Non-access stratum (NAS) security mode command mismatch with NAS count avoidance

Abstract

A method includes transmitting, by a core network entity of a core network of a wireless communication system, to a user equipment (UE), a non-access stratum (NAS) security mode command (SMC) message including information regarding security capabilities of the UE, information for establishing a security context between the UE and the core network, and a first NAS security mode message transaction identifier (ID); receiving, by the core network entity, from the UE, a NAS security mode complete message including a second NAS security mode message transaction ID; and generating, by the core network entity, based on a comparison of the first NAS security mode message transaction ID and the second NAS security mode message transaction ID satisfying a condition, a security key, wherein the security key is usable to protect communications between the UE and an apparatus of an access network of the wireless communication system.

Description

NON-ACCESS STRATUM (NAS) SECURITY MODE COMMAND MISMATCH WITH NAS COUNT AVOIDANCEFIELD

[0001] Various example embodiments relate generally to wireless networks and, more particularly, to a non-access stratum (NAS) security mode command (SMC) procedure.BACKGROUND

[0002] Wireless networking provides significant advantages for user mobility. A user’s ability to remain connected while on the move provides advantages not only for the user, but also provides greater efficiency and productivity for society as a whole. As user expectations for, e.g., security, become more demanding, technology for wireless networking must also keep pace with such expectations. Accordingly, there is continuing interest in improving wireless networking technology.SUMMARY

[0003] As used herein, the term “entity” may refer to a distinct component of an architecture or device, a network device, a network node, a network function, or any other devices (physical or virtual) in a communication network.

[0004] In accordance with aspects of the present disclosure, a method includes transmitting, by a core network entity of a core network of a wireless communication system, to a user equipment (UE), a non-access stratum (NAS) security mode command (SMC) message including information regarding security capabilities of the UE, information for establishing a security context between the UE and the core network, and a first NAS security mode message transaction identifier (ID); receiving, by the core network entity, from the UE, a NAS security mode complete message including a second NAS security mode message transaction ID; and generating, by the core network entity, based on a comparison of the first NAS security mode message transaction ID and the second NAS security mode message transaction ID satisfying a condition, a security key, where the security key is usable to protect communications between the UE and an apparatus of an access network of the wireless communication system.

[0005] In an aspect of the method, the generating the security key is further based on a match between the second NAS security mode message transaction ID in the NAS securitymode complete message and the first NAS security mode message transaction ID in the NAS SMC message.

[0006] In an aspect of the method, the first NAS security mode message transaction ID in the NAS SMC message includes a first NAS ID specific to the transmission of the NAS SMC message, and the second NAS security mode message transaction ID in the NAS security mode complete message includes a second NAS ID.

[0007] In an aspect of the method, the first NAS security mode message transaction ID in the NAS SMC message includes a first bitmap including an indication of a number of retransmissions of the NAS SMC message, and the second NAS security mode message transaction ID in the NAS security mode complete message includes a second bitmap.

[0008] In an aspect of the method, the first NAS security mode message transaction ID in the NAS SMC message corresponds to a NAS downlink message sequence number, and the second NAS security mode message transaction ID in the NAS security mode complete message corresponds to a NAS uplink message sequence number.

[0009] In an aspect of the method, the transmitting the NAS SMC message is based on a retransmission timer expiration.

[0010] In an aspect of the method, the method further includes generating, by the core network entity, based on the retransmission timer expiration, the first NAS security mode message transaction ID.

[0011] In an aspect of the method, the method further includes receiving, by the core network entity from the UE, another NAS security mode complete message including a third NAS security mode message transaction ID; and continuing, by the core network entity, based on a comparison of the first NAS security mode message transaction ID and the third NAS security mode message transaction ID failing to satisfy the condition, to monitor for a NAS security mode complete message without generating a security key.

[0012] In an aspect of the method, the method further includes maintaining, by the core network entity, based on a comparison of the first NAS security mode message transaction ID and the third NAS security mode message transaction ID failing to satisfy the condition, a retransmission timer.

[0013] In an aspect of the method, the method further includes receiving, by the core network entity from the UE, a registration request message including an indication of whether the UE supports NAS security mode message transaction identification.

[0014] In accordance with aspects of the present disclosure, a method includes receiving, by a user equipment (UE), from a core network entity of a core network of a wirelesscommunication system, a non-access stratum (NAS) security mode command (SMC) message including information regarding security capabilities of the UE, integrity key information, and a first NAS security mode message transaction identifier (ID); generating, by the UE, based on the first NAS security mode message transaction ID, a second NAS security mode message transaction ID; and transmitting, by the UE, to the core network entity, a NAS security mode complete message including the second NAS security mode message transaction ID.

[0015] In an aspect of the method, the first NAS security mode message transaction ID in the NAS SMC message includes a NAS ID specific to the transmission of the NAS SMC message.

[0016] In an aspect of the method, the generating the second NAS security mode message transaction ID includes setting, by the UE, based on the NAS ID in the NAS SMC message, the second NAS security mode message transaction ID.

[0017] In an aspect of the method, the first NAS security mode message transaction ID in the NAS SMC message includes an indication of a number of retransmissions associated with the NAS SMC message.

[0018] In an aspect of the method, the generating the second NAS security mode message transaction ID includes setting, by the UE, based on the number of retransmissions associated with the NAS SMC message, the second NAS security mode message transaction ID.

[0019] In an aspect of the method, the method further includes transmitting, by the UE to the core network entity, a registration request message including an indication of whether the UE supports NAS security mode message transaction identification.

[0020] According to some aspects, there is provided the subject matter of the independent claims. Some further aspects are defined in the dependent claims.BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Some example embodiments will now be described with reference to the accompanying drawings.

[0022] FIG. 1 is a diagram of an example embodiment of wireless networking between a network system and a user equipment (UE), according to one illustrated aspect of the disclosure;

[0023] FIG. 2 is a diagram of example components of a network system, according to one illustrated aspect of the disclosure;

[0024] FIG. 3 is a diagram of an example embodiment of operations of a NAS security mode command (SMC) procedure, according to one illustrated aspect of the present disclosure;

[0025] FIG. 4 is a diagram of an example embodiment of operations of an uplink and downlink NAS count increment procedure, according to one illustrated aspect of the present disclosure;

[0026] FIG. 5 is a diagram illustrating an example security key misalignment scenario, according to one illustrated aspect of the present disclosure;

[0027] FIG. 6 is a diagram of an example embodiment of operations of a NAS SMC procedure with support for avoiding a mismatch in NAS SMCs and associated NAS counts between a UE and a network, according to one illustrated aspect of the present disclosure;

[0028] FIG. 7 is a diagram of an example embodiment of a NAS security mode message transaction identifier, according to one illustrated aspect of the present disclosure;

[0029] FIG. 8 is a diagram of an example embodiment of operations of a NAS SMC procedure with support for avoiding a mismatch in NAS SMCs and associated NAS counts between a UE and a network, according to one illustrated aspect of the present disclosure;

[0030] FIG. 9 is a diagram of an example embodiment of operations of a NAS SMC procedure with support for avoiding a mismatch in NAS SMCs and associated NAS counts between a UE and a network, according to one illustrated aspect of the present disclosure;

[0031] FIG. 10 is a diagram of an example embodiment of operations of a NAS SMC procedure with support for avoiding a mismatch in NAS SMCs and associated NAS counts between a UE and a network, according to one illustrated aspect of the present disclosure;

[0032] FIG. 11 is a diagram of an example embodiment of operations of a NAS SMC procedure with support for avoiding a mismatch in NAS SMCs and associated NAS counts between a UE and a network, according to one illustrated aspect of the present disclosure;

[0033] FIG. 12 is a flow diagram of example operations of a network apparatus performing a NAS SMC procedure, according to one illustrated aspect of the present disclosure;

[0034] FIG. 13 is a flow diagram of example operations of a UE performing a NAS SMC procedure, according to one illustrated aspect of the present disclosure; and

[0035] FIG. 14 is a diagram of example embodiment of components of a UE or of a network apparatus, according to one illustrated aspect of the present disclosure.DETAILED DESCRIPTION

[0036] In the following description, certain specific details are set forth in order to provide a thorough understanding of disclosed aspects. However, one skilled in the relevant art will recognize that aspects may be practiced without one or more of these specific details or with other methods, components, materials, etc. In other instances, well-known structures associatedwith transmitters, receivers, or transceivers have not been shown or described in detail to avoid unnecessarily obscuring descriptions of the aspects.

[0037] Reference throughout this specification to “one aspect” or “an aspect” means that a particular feature, structure, or characteristic described in connection with the aspect is included in at least one aspect. Thus, the appearances of the phrases “in one aspect” or “in an aspect” in various places throughout this specification are not necessarily all referring to the same aspect. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more aspects.

[0038] Embodiments described in the present disclosure may be implemented in wireless networking apparatuses, such as, without limitation, apparatuses utilizing Worldwide Interoperability for Microwave Access (WiMAX), Global System for Mobile communications (GSM, 2G), GSM EDGE radio access Network (GERAN), General Packet Radio Service (GRPS), Universal Mobile Telecommunication System (UMTS, 3G) based on basic wideband- code division multiple access (W-CDMA), high-speed packet access (HSPA), Long Term Evolution (LTE), LTE-Advanced, enhanced LTE (eLTE), 5G New Radio (5G NR), 5G Advance, 6G (and beyond) and 802.1 lax (Wi-Fi 6), among other wireless networking systems. The term ‘eLTE’ here denotes the LTE evolution that connects to a 5G core. LTE is also known as evolved UMTS terrestrial radio access (EUTRA) or as evolved UMTS terrestrial radio access network (EUTRAN).

[0039] A wireless communication system may include a non-access stratum (NAS) and an access stratum (AS). The NAS is a protocol between a user equipment (UE) and a core network of the wireless communication system. The NAS protocol may provide various functions, for example, but are not limited to, supporting traffic and signaling messages between the core network and the UE, managing the establishment of communication sessions, and maintaining continuous communications with the UE as the UE moves to different areas. The AS is a protocol between a UE and an access network of the wireless communication system. The AS protocol may provide radio access or air interface for radio communications between the UE and the access network. Security is an important aspect of wireless communications. Security keys used for NAS and AS protection may be dependent on the particular security algorithms in use. The NAS and AS security keys are derived at the core network and at the UE from security key parameters that are generated during a NAS level authentication and key agreement (AKA) procedure.

[0040] In a Third Generation Partnership Project (3GPP) wireless communication system, a NAS security mode command (SMC) procedure may be used to establish a NAS securitycontext between a UE and a core network entity (e.g., an access and mobility management (AMF)) of a core network of the wireless communication system. A NAS security context may include, for example, but is not limited to, a security key (e.g., an AMF key (KAMF)), a ciphering algorithm, an integrity algorithm, and a set of security parameters (e.g., NAS count, NAS integrity key, NAS encryption key). The NAS SMC procedure may include a roundtrip of messages between the AMF and the UE, for example, as described in the 3GPP technical document TS 33.501 V18.2.0 (2023-06) (“TS 33.501 document”) section 6.7.2, which is hereby incorporated by reference herein in its entirety. For instance, the AMF may send a NAS SMC message to the UE, and the UE may respond with a NAS security mode complete message.

[0041] A UE may initiate a registration with a core network by transmitting a registration request to the core network via an access network. In an example, the UE may include information regarding the UE security capabilities in the registration request. For instance, the registration request may include one or more information elements (IES) indicating the UE security capabilities. The NAS SMC procedure is designed to protect the registration request against a man-in-the-middle attack where the attacker modifies those IEs that indicate the UE security capabilities. If the NAS SMC procedure completes successfully, the UE is attached to the core network knowing that no bidding down attack has happened. In case a bidding down attack was attempted, the verification of the NAS SMC may fail, and the UE may respond with a reject message, meaning that the UE may not attach to the core network.

[0042] As part of performing the NAS SMC procedure, the AMF and the UE may independently maintain and track two separate NAS counters, an uplink NAS count and a downlink NAS count. The downlink NAS count and uplink NAS count may be set to the same value (e.g., a value of 0) at the start of the NAS SMC procedure. The AMF may increment a local downlink NAS count at the AMF for each transmitted NAS SMC message, and the UE may increment a local downlink NAS count at the UE for each received NAS SMC message that successfully passes a NAS security check. In a similar way, the UE may increment a local uplink NAS count at the UE for each transmitted NAS security mode complete message, and the AMF may increment a local uplink NAS count at the AMF for each received NAS security mode complete message that successfully passes a NAS security check. Further, the AMF may generate a message sequence number to be included in a NAS SMC message (for transmission to a UE) using a current downlink NAS count at the AMF. Similarly, the UE may generate a sequence number to in included in a NAS security mode complete message (for transmission to the AMF) using a current uplink NAS count at the UE. In an example, a NAS count valuemay be a 24-bit value and a respective sequence number may correspond to the lowest 8 bits of the NAS count value.

[0043] At the end of a successful NAS SMC procedure, each of the AMF and the UE may separately generate a security key (e.g., a gNB key (K8NB)) to be used for protecting AS communications between the UE and an access node (e.g., a base station). To that end, the AMF may generate the security key based on a NAS count associated with a NAS security mode complete message received from the UE (e.g., using the NAS count as an input to a key derivation function (KDF)). The AMF may transmit the generated security key to the base station. In a similar way, after the UE transmitted a NAS security mode complete message to the AMF, the UE may generate the security key based on a NAS count associated with the transmitted NAS security mode complete message (e.g., using the NAS count as an input to the same KDF as the AMF). The base station may utilize the security key generated by the AMF, and the UE may utilize the security key generated by the UE for AS communications with each other (e.g., to perform an AS SMC procedure). For instance, the base station may transmit, to the UE, a message (e.g., an AS SMC message) generated with security protection using the AMF generated security key, and the UE may receive the message and verify the received message using the UE generated security key generated. Under a normal operating condition, a NAS SMC message from the AMF may successfully arrive at the UE, and a corresponding response (a NAS security mode complete message) may successfully arrive at the AMF, and thus the AMF and the UE may each generate a security key (e.g., K8NB) for AS communications based on the NAS count from the same NAS security mode complete message.

[0044] As used herein, and unless indicated otherwise, the terms “network system”, “network side”, and “network” (where used alone) may include both access network components and core network components.

