present invention further provides a computer storage medium. The storage medium may be non-volatile, that is, content is not lost after powering-off. The storage medium stores a software program, and when the software program is read and executed by one or more processors, the method provided in the eighth aspect or any possible embodiment of the eighth aspect may be implemented. 
     According to a fifteenth aspect, an embodiment of the present invention further provides another computer storage medium. The storage medium may be non-volatile, that is, content is not lost after powering-off. The storage medium stores a software program, and when the software program is read and executed by one or more processors, the method provided in the ninth aspect or any possible embodiment of the ninth aspect may be implemented. 
     According to a sixteenth aspect, an embodiment of the present invention further provides another computer storage medium. The storage medium may be non-volatile, that is, content is not lost after powering-off. The storage medium stores a software program, and when the software program is read and executed by one or more processors, the method provided in the tenth aspect or any possible embodiment of the tenth aspect may be implemented. 
     According to a seventeenth aspect, an embodiment of the present invention further provides another computer storage medium. The storage medium may be non-volatile, that is, content is not lost after powering-off. The storage medium stores a software program, and when the software program is read and executed by one or more processors, the method provided in the eleventh aspect or any possible embodiment of the eleventh aspect may be implemented. 
     The embodiments of the present invention are implemented, so that when the terminal is handed over from the first AN to the second AN for communication, the terminal and the second AN both obtain the second reference value, and encryption and/or integrity protection are/is subsequently performed between the terminal and the second AN by using the second reference value instead of still using the first reference value. In this way, when an attacker intercepts the first reference value used before the terminal is handed over and the second reference value used after the terminal is handed over, because the first reference value is different from the second reference value, the attacker does not deduce that the first reference value and the second reference value come from a same terminal, thereby improving security performance of the terminal. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       To describe the technical solutions in the embodiments of the present invention or in the background more clearly, the following briefly describes the accompanying drawings required for describing the embodiments of the present invention or the background. 
         FIG. 1A  is a schematic structural diagram of a PDCP format in the prior art; 
         FIG. 1B  is a schematic diagram of an encryption/decryption scenario in the prior art; 
         FIG. 2  is a schematic structural diagram of a communications system according to an embodiment of the present invention; 
         FIG. 3A  is a schematic flowchart of a communication method according to an embodiment of the present invention; 
         FIG. 3B  is a schematic flowchart of another communication method according to an embodiment of the present invention; 
         FIG. 3C  is a schematic flowchart of another communication method according to an embodiment of the present invention; 
         FIG. 3D  is a schematic flowchart of another communication method according to an embodiment of the present invention; 
         FIG. 3E  is a schematic flowchart of another communication method according to an embodiment of the present invention; 
         FIG. 3F  is a schematic flowchart of another communication method according to an embodiment of the present invention; 
         FIG. 3G  is a schematic flowchart of another communication method according to an embodiment of the present invention; 
         FIG. 3H  is a schematic flowchart of another communication method according to an embodiment of the present invention; 
         FIG. 3I  is a schematic flowchart of another communication method according to an embodiment of the present invention; 
         FIG. 3J  is a schematic flowchart of another communication method according to an embodiment of the present invention; 
         FIG. 4  is a schematic structural diagram of an access network node according to an embodiment of the present invention; 
         FIG. 5  is a schematic structural diagram of another access network node according to an embodiment of the present invention; 
         FIG. 6  is a schematic structural diagram of a terminal according to an embodiment of the present invention; 
         FIG. 7  is a schematic structural diagram of another access network node according to an embodiment of the present invention; 
         FIG. 8  is a schematic structural diagram of another access network node according to an embodiment of the present invention; 
         FIG. 9  is a schematic structural diagram of another terminal according to an embodiment of the present invention; 
         FIG. 10  is a schematic structural diagram of an MM according to an embodiment of the present invention; and 
         FIG. 11  is a schematic structural diagram of another MM according to an embodiment of the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     The following describes the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. 
       FIG. 2  is a schematic architectural diagram of a communications system  20  according to an embodiment of the present invention. The communications system  10  includes a terminal  201 , a first access network node  202 , a second access network node  203 , a mobility management node (MM)  204 . The following first describes the network elements. 
     The terminal  201  may be a smart device, for example, a mobile phone, a tablet computer, a notebook computer, a desktop computer, a palmtop computer, a mobile Internet device (MID), or a wearable device (for example, a smartwatch, a smart band, or a pedometer); or may be a device providing a control service or a forwarding service, for example, a server, a gateway, or a controller; or may be an Internet of Things device, for example, an ammeter, a water meter, a vehicle, a home appliance, a sensor, or another device; or may be another device that can be connected to a network (for example, a wireless cellular network, a wireless fidelity (Wi-Fi) network, a Bluetooth network, an optical network, a ZigBee network, or a wireless sensor network). For ease of description, the terminal may also be briefly referred to as UE subsequently. 
     The first access network node  202  and the second access network node  203  are two different access network nodes (AN). The AN may be a base station (an NB, an eNB, or a gNB), a wireless access point (Wireless Access Point, AP), a Bluetooth access point, a wired access point (for example, a gateway or a modem), or the like. For ease of description, the first access network node  202  may be referred to as a first AN subsequently, and the second access network node  203  may be referred to as a second AN subsequently. 
     The mobility management node  204  may be an access and mobility management function (AMF) network element, a mobility management entity (MME), another controller network element or manager network element on a network side, or the like. For ease of description, the mobility management node  104  may be briefly referred to as an MM subsequently. It should be noted that there may be no MM in some embodiments. 
     In this embodiment of the present invention, the terminal  201  first establishes a communication connection to the first AN. A value of a target parameter used for encryption and integrity protection when data is transmitted between the terminal  201  and the first AN is a first reference value. Subsequently, the terminal  201  is handed over to the second AN to establish a communication connection to the second AN. A value of the target parameter used for encryption and integrity protection when data is transmitted between the terminal  201  and the second AN is a second reference value. The first AN and the second AN may be connected to each other through an interface. The target parameter is a collective term for one or more other parameters that represent a value or values. For example, an attribute of the target parameter includes at least the following several cases. In a first case, the target parameter is a counter, where the counter includes a counting parameter (for example, an HFN) and a sequence number SN. In a second case, the target parameter is a sequence number SN. In the second case, the HFN is used as an example, and the target parameter includes one value or two values. That “the value of the target parameter is the first reference value” may specifically mean that the HFN in the target parameter is the first reference value (in this case, the first reference value includes one value), or may specifically mean that the SN in the target parameter is the first reference value (in this case, the first reference value includes one value), or may specifically mean that the HFN and the SN in the target parameter each are one of two values in the first reference value (in this case, the first reference value includes two values). Optionally, after the terminal is handed over to the second AN to be connected to the second AN, a part of data sent by the terminal to the first AN may need to be sent by the first AN to the second AN. In this case, a value of the target parameter used for encryption and integrity protection when data is transmitted between the first AN and the second AN is the second reference value rather than the first reference value. With reference to a method embodiment shown in  FIG. 3A , the following uses a cellular network scenario as an example to describe how each related network element obtains the second reference value. 
       FIG. 3A  is a schematic flowchart of a communication method according to an embodiment of the present invention. The method may be implemented based on the communications system  20  shown in  FIG. 2 . During execution, the method includes but is not limited to the following steps. 
     Step S 3001 : A terminal sends a measurement report to a first AN. 
     Specifically, each cell in a cellular network has an AN (for example, a base station) corresponding to the cell. The terminal is currently located in signal coverage of a serving cell and a neighboring cell of the serving cell. In addition to one primary cell (PCell), the serving cell may further include at least one secondary cell (SCell). When the serving cell includes a secondary cell (SCell), a SCell having highest signal strength is a primary secondary cell (PSCell). The terminal establishes a radio connection (RRC connected) by using the primary cell. 
     The terminal detects in real time signal quality of a cell in which the terminal is located. The signal quality may include at least one of reference signal received power (RSRP) and reference signal received quality (RSRQ), or may include another parameter used to represent signal quality. In this embodiment of the present invention, the PCell in which the terminal is currently located is corresponding to the first AN (in other words, the primary cell is provided by a cell corresponding to the first AN), and the terminal detects signal quality of the current cell in which the terminal is located and sends the measurement report (Measurement Report) to the first AN. 
