Key derivation methods and apparatuses, and terminal, network-side device and readable storage medium

Abstract

The present application belongs to the technical field of communications. Disclosed are key derivation methods and apparatuses, and a terminal, a network-side device and a readable storage medium. A key derivation method in the embodiments of the present application comprises: a first network element receiving a path switching message from a first access network device, wherein the path switching message is used for establishing a signaling connection between a user equipment (UE) and a core network; the first network element determining, on the basis of the path switching message, whether to execute the derivation of a next hop (NH) for the UE; and the first network element sending a path switching acknowledgement message to the first access network device, wherein the path switching acknowledgement message is used for responding to the path switching message.

Description

Method, apparatus, terminal, network side device and readable storage medium for deriving a key

[0001] Cross-reference to Related Applications

[0002] The present application claims the priority of the Chinese patent application No. 202411033886.X filed on July 30, 2024, and the partial priority of the Chinese patent application No. 202411326637.X filed on September 23, 2024, the whole contents of which are hereby incorporated by reference. TECHNICAL FIELD

[0003] The present application belongs to the field of communication technology, and specifically relates to a method, network element, device and readable storage medium for deriving a key. BACKGROUND

[0004] Release 19 mobility enhancement project supports L1 / L2 triggered mobility (LTM) across Inter-CU. Inter-CU handover involves the change of base station, in order to protect the communication between the user equipment (UE) and different base stations, the keys used between the UE and different base stations are different, that is, there is key isolation between the keys between the UE and different base stations, so that the security of one key is not affected after the other key is attacked.

[0005] In the related art, the method for guaranteeing key isolation is to send a next hop (NH) value to the target base station by the access and mobility management function (AMF), so that the target base station derives the key according to the NH, and the NH is derived by the AMF according to Kamf and the last used NH, so it is a circular derivation method, which needs to identify the number of derivations to the UE through the next hop chaining count (NCC) value in the radio resource control (RRC) message, so that the UE can also derive the correct NH according to the NCC. However, in the LTM scenario, there is no RRC message interaction between the UE and the base station, so the UE cannot synchronize the NCC with the base station, resulting in different keys used by the UE and the network side, thereby affecting the stability and performance of the communication. Therefore, how to guarantee the synchronization of the keys between the terminal and the network side in the LTM is a problem to be solved. SUMMARY

[0006] The embodiment of the application provides a method and device for deriving a key, a terminal, a network side device and a readable storage medium, which can avoid the problem of key asynchronization of a UE and a network side caused by NCC value change, thereby improving the stability and performance of communication.

[0007] In a first aspect, a method for deriving a key is provided. The method comprises: receiving, by a first network element, a path switch message from a first access network device, the path switch message being used to establish a signaling connection between a user equipment (UE) and a core network; determining, by the first network element, whether to perform a next hop value (NH) derivation for the UE according to the path switch message; and sending, by the first network element, a path switch acknowledgement message to the first access network device, the path switch acknowledgement message being used to respond to the path switch message.

[0008] In a second aspect, a method for deriving a key is provided. The method comprises: sending, by a first access network device, a path switch message to a first network element, the path switch message being used to establish a signaling connection between a user equipment (UE) and a core network; and receiving, by the first access network device, a path switch acknowledgement message from the first network element, the path switch acknowledgement message being used to respond to the path switch message; wherein the path switch message contains a first indication under a first condition, the first indication indicating that the first network element does not perform the NH derivation.

[0009] In a third aspect, a method for deriving a key is provided. The method comprises: receiving, by a UE, a LTM switch message from a second access network device, the LTM switch message indicating that the UE switches to a first access network device; performing, by the UE, a horizontal key derivation to obtain a first key for communicating with the first access network device under a first condition; and accessing, by the UE, the first access network device through the LTM switch.

[0010] In a fourth aspect, a method for deriving a key is provided. The method comprises: receiving, by a UE, a LTM switch message from a second access network device, the LTM switch message indicating that the UE switches to a first access network device; performing, by the UE, a horizontal key derivation to obtain a first key for communicating with the first access network device under a first condition; and accessing, by the UE, the first access network device through the LTM switch.

[0011] In a fifth aspect, a method for deriving a key is provided. The method comprises: selecting, by a second access network device, N first access network devices, and sending, by the second access network device, information for communicating with a UE to the N first access network devices, the N being less than or equal to M-2, and the M representing a number of all values of NCC; receiving, by the second access network device, LTM configuration information from the N first access network devices, the LTM configuration information including NCC; and sending, by the second access network device, the LTM configuration information to the UE.

[0012] In a sixth aspect, a device for deriving a key is provided, the device comprising: a receiving module, a processing module and a sending module, wherein: the receiving module is configured to receive a path switch message from a first access network device, the path switch message being used to establish a signaling connection between a user equipment (UE) and a core network; the processing module is configured to determine whether to perform a derivation of a next hop value (NH) for the UE according to the path switch message; and the sending module is configured to send a path switch acknowledgement message to the first access network device, the path switch acknowledgement message being used to respond to the path switch message.

[0013] In a seventh aspect, a device for deriving a key is provided, the device comprising: a sending module and a receiving module, wherein: the sending module is configured to send a path switch message to a first network element, the path switch message being used to establish a signaling connection between a user equipment (UE) and a core network; and the receiving module is configured to receive a path switch acknowledgement message from the first network element, the path switch acknowledgement message being used to respond to the path switch message; wherein the path switch message comprises a first indication indicating that the first network element does not perform a derivation of a next hop value (NH) if a first condition is satisfied.

[0014] In an eighth aspect, a device for deriving a key is provided, the device comprising: a receiving module and a processing module, wherein: the receiving module is configured to receive a LTM switch message from a second access network device, the LTM switch message indicating that the UE switches to a first access network device; the processing module is configured to perform a horizontal key derivation to obtain a first key used for communication with the first access network device if a first condition is satisfied; and the processing module is further configured to access the first access network device through the LTM switch.

[0015] In a ninth aspect, a device for deriving a key is provided, the device comprising: a receiving module and a processing module, wherein: the receiving module is configured to receive N third NCCs from a second access network device; the processing module is configured to derive a first key used for communication with a first access network device according to a fourth NCC and a fifth NCC saved by the UE, the N third NCCs comprising the fourth NCC; and the processing module is further configured to determine a sixth NCC according to the fourth NCC, the sixth NCC being used to replace the fifth NCC.

[0016] In a tenth aspect, a device for deriving a key is provided, the device comprising a processing module, a sending module and a receiving module, wherein: the processing module is configured to select N first access network devices; the sending module is configured to send information related to UE communication to the N first access network devices selected by the processing module, N being less than or equal to M-2, M representing the number of all values of NCC; the receiving module is configured to receive LTM configuration information from the N first access network devices, the LTM configuration information comprising NCC; and the sending module is further configured to send the LTM configuration information to the UE.

[0017] In an eleventh aspect, a device for deriving a key is provided, the device being configured to perform the steps of the method of the first aspect, or to perform the steps of the method of the second aspect, or to perform the steps of the method of the third aspect, or to perform the steps of the method of the fourth aspect.

[0018] In a twelfth aspect, a terminal is provided, the terminal comprising a processor and a memory, the memory storing programs or instructions executable on the processor, the programs or instructions being executed by the processor to implement the steps of the method of the third aspect or the fourth aspect.

[0019] In a thirteenth aspect, a terminal is provided, the terminal comprising a processor and a communication interface, wherein the communication interface is configured to receive an LTM switching message from a second access network device, the LTM switching message indicating that the UE switches to a first access network device, and the processor is configured to, if a first condition is met, perform horizontal key derivation to obtain a first key for communication with the first access network device, and access the first access network device through LTM switching; or the communication interface is configured to receive N third NCCs from a second access network device, the N third NCCs comprising a fourth NCC; and the processor is configured to derive a first key for communication with a first access network device according to the fourth NCC and a fifth NCC saved by the UE, and to determine a sixth NCC according to the fourth NCC, the sixth NCC being used to replace the fifth NCC.

[0020] In a fourteenth aspect, a network-side device is provided, the network-side device comprising a processor and a memory, the memory storing programs or instructions executable on the processor, the programs or instructions being executed by the processor to implement the steps of the method of the first aspect, or to implement the steps of the method of the second aspect, or to implement the steps of the method of the fifth aspect.

[0021] In a fifteenth aspect, a network-side device is provided, comprising a processor and a communication interface, wherein the communication interface is configured to receive a path switch message from a first access network device, the path switch message being configured to establish a signaling connection between a user equipment (UE) and a core network, and the processor is configured to determine whether to perform a derivation of a next hop value (NH) for the UE according to the path switch message, and to send a path switch acknowledgement message to the first access network device, the path switch acknowledgement message being configured to respond to the path switch message; or the communication interface is configured to send the path switch message to a first network element, the path switch message being configured to establish the signaling connection between the UE and the core network, and the communication interface is further configured to receive a path switch acknowledgement message from the first network element, the path switch acknowledgement message being configured to respond to the path switch message, wherein the path switch message comprises a first indication indicating that the first network element does not perform the derivation of the NH, when a first condition is satisfied; or the processor is configured to select N first access network devices, and the communication interface is configured to send information related to a communication of the UE to the N first access network devices, wherein N is less than or equal to M-2, and M represents a number of all values of an NCC, and the communication interface is further configured to receive LTM configuration information from the N first access network devices, the LTM configuration information comprising the NCC, and the communication interface is further configured to send the LTM configuration information to the UE.

[0022] In a sixteenth aspect, a readable storage medium is provided, wherein a program or instructions are stored on the readable storage medium, and the program or instructions are executed by a processor to implement steps of the method according to the first aspect, or to implement steps of the method according to the second aspect, or to implement steps of the method according to the third aspect, or to implement steps of the method according to the fourth aspect, or to implement steps of the method according to the fifth aspect.

[0023] In a seventeenth aspect, a wireless communication system is provided, comprising a terminal and a network-side device, wherein the terminal is configured to implement steps of the method according to the third aspect or the fourth aspect, and the network-side device is configured to implement steps of the method according to the first aspect, or to implement steps of the method according to the second aspect, or to implement steps of the method according to the fifth aspect.

[0024] In an eighteenth aspect, a chip is provided, comprising a processor and a communication interface, wherein the communication interface is coupled to the processor, and the processor is configured to run a program or instructions to implement the method according to the first aspect, or to implement the method according to the second aspect, or to implement the method according to the third aspect, or to implement the method according to the fourth aspect, or to implement the method according to the fifth aspect.

[0025] In a nineteenth aspect, a computer program / program product is provided, which is stored in a storage medium, and is executed by at least one processor to implement the steps of the method according to the first aspect, or to implement the steps of the method according to the second aspect, or to implement the steps of the method according to the third aspect, or to implement the steps of the method according to the fourth aspect, or to implement the steps of the method according to the fifth aspect.

[0026] In the embodiments of the present application, the first network element receives a path switching message from the first access network device, the path switching message being used to establish a signaling connection between the UE and the core network, and the first network element determines whether to perform the derivation of the NH for the UE according to the path switching message, and sends a path switching confirmation message to the first access network device, the path switching confirmation message being used to respond to the path switching message. Through the method, the first network element can determine whether to perform the derivation of the NH or not according to the path switching message, thereby being able to reduce the number of unnecessary NH derivations, and thus reduce the number of times of using the NCC value to track the number of NH derivations, so that the NCC value is not frequently updated and reset, and thus the problem of key asynchronization of the UE and the network side caused by the change of the NCC value is avoided, thereby improving the stability and performance of the communication. BRIEF DESCRIPTION OF DRAWINGS

[0027] FIG. 1 is a block diagram of a wireless communication system according to an embodiment of the present application;

[0028] FIG. 2 is a flowchart of a method for deriving a key according to an embodiment of the present application;

[0029] FIG. 3 is a flowchart of a method for deriving a key according to another embodiment of the present application;

[0030] FIG. 4 is a flowchart of a method for deriving a key according to another embodiment of the present application;

[0031] FIG. 5 is a flowchart of a method for deriving a key according to another embodiment of the present application;

[0032] FIG. 6 is a flowchart of a method for deriving a key according to another embodiment of the present application;

[0033] FIG. 7 is a schematic structural diagram of a device for deriving a key according to an embodiment of the present application;

[0034] FIG. 8 is a schematic structural diagram of a device for deriving a key according to another embodiment of the present application;

[0035] FIG. 9 is a schematic structural diagram of a device for deriving a key according to another embodiment of the present application;

[0036] FIG. 10 is a schematic structural diagram of a device for deriving a key according to another embodiment of the present application;

[0037] FIG. 11 is a structural schematic diagram of a communication device according to an embodiment of the present application;

[0038] FIG. 12 is a hardware structural schematic diagram of a terminal according to an embodiment of the present application;

[0039] FIG. 13 is a structural schematic diagram of a network side device according to an embodiment of the present application;

[0040] FIG. 14 is another structural schematic diagram of a network side device according to an embodiment of the present application. DETAILED DESCRIPTION

[0041] The technical solutions in the embodiments of the present application will be clearly described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all of them. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art belong to the scope of protection of the present application.

[0042] The terms "first", "second", and the like in the present application are used to distinguish similar objects, and are not used to describe a specific order or sequence. It should be understood that the terms used in this way can be interchanged under appropriate circumstances, so that the embodiments of the present application can be implemented in an order other than that illustrated or described herein, and the objects distinguished by "first", "second" are usually a category and do not limit the number of objects, for example, the first object can be one or more. In addition, "or" in the present application means at least one of the connected objects. For example, the protection scope of "A or B" at least covers three schemes, namely, scheme one: including A and not including B; scheme two: including B and not including A; scheme three: including A and B. In addition, the terms "A and / or B", "at least one of A and B", "at least one of A or B" also at least cover the above three schemes, respectively. The character " / " generally represents that the objects before and after are in an "or" relationship.

[0043] The term "indication" in the present application can be a direct indication (or explicit indication) or an indirect indication (or implicit indication). The direct indication can be understood as that the sender explicitly informs the receiver of specific information, operations to be performed or requested results, etc. in the indication sent by the sender. The indirect indication can be understood as that the receiver determines the corresponding information according to the indication sent by the sender, or judges and determines the operations to be performed or the requested results according to the judgment result.

[0044] It is worth noting that the technology described in the embodiments of the present application is not limited to Long Term Evolution (LTE) / LTE-Advanced (LTE-A) systems, but can also be used in other wireless communication systems, such as Code Division Multiple Access (CDMA), Time Division Multiple Access (TDMA), Frequency Division Multiple Access (FDMA), Orthogonal Frequency Division Multiple Access (OFDMA), Single-carrier Frequency-Division Multiple Access (SC-FDMA) or other systems. The terms "system" and "network" in the embodiments of the present application are often used interchangeably, and the described technology can be used in the above-mentioned systems and radio technologies, as well as in other systems and radio technologies. The following description describes a New Radio (NR) system for the purpose of example, and NR terminology is used in most of the following description, but these technologies can also be applied to systems other than NR systems, such as 6th Generation (6G) communication systems.

[0045] FIG. 1 shows a block diagram of a wireless communication system to which embodiments of the present application can be applied. The wireless communication system includes a terminal 11 and a network-side device 12. The terminal 11 can be a terminal-side device such as a mobile phone, a Tablet Personal Computer, a Laptop Computer, a notebook computer, a Personal Digital Assistant (PDA), a palmtop computer, a netbook, an Ultra-mobile Personal Computer (UMPC), a Mobile Internet Device (MID), an Augmented Reality (AR) device, a Virtual Reality (VR) device, a robot, a wearable device, a flight vehicle, a Vehicle User Equipment (VUE), a shipboard device, a Pedestrian User Equipment (PUE), a smart home (a home device with a wireless communication function such as a refrigerator, a television, a washing machine, or furniture), a game console, a Personal Computer (PC), a kiosk, or a self-service machine. The wearable device includes a smart watch, a smart bracelet, a smart earphone, smart glasses, smart jewelry (a smart bracelet, a smart necklace, a smart ring, a smart necklace, a smart anklet, a smart necklace, etc.), a smart wristband, smart clothes, etc. The vehicle-mounted device can also be referred to as a vehicle-mounted terminal, a vehicle-mounted controller, a vehicle-mounted module, a vehicle-mounted component, a vehicle-mounted chip, or a vehicle-mounted unit, etc. It should be noted that the specific type of the terminal 11 is not limited in the embodiments of the present application. The network-side device 12 can include an access network device or a core network device. The access network device can also be referred to as a Radio Access Network (RAN) device, a radio access network function, or a radio access network unit. The access network device can include a base station, a Wireless Local Area Network (WLAN) Access Point (AP), or a Wireless Fidelity (WiFi) node, etc.The base station can be referred to as a Node B (NB), an evolved Node B (eNB), a next generation Node B (gNB), a New Radio Node B (NR Node B), an access point, a relay station (RBS), a serving base station (SBS), a base transceiver station (BTS), a radio base station, a radio transceiver, a basic service set (BSS), an extended service set (ESS), a home Node B (HNB), a home evolved Node B, a transmit / receive point (TRP), or some other suitable terminology in the art, and is not limited to a particular technical terminology, provided that the same technical effect is achieved. It should be noted that in the embodiments of the present application, only the base station in the NR system is taken as an example for introduction, and the specific type of the base station is not limited.