[0045] 3GPP technical document TS 24.501 VI 8.3.1 (2023-06) (“TS 24.501 document”) section 5.4, which is hereby incorporated by reference herein in its entirety, specifies handling of various abnormal cases that may occur on the network side for a NAS SMC procedure. The TS 24.501 document specifies the usage of a retransmission timer for the AMF. More specifically, the AMF may start a retransmission timer (e.g., referred to as a timer T3560) after transmitting a NAS SMC message to the UE. The AMF may, on the first expiry of the timer T3560, retransmit the NAS SMC message and may reset and restart timer T3560. This retransmission may be repeated four times. That is, on the fifth expiry of timer T3560, the NASSMC procedure is to be aborted. The AMF may, upon receipt of the NAS security mode complete message, stop the timer T3560.

[0046] In a certain scenario, there may be a delay (e.g., due to an unstable condition in the radio interface) in the UE in responding to an initial NAS SMC message transmitted by the AMF. For instance, the NAS security mode complete message transmitted by the UE in response to the initial NAS SMC message may arrive at the AMF after the AMF retransmitted the NAS SMC message (due to an expiry of T3560 timer). Meanwhile, the UE may successfully handle the retransmitted NAS SMC message. As will be discussed more fully below, such a scenario may result in the UE generating a security key (e.g., K8NB) based on an uplink NAS count value associated with a UE response for the retransmitted NAS SMC message while the AMF generates a security key (e.g., K8NB) based on an uplink NAS count value associated with a UE response for the initially transmitted NAS SMC message. That is, there is a mismatch in NAS SMCs and associated NAS counts between the UE and the AMF for key generation. As a result, the security key (e.g., K8NB) generated by the UE is different from the security key (e.g., K8NB) generated by the AMF, causing a security key mismatch or misalignment between the AMF and the UE. As discussed above, the AMF transfers the AMF generated security key to a respective base station for subsequent AS communications (e.g., AS SMC procedure) with the UE. However, due to the security key mismatch, the UE may fail to verify the AS communications received from the base station.

[0047] Aspects of the present disclosure provide techniques for performing a NAS SMC procedure with support for avoiding a mismatch in NAS SMCs and associated NAS counts between a UE and a network. For example, a message transaction identifier (ID) (e.g., an additional message field) may be added to a downlink NAS SMC message and to an uplink NAS security mode complete message in a NAS SMC procedure. The network (e.g., an AMF) may transmit a NAS SMC message with a NAS security mode message transaction ID. The NAS security mode message transaction ID may identify that particular transmission of the NAS SMC message. In other words, an initially transmitted NAS SMC message and each subsequent retransmitted NAS SMC message(s) may include a different NAS security mode message transaction ID. When the UE responds to a NAS SMC message, the UE may transmit a NAS security mode complete message with the same NAS security mode message transaction ID as the NAS security mode message transaction ID in the received NAS SMC message. Upon the AMF receiving a NAS security mode complete message, the AMF may generate a security key (e.g., K8NB) if the NAS security mode message transaction ID in the NAS security mode complete message matches the NAS security mode message transaction ID in the most recentlytransmitted NAS SMC message. Otherwise, a new retransmission message (NAS SMC message) is transmitted by the AMF.

[0048] According to an aspect of the present disclosure, a core network entity (e.g., an AMF) of a core network of a wireless communication system may transmit, to a UE, a NAS SMC message including a first NAS security mode message transaction ID. The NAS SMC message may further include information regarding security capabilities of the UE (e.g., a replay of UE security capabilities), information (e.g., key set identifiers (ngKSI), ciphering algorithm, integrity algorithm, message authentication code-integrity (MAC-I)) for establishing a security context between the UE and the core network. The core network entity may receive, from the UE, a NAS security mode complete message including a second NAS security mode message transaction ID. The core network entity may generate, based on a comparison of the first NAS security mode message transaction ID and the second NAS security mode message transaction ID satisfying a condition, a security key (e.g., K8NB). The security key may be usable to protect AS communications between the UE and an apparatus (e.g., a base station) of an access network of the wireless communication system. In aspects, the generating the security key may be further based on a match between the second NAS security mode message transaction ID in the NAS security mode complete message and the second NAS security mode message transaction ID in the NAS SMC message. For instance, when the comparison is a match, the core network entity may use an uplink NAS count associated with the received NAS security mode complete message as an input to a KDF to generate the security key.

[0049] In aspects, the first NAS security mode message transaction ID in the NAS SMC message may include a first NAS ID specific to the transmission of the NAS SMC message. The second NAS security mode message transaction ID in the NAS security mode complete message may include a second NAS ID, where the NAS security mode complete message may be a response to a NAS SMC message associated with the second NAS ID. For instance, the core network entity may generate a new (or unique) NAS ID for each NAS SMC message to be transmitted to the UE, and when the UE responds to a received NAS SMC message, the UE may set an NAS ID in a NAS security mode complete message to be transmitted to the core network entity based on the NAS ID in the received NAS SMC message.

[0050] In aspects, the first NAS security mode message transaction ID in the NAS SMC message may include a first bitmap including an indication of a number of retransmissions (e.g., 0, 1, 2, 3 or more) of the NAS SMC message. The second NAS security mode message transaction ID in the NAS security mode complete message may include a second bitmap,where the NAS security mode complete message may be a response to a NAS SMC message associated with the second bitmap. For instance, for each NAS SMC message to be transmitted by the core network entity, the core network entity may set a bitmap in the NAS SMC message to a value corresponding to a number of transmissions of the NAS SMC message. For example, a value of 0 may indicate an initial transmission, a value of 1 may indicate a first retransmission, a value of 2 may indicate a second retransmission, and so on. When the UE responds to a received NAS SMC message, the UE may set a bitmap in a NAS security mode complete message to be transmitted to the core network entity based on the bitmap in the received NAS SMC message.

[0051] In aspects, the transmitting the NAS SMC message may be further based on a retransmission timer (e.g., T3560 timer) expiration. In aspects, the core network entity may further generate, based on the retransmission timer expiration, the first NAS security mode message transaction ID.

[0052] In aspects, the core network entity may further receive, from the UE, another NAS security mode complete message including a third NAS security mode message transaction ID. The core network entity may continue, based on a comparison of the first NAS security mode message transaction ID and the third NAS security mode message transaction ID failing to satisfy the condition, to monitor for a NAS security mode complete message without generating a security key (e.g., K8NB). That is, the core network entity may refrain from generating a security key when the comparison fails to satisfy the condition. In aspects, the core network entity may further maintain a retransmission timer (e.g., T3560 timer) based on a comparison of the first NAS security mode message transaction ID and the third NAS security mode message transaction ID failing to satisfy the condition. That is, the core network entity may refrain from stopping the retransmission timer when the comparison fails to satisfy the condition.

[0053] In aspects, the core network entity may further receive, from the UE, a registration request message including an indication of whether the UE supports NAS security mode message transaction identification. For instance, based on the UE supporting NAS security mode message transaction identification, the core network entity may use the NAS security mode message transaction ID as discussed above to determine whether to generate a security key (e.g., K8NB) or not.

[0054] For backward compatibility, meaning that when the UE does not support NAS security mode message transaction identification, the core network entity may utilize NAS message sequence numbers to perform similar comparison prior to generating a security key(e.g., K8NB). For instance, the first NAS security mode message transaction ID in the NAS SMC message may correspond to a NAS downlink message sequence number, the second NAS security mode message transaction ID in the NAS security mode complete message may correspond to a NAS uplink message sequence number, and the core network entity may generate a security key if the NAS uplink message sequence number in the received NAS security mode complete message matches the NAS downlink message sequence number in the transmitted NAS SMC message. Such and other aspects will be described in more detail later herein.

[0055] Aspects of the present disclosure may provide several benefits. For example, the addition of a NAS security mode message transaction ID to a NAS SMC message (transmitted by an AMF) and to a NAS security mode complete message (transmitted by a UE) can ensure that the AMF will wait for a response (a NAS security mode complete message) for a last retransmitted NAS SMC message before generating or calculating a security key (e.g., K8NB). In this way, a security key generated by the AMF may match the security key generated by the UE, and thus avoiding the NAS SMC mismatch and key misalignment issues discussed above. The alternate mechanisms of reusing NAS message sequence numbers can ensure that the AMF will wait for a response (a NAS security mode complete message) for a last retransmitted NAS SMC message before generating or calculating a security key (e.g., K8NB), and thus avoiding the NAS SMC mismatch and key misalignment issues discussed above without modifying the NAS SMC message structure and NAS security mode complete message structure. While the present disclosure is described in the context of a NAS SMC procedure, the present disclosure is applicable for any NAS procedure that utilizes roundtrip messages and retransmissions.

[0056] The present disclosure may use the term “serving network device” to refer to a network node or network device (or a portion thereof) that services a UE. As used herein, the terms “transmit to,” “receive from,” and “cooperate with,” (and their variations) include communications that may or may not involve communications through one or more intermediate devices or nodes. The term “acquire” (and its variations) includes acquiring in the first instance or reacquiring after the first instance. The term “connection” may mean a physical connection or a logical connection.

[0057] The present disclosure uses 5G NR as an example of a wireless network and may use smartphones and / or uncrewed aerial vehicles as an example of UEs. It is intended and shall be understood that such examples are merely illustrative, and the present disclosure is applicable to other wireless networks and user equipment.

[0058] FIG. 1 is a diagram depicting an example of wireless networking between a network system 100 and a user equipment (UE) 150. The network system 100 may include one or more network nodes 120, one or more servers 110, and / or one or more network equipment 130 (e.g., test equipment). The network nodes 120 will be described in more detail below. As used herein, the term “network apparatus” may refer to any component of the network system 100, such as the server 110, the network node 120, the network equipment 130, any component(s) of the foregoing, and / or any other component(s) of the network system 100. Examples of network apparatuses include, without limitation, apparatuses implementing aspects of 5G NR, among others. The present disclosure describes embodiments related to 5G NR and embodiments that involve aspects defined by 3GPP. However, it is contemplated that embodiments relating to other wireless networking technologies are encompassed within the scope of the present disclosure.

[0059] The following description provides further details of examples of network nodes. In a 5G NR network, a gNodeB (also known as gNB) may include, e.g., a node that provides NR user plane and control plane protocol terminations towards the UE and that is connected via a next generation (NG) interface to the 5G core (5GC), e.g., according to 3GPP TS 38.300 V16.6.0 (2021-06) section 3.2, which is hereby incorporated by reference herein.

[0060] A gNB supports various protocol layers, e.g., Layer 1 (LI) - physical layer, Layer 2 (L2), and Layer 3 (L3).

[0061] The layer 2 (L2) of NR is split into the following sublayers: Medium Access Control (MAC), Radio Link Control (RLC), Packet Data Convergence Protocol (PDCP) and Service Data Adaptation Protocol (SDAP), where, e.g.: o The physical layer offers to the MAC sublayer transport channels; o The MAC sublayer offers to the RLC sublayer logical channels; o The RLC sublayer offers to the PDCP sublayer RLC channels; o The PDCP sublayer offers to the SDAP sublayer radio bearers; o The SDAP sublayer offers to 5GC quality of service (QoS) flows; o Control channels include broadcast control channel (BCCH) and physical control channel (PCCH).

[0062] Layer 3 (L3) includes, e.g., radio resource control (RRC), e.g., according to 3GPP TS 38.300 V16.6.0 (2021-06) section 6, which is hereby incorporated by reference herein.

[0063] A gNB central unit (gNB-CU) includes, e.g., a logical node hosting, e.g., RRC, SDAP, and PDCP protocols of the gNB or RRC and PDCP protocols of the en-gNB, that controls the operation of one or more gNB distributed units (gNB-DUs). The gNB-CUterminates the Fl interface connected with the gNB-DU. A gNB-CU may also be referred to herein as a CU, a central unit, a centralized unit, or a control unit.

[0064] A gNB Distributed Unit (gNB-DU) includes, e.g., a logical node hosting, e.g., RLC, media access control (MAC), and physical (PHY) layers of the gNB or en-gNB, and its operation is partly controlled by the gNB-CU. One gNB-DU supports one or multiple cells. One cell is supported by only one gNB-DU. The gNB-DU terminates the Fl interface connected with the gNB-CU. A gNB-DU may also be referred to herein as DU or a distributed unit.

[0065] As used herein, the term “network node” may refer to any of a gNB, a gNB-CU, or a gNB-DU, or any combination of them. A RAN (radio access network) node or network node such as, e.g., a gNB, gNB-CU, or gNB-DU, or parts thereof, may be implemented using, e.g., an apparatus with at least one processor and / or at least one memory with processor-readable instructions (“program”) configured to support and / or provision and / or process CU and / or DU related functionality and / or features, and / or at least one protocol (sub-)layer of a RAN (radio access network), e.g., layer 2 and / or layer 3. Different functional splits between the central and distributed unit are possible. An example of such an apparatus and components will be described in connection with FIG. 14 below.

[0066] The gNB-CU and gNB-DU parts may, e.g., be co-located or physically separated. The gNB-DU may even be split further, e.g., into two parts, e.g., one including processing equipment and one including an antenna. A central unit (CU) may also be called baseband unit / radio equipment controller / cloud-RAN / virtual-RAN (BBU / REC / C-RAN / V-RAN), open- RAN (O-RAN), or part thereof. A distributed unit (DU) may also be called remote radio head / remote radio unit / radio equipment / radio unit (RRH / RRU / RE / RU), or part thereof. Hereinafter, in various example embodiments of the present disclosure, a network node, which supports at least one of central unit functionality or a layer 3 protocol of a radio access network, may be, e.g., a gNB-CU. Similarly, a network node, which supports at least one of distributed unit functionality or a layer 2 protocol of the radio access network, may be, e.g., a gNB-DU.

[0067] A gNB-CU may support one or multiple gNB-DUs. A gNB-DU may support one or multiple cells and, thus, could support a serving cell for a user equipment (UE) or support a candidate cell for handover, dual connectivity, and / or carrier aggregation, among other procedures.

[0068] The UE 150 may be or include a wireless or mobile device, an apparatus with a radio interface to interact with a RAN (radio access network), a smartphone, an in-vehicle apparatus, an Internet of Things (loT) device, or a machine-to-machine (M2M) device, amongother types of user equipment. Such UE 150 may include: at least one processor; and at least one memory including program code; where the at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus at least to perform certain operations, such as, e.g., RRC connection to the RAN. An example of components of a UE will be described in connection with FIG. 9. In embodiments, the UE 150 may be configured to generate a message (e.g., including a cell ID) to be transmitted via radio towards a RAN (e.g., to reach and communicate with a serving cell). In embodiments, the UE 150 may generate and transmit and receive RRC messages containing one or more RRC PDUs (packet data units). Persons skilled in the art will understand RRC protocol as well as other procedures a UE may perform.