     Step S 3002 : The first AN receives the measurement report, and determines, based on the measurement report, that the terminal meets a condition of being handed over from the first AN to the second AN. 
     Specifically, the first AN determines, based on the measurement report, whether the terminal meets the cell handover condition. Cell handover herein mainly means switching of the PCell. If the terminal does not meet the cell handover condition, no cell handover procedure is performed; or if the terminal meets the cell handover condition, a cell handover procedure is performed. For a process of determining whether cell handover needs to be performed and how cell handover is performed, refer to an execution manner in the prior art. If the terminal meets a condition of switching the primary cell from one cell to another cell, an AN corresponding to the another cell may be referred to as the second AN, to facilitate subsequent description. In this way, that the terminal meets a condition of switching the primary cell from one cell to another cell may be alternatively described as follows: The terminal meets the condition of being handed over from the first AN to the second AN. In addition, in actual application, there may be a case in which a cell before handover and a cell after handover are corresponding to a same AN. However, the present invention focuses on a case in which the cell before handover and the cell after handover are corresponding to different ANs (that is, the first AN and the second AN are two different ANs). 
     It should be noted that, when the terminal communicates with the first AN, encryption and/or integrity protection (including three cases: encryption, integrity protection, or encryption and integrity protection) need/needs to be performed on transmitted data. In this embodiment of the present invention, a value of a target parameter used for encryption and/or integrity protection between the terminal and the first AN may be equal to a first reference value. Optionally, the target parameter is a counter, and the counter includes a hyper frame number HFN and a sequence number SN. Optionally, the target parameter is a sequence number SN. 
     Step S 3003 : The first AN sends a target message to the second AN, to instruct the second AN to obtain a second reference value. 
     Specifically, if the first AN determines that the terminal meets the condition of being handed over from the first AN to the second AN, the first AN sends the target message to the second AN. The target message is used to instruct the second AN to obtain the second reference value. The second reference value and the first reference value have a same attribute but different specific values. For example, if the target parameter is a counter, the first reference value is values of an HFN and an SN in the counter, that the value of the target parameter is equal to the first reference value specifically means that HFN=100 and SN=1000, and that a value of the target parameter is equal to the second reference value specifically means that HFN=200 and SN=2000. Alternatively, if the target parameter is a counter, the first reference value is a value of an HFN in the counter, that the value of the target parameter is equal to the first reference value specifically means that HFN=100, and that a value of the target parameter is equal to the second reference value specifically means that HFN=200. Alternatively, if the target parameter is a counter, the first reference value is a value of an SN in the counter, that the value of the target parameter is equal to the first reference value specifically means that SN=1000, and that a value of the target parameter is equal to the second reference value specifically means that SN=2000. Alternatively, if the target parameter is an SN, that the value of the target parameter is equal to the first reference value specifically means that SN=1000, and that a value of the target parameter is equal to the second reference value specifically means that SN=2000. It may be understood that, in addition to the values mentioned in the foregoing examples, the HFN and the SN may have other values. The second reference value is used as a value of the target parameter used for encryption and/or integrity protection when the second AN and the terminal communicate with each other. 
     Step S 3004 : The second AN obtains the second reference value based on the target message. 
     Specifically, the second AN obtains the second reference value in a plurality of possible manners. For example, the first AN generates the second reference value and encapsulates the second reference value into the target message, and the second AN parses the target message to obtain the second reference value. For another example, after receiving the target message, the second AN generates the second reference value. For another example, a related network element (for example, an MM) on a network side generates the second reference value and then sends the second reference value to the second AN, and correspondingly, the second AN receives and obtains the second reference value. For another example, the terminal generates the second reference value and then sends the second reference value to the second AN, and correspondingly, the second AN receives and obtains the second reference value. It should be noted that, when a network element generating the second reference value is another network element other than the first AN and the second AN, the first AN or the second AN may send an instruction (or a “request”) to the another network element, to trigger the another network element to generate the second reference value. In addition, if a parameter required for generating the second reference value exists in a network element (or “several network elements”) in the communications system, the network element may send the required parameter to a network element generating the second reference value. For example, if the second AN generates the second reference value and a parameter required for generating the second reference value includes the first reference value, the first AN may send the first parameter to the second AN. 
     A manner of generating the second reference value is not limited herein. In an optional solution, the second reference value may be randomly generated by using a randomized algorithm. In another optional solution, the second reference value may be derived according to a preset rule. For example, a predefined key derivation function may be used, some parameters are used as input of the key derivation function, and output of the key derivation function is the second reference value. Optionally, SN2=function ((at least one of an SN1, a UEID, an ANID1, a key, a nonce, a random number, a C-RNTI, a cell ID, a session ID, an EPS bearer ID, a radio bearer ID, a transport channel ID, a logical channel ID, a “USN”, and a “DSN”)). The SN2 is the second reference value. The function is a parameter derivation function (for example, a key derivation function (KDF), a hash function, a message authentication code (MAC), or a hash-based message authentication code (HMAC)). The SN1 is the first reference value. The UEID is an identity of the terminal. The ANID1 is an identifier of the first AN. The key is a secure key (for example, an AN key (K_AN1) of the first AN, an encryption key (K_enc), or an integrity protection key (K_int)) shared between the UE and the first AN. The nonce is a fresh parameter. The random number is a random number. The C-RNTI is a cell radio network temporary identifier. The cell ID is a cell identifier. The radio bearer ID is a radio bearer identifier. The transport channel ID is a transport channel identifier. The logical channel ID is a logical channel identifier. The “USN” is a preset uplink character string. The “DSN” is a preset downlink character string. 
     Step S 3005 : The terminal is configured to obtain the second reference value. 
     Specifically, the terminal obtains the second reference value in a plurality of possible manners. For example, the related network element (for example, the MM, the first AN, or the second AN) on the network side generates the second reference value and sends the second reference value to the terminal, and correspondingly, the terminal receives and obtains the second reference value. For another example, the first AN or the second AN sends an instruction to the terminal, and the terminal receives the instruction and generates the second reference value. It should be noted that, when a network element generating the second reference value is another network element other than the first AN and the second AN, the first AN or the second AN may send an instruction (or a “request”) to the another network element, to trigger the another network element to generate the second reference value. In addition, if a parameter required for generating the second reference value exists in a network element (or “several network elements”) in the communications system, the network element may send the required parameter to a network element generating the second reference value. For example, if the second AN generates the second reference value and a parameter required for generating the second reference value includes the first reference value, the first AN may send the first parameter to the second AN. For example, the UE and a network (for example, the first AN, the second AN, or the MM) respectively generate the second reference value. If a fresh parameter (a parameter that the UE does not have) or an identifier, for example, the nonce or the random number, is used in a process in which the network element on the network side generates the SN2, the network element on the network side needs to send the fresh parameter to the UE, so that the UE uses the fresh parameter when generating the second reference value. If a fresh parameter (a parameter that the UE does not have) or an identifier, for example, the nonce or the random number, is used in a process in which the UE generates the SN2, the UE needs to send the fresh parameter to the network element on the network side, so that the network element on the network side uses the fresh parameter when generating the second reference value. 
     If the second reference value is generated by the terminal, for a manner of generating the second reference value, refer to the foregoing description. 
     Step S 3006 : The terminal transmits data with the second AN. 
     Specifically, when the terminal transmits the data with the second AN, encryption and/or integrity protection needs to be performed on the transmitted data. The target parameter is used during encryption and/or integrity protection, and the value of the target parameter is the second reference value rather than the first reference value. That “the target parameter is used during encryption and/or integrity protection” includes the following several cases. In a first case, the value of the target parameter is used as a parameter used for encryption and/or integrity protection. In a second case, a parameter derived based on the value of the target parameter is used as a parameter used for encryption and/or integrity protection. In a third case, the target parameter and another parameter value are used together as a parameter used for encryption and/or integrity protection. For example, when the target parameter is a sequence number SN, the SN and the HFN are used together as the parameter used for encryption and/or integrity protection, and in this case, the HFN may be 0 or another default initial value. 