[0046] The core network device can also be referred to as a core network node, a core network function, or a core network network element, etc., which includes but is not limited to at least one of the following: a mobility management entity (MME), an access and mobility management function (AMF), a session management function (SMF), a user plane function (UPF), a policy control function (PCF), a policy and charging rules function (PCRF), an edge application server discovery function (EASDF), a unified data management (UDM), a unified data repository (UDR), a home subscriber server (HSS), a centralized network configuration (CNC), a network repository function (NRF), a network exposure function (NEF), a local NEF (L-NEF), a binding support function (BSF), an application function (AF), a location management function (LMF), a gateway mobile location center (GMLC), a network data analytics function (NWDAF), etc. It should be noted that only the core network device in the NR system is taken as an example for introduction in the embodiments of the present application, and the specific type of the core network device is not limited. If the name of the core network device mentioned in the embodiments of the present application changes in the subsequent protocol version (for example, 6G), it is also within the protection scope of the present application.

[0047] Optionally, the core network device can be implemented by one or more function modules in one device, or can be jointly implemented by multiple devices, and the embodiments of the present application do not make a specific limitation hereon. It can be understood that the above function modules can be network elements in a hardware device, can be software function modules running on a dedicated hardware, or can be virtualized function modules instantiated on a platform (for example, a cloud platform).

[0048] The following explains the terms and related technologies involved in the embodiments of the present application.

[0049] 1. LTM

[0050] LTM, which stands for L1 / L2 triggered mobility, is a mobility management mechanism proposed in 3GPP R18 and later versions. LTM aims to shorten the terminal handover delay and interruption delay through L1 (physical layer) and L2 (data link layer) triggering, thereby improving user experience. In Release 19, the LTM framework is extended to support handover between different base stations (gNB) serving cells, that is, LTM is not limited to inter-cell handover within a single base station, but can also support cross-base station handover.

[0051] 2. Key derivation of initial connection establishment process

[0052] During initial connection establishment, KgNB is derived from AMF and is associated with NCC = 0.

[0053] It is worth noting that the value of NCC = 1 is not used during initial AS context establishment, because after AMF completes authentication and generates KgNB, it sets NCC = 0, and at the same time, it also generates NH1 according to Kamf and KgNB. At this time, NCC = 1. When HO occurs, the UE always receives NCC = 0 from the SgNB, at which time the UE and the SgNB actually use KgNB to make a horizontal derivation, but on the network side, whether it is an Xn HO triggered path switch or an N2 HO triggered Handover Require, it will trigger the AMF to perform a new NH derivation, at which time the AMF generates NH2 according to Kamf and NH1, at which time NCC = 2 and is used for subsequent key derivation, so the NH of NCC = 1 is not used.

[0054] 3. Key derivation of Xn handover process

[0055] The inter-gNB handover process at least includes the following steps:

[0056] a) The source gNB initiates the handover, sends a HANDOVER REQUEST to the target gNB over the Xn interface. When the source gNB has unused {NH, NCC}, vertical key derivation (also known as longitudinal key derivation) is performed, otherwise horizontal key derivation (also known as transversal key derivation) is performed, where NH (Next Hop) is derived from the AMF's key (K AMF ), and NCC is the Next Hop Chaining Counter for NH; if vertical key derivation is performed, the source gNB computes a new key (K gNB ) from NH, and the target cell's Physical Cell Identifier (PCI), and the target cell's Absolute Radio Frequency Channel Number - Downlink (ARFCN-DL) as inputs; if horizontal key derivation is performed, the source gNB computes KgNB* from the currently used key K gNB , the target cell's PCI, and the target ARFCN-DL as inputs; the derived K gNB * and NCC are carried in the HANDOVER REQUEST.

[0057] b) The target gNB provides K gNB * as the subsequent used key, and provides the target cell's RRC configuration in the HANDOVER REQUEST ACKNOWLEDGE, which contains K gNB * and the corresponding NCC.

[0058] c) The source gNB forwards the RRC reconfiguration message carried in the HANDOVER REQUEST ACKNOWLEDGE to the UE.

[0059] d) The UE and the source gNB disconnect, and the UE establishes an RRC connection with the target gNB, and replies with an RRC reconfiguration complete.

[0060] If the NCC value received by the UE in the RRC reconfiguration message is the same as the NCC associated with the currently used K gNB , the UE derives K gNB from the currently used K gNB* , the target PCI, and the target ARFCN-DL.

[0061] If the NCC value received by the UE in the RRC reconfiguration message is different from the NCC associated with the currently used K gNBIf the associated NCC is different, the UE first synchronizes the NCC and NH, i.e. the UE derives the new K amf and NH, and then derives K gNB * vertically from the synchronized NH, target PCI and target ARFCN-DL gNB * is used by the UE for communication with the target gNB gNB .

[0062] e) After the handover is completed, the target gNB sends a path switching message (NGAP PATH SWITCH REQUEST) message to the AMF. After receiving the message, the AMF increments the locally saved NCC by 1, and derives a new NH from K AMF and the NH corresponding to the previous NCC, and sends the new {NH, NCC} to the target gNB through a path switching confirmation message (NGAP PATH SWITCH REQUEST ACKNOWLEDGE) for subsequent handover, and deletes the saved previous {NH, NCC}.

[0063] 4. Key derivation in N2 handover procedure

[0064] When there is no Xn interface, inter-gNB N2 based handover is achieved through signaling interaction over the N2 interface.

[0065] It should be noted that in the N2 handover (HO), since there is no Xn interface, the source gNB and the target gNB cannot directly interact with each other, and the preparation of the candidate target cell needs to be realized through the AMF through the N2 interface. The main NG interface signaling involved includes:

[0066] - the handover requirement message (HANDOVER REQUIRED) sent by the source gNB to the AMF;

[0067] - the HANDOVER REQUEST sent by the AMF to the target gNB;

[0068] - the HANDOVER REQUEST ACKNOWLEDGE returned by the target gNB to the AMF;

[0069] - the HANDOVER COMMAND returned by the AMF to the source gNB;

[0070] When the handover does not involve the change of the AMF, the S-AMF and the T-AMF are the same node, and the signaling interaction between them can be omitted.

[0071] Taking the case that the AMF does not change as an example, the key derivation behavior of the network side is as follows:

[0072] Step 1: After the AMF receives the handover demand message from the source base station, the AMF adds 1 to the locally saved NCC value, calculates a new NH according to K AMF , and sends {NH, NCC} to the target gNB.

[0073] Step 2: The target gNB calculates K gNB* according to NH, target PCI and target ARFCN-DL. gNB* The target gNB uses K gNB as K gNB when the UE switches to the target cell. The target gNB associates NCC with the target K gNB , and includes the received NCC in the RRC reconfiguration message, transmits it to the AMF, and the AMF transmits it to the source gNB, which sends it to the UE through the RRC reconfiguration message.

[0074] It should be noted that the key derivation behavior of the UE side is similar to the UE behavior of the key derivation of the Xn handover process, and will not be repeated here.

[0075] In the related art, in the Xn handover or N2 handover process, the AMF generates a new NH and NCC, and then sends the new NCC to the UE through the radio access network (RAN), so that the UE can also derive a new NH and update the NCC. Therefore, in the case where the RAN sends NCC to the UE, the NCC between the UE and the AMF can be consistent. However, under LTM, there is no RRC message interaction between the UE and the RAN, and the NCC cannot be synchronized, and the value of the NCC is small, so it will cause the NCC to be out of synchronization, and ultimately cause the keys used by the UE and the network side to be out of synchronization.

[0076] For example, assuming that the current NCC of the UE, SgNB and AMF is 1, the UE performs 8 times of inter-CU LTM in succession and then returns to the SgNB. Since there is no RRC message notification in the inter-CU LTM, the NCC used by the UE to derive the key in the SgNB is still 1, but the NCC on the AMF side has changed from 1 to 8 and then flipped back to 1 due to the bit limit of the NCC. The NH of the current SgNB through the path switch by the AMF is the K amfNH8, while NCC is 1. Assuming the UE performs a legacy HO from the SgNB, the SgNB derives KgNB* to the target base station through NH8, target cell ID, target ARFCN-DL, the SgNB informs the UE with an RRC message carrying NCC = 1, the UE compares the NCC = 1 used in the SgNB with the newly sent NCC = 1 by the SgNB, and determines that horizontal derivation is needed, i.e., KgNB is derived from KgNB*. gNB &It can be seen that the key of the UE and the key of the target base station are out of synchronization.

[0077] It should be noted that the legacy HO is a handover process judged and controlled by the network side when the UE moves from the coverage of one base station to the coverage of another base station, in order to maintain communication continuity and service quality.

[0078] The method for deriving a key provided by the embodiment of the application includes that an AMF receives a path switching message from a target gNB, the path switching message being used to establish a signaling connection between the UE and the core network, and a first network element determines whether to perform NH derivation for the UE according to the path switching message, and sends a path switching confirmation message to the target gNB, the path switching confirmation message being used to respond to the path switching message. Through the method, the AMF can determine whether to perform NH derivation or not according to the path switching message, so as to reduce the number of unnecessary NH derivations, thereby reducing the frequency of tracking the number of NH derivations by using the NCC value, so that the NCC value is not updated and reset frequently, thereby avoiding the problem of key out of synchronization between the UE and the network side caused by the change of the NCC value, and further improving the stability and performance of communication.

[0079] The method for deriving a key provided by the embodiment of the application will be described in detail in combination with some embodiments and application scenarios thereof and with reference to the accompanying drawings.

[0080] FIG. 2 is a flowchart of the method for deriving a key provided by the embodiment of the application, as shown in FIG. 2, the method for deriving a key can include the following steps 201 to 205:

[0081] Step 201: A first access network device sends a path switching message to a first network element.

[0082] Step 202: The first network element receives the path switching message from the first access network device.

[0083] The path switching message is used to establish a signaling connection between the UE and the core network.

[0084] In some embodiments of the present application, the path switching message contains a first indication indicating that the first network element does not perform derivation of the NH in the case that a first condition is met; or the first indication is not contained in the path switching message in the case that a second condition is met.

[0085] In some embodiments of the present application, the path switching message contains a first indication, which does not indicate that the first network element performs derivation of the NH in the case that a first condition is met, or which indicates that the first network element does not perform derivation of the NH in the case that a second condition is met.

[0086] In some embodiments of the present application, the first indication can be an LTM indication. The LTM indication is used to indicate that LTM switching is performed, for example, the LTM indication is used to indicate that the UE is currently performing LTM switching.

[0087] In some embodiments of the present application, the first condition includes that the UE accesses the first access network device through LTM switching for the first time.

[0088] In some embodiments of the present application, the second condition includes that the UE accesses the first access network device through LTM switching for the first time.

[0089] In some embodiments of the present application, the first access network device can be a base station, which can be a 5G base station, i.e., gNB.

[0090] In some embodiments of the present application, the first access network device can be an access network device to which the UE accesses after leaving the source access network device in the Inter-CU LTM scenario.

[0091] Further, the first access network device can be an access network device to which the UE accesses for the first time, or the first access network device can be an access network device to which the UE accesses for the first time.

[0092] It should be noted that the first access is the first time access, and the non-first access is the non-first time access.

[0093] Exemplarily, the first access network device can be a target base station TgNB to which the UE needs to switch for the first time from a currently connected base station in the Inter-CU LTM scenario.

[0094] Exemplarily, the first access network device can be an access network device to which the UE switches back from the TgNB after switching from the SgNB to the TgNB in the Inter-CU LTM scenario, i.e., the SgNB. It can be understood that the SgNB is an access network device to which the UE accesses for the first time.

[0095] It should be noted that the base station first accessed by the UE or the base station not first accessed by the UE refers to the base station to which the UE needs to switch from the currently connected base station, that is, the base station to which the UE needs to access.

[0096] In some embodiments of the present application, the first network element can be an AMF.

[0097] In some embodiments of the present application, the path switching message can be a Path Switch.

[0098] Exemplarily, taking the first network element as an AMF and the first access network device as TgNB1 as an example, if the UE first accesses TgNB1, TgNB1 does not carry the first indication in the path switching message; if the UE is not first accessing TgNB1, TgNB1 carries the first indication in the path switching message, which indicates that the AMF does not perform NH derivation.

[0099] Exemplarily, taking the first network element as an AMF and the first access network device as TgNB1 as an example, since the UE currently performs LTM switching, TgNB1 always carries an LTM indication in the path switching message, which is used to indicate that LTM switching is performed. If the UE first accesses TgNB1, the LTM indication simultaneously indicates that the AMF performs NH derivation, for example, setting its value to 1; or if the UE is not first accessing TgNB1, the LTM indication simultaneously indicates that the AMF does not perform NH derivation, for example, setting its value to 0.

[0100] Wherein, the first access refers to access through LTM. That is, the UE reports signal measurement results to the currently connected base station, and the currently connected base station sends an L1 or L2 indication to the UE according to the signal measurement results, so that the UE switches to the first access network device.

[0101] It can be understood that the LTM indication can have two functions, that is, indicating that LTM switching is performed and indicating that the AMF performs NH derivation when the UE first accesses TgNB1.

[0102] In some embodiments of the present application, the first access network device accepts the UE to access through LTM switching, and sends a path switching message to the first network element.

[0103] In the embodiments of the present application, by introducing the judgment of the first access network device on whether the UE is first accessed, when not first accessed, the first access network device indicates that the first network element does not perform NH derivation, so that the use of NCC can be reduced, thereby avoiding the key synchronization between the UE and the access network device caused by the change of NCC.

[0104] Step 203: The first network element determines whether to perform NH derivation for the UE according to the path switching message.

[0105] It should be noted that the derivation of the NH for the UE can also be replaced by deriving an access layer key for the UE, performing key isolation for the UE, requesting vertical derivation parameters for the UE, etc. The subsequent description of the judgment can also be replaced by the first network element determining whether to derive an access layer key for the UE according to the path switching message, the first network element determining whether to perform key isolation for the UE according to the path switching message, the first network element determining whether to request vertical derivation parameters for the UE according to the path switching message, etc.

[0106] The subsequent description of the first network element determining to perform the derivation of the NH for the UE according to the path switching message can also be replaced by the first network element determining to derive an access layer key for the UE according to the path switching message, the first network element determining to perform key isolation for the UE according to the path switching message, the first network element determining to request vertical derivation parameters for the UE according to the path switching message, etc.

[0107] In some embodiments of the present application, in the case of including the first indication in the path switching message, the first network element can determine whether to perform the derivation of the NH for the UE according to the first indication carried in the path switching message, or the first network element can determine not to perform the derivation of the NH for the UE in the case of parsing the first indication from the path switching message.

[0108] In some embodiments of the present application, the first network element can obtain the first indication from the context of the UE according to the path switching message, and determine whether to perform the derivation of the NH for the UE according to the first indication.

[0109] Step 204: The first network element sends a path switching confirmation message to the first access network device.

[0110] The path switching confirmation message is used to respond to the path switching message.

[0111] In some embodiments of the present application, the path switching confirmation message can be a Path Switch ACK.

[0112] In some embodiments of the present application, if the first network element determines not to perform the derivation of the NH for the UE, the path switching confirmation message contains a first NH and a first NCC, and the first NH and the first NCC are the NH and the NCC currently saved by the first network element, or are preset values.

[0113] In some embodiments of the present application, if the first network element determines not to perform the derivation of the NH for the UE, the path switching confirmation message contains a second NH and a second NCC, and the second NH and the second NCC are generated by the first network element.

[0114] In some embodiments of the present application, the preset value includes at least one of a preset NH value and a preset NCC value. Illustratively, the preset NH value and the preset NCC value can be 0.

[0115] It should be noted that the preset value can be set according to actual needs, and the embodiments of the present application do not limit this.

[0116] Step 205: The first access network device receives a path switching confirmation message from the first network element.

[0117] Illustratively, taking the first network element as AMF and the first access network device as TgNB as an example, the TgNB sends a path switching message to the AMF. After the AMF receives the path switching message from the TgNB, it determines whether to perform the derivation of NH for the UE according to the path switching message. Further, if the AMF determines not to perform the derivation of NH for the UE, it sends a path switching confirmation message carrying the currently saved NH and NCC to the TgNB, or sends a path switching confirmation message carrying a preset NH and a preset NCC value to the TgNB.

[0118] It should be noted that steps 201 to 205 are applicable to the scenario of implementing LTM of Inter-CU through Xn interface signaling interaction, and the scenario of implementing LTM of Inter-CU through N2 interface signaling interaction.

[0119] The method for deriving a key provided by the embodiments of the present application, the first network element receives a path switching message from the first access network device, the path switching message is used to establish a signaling connection between the UE and the core network, the first network element determines whether to perform the derivation of NH for the UE according to the path switching message, and sends a path switching confirmation message to the first access network device, the path switching confirmation message is used to respond to the path switching message. Through this method, the first network element can determine whether to perform the derivation of NH or not to perform the derivation of NH according to the path switching message, so as to reduce the number of unnecessary NH derivation times, thereby reducing the number of times of using NCC value to track the number of NH derivation times, so that the NCC value will not be frequently updated and reset, in this way, the problem of key asynchronization caused by the change of NCC value of the UE and the network side is avoided, thereby improving the stability and performance of communication.

[0120] In some embodiments of the present application, the step 203 can be implemented by the following step 203a.

[0121] Step 203a: In the case where the path switching message contains the first indication, the first network element determines not to perform the derivation of NH for the UE.

[0122] In some embodiments of the present application, the first indication is used to indicate the execution of layer 1 / layer 2 triggered mobility LTM switching.

[0123] Exemplarily, taking the first network element as an AMF, the first access network device as an In TgNB1, and the case that the first indication is carried in the path switching message sent by the TgNB1 as an example, after detecting the first indication, the AMF determines not to perform the derivation of the NH for the UE.

[0124] In the embodiments of the present application, in the case that the UE does not access the first access network device for the first time, the first access network device sends the path switching message containing the first indication to the first network element, and the first network element can determine not to perform the derivation of the NH for the UE in the case that the first indication is carried in the path switching message from the first access network device, so that the derivation of the NH for the UE can be avoided in the case that the UE does not access the first access network device for the first time, thereby reducing the number of derivations of the NH, so that the NCC value will not be increased frequently due to the increase of the number of derivations of the NH, thereby avoiding the key synchronization caused by the change of the NCC value.