[0069] With continuing reference to FIG. 1, in the example of a 5G NR network, the network system 100 provides one or more cells, which define a coverage area of the network system 100. As described above, the network system 100 may include a gNB of a 5G NR network or may include any other apparatus configured to control radio communication and manage radio resources within a cell. As used herein, the term “resource” may refer to radio resources, such as a resource block (RB), a physical resource block (PRB), a radio frame, a subframe, a time slot, a sub-band, a frequency region, a sub-carrier, a beam, etc. In embodiments, the network node 120 may be called a base station.

[0070] FIG. 1 provides an example and is merely illustrative of a network system 100 and a UE 150. Persons skilled in the art will understand that the network system 100 includes components not illustrated in FIG. 1 and will understand that other user equipment may be in communication with the network system 100.

[0071] FIG. 2 is a block diagram of example components of the network system 100 of FIG. 1. A 5G NR network may be described as an example of the network system 100, and it is intended that aspects of the following description shall be applicable to other types of network systems, as well. The network system may operate in accordance with the signals and connections shown in FIG. 1 such that the UE 150 is in communication with the network system 100 through the RAN 225. Additionally, the network system may be divided into user plane components and functions and control plane components and functions, as shown and described herein. Unless indicated otherwise, the terms “component”, “function”, and “service” may be used interchangeably herein, and they may refer to and be implemented by instructions executed by one or more processors.

[0072] Example functions of the components are described below. The example functions are merely illustrative, and it shall be understood that additional operations and functions maybe performed by the components described herein. Additionally, the connections between components may be virtual connections over service-based interfaces such that any component may communicate with any other component. In this manner, any component may act as a service “producer,” for any other component that is a service “consumer,” to provide services for network functions.

[0073] For example, a control network (CN) 210 is described in the control plane of the network system. The CN 210 includes an authentication server function (AUSF) 211, an AMF 212, and a session management function (SMF) 213. The CN 210 also includes a network slice selection function (NSSF) 214, a NEF 215, a network repository function (NRF) 216, and a UDM 217, which may include UDR 224.

[0074] Additional components and functions of the CN 210 include an application function (AF) 218 and a PCF 219.

[0075] The user plane includes the UE 150, a radio access network (RAN) 225, a user plane function (UPF) 226, and a data network (DN) 227. The RAN 225 may include one or more components described in connection with FIG. 1, such as one or more network nodes. However, the RAN 225 may not be limited to such components. The UPF 226 provides connection for data being transmitted over the RAN 225. The DN 227 identifies services from service providers, Internet access, and third-party services, for example.

[0076] The AMF 212 processes connection and mobility tasks. The AUSF 211 receives authentication requests from the AMF 212 and interacts with UDM 217 to authenticate and validate network responses for determination of successful authentication. The SMF 213 conducts PDU session management, as well as manages session context with the UPF 226.

[0077] The NSSF 214 may select a network slicing instance (NSI) and determine the allowed network slice selection assistance information (NSSAI). This selection and determination are utilized to set the AMF 212 to provide service to the UE 150. The NEF 215 secures access to network services for third parties to create specialized network services. The NRF 216 acts as a repository to store network functions to allow the functions to register with and discover each other.

[0078] The UDM 217 generates authentication vectors for use by the AUSF 211 and AMF 212 and provides user identification handling. The UDM 217 may be connected to the UDR 224 which stores data associated with authentication, applications, or the like. The AF 218 provides application services to a user (e.g., streaming services, etc.). The PCF 219 provides policy control functionality. For example, the PCF 219 may assist in network slicing andmobility management, as well as provide QoS and charging functionality. In some instances, the UDM 217 and / or UDR 224 may be referred to as a network data component.

[0079] In some examples, the AMF 212 may perform a NAS SMC procedure with a UE 150. According to aspects of the present disclosure, the AMF 212 may transmit, to a UE 150, a NAS SMC message including a first NAS security mode message transaction ID. The NAS SMC message may further include information regarding security capabilities of the UE 150 (e.g., a replay of UE 150 security capabilities), information (e.g., key set identifiers (ngKSI), ciphering algorithm, integrity algorithm, NAS message authentication code) for establishing a security context between the UE 150 and the core network. The AMF 212 may receive, from the UE 150, a NAS security mode complete message including a second NAS security mode message transaction ID. The AMF 212 may generate, based on a comparison of the first NAS security mode message transaction ID and the second NAS security mode message transaction ID satisfying a condition, a security key (e.g., K8NB), where the security key is usable to protect AS communications between the UE 150 and the RAN 225. Mechanisms for performing a NAS SMC procedure with support for avoidance of a NAS SMC mismatch and associated NAS count at a UE and at a network for security key generation will be discussed more fully below.

[0080] FIG. 2 is merely an example of components of a network system, and variations are contemplated to be within the scope of the present disclosure. In embodiments, the network system may include other components not illustrated in FIG. 2. In embodiments, the network system may not include every component illustrated in FIG. 2. In embodiments, the components and connections may be implemented with different connections than those illustrated in FIG. 2. Such and other embodiments are contemplated to be within the scope of the present disclosure.

[0081] FIG. 3 is a diagram of an example embodiment of operations of a NAS SMC procedure, according to one illustrated aspect of the present disclosure. It will be understood that a described signal may have associated operations and a described operation may have associated signals. Accordingly, a described signal may also involve an operation and a described operation may also involve a signal. Additionally, FIG. 3 will describe signals between and operations performed by various network components, such as those shown at the top of FIG. 3. Specifically, the components include a UE (e.g., the UE 150 of FIG. 1) and an AMF (e.g., the AMF 212 of FIG. 2) of a core network of a wireless communication system (e.g., the network system of FIG. 1 and 2). The network components are illustrative, and it is contemplated that other components may be involved in the signals or may perform theoperations. In some examples, each of the network components may implement the operations using an apparatus with components as shown in FIG. 14. One or more of the following operations may be implemented in connection with the operations of the present disclosure, such as the examples discussed above with reference to FIGS. 1-2.

[0082] The NAS SMC procedure shown in FIG. 3 may be used to establish a NAS security context between the UE and the AMF. This procedure may include a roundtrip of messages between the AMF and the UE. The AMF may transmit a NAS SMC message to the UE, and the UE may reply with a NAS security mode complete message.

[0083] The NAS SMC procedure is designed to protect the registration request against a man-in-the-middle attack where the attacker modifies IES that indicate the UE security capabilities in the registration request. If the NAS SMC procedure completes successfully, the UE is attached to the core network knowing that no bidding down attack has happened. In case a bidding down attack was attempted, the verification of the NAS SMC may fail, and the UE may respond with a reject message, meaning that the UE may not attach to the core network.

[0084] As shown in FIG. 3, at operation 301a, the AMF starts (or activates) a NAS integrity protection before transmitting a NAS SMC message to the UE. The activation may include configuring and / or activating a function that performs NAS integrity protection.

[0085] At operation 301b, the AMF transmits, and the UE receives a NAS SMC message. The NAS SMC message may include UE security capabilities and information for establishing a security context (a UE security context) between the UE and the AMF. The UE security capabilities may be a replay of the UE security capabilities received by the AMF during a registration request. The information for establishing the security context may include, for example, but is not limited to, selected NAS integrity algorithms and an ngKSI for identifying KAMF- The NAS SMC message may also include a K_AMF_change_flag (carried in the additional 5G security parameters IE specified, for example, as described in TS 24.501 document) to indicate a new KAMF is calculated. The NAS SMC message may also include a flag requesting the complete initial NAS message (that was transmitted to the AMF during an initial registration request) and anti-bidding down between architectures (ABBA) parameter(s). In the case of a horizontal derivation of the KAMF during mobility registration update or during multiple registrations in the same public land mobile network (PLMN), the K_AMF_change_flag may be included in the NAS SMC message, for example, as described in clause 6.9.3 of the TS 24.501 document. The NAS SMC message may be integrity protected (but not ciphered) with a NAS integrity key based on the KAMF indicated by the ngKSI in the NAS SMC message. For instance, the NAS SMC message may further include a NAS- messageauthentication code (NAS-MAC) calculated based on the NAS integrity key and the NAS integrity algorithm. In some instances, NAS-MAC may also be referred to as MAC-I, for example, as described in Annex D.3 of TS 33.501 document.

[0086] In case the network supports interworking (e.g., between a 5G core and an evolved packet core (EPC)) using an N26 interface between a mobility management entity (MME) and the AMF, the AMF may also include the selected evolved packet system (EPS) NAS algorithms to be used after mobility to an EPS in the NAS SMC message. The UE may store the algorithms for use after mobility to the EPS using the N26 interface between MME and AMF. The AMF may store the selected EPS NAS algorithms in the UE security context.

[0087] When a change of AMF happens either due to an N2-handover or idle mode mobility, the selected EPS NAS algorithms may be included in the 5G UE security context and provided to the target AMF as part of the 5G UE security context. Persons skilled in the art will understand N2-handover.

[0088] At operation 301c, the AMF starts (or activates) NAS uplink deciphering after transmitting the NAS SMC message. The activation may include configuring and / or activating a function that implements NAS uplink deciphering.

[0089] At operation 302a, the UE verifies the NAS SMC message. For instance, the UE may check that the UE security capabilities transmitted by the AMF match the UE security capabilities stored in the UE to ensure that these UE security capabilities are not modified by an attacker. The UE may also verify the integrity protection of the NAS SMC message using the indicated NAS integrity algorithm and an NAS integrity key based on the KAMF identified by the indicated ngKSI. For instance, the UE may calculate a NAS-MAC based on the NAS integrity algorithm and an NAS integrity key and verify the calculated expected NAS-MAC (XNAS-MAC) against the NAS-MAC included in the received NAS SMC message. If the verification of the integrity of the NAS SMC message is successful, the UE may start NAS integrity protection, ciphering, and / or deciphering on NAS messages with a security context indicated by the ngKSI.

[0090] In case the NAS SMC message includes a K_AMF_change_flag, the UE may derive a new KAMF as described in Annex A.13 of the TS 33.501 document and set NAS counts (e.g., local uplink and downlink NAS counts at the UE) to zero. Mechanisms for maintaining and tracking NAS counts will be discussed more fully below with reference to FIG. 4.

[0091] At operation 302b, based on the successful verification at operation 302a, the UE transmits, and the AMF receives a NAS security mode complete message (to confirm a successful completion of the NAS SMC). The transmitted NAS security mode completemessage may be ciphered and integrity protected (based on the security context). The NAS security mode complete message may include a permanent equipment identifier (PEI) in case the AMF requested for the PEI in the NAS SMC message. The AMF may set the NAS counts (e.g., local uplink and downlink NAS counts at the AMF) to zero if a horizontal derivation of the KAMF is performed. In an example, the UE may include, in the NAS security mode complete message, the complete initial NAS message that was transmitted to the AMF during an initial requestion request. The initial NAS message is a first message that the UE transmitted to the AMF after the UE transitions from an idle state, for example, as described in the TS 33.501 document, subclause 6.4.6.

[0092] If, however, the verification of the NAS SMC message at operation 302a fails at the UE, the UE may reply with a NAS security mode reject message (see the TS 24.501 document). The NAS security mode reject message and all subsequent NAS messages may be protected with the previous, if any, 5G NAS security context, i.e., the 5G NAS security context used prior to the failed NAS SMC message. If no 5G NAS security context existed prior to the NAS SMC message, the NAS security mode reject message may remain unprotected.

[0093] At operation 301c, the AMF deciphers and checks the integrity protection on the NAS security mode complete message using the key(s) and algorithm(s) indicated in the NAS SMC message. If the integrity protection check is a pass and the AMF successfully deciphered the NAS security mode complete message, a security context is established for the UE. In an example, the security context may include the indicated ngKSI, the KAMF identified from the ngKSI, the UE security capabilities, uplink and downlink NAS counts of the AMF.

[0094] At operation 301d, after successfully receiving (e.g., including deciphering and integrity protection check) the NAS security mode complete message, the AMF may start NAS downlink ciphering using the established security context.

[0095] As will be discussed more fully below with reference to FIG. 4, as part of performing the NAS SMC procedure, the AMF and the UE may independently maintain and track a downlink NAS count and an uplink NAS count. For instance, the UE may increment a local uplink NAS count (e.g., a 24-bit value) at the UE for each transmitted NAS message. In some examples, if the UE determines that the uplink NAS count map wrap around after transmitting the NAS security mode complete message at operation 302b, the UE may transmit a NAS security mode reject message and releases the NAS connection instead of transmitting the NAS security mode complete message.

[0096] In some examples, if the AMF successfully validated the NAS security mode complete message, the AMF has successfully confirmed that the subscription permanentidentifier (SUPI) received from the home network of the UE matches the SUPI used by the UE. However, an integrity check failure of the NAS security mode complete message at the AMF can have other causes than a mismatch of the SUPIs.

[0097] FIG. 3 is merely an example of signals and operations, and variations are contemplated to be within the scope of the present disclosure. In embodiments, the signals and operations may include others not illustrated in FIG. 3. In embodiments, the signals and operations may not include every signal and operation illustrated in FIG. 3. In embodiments, the signals and operations may be implemented with different connections than those illustrated in FIG. 3. Such and other embodiments are contemplated to be within the scope of the present disclosure.

[0098] FIG. 4 is a diagram of an example embodiment of operations of an uplink and downlink NAS count increment procedure, according to one illustrated aspect of the present disclosure. It will be understood that a described signal may have associated operations and a described operation may have associated signals. Accordingly, a described signal may also involve an operation and a described operation may also involve a signal. Additionally, FIG. 4 will describe signals between and operations performed by various network components, such as those shown at the top of FIG. 4. Specifically, the components include a UE (e.g., the UE 150 of FIG. 1) and an AMF (e.g., the AMF 212 of FIG. 2) of a core network of a wireless communication system (e.g., the network system of FIG. 1 and 2). The network components are illustrative, and it is contemplated that other components may be involved in the signals or may perform the operations. In some examples, each of the network components may implement the operations using an apparatus with components as shown in FIG. 14. One or more of the following operations may be implemented in connection with the operations of the present disclosure, such as the examples discussed above with reference to FIGS. 1-3.