     It should be noted that a sequence of performing the foregoing steps S 3001  to S 3006  is not limited herein. Solutions that are obtained by performing the foregoing steps in various sequences and that are logically implementable fall within the scope of the embodiments of the present invention. 
     In the method described in  FIG. 3A , when the terminal is handed over from the first AN to the second AN for communication, the terminal and the second AN both obtain the second reference value, and encryption and/or integrity protection are/is subsequently performed between the terminal and the second AN by using the second reference value instead of still using the first reference value. In this way, when an attacker intercepts the first reference value used before the terminal is handed over and the second reference value used after the terminal is handed over, because the first reference value is different from the second reference value, the attacker does not deduce that the first reference value and the second reference value come from a same terminal, thereby improving security performance of the terminal. 
     It should be noted that the method embodiment shown in  FIG. 3A  mentions a case in which the manner of generating the second reference value includes a plurality of possible cases. For ease of understanding, the following describes execution procedures of several possible cases in more detail with reference to  FIG. 3B  to  FIG. 3J . 
       FIG. 3B  is a schematic flowchart of another communication method according to an embodiment of the present invention. The method includes but is not limited to the following steps, and UE is used below to represent the terminal described above. 
     Step S 3101 : The UE sends a measurement report measurement report to a first AN. 
     Step S 3102 : The first AN receives the measurement report, and determines, based on the measurement report, that the UE can be handed over to a second AN. 
     Step S 3103 : The first AN generates a second reference value, where the second reference value is not equal to the first reference value. 
     Step S 3104 : The first AN sends a handover request to the second AN, to request to hand over the UE to a cell corresponding to the second AN. 
     Step S 3105 : The second AN receives the handover request, and feeds back, to the first AN, a response to the handover request, where the response to the handover request is used to acknowledge that the UE is to be handed over to the cell corresponding to the second AN. 
     Step S 3106 : The first AN receives the response to the handover request, and sends the second reference value to the UE based on the response. 
     Step S 3107 : The first AN sends the second reference value to the second AN based on the response. 
     Step S 3108 : The first AN sends, to the second AN, data that is from the UE and that is cached before handover, where a value of a target parameter used to perform encryption and/or integrity protection on the data is the second reference value rather than the first reference value. 
     Step S 3109 : The UE transmits data with the second AN, where a value of the target parameter used to perform encryption and/or integrity protection on the data is the second reference value rather than the first reference value. 
     It should be noted that, a sequence of performing some of the foregoing steps S 3101  to S 3109  may be adjusted, and solutions that are obtained by performing the foregoing steps in various sequences and that are logically implementable fall within the scope of the embodiments of the present invention. For example, the entire solution is logically implementable when step S 3103  is performed after step S 3105 . For another example, the second reference value may be sent to the second AN immediately after step S 3103  rather than in step S 3107 . In a variant solution, the first AN does not generate the second reference value, but generates a parameter X and sends the parameter X to the UE. The UE generates the second reference value based on the parameter X and the first reference value, and the first AN also calculates the second reference value based on the parameter X and the first reference value. Then, the first AN sends the second reference value to the second AN, or the first AN sends both the parameter X and the first reference value to the second AN, so that the second AN calculates the second reference value based on the parameter X and the first reference value. In this way, the second AN and the UE both obtain the second reference value. 
       FIG. 3C  is a schematic flowchart of another communication method according to an embodiment of the present invention. The method includes but is not limited to the following steps, and UE is used below to represent the terminal described above. 
     Step S 3201 : The UE sends a measurement report measurement report to a first AN. 
     Step S 3202 : The first AN receives the measurement report, and determines, based on the measurement report, that the UE can be handed over to a second AN. 
     Step S 3203 : The first AN generates a second reference value, where the second reference value is not equal to the first reference value. 
     Step S 3204 : The first AN sends a handover request to the second AN, to request to hand over the UE to a cell corresponding to the second AN. 
     Step S 3205 : The second AN receives the handover request, and feeds back, to the first AN, a response to the handover request, where the response to the handover request is used to acknowledge that the UE is to be handed over to the cell corresponding to the second AN. 
     Step S 3206 : The first AN receives the response to the handover request, and sends a parameter generation request to the UE based on the response, where the parameter generation request is control information or signaling. Optionally, the parameter generation request may be a response to the measurement report, to indicate that it is acknowledged that the UE can be handed over to the cell corresponding to the second AN. Optionally, the parameter generation request includes an indicator, to instruct the UE to generate the second reference value. For the parameter generation request in another embodiment, refer to the description herein. 
     Step S 3207 : The UE receives the parameter generation request, and generates the second reference value, where the parameter generation request may be considered as a trigger condition of generating the second reference value. Optionally, the UE may identify the indicator in the parameter generation request, to trigger generation of the second reference value. For the parameter generation request in another embodiment, refer to the description herein. 
     Step S 3208 : The first AN sends the second reference value to the second AN based on the response to the handover request. 
     Step S 3209 : The first AN sends, to the second AN, data that is from the UE and that is cached before handover, where a value of a target parameter used to perform encryption and/or integrity protection on the data is the second reference value rather than the first reference value. 
     Step S 3210 : The UE transmits data with the second AN, where a value of the target parameter used to perform encryption and/or integrity protection on the data is the second reference value rather than the first reference value. 
     It should be noted that, a sequence of performing some of the foregoing steps S 3201  to S 3210  may be adjusted, and solutions that are obtained by performing the foregoing steps in various sequences and that are logically implementable fall within the scope of the embodiments of the present invention. For example, the entire solution is logically implementable when step S 3203  is performed after step S 3205 . For another example, the second reference value may be sent to the second AN immediately after step S 3203  rather than in step S 3208 . In a variant solution, the first AN and the terminal do not generate the second reference value but generate a parameter X. Subsequently, the terminal and the first AN both generate the second reference value based on the parameter X and the first reference value. Then, the first AN sends the second reference value to the second AN, or the first AN sends both the parameter X and the first reference value to the second AN, so that the second AN calculates the second reference value based on the parameter X and the first reference value. In this way, the second AN and the UE both obtain the second reference value. 
       FIG. 3D  is a schematic flowchart of another communication method according to an embodiment of the present invention. The method includes but is not limited to the following steps, and UE is used below to represent the terminal described above. 
     Step S 3301 : The UE sends a measurement report measurement report to a first AN. 
     Step S 3302 : The first AN receives the measurement report, and determines, based on the measurement report, that the UE can be handed over to a second AN. 
     Step S 3303 : The first AN sends a handover request to the second AN, to request to hand over the UE to a cell corresponding to the second AN. 
     Step S 3304 : The second AN receives the handover request, and generates a second reference value based on the handover request, where the second reference value is not equal to the first reference value. 
     Step S 3305 : The second AN sends, to the first AN, a response to the handover request, where the response to the handover request is used to acknowledge that the UE is to be handed over to the cell corresponding to the second AN, and the response includes the second reference value. 
     Step S 3306 : The first AN receives the response to the handover request, parses out the second reference value in the response, and then sends the second reference value to the UE. 
     Step S 3307 : The first AN sends, to the second AN, data that is from the UE and that is cached before handover, where a value of a target parameter used to perform encryption and/or integrity protection on the data is the second reference value rather than the first reference value. 
     Step S 3308 : The UE transmits data with the second AN, where a value of the target parameter used to perform encryption and/or integrity protection on the data is the second reference value rather than the first reference value. 
     It should be noted that, a sequence of performing some of the foregoing steps S 3301  to S 3308  may be adjusted, and solutions that are obtained by performing the foregoing steps in various sequences and that are logically implementable fall within the scope of the embodiments of the present invention. For example, the entire solution is logically implementable when step S 3307  is performed after step S 3308 . In a variant solution, the second AN does not generate the second reference value, but generates a parameter X and sends the parameter X to the first AN. The first AN sends the parameter X to the UE. The UE generates the second reference value based on the parameter X and the first reference value, and the first AN also calculates the second reference value based on the parameter X and the first reference value. Then, the first AN sends the second reference value to the second AN, or the first AN sends the first reference value to the second AN, so that the second AN calculates the second reference value based on the parameter X and the first reference value. In this way, the second AN and the UE both obtain the second reference value. In another variant solution, after generating the second reference value, the second AN directly sends the second reference value to the UE, but does not send the second reference value to the first AN. The first AN does not need to perform step S 3307 . 