[0125] In some embodiments of the present application, the path switching message contains the first indication; exemplarily, the step 203 can be implemented through the following step 203b.

[0126] Step 203b: The first network element determines whether to perform the derivation of the NH for the UE according to the first indication.

[0127] In some embodiments of the present application, the step 203b can include the following step 203b1 or step 203b2.

[0128] Step 203b1: In the case that the first indication indicates to perform the derivation of the NH for the UE, the first network element determines to perform the derivation of the NH for the UE.

[0129] Step 203b2: In the case that the first indication indicates not to perform the derivation of the NH for the UE, the first network element determines not to perform the derivation of the NH for the UE.

[0130] In some embodiments of the present application, the first access network device judges whether to indicate the first network element to perform the derivation of the NH for the UE, and indicates the first network element to perform the derivation of the NH or not to perform the derivation of the NH through the first indication.

[0131] Exemplarily, taking the first network element as an AMF, the first access network device as an In TgNB1, and the case that the first indication is carried in the path switching message sent by the TgNB1 as an example, if the UE accesses the TgNB1 for the first time, the first indication is contained in the path switching message sent by the TgNB1, and the first indication indicates the AMF to perform the derivation of the NH; or, if the UE does not access the TgNB1 for the first time, the first indication is contained in the path switching message sent by the TgNB1, and the first indication indicates the AMF not to perform the derivation of the NH.

[0132] Further, if the first indication is used to indicate that the AMF derives the NH, the value thereof can be set to 1; or if the first indication is used to indicate that the AMF does not derive the NH, the value thereof can be set to 0.

[0133] In some embodiments of the present application, the first network element can obtain the first indication from the path switching message, and determine whether to perform the derivation of the NH for the UE according to the first indication.

[0134] For example, in the case that the path switching message sent by the TgNB1 contains the first indication and the first indication indicates that the AMF does not derive the NH, the AMF determines not to perform the derivation of the NH for the UE according to the first indication.

[0135] For another example, in the case that the path switching message sent by the TgNB1 carries the first indication and the first indication indicates that the AMF derives the NH, the AMF performs the derivation of the NH for the UE according to the first indication.

[0136] In the embodiments of the present application, in the case that the first network element carries the first indication in the path switching message of the first access network device to indicate that the derivation of the NH is not performed, the first network element determines not to perform the derivation of the NH for the UE, so that the derivation of the NH for the UE is not performed according to the first indication in the case that the UE accesses the first access network device for the first time, thus reducing the number of times of the derivation of the NH, so that the NCC value does not increase frequently due to the increase in the number of times of the derivation of the NH, thereby avoiding the key synchronization caused by the change of the NCC value; or in the case that the first network element carries the first indication in the path switching message of the first access network device to indicate that the derivation of the NH is performed, the first network element performs the derivation of the NH for the UE, so that the derivation of the NH for the UE is performed in the case that the UE accesses the first access network device for the first time, so that the UE can generate a new key through the derived NH when performing the normal inter-base station switching (such as Xn switching) next time, so that the UE can use the new key to communicate after switching to a new base station, thereby ensuring the security of the communication.

[0137] It should be noted that steps 203a and 203b are applicable to the scenario of realizing the LTM of the Inter-CU through the Xn interface signaling interaction, and the scenario of realizing the LTM of the Inter-CU through the N2 interface signaling interaction.

[0138] In some embodiments of the present application, before the above step 201, the method for deriving the key provided by the embodiments of the present application can further include the following step 206:

[0139] Step 206: The first network element receives the first indication from the second access network device, and saves the first indication in the context of the UE.

[0140] In combination with the above step 206, the above step 203 can be implemented by the following step 203c.

[0141] Step 203c: The first network element obtains the first indication from the context of the UE according to the path switching message, and determines whether to perform the derivation of the NH for the UE according to the first indication.

[0142] In some embodiments of the present application, the second access network device can send the first indication to the first network element.

[0143] In some embodiments of the present application, the above second access network device can be a base station, which can be a 5G base station, i.e., gNB.

[0144] It should be noted that the second access network device can be a source base station SgNB.

[0145] In some embodiments of the present application, the second access network device can be the access network device currently connected by the UE in the LTM scenario of Inter-CU, i.e., the source access network device to which the UE needs to switch to other access network devices.

[0146] It should be noted that the interpretation of the first indication can refer to the description of the above embodiments, which will not be repeated here.

[0147] In some embodiments of the present application, the first network element obtains the context of the UE according to the identifier of the UE in the path switching message. The identifier of the UE can be RAN UE NGAP ID, AMF UE NGAP ID.

[0148] In some embodiments of the present application, the second access network device can send the first indication to the first network element alone; or the second access network device can send a switching requirement message to the first network element, and carry the first indication in the switching requirement message.

[0149] In some embodiments of the present application, the above switching requirement message can be Handover Required.

[0150] Exemplarily, taking the first network element as AMF and the second access network device as SgNB as an example, the SgNB sends the LTM indication to the AMF, and the AMF can save the LTM indication in the context of the UE after receiving the LTM indication.

[0151] Exemplarily, taking the first network element as AMF and the second access network device as SgNB as an example, the SgNB sends a switching requirement message to the AMF, the switching requirement message contains the identifier of the candidate cell and the LTM indication, and the AMF saves the LTM indication in the context of the UE after receiving the switching requirement message.

[0152] It should be noted that the SgNB can send the first indication to the AMF alone, or send a handover demand message containing the first indication to the AMF.

[0153] In some embodiments of the present application, after the first network element saves the first indication from the second access network device in the context of the UE, upon receiving the path switching message from the first access network device, the first network element can obtain the first indication in the context of the UE according to the path switching message, and determine whether to perform the derivation of the NH for the UE according to the first indication.

[0154] It should be noted that the first network element can save other indications obtained by converting the first indication into the context of the UE, and then the first network element obtains the other indications from the context of the UE according to the path switching message, and determines whether to perform the derivation of the NH for the UE according to the other indications.

[0155] Exemplarily, taking the first network element as the AMF, the first access network device as the TgNB, and the second access network device as the SgNB as an example, the SgNB sends a handover demand message containing the LTM indication to the AMF, the AMF receives the handover demand message and saves the LTM indication contained in the handover demand message in the context of the UE, and then the AMF receives the path switching message from the TgNB, obtains the context of the UE according to the path switching message, and determines whether to perform the derivation of the NH for the UE according to whether the LTM indication is contained in the context of the UE.

[0156] Further, in the case that the context of the UE contains the LTM indication, the AMF performs the derivation of the NH for the UE, or in the case that the context of the UE does not contain the LTM indication, the AMF does not perform the derivation of the NH for the UE.

[0157] In some embodiments of the present application, the AMF performs the derivation of the NH to obtain the second NH and the second NCC, and saves the second NH and the second NCC in the context of the UE.

[0158] In the embodiments of the present application, the second access network device can send the first indication to the first network element, and the first network element can first save the first indication in the context of the UE, and then obtain the first indication from the context of the UE when receiving the path switching message from the first access network device, and determine whether to perform the derivation of the NH for the UE according to the indication, so that the first network element can determine whether to perform the derivation of the NH according to the indication of the second access network device, thereby being able to not perform the derivation of the NH for the UE in the case that the UE accesses the first access network device from the second access network device through the LTM for the first time, thereby avoiding the key between the UE and the access network device out of synchronization caused by the change of the NCC.

[0159] In some embodiments of the present application, the method for deriving a key provided by the embodiments of the present application can further include the following step 207:

[0160] Step 207: The first network element does not establish a signaling connection between the UE and the core network according to the first indication.

[0161] In some embodiments of the present application, after the first network element receives the first indication from the second access network device, the first network element does not establish a signaling connection between the UE and the core network according to the first indication.

[0162] For example, taking the first network element as AMF, the first access network device as TgNB1, and the second access network device as SgNB, the SgNB sends a handover requirement message to the AMF, the handover requirement message containing an LTM indication, the AMF receives the handover requirement message and saves the LTM indication contained in the handover requirement message in the UE context, and then the AMF does not establish a signaling connection between the UE and the core network according to the LTM indication.

[0163] It should be noted that the AMF can not trigger the SMF to establish a user plane channel according to the LTM indication. For example, a session management context update request is not sent to the SMF, or a session management context update request carrying a suspension indication is sent to the SMF, the suspension indication indicating that the SMF does not establish an N3 tunnel temporarily.

[0164] In some embodiments of the present application, the AMF can learn from the LTM indication that the UE has not moved to the base station at present, and therefore does not establish a user plane, i.e., does not establish a signaling connection between the UE and the core network, thereby facilitating the reduction of the interaction complexity of the core network.

[0165] In some embodiments of the present application, after the above step 206, the method for deriving a key provided by the embodiments of the present application can further include the following step 208:

[0166] Step 208: The first network element saves the second NH and the second NCC corresponding to the first access network device according to the first indication.

[0167] In some embodiments of the present application, if the first network element determines not to perform NH derivation for the UE, the above handover confirmation message contains the second NH and the second NCC.

[0168] It should be noted that step 208 can be performed before step 204 described above. That is, the first network element receives the first indication from the second access network device and saves the first indication in the context of the UE, the first access network device sends the path switching message to the first network element, the first network element sends the path switching confirmation message to the first access network device, the first network element obtains the first indication from the context of the UE according to the path switching message, and saves the second NH and the second NCC corresponding to the first access network device according to the first indication.

[0169] In some embodiments of the present application, the second NH and the second NCC described above are generated by the first network element. In some embodiments of the present application, after the first network element receives and saves the first indication from the second access network device, the path switching message from the first access network device is received, the context of the UE is obtained by the first network element according to the path switching message, and if the first indication in the context of the UE indicates that NH derivation is not performed, the NH and the NCC in the context of the UE are taken as the second NH and the associated second NCC.

[0170] For example, in combination with the above example, after the AMF receives and saves the first indication, the path switching message from the AMF is received, the context of the UE is obtained by the AMF according to the path switching message, and according to the first indication contained in the context of the UE, the path switching confirmation message containing NH1 and NCC1 in the current context of the UE is sent to TgNB1.

[0171] In some embodiments of the present application, the first network element can perform NH derivation to obtain the second NH and the second NCC when the UE accesses the first access network device for the first time, and save the second NH and the second NCC in the context of the UE. The first network element takes the NH and the NCC in the context of the UE as the second NH and the second NCC when the UE accesses the first access network device for the second time.

[0172] In some embodiments of the present application, the first network element can determine whether the UE accesses the first access network device for the first time according to the access indication in the context of the UE. When the access indication corresponding to the first access network device is not contained in the context of the UE, the first network element determines that the UE accesses the first access network device for the first time, and generates and saves the access indication corresponding to the first access network device. When the access indication corresponding to the first access network device is contained in the context of the UE, the first network element determines that the UE accesses the first access network device for the second time.

[0173] In some embodiments of the present application, the first network element sends the path switching confirmation message containing the second NH and the second NCC described above to the first access network device in response to the path switching message from the first access network device.

[0174] Exemplarily, in combination with the above example, after the AMF receives and saves the LTM indication, the AMF receives a path switching message from the AMF, obtains the context of the UE according to the path switching message, and determines to perform the derivation of the NH for the UE according to the LTM indication contained in the context of the UE and the access indication of TgNB1 not contained in the context of the UE, the AMF sends a path switching confirmation message to TgNB1, and the message contains NH2 and NCC2. NH2 and NCC2 are derived according to NH1 in the current context.

[0175] Exemplarily, in combination with the above example, after the AMF receives and saves the LTM indication, the AMF receives a path switching message from the first access network device, obtains the context of the UE according to the path switching message, and determines not to perform the derivation of the NH for the UE according to the LTM indication contained in the context of the UE and the access indication of TgNB1 contained in the context of the UE, the AMF sends a path switching confirmation message to TgNB1, and the message contains NH1 and NCC1 in the current context of the UE.

[0176] In the embodiment of the present application, the first network element can determine not to perform the derivation of the NH for the UE according to the first indication, and send the current NH and the NCC corresponding to the NH to TgNB1, so as to not need to derive the NH again, reduce the change of the NCC value, and further prevent the key out-of-sync caused by the reset of the NCC value.

[0177] It should be noted that steps 206, 203c, 207, and 208 are applicable to the scenario of realizing the LTM of Inter-CU through N2 interface signaling interaction.

[0178] In some possible implementation manners, the method for deriving a key provided by the embodiment of the present application can further include the following step 209:

[0179] Step 209: If the switching confirmation message includes key-related information, the first access network device ignores the key-related information.

[0180] The key-related information includes at least one of the following: NH, NCC.

[0181] In some embodiments of the present application, under the condition of satisfying the first condition, after the first access network device receives the path switching confirmation message from the first network element, if the switching confirmation message includes key-related information, the first access network device ignores the key-related information.

[0182] Exemplarily, taking the first access network device as TgNB1 and the first network element as AMF as an example, in the case that the UE does not access TgNB1 for the first time, after receiving the NH and NCC, TgNB1 ignores the NH and NCC.

[0183] It should be noted that in the LTM scenario, the TgNB can not derive a new key according to the NH and the NCC, and therefore, the TgNB can ignore the NH and the NCC upon receiving them and not perform subsequent processing.

[0184] In the embodiments of the present application, in the case where the UE does not access the first access network device for the first time, the first access network device ignores the received NH and NCC without processing them, thereby saving network resources.

[0185] In some possible implementation manners, the method for deriving a key provided by the embodiments of the present application can further include the following step 210:

[0186] Step 210: If the handover confirmation message includes key-related information, the first access network device saves the key-related information.

[0187] The key-related information is used for next Xn handover, and the key-related information includes at least one of the following: NH, NCC.

[0188] In some embodiments of the present application, in the case where the second condition is met, after the first access network device receives the path handover confirmation message from the first network element, if the handover confirmation message includes key-related information, the first access network device saves the key-related information.

[0189] Exemplarily, taking the first access network device as TgNB1 and the first network element as AMF as an example, in the case where the UE accesses the TgNB1 for the first time, the TgNB1 saves the NH and NCC after receiving them.

[0190] It should be noted that in the Xn handover scenario, the TgNB can need to derive a new key according to the NH and the NCC, and therefore, the TgNB can save the NH and the NCC upon receiving them to use them as derivation parameters in the next Xn handover. However, for the next LTM handover, the NH and the NCC are not used as derivation parameters.

[0191] It should be noted that in communication, Xn handover and LTM (L1 / L2 triggered mobility) handover are two different handover mechanisms, each having different characteristics and application scenarios. Xn handover specifically refers to handover in a 5G network, allowing a UE to switch from one 5G base station to another 5G base station to support various different scenarios and application requirements, and Xn handover is usually based on an Xn interface. LTM handover is the latest research content of 3GPP R18, aiming to shorten the terminal handover delay and interruption delay and improve user experience, and it introduces a new mechanism that allows the network to trigger the terminal to obtain the TA (time advance) of the target cell through PDCCH before cell handover, thereby completing uplink synchronization in advance.

[0192] In the embodiments of the present application, in the case that the UE accesses the TgNB1 for the first time, the TgNB1 saves the received NH and NCC as the KgNB derivation parameters for the next normal Xn handover, thereby ensuring the security of communication in the next Xn handover scenario after the LTM ends.

[0193] In some embodiments of the present application, the method for deriving a key provided by the embodiments of the present application can further include the following steps 211 and 212:

[0194] Step 211: The first access network device accepts the UE to access through LTM handover.

[0195] Step 212: The first access network device determines a first key for communication with the UE.

[0196] It should be noted that steps 211 and 212 can be performed before step 201, i.e., before the first access network device sends the path switching message to the first network element, the first access network device accepts the UE to access through LTM handover and determines a first key for communication with the UE.

[0197] In some embodiments of the present application, before the first access network device accepts the UE to access through LTM handover, the first access network device can receive an access message from the UE.

[0198] In some embodiments of the present application, in the case that the first access network device accepts the UE to access through LTM handover, the first access network device determines a first key for communication with the UE.

[0199] In some embodiments of the present application, the above step 212 can be implemented through the following step 212a or step 212b.

[0200] Step 212a: In the case that a first condition is met, the first access network device performs horizontal key derivation to obtain the first key.

[0201] In some embodiments of the present application, in the case that the UE accesses the first access network device through LTM handover for the first time, the first access network device performs horizontal key derivation to obtain the first key.

[0202] It should be noted that horizontal key derivation is a process of deriving a new key based on the currently activated key. Specifically, horizontal key derivation (or horizontal derivation) refers to a process of deriving a new key based on an existing key (such as a base key or a master key) in a specific communication process, and such derivation is performed in a “horizontal” manner, i.e., based on the currently activated key.

[0203] Exemplarily, taking the first access network device TgNB1 as an example, if the UE is not accessing the TgNB1 for the first time, the TgNB1 will derive KgNB**1 from the saved KgNB*1 and determine KgNB**1 as the key used by the UE, wherein the TgNB1 derives KgNB**1 from KgNB*1, a physical cell identifier (target PCI1) of the TgNB1, and an absolute radio frequency channel number (ARFCN-DL) of the TgNB1, and saves KgNB**1 in T1 configuration. The first access refers to access through the LTM.

[0204] It should be noted that the absolute radio frequency channel number of the TgNB1 can be represented as target ARFCN-DL1

[0205] In step 212b, the first access network device determines the key in the T1 configuration as the first key when the second condition is met.

[0206] Exemplarily, taking the first access network device TgNB1 as an example, if the UE is accessing the TgNB1 for the first time, the TgNB1 determines KgNB*1 in the T1 configuration as the key used by the TgNB1.