[0099] At a high level, the AMF and UE may independently maintain and track a downlink NAS count (associated with downlink NAS messages from the AMF to the UE) and an uplink NAS count (associated with uplink NAS messages from the UE to the AMF). The downlink NAS count and uplink NAS count may be reset to the same value at the start of the NAS SMC procedure. The AMF may increment a local downlink NAS count at the AMF for each transmitted NAS SMC message, and the UE may increment a local downlink NAS count at the UE for each received NAS SMC message that successfully passes a NAS security check. In a similar way, the UE may increment a local uplink NAS count at the UE for each transmitted NAS security mode complete message, and the AMF may increment a local uplink NAS countat the AMF for each received NAS security mode complete message that successfully passes a NAS security check.

[0100] For example, at operation 401, the AMF sets a downlink NAS count and an uplink NAS count at the AMF to values of 0. A NAS count value may correspond to a combination of an overflow value and a NAS message sequence number (e.g., denoted as SQN), for example, calculated by applying a logical OR operation to the overflow value and the SQN. In an example, a NAS count may be a 24-bit value, the SQN may correspond to the lower 8 bits of the NAS count, and the overflow value may correspond to the upper 16 bits of the NAS count.

[0101] At operation 402a, the AMF transmits, and the UE receives a NAS SMC message. The NAS SMC message may include a MAC-I and an SQN set to a value of 0 (e.g., based on a current AMF downlink NAS count). The NAS SMC message may also include other information as discussed above with reference to operation 301b of FIG. 3. The MAC-I may be used for integrity protection. In an example, the MAC-I may be calculated based on an integrity algorithm and an integrity key and may be used by a receiver to check on the integrity of the respective message. That is, the NAS SMC message may be integrity protected.

[0102] At operation 402b, after transmitting the NAS SMC message, the AMF increments the AMF downlink NAS count by 1 , and thus the AMF downlink NAS count may have a value of 1 after the increment.

[0103] At operation 403a, the UE may verify the integrity of the received NAS SMC message. If the verification is a success, the UE increments the downlink NAS count at the UE by 1. The UE uses the SQN value included in the NAS SMC message along with the calculated NAS-MAC (or MAC-I) value in the NAS SMC message for the verification.

[0104] At operation 403b, after successfully receiving and verifying the NAS SMC message from the AMF and incrementing the UE downlink NAS count, the UE downlink NAS count has a value of 1. For instance, the UE may have set the UE downlink NAS count to 0 at the start of the NAS SMC procedure.

[0105] At operation 403c, prior to transmitting a response to the NAS SMC message received at operation 302a, the UE may have an uplink NAS count with a value of 0. For instance, the UE may have set the UE uplink NAS count to 0 at the start of the NAS SMC procedure.

[0106] At operation 404a, based on the successful verification of the NAS SMC message, the UE transmits, and the AMF receives a NAS security mode complete message. The NAS security mode complete message may be ciphered (e.g., using a security context establishedbased on information in the NAS SMC message as discussed above with reference to operation 302b of FIG. 3) and may include a MAC-I. The NAS security mode complete message may also include an SQN set to a value of 0 (e.g., based on a current UE uplink NAS count). If, however, the verification fails, the UE may transmit a NAS security mode reject message to indicate a rejection of the NAS SMC.

[0107] At operation 404b, after transmitting the NAS security mode complete message, the UE increments the UE uplink NAS count by 1 , and thus the UE uplink NAS count may have a value of 1 after the increment.

[0108] At operation 405, the AMF may verify the received NAS security mode complete message. The verification may include deciphering and integrity protection check. After successfully receiving and verifying the NAS security mode complete message from the UE, the AMF increments the AMF uplink NAS count by 1 , and thus the AMF uplink NAS count may have a value of 1 after the increment.

[0109] If the AMF fails to verify the NAS security mode complete message or receives a NAS security mode reject message instead of a NAS security mode complete message, the AMF may abort the NAS SMC procedure and perform error handling (e.g., retry the NAS SMC procedure).

[0110] FIG. 4 is merely an example of signals and operations, and variations are contemplated to be within the scope of the present disclosure. In embodiments, the signals and operations may include others not illustrated in FIG. 4. In embodiments, the signals and operations may not include every signal and operation illustrated in FIG. 4. In embodiments, the signals and operations may be implemented with different connections than those illustrated in FIG. 4. Such and other embodiments are contemplated to be within the scope of the present disclosure.

[0111] As will be discussed more fully below with reference to FIG. 5, the AMF may use an uplink NAS count in a NAS security mode complete message (received from the UE) as an input to a KDF to generate a security key (e.g., K8NB) and transmit the generated key to a respective access network node (e.g., a base station), The security key may be used to protect subsequent communications (e.g., for performing an AS SMC procedure) between the UE and the base station. The UE may use the UE uplink NAS count included in a NAS security mode complete message (transmitted to the AMF) as an input to the same KDF to generate a security key (e.g., K8NB) for performing the AS SMC procedure with the access network node. As an example, in an AS SMC procedure, the access network node may transmit an AS SMC message to the UE, where the AS SMC message may be security protected (e.g., ciphered and integrityprotected) using the AMF generated security key. If the UE successfully verifies (e.g., deciphers and checks for integrity protection) the AS SMC message, the UE may respond with an AS security mode complete message. If, however, the verification fails, the UE may respond with an AS security mode reject message. Persons skilled in the art will understand the AS SMC procedure.

[0112] Under a normal operating condition, the NAS SMC message transmitted by the AMF at operation 301b may successfully reach the UE, and the corresponding NAS security mode complete message transmitted by the UE at operation 302b may successfully reach the AMF. However, in certain scenarios, the NAS SMC message may not reach the UE. As discussed above, the AMF may perform a retransmission of the NAS SMC message. To that end, the AMF may start a retransmission timer (e.g., timer T3560) after transmitting a NAS SMC message to the UE. The AMF may, on the first expiry of the timer T3560, retransmit the NAS SMC message and may reset and restart timer T3560. This retransmission may be repeated four times. That is, on the fifth expiry of timer T3560, the NAS SMC procedure is to be aborted. The AMF may, upon receipt of the NAS security mode complete message, stop the timer T3560.

[0113] FIG. 5 is a diagram illustrating an example security key misalignment scenario, according to one illustrated aspect of the present disclosure. It will be understood that a described signal may have associated operations and a described operation may have associated signals. Accordingly, a described signal may also involve an operation and a described operation may also involve a signal. Additionally, FIG. 5 will describe signals between and operations performed by various network components, such as those shown at the top of FIG. 5. Specifically, the components include a UE (e.g., the UE 150 of FIG. 1), a gNB (e.g., the network node 120 of FIG. 1 or a node in the RAN 225 of FIG. 2), and an AMF (e.g., the AMF 212 of FIG. 2) of a core network of a wireless communication system (e.g., the network system of FIG. 1 and 2). The network components are illustrative, and it is contemplated that other components may be involved in the signals or may perform the operations. In some examples, each of the network components may implement the operations using an apparatus with components as shown in FIG. 14. One or more of the following operations may be implemented in connection with the operations of the present disclosure, such as the examples discussed above with reference to FIGS. 1-4.

[0114] In FIG. 5, uplink communications from the UE to the AMF may be transmitted via the gNB, and downlink communications from the AMF to the UE may be transmitted via the gNB. Additionally, each of the AMF and the UE may perform uplink and downlink NAS countincrements as discussed above with reference to FIG. 4. For simplicity, the uplink and downlink NAS count increments are not shown in FIG. 5.

[0115] At operation 501, the UE transmits, and the AMF receives a registration request message. The registration request message may include various information, for example, including, but not limited to, a registration type, the UE network capabilities, and the UE security capabilities.

[0116] At operation 502, the AMF starts a primary authentication procedure with the UE. Persons skilled in the art will understand the primary authentication procedure.

[0117] At operation 503a, the AMF transmits, and the UE receives a NAS SMC message, denoted as NAS SMC#1. The NAS SMC#1 may be integrity protected and may include substantially similar information as discussed above with reference to operations 301b of FIG. 3

[0118] At operation 503b, after transmitting the NAS SMC#1 message, the AMF starts a retransmission timer, denoted as T3560#l. The AMF may configure the retransmission timer with a certain duration, for example, as specified by the TS 24.501 document.

[0119] At operation 503c, upon the UE receiving the NAS SMC#1, the UE verifies (e.g., checks for integrity) the NAS SMC#1. In the illustrated example scenario, the verification is successful, and thus the UE proceeds to perform operations 503d and 503e. At operation 503d, the UE replies to the AMF by transmitting a NAS security mode complete message, denoted as the NAS SMP#1. The NAS SMP#1 may be ciphered and integrity protected based on information in the NAS SMC#1. At operation 503e, based on the successful verification, the UE generates a security key, denoted as K8NB#1 , using the uplink NAS count in NAS SMP#1.

[0120] At operation 504a, the retransmission timer T3560#l expires.

[0121] At operation 504b, based on the expiration of the retransmission timer and the NAS SMP#1 is not received by the AMF (e.g., due to the condition of the air interface is not stable, or the link between the UE and AMF is not stable at the time), the AMF transmits a new NAS SMC message, denoted as NAS SMC#2, to the UE. The NAS SMC#2 is a retransmission of the NAS SMC#1. At operation 504c, the AMF starts a new retransmission timer, denoted as T3560#2. The retransmission timer may be implemented in any suitable way. For instance, the T3560#2 and the T3560#l may be based on the same hardware and / or software counter or different hardware and / or software counters.

[0122] At operation 504d, upon the UE receiving the NAS SMC#2, the UE verifies (e.g., checks for integrity) the NAS SMC#2. In the illustrated example scenario, the verification is a success, and thus the UE proceeds to perform operations 504e and 504f. At operation 504e, theUE replies to the AMF by transmitting a NAS security mode complete message, denoted as NAS SMP#2. The NAS SMP#2 may be ciphered and integrity protected based on information in the NAS SMC#2. At operation 504f, the UE generates a security key, denoted as K8NB#2, using the uplink NAS count in NAS SMP#2.

[0123] At operation 505a, because the AMF receives NAS SMP#1 before the NAS SMP#2, at operation 505a, the AMF proceeds to verify (e.g., deciphers and checks for integrity) NAS SMP#1. In the illustrated example scenario, the verification is a success, and thus the AMF proceeds to generate a security key, denoted as K8NB#1 , using the uplink NAS count in NAS SMP#1. Further, based on the successful reception of NAS SMP#1 (indicating a successful completion of NAS SMC), the AMF may stop the retransmission timer T3560#2. At operation 505b, the AMF transmits an initial context setup message to a gNB in communication with the UE, where the initial context setup message includes the KgNB#l.

[0124] At operation 506a, the gNB transmits, and the UE receives an AS SMC message (e.g., ciphered and integrity protected) with keys generated using K8NB#1 as an input, while the UE verifies (e.g., deciphers and integrity protection checks) the AS SMC using keys generated using KgNB#2 as an input. That is, the gNB and the UE use different security keys for AS communications. As a result, the verification at the UE may fail. At operation 506b, because of the verification failure, the UE transmits, and the gNB receives an AS SMC failure message.

[0125] At operation 507, based on the received AS SMC failure message, the gNB transmits, and the UE receives a RRC release message. In an example, the RRC release message may include a wait time, denoted as waitTime, specifying an amount of time that the UE may wait before initiating another RRC connection request.

[0126] FIG. 5 is merely an example of signals and operations, and variations are contemplated to be within the scope of the present disclosure. In embodiments, the signals and operations may include others not illustrated in FIG. 5. In embodiments, the signals and operations may not include every signal and operation illustrated in FIG. 5. In embodiments, the signals and operations may be implemented with different connections than those illustrated in FIG. 5. Such and other embodiments are contemplated to be within the scope of the present disclosure.

[0127] As can be observed from the example scenario shown in FIG. 5, there is a security key misalignment between the UE and the gNB where the UE utilizes the K8NB#2 (generated based on an uplink NAS count associated with the response NAS SMP#2 for NAS SMC#2) while the AMF provides the gNB with the K8NB#1 (generated based on an uplink NAS count associated with the response NAS SMP#1 for NAS SMC#1). As can be further observed, thesecurity key misalignment is caused by the NAS SMP#1 (the response to NAS SMC#1) arrives at the AMF after the AMF retransmitted the NAS SMC message (the NAS SMC#2) due to an expiry of the timer T3560#l, and meanwhile, the UE handles the NAS SMC#2 successfully.

[0128] Accordingly, the present disclosure provides techniques for performing a NAS SMC procedure with support for avoiding a mismatch in NAS SMCs and associated NAS counts at a UE and at a network when security keys (e.g., K8NB) are generated.

[0129] The following will describe example operations for avoiding a security key misalignment between a UE and a gNB. FIG. 6 and 8-11 show example signals and operations for performing a NAS SMC procedure with support for avoiding a mismatch in NAS SMCs and associated NAS counts at a UE and at a network. FIG. 7 shows an example NAS security mode message transaction ID. FIG. 12 shows example operations of a network apparatus (e.g., a core network entity), and FIG. 13 shows example operations of a UE. In FIGS. 6 and 8-11, uplink communications from the UE to the AMF may be transmitted via the gNB, and downlink communications from the AMF to the UE may be transmitted via the gNB as discussed above with reference to FIG. 5. For simplicity, the gNB is not shown in FIGS. 6 and 8-11. Additionally, each of the AMF and the UE may perform uplink and downlink NAS count increments as discussed above with reference to FIG. 4. For simplicity, the uplink and downlink NAS count increments are not shown in FIGS. 6, 8, and 10-11.

[0130] FIG. 6 is a diagram of an example embodiment of operations of a NAS SMC procedure with support for avoiding a mismatch in NAS SMCs and associated NAS counts between a UE and a network, according to one illustrated aspect of the present disclosure. It will be understood that a described signal may have associated operations and a described operation may have associated signals. Accordingly, a described signal may also involve an operation and a described operation may also involve a signal. Additionally, FIG. 6 will describe signals between and operations performed by various network components, such as those shown at the top of FIG. 6. Specifically, the components include a UE (e.g., the UE 150 of FIG. 1) and an AMF (e.g., the AMF 212 of FIG. 2) of a core network of a wireless communication system (e.g., the network system of FIG. 1 and 2). The network components are illustrative, and it is contemplated that other components may be involved in the signals or may perform the operations. In some examples, each of the network components may implement the operations using an apparatus with components as shown in FIG. 14. One or more of the following operations may be implemented in connection with the operations of the present disclosure, such as the examples discussed above with reference to FIGS. 1-5.