       FIG. 3E  is a schematic flowchart of another communication method according to an embodiment of the present invention. The method includes but is not limited to the following steps, and UE is used below to represent the terminal described above. 
     Step S 3401 : The UE sends a measurement report measurement report to a first AN. 
     Step S 3402 : The first AN receives the measurement report, and determines, based on the measurement report, that the UE can be handed over to a second AN. 
     Step S 3403 : The first AN sends a handover request to the second AN, to request to hand over the UE to a cell corresponding to the second AN. 
     Step S 3404 : The second AN receives the handover request, and generates a second reference value based on the handover request, where the second reference value is not equal to the first reference value. 
     Step S 3405 : The second AN sends, to the first AN, a response to the handover request, where the response to the handover request is used to acknowledge that the UE is to be handed over to the cell corresponding to the second AN. 
     Step S 3406 : The first AN receives the response to the handover request, and sends a parameter generation request to the UE, to indicate that it is acknowledged that the UE can be handed over to the cell corresponding to the second AN, where the response to the handover request may be considered as a trigger condition of sending the parameter generation request. Optionally, the parameter generation request includes an indicator, to instruct the UE to generate the second reference value. For the parameter generation request in another embodiment, refer to the description herein. 
     Step S 3407 : The UE receives the parameter generation request, and generates the second reference value, where the parameter generation request may be considered as a trigger condition of generating the second reference value. Optionally, the UE may identify the indicator in the parameter generation request, to trigger generation of the second reference value. For the parameter generation request in another embodiment, refer to the description herein. 
     Step S 3408 : The first AN sends, to the second AN, data that is from the UE and that is cached before handover, where a value of a target parameter used to perform encryption and/or integrity protection on the data is the second reference value rather than the first reference value. 
     Step S 3409 : The UE transmits data with the second AN, where a value of the target parameter used to perform encryption and/or integrity protection on the data is the second reference value rather than the first reference value. 
     It should be noted that, a sequence of performing some of the foregoing steps S 3401  to S 3409  may be adjusted, and solutions that are obtained by performing the foregoing steps in various sequences and that are logically implementable fall within the scope of the embodiments of the present invention. For example, the entire solution is logically implementable when step S 3408  is performed after step S 3409 . In a variant solution, the second AN does not generate the second reference value, but generates a parameter X and sends the parameter X to the first AN. The first AN calculates the second reference value based on the parameter X and the first reference value. Then, the first AN sends the second reference value to the second AN, or the first AN sends the first reference value to the second AN, so that the second AN calculates the second reference value based on the parameter X and the first reference value. Similarly, the UE also generates the parameter X in a same manner, and then generates a second parameter based on the parameter X and the first reference value. In this way, the second AN and the UE both obtain the second reference value. 
       FIG. 3F  is a schematic flowchart of another communication method according to an embodiment of the present invention. The method includes but is not limited to the following steps, and UE is used below to represent the terminal described above. 
     Step S 3501 : The UE sends a measurement report measurement report to a first AN. 
     Step S 3502 : The first AN receives the measurement report, and determines, based on the measurement report, that the UE can be handed over to a second AN. 
     Step S 3503 : The first AN sends a handover request to the second AN, to request to hand over the UE to a cell corresponding to the second AN. 
     Step S 3504 : The second AN receives the handover request, and sends a target request to an MM based on the handover request, where the handover request may be considered as a trigger condition of sending the target request by the second AN. 
     Step S 3505 : The MM receives the target request, and generates a second reference value, where the target request may be considered as a trigger condition of generating the second reference value by the MM, and the second reference value is not equal to the first reference value. 
     Step S 3506 : The MM sends the second reference value to the second AN. 
     Step S 3507 : The second AN receives the second reference value. 
     Step S 3508 : The second AN sends, to the first AN, a response to the handover request, where the response to the handover request is used to acknowledge that the UE is to be handed over to the cell corresponding to the second AN, and the response includes the second reference value. 
     Step S 3509 : The first AN receives the response to the handover request, and sends the second reference value to the UE, where the response to the handover request may be considered as a trigger condition of sending the second reference value. 
     Step S 3510 : The UE receives the second reference value. 
     Step S 3511 : The first AN sends, to the second AN, data that is from the UE and that is cached before handover, where a value of a target parameter used to perform encryption and/or integrity protection on the data is the second reference value rather than the first reference value. 
     Step S 3512 : The UE transmits data with the second AN, where a value of the target parameter used to perform encryption and/or integrity protection on the data is the second reference value rather than the first reference value. 
     It should be noted that, a sequence of performing some of the foregoing steps S 3501  to S 3512  may be adjusted, and solutions that are obtained by performing the foregoing steps in various sequences and that are logically implementable fall within the scope of the embodiments of the present invention. For example, the entire solution is logically implementable when step S 3511  is performed after step S 3512 . In a variant solution, the MM does not generate the second reference value, but generates a parameter X and sends the parameter X to the first AN. The first AN also sends the parameter X to the UE. The UE and the first AN both calculate the second reference value based on the parameter X and the first reference value. Then, the first AN sends the second reference value to the second AN, or the first AN sends the first reference value and the parameter X to the second AN, so that the second AN calculates the second reference value based on the parameter X and the first reference value. In this way, the second AN and the UE both obtain the second reference value. In another variant solution, after obtaining the second reference value, the second AN does not send the second reference value to the first AN, but directly sends the second reference value to the UE. In another variant solution, after generating the second reference value, the MM directly sends the second reference value to each of the second AN and the UE, and the first AN does not need to obtain the second reference value. In another variant solution, after generating the second reference value, the MM sends the second reference value to the first AN, but does not need to send the second reference value to the second AN. Subsequently, the first AN sends the second reference value to the UE and the second AN. 
       FIG. 3G  is a schematic flowchart of another communication method according to an embodiment of the present invention. The method includes but is not limited to the following steps, and UE is used below to represent the terminal described above. 
     Step S 3601 : The UE sends a measurement report measurement report to a first AN. 
     Step S 3602 : The first AN receives the measurement report, and determines, based on the measurement report, that the UE can be handed over to a second AN. 
     Step S 3603 : The first AN sends a handover request to the second AN, to request to hand over the UE to a cell corresponding to the second AN. 
     Step S 3604 : The second AN receives the handover request, and sends a target request to an MM based on the handover request, where the handover request may be considered as a trigger condition of sending the target request by the second AN. 
     Step S 3605 : The MM receives the target request, and generates a second reference value, where the target request may be considered as a trigger condition of generating the second reference value by the MM, and the second reference value is not equal to the first reference value. 
     Step S 3606 : The MM sends the second reference value to the second AN. 
     Step S 3607 : The second AN sends, to the first AN, a response to the handover request, where the response to the handover request is used to acknowledge that the UE is to be handed over to the cell corresponding to the second AN. 
     Step S 3608 : The first AN receives the response to the handover request, and sends a parameter generation request to the UE, to indicate that it is acknowledged that the UE can be handed over to the cell corresponding to the second AN, where the response to the handover request may be considered as a trigger condition of sending the parameter generation request. 
     Step S 3609 : The UE receives the parameter generation request, and generates the second reference value, where the parameter generation request may be considered as a trigger condition of generating the second reference value. 
     Step S 3610 : The first AN sends, to the second AN, data that is from the UE and that is cached before handover, where a value of a target parameter used to perform encryption and/or integrity protection on the data is the second reference value rather than the first reference value. 
     Step S 3611 : The UE transmits data with the second AN, where a value of the target parameter used to perform encryption and/or integrity protection on the data is the second reference value rather than the first reference value. 