[0207] Exemplarily, taking the first access network device TgNB1 as an example, the TgNB1 derives the key according to the source base station configuration information and the configuration information indicated by the L1 message.

[0208] It should be noted that the configuration information indicated by the L1 message can be the configuration information indicated by the LTM switching message sent by the SgNB to the UE.

[0209] In the embodiments of the present application, by introducing the judgment of whether the UE is accessing the first access network device for the first time, the first access network device derives the transverse key once when the UE is not accessing the first access network device for the first time, so that the UE can use a new key to communicate after reselecting to the first access network device each time, which can prevent the reuse of the key stream caused by the PDCP COUNT rollover, and can reduce the use of NCC, so that more second access network devices can select more cells.

[0210] In some embodiments of the present application, the method for deriving a key provided by the embodiments of the present application can further include steps 213 and 214.

[0211] Step 213: The first access network device receives information from the second access network device that is communicating with the UE.

[0212] Step 214: The first access network device sends LTM configuration information to the second access network device.

[0213] The LTM configuration information mentioned above includes NCC.

[0214] In some embodiments of this application, the second access network device can send information about communication with the UE to the first access network device. The second access network device can send information about communication with the UE to the first access network device via a handover request message.

[0215] In some embodiments of this application, the information communicated with the UE may include a target cell identifier, such as target PCI1.

[0216] In some embodiments of this application, the second access network device can receive LTM configuration information from the first access network device. The second access network device can receive LTM configuration information from the first access network device via a Handover Request ACK message.

[0217] In some embodiments of this application, the LTM configuration information includes the configuration information (T1 configuration) of TgNB1, which includes at least one of the following: NCC1, target PCI1, and target ARFCN-DL1.

[0218] For example, taking TgNB1 as the first access network device and SgNB as the second access network device, TgNB1 receives information about communicating with the UE from SgNB and sends T1 configuration of TgNB1 to SgNB. The T1 configuration includes at least NCC1 corresponding to TgNB1.

[0219] It should be noted that steps 213 and 214 can be performed before step 201 above.

[0220] It should be noted that steps 209-214 apply to scenarios where LTM of Inter-CU is implemented through Xn interface signaling interaction, and scenarios where LTM of Inter-CU is implemented through N2 interface signaling interaction.

[0221] Figure 3 is a flowchart illustrating a method for deriving a key according to an embodiment of this application. As shown in Figure 3, the method for deriving a key may include the following steps 301 to 304:

[0222] Step 301: The second access network device sends an LTM switching message to the UE.

[0223] The LTM switching message indicates that the UE switches to the first access network device.

[0224] It should be noted that the description of the second access network device can refer to the description of the above embodiments, which will not be repeated here.

[0225] In some embodiments of the present application, the LTM switching message can be an L1 message.

[0226] Step 302: The UE receives the LTM switching message from the second access network device.

[0227] Step 303: If the first condition is met, the UE performs horizontal key derivation to obtain a first key for communicating with the first access network device.

[0228] In some embodiments of the present application, the first condition includes that the UE accesses the first access network device through LTM switching for the first time.

[0229] In some embodiments of the present application, if the UE accesses the first access network device for the first time, the UE performs horizontal key derivation to obtain a first key for communicating with the first access network device.

[0230] For example, taking TgNB1 as the first access network device, if the UE accesses TgNB1 for the first time, the UE derives KgNB**1 from KgNB*1, target PCI1 of TgNB1, and ARFCN-DL of TgNB1, and determines KgNB**1 as the key used by TgNB1, wherein the UE saves KgNB**1 in T1 configuration. The first access refers to access through LTM.

[0231] In some embodiments of the present application, if the first condition is met, the UE determines the key in T1 configuration as the first key.

[0232] For example, taking TgNB1 as the first access network device, if the UE accesses TgNB1 for the first time, the UE determines KgNB*1 in T1 configuration as the key used by TgNB1.

[0233] In some embodiments of the present application, in the case that the second condition is met, i.e., the UE accesses the first access network device for the first time, the UE can determine the first key in the following manner.

[0234] In some embodiments of the present application, the above-mentioned second condition comprises that the UE accesses the first access network device for the first time through LTM switching.

[0235] Manner one: the UE determines the key in the T1 configuration as the first key.

[0236] Exemplarily, taking the first access network device TgNB1 as an example, if the UE accesses TgNB1 for the first time, the UE determines KgNB*1 in the T1 configuration as the key used by TgNB1.

[0237] It should be noted that the UE can derive the key in advance according to the LTM configuration information (i.e., T1 configuration) after obtaining the LTM configuration information; or the UE can derive the key based on the LTM configuration information after receiving the LTM switching message from the SgNB after obtaining the LTM configuration information.

[0238] Manner two: the UE derives the first key according to the source base station configuration information and the configuration information indicated by the L1 message (i.e., the LTM configuration message).

[0239] Exemplarily, taking the first access network device TgNB1 as an example, the UE derives the key used by TgNB1 according to the source base station configuration information and the configuration information indicated by the L1 message.

[0240] Specifically, if the NCC used by the SgNB (i.e., the NCC1 used for deriving the key used by the SgNB) is different from the NCC in the indicated configuration information, the UE derives a new NH according to the current Kamf and NH, and derives KgNB* according to the new NH, target PCI, and target ARFCN-DL, and saves it in the configuration information. If the NCC currently used by the UE is the same as the NCC in each configuration information, the UE derives KgNB* according to the KgNB, target PCI, and target ARFCN-DL saved in the configuration information, and saves it in the configuration information.

[0241] It should be noted that, in the above steps, since the NCC1 currently used by the UE (i.e., the NCC1 used for deriving the key used by the SgNB) is different from the NCC2 in the T1 configuration, the UE derives NH2 from Kamf and NH1 once according to the difference between NCC2 and NCC1 (assuming 1), and derives KgNB*1 from NH2, target PCI1, target ARFCN-DL1, and saves KgNB*1 in the T1 configuration, and determines KgNB*1 as the key used by the TgNB1.

[0242] Step 304: The UE accesses the first access network device through LTM switching.

[0243] In some embodiments of the present application, the UE can access the first access network device from the currently connected access network device (i.e., the second access network device) through LTM switching.

[0244] It should be noted that steps 301 to 304 can be performed before step 201 described above.

[0245] The method for deriving a key provided by the embodiments of the present application can, in the case that the UE is not accessing the first access network device for the first time, perform horizontal key derivation to obtain the key for communication with the first access network device. In this way, by introducing the judgment of the UE whether it is accessing for the first time, once the horizontal key derivation is performed by the UE when not accessing for the first time, the UE can use a new key for communication after reselecting to a new access network device each time, which can prevent key stream reuse caused by PDCP COUNT rollover, and can also reduce the use of NCC.

[0246] In some embodiments of the present application, the method for deriving a key provided by the embodiments of the present application further includes the following steps:

[0247] Step 305: The UE receives LTM configuration information from the second access network device.

[0248] In some embodiments of the present application, the UE receiving LTM configuration information from the second access network device can include the UE receiving N third NCCs from the second access network device.

[0249] Specifically, the UE receives N LTM configuration information from the second access network device, the LTM configuration information is associated with the first access network device, and the LTM configuration information includes a third NCC.

[0250] Exemplarily, assuming N is 2, the SgNB sends to the UE the configuration information T1 configuration of the TgNB1 and the configuration information T2 configuration of the TgNB2, the T1 configuration contains the NCC1, the target PCI1 and the target ARFCN-DL1, and the T2 configuration contains the NCC2, the target PCI2 and the target ARFCN-DL2. The T1 configuration is associated with the TgNB1 indicated by the target PCI1, and the T2 configuration is associated with the TgNB2 indicated by the target PCI2.

[0251] In some embodiments of the present application, the method for deriving the key further comprises step 305a:

[0252] Step 305a: the UE associates the fifth NCC with the first access network device. Specifically, the UE saves the fifth NCC into the configuration information associated with the first access network device.

[0253] The fifth NCC is the NCC currently saved by the UE.

[0254] Exemplarily, in combination with the above example, assuming N is 2, the UE receives two sets of configuration information T1 configuration and T2 configuration, and assuming the fifth NCC saved by the UE is NCC0, then the UE saves the NCC0 into the T1 configuration and the T2 configuration.

[0255] In some embodiments of the present application, the method for deriving the key further comprises step 305b:

[0256] Step 305b: the UE determines a sixth NCC according to the fourth NCC, and the sixth NCC is used to replace the fifth NCC. It can be understood that the UE takes the sixth NCC as the saved NCC, which is used for deriving the first key in the next round.

[0257] In some embodiments of the present application, the fourth NCC is the NCC in the N third NCCs which has the largest difference with the fifth NCC.

[0258] Exemplarily, in combination with the above example, since the difference between NCC1 and NCC0 is 2 and the difference between NCC2 and NCC0 is 0, the NCC with the largest difference from NCC0 in NCC1 and NCC2 is NCC1, and thus the UE takes NCC1 as the saved NCC. It should be noted that the NCC has 8 values, the minimum value is 0, the maximum value is 7, and it is assumed that the value of the fourth NCC received by the UE is greater than or equal to the value of the fifth NCC saved by the UE, and thus when the fourth NCC is greater than the fifth NCC, the difference is the fourth NCC minus the fifth NCC, that is, it is assumed that the fourth NCC is 6 and the fifth NCC is 2, the difference is 6-2=4; when the fourth NCC is less than the fifth NCC, the difference is the fourth NCC+8 minus the fifth NCC, that is, it is assumed that the fourth NCC is 2 and the fifth NCC is 6, the difference is 2+8-6=4.

[0259] It should be understood that the replacement of the sixth NCC for the fifth NCC means that the UE determines the sixth NCC as the NCC saved by the UE and uses it to replace the fifth NCC in the next step 305a.

[0260] In some embodiments of the present application, the method for deriving a key provided by the embodiments of the present application further includes the following steps 306 or 307:

[0261] Step 306: In the case where the second condition is met, the UE derives a first key for communicating with the first access network device according to the LTM configuration information.

[0262] In some embodiments of the present application, the second access network device can send the LTM configuration information to the UE.

[0263] In some embodiments of the present application, the LTM configuration information contains configuration information of the first access network device. Exemplarily, the LTM configuration information contains configuration information of TgNB1, which contains at least one of the following: NCC1, target PCI1, target ARFCN-DL1.

[0264] Exemplarily, taking TgNB1 as the first access network device and SgNB as the second access network device as an example, the SgNB sends T1 configuration of TgNB1 to the UE, and the T1 configuration contains at least NCC1 corresponding to TgNB1.

[0265] It should be noted that in the case where the second condition is met, the process of deriving a first key for communicating with the first access network device according to the LTM configuration information by the UE is described in the above-mentioned mode two, which will not be described here.

[0266] It should be noted that the steps 305 and 306 can be performed before the step 301, or the step 305 can be performed before the step 301, and the step 306 can be performed after the step 301, and the embodiments of the present application do not make any limitation in this regard.

[0267] In the embodiments of the present application, after receiving the LTM configuration message from the SgNB, in the case that the UE accesses the TgNB1 through the LTM for the first time, the UE can derive the key for communicating with the TgNB1 through the LTM configuration message, thus the UE can derive the key through the pre-configured information, thereby improving the key derivation efficiency in the handover process.

[0268] It should be noted that the explanation and description of this embodiment can refer to the related description of the above embodiments, which will not be repeated here.

[0269] Step 307: The UE derives a first key for communicating with the first access network device according to the fourth NCC and the fifth NCC saved by the UE, and the N third NCCs include the fourth NCC.

[0270] In some embodiments of the present application, the UE can obtain information indicating the first access network device according to the LTM handover message (corresponding to step 302), and then derive a first key for communicating with the first access network device according to the fourth NCC in the configuration information of the first access network device and the fifth NCC saved by the UE (corresponding to steps 305 and 307).

[0271] Exemplarily, assuming that N is 2, the SgNB sends the UE the configuration information T1 configuration of the TgNB1 and the configuration information T2 configuration of the TgNB2, the T1 configuration contains the NCC1, the target PCI1 and the target ARFCN-DL1, and the T2 configuration contains the NCC2, the target PCI2 and the target ARFCN-DL2. The T1 configuration is associated with the TgNB1 indicated by the target PCI1, and the T2 configuration is associated with the TgNB2 indicated by the target PCI2. The UE receives the two sets of configuration information T1 configuration and T2 configuration, assuming that the fifth NCC saved by the UE is NCC0, the UE saves the NCC0 into the T1 configuration and the T2 configuration. After the UE receives the LTM switching message sent by the SgNB, assuming that the UE is instructed to switch to the TgNB1, the UE derives the first key used by the TgNB1 according to the NCC0 in the T1 configuration and the NCC1.

[0272] Exemplarily, if the NCC0 saved by the UE (assuming that the NCC0=0) is different from the NCC1 (assuming that the NCC1=2), the UE derives the new NH1 according to the difference between the NCC1 and the NCC0=2-0=2, according to the current Kamf and the NH0 corresponding to the NCC0, and thus the cycle is repeated twice (i.e., the new NH2 is derived according to the current Kamf and the NH1), and then KgNB1* is derived according to the new NH2, the target PCI1 and the target ARFCN-DL1. If the NCC0 saved by the UE (assuming that the NCC0=0) is the same as the NCC1 (assuming that the NCC1=0), the UE derives KgNB1* according to the KgNB1, the target PCI1 and the target ARFCN-DL1 saved in the configuration information.

[0273] In some embodiments of the present application, the method for deriving the key provided by the embodiments of the present application can further include the following step 308:

[0274] Step 308: the UE receives M seventh NCCs from the second access network device.

[0275] This can be that the second access network device wants to adjust the candidate first access network device, for example, delete the TgNB1, add the TgNB3, etc. In the case of adding a new candidate first access network device, the UE can receive M seventh NCCs from the second access network device again.

[0276] It should be understood that step 308 can be understood as performing step 305a again.

[0277] In some embodiments of the present application, the method for deriving a key provided by the embodiments of the present application can further include the following step 309:

[0278] Step 309: The UE determines a ninth NCC according to the eighth NCC, and the ninth NCC is used to replace the sixth NCC.

[0279] It should be understood that step 309 can be understood as performing step 305b again.

[0280] In some embodiments of the present application, the method for deriving a key provided by the embodiments of the present application can further include the following step 310:

[0281] Step 310: The UE derives the first key for communicating with the first access network device according to the eighth NCC and the sixth NCC, and the M seventh NCCs include the eighth NCC.

[0282] It should be understood that step 310 can be understood as performing step 307 again.

[0283] Since there are only 8 values of NCC, assuming that the UE has 7 candidate base stations at the same time in an extreme case, all the 8 values of NCC are used up, in this case, the NCC is increased again, which causes the NCC to flip (from 7 to 0), since the UE originally saved NCC is not updated, the UE cannot perceive the NCC flip, and thus cannot support the network side to initiate the release and addition of candidate cells. By updating the NCC, the UE always has a newer NCC, which can support the release and addition of candidate cells.

[0284] FIG. 4 is a flow diagram of a method for deriving a key provided by an embodiment of the present application, as shown in FIG. 4, the method for deriving a key can include the following steps 401 to 404:

[0285] Step 401: The second access network device selects N first access network devices, and sends information for communicating with a UE to the N first access network devices.

[0286] Wherein, N is less than or equal to M-2, and M represents the number of all values of NCC.

[0287] In some embodiments of the present application, all values of NCC can include 1-8, that is, there are 8 values of NCC, that is, M is equal to 8.

[0288] It should be noted that the value of NCC can be determined according to actual conditions, and the embodiments of the present application do not limit this.

[0289] In some embodiments of the present application, N can be less than or equal to 6, that is, 8 minus 2.

[0290] Exemplarily, taking the second access network device SgNB as an example, since the current value of NCC is 8, the SgNB selects at most 6 target access network devices (i.e. the first access network device), that is, there are 7 access network devices that can simultaneously perform LTM.

[0291] It can be understood that the access network devices that simultaneously perform LTM include the selected 6 access network devices and the SgNB, so there are 7 access network devices.

[0292] It should be noted that the access network device in the embodiments of the present application, for example, the first access network device, can be identified by a cell.

[0293] In some embodiments of the present application, the information for communicating with the UE can be carried by the handover request message.

[0294] In some embodiments of the present application, after the second access network device selects N first access network devices, it can perform key derivation for each first access network device to obtain the key of each access network device, and send a handover request message to each of the N first access network devices, the handover request message including the key of each first access network device and the corresponding NCC.

[0295] Exemplarily, taking the N first access network devices including TgNB1 and TgNB2 as an example, the SgNB derives the key KgNB*1 of TgNB1 and sends a handover request message to TgNB1, the message containing KgNB*1 and the corresponding NCC. If the SgNB has unused NH, then KgNB*1 is derived according to the unused NH2, PCI1, ARFCN-DL1, otherwise the SgNB uses KgNB, PCI1, ARFCN-DL1 to derive KgNB*1. Similarly, the SgNB derives KgNB*2 and sends a handover request message to TgNB2, the message containing KgNB*2 and the corresponding NCC.

[0296] In the embodiments of the present application, since there are at most 8 values of NCC in 5G, and according to the prior art, if a base station is an initial access, there may be an unused NCC value (NCC = 1), therefore, all cells performing LTM are at most 7, so one cell uses one NCC corresponding NH, thereby avoiding key out-of-sync.

[0297] Step 402: The second access network device receives LTM configuration information from the N first access network devices.

[0298] The LTM configuration information includes the NCC, the target PCI, and the target ARFCN-DL.

[0299] In some embodiments of the present application, the LTM configuration information can be carried by the handover response message.