[0131] At operation 601, the UE transmits, and the AMF receives a registration message. The registration message may be a registration request similar to the registration request discussed above with reference to operation 501 of FIG. 5, and may optionally include an indication of whether the UE supports NAS security mode message transaction identification handling.

[0132] At operation 602, upon receiving the registration message, the AMF stores the UE capability. If the UE indicated support for NAS security mode message transaction identification, the AMF may proceed to include a NAS security mode message transaction ID in a NAS SMC message to the UE and may check for a NAS security mode message transaction ID in a NAS security mode complete message from the UE prior to generating a security key (e.g., K8NB) as shown in below operations. If, however, the UE indicated NAS security mode message transaction identification is not supported, the AMF may perform the NAS SMC procedure as discussed above with reference to FIGS. 2-4.

[0133] At operation 603, based on the UE supporting NAS security mode message transaction ID handling, the AMF sets a downlink bitmap (e.g., a first bitmap) to be included in a NAS SMC message for transmission to the UE. As will be discussed below with reference to FIG. 7, the AMF may set the downlink bitmap to indicate a number of retransmissions associated with the NAS SMC message. The first bitmap may serve as a NAS security mode message transaction ID for the NAS SMC message.

[0134] FIG. 7 is a diagram of an example embodiment of a NAS security mode message transaction identifier, according to one illustrated aspect of the present disclosure. As shown in FIG. 7, a NAS security mode message transaction ID may include a plurality of bits. In the illustrated example of FIG. 7, the NAS security mode message transaction ID includes 8 bits, where the lower 3 bits (least significant bits) are used to indicate a number of retransmissions for an NAS SMC message and the upper 5 bits (most significant bits) are spared (or reserved). For an initial transmission of an NAS SMC message, the AMF may set the lower 3 bits of the NAS security mode message transaction ID to 0. For a first retransmission transmission of an NAS SMC message, the AMF may set the lower 3 bits to indicate a value of 1. For a second retransmission transmission of an NAS SMC message, the AMF may set the lower 3 bits to indicate a value of 2. For a third retransmission transmission of an NAS SMC message, the AMF may set the lower 3 bits to indicate a value of 3. For a fourth retransmission transmission of an NAS SMC message, the AMF may set the lower 3 bits to indicate a value of 4.

[0135] The NAS security mode message transaction ID of FIG. 7 is merely illustrative, and variations are contemplated to be within the scope of the present disclosure. In general, theNAS security mode message transaction ID may use any suitable number of bits (e.g., 2, 3, 4, 5 or more) and any suitable bit positions to indicate the number of retransmissions associated with a NAS SMC message transmission.

[0136] Returning to FIG. 6, at operation 604, the AMF transmits, and the UE receives a NAS SMC message. The NAS SMC message may include the downlink bitmap. The NAS SMC message may also include other information (e.g., ngKSI, selected NAS integrity algorithms, MAC-I, etc.) as discussed above with reference to operation 301b of FIG. 3 and / or operation 402a of FIG. 4. The NAS SMC message may be integrity protected as discussed above with reference to operation 301b of FIG. 3. Upon transmitting the NAS SMC message, the AMF may start a retransmission timer as discussed above.

[0137] At operation 605a, upon receiving the NAS SMC message, the UE verifies the received NAS SMC message and the downlink bitmap. For instance, the verification may include verifying the integrity protection of the NAS SMC message (e.g., using information indicated by the NAS SMC message) and checking whether the UE security capabilities transmitted by the AMF matches the UE security capabilities stored at the UE. In the illustrated example, the verification is a success. Based on the successful verification, the UE increments the UE downlink NAS count by 1 and proceeds to perform operations 605b and 606.

[0138] At operation 605b, the UE sets an uplink bitmap according to the downlink bitmap in the received NAS SMC message. For instance, the UE may set the uplink bitmap to the downlink bitmap in the received NAS SMC message. The UE may include the uplink bitmap in a NAS security mode complete message to be transmitted to the AMF in response to the received NAS SMC message.

[0139] At operation 606, the UE transmits, and the AMF receives the NAS security mode complete message including the uplink bitmap. The UE may integrity protect and cipher the NAS security mode complete message according to the information provided in the NAS SMC message.

[0140] At operation 607, upon receiving the NAS security mode complete message, the AMF verifies the received NAS security mode complete message. The verification may include deciphering the NAS security mode complete message and check for integrity protection on the NAS security mode complete message (e.g., based on information, such as NAS integrity algorithm and ngKSI included in the NAS SMC message as discussed above with reference to operation 301b of FIG.3). In the illustrated example, the verification is a success. Based on the successful verification, the AMF increments the AMF downlink NAS count by 1. The AMF also verifies if the received uplink bitmap corresponds to a response for the downlink bitmapincluded in the NAS SMC message transmitted at operation 604. That is, the AMF may compare the uplink bitmap (in the received NAS security mode complete message) and the downlink bitmap (included in the last transmitted NAS SMC message). If the comparison results in a match, the AMF generates a security key (e.g., K8NB) based on the uplink NAS count associated with the received NAS security mode complete message. For instance, the AMF may determine the uplink NAS count based on the SQN in the received NAS security mode complete message and an estimated uplink overflow value.

[0141] If, however, the comparison indicates a mismatch between the uplink bitmap and the downlink bitmap, the AMF may continue to monitor for a NAS security mode complete message from the UE that is a response to the NAS SMC message transmitted at operation 604. That is, the AMF may wait for the corresponding bitmap response from UE. Further, the AMF may maintain (e.g., refrain from stopping) the retransmission timer and retransmit the NAS SMC message upon an expiry of the retransmission timer. That is, if the AMF receives a NAS security mode complete message with an uplink bitmap different than a downlink bitmap in a latest transmitted NAS SMC message, the AMF may maintain the retransmission timer, continue to monitor for a NAS security mode complete message without generating a security key.

[0142] As will be discussed more fully below with reference to FIGS. 10-11, the generation of the security key based on a match between the downlink bitmap (in the transmitted NAS SMC message) and the uplink bitmap (in the received NAS security mode complete message) and allowing the retransmission timer to continue when there is a mismatch (from the comparison) can avoid the key misalignment issue discussed herein.

[0143] In some instances, the verification of the NAS SMC message by the UE at operation 605a may fail, and thus the UE may transmit a NAS security mode reject message instead. In some instances, the verification of the NAS security mode complete message by the AMF at operation 607 may fail. If the AMF fails to verify the NAS security mode complete message or receives a NAS security mode reject message instead of a NAS security mode complete message, the AMF may abort the NAS SMC procedure and perform error handling (e.g., retry the NAS SMC procedure).

[0144] FIG. 6 is merely an example of signals and operations, and variations are contemplated to be within the scope of the present disclosure. In embodiments, the signals and operations may include others not illustrated in FIG. 6. In embodiments, the signals and operations may not include every signal and operation illustrated in FIG. 6. In embodiments, the signals and operations may be implemented with different connections than those illustratedin FIG. 6. Such and other embodiments are contemplated to be within the scope of the present disclosure.

[0145] FIG. 8 is a diagram of an example embodiment of operations of a NAS SMC procedure with support for avoiding a mismatch in NAS SMCs and associated NAS counts between a UE and a network, according to one illustrated aspect of the present disclosure. It will be understood that a described signal may have associated operations and a described operation may have associated signals. Accordingly, a described signal may also involve an operation and a described operation may also involve a signal. Additionally, FIG. 8 will describe signals between and operations performed by various network components, such as those shown at the top of FIG. 8. Specifically, the components include a UE (e.g., the UE 150 of FIG. 1) and an AMF (e.g., the AMF 212 of FIG. 2) of a core network of a wireless communication system (e.g., the network system of FIG. 1 and 2). The network components are illustrative, and it is contemplated that other components may be involved in the signals or may perform the operations. In some examples, each of the network components may implement the operations using an apparatus with components as shown in FIG. 14. One or more of the following operations may be implemented in connection with the operations of the present disclosure, such as the examples discussed above with reference to FIGS. 1-6.

[0146] Generally speaking, the signals and operations of FIG. 8 include features similar to the operations of FIG. 6 in many respects. For example, the operations 801 and 802 are similar to operations 601 and 602, respectively. Accordingly, for brevity, details of those operations will not be repeated here and can be referred to the corresponding descriptions above.

[0147] At operation 803, based on the UE supporting NAS security mode message transaction ID handling (e.g., indicated in the registration message at operation 801), the AMF generates a new NAS ID (e.g., a first NAS ID) to be included in a NAS SMC message for transmission to the UE. The NAS ID may serve as a NAS security mode message transaction ID for the NAS SMC message.

[0148] At operation 804, the AMF transmits, and the UE receives a NAS SMC message. The NAS SMC message may include the NAS ID. The NAS SMC message may also include other information (e.g., ngKSI, selected NAS integrity algorithms, MAC-I, etc.) as discussed above with reference to operation 301b of FIG. 3 and / or operation 402a of FIG. 4. The NAS SMC message may be integrity protected as discussed above with reference to operation 301b of FIG. 3. Upon transmitting the NAS SMC message, the AMF may start a retransmission timer as discussed above.

[0149] At operation 805, upon receiving the NAS SMC message, the UE verifies the received NAS SMC message. For instance, the verification may include verifying the integrity protection of the NAS SMC message (e.g., using information indicated by the NAS SMC message) and checking the UE security capabilities transmitted by the AMF match the UE security capabilities stored in the UE and. If the verification is a success, the UE increments the UE downlink NAS count by 1 and determines to respond to the received NAS SMC message with the same NAS ID as the NAS ID received in the NAS SMC message.

[0150] At operation 806, the UE transmits, and the AMF receives the NAS security mode complete message including the NAS ID. The UE may integrity protect and cipher the NAS security mode complete message according to the information provided in the NAS SMC message.

[0151] At operation 807, upon receiving the NAS security mode complete message, the AMF verifies the received NAS security mode complete message. The verification may include deciphering the NAS security mode complete message and check for integrity protection check on the NAS security mode complete message (e.g., based on information, such as NAS integrity algorithm and ngKSI included in the NAS SMC message as discussed above with reference to operation 301b of FIG.3). If the verification is a success, the AMF increments the AMF uplink NAS count by 1. The AMF also verifies if the NAS ID in the received NAS security mode complete message is the same as the NAS ID included in the NAS SMC message transmitted at operation 804. That is, the AMF may compare the NAS ID in the received NAS security mode complete message and the NAS ID included in the last transmitted NAS SMC message. If the comparison results in a match, the AMF generates a security key (e.g., K8NB) based on the uplink NAS count associated with the received NAS security mode complete message. For instance, the AMF may determine the uplink NAS count based on the SQN in the received NAS security mode complete message and an estimated uplink overflow value. If, however, there is a mismatch, the AMF may maintain (e.g., refrain from stopping) the retransmission timer, continue to monitor for a NAS security mode complete message without generating a security key as discussed above with reference to operation 607 of FIG. 6. Upon an expiration of the retransmission timer, the AMF may retransmit the NAS SMC message.

[0152] As will be discussed more fully below with reference to FIGS. 10-11, the generation of the security key based on a NAS ID match (between the transmitted NAS SMC message and the received NAS security mode complete message from the comparison) and allowing the retransmission timer to continue when there is a NAS ID mismatch (from the comparison) can avoid the key misalignment issue discussed herein.

[0153] In some instances, the verification of the NAS SMC message by the UE at operation 805a may fail, and thus the UE may transmit a NAS security mode reject message instead. In some instances, the verification of the NAS security mode complete message by the AMF at operation 807 may fail. If the AMF fails to verify the NAS security mode complete message or receives a NAS security mode reject message instead of a NAS security mode complete message, the AMF may abort the NAS SMC procedure and perform error handling (e.g., retry the NAS SMC procedure).

[0154] FIG. 8 is merely an example of signals and operations, and variations are contemplated to be within the scope of the present disclosure. In embodiments, the signals and operations may include others not illustrated in FIG. 8. In embodiments, the signals and operations may not include every signal and operation illustrated in FIG. 8. In embodiments, the signals and operations may be implemented with different connections than those illustrated in FIG. 8. Such and other embodiments are contemplated to be within the scope of the present disclosure.

[0155] FIG. 9 is a diagram of an example embodiment of operations of a NAS SMC procedure with support for avoiding a mismatch in NAS SMCs and associated NAS counts between a UE and a network, according to one illustrated aspect of the present disclosure. It will be understood that a described signal may have associated operations and a described operation may have associated signals. Accordingly, a described signal may also involve an operation and a described operation may also involve a signal. Additionally, FIG. 9 will describe signals between and operations performed by various network components, such as those shown at the top of FIG. 9. Specifically, the components include a UE (e.g., the UE 150 of FIG. 1) and an AMF (e.g., the AMF 212 of FIG. 2) of a core network of a wireless communication system (e.g., the network system of FIG. 1 and 2). The network components are illustrative, and it is contemplated that other components may be involved in the signals or may perform the operations. In some examples, each of the network components may implement the operations using an apparatus with components as shown in FIG. 14. One or more of the following operations may be implemented in connection with the operations of the present disclosure, such as the examples discussed above with reference to FIGS. 1-5.

[0156] Generally speaking, the signals and operations of FIG. 9 include features similar to the operations of FIG. 4 in many respects. For example, the operations 901, 902a, 902b, 903a, 903b, 903c, 904a, 904b, and 905 are similar to operations 401, 402a, 402b, 403a, 403b, 403c, 404a, 404b, and 405, respectively. Accordingly, for brevity, details of those operations will not be repeated here and can be referred to the corresponding descriptions above.