     It should be noted that, a sequence of performing some of the foregoing steps S 3601  to S 3611  may be adjusted, and solutions that are obtained by performing the foregoing steps in various sequences and that are logically implementable fall within the scope of the embodiments of the present invention. For example, the entire solution is logically implementable when step S 3610  is performed after step S 3611 . In a variant solution, the MM does not generate the second reference value, but generates a parameter X and sends the parameter X to the second AN. The second AN sends the parameter X to the first AN. The first AN calculates the second reference value based on the parameter X and the first reference value. Then, the first AN sends the second reference value to the second AN, or the first AN sends the first reference value to the second AN, so that the second AN calculates the second reference value based on the parameter X and the first reference value. Similarly, the UE also generates the parameter X in a same manner, and then generates a second parameter based on the parameter X and the first reference value. In this way, the second AN and the UE both obtain the second reference value. In another variant solution, the MM does not generate the second reference value, but generates a parameter X and sends the parameter X to the second AN. The first AN also sends the first reference value to the second AN. The second AN generates the second reference value based on the parameter X and the first reference value. Similarly, the UE also generates the parameter X in a same manner, and then generates a second parameter based on the parameter X and the first reference value. In this way, the second AN and the UE both obtain the second reference value. 
       FIG. 3H  is a schematic flowchart of another communication method according to an embodiment of the present invention. The method includes but is not limited to the following steps, and UE is used below to represent the terminal described above. 
     Step S 3701 : The UE sends a measurement report measurement report to a first AN. 
     Step S 3702 : The first AN receives the measurement report, and determines, based on the measurement report, that the UE can be handed over to a second AN. 
     Step S 3703 : The first AN sends a target request to an MM, to request the MM to generate a second reference value. 
     Step S 3704 : The MM receives the target request, and generates the second reference value, where the target request may be considered as a trigger condition of generating the second reference value by the MM, and the second reference value is not equal to the first reference value. 
     Step S 3705 : The MM sends the second reference value to the first AN. 
     Step S 3706 : The first AN receives the second reference value, and sends a handover request to the second AN, to request to hand over the UE to a cell corresponding to the second AN. 
     Step S 3707 : The second AN receives the handover request, and sends, to the first AN, a response to the handover request, where the response to the handover request is used to acknowledge that the UE is to be handed over to the cell corresponding to the second AN. 
     Step S 3708 : The first AN receives the response to the handover request, and sends the second reference value to the UE, where the response to the handover request may be considered as a trigger condition of sending the second reference value by the UE. 
     Step S 3709 : The first AN sends the second reference value to the second AN. 
     Step S 3710 : The first AN sends, to the second AN, data that is from the UE and that is cached before handover, where a value of a target parameter used to perform encryption and/or integrity protection on the data is the second reference value rather than the first reference value. 
     Step S 3711 : The UE transmits data with the second AN, where a value of the target parameter used to perform encryption and/or integrity protection on the data is the second reference value rather than the first reference value. 
     It should be noted that, a sequence of performing some of the foregoing steps S 3701  to S 3711  may be adjusted, and solutions that are obtained by performing the foregoing steps in various sequences and that are logically implementable fall within the scope of the embodiments of the present invention. For example, the entire solution is logically implementable when step S 3710  is performed after step S 3711 . In a variant solution, the MM does not generate the second reference value, but generates a parameter X and sends the parameter X to the first AN. The first AN also sends the parameter X to the UE. The UE and the first AN both calculate the second reference value based on the parameter X and the first reference value. Then, the first AN sends the second reference value to the second AN, or the first AN sends the first reference value and the parameter X to the second AN, so that the second AN calculates the second reference value based on the parameter X and the first reference value. In this way, the second AN and the UE both obtain the second reference value. 
       FIG. 3I  is a schematic flowchart of another communication method according to an embodiment of the present invention. The method includes but is not limited to the following steps, and UE is used below to represent the terminal described above. 
     Step S 3801 : The UE sends a measurement report measurement report to a first AN. 
     Step S 3802 : The first AN receives the measurement report, and determines, based on the measurement report, that the UE can be handed over to a second AN. 
     Step S 3803 : The first AN sends a target request to an MM, to request the MM to generate a second reference value. 
     Step S 3804 : The MM receives the target request, and generates the second reference value, where the target request may be considered as a trigger condition of generating the second reference value by the MM, and the second reference value is not equal to the first reference value. 
     Step S 3805 : The MM sends the second reference value to the first AN. 
     Step S 3806 : The first AN receives the second reference value, and sends a handover request to the second AN, to request to hand over the UE to a cell corresponding to the second AN. 
     Step S 3807 : The second AN receives the handover request, and sends, to the first AN, a response to the handover request, where the response to the handover request is used to acknowledge that the UE is to be handed over to the cell corresponding to the second AN. 
     Step S 3808 : The first AN receives the response to the handover request, and sends a parameter generation request to the UE, to indicate that it is acknowledged that the UE can be handed over to the cell corresponding to the second AN, where the response to the handover request may be considered as a trigger condition of sending the parameter generation request. 
     Step S 3809 : The UE receives the parameter generation request, and generates the second reference value, where the parameter generation request may be considered as a trigger condition of generating the second reference value. 
     Step S 3810 : The first AN sends the second reference value to the second AN. 
     Step S 3811 : The first AN sends, to the second AN, data that is from the UE and that is cached before handover, where a value of a target parameter used to perform encryption and/or integrity protection on the data is the second reference value rather than the first reference value. 
     Step S 3812 : The UE transmits data with the second AN, where a value of the target parameter used to perform encryption and/or integrity protection on the data is the second reference value rather than the first reference value. 
     It should be noted that, a sequence of performing some of the foregoing steps S 3801  to S 3812  may be adjusted, and solutions that are obtained by performing the foregoing steps in various sequences and that are logically implementable fall within the scope of the embodiments of the present invention. For example, the entire solution is logically implementable when step S 3811  is performed after step S 3812 . In a variant solution, the MM does not generate the second reference value, but generates a parameter X and sends the parameter X to the first AN. The first AN calculates the second reference value based on the parameter X and the first reference value. Then, the first AN sends the second reference value to the second AN, or the first AN sends the first reference value and the parameter X to the second AN, so that the second AN calculates the second reference value based on the parameter X and the first reference value. Similarly, the UE also generates the parameter X in a same manner, and then generates a second parameter based on the parameter X and the first reference value. In this way, the second AN and the UE both obtain the second reference value. 
       FIG. 3J  is a schematic flowchart of another communication method according to an embodiment of the present invention. The method includes but is not limited to the following steps, and UE is used below to represent the terminal described above. 
     Step S 3901 : The UE sends a measurement report measurement report to a first AN. 
     Step S 3902 : The first AN receives the measurement report, and determines, based on the measurement report, that the UE can be handed over to a second AN. 
     Step S 3903 : The first AN sends a handover request to the second AN, to request to hand over the UE to a cell corresponding to the second AN. 
     Step S 3904 : The second AN sends, to the first AN, a response to the handover request, where the response to the handover request is used to acknowledge that the UE is to be handed over to the cell corresponding to the second AN. 
     Step S 3905 : The first AN sends a parameter generation request to the UE, to indicate that it is acknowledged that the UE can be handed over to the cell corresponding to the second AN. 
     Step S 3906 : The UE receives the parameter generation request, and generates a second reference value, where the parameter generation request may be considered as a trigger condition of generating the second reference value, and the second reference value is not equal to the first reference value. 
     Step S 3907 : The UE sends the second reference value to the first AN. 
     Step S 3908 : The first AN sends the second reference value to the second AN. 
     Step S 3909 : The first AN sends, to the second AN, data that is from the UE and that is cached before handover, where a value of a target parameter used to perform encryption and/or integrity protection on the data is the second reference value rather than the first reference value. 
     Step S 3910 : The UE transmits data with the second AN, where a value of the target parameter used to perform encryption and/or integrity protection on the data is the second reference value rather than the first reference value. 
     It should be noted that, a sequence of performing some of the foregoing steps S 3901  to S 3910  may be adjusted, and solutions that are obtained by performing the foregoing steps in various sequences and that are logically implementable fall within the scope of the embodiments of the present invention. For example, the entire solution is logically implementable when step S 3909  is performed after step S 3910 . Possibly, the UE does not send the second reference value to the first AN, but directly sends the second reference value to the second AN. In this way, there is no step S 3907 . In another variant solution, the UE does not generate the second reference value, but generates a parameter X and sends the parameter X to the first AN. The first AN calculates the second reference value based on the parameter X and the first reference value. Then, the first AN sends the second reference value to the second AN, or the first AN sends the first reference value and the parameter X to the second AN, so that the second AN calculates the second reference value based on the parameter X and the first reference value. The UE also generates a second parameter based on the parameter X and the first reference value in a same manner. In this way, the second AN and the UE both obtain the second reference value. 