[0300] For example, in combination with the above example, the SgNB receives the handover response message from the TgNB1, which contains the configuration information T1 configuration of the TgNB1, and the configuration information contains the NCC2, the target PCI1, and the target ARFCN-DL1. In addition, the SgNB receives the handover response message from the TgNB2, which contains the configuration information T2 configuration of the TgNB2, and the configuration information contains the NCC2, the target PCI2, and the target ARFCN-DL2.

[0301] Step 403: The second access network device sends the LTM configuration information to the UE.

[0302] In some embodiments of the present application, the LTM configuration information can be carried by the RRC reconfiguration message, which contains the configuration information of each candidate cell relayed by the SgNB.

[0303] For example, in combination with the above example, the SgNB sends the LTM configuration message to the UE, which contains the configuration information of each candidate cell relayed by the SgNB.

[0304] For example, the UE can save the configuration information of each cell, in particular, the UE also saves the cell configuration of the current SgNB, denoted as S configuation, which includes KgNB, PCI0, ARFCN-DL0, etc.

[0305] Step 404: The UE receives the LTM configuration information from the second access network device.

[0306] It should be noted that steps 401 to 404 can be performed before steps 301 to 304, and steps 301 to 304 can be performed before step 201.

[0307] In some embodiments of the present application, the UE receiving the LTM configuration information from the second access network device in step 404 can include the following step 404a:

[0308] Step 404a: The UE receives N third NCCs from the second access network device.

[0309] Specifically, the UE receives N pieces of LTM configuration information from the second access network device, the LTM configuration information is associated with the first access network device, and the LTM configuration information includes a third NCC.

[0310] For example, assuming that N is 2, the SgNB sends the UE the configuration information T1 configuration of the TgNB1 and the configuration information T2 configuration of the TgNB2, the T1 configuration includes the NCC1, the target PCI1, and the target ARFCN-DL1, and the T2 configuration includes the NCC2, the target PCI2, and the target ARFCN-DL2. The T1 configuration is associated with the TgNB1 indicated by the target PCI1, and the T2 configuration is associated with the TgNB2 indicated by the target PCI2.

[0311] In some embodiments of the present application, the method for deriving a key provided by the embodiments of the present application can further include the following step 405:

[0312] Step 405: The UE derives N first keys for communicating with N first access network devices according to the N third NCCs and the fifth NCC.

[0313] The fifth NCC is an NCC currently saved by the UE.

[0314] For example, in combination with the above example, assuming that N is 2, the UE receives two sets of configuration information T1 configuration and T2 configuration, then the N third NCCs include the NCC1 and the NCC2, and assuming that the fifth NCC saved by the UE is the NCC0, the UE derives the first key used by the TgNB1 according to the NCC1 and the NCC0, and derives the first key used by the TgNB2 according to the NCC2 and the NCC0.

[0315] For example, for the T1 configuration, if the NCC0 (assuming NCC0 = 0) saved by the UE is different from the NCC1 (assuming NCC1 = 2), the UE derives a new NH1 according to the difference between the NCC1 and the NCC0 = 2-0 = 2, according to the current Kamf and the NH0 corresponding to the NCC0, and so on for two times (i.e., derives a new NH2 according to the current Kamf and the NH1), and derives the KgNB1* according to the new NH2, the target PCI1 and the target ARFCN-DL1. For the T2 configuration, if the NCC0 (assuming NCC0 = 0) saved by the UE is the same as the NCC2 (assuming NCC2 = 0), the UE derives the KgNB2* according to the KgNB2, the target PCI2 and the target ARFCN-DL2 saved in the configuration information.

[0316] It can be understood that the derivation of the N first keys for communication with the N first access network devices in the above step 405 can be achieved by the UE deriving a first key for communication with a first access network device according to a fourth NCC and a fifth NCC saved by the UE, wherein the N third NCCs include the fourth NCC.

[0317] For example, the UE iterates each of the N third NCCs as the fourth NCC to derive N first keys for communication with the N first access network devices, respectively, according to the fifth NCC.

[0318] It should be noted that the above step 405 can be performed before the above step 301.

[0319] In some embodiments of the present application, the method for deriving a key provided by the embodiments of the present application can further include the following step 406:

[0320] Step 406: The UE associates the first key with the first access network device.

[0321] Specifically, the UE saves the first key into the configuration information associated with the first access network device.

[0322] For example, in combination with the above example, the UE saves the KgNB1* into the T1 configuration and saves the KgNB2* into the T2 configuration.

[0323] In some embodiments of the present application, the method for deriving a key provided by the embodiments of the present application can further include the following step 407:

[0324] Step 407: The UE determines a sixth NCC according to the fourth NCC, and the sixth NCC is used to replace the fifth NCC. It can be understood that the UE takes the sixth NCC as the saved NCC for derivation of the next round of first keys.

[0325] In some embodiments of the present application, the fourth NCC is the NCC with the largest difference from the fifth NCC among the N third NCCs.

[0326] For example, in combination with the above example, since the difference between NCC1 and NCC0 is 2 and the difference between NCC2 and NCC0 is 0, the NCC with the largest difference from NCC0 among NCC1 and NCC2 is NCC1, and the UE takes NCC1 as the saved NCC. It should be noted that there are 8 values of NCC, the minimum value is 0, and the maximum value is 7, and it is assumed that the value of the fourth NCC received by the UE is greater than or equal to the value of the fifth NCC saved by the UE, so when the fourth NCC is greater than the fifth NCC, the difference is the fourth NCC minus the fifth NCC, that is, it is assumed that the fourth NCC is 6 and the fifth NCC is 2, the difference is 6-2=4; when the fourth NCC is less than the fifth NCC, the difference is the fourth NCC+8 minus the fifth NCC, that is, it is assumed that the fourth NCC is 2 and the fifth NCC is 6, the difference is 2+8-6=4.

[0327] It should be understood that the sixth NCC is used to replace the fifth NCC means that the UE determines the sixth NCC as the NCC saved by the UE and used to replace the fifth NCC in the next step 405.

[0328] In some embodiments of the present application, the method for deriving keys provided by the embodiments of the present application can further include the following step 408:

[0329] Step 408: The UE receives M seventh NCCs from the second access network device again.

[0330] This can be that the second access network device wants to adjust the candidate first access network device, for example, delete TgNB1, add TgNB3, etc., in the case of adding a new candidate first access network device, the UE can receive M seventh NCCs from the second access network device again.

[0331] It should be understood that step 408 can be understood as performing step 404a again.

[0332] In some embodiments of the present application, the method for deriving keys provided by the embodiments of the present application can further include the following step 409:

[0333] Step 409: The UE derives M first keys for communication with M first access network devices according to the M seventh NCCs and the sixth NCC.

[0334] It can be understood that the derivation in the above step 409 of obtaining M first keys for communication with M first access network devices can be achieved by the UE deriving the first key for communication with the first access network device according to the eighth NCC and the sixth NCC, the M seventh NCCs containing the eighth NCC.

[0335] Exemplarily, the UE traverses each of the N seventh NCCs as the eighth NCC, respectively derives N first keys for communication with N first access network devices with the sixth NCC.

[0336] It should be understood that step 409 can be understood as performing step 405 again.

[0337] In some embodiments of the present application, the method for deriving keys provided by the embodiments of the present application can further include the following step 413:

[0338] Step 410: The UE determines a ninth NCC according to the eighth NCC, and the ninth NCC is used to replace the sixth NCC.

[0339] It should be understood that step 410 can be understood as performing step 407 again.

[0340] Exemplarily, in combination with the above example, assuming that M is 3, the UE receives 3 sets of configuration information T3 configuration and T4 configuration, and T5 configuration, the M seventh NCCs include NCC3 (assuming NCC3=3), NCC4 (assuming NCC4=4), and NCC5 (assuming NCC5=5), the sixth NCC saved by the UE is NCC1, the UE derives the first key used by TgNB3 according to NCC3 and NCC1, the UE derives the first key used by TgNB4 according to NCC4 and NCC1, and the UE derives the first key used by TgNB5 according to NCC5 and NCC1. Since the difference between NCC3 and NCC1 is 2, the difference between NCC4 and NCC1 is 3, and the difference between NCC5 and NCC1 is 4, the NCC with the largest difference from NCC1 among NCC3, NCC4, and NCC5 is NCC5, and therefore the UE saves NCC5 as the saved NCC. Since there are only 8 values of NCC, assuming that the UE has 7 candidate base stations at the same time in an extreme case, all the 8 values of NCC are used up, in which case, increasing the NCC will cause the NCC to flip (from 7 to 0), since the NCC saved by the UE is not updated, the UE cannot perceive the NCC flip, and therefore cannot support the network side to initiate the release and addition of the candidate cell. By updating the NCC, the UE always has a newer NCC, which can support the release and addition of the candidate cell.

[0341] It should be noted that the above steps 408 to 410 can also be performed after the above step 307, and the embodiments of the present application do not limit this.

[0342] In some embodiments of the present application, the process in which the second access network device sends the information related to the communication of the UE to the first access network device in the above step 401 can include the following step 401a:

[0343] Step 401a: The second access network device sends the information related to the communication of the UE to the N first access network devices through the first network element.

[0344] In some embodiments of the present application, the method for deriving the key provided by the embodiments of the present application can further include the following step 404:

[0345] Step 411: The second access network device sends a first indication to the first network element.

[0346] The above first indication indicates that the first network element does not perform derivation of the NH.

[0347] It should be noted that step 411 can be performed after the above step 403.

[0348] In some embodiments of the present application, the first indication can also be used to indicate performing LTM switching.

[0349] In some embodiments of the present application, the first network element can receive the first indication from the second access network device.

[0350] It should be noted that the explanation of this embodiment can refer to the related description of the above-mentioned embodiments, which will not be repeated here.

[0351] The method for deriving a key provided by the embodiments of the present application is exemplarily described below through specific embodiments.

[0352] Embodiment one:

[0353] As shown in FIG. 5, taking the first access network device including TgNB1 and TgNB2, the second access network device as SgNB, and the first network element as AMF as an example, the method for deriving a key can include the following steps 501 to 525:

[0354] Step 501: SgNB selects candidate cells.

[0355] Exemplarily, in the case that the UE currently uses KgNB0 to communicate with the SgNB, the SgNB configures the configuration information (including key derivation information) of each candidate cell for the UE in advance.

[0356] Wherein, it is assumed that KgNB0 is derived based on NH1 corresponding to NCC1.

[0357] Exemplarily, the SgNB selects at most N-2 candidate cells, wherein N represents all value ranges of NCC. Since the current value of NCC is 8, the SgNB selects at most 6 candidate cells, i.e., there are 7 cells for simultaneous LTM.

[0358] It should be noted that the above-mentioned candidate cell can represent a base station identified by the candidate cell.

[0359] Step 502: SgNB sends a third handover request message to TgNB1.

[0360] Exemplarily, the SgNB derives KgNB*1 and sends a third handover request message to TgNB1, which contains KgNB*1 and corresponding NCC. If the SgNB has unused NH, then KgNB*1 is derived according to the unused NH2, PCI1, and ARFCN-DL1, otherwise the SgNB derives KgNB*1 using KgNB, PCI1, and ARFCN-DL1. Wherein PCI1 and ARFCN-DL1 respectively indicate the physical cell identifier and the downlink absolute radio frequency channel number of TgNB1.

[0361] Step 503: The SgNB sends a fourth handover request message to the TgNB2.

[0362] Exemplarily, the SgNB derives KgNB*2 and sends the fourth handover request message to the TgNB2, which contains KgNB*2 and corresponding NCC.

[0363] Step 504: The SgNB receives a third handover request response message from the TgNB1.

[0364] The third handover request response message contains the configuration information (T1 configuration) of the TgNB1, which includes NCC2, target PCI1, and target ARFCN-DL1.

[0365] Step 505: The SgNB receives a fourth handover request response message from the TgNB2.

[0366] The fourth handover request response message contains the configuration information (T2 configuration) of the TgNB2, which includes NCC2, target PCI2, and target ARFCN-DL2.

[0367] Step 506: The SgNB sends an RRC reconfiguration message to the UE.

[0368] The RRC reconfiguration message can contain the configuration information of each candidate cell relayed by the SgNB, i.e., the LTM configuration information.

[0369] Step 507: The UE saves the configuration information of each cell.

[0370] In particular, the UE also saves the cell configuration (S configuration) of the current SgNB, including KgNB0, PCI0, and ARFCN-DL0.

[0371] Optionally, the UE associates the currently used NCC with the configuration information of each cell. Specifically, the UE saves the currently used NCC into the configuration information of each cell, and the related process can refer to the related description of FIG. 4.

[0372] Optionally, after step 507, step 508 can also be included.

[0373] Step 508: The UE derives the key in advance according to the configuration information.

[0374] Exemplarily, if the NCC currently used by the UE (i.e. the NCC1 derived from the key used by the SgNB) is different from the NCC in each configuration information, the UE derives a new NH according to the current Kamf and NH, and derives KgNB* according to the new NH, target PCI, target ARFCN-DL and saves it in the configuration information. If the NCC currently used by the UE is the same as the NCC in each configuration information, the UE derives KgNB* according to the KgNB, target PCI, target ARFCN-DL saved in the configuration information, and saves it in the configuration information.

[0375] In this step, since the NCC1 currently used by the UE is different from the NCC2 in the T1 configuration, the UE derives NH2 from NH1 and Kamf once according to the difference between NCC2 and NCC1 (assuming 1), and derives KgNB*1 from NH2, target PCI1, target ARFCN-DL1 and saves it in the T1 configuration; similarly, since the NCC1 currently used by the UE is different from the NCC2 in the T2 configuration, the UE derives NH2 from NH1 and Kamf once according to the difference between NCC2 and NCC1 (assuming 1), and derives KgNB*2 from NH2, target PCI2, target ARFCN-DL2 and saves it in the T2 configuration.

[0376] Optionally, the UE determines the NCC saved by the UE according to the NCC in each configuration information, for derivation of the first key in the next round, and the related process can refer to the related process of FIG. 4.

[0377] Step 509: The UE sends an RRC reconfiguration complete message to the SgNB.

[0378] The RRC reconfiguration complete message is used to indicate completion of the configuration of the RRC.

[0379] Step 510: The UE reports a measurement report of L1 to the SgNB.

[0380] Exemplarily, in the case that the UE switches to the TgNB1 and accesses for the first time, the SgNB knows that the UE is about to move to the TgNB1 with better signal according to the measurement report of the UE, and informs the UE to access the TgNB1.

[0381] Step 511: The SgNB sends an L1 message to the UE according to the measurement report.

[0382] The L1 message is used to instruct the UE to access the TgNB1.

[0383] Step 512: UE enables T1 configuration according to L1 message.

[0384] Exemplarily, UE has the following four ways to determine the key used with TgNB1:

[0385] Way one: UE derives the key according to source base station configuration information and configuration information indicated by L1 message. If UE uses NCC (i.e. NCC1 used for deriving the key used with SgNB) different from NCC in the indicated configuration information, UE derives new NH from current Kamf and NH, and derives KgNB* from new NH, target PCI, target ARFCN-DL, and saves in the configuration information. If UE uses NCC same as NCC in each configuration information, UE derives KgNB* from KgNB, target PCI, target ARFCN-DL saved in the configuration information, and saves in the configuration information.

[0386] In this step, since UE uses NCC1 (i.e. NCC1 used for deriving the key used with SgNB) different from NCC2 in T1 configuration, UE derives NH2 from Kamf and NH1 for 1 time according to the difference (assuming 1) between NCC2 and NCC1, and derives KgNB*1 from NH2, target PCI1, target ARFCN-DL1, and saves KgNB*1 in T1 configuration, and determines KgNB*1 as the key used with TgNB1.

[0387] Way two: if UE accesses TgNB1 for the first time, UE determines KgNB*1 in T1 configuration as the key used with TgNB1; if UE does not access TgNB1 for the first time, UE derives KgNB**1 from saved KgNB*1, and determines KgNB**1 as the key used with TgNB1, wherein UE derives KgNB**1 from KgNB*1, target PCI1, target ARFCN-DL1, and saves KgNB**1 in T1 configuration (and so on). Wherein, the first access means access by LTM. In this step, since UE accesses TgNB1 for the first time, UE determines KgNB*1 as the key used with TgNB1.

[0388] It should be noted that the mode one and the mode two are modes that can be used when the step 508 is performed.

[0389] Mode three: the UE determines KgNB*1 in the T1 configuration as the key used by TgNB1.

[0390] Mode four: if the UE accesses TgNB1 for the first time, the UE derives the key according to the configuration information of the source base station and the configuration information indicated by the L1 message. If the UE does not access TgNB1 for the first time, the UE derives KgNB**1 from KgNB*1 saved, and determines KgNB**1 as the key used by TgNB1, wherein the UE derives KgNB**1 from KgNB*1, target PCI1, and target ARFCN-DL1, and saves KgNB**1 in the T1 configuration. The first time access refers to the access through the LTM mode.

[0391] It should be noted that the mode three and the mode four are modes that can be used when the step 5 is not performed.

[0392] Step 513: the UE sends an access message to TgNB1.

[0393] TgNB1 has the following two methods to determine the key used by the UE:

[0394] Mode one: TgNB1 determines the saved KgNB*1 as the key used by the UE.

[0395] Mode two: if the UE accesses TgNB1 for the first time, TgNB1 determines the saved KgNB*1 as the key used by the UE; if the UE does not access TgNB1 for the first time, TgNB1 derives KgNB**1 from KgNB*1 saved, and determines the derived KgNB**1 as the key used by the UE. TgNB1 derives KgNB**1 from KgNB*1, target PCI1, and target ARFCN-DL1, and saves KgNB**1 in the context of the UE. The first time access refers to the access through the LTM mode. In this process, the UE accesses TgNB1 for the first time, so TgNB1 determines KgNB*1 as the key used by the UE.