[0157] At operation 906, upon successfully receiving the NAS security mode complete message from the UE, the AMF generates a security key (e.g., K8NB) based on a match between the downlink SQN in the NAS SMC message transmitted at operations 902a and the uplink SQN in the NAS security mode complete message received at operation 904a. To that end, the AMF may verify the NAS security mode complete message. The verification may include deciphering the NAS security mode complete message and checking for integrity protection on the NAS security mode complete message (e.g., based on information, such as NAS integrity algorithm and ngKSI included in the NAS SMC message as discussed above with reference to operation 301b of FIG.3). If the verification is a success, the AMF may compare the downlink SQN to the uplink SQN. Based on a match from the comparison result, the AMF generates the security key. If the comparison indicates a mismatch (e.g., the downlink SQN is greater than the uplink SQN), the AMF may maintain (e.g., refrain from stopping) the retransmission timer, continue to monitor for a NAS security mode complete message without generating a security key as discussed above with reference to operation 607 of FIG. 6. Upon an expiration of the retransmission timer, the AMF may retransmit the NAS SMC message.

[0158] As will be discussed more fully below with reference to FIGS. 10-11, the generation of the security key when there is a match between the downlink SQN (in the transmitted NAS SMC message) and the uplink SQN (in the received NAS security mode complete message) and allowing the retransmission timer to continue when there is a mismatch (from the comparison) can avoid the key misalignment issue discussed herein.

[0159] FIG. 9 is merely an example of signals and operations, and variations are contemplated to be within the scope of the present disclosure. In embodiments, the signals and operations may include others not illustrated in FIG. 9. In embodiments, the signals and operations may not include every signal and operation illustrated in FIG. 9. In embodiments, the signals and operations may be implemented with different connections than those illustrated in FIG. 9. Such and other embodiments are contemplated to be within the scope of the present disclosure.

[0160] FIG. 10 is a diagram of an example embodiment of operations of a NAS SMC procedure with support for avoiding a mismatch in NAS SMCs and associated NAS counts between a UE and a network. It will be understood that a described signal may have associated operations and a described operation may have associated signals. Accordingly, a described signal may also involve an operation and a described operation may also involve a signal. Additionally, FIG. 10 will describe signals between and operations performed by various network components, such as those shown at the top of FIG. 10. Specifically, the componentsinclude a UE (e.g., the UE 150 of FIG. 1) and an AMF (e.g., the AMF 212 of FIG. 2) of a core network of a wireless communication system (e.g., the network system of FIG. 1 and 2). The network components are illustrative, and it is contemplated that other components may be involved in the signals or may perform the operations. In some examples, each of the network components may implement the operations using an apparatus with components as shown in FIG. 10. One or more of the following operations may be implemented in connection with the operations of the present disclosure, such as the examples discussed above with reference to FIGS. 6 and 8-9.

[0161] At operation 1010, the AMF sets (or generates) a first NAS security mode message transaction ID to a certain value. In one aspect, the NAS security mode message transaction ID may be bitmap indicating a number of retransmissions for a NAS SMC message to be transmitted to the UE as discussed above with reference to FIGS. 6-7. In another aspect, the NAS security mode message transaction ID may be a NAS ID specific to the transmission of an upcoming NAS SMC message (e.g., at operation 1012) as discussed above with reference to FIG. 8. In yet another aspect, the NAS security mode message transaction ID may be a NAS downlink message SQN as discussed above with reference to FIGS. 4 and 9.

[0162] At operation 1012, the AMF transmits, and the UE receives the NAS SMC message including a first NAS security mode message transaction ID. The NAS SMC message may further include information regarding security capabilities of the UE (e.g., a replay of UE security capabilities), information (e.g., key set identifiers (ngKSI), ciphering algorithm, integrity algorithm, NAS message authentication code) for establishing a security context between the UE and the core network. The AMF may integrity protect the NAS SMC message.

[0163] At operation 1014, after transmitting the NAS SMC message to the UE, the AMF starts a retransmission timer (e.g., a timer T3560). The AMF may configure a duration 1030 for the retransmission timer. In an example, the duration 1030 may be set according to a T3560 timer duration specified the 3GPP standard. In general, the duration 1030 may be any suitable time value (e.g., with consideration for a roundtrip delay between the AMF and the UE).

[0164] At operation 1016, upon receiving the NAS SMC message, the UE may set a second NAS security mode message transaction ID to be included in a response (e.g., a NAS security mode complete message) to the received NAS SMC message. When the first NAS security mode message transaction ID is a downlink bitmap or a NAS ID, the UE may set the second NAS security mode message transaction ID to the first NAS security mode message transaction ID in the NAS SMC message received at operation 1012. When the first NAS security mode message transaction ID is a NAS downlink message SQN, the second NAS security modemessage transaction ID is a NAS uplink message SQN, where the UE may generate the NAS uplink message SQN according to the UE uplink NAS count. Prior to setting the second NAS security mode message transaction ID, the UE may verify (e.g., check for integrity protection) the received NAS SMC message and set the second NAS security mode message transaction ID based on a successful verification.

[0165] At operation 1018, the UE transmits, and the AMF receives the NAS security mode complete message including the second NAS security mode message transaction ID. As shown, the NAS security mode complete message arrives at the AMF before the retransmission timer expires. The NAS security mode complete message may be ciphered and integrity protected as discussed above.

[0166] At operation 1020, upon receiving the NAS security mode complete message, the AMF compares the first NAS security mode message transaction ID (in the last transmitted NAS SMC message) and the second NAS security mode message transaction ID (in the received NAS security mode complete message). Prior to the comparison, the AMF may verify (e.g., deciphered and checks for integrity protection) the received NAS security mode complete message and perform the comparison based on a successful verification as discussed above.

[0167] At operation 1022, the AMF determines whether the comparison satisfies a condition. For instance, the condition may correspond to a match between the first NAS security mode message transaction ID (in the last transmitted NAS SMC message) and the second NAS security mode message transaction ID (in the received NAS security mode complete message). If the comparison satisfies the condition, the AMF proceeds to perform operation 1026. At operation 1026, the AMF generates a security key (e.g., K8NB), for example, using an uplink NAS count associated with the NAS security mode complete message as an input to a KDF.

[0168] If, however, the comparison fails to satisfy the condition at operation 1022, the AMF proceeds to operation 1024. At operation 1024, the AMF maintains (e.g., refrain from stopping) the retransmission timer, continues to monitor for a NAS security mode complete message, and refrain from generating a security key.

[0169] FIG. 10 is merely an example of signals and operations, and variations are contemplated to be within the scope of the present disclosure. In embodiments, the signals and operations may include others not illustrated in FIG. 10. In embodiments, the signals and operations may not include every signal and operation illustrated in FIG. 10. In embodiments, the signals and operations may be implemented with different connections than those illustratedin FIG. 10. Such and other embodiments are contemplated to be within the scope of the present disclosure.

[0170] FIG. 11 is a diagram of an example embodiment of operations of a NAS SMC procedure with support for avoiding a mismatch in NAS SMCs and associated NAS counts between a UE and a network. It will be understood that a described signal may have associated operations and a described operation may have associated signals. Accordingly, a described signal may also involve an operation and a described operation may also involve a signal. Additionally, FIG. 11 will describe signals between and operations performed by various network components, such as those shown at the top of FIG. 10. Specifically, the components include a UE (e.g., the UE 150 of FIG. 1) and an AMF (e.g., the AMF 212 of FIG. 2) of a core network of a wireless communication system (e.g., the network system of FIG. 1 and 2). The network components are illustrative, and it is contemplated that other components may be involved in the signals or may perform the operations. In some examples, each of the network components may implement the operations using an apparatus with components as shown in FIG. 11. One or more of the following operations may be implemented in connection with the operations of the present disclosure, such as the examples discussed above with reference to FIGS. 6 and 8-10.

[0171] At operation 1110, the AMF sets (or generates) a first NAS security mode message transaction ID to a certain value. For instance, the first NAS security mode message transaction ID may be a downlink bitmap, a NAS ID, or a NAS message SQN as discussed above with reference to operation 1010 of FIG. 10. If the first NAS security mode message transaction ID is a downlink bitmap, the AMF may set the downlink bitmap to a value of 0 to indicate an initial transmission of a NAS SMC message.

[0172] At operation 1112, the AMF transmits, and the UE receives a first NAS SMC message including the first NAS security mode message transaction ID. The first NAS SMC message may also include other information as discussed above with reference to operation 1012 of FIG. 11. The first NAS SMC message may be integrity protected.

[0173] At operation 1114, after transmitting the first NAS SMC message to the UE, the AMF starts a first retransmission timer (e.g., a first timer T3560). The AMF may configure a duration 1140 for the first retransmission timer. In an example, the duration 1140 may be set according to a T3560 timer duration specified the 3GPP standard. In general, the duration 1140 may be any suitable time value (e.g., with consideration for a roundtrip delay between the AMF and the UE).

[0174] At operation 1116, based on an expiration of the first retransmission timer, the AMF sets a second NAS security mode message transaction ID. If the first NAS security mode message transaction ID is a NAS ID, the AMF may generate a new NAS ID and set the second NAS security mode message transaction ID to newly generated NAS ID. If the first NAS security mode message transaction ID is a downlink bitmap, the AMF may set the downlink bitmap to a value of 1 to indicate that an upcoming second NAS SMC message transmission (e.g., at operation 1118) is a first retransmission of the first NAS SMC message. If the first NAS security mode message transaction ID is a NAS downlink message SQN, the AMF may set the second NAS security mode message transaction ID according to a current AMF downlink NAS count.

[0175] At operation 1118, the AMF transmits a second NAS SMC message to the UE including the second NAS security mode message transaction ID. The second NAS SMC message is a retransmission of the first NAS SMC message. The second NAS SMC message may be integrity protected.

[0176] At operation 1120, after transmitting the second NAS SMC message to the UE, the AMF starts a second retransmission timer (e.g., a second timer T3560). The AMF may configure the same duration 1140 for the second retransmission timer.

[0177] At operation 1122, upon the UE receiving the first NAS SMC message, the UE sets a third NAS security mode message transaction ID to be included in a response (e.g., a first NAS security mode complete message) to be transmitted to the AMF. If the first NAS security mode message transaction ID is a downlink bitmap or a NAS ID, the UE may set the third NAS security mode message transaction ID to the first NAS security mode message transaction ID in the first NAS SMC message received at operation 1112. If the first NAS security mode message transaction ID is a NAS downlink message SQN, the third NAS security mode message transaction ID is a NAS uplink message SQN, and thus the UE may generate the NAS uplink message SQN according to a current UE uplink NAS count. Prior to setting the third NAS security mode message transaction ID, the UE may verify (e.g., check for integrity protection) the received first NAS SMC message and set the third NAS security mode message transaction ID based on a successful verification.

[0178] At operation 1124, the UE transmits, and the AMF receives the first NAS security mode complete message including the third NAS security mode message transaction ID. As shown, the first NAS security mode complete message responsive to the first NAS SMC message arrives at the AMF after the AMF retransmits the first NAS SMC message (as the second NAS SMC message) based on the expiration of the first retransmission timer.

[0179] At operation 1125, after transmitting the first NAS security mode complete message, the UE generates a first security key (e.g., K8NB) using the uplink NAS count in the first NAS security mode complete message.

[0180] At operation 1126, upon the AMF receiving the first NAS security mode complete message, the AMF maintains the first retransmission timer, continues to monitor for a NAS security mode complete message, and refrain from generating a security key based on a comparison of the second NAS security mode message transaction ID (in the received first NAS security mode complete message) and the first NAS security mode message transaction ID (in the latest transmitted second NAS SMC message) fails to satisfy a condition (e.g., a match condition). The comparison indicates a mismatch because the first NAS security mode complete message is responsive to the first NAS SMC message and not the latest second NAS SMC message (the retransmitted NAS SMC message). Prior to the comparison, the AMF may verify (e.g., deciphered and checks for integrity protection) the received first NAS security mode complete message and perform the comparison based on a successful verification as discussed above.

[0181] At operation 1128, upon the UE receiving the second NAS SMC message from operation 1118, the UE sets a fourth NAS security mode message transaction ID to be included in a response (e.g., a second NAS security mode complete message) to be transmitted to the AMF. If the second NAS security mode message transaction ID is a downlink bitmap or a NAS ID, the UE may set the fourth NAS security mode message transaction ID to the second NAS security mode message transaction ID in the second NAS SMC message received at operation 1118. If the second NAS security mode message transaction ID is a NAS downlink message SQN, the fourth NAS security mode message transaction ID is a NAS uplink message SQN, and thus the UE may generate the NAS uplink message SQN according to a current UE uplink NAS count. Prior to setting the fourth NAS security mode message transaction ID, the UE may verify (e.g., check for integrity protection) the received second NAS SMC message and set the fourth NAS security mode message transaction ID based on a successful verification.

[0182] At operation 1130, the UE transmits, and the AMF receives the second NAS security mode complete message including the fourth NAS security mode message transaction ID.

[0183] At operation 1131, after transmitting the second NAS security mode complete message, the UE generates a second security key (e.g., K8NB) using the uplink NAS count in the second NAS security mode complete message.

[0184] In the illustrated example of FIG. 11, the second NAS security mode complete message arrives at the AMF before the second retransmission timer expires. At operation 1132, upon the AMF receiving the second NAS security mode complete message, the AMF generates a security key (e.g., K8NB) based on a comparison of the transmitted second NAS security mode message transaction ID (in the latest transmitted second NAS SMC message) and the received fourth NAS security mode message transaction ID satisfies a condition (e.g., a match condition). The comparison indicates a match because the second NAS security mode complete message is responsive to the second NAS SMC message. Prior to the comparison, the AMF may verify (e.g., deciphered and checks for integrity protection) the received second NAS security mode complete message and perform the comparison based on a successful verification as discussed above.

[0185] Subsequently, the AMF may transfer the AMF generated security key to a respective gNB in communication with the UE, where the gNB may use the AMF generated security key, and the UE may use the latest security key (the second security key) generated by the UE for AS communications.

[0186] As can be observed from FIG. 11 , the security key generated by the AMF and the latest security key (the second security key) generated by the UE are both based on the second NAS security mode complete message. As such, while the response (the first NAS security mode complete message) for the first NAS SMC message arrives at the AMF after the AMF retransmits the first NAS SMC message (as the second NAS SMC message) and the UE successfully handles the second NAS SMC message, there is no security key misalignment between the UE and the network.

[0187] FIG. 11 is merely an example of signals and operations, and variations are contemplated to be within the scope of the present disclosure. In embodiments, the signals and operations may include others not illustrated in FIG. 11. In embodiments, the signals and operations may not include every signal and operation illustrated in FIG. 11. In embodiments, the signals and operations may be implemented with different connections than those illustrated in FIG. 11. Such and other embodiments are contemplated to be within the scope of the present disclosure.