     The foregoing describes some solutions of the embodiments of the present invention in more detail with reference to  FIG. 3B  to  FIG. 3J . The solutions are only used as examples for description. In addition to the listed solutions, there are other solutions obtained through change based on the ideas of the embodiments of the present invention, and the solutions all fall within the protection scope of this application. In addition, the parameter X mentioned in the foregoing embodiments is a general concept. During specific embodiments, the parameter X may be specified as a parameter as required, and is used as input for generating the second reference value. 
     The foregoing describes in detail the method in the embodiments of the present invention, and the following provides an apparatus in the embodiments of the present invention. 
       FIG. 4  is a schematic structural diagram of an access network node  40  according to an embodiment of the present invention. The access network node  40  may be referred to as a first AN, the first AN includes a determining unit  401  and a first sending unit  402 , and the units are described as follows: 
     The determining unit  401  is configured to determine that a terminal accessing the first AN meets a condition of being handed over from the first AN to a second AN, where a value of a target parameter used for encryption and/or integrity protection when the terminal and the first AN communicate with each other before the terminal is handed over to the second AN is equal to a first reference value, and the target parameter is a counter or a sequence number SN. The first sending unit  402  is configured to send a target message to the second AN, to instruct the second AN to obtain a second reference value, where the second reference value is used as a value of the target parameter used for encryption and/or integrity protection when the second AN and the terminal communicate with each other. 
     The foregoing units are run, so that when the terminal is handed over from the first AN to the second AN for communication, the terminal and the second AN both obtain the second reference value, and encryption and/or integrity protection are/is subsequently performed between the terminal and the second AN by using the second reference value instead of still using the first reference value. In this way, when an attacker intercepts the first reference value used before the terminal is handed over and the second reference value used after the terminal is handed over, because the first reference value is different from the second reference value, the attacker does not deduce that the first reference value and the second reference value come from a same terminal, thereby improving security performance of the terminal. 
     In an optional solution, the first AN further includes a second processing unit, where the second processing unit is configured to, before the first sending unit  402  sends the target message to the second AN to instruct the second AN to obtain the second reference value, send a target request to an MM to request the MM to generate the second reference value, and receive the second reference value that is generated by the MM based on the target request and that is sent by the MM, where the target message includes the second reference value. 
     In another optional solution, the first AN further includes a calculation unit, where the calculation unit is configured to, before the first sending unit  402  sends the target message to the second AN to instruct the second AN to obtain the second reference value, randomly generate the second reference value by using a randomized algorithm, or derive the second reference value according to a preset rule, where the target message includes the second reference value. 
     In another optional solution, the first AN further includes a second sending unit, where the second sending unit is configured to send the second reference value to the terminal. 
     In another optional solution, the first AN further includes a third sending unit, where the third sending unit is configured to send a parameter generation request to the terminal, so that the terminal randomly generates the second reference value based on the parameter generation request by using the randomized algorithm, or derives the second reference value based on the parameter generation request according to the preset rule. 
     It should be noted that for embodiment of the units, refer to corresponding descriptions in the method embodiment shown in  FIG. 3A . 
     According to the access network node  40  described in  FIG. 4 , when the terminal is handed over from the first AN to the second AN for communication, the terminal and the second AN both obtain the second reference value, and encryption and/or integrity protection are/is subsequently performed between the terminal and the second AN by using the second reference value instead of still using the first reference value. In this way, when an attacker intercepts the first reference value used before the terminal is handed over and the second reference value used after the terminal is handed over, because the first reference value is different from the second reference value, the attacker does not deduce that the first reference value and the second reference value come from a same terminal, thereby improving security performance of the terminal. 
       FIG. 5  is a schematic structural diagram of an access network node  50  according to an embodiment of the present invention. The access network node  50  is a second AN, the second AN includes a first receiving unit  501  and an obtaining unit  502 , and the units are described as follows: 
     The first receiving unit  501  is configured to receive a target message sent by a first AN, where the target message is a message sent by the first AN when the first AN determines that the terminal meets a condition of being handed over from the first AN to the second AN, a value of a target parameter used for encryption and/or integrity protection when the terminal and the first AN communicate with each other before the terminal is handed over to the second AN is equal to a first reference value, and the target parameter is a counter or a sequence number SN. The obtaining unit  502  is configured to obtain a second reference value based on the target message, where the second reference value is used as a value of the target parameter used for encryption and/or integrity protection when the second AN and the terminal communicate with each other. 
     The foregoing units are run, so that when the terminal is handed over from the first AN to the second AN for communication, the terminal and the second AN both obtain the second reference value, and encryption and/or integrity protection are/is subsequently performed between the terminal and the second AN by using the second reference value instead of still using the first reference value. In this way, when an attacker intercepts the first reference value used before the terminal is handed over and the second reference value used after the terminal is handed over, because the first reference value is different from the second reference value, the attacker does not deduce that the first reference value and the second reference value come from a same terminal, thereby improving security performance of the terminal. 
     In another optional solution, the target message includes the second reference value, and that the obtaining unit  502  obtains a second reference value based on the target message is specifically: parsing out the second reference value from the target message. 
     In another optional solution, that the obtaining unit  502  obtains a second reference value based on the target message is specifically: randomly generating the second reference value based on the target message by using a randomized algorithm, or deriving the second reference value based on the target message according to a preset rule. 
     In another optional solution, that the obtaining unit  502  obtains a second reference value based on the target message is specifically: sending a target request to an MM based on the target message, to request the MM to generate the second reference value; and receiving the second reference value sent by the MM. 
     In another optional solution, the second AN further includes a fourth sending unit, where the fourth sending unit is configured to, after the obtaining unit  502  obtains the second reference value based on the target message, send the second reference value to the first AN, so that the first AN sends the second reference value to the terminal. 
     In another optional solution, the second AN further includes a fifth sending unit, where the fifth sending unit is configured to, after the second AN obtains the second reference value based on the target message, send the second reference value to the terminal. 
     It should be noted that for embodiments of the units, refer to corresponding descriptions in the method embodiment shown in  FIG. 3A . 
     According to the access network node  50  described in  FIG. 5 , when the terminal is handed over from the first AN to the second AN for communication, the terminal and the second AN both obtain the second reference value, and encryption and/or integrity protection are/is subsequently performed between the terminal and the second AN by using the second reference value instead of still using the first reference value. In this way, when an attacker intercepts the first reference value used before the terminal is handed over and the second reference value used after the terminal is handed over, because the first reference value is different from the second reference value, the attacker does not deduce that the first reference value and the second reference value come from a same terminal, thereby improving security performance of the terminal. 
       FIG. 6  is a schematic structural diagram of a terminal  60  according to an embodiment of the present invention. The terminal  60  includes a processing unit  601 . The processing unit  601  is configured to, when the terminal meets a condition of being handed over from a first AN to a second AN, generate a second reference value, or receive the second reference value sent by the first AN, or receive the second reference value sent by the second AN, where the second reference value is used as a value of a target parameter used for encryption and/or integrity protection when the second AN and the terminal communicate with each other, a value of the target parameter used for encryption and/or integrity protection when the terminal and the first AN communicate with each other before the terminal is handed over to the second AN is equal to a first reference value, and the target parameter is a counter or a sequence number SN. 
     The foregoing unit is run, so that when the terminal is handed over from the first AN to the second AN for communication, the terminal and the second AN both obtain the second reference value, and encryption and/or integrity protection are/is subsequently performed between the terminal and the second AN by using the second reference value instead of still using the first reference value. In this way, when an attacker intercepts the first reference value used before the terminal is handed over and the second reference value used after the terminal is handed over, because the first reference value is different from the second reference value, the attacker does not deduce that the first reference value and the second reference value come from a same terminal, thereby improving security performance of the terminal. 