[0396] Step 514: TgNB1 judges whether it is necessary to indicate that the AMF does not perform the derivation of NH.

[0397] Manner one: if the UE accesses the TgNB1 for the first time, the TgNB1 does not carry the first indication in the path switching message; if the UE does not access the TgNB1 for the first time, the TgNB1 carries the first indication in the path switching message, and the first indication is used to indicate that the AMF does not perform the derivation of the NH.

[0398] Manner two: the TgNB1 carries the first indication in the path switching message. If the UE accesses the TgNB1 for the first time, the first indication is used to indicate that the AMF performs the derivation of the NH, for example, the value thereof is set to 1; if the UE does not access the TgNB1 for the first time, the first indication is used to indicate that the AMF does not perform the derivation of the NH, for example, the value thereof is set to 0.

[0399] The above first access specifically refers to the access through the LTM.

[0400] In this step, since the UE accesses the TgNB1 for the first time, it is not necessary to indicate that the AMF performs the derivation of the NH.

[0401] Step 515: the TgNB1 sends a first path switching message to the AMF.

[0402] The first path switching message is used to establish the path connection with the core network.

[0403] Step 516: the AMF sends a first path switching confirmation message to the TgNB1.

[0404] The message contains NH3 and NCC3. The AMF derives NH3 according to Kamf and the current NH2, and obtains NCC3 by adding 1 to the current NCC2.

[0405] Step 517: the TgNB1 saves NH3 and NCC3.

[0406] If the UE accesses the TgNB1 for the first time, the TgNB1 saves NH3 and NCC3; if the UE does not access the TgNB1 for the first time, the TgNB1 ignores NH3 and NCC3.

[0407] In this step, since the UE accesses the TgNB1 for the first time, the TgNB1 saves NH3 and NCC3.

[0408] Exemplarily, during the process that the UE still stays in the LTM mode, the TgNB1 does not use NH3 as the parameter for the next KgNB derivation, but uses NH3 as the KgNB derivation parameter for the next normal Xn switching.

[0409] Step 518: the UE reports a measurement report of L1 to the TgNB1.

[0410] Exemplarily, in the case that the UE switches to the SgNB, the TgNB1 knows that the UE is about to move to the SgNB with better signal according to the measurement report of the UE, and informs the UE to access the SgNB.

[0411] It should be noted that the UE accesses the SgNB for the first time.

[0412] Step 519: The TgNB1 sends an L1 message to the UE according to the measurement report.

[0413] The L1 message is used to instruct the UE to access the SgNB.

[0414] Step 520: The UE enables S configuration according to the L1 message.

[0415] Exemplarily, the UE can determine KgNB0 as the key used by the SgNB based on the above-mentioned manner one or three.

[0416] Alternatively, the UE can also determine KgNB*0 as the key used by the SgNB based on the above-mentioned manner two or four, since the UE is not accessing the SgNB for the first time, and the UE derives KgNB*0 according to KgNB0, PCI0 and ARFCN-DL0. It should be noted that the S configuration is the configuration of the SgNB.

[0417] Step 521: The UE sends an access message to the SgNB.

[0418] Exemplarily, the SgNB can determine KgNB0 as the key used by the UE based on the above-mentioned manner one.

[0419] Alternatively, the SgNB can determine KgNB*0 as the key used by the SgNB based on the above-mentioned manner two, since the UE is not accessing the SgNB for the first time, and the SgNB derives KgNB*0 according to KgNB0, PCI0 and ARFCN-DL0.

[0420] Step 522: The SgNB determines whether to instruct the AMF to derive the key for the UE.

[0421] Step 523: The SgNB sends a second path switching message to the AMF.

[0422] The second path switching message is used to establish a connection between the UE and the core network.

[0423] In particular, the SgNB determines whether to instruct the AMF not to derive the NH, which can be referred to the above-mentioned steps. In this step, since the UE is not accessing the SgNB for the first time, the SgNB instructs the AMF not to derive the NH, and the path switching message contains the first indication.

[0424] Step 524: The AMF determines not to derive the NH according to the first indication.

[0425] Step 525: The AMF sends a second path switch confirmation message to the SgNB.

[0426] Exemplarily, the second path switch confirmation message can contain the NH and the NCC. Alternatively, the AMF can take the current NH3 and NCC3 as the NH and the NCC according to the first indication, or take a preset value as the NH and the NCC, for example, all 0.

[0427] Exemplarily, the SgNB ignores the NH and the NCC after receiving the NH and the NCC. Alternatively, the SgNB ignores the NH and the NCC in the case that the UE is not the first time to access or has indicated the AMF not to derive the NH.

[0428] In the embodiment of the application, the UE triggers continuous path switches in continuous inter-CU LTM, but the AMF has to derive the NH once after each path switch, which will cause NCC+1. However, the NCC has only 3 bits and at most 8 values, so if the UE performs inter-CU LTM 8 times in succession, the NCC will have no value available and will be flipped. Once this happens, the UE side will be out of synchronization by comparing the NCC to derive the key. Therefore, in order to prevent the above situation from occurring and considering that there are currently at most 6 candidate cells, the present scheme introduces the judgment of whether the UE is the first time to access the candidate cell, and indicates the AMF not to derive the NH when the UE is not the first time to access. In this way, the AMF at most derives the NH 7 times at the same time, which can make the NH derived by the AMF not flipped, thereby ensuring that the derivation of the NH is not out of synchronization.

[0429] As shown in FIG. 6, taking the first access network device including TgNB1 and TgNB2, the second access network device as the SgNB, and the first network element as the AMF as an example, the method for deriving the key can include the following steps 601 to 622:

[0430] Step 601: The SgNB selects a candidate cell.

[0431] Exemplarily, in the case that the UE currently uses KgNB0 to communicate with the SgNB for protection, the SgNB configures the configuration information (including key derivation information) of each candidate cell for the UE in advance.

[0432] Exemplarily, the SgNB selects at most N-2 candidate cells, where N represents all value ranges of the NCC. Since the current value of the NCC is 8, the SgNB selects at most 6 candidate cells, that is, there are 7 cells performing LTM at the same time.

[0433] Optionally, the candidate cells selected by the SgNB belong to the same AMF as the SgNB.

[0434] Exemplarily, assume that the SgNB selects TgNB1 and TgNB2 as candidate cells.

[0435] Step 602: The SgNB sends a first handover requirement message to the AMF.

[0436] Exemplarily, the handover requirement message contains the ID of the candidate cell (e.g. the PCI of TgNB1), and can also include the LTM indication. The AMF saves the LTM indication in the context of the UE.

[0437] Optionally, the AMF saves the PCI1 of TgNB1 and the LTM indication into the context of the UE.

[0438] Step 603: The SgNB sends a second handover requirement message to the AMF.

[0439] Exemplarily, the message contains the ID of the candidate cell (e.g. the PCI of TgNB2), and can also contain the LTM indication. The AMF saves the LTM indication in the context of the UE.

[0440] Optionally, the AMF saves the PCI2 of TgNB2 and the LTM indication into the context of the UE.

[0441] It is worth noting that the SgNB can also send a handover requirement message to the AMF, but the message contains the ID of all candidate cells and the LTM indication.

[0442] Step 604: The AMF sends a first handover request message to TgNB1.

[0443] Exemplarily, the first handover request message carries NH3, NCC3.

[0444] Exemplarily, the AMF derives NH according to the first handover request message, and sends the new [NH3, NCC3] to the candidate cell (TgNB1). The AMF derives a new NH (denoted as NH3) according to the current Kamf and the current NH, and sets a new NCC = current NCC + 1 (denoted as NCC3).

[0445] Optionally, the AMF saves the PCI1 of TgNB1, NH3, NCC3 into the context of the UE according to the LTM indication.

[0446] Optionally, the AMF does not trigger the SMF to establish a user plane channel according to the LTM indication, i.e. does not establish the connection between the UE and the core network.

[0447] Step 605: TgNB1 derives KgNB*1 vertically using NH3 related to NCC3.

[0448] Illustratively, TgNB1 computes KgNB*1 according to NH3, PCI1 and ARFCN-DL1 of itself.

[0449] Step 606: AMF sends second handover request message to TgNB2.

[0450] Illustratively, AMF derives NH according to the second handover request message and sends new [NH4, NCC4] to TgNB2.

[0451] Optionally, AMF saves PCI2, NH4, NCC4 of TgNB2 into the context of UE according to the LTM indication.

[0452] Optionally, AMF does not trigger SMF to establish user plane tunnel according to the LTM indication.

[0453] In this way, AMF learns from the LTM indication that the UE has not moved to the base station at present, and therefore does not establish the user plane, which is beneficial to reduce the interaction complexity of the core network.

[0454] Step 607: TgNB2 derives KgNB*2 vertically using NH4 related to NCC4.

[0455] Illustratively, TgNB2 computes KgNB*2 according to NH4, PCI2 and ARFCN-DL2 of itself.

[0456] Step 608: AMF receives first handover request response message from TgNB1.

[0457] The message contains T1 configuration of TgNB1, which contains NCC3, target PCI1, target ARFCN-DL1.

[0458] Step 609: AMF receives second handover request response message from TgNB2.

[0459] The message contains T2 configuration of TgNB2, which contains NCC4, target PCI2, target ARFCN-DL2.

[0460] Step 610: AMF sends first handover command message to SgNB.

[0461] The first handover command message contains T1 configuration.

[0462] Step 611: The AMF sends a second handover command message to the SgNB.

[0463] Wherein, the second handover command message contains T2 configuration.

[0464] It is worth noting that the AMF can also send a handover command message to the SgNB, but the message contains the configuration information of all candidate cells.

[0465] Step 612: The SgNB sends an RRC reconfiguration message to the UE.

[0466] Wherein, the message contains the configuration information of each candidate cell relayed by the SgNB.

[0467] Step 613: The UE saves the cell configuration of the SgNB, the cell configuration of TgNB1 and the cell configuration of TgNB2.

[0468] Exemplarily, the UE saves the configuration information of each cell, in particular, the UE also saves the cell configuration of the current SgNB (denoted as Sconfiguation (including KgNB0, PCI0, ARFCN-DL0)).

[0469] Optionally, the UE associates the currently used NCC with the configuration information of each cell. Specifically, the UE saves the currently used NCC into the configuration information of each cell, and the related process can refer to the related steps of FIG. 4.

[0470] Optionally, the UE can derive the key in advance according to the configuration information. If the NCC currently used by the UE (i.e. the NCC1 used to derive the key used by the SgNB) is different from the NCC in each configuration information, the UE derives a new NH according to the current Kamf and NH, and derives KgNB* according to the new NH, target PCI and target ARFCN-DL, and saves it in the configuration information. If the NCC currently used by the UE is the same as the NCC in each configuration information, the UE derives KgNB* according to the KgNB, target PCI and target ARFCN-DL saved in the configuration information, and saves it in the configuration information.

[0471] In this step, since the NCC1 currently used by the UE is different from the NCC2 in the T1 configuration, the UE obtains NH2 from Kamf and NH1 by derivation once according to the difference between NCC2 and NCC1 (assuming 1), and obtains KgNB*1 from NH2, target PCI1, target ARFCN-DL1, and saves KgNB*1 in the T1 configuration; similarly, since the NCC1 currently used by the UE is different from the NCC3 in the T2 configuration, the UE obtains NH3 from Kamf and NH1 by derivation twice according to the difference between NCC3 and NCC1 (assuming 2), and obtains KgNB*2 from NH3, target PCI2, target ARFCN-DL2, and saves KgNB*2 in the T2 configuration.

[0472] Optionally, after step 613, step 614 can be further included: the UE obtains the key KgNB1 of the TgNB1 according to the cell configuration of the TgNB1, or obtains the key KgNB2 of the TgNB2 according to the cell configuration of the TgNB2.

[0473] Optionally, the UE determines the NCC saved by the UE according to the NCC in each configuration information, for derivation of the first key in the next round, and the related process can refer to the related steps of FIG. 4.

[0474] Step 615: The UE sends an RRC reconfiguration complete message to the SgNB, for indicating completion of the configuration of the RRC.

[0475] Step 616: The UE reports a measurement report of L1 to the SgNB.

[0476] Exemplarily, in the case that the UE switches to the TgNB1 and accesses the TgNB1 for the first time, the SgNB knows that the UE is about to move to the TgNB1 with better signal according to the measurement report of the UE, and notifies the UE to access the TgNB1.

[0477] Step 617: The SgNB sends an L1 message to the UE according to the measurement report.

[0478] The L1 message is used to instruct the UE to access the TgNB1.

[0479] Step 618: The UE enables the configuration of the TgNB1.

[0480] Exemplarily, the UE enables the T1 configuration according to the L1 message.

[0481] Step 619: The UE sends an access message to the TgNB1.

[0482] Step 620: TgNB1 sends a path switch message to AMF.

[0483] The path switch message is used to establish the connection between UE and core network.

[0484] Optionally, TgNB1 judges whether to indicate AMF not to perform NH derivation:

[0485] Method one: If UE accesses TgNB1 for the first time, AMF does not carry LTM indication in the path switch message; if UE does not access TgNB1 for the first time, AMF carries LTM indication in the path switch message, and the LTM indication is used to indicate that AMF does not perform NH derivation.

[0486] Method two: AMF carries LTM indication in the path switch message. If UE accesses TgNB1 for the first time, LTM indication is used to indicate that AMF performs NH derivation, for example, setting its value to 1; if UE does not access TgNB1 for the first time, LTM indication is used to indicate that AMF does not perform NH derivation, for example, setting its value to 0.

[0487] The first access specifically refers to access through LTM.

[0488] Step 621: AMF does not perform NH derivation for UE according to LTM indication.

[0489] For example, AMF determines not to perform NH derivation according to LTM indication. Optionally, AMF can determine according to LTM indication received and saved in step 602 or step 603, or according to LTM indication obtained in step 620.

[0490] For example, if the context of UE obtained by AMF from the path switch message contains LTM indication, AMF determines not to perform NH derivation according to the LTM indication. If the context of UE does not contain LTM indication, AMF performs NH derivation.

[0491] For example, if the context of UE obtained by AMF from the path switch message contains LTM indication for TgNB1, AMF determines not to perform NH derivation according to the LTM indication. If the context of UE does not contain LTM indication for TgNB1, AMF performs NH derivation.

[0492] Step 622: AMF sends a path switch confirmation message to TgNB1.

[0493] Optionally, the path switch confirmation message can contain NH, NCC.

[0494] Optionally, the AMF indicates NH3 and NC3 corresponding to TgNB1 as NH and NCC according to the LTM, or a preset value as NH and NCC, for example, all 0.

[0495] Illustratively, the SgNB ignores NH and NCC after receiving NH and NCC. Optionally, the SgNB ignores NH and NCC in the case that the UE is not first access or has indicated the AMF not to derive NH.

[0496] The method for deriving a key provided by the embodiments of the present application, after the UE switches to the target base station through the LTM, the target base station determines whether the UE is first access, thereby determining to carry a first indication in the path switching message, so that the AMF can not derive NH according to the first indication, thereby preventing the value of NCC from being quickly consumed and reset, and ultimately causing the keys used by the UE and the network side to be out of synchronization.

[0497] The method for deriving a key provided by the embodiments of the present application, the execution subject can be a device for deriving a key. In the embodiments of the present application, the device for deriving a key is taken as an example to illustrate the device for deriving a key provided by the embodiments of the present application.

[0498] The embodiments of the present application provide a device for deriving a key. As an example, the device for deriving a key can be a communication device or a component in the communication device, such as a chip. The communication device can be a terminal, a network side device, a server, etc. Illustratively, the terminal can include but is not limited to the types of the terminal 11 listed above, the network side device can include but is not limited to the types of the network side device 12 listed above, and the embodiments of the present application do not make specific limitations.

[0499] The device for deriving a key comprises a receiving module, a sending module and a processing module. The receiving module, the sending module and the processing module can be implemented by software or by hardware. When implemented by hardware, the processing module can be implemented by a processor. For example, the processor can include a general-purpose processor, a dedicated processor, a central processing unit (CPU), a microprocessor, a digital signal processor (DSP), an artificial intelligent (AI) processor, a graphics processing unit (GPU), an application specific integrated circuit (ASIC), a network processor (NP), a field programmable gate array (FPGA) or other programmable logic device, a gate circuit, a transistor, a discrete hardware component, etc. The receiving module and the sending module can be implemented by a communication interface, which can include one or more of a transceiver, a pin, a circuit, a bus, a radio frequency unit, etc.

[0500] Referring to FIG. 7, in some possible implementation manners, when the device for deriving a key is a first network element or a component in the first network element, the device 700 for deriving a key comprises a receiving module 701, configured to receive a path switching message from a first access network device, the path switching message being used to establish a signaling connection between a UE and a core network; a processing module 702, configured to determine whether to perform derivation of a next hop value NH for the UE according to the path switching message; and a sending module 703, configured to send a path switching confirmation message to the first access network device, the path switching confirmation message being used to respond to the path switching message.

[0501] In some embodiments of the present application, the processing module is specifically configured to determine, in a case where the path switching message contains the first indication, that the first network element does not perform derivation of the next hop value NH for the UE.

[0502] In some embodiments of the present application, the path switching message contains the first indication; and the processing module is specifically configured to determine whether to perform derivation of the NH for the UE according to the first indication.

[0503] In some embodiments of the present application, the receiving module is further configured to receive a first indication from the second access network device before receiving the path switching message from the first access network device; the processing module is further configured to save the first indication received by the receiving module in a context of the UE; and the processing module is specifically configured to acquire the first indication from the context of the UE according to the path switching message, and determine whether to perform derivation of the NH for the UE according to the first indication.