[0188] FIG. 12 is a flow diagram of example operations of a network apparatus, according to one illustrated aspect of the present disclosure. In an aspect, the network apparatus may be an apparatus or network node of a core network entity of a core network of a wireless communication system. In an aspect, the core network entity may correspond to an AMF as discussed above with reference to FIGS. 2-6 and 8-11, and the wireless communication systemmay be a network system as discussed above with reference to FIGS. 1-2. In some examples, the network apparatus may implement the operations using an apparatus with components as shown in FIG. 14. The operations of FIG. 12 may include similar mechanisms as discussed above with reference to FIGS. 1-11.

[0189] At block 1202, a core network entity of a core network of a wireless communication system transmits, to a UE, a NAS SMC message including information regarding security capabilities of the UE (e.g., a replay of UE security capabilities), information (e.g., key set identifiers (ngKSI), ciphering algorithm, integrity algorithm, NAS message authentication code) for establishing a security context between the UE and the core network, and a first NAS security mode message transaction ID.

[0190] At block 1204, the core network entity receives, from the UE, a NAS security mode complete message including a second NAS security mode message transaction ID.

[0191] At block 1206, the core network entity generates, based on a comparison of the first NAS security mode message transaction ID and the second NAS security mode message transaction ID satisfying a condition, a security key (e.g., K8NB), where the security key is usable to protect AS communications between the UE and an apparatus (e.g., a base station) of an access network of the wireless communication system. In aspects, the generating the security key may be further based on a match between the second NAS security mode message transaction ID in the NAS security mode complete message and the second NAS security mode message transaction ID in the NAS SMC message. For instance, when the comparison is a match, the core network entity may use an uplink NAS count associated with the received NAS security mode complete message as an input to a KDF to generate the security key.

[0192] In aspects, the first NAS security mode message transaction ID in the NAS SMC message may include a first NAS ID specific to the transmission of the NAS SMC message. The second NAS security mode message transaction ID in the NAS security mode complete message may include a second NAS ID, where the NAS security mode complete message may be a response for a NAS SMC message associated with the second NAS ID, for example, as discussed above with reference to FIGS. 8 and 10-11.

[0193] In aspects, the first NAS security mode message transaction ID in the NAS SMC message may include a first bitmap including an indication of a number of retransmissions of the NAS SMC message. The second NAS security mode message transaction ID in the NAS security mode complete message may include a second bitmap, where the NAS security mode complete message may be a response for a NAS SMC message associated with the second bitmap, for example, as discussed above with reference to FIGS. 6-7 and 10-11.

[0194] In aspects, the first NAS security mode message transaction ID in the NAS SMC message corresponds to a NAS downlink message sequence number, and the second NAS security mode message transaction ID in the NAS security mode complete message corresponds to a NAS uplink message sequence number, for example, as discussed above with reference to FIGS. 9-11.

[0195] In aspects, the transmitting the NAS SMC message at block 1202 may be further based on a retransmission timer (e.g., T3560 timer) expiration. In aspects, the core network entity may further generate, based on the retransmission timer expiration, the first NAS security mode message transaction ID.

[0196] In aspects, the core network entity may further receive, from the UE, another NAS security mode complete message including a third NAS security mode message transaction ID. The core network entity may continue, based on a comparison of the first NAS security mode message transaction ID and the third NAS security mode message transaction ID failing to satisfy the condition, to monitor for a NAS security mode complete message without generating a security key (e.g., K8NB). That is, the core network entity may refrain from generating a security key when the comparison fails to satisfy the condition. In aspects, the core network entity may further maintain a retransmission timer (e.g., T3560 timer) based on a comparison of the first NAS security mode message transaction ID and the third NAS security mode message transaction ID failing to satisfy the condition. That is, the core network entity may refrain from stopping the retransmission timer when the comparison fails to satisfy the condition.

[0197] In aspects, the core network entity may further receive, from the UE, a registration request message including an indication of whether the UE supports NAS security mode message transaction identification.

[0198] The operations of FIG. 12 are merely illustrative, and variations are contemplated to be within the scope of the present disclosure. In embodiments, the operations may include other blocks not illustrated in FIG. 12. In embodiments, the operations may not include every block illustrated in FIG. 12. In embodiments, the operation may be implemented in a different order than that illustrated in FIG. 12. Such and other embodiments are contemplated to be within the scope of the present disclosure.

[0199] FIG. 13 is a flow diagram of example operations of a UE, according to one illustrated aspect of the present disclosure. In an aspect, the UE may correspond to the UE discussed above with reference to FIGS. 1-6 and 8-11. In some examples, the UE may implement the operations using an apparatus with components as shown in FIG. 14. Theoperations of FIG. 13 may include similar mechanisms as discussed above with reference to FIGS. 1-11.

[0200] At block 1302, a UE receives, from a core network entity of a core network of a wireless communication system, a NAS SMC message including information regarding security capabilities of the UE, integrity key information, and a first NAS security mode message transaction ID. The core network entity may be an AMF as discussed above with reference to FIGS. 2-6 and 8-11, and the wireless communication system may be a network system as discussed above with reference to FIGS. 1-2.

[0201] At block 1304, the UE generates, based on the first NAS security mode message transaction ID, a second NAS security mode message transaction ID.

[0202] At block 1306, the UE transmits, to the core network entity, the NAS security mode complete message including the second NAS security mode message transaction ID.

[0203] In aspects, the first NAS security mode message transaction ID in the NAS SMC message includes a NAS ID specific to the transmission of the NAS SMC message. In aspects, as part of generating the second NAS security mode message transaction ID at block 1304, the UE sets, based on the NAS ID in the NAS SMC message, the second NAS security mode message transaction ID.

[0204] In aspects, the first NAS security mode message transaction ID in the NAS SMC message includes an indication of a number of retransmissions associated with the NAS SMC message. In aspects, as part of generating the second NAS security mode message transaction ID at block 1304, the UE sets, based on the number of retransmissions associated with the NAS SMC message, the second NAS security mode message transaction ID.

[0205] In aspects, the UE further transmits, to the core network entity, a registration request message including an indication of whether the UE supports NAS security mode message transaction identification.

[0206] The operations of FIG. 13 are merely illustrative, and variations are contemplated to be within the scope of the present disclosure. In embodiments, the operations may include other blocks not illustrated in FIG. 13. In embodiments, the operations may not include every block illustrated in FIG. 13. In embodiments, the operation may be implemented in a different order than that illustrated in FIG. 13. Such and other embodiments are contemplated to be within the scope of the present disclosure.

[0207] Referring now to FIG. 14, there is shown a block diagram of example components of a UE or a network apparatus. The apparatus includes an electronic storage 1410, a processor 1420, a memory 1450, and a network interface 1440. The various components may becommunicatively coupled with each other. The processor 1420 may be and may include any type of processor, such as a single-core central processing unit (CPU), a multi-core CPU, a microprocessor, a digital signal processor (DSP), a System-on-Chip (SoC), or any other type of processor. The memory 1450 may be a volatile type of memory, e.g., RAM, or a non-volatile type of memory, e.g., NAND flash memory. The memory 1450 includes processor-readable instructions that are executable by the processor 1420 to cause the apparatus to perform various operations, including those mentioned herein, such as the operations of FIGS. 6 and 8-13.

[0208] The electronic storage 1410 may be and include any type of electronic storage used for storing data, such as hard disk drive, solid state drive, and / or optical disc, among other types of electronic storage. The electronic storage 1410 stores processor-readable instructions for causing the apparatus to perform its operations and stores data associated with such operations, such as storing data relating to 5G NR standards, among other data. The network interface 1440 may implement wireless networking technologies such as 5G NR and / or other wireless networking technologies.

[0209] The components shown in FIG. 14 are merely examples, and persons skilled in the art will understand that an apparatus includes other components not illustrated and may include multiples of any of the illustrated components. Such and other embodiments are contemplated to be within the scope of the present disclosure.

[0210] In general, the various operations of methods described herein may be performed by any suitable means (e.g., the processor 1420 and the memory 1450) capable of performing the corresponding operations. The means may include various hardware and / or software component(s) and / or module(s), including, but not limited to the components of FIG. 14.

[0211] Further embodiments of the present disclosure include the following examples.

[0212] Example 1.1. A method comprising: transmitting, by a core network entity of a core network of a wireless communication system, to a user equipment (UE), a non-access stratum (NAS) security mode command (SMC) message comprising information regarding security capabilities of the UE, information for establishing a security context between the UE and the core network, and a first NAS security mode message transaction identifier (ID); receiving, by the core network entity, from the UE, a NAS security mode complete message comprising a second NAS security mode message transaction ID; and generating, by the core network entity, based on a comparison of the first NAS security mode message transaction ID and the second NAS security mode message transaction ID satisfying a condition, a security key, wherein the security key is usable to protectcommunications between the UE and an apparatus of an access network of the wireless communication system.

[0213] Example 1.2. The method of Example 1.1, wherein the generating the security key is further based on a match between the second NAS security mode message transaction ID in the NAS security mode complete message and the first NAS security mode message transaction ID in the NAS SMC message.

[0214] Example 1.3. The method of Example 1.1 or Example 1.2, wherein: the first NAS security mode message transaction ID in the NAS SMC message comprises a first NAS ID specific to the transmission of the NAS SMC message, and the second NAS security mode message transaction ID in the NAS security mode complete message comprises a second NAS ID.

[0215] Example 1.4. The method of Example 1.1 or Example 1.2, wherein: the first NAS security mode message transaction ID in the NAS SMC message comprises a first bitmap comprising an indication of a number of retransmissions of the NAS SMC message, and the second NAS security mode message transaction ID in the NAS security mode complete message comprises a second bitmap.

[0216] Example 1.5. The method of Example 1.1 or Example 1.2, wherein: the first NAS security mode message transaction ID in the NAS SMC message corresponds to a NAS downlink message sequence number, and the second NAS security mode message transaction ID in the NAS security mode complete message corresponds to a NAS uplink message sequence number.

[0217] Example 1.6. The method of any one of Example 1.1-1.4, wherein the transmitting the NAS SMC message is based on a retransmission timer expiration.

[0218] Example 1.7. The method of Example 1.6, further comprising: generating, by the core network entity, based on the retransmission timer expiration, the first NAS security mode message transaction ID.

[0219] Example 1.8. The method of any one of Examples 1.1-1.7, further comprising: receiving, by the core network entity from the UE, another NAS security mode complete message comprising a third NAS security mode message transaction ID; and continuing, by the core network entity, based on a comparison of the first NAS security mode message transaction ID and the third NAS security mode message transaction ID failing to satisfy the condition, to monitor for a NAS security mode complete message without generating a security key.

[0220] Example 1.9. The method of Example 1.8, further comprising: maintaining, by the core network entity, based on a comparison of the first NAS security mode message transaction ID and the third NAS security mode message transaction ID failing to satisfy the condition, a retransmission timer.

[0221] Example 1.10. The method of any one of Examples 1.1-1.9, further comprising: receiving, by the core network entity from the UE, a registration request message comprising an indication of whether the UE supports NAS security mode message transaction identification.

[0222] Example 2.1. A method comprising: receiving, by a user equipment (UE), from a core network entity of a core network of a wireless communication system, a non-access stratum (NAS) security mode command (SMC) message comprising information regarding security capabilities of the UE, integrity key information, and a first NAS security mode message transaction identifier (ID); generating, by the UE, based on the first NAS security mode message transaction ID, a second NAS security mode message transaction ID; and transmitting, by the UE, to the core network entity, a NAS security mode complete message comprising the second NAS security mode message transaction ID.

[0223] Example 2.2. The method of claim Example 2.1, wherein the first NAS security mode message transaction ID in the NAS SMC message comprises a NAS ID specific to the transmission of the NAS SMC message.

[0224] Example 2.3. The method of Example 2.2, wherein the generating the second NAS security mode message transaction ID comprises: setting, by the UE, based on the NAS ID in the NAS SMC message, the second NAS security mode message transaction ID.

[0225] Example 2.4. The method of Example 2.1, wherein the first NAS security mode message transaction ID in the NAS SMC message comprises an indication of a number of retransmissions associated with the NAS SMC message.

[0226] Example 2.5. The method of Example 2.1, wherein the generating the second NAS security mode message transaction ID comprises: setting, by the UE, based on the number of retransmissions associated with the NAS SMC message, the second NAS security mode message transaction ID.

[0227] Example 2.6. The method of any one of Examples 2.1-2.5, further comprising:transmitting, by the UE to the core network entity, a registration request message comprising an indication of whether the UE supports NAS security mode message transaction identification.

[0228] Example 3.1. An apparatus comprising: at least one processor; and at least one memory storing instructions which, when executed by the processor, cause the apparatus at least to perform: transmitting, by a core network entity of a core network of a wireless communication system, to a user equipment (UE), a non-access stratum (NAS) security mode command (SMC) message comprising information regarding security capabilities of the UE, information for establishing a security context between the UE and the core network, and a first NAS security mode message transaction identifier (ID); receiving, by the core network entity, from the UE, a NAS security mode complete message comprising a second NAS security mode message transaction ID; and generating, by the core network entity, based on a comparison of the first NAS security mode message transaction ID and the second NAS security mode message transaction ID satisfying a condition, a security key, wherein the security key is usable to protect communications between the UE and an apparatus of an access network of the wireless communication system.

[0229] Example 3.2. The apparatus of Example 3.1, wherein the generating the security key is further based on a match between the second NAS security mode message transaction ID in the NAS security mode complete message and the first NAS security mode message transaction ID in the NAS SMC message.

[0230] Example 3.3. The apparatus of Example 3.1 or Example 3.2, wherein: the first NAS security mode message transaction ID in the NAS SMC message comprises a first NAS ID specific to the transmission of the NAS SMC message, and the second NAS security mode message transaction ID in the NAS security mode complete message comprises a second NAS ID.

[0231] Example 3.4. The apparatus of Example 3.1 or Example 3.2, wherein: the first NAS security mode message transaction ID in the NAS SMC message comprises a first bitmap comprising an indication of a number of retransmissions of the NAS SMC message, andthe second NAS security mode message transaction ID in the NAS security mode complete message comprises a second bitmap.