     In an optional solution, that the terminal generates a second reference value is specifically: receiving a parameter generation request sent by the first AN when the first AN determines that the terminal meets the condition of being handed over from the first AN to the second AN; and randomly generating the second reference value based on the parameter generation request by using a randomized algorithm, or deriving the second reference value based on the parameter generation request according to the preset rule. 
     It should be noted that for embodiments of the units, refer to corresponding descriptions in the method embodiment shown in  FIG. 3A . 
     According to the terminal  60  described in  FIG. 6 , when the terminal is handed over from the first AN to the second AN for communication, the terminal and the second AN both obtain the second reference value, and encryption and/or integrity protection are/is subsequently performed between the terminal and the second AN by using the second reference value instead of still using the first reference value. In this way, when an attacker intercepts the first reference value used before the terminal is handed over and the second reference value used after the terminal is handed over, because the first reference value is different from the second reference value, the attacker does not deduce that the first reference value and the second reference value come from a same terminal, thereby improving security performance of the terminal. 
       FIG. 7  shows an access network node  70  according to an embodiment of the present invention. The access network node  70  is a first AN. The first AN includes a processor  701 , a memory  702 , and a transceiver  703 . The processor  701 , the memory  702 , and the transceiver  703  are connected to each other by using a bus. 
     The memory  702  includes but is not limited to a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM), or a compact disc read-only memory (CD-ROM). The memory  702  is configured to store a related instruction and related data. The transceiver  703  is configured to receive and send data. 
     The processor  701  may be one or more central processing units (CPU). When the processor  701  is one CPU, the CPU may be a single-core CPU, or may be a multi-core CPU. 
     The processor  701  of the first AN is configured to read program code stored in the memory  702 , to perform the following operations:
         determining that a terminal accessing the first AN meets a condition of being handed over from the first AN to a second AN, where a value of a target parameter used for encryption and/or integrity protection when the terminal and the first AN communicate with each other before the terminal is handed over to the second AN is equal to a first reference value, and the target parameter is a counter or a sequence number SN; and sending a target message to the second AN by using the transceiver  703 , to instruct the second AN to obtain a second reference value, where the second reference value is used as a value of the target parameter used for encryption and/or integrity protection when the second AN and the terminal communicate with each other.       

     The foregoing operations are performed, so that when the terminal is handed over from the first AN to the second AN for communication, the terminal and the second AN both obtain the second reference value, and encryption and/or integrity protection are/is subsequently performed between the terminal and the second AN by using the second reference value instead of still using the first reference value. In this way, when an attacker intercepts the first reference value used before the terminal is handed over and the second reference value used after the terminal is handed over, because the first reference value is different from the second reference value, the attacker does not deduce that the first reference value and the second reference value come from a same terminal, thereby improving security performance of the terminal. 
     In an optional solution, before the processor  701  sends the target message to the second AN by using the transceiver  703 , to instruct the second AN to obtain the second reference value, the processor  701  is further configured to send a target request to an MM by using the transceiver  703 , to request the MM to generate the second reference value, and receive the second reference value that is generated by the MM based on the target request and that is sent by the MM, where the target message includes the second reference value. 
     In another optional solution, before the processor  701  sends the target message to the second AN by using the transceiver  703 , to instruct the second AN to obtain the second reference value, the processor  701  is further configured to randomly generate the second reference value by using a randomized algorithm, or derive the second reference value according to a preset rule, where the target message includes the second reference value. 
     In another optional solution, the processor  701  is further configured to send the second reference value to the terminal by using the transceiver  703 . 
     In another optional solution, the processor  701  is further configured to send a parameter generation request to the terminal by using the transceiver  703 , so that the terminal randomly generates the second reference value based on the parameter generation request by using the randomized algorithm, or derives the second reference value based on the parameter generation request according to the preset rule. 
     It should be noted that for embodiments of the operations, refer to corresponding descriptions in the method embodiment shown in  FIG. 3A . 
     According to the device  70  described in  FIG. 7 , when the terminal is handed over from the first AN to the second AN for communication, the terminal and the second AN both obtain the second reference value, and encryption and/or integrity protection are/is subsequently performed between the terminal and the second AN by using the second reference value instead of still using the first reference value. In this way, when an attacker intercepts the first reference value used before the terminal is handed over and the second reference value used after the terminal is handed over, because the first reference value is different from the second reference value, the attacker does not deduce that the first reference value and the second reference value come from a same terminal, thereby improving security performance of the terminal. 
       FIG. 8  shows an access network node  80  according to an embodiment of the present invention. The access network node  80  is a second AN. The second AN includes a processor  801 , a memory  802 , and a transceiver  803 . The processor  801 , the memory  802 , and the transceiver  803  are connected to each other by using a bus. 
     The memory  802  includes but is not limited to a RAM, a ROM, an EPROM, or a CD-ROM. The memory  802  is configured to store a related instruction and related data. The transceiver  803  is configured to receive and send data. 
     The processor  801  may be one or more CPUs. When the processor  801  is one CPU, the CPU may be a single-core CPU, or may be a multi-core CPU. 
     The processor  801  of the second AN is configured to read program code stored in the memory  802 , to perform the following operations:
         receiving, by using the transceiver  803 , a target message sent by a first AN, where the target message is a message sent by the first AN when the first AN determines that the terminal meets a condition of being handed over from the first AN to the second AN, a value of a target parameter used for encryption and/or integrity protection when the terminal and the first AN communicate with each other before the terminal is handed over to the second AN is equal to a first reference value, and the target parameter is a counter or a sequence number (SN); and obtaining a second reference value based on the target message, where the second reference value is used as a value of the target parameter used for encryption and/or integrity protection when the second AN and the terminal communicate with each other.       

     The foregoing operations are performed, so that when the terminal is handed over from the first AN to the second AN for communication, the terminal and the second AN both obtain the second reference value, and encryption and/or integrity protection are/is subsequently performed between the terminal and the second AN by using the second reference value instead of still using the first reference value. In this way, when an attacker intercepts the first reference value used before the terminal is handed over and the second reference value used after the terminal is handed over, because the first reference value is different from the second reference value, the attacker does not deduce that the first reference value and the second reference value come from a same terminal, thereby improving security performance of the terminal. 
     In an optional solution, the target message includes the second reference value, and that the processor  801  obtains a second reference value based on the target message is specifically: parsing out the second reference value from the target message. 
     In another optional solution, that the processor  801  obtains a second reference value based on the target message is specifically: randomly generating the second reference value based on the target message by using a randomized algorithm, or deriving the second reference value based on the target message according to a preset rule. 
     In another optional solution, that the processor  801  obtains a second reference value based on the target message is specifically: sending a target request to an MM based on the target message by using the transceiver  803 , to request the MM to generate the second reference value; and receiving, by using the transceiver  803 , the second reference value sent by the MM. 
     In another optional solution, after the processor  801  is configured to obtain the second reference value based on the target message, the processor  801  is further configured to send the second reference value to the first AN by using the transceiver  803 , so that the first AN sends the second reference value to the terminal. 
     In another optional solution, after the processor  801  is configured to obtain the second reference value based on the target message, the processor  801  is further configured to send the second reference value to the terminal by using the transceiver  803 . 
     It should be noted that for embodiments of the operations, refer to corresponding descriptions in the method embodiment shown in  FIG. 3A . 
     According to the access network node  80  described in  FIG. 8 , when the terminal is handed over from the first AN to the second AN for communication, the terminal and the second AN both obtain the second reference value, and encryption and/or integrity protection are/is subsequently performed between the terminal and the second AN by using the second reference value instead of still using the first reference value. In this way, when an attacker intercepts the first reference value used before the terminal is handed over and the second reference value used after the terminal is handed over, because the first reference value is different from the second reference value, the attacker does not deduce that the first reference value and the second reference value come from a same terminal, thereby improving security performance of the terminal. 
       FIG. 9  shows a terminal  90  according to an embodiment of the present invention. The terminal  90  includes a processor  901 , a memory  902 , and a transceiver  903 . The processor  901 , the memory  902 , and the transceiver  903  are connected to each other by using a bus. 
     The memory  902  includes but is not limited to a RAM, a ROM, an EPROM, or a CD-ROM. The memory  902  is configured to store a related instruction and related data. The transceiver  903  is configured to receive and send data. 