[0504] In some embodiments of the present application, the processing module is further configured to, in a case where the first network element obtains the context of the UE according to the path switching message, and determines to perform derivation of the NH for the UE according to the first indication in the context of the UE, not establish the signaling connection between the UE and the core network according to the first indication.

[0505] In some embodiments of the present application, the processing module is specifically configured to:

[0506] determine to perform derivation of the NH for the UE in a case where the first indication indicates to perform derivation of the NH for the UE;

[0507] or, determine not to perform derivation of the NH for the UE in a case where the first indication indicates not to perform derivation of the NH for the UE.

[0508] In some embodiments of the present application, the processing module is further configured to save a second NH and a second NCC corresponding to the first access network device according to the first indication after receiving the first indication from the second access network device; and in a case where the processing module determines not to perform derivation of the NH for the UE, the path switching confirmation message contains the second NH and the second NCC.

[0509] In some embodiments of the present application, in a case where the processing module determines not to perform derivation of the NH for the UE, the path switching confirmation message contains a first NH and a first NCC, the first NH and the first NCC being a NH and a NCC currently saved by the first network element, or being preset values.

[0510] The device for deriving a key provided in the embodiments of the present application receives a path switching message from a first access network device, the path switching message being used to establish a signaling connection between a UE and a core network, determines whether to perform NH derivation for the UE according to the path switching message, and sends a path switching confirmation message to the first access network device, the path switching confirmation message being used to respond to the path switching message. Through the method, the device for deriving a key can determine whether to perform NH derivation or not to perform NH derivation according to the path switching message, thereby reducing the number of unnecessary NH derivation times, thus reducing the number of times of using the NCC value to track the number of NH derivation times, so that the NCC value is not frequently updated and reset, in this way, the problem of key asynchronization caused by the change of the NCC value of the UE and the network side is avoided, thereby improving the stability and performance of communication.

[0511] Referring to FIG. 8, in some possible implementation manners, when the device for deriving a key is a first access network device or a component in the first access network device, the device comprises: a sending module 801, configured to send a path switching message to a first network element, the path switching message being used to establish a signaling connection between a user equipment (UE) and a core network; and a receiving module 802, configured to receive a path switching confirmation message from the first network element, the path switching confirmation message being used to respond to the path switching message; wherein the path switching message contains a first indication under a first condition, and the first indication indicates that the first network element does not perform NH derivation.

[0512] In some embodiments of the present application, the first condition comprises that the UE accesses the first access network device through LTM switching for the first time.

[0513] In some embodiments of the present application, the processing module is configured to, after receiving the path switching confirmation message from the first network element under the first condition, ignore key-related information if the switching confirmation message includes the key-related information, the key-related information including at least one of the following: NH and NCC.

[0514] In some embodiments of the present application, the processing module is configured to accept the UE to access through LTM switching, and the processing module is further configured to determine a first key used for communication with the UE.

[0515] In some embodiments of the present application, the processing module is specifically configured to, under the first condition, perform horizontal key derivation to obtain the first key.

[0516] In some embodiments of the present application, the processing module is further configured to, after receiving the path switching confirmation message from the first network element under the first condition, save key-related information if the switching confirmation message includes the key-related information, the key-related information being used for next Xn switching, the key-related information including at least one of the following: NH and NCC.

[0517] In some embodiments of the present application, the receiving module is further configured to receive information about communication of the UE from the second access network device; and the sending module is further configured to send LTM configuration information to the second access network device, the LTM configuration information comprising the NCC.

[0518] Specifically, referring to FIG. 9, when the device for deriving a key is a terminal or a component in a terminal, the device 900 for deriving a key comprises a receiving module 901 configured to receive an LTM switching message from a second access network device, the LTM switching message indicating that the UE switches to a first access network device; and a processing module 902 configured to derive a first key for communication with the first access network device in a horizontal manner if a first condition is met, and further configured to access the first access network device through LTM switching.

[0519] In some embodiments of the present application, the first condition comprises that the UE accesses the first access network device through LTM switching for the first time.

[0520] In some embodiments of the present application, the receiving module is further configured to receive LTM configuration information from the second access network device; and the processing module is further configured to derive the first key for communication with the first access network device according to the LTM configuration information if a second condition is met.

[0521] In some embodiments of the present application, the second condition comprises that the UE accesses the first access network device through LTM switching for the first time.

[0522] Specifically, in another embodiment of the present application, referring to FIG. 9, when the device for deriving a key is a terminal or a component in a terminal, the device 900 for deriving a key comprises a receiving module 901 configured to receive N third NCCs from a second access network device; and a processing module 902 configured to derive a first key for communication with a first access network device according to a fourth NCC and a fifth NCC saved by the UE, the N third NCCs containing the fourth NCC; and further configured to determine a sixth NCC according to the fourth NCC, the sixth NCC being used to replace the fifth NCC.

[0523] In some embodiments of the present application, the fourth NCC is the NCC in the N third NCCs that is most different from the fifth NCC.

[0524] In some embodiments of the present application, the processing module is specifically configured to derive N first keys for communication with N first access network devices according to the N third NCCs and the fifth NCC.

[0525] In some embodiments of the present application, the processing module is further configured to associate the first key with the first access network device.

[0526] The receiving module is further configured to receive an LTM switching message from the second access network device, the LTM switching message indicating that the UE switches to the first access network device.

[0527] The processing module is further configured to access the first access network device using the first key.

[0528] In some embodiments of the present application, the receiving module is further configured to receive an LTM switching message from the second access network device, the LTM switching message indicating that the UE switches to the first access network device.

[0529] In some embodiments of the present application, the processing module is further configured to associate the fifth NCC with the first access network device.

[0530] In some embodiments of the present application, the receiving module is specifically configured to receive N LTM configuration information from the second access network device, the LTM configuration information being associated with the first access network device, and the LTM configuration information including the third NCC.

[0531] In some embodiments of the present application, the receiving module is further configured to receive M seventh NCCs from the second access network device.

[0532] The processing module is further configured to derive the first key for communicating with the first access network device according to an eighth NCC and the sixth NCC, the M seventh NCCs containing the eighth NCC.

[0533] The processing module is further configured to determine a ninth NCC according to the eighth NCC, the ninth NCC being used to replace the sixth NCC.

[0534] Referring to FIG. 10, in some possible implementation manners, when the device for deriving a key is the second access network device or a component in the second access network device, the device includes: a processing module 1000, configured to select N first access network devices; a sending module 1001, configured to send information for communicating with a UE to the N first access network devices selected by the processing module, N being less than or equal to M-2, M representing the number of all values of NCC; a receiving module 1002, configured to receive LTM configuration information from the N first access network devices, the LTM configuration information including NCC; and a sending module 1003, further configured to send the LTM configuration information to the UE.

[0535] In some embodiments of the present application, the sending module is specifically configured to send the information for communicating with the UE to the N first access network devices through the first network element.

[0536] In some embodiments of the present application, the sending module is further configured to send a first indication to the first network element, the first indication indicating whether the first network element performs derivation of the NH.

[0537] The device for deriving a key provided by the embodiments of the present application can implement each process achieved by the method embodiments and achieve the same technical effects. To avoid repetition, details are not described herein.

[0538] As shown in FIG. 11, the embodiments of the present application further provide a communication device 2000, which includes a processor 2002 and a memory 2002, and the memory 2002 stores programs or instructions executable on the processor 2002. For example, when the communication device 2000 is a terminal, the programs or instructions are executed by the processor 2002 to implement each step of the method embodiments for deriving a key and achieve the same technical effects. When the communication device 2000 is a network-side device, the programs or instructions are executed by the processor 2002 to implement each step of the method embodiments for deriving a key and achieve the same technical effects. To avoid repetition, details are not described herein.

[0539] The embodiments of the present application further provide a terminal, which includes a processor and a communication interface. The communication interface is coupled to the processor, and the processor is configured to run programs or instructions to implement the steps in the above method embodiments. The terminal embodiments correspond to the above terminal-side method embodiments. Each implementation process and implementation manner of the above method embodiments can be applied to the terminal embodiments and achieve the same technical effects. The terminal can be the device for deriving a key shown in FIG. 9. Specifically, FIG. 12 is a schematic diagram of a hardware structure of a terminal according to an embodiment of the present application.

[0540] The terminal 100 includes, but is not limited to, at least part of the components such as a radio frequency unit 101, a network module 102, an audio output unit 103, an input unit 104, a sensor 105, a display unit 106, a user input unit 107, an interface unit 108, a memory 109, and a processor 110.

[0541] Those skilled in the art can understand that the terminal 100 can further include a power supply (such as a battery) for supplying power to each component. The power supply can be logically connected to the processor 110 through a power management system, so as to realize functions such as management of charging, discharging, and power consumption management through the power management system. The terminal structure shown in FIG. 12 does not constitute a limitation on the terminal. The terminal can include more or fewer components than those shown in the figure, or combine certain components, or have different component arrangements, which are not described herein.

[0542] It should be understood that in the embodiments of the present application, the input unit 104 can include a graphics processor 1041 and a microphone 1042, and the graphics processor 1041 processes image data of a still picture or a video obtained by an image capture device (such as a camera) in a video capture mode or an image capture mode. The display unit 106 can include a display panel 1061, which can be configured in the form of a liquid crystal display, an organic light-emitting diode, etc. The user input unit 107 includes at least one of a touch panel 1071 and other input devices 1072. The touch panel 1071 is also called a touch screen. The touch panel 1071 can include two parts of a touch detection device and a touch controller. The other input devices 1072 can include, but are not limited to, a physical keyboard, function keys (such as volume control keys, on-off keys, etc.), a trackball, a mouse, a joystick, etc., which will not be described here.

[0543] In the embodiments of the present application, after the radio frequency unit 101 receives the downlink data from the network side device, it can be transmitted to the processor 110 for processing; in addition, the radio frequency unit 101 can send uplink data to the network side device. Generally, the radio frequency unit 101 includes, but is not limited to, an antenna, an amplifier, a transceiver, a coupler, a low noise amplifier, a duplexer, etc.

[0544] The memory 109 can be used to store software programs or instructions and various data. The memory 109 can mainly include a first storage area storing programs or instructions and a second storage area storing data, wherein the first storage area can store an operating system, application programs or instructions required by at least one function (such as a sound playing function, an image playing function, etc.), and the like. In addition, the memory 109 can include a volatile memory or a non-volatile memory. The non-volatile memory can be a Read-Only Memory (ROM), a Programmable ROM (PROM), an Erasable PROM (EPROM), an Electrically EPROM (EEPROM), or a flash memory. The volatile memory can be a Random Access Memory (RAM), a Static RAM (SRAM), a Dynamic RAM (DRAM), a Synchronous DRAM (SDRAM), a Double Data Rate SDRAM (DDR SDRAM), an Enhanced SDRAM (ESDRAM), a Synch link DRAM (SLDRAM), and a Direct Rambus RAM (DRRAM). The memory 109 in the embodiments of the present application includes but is not limited to these and any other suitable types of memory.

[0545] The processor 110 can include one or more processing units; optionally, the processor 110 integrates an application processor and a modem processor, wherein the application processor mainly processes operations related to an operating system, a user interface, and an application program, and the modem processor mainly processes wireless communication signals, such as a baseband processor. It can be understood that the above-mentioned modem processor can also not be integrated into the processor 110.

[0546] The radio frequency unit 101 is configured to receive an LTM switching message from the second access network device, the LTM switching message indicating that the UE switches to the first access network device; the processor 110 is configured to perform horizontal key derivation to obtain a first key for communication with the first access network device if a first condition is met; and the processor 110 is further configured to access the first access network device through the LTM switching.

[0547] In some embodiments of the present application, the first condition comprises that the UE accesses the first access network device through LTM switching for the first time.

[0548] In some embodiments of the present application, the radio frequency unit 101 is further configured to receive LTM configuration information from the second access network device; and the processor 110 is further configured to derive a first key for communicating with the first access network device according to the LTM configuration information when a second condition is met.

[0549] In some embodiments of the present application, the second condition comprises that the UE accesses the first access network device through LTM switching for the first time.

[0550] It can be understood that the implementation process of each implementation manner mentioned in the present embodiment can refer to the related description of the method embodiment and achieve the same or corresponding technical effects. To avoid repetition, it will not be described here again.

[0551] Alternatively, the radio frequency unit 101 is configured to receive N third NCCs from the second access network device; the processor 110 is configured to derive a first key for communicating with the first access network device according to a fourth NCC and a fifth NCC saved by the UE, the N third NCCs containing the fourth NCC; and the processor 110 is further configured to determine a sixth NCC according to the fourth NCC, the sixth NCC being used to replace the fifth NCC.

[0552] In some embodiments of the present application, the fourth NCC is the NCC with the largest difference from the fifth NCC among the N third NCCs.

[0553] In some embodiments of the present application, the processor 110 is specifically configured to derive N first keys for communicating with N first access network devices according to the N third NCCs and the fifth NCC.

[0554] In some embodiments of the present application, the processor 110 is further configured to associate the first key with the first access network device.

[0555] The radio frequency unit 101 is further configured to receive an LTM switching message from the second access network device, the LTM switching message indicating that the UE switches to the first access network device.

[0556] The processor 110 is further configured to access the first access network device using the first key.

[0557] In some embodiments of the present application, the radio frequency unit 101 is further configured to receive an LTM switching message from the second access network device, the LTM switching message indicating that the UE switches to the first access network device.

[0558] In some embodiments of the present application, after the radio frequency unit receives N third NCCs from the second access network device, the processor 110 is further configured to associate the fifth NCC with the first access network device by the UE.

[0559] In some embodiments of the present application, the radio frequency unit 101 is specifically configured to receive N LTM configuration information from the second access network device, the LTM configuration information being associated with the first access network device, and the LTM configuration information including the third NCC.

[0560] In some embodiments of the present application, the radio frequency unit 101 is further configured to receive M seventh NCCs from the second access network device.

[0561] The processor 110 is further configured to derive the first key for communicating with the first access network device according to the eighth NCC and the sixth NCC, and the M seventh NCCs include the eighth NCC.

[0562] The processor 110 is further configured to determine a ninth NCC according to the eighth NCC, and the ninth NCC is used to replace the sixth NCC.

[0563] It can be understood that the implementation process of each implementation mode mentioned in the embodiment can refer to the related description of the method embodiment and achieve the same or corresponding technical effects. To avoid repetition, it will not be described here.

[0564] The embodiment of the present application also provides a network side device, which includes a processor and a communication interface, the communication interface and the processor are coupled, and the processor is used to run programs or instructions to realize the steps of the above-mentioned method embodiment. The network side device embodiment corresponds to the above-mentioned network side device method embodiment, and each implementation process and implementation mode of the above-mentioned method embodiment can be applied to the network side device embodiment and can achieve the same technical effects.

[0565] Specifically, the embodiment of the present application also provides a network side device, which can be the device for deriving the key shown in FIG. 8 or FIG. 10. As shown in FIG. 13, the network side device 3000 includes an antenna 3001, a radio frequency device 3002, a baseband device 3003, a processor 3004 and a memory 3005. The antenna 3001 is connected with the radio frequency device 3002. In the uplink direction, the radio frequency device 3002 receives information through the antenna 3001, and sends the received information to the baseband device 3003 for processing. In the downlink direction, the baseband device 3003 processes the information to be sent and sends it to the radio frequency device 3002, and the radio frequency device 3002 processes the received information and sends it out through the antenna 3001.

[0566] The method performed by the network side device in the above embodiments can be implemented in the baseband device 3003, which includes a baseband processor.

[0567] The baseband device 3003 may, for example, include at least one baseband board on which a plurality of chips are disposed, as shown in FIG. 13. One of the chips is, for example, a baseband processor, which is connected with the memory 3005 through a bus interface to invoke a program in the memory 2005 and perform the network device operations shown in the above method embodiments.

[0568] The network side device may, for example, further include a network interface 3006, which is, for example, a common public radio interface (CPRI).

[0569] Specifically, the network side device 3000 of the embodiments of the present application further includes instructions or programs stored in the memory 3005 and executable on the processor 3004, and the processor 3004 invokes the instructions or programs in the memory 3005 to perform the method performed by each module shown in FIG. 8 or FIG. 10 and achieve the same technical effects. To avoid repetition, details are not described herein.

[0570] Specifically, the embodiments of the present application further provide a network side device. As shown in FIG. 14, the network side device 4000 includes a processor 4001, a network interface 4002 and a memory 4003. The network side device can be the device for deriving a key shown in FIG. 7. The network interface 4002 is, for example, a common public radio interface (CPRI).

[0571] Specifically, the network side device 4000 of the embodiments of the present application further includes instructions or programs stored in the memory 4003 and executable on the processor 4001, and the processor 4001 invokes the instructions or programs in the memory 4003 to perform the method performed by each module shown in FIG. 7 and achieve the same technical effects. To avoid repetition, details are not described herein.

[0572] The embodiments of the present application further provide a readable storage medium, which stores programs or instructions. The programs or instructions are executed by a processor to implement each process of the above method embodiments for deriving a key and achieve the same technical effects. To avoid repetition, details are not described herein.

[0573] The processor is the processor in the terminal in the above-described embodiments. The readable storage medium includes a computer readable storage medium, such as a computer readable only memory (ROM), a random access memory (RAM), a magnetic disk or an optical disk, etc. In some examples, the readable storage medium can be a non-transitory readable storage medium.

[0574] The embodiment of the present application further provides a chip, which comprises a processor and a communication interface, wherein the communication interface is coupled with the processor, the processor is used to run programs or instructions, to realize each process of the method for deriving a key and to achieve the same technical effects. To avoid repetition, details are not described herein.

[0575] It should be understood that the chip mentioned in the embodiment of the present application can also be referred to as a system chip, a system on chip, a chip system or a system on chip, etc.