     The processor  901  may be one or more CPUs. When the processor  901  is one CPU, the CPU may be a single-core CPU, or may be a multi-core CPU. 
     The processor  901  of the terminal  90  is configured to read program code stored in the memory  902 , to perform the following operations:
         if the terminal meets a condition of being handed over from a first AN to a second AN, generating a second reference value, or receiving, by using the transceiver  903 , the second reference value sent by the first AN, or receiving, by using the transceiver  903 , the second reference value sent by the second AN, where the second reference value is used as a value of a target parameter used for encryption and/or integrity protection when the second AN and the terminal communicate with each other, a value of the target parameter used for encryption and/or integrity protection when the terminal and the first AN communicate with each other before the terminal is handed over to the second AN is equal to a first reference value, and the target parameter is a counter or a sequence number SN.       

     The foregoing operations are performed, so that when the terminal is handed over from the first AN to the second AN for communication, the terminal and the second AN both obtain the second reference value, and encryption and/or integrity protection are/is subsequently performed between the terminal and the second AN by using the second reference value instead of still using the first reference value. In this way, when an attacker intercepts the first reference value used before the terminal is handed over and the second reference value used after the terminal is handed over, because the first reference value is different from the second reference value, the attacker does not deduce that the first reference value and the second reference value come from a same terminal, thereby improving security performance of the terminal. 
     In an optional solution, that the processor  901  generates a second reference value is specifically: receiving, by using the transceiver  903 , a parameter generation request sent by the first AN when the first AN determines that the terminal meets the condition of being handed over from the first AN to the second AN; and randomly generating the second reference value based on the parameter generation request by using a randomized algorithm, or deriving the second reference value based on the parameter generation request according to the preset rule. 
     It should be noted that for embodiments of the operations, refer to corresponding descriptions in the method embodiment shown in  FIG. 3A . 
     According to the terminal  90  described in  FIG. 9 , when the terminal is handed over from the first AN to the second AN for communication, the terminal and the second AN both obtain the second reference value, and encryption and/or integrity protection are/is subsequently performed between the terminal and the second AN by using the second reference value instead of still using the first reference value. In this way, when an attacker intercepts the first reference value used before the terminal is handed over and the second reference value used after the terminal is handed over, because the first reference value is different from the second reference value, the attacker does not deduce that the first reference value and the second reference value come from a same terminal, thereby improving security performance of the terminal. 
       FIG. 10  is a schematic structural diagram of a mobility management network element MM according to an embodiment of the present invention. The MM may include a receiving unit  1001 , a generation unit  1002 , and a sending unit  1003 , and the units are described as follows: 
     The receiving unit  1001  is configured to receive a target message, where the target message is sent by a first access network node (AN) or a second access network node AN to the MM when a terminal meets a condition of being handed over from the first AN to the second AN. The generation unit  1002  is configured to generate a second reference value based on the target message. The sending unit  1003  is configured to send the second reference value to the second AN, where the second reference value is used as a value of a target parameter used for encryption and/or integrity protection when the second AN and the terminal communicate with each other, a value of the target parameter used for encryption and/or integrity protection when the terminal and the first AN communicate with each other before the terminal is handed over to the second AN is equal to a first reference value, and the target parameter is a counter or a sequence number (SN). 
     The foregoing steps are performed, so that when the terminal is handed over from the first AN to the second AN for communication, the terminal and the second AN both obtain the second reference value, and encryption and/or integrity protection are/is subsequently performed between the terminal and the second AN by using the second reference value instead of still using the first reference value. In this way, when an attacker intercepts the first reference value used before the terminal is handed over and the second reference value used after the terminal is handed over, because the first reference value is different from the second reference value, the attacker does not deduce that the first reference value and the second reference value come from a same terminal, thereby improving security performance of the terminal. 
     In a possible embodiment, that the sending unit  1003  sends the second reference value to the second AN is specifically: sending the second reference value to the first AN, so that the first AN sends the second reference value to the second AN. 
     It should be noted that for embodiments of the units, refer to corresponding descriptions in the method embodiment shown in  FIG. 3A . 
     According to the MM described in  FIG. 10 , when the terminal is handed over from the first AN to the second AN for communication, the terminal and the second AN both obtain the second reference value, and encryption and/or integrity protection are/is subsequently performed between the terminal and the second AN by using the second reference value instead of still using the first reference value. In this way, when an attacker intercepts the first reference value used before the terminal is handed over and the second reference value used after the terminal is handed over, because the first reference value is different from the second reference value, the attacker does not deduce that the first reference value and the second reference value come from a same terminal, thereby improving security performance of the terminal. 
       FIG. 11  shows a mobility management network element MM  110  according to an embodiment of the present invention. The MM  110  includes a processor  1101 , a memory  1102 , and a transceiver  1103 . The processor  1101 , the memory  1102 , and the transceiver  1103  are connected to each other by using a bus. 
     The memory  1102  includes but is not limited to a RAM, a ROM, an EPROM, or a CD-ROM. The memory  1102  is configured to store a related instruction and related data. The transceiver  1103  is configured to receive and send data. 
     The processor  1101  may be one or CPUs. When the processor  1101  is one CPU, the CPU may be a single-core CPU, or may be a multi-core CPU. 
     The processor  1101  of the MM is configured to read program code stored in the memory  1102 , to perform the following operations:
         receiving a target message by using the transceiver  1103 , where the target message is sent by a first access network node (AN) or a second access network node (AN) to the MM when a terminal meets a condition of being handed over from the first AN to the second AN; generating a second reference value based on the target message; and sending the second reference value to the second AN by using the transceiver  1103 , where the second reference value is used as a value of a target parameter used for encryption and/or integrity protection when the second AN and the terminal communicate with each other, a value of the target parameter used for encryption and/or integrity protection when the terminal and the first AN communicate with each other before the terminal is handed over to the second AN is equal to a first reference value, and the target parameter is a counter or a sequence number (SN).       

     The foregoing operations are performed, so that when the terminal is handed over from the first AN to the second AN for communication, the terminal and the second AN both obtain the second reference value, and encryption and/or integrity protection are/is subsequently performed between the terminal and the second AN by using the second reference value instead of still using the first reference value. In this way, when an attacker intercepts the first reference value used before the terminal is handed over and the second reference value used after the terminal is handed over, because the first reference value is different from the second reference value, the attacker does not deduce that the first reference value and the second reference value come from a same terminal, thereby improving security performance of the terminal. 
     In a possible embodiment, that the processor  1101  sends the second reference value to the second AN by using the transceiver  1103  is specifically: sending the second reference value to the first AN by using the transceiver  1103 , so that the first AN sends the second reference value to the second AN. 
     It should be noted that for embodiments of the operations, refer to corresponding descriptions in the method embodiment shown in  FIG. 3A . 
     According to the MM described in  FIG. 11 , when the terminal is handed over from the first AN to the second AN for communication, the terminal and the second AN both obtain the second reference value, and encryption and/or integrity protection are/is subsequently performed between the terminal and the second AN by using the second reference value instead of still using the first reference value. In this way, when an attacker intercepts the first reference value used before the terminal is handed over and the second reference value used after the terminal is handed over, because the first reference value is different from the second reference value, the attacker does not deduce that the first reference value and the second reference value come from a same terminal, thereby improving security performance of the terminal. In conclusion, the embodiments of the present invention are implemented, so that when the terminal is handed over from the first AN to the second AN for communication, the terminal and the second AN both obtain the second reference value, and encryption and/or integrity protection are/is subsequently performed between the terminal and the second AN by using the second reference value instead of still using the first reference value. In this way, when an attacker intercepts the first reference value used before the terminal is handed over and the second reference value used after the terminal is handed over, because the first reference value is different from the second reference value, the attacker does not deduce that the first reference value and the second reference value come from a same terminal, thereby improving security performance of the terminal. 
     A person of ordinary skill in the art may understand that all or some of the procedures of the methods in the embodiments may be implemented by a computer program instructing related hardware. The program may be stored in a computer readable storage medium. When the program runs, the procedures of the methods in the embodiments are performed. The foregoing storage medium includes: any medium that can store program code, for example, a ROM, a random access memory RAM, a magnetic disk, or an optical disc.