[0576] The embodiment of the present application further provides a computer program / program product, which is stored in a storage medium and is executed by at least one processor to realize each process of the method for deriving a key and to achieve the same technical effects. To avoid repetition, details are not described herein.

[0577] The embodiment of the present application further provides a communication system, which comprises a terminal and a network side device. The terminal can be used to execute the steps of the method for deriving a key on the UE side. The network side device can be used to execute the steps of the method for deriving a key on the first network element side and the access network device side.

[0578] It should be noted that, in this document, the term "comprising" or "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that processes, methods, articles or devices including a series of elements not only include those elements, but also include other elements not explicitly listed, or further include elements inherent to such processes, methods, articles or devices. Without more limitations, the element defined by the statement "comprising a" does not exclude the presence of additional identical elements in the process, method, article or device including the element. In addition, it should be pointed out that the scope of the method and device in the embodiment of the present application is not limited to the order of performing the functions shown or discussed, but can also include performing the functions in a substantially simultaneous manner or in a reverse order, for example, the described method can be performed in an order different from the described order, and various steps can be added, omitted or combined. In addition, the features described with reference to some examples can be combined in other examples.

[0579] Through the description of the above embodiments, those skilled in the art can clearly understand that the above-mentioned example methods can be realized by means of a computer software product and a general hardware platform as necessary, and of course can also be realized by hardware. The computer software product is stored in a storage medium (such as a ROM, a RAM, a magnetic disc, an optical disc, etc.), and includes a plurality of instructions for enabling a terminal or a network side device to execute the method described in each embodiment of the present application.

[0580] The embodiments of the present application are described above in combination with the drawings, but the present application is not limited to the specific embodiments described above, and the specific embodiments described above are merely illustrative rather than limiting. Those skilled in the art can make many forms of embodiments under the inspiration of the present application without departing from the scope of the present application and the scope protected by the claims, and these embodiments all belong to the protection of the present application.

Claims

1. A method for deriving a key, the method comprising: receiving, by a first network element, a path switch message from a first access network device, the path switch message being used to establish a signaling connection between a user equipment (UE) and a core network; determining, by the first network element, whether to perform a next hop value (NH) derivation for the UE according to the path switch message; sending, by the first network element, a path switch acknowledgement message to the first access network device, the path switch acknowledgement message being used to respond to the path switch message.

2. The method of claim 1, wherein, the path switch message comprises a first indication; determining, by the first network element, whether to perform the NH derivation for the UE according to the path switch message comprises: determining, by the first network element, whether to perform the NH derivation for the UE according to the first indication.

3. The method of claim 1 or 2, wherein, determining, by the first network element, whether to perform a next hop value (NH) derivation for the UE according to the path switch message comprises: in a case where the path switch message comprises a first indication, determining, by the first network element, not to perform the NH derivation for the UE.

4. The method of claim 1, wherein, before the receiving, by the first network element, the path switch message from the first access network device, the method further comprising: receiving, by the first network element, the first indication from a second access network device and saving the first indication in a context of the UE; determining, by the first network element, whether to perform the NH derivation for the UE according to the path switch message comprises: obtaining, by the first network element, the first indication from the context of the UE according to the path switch message and determining whether to perform the NH derivation for the UE according to the first indication.

5. The method of claim 4, wherein, in a case where the first network element obtains the context of the UE according to the path switch message and determines to perform the NH derivation for the UE according to the first indication in the context of the UE, the method further comprising: not establishing, by the first network element, the signaling connection between the UE and the core network according to the first indication.

6. The method of any one of claims 3 to 5, wherein, determining, by the first network element, whether to perform the NH derivation for the UE according to the first indication comprises: in a case where the first indication indicates to perform the NH derivation for the UE, determining, by the first network element, to perform the NH derivation for the UE; or, in a case where the first indication indicates not to perform the NH derivation for the UE, determining, by the first network element, not to perform the NH derivation for the UE.

7. The method of any one of claims 4 to 6, wherein, after the receiving, by the first network element, the first indication from the second access network device, the method further comprising: saving, by the first network element, a second NH and a second next hop chain count (NCC) corresponding to the first access network device according to the first indication; wherein, in a case where the first network element determines not to perform the NH derivation for the UE, the path switch acknowledgement message comprises the second NH and the second NCC.

8. The method of any one of claims 2 to 6, wherein, in a case where the first network element determines not to perform the NH derivation for the UE, the path switch acknowledgement message comprises a first NH and a first NCC, the first NH and the first NCC being a NH and a NCC currently saved by the first network element or being preset values.

9. The method of any one of claims 2 to 8, wherein, the first indication is used to indicate a layer 1 / layer 2 triggered mobility (LTM) switch.

10. A method for deriving a key, the method comprising: sending, by a first access network device, a path switch message to a first network element, the path switch message being used to establish a signaling connection between a user equipment (UE) and a core network; receiving, by the first access network device, a path switch acknowledgement message from the first network element, the path switch acknowledgement message being used to respond to the path switch message; wherein the path switch message contains a first indication indicating that the first network element does not perform a new handover (NH) derivation, in a case that a first condition is met.

11. The method of claim 10, wherein, the first condition comprises: the UE accesses the first access network device through a last mile technology (LTM) handover for a non-first time.

12. The method of claim 10 or 11, wherein, after the first access network device receives the path switch acknowledgement message from the first network element in the case that the first condition is met, the method further comprises: if the path switch acknowledgement message includes key related information, the first access network device ignores the key related information, the key related information including at least one of a new handover (NH) and a next cell change (NCC).

13. The method of any one of claims 10 to 12, wherein, before the first access network device sends the path switch message to the first network element, the method further comprises: the first access network device accepts the UE to access through the LTM handover; the first access network device determines a first key for communicating with the UE.

14. The method of claim 13, wherein, the first access network device determining the first key for communicating with the UE comprises: in the case that the first condition is met, the first access network device performs a horizontal key derivation to obtain the first key.

15. The method of claim 14, wherein, after the first access network device receives the path switch acknowledgement message from the first network element in the case that the first condition is met, the method further comprises: if the path switch acknowledgement message includes key related information, the first access network device saves the key related information, the key related information being used for a next Xn handover, the key related information including at least one of the NH and the NCC.

16. The method of any one of claims 10 to 15, wherein, the method further comprises: the first access network device receives information for communicating with the UE from a second access network device; the first access network device sends LTM configuration information to the second access network device, the LTM configuration information including the NCC.

17. The method of any one of claims 10 to 16, wherein, the first indication is used to indicate that the LTM handover is performed.

18. A method for deriving a key, the method comprising: receiving, by a user equipment (UE), a last mile technology (LTM) handover message from a second access network device, the LTM handover message indicating that the UE switches to a first access network device; in a case that a first condition is met, performing, by the UE, a horizontal key derivation to obtain a first key for communicating with the first access network device; accessing, by the UE, the first access network device through the LTM handover.

19. The method of claim 18, wherein, the first condition comprises: the UE accesses the first access network device through the LTM handover for a non-first time.

20. The method of claim 18 or 19, wherein, the method further comprises: receiving, by the UE, LTM configuration information from the second access network device; in a case that a second condition is met, deriving, by the UE, the first key for communicating with the first access network device according to the LTM configuration information.

21. The method of claim 20, wherein, the second condition comprises: the UE accesses the first access network device through the LTM handover for a first time. 22.A method for deriving a key, the method comprising: receiving, by a UE, N third NCCs from a second access network device; deriving, by the UE, a first key for communicating with a first access network device based on a fourth NCC and a fifth NCC saved by the UE, the N third NCCs including the fourth NCC; determining, by the UE, a sixth NCC based on the fourth NCC, the sixth NCC being used to replace the fifth NCC.

23. The method of claim 22, wherein, the fourth NCC is the NCC in the N third NCCs that is furthest from the fifth NCC.

24. The method of claim 22 or 23, wherein, deriving, by the UE, a first key for communicating with a first access network device based on a fourth NCC and a fifth NCC saved by the UE, comprises: deriving, by the UE, N first keys for communicating with N first access network devices based on the N third NCCs and the fifth NCC.

25. The method of any one of claims 22 to 24, wherein, after deriving, by the UE, a first key for communicating with a first access network device based on a fourth NCC and a fifth NCC saved by the UE, the method further comprises at least one of: associating, by the UE, the first key with the first access network device; receiving, by the UE, an LTM handover message from the second access network device, the LTM handover message indicating the UE to hand over to the first access network device; accessing, by the UE, the first access network device using the first key.

26. The method of claim 22 or 23, wherein, before deriving, by the UE, a first key for communicating with a first access network device based on a fourth NCC and a fifth NCC saved by the UE, the method further comprises: receiving, by the UE, an LTM handover message from the second access network device, the LTM handover message indicating the UE to hand over to the first access network device.

27. The method of claim 26, wherein, after receiving, by the UE, N third NCCs from a second access network device, the method further comprises: associating, by the UE, the fifth NCC with the first access network device.

28. The method of any one of claims 22-27, wherein, receiving, by a UE, N third NCCs from a second access network device, comprises: receiving, by the UE, N LTM configuration information from the second access network device, the LTM configuration information being associated with the first access network device, the LTM configuration information including the third NCC.

29. The method of any one of claims 22 to 28, wherein, the method further comprises: receiving, by the UE, M seventh NCCs from the second access network device; deriving, by the UE, the first key for communicating with the first access network device based on an eighth NCC and a sixth NCC saved by the UE, the M seventh NCCs including the eighth NCC; determining, by the UE, a ninth NCC based on the eighth NCC, the ninth NCC being used to replace the sixth NCC. 30.A method for deriving a key, the method comprising: selecting, by a second access network device, N first access network devices, and sending information for communicating with a UE to the N first access network devices, the N being less than or equal to M-2, the M representing a number of all values of NCCs; receiving, by the second access network device, LTM configuration information from the N first access network devices, the LTM configuration information including NCCs; The second access network device sends the LTM configuration information to the UE.

31. The method of claim 30, wherein, The second access network device sends information related to UE communication to the N first access network devices, including: The second access network device sends information related to UE communication to the N first access network devices through a first network element.

32. The method of claim 30 or 31, wherein, The method further includes: The second access network device sends a first indication to a first network element, the first indication indicating whether the first network element performs derivation of NH.

33. The method of any one of claims 30-32, wherein, The first indication is used to indicate performing LTM switching.

34. An apparatus for deriving a key, the apparatus comprising: The receiving module, the processing module, and the sending module, wherein: The receiving module is configured to receive a path switching message from a first access network device, the path switching message being used to establish a signaling connection between the UE and a core network; The processing module is configured to determine whether to perform derivation of a next hop value (NH) for the UE according to the path switching message; The sending module is configured to send a path switching confirmation message to the first access network device, the path switching confirmation message being used to respond to the path switching message.

35. The apparatus of claim 34, wherein, The path switching message contains a first indication; and the processing module is specifically configured to determine whether to perform derivation of NH for the UE according to the first indication.

36. The apparatus of claim 34 or 35, wherein, The processing module is specifically configured to determine not to perform derivation of NH for the UE when the path switching message contains the first indication.

37. The apparatus of claim 34, wherein, The receiving module is further configured to receive a first indication from a second access network device before receiving the path switching message from the first access network device; The processing module is further configured to save the first indication received by the receiving module in a context of the UE; The processing module is specifically configured to obtain the first indication from the context of the UE according to the path switching message, and determine whether to perform derivation of NH for the UE according to the first indication in the context of the UE.

38. The apparatus of claim 37, wherein, The processing module is further configured to not establish the signaling connection between the UE and the core network according to the first indication when the first network element obtains the context of the UE according to the path switching message, and determines to perform derivation of NH for the UE according to the first indication in the context of the UE.

39. The apparatus of any one of claims 36-38, wherein, The processing module is specifically configured to: determine to perform derivation of NH for the UE when the first indication indicates performing derivation of NH for the UE; or determine not to perform derivation of NH for the UE when the first indication indicates not performing derivation of NH for the UE.

40. The apparatus of any one of claims 37-39, wherein, The processing module is further configured to save a second NH and a second NCC corresponding to the first access network device according to the first indication after receiving the first indication from the second access network device; wherein the path switching confirmation message contains the second NH and the second NCC if the processing module determines not to perform derivation of NH for the UE.

41. The apparatus of any one of claims 35-39, wherein, If the processing module determines not to derive the NH for the UE, the path switching acknowledgement message comprises a first NH and a first NCC, the first NH and the first NCC being a NH and an NCC currently saved by the first network element, or being preset values.

42. An apparatus for deriving a key, the apparatus comprising: The sending module and the receiving module, wherein: The sending module is configured to send a path switching message to the first network element, the path switching message being used to establish a signaling connection between a user equipment (UE) and a core network. The receiving module is configured to receive a path switching acknowledgement message from the first network element, the path switching acknowledgement message being used to respond to the path switching message. The path switching message comprises a first indication indicating that the first network element does not perform derivation of the NH, if a first condition is met.

43. The apparatus of claim 42, wherein, The first condition comprises: The UE accesses the first access network device through LTM switching for the first time.

44. The device of claim 42 or 43, wherein, The apparatus further comprises a processing module. The processing module is configured to, if the first condition is met, after receiving the path switching acknowledgement message from the first network element, ignore key-related information included in the switching acknowledgement message, the key-related information comprising at least one of a NH and an NCC.

45. The apparatus of any one of claims 42-44, wherein, The apparatus further comprises a processing module. The processing module is configured to accept access of the UE through LTM switching. The processing module is further configured to determine a first key used for communication with the UE.

46. The device of claim 45, wherein, The processing module is specifically configured to, if the first condition is met, perform horizontal key derivation to obtain the first key.

47. The device of claim 46, wherein, The processing module is further configured to: If the first condition is met, after receiving the path switching acknowledgement message from the first network element, if the switching acknowledgement message includes key-related information, save the key-related information, the key-related information being used for next Xn switching, the key-related information comprising at least one of a NH and an NCC.

48. The apparatus of any one of claims 42-47, wherein: The receiving module is further configured to receive information from a second access network device for communication with the UE. The sending module is further configured to send LTM configuration information to the second access network device, the LTM configuration information comprising an NCC.

49. An apparatus for deriving a key, the apparatus comprising: The receiving module and the processing module, wherein: The receiving module is configured to receive an LTM switching message from a second access network device, the LTM switching message indicating that the UE switches to a first access network device. The processing module is configured to, if a first condition is met, perform horizontal key derivation to obtain a first key used for communication with the first access network device. The processing module is further configured to access the first access network device through LTM switching; or The receiving module is configured to receive N third NCCs from a second access network device. The processing module is configured to derive a first key used for communication with the first access network device according to a fourth NCC and a fifth NCC saved by the UE, the N third NCCs comprising the fourth NCC. The processing module is further configured to determine a sixth NCC according to the fourth NCC, and the sixth NCC is used to replace the fifth NCC.

50. The device of claim 49, wherein, The first condition comprises: The UE accesses the first access network device through the LTM switching for the first time.

51. The device of claim 49, wherein, The fourth NCC is the NCC with the largest difference from the fifth NCC among the N third NCCs.

52. An apparatus for deriving a key, the apparatus comprising: The processing module, the sending module, and the receiving module, wherein: The processing module is configured to select N first access network devices; The sending module is configured to send information related to UE communication to the N first access network devices selected by the processing module, and N is less than or equal to M-2, and M represents the number of all values of NCC. The receiving module is configured to receive LTM configuration information from the N first access network devices, and the LTM configuration information comprises NCC. The sending module is further configured to send the LTM configuration information to the UE.

53. The device of claim 52, wherein, The sending module is specifically configured to send the information related to UE communication to the N first access network devices through a first network element.

54. The device of claim 52 or 53, wherein, The sending module is further configured to send a first indication to the first network element, and the first indication indicates whether the first network element performs derivation of the NH. 55.A terminal comprising a processor and a memory, wherein the memory stores programs or instructions executable on the processor, and the programs or instructions, when executed by the processor, implement steps of the method for deriving a key according to any one of claims 18 to 21, or implement steps of the method for deriving a key according to any one of claims 22 to 29. 56.A network-side device comprising a processor and a memory, wherein the memory stores programs or instructions executable on the processor, and the programs or instructions, when executed by the processor, implement steps of the method for deriving a key according to any one of claims 1 to 9, or implement steps of the method for deriving a key according to any one of claims 10 to 17, or implement steps of the method for deriving a key according to any one of claims 30 to 33. 57.A readable storage medium, wherein the readable storage medium stores programs or instructions, and the programs or instructions, when executed by a processor, implement the method for deriving a key according to any one of claims 1 to 9, or implement steps of the method for deriving a key according to any one of claims 10 to 17, or implement steps of the method for deriving a key according to any one of claims 18 to 21, or implement steps of the method for deriving a key according to any one of claims 22 to 29, or implement steps of the method for deriving a key according to any one of claims 30 to 33.

58. A computer program product stored in a storage medium, the computer program product being executed by at least one processor to implement the method of deriving a key as claimed in any one of claims 1-9, or to implement the steps of the method of deriving a key as claimed in any one of claims 10 to 17, or to implement the steps of the method of deriving a key as claimed in any one of claims 18 to 21, or to implement the steps of the method of deriving a key as claimed in any one of claims 22 to 29, or to implement the steps of the method of deriving a key as claimed in any one of claims 30 to 33.

59. A chip comprising a processor and a communication interface, the communication interface and the processor being coupled, the processor being configured to run a program or instructions to implement the method of deriving a key as claimed in any one of claims 1-9, or to implement the steps of the method of deriving a key as claimed in any one of claims 10 to 17, or to implement the steps of the method of deriving a key as claimed in any one of claims 18 to 21, or to implement the steps of the method of deriving a key as claimed in any one of claims 22 to 29, or to implement the steps of the method of deriving a key as claimed in any one of claims 30 to 33.

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