[0232] Example 3.5. The apparatus of Example 3.1 or Example 3.2, wherein: the first NAS security mode message transaction ID in the NAS SMC message corresponds to a NAS downlink message sequence number, and the second NAS security mode message transaction ID in the NAS security mode complete message corresponds to a NAS uplink message sequence number.

[0233] Example 3.6. The apparatus of any one of Example 3.1-3.4, wherein the transmitting the NAS SMC message is based on a retransmission timer expiration.

[0234] Example 3.7. The apparatus of Example 3.6, further comprising: generating, by the core network entity, based on the retransmission timer expiration, the first NAS security mode message transaction ID.

[0235] Example 3.8. The apparatus of any one of Examples 3.1-3.7, further comprising: receiving, by the core network entity from the UE, another NAS security mode complete message comprising a third NAS security mode message transaction ID; and continuing, by the core network entity, based on a comparison of the first NAS security mode message transaction ID and the third NAS security mode message transaction ID failing to satisfy the condition, to monitor for a NAS security mode complete message without generating a security key.

[0236] Example 3.9. The apparatus of Example 3.8, further comprising: maintaining, by the core network entity, based on a comparison of the first NAS security mode message transaction ID and the third NAS security mode message transaction ID failing to satisfy the condition, a retransmission timer.

[0237] Example 3.10. The apparatus of any one of Examples 3.1-3.9, further comprising: receiving, by the core network entity from the UE, a registration request message comprising an indication of whether the UE supports NAS security mode message transaction identification.

[0238] Example 4.1. A user equipment (UE) comprising: at least one processor; and at least one memory storing instructions which, when executed by the processor, cause the apparatus at least to perform: receiving, by a user equipment (UE), from a core network entity of a core network of a wireless communication system, a non-access stratum (NAS) security mode command (SMC) message comprising information regarding security capabilitiesof the UE, integrity key information, and a first NAS security mode message transaction identifier (ID); generating, by the UE, based on the first NAS security mode message transaction ID, a second NAS security mode message transaction ID; and transmitting, by the UE, to the core network entity, a NAS security mode complete message comprising the second NAS security mode message transaction ID.

[0239] Example 4.2. The UE of Example 4.1 , wherein the first NAS security mode message transaction ID in the NAS SMC message comprises a NAS ID specific to the transmission of the NAS SMC message.

[0240] Example 4.3. The UE of Example 4.2, wherein the generating the second NAS security mode message transaction ID comprises: setting, by the UE, based on the NAS ID in the NAS SMC message, the second NAS security mode message transaction ID.

[0241] Example 4.4. The UE of Example 4.1 , wherein the first NAS security mode message transaction ID in the NAS SMC message comprises an indication of a number of retransmissions associated with the NAS SMC message.

[0242] Example 4.5. The UE of Example 4.1, wherein the generating the second NAS security mode message transaction ID comprises: setting, by the UE, based on the number of retransmissions associated with the NAS SMC message, the second NAS security mode message transaction ID.

[0243] Example 4.6. The UE of any one of Examples 4.1-4.5, further comprising: transmitting, by the UE to the core network entity, a registration request message comprising an indication of whether the UE supports NAS security mode message transaction identification.

[0244] Example 5.1. An apparatus comprising: means for transmitting, by a core network entity of a core network of a wireless communication system, to a user equipment (UE), a non-access stratum (NAS) security mode command (SMC) message comprising information regarding security capabilities of the UE, information for establishing a security context between the UE and the core network, and a first NAS security mode message transaction identifier (ID); means for receiving, by the core network entity, from the UE, a NAS security mode complete message comprising a second NAS security mode message transaction ID; and means for generating, by the core network entity, based on a comparison of the first NAS security mode message transaction ID and the second NAS security mode messagetransaction ID satisfying a condition, a security key, wherein the security key is usable to protect communications between the UE and an apparatus of an access network of the wireless communication system.

[0245] Example 5.2. The apparatus of Example 5.1, wherein the generating the security key is further based on a match between the second NAS security mode message transaction ID in the NAS security mode complete message and the first NAS security mode message transaction ID in the NAS SMC message.

[0246] Example 5.3. The apparatus of Example 5.1 or Example 5.2, wherein: the first NAS security mode message transaction ID in the NAS SMC message comprises a first NAS ID specific to the transmission of the NAS SMC message, and the second NAS security mode message transaction ID in the NAS security mode complete message comprises a second NAS ID.

[0247] Example 5.4. The apparatus of Example 5.1 or Example 5.2, wherein: the first NAS security mode message transaction ID in the NAS SMC message comprises a first bitmap comprising an indication of a number of retransmissions of the NAS SMC message, and the second NAS security mode message transaction ID in the NAS security mode complete message comprises a second bitmap.

[0248] Example 5.5. The apparatus of Example 5.1 or Example 5.2, wherein: the first NAS security mode message transaction ID in the NAS SMC message corresponds to a NAS downlink message sequence number, and the second NAS security mode message transaction ID in the NAS security mode complete message corresponds to a NAS uplink message sequence number.

[0249] Example 5.6. The apparatus of any one of Example 5.1-5.4, wherein the transmitting the NAS SMC message is based on a retransmission timer expiration.

[0250] Example 5.7. The apparatus of Example 5.6, further comprising: means for generating, by the core network entity, based on the retransmission timer expiration, the first NAS security mode message transaction ID.

[0251] Example 5.8. The apparatus of any one of Examples 5.1-5.7, further comprising: means for receiving, by the core network entity from the UE, another NAS security mode complete message comprising a third NAS security mode message transaction ID; and means for continuing, by the core network entity, based on a comparison of the first NAS security mode message transaction ID and the third NAS security mode messagetransaction ID failing to satisfy the condition, to monitor for a NAS security mode complete message without generating a security key.

[0252] Example 5.9. The apparatus of Example 5.8, further comprising: means for maintaining, by the core network entity, based on a comparison of the first NAS security mode message transaction ID and the third NAS security mode message transaction ID failing to satisfy the condition, a retransmission timer.

[0253] Example 5.10. The apparatus of any one of Examples 5.1-5.9, further comprising: means for receiving, by the core network entity from the UE, a registration request message comprising an indication of whether the UE supports NAS security mode message transaction identification.

[0254] Example 6.1. A user equipment (UE) comprising: means for receiving, by a user equipment (UE), from a core network entity of a core network of a wireless communication system, a non-access stratum (NAS) security mode command (SMC) message comprising information regarding security capabilities of the UE, integrity key information, and a first NAS security mode message transaction identifier (ID); means for generating, by the UE, based on the first NAS security mode message transaction ID, a second NAS security mode message transaction ID; and means for transmitting, by the UE, to the core network entity, a NAS security mode complete message comprising the second NAS security mode message transaction ID.

[0255] Example 6.2. The UE of Example 6.1 , wherein the first NAS security mode message transaction ID in the NAS SMC message comprises a NAS ID specific to the transmission of the NAS SMC message.

[0256] Example 6.3. The UE of Example 6.2, wherein the generating the second NAS security mode message transaction ID comprises: means for setting, by the UE, based on the NAS ID in the NAS SMC message, the second NAS security mode message transaction ID.

[0257] Example 6.4. The UE of Example 6.1 , wherein the first NAS security mode message transaction ID in the NAS SMC message comprises an indication of a number of retransmissions associated with the NAS SMC message.

[0258] Example 6.5. The UE of Example 6.1, wherein the generating the second NAS security mode message transaction ID comprises: means for setting, by the UE, based on the number of retransmissions associated with the NAS SMC message, the second NAS security mode message transaction ID.

[0259] Example 6.6. The UE of any one of Examples 6.1-6.5, further comprising:means for transmitting, by the UE to the core network entity, a registration request message comprising an indication of whether the UE supports NAS security mode message transaction identification.

[0260] Example 7. A non-transitory processor-readable medium including program code, which when executed by one or more processors, causes the one or more processors at least to perform the method of any one of Examples 1.1-1.10.

[0261] Example 8. A non-transitory processor-readable medium including program code, which when executed by one or more processors, causes the one or more processors at least to perform the method of any one of Examples 2.1-2.6.

[0262] The embodiments and aspects disclosed herein are examples of the present disclosure and may be embodied in various forms. For instance, although certain embodiments herein are described as separate embodiments, each of the embodiments herein may be combined with one or more of the other embodiments herein. Specific structural and functional details disclosed herein are not to be interpreted as limiting, but as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present disclosure in virtually any appropriately detailed structure. Like reference numerals may refer to similar or identical elements throughout the description of the figures.

[0263] The phrases “in an aspect,” “in aspects,” “in various aspects,” “in some aspects,” or “in other aspects” may each refer to one or more of the same or different aspects in accordance with this present disclosure. The phrase “a plurality of’ may refer to two or more.

[0264] The phrases “in an embodiment,” “in embodiments,” “in various embodiments,” “in some embodiments,” or “in other embodiments” may each refer to one or more of the same or different embodiments in accordance with the present disclosure. A phrase in the form “A or B” means “(A), (B), or (A and B).” A phrase in the form “at least one of A, B, or C” means “(A); (B); (C); (A and B); (A and C); (B and C); or (A, B, and Q.”

[0265] Any of the herein described methods, programs, algorithms or codes may be converted to, or expressed in, a programming language or computer program. The terms “programming language” and “computer program,” as used herein, each include any language used to specify instructions to a computer, and include (but is not limited to) the following languages and their derivatives: Assembler, Basic, Batch files, BCPL, C, C+, C++, Delphi, Fortran, Java, JavaScript, machine code, operating system command languages, Pascal, Perl, PL1, Python, scripting languages, Visual Basic, metalanguages which themselves specify programs, and all first, second, third, fourth, fifth, or further generation computer languages. Also included are database and other data schemas, and any other meta-languages. Nodistinction is made between languages which are interpreted, compiled, or use both compiled and interpreted approaches. No distinction is made between compiled and source versions of a program. Thus, reference to a program, where the programming language could exist in more than one state (such as source, compiled, object, or linked) is a reference to any and all such states. Reference to a program may encompass the actual instructions and / or the intent of those instructions.

[0266] While aspects of the present disclosure have been shown in the drawings, it is not intended that the present disclosure be limited thereto, as it is intended that the present disclosure be as broad in scope as the art will allow and that the specification be read likewise. Therefore, the above description should not be construed as limiting, but merely as exemplifications of particular aspects. Those skilled in the art will envision other modifications within the scope and spirit of the claims appended hereto.

Claims

Claims:

1. A method comprising: transmitting, by a core network entity of a core network of a wireless communication system, to a user equipment (UE), a non-access stratum (NAS) security mode command (SMC) message comprising information regarding security capabilities of the UE, information for establishing a security context between the UE and the core network, and a first NAS security mode message transaction identifier (ID); receiving, by the core network entity, from the UE, a NAS security mode complete message comprising a second NAS security mode message transaction ID; and generating, by the core network entity, based on a comparison of the first NAS security mode message transaction ID and the second NAS security mode message transaction ID satisfying a condition, a security key, wherein the security key is usable to protect communications between the UE and an apparatus of an access network of the wireless communication system.

2. The method of claim 1, wherein the generating the security key is further based on a match between the second NAS security mode message transaction ID in the NAS security mode complete message and the first NAS security mode message transaction ID in the NAS SMC message.

3. The method of claim 1 or claim 2, wherein: the first NAS security mode message transaction ID in the NAS SMC message comprises a first NAS ID specific to the transmission of the NAS SMC message, and the second NAS security mode message transaction ID in the NAS security mode complete message comprises a second NAS ID.

4. The method of claim 1 or claim 2, wherein: the first NAS security mode message transaction ID in the NAS SMC message comprises a first bitmap comprising an indication of a number of retransmissions of the NAS SMC message, and the second NAS security mode message transaction ID in the NAS security mode complete message comprises a second bitmap.

5. The method of claim 1 or claim 2, wherein: the first NAS security mode message transaction ID in the NAS SMC message corresponds to a NAS downlink message sequence number, and the second NAS security mode message transaction ID in the NAS security mode complete message corresponds to a NAS uplink message sequence number.

6. The method of any one of claims 1-4, wherein the transmitting the NAS SMC message is based on a retransmission timer expiration.

7. The method of claim 6, further comprising: generating, by the core network entity, based on the retransmission timer expiration, the first NAS security mode message transaction ID.

8. The method of any one of claims 1-7, further comprising: receiving, by the core network entity from the UE, another NAS security mode complete message comprising a third NAS security mode message transaction ID; and continuing, by the core network entity, based on a comparison of the first NAS security mode message transaction ID and the third NAS security mode message transaction ID failing to satisfy the condition, to monitor for a NAS security mode complete message without generating a security key.

9. The method of claim 8, further comprising: maintaining, by the core network entity, based on a comparison of the first NAS security mode message transaction ID and the third NAS security mode message transaction ID failing to satisfy the condition, a retransmission timer.

10. The method of any one of claims 1-9, further comprising: receiving, by the core network entity from the UE, a registration request message comprising an indication of whether the UE supports NAS security mode message transaction identification.

11. A method comprising:receiving, by a user equipment (UE), from a core network entity of a core network of a wireless communication system, a non-access stratum (NAS) security mode command (SMC) message comprising information regarding security capabilities of the UE, integrity key information, and a first NAS security mode message transaction identifier (ID); generating, by the UE, based on the first NAS security mode message transaction ID, a second NAS security mode message transaction ID; and transmitting, by the UE, to the core network entity, a NAS security mode complete message comprising the second NAS security mode message transaction ID.

12. The method of claim 11, wherein the first NAS security mode message transaction ID in the NAS SMC message comprises a NAS ID specific to the transmission of the NAS SMC message.

13. The method of claim 12, wherein the generating the second NAS security mode message transaction ID comprises: setting, by the UE, based on the NAS ID in the NAS SMC message, the second NAS security mode message transaction ID.

14. The method of claim 11, wherein the first NAS security mode message transaction ID in the NAS SMC message comprises an indication of a number of retransmissions associated with the NAS SMC message.

15. The method of claim 14, wherein the generating the second NAS security mode message transaction ID comprises: setting, by the UE, based on the number of retransmissions associated with the NAS SMC message, the second NAS security mode message transaction ID.

16. The method of any one of claims 11-15, further comprising: transmitting, by the UE to the core network entity, a registration request message comprising an indication of whether the UE supports NAS security mode message transaction identification.

17. An apparatus comprising: at least one processor; andat least one memory storing instructions which, when executed by the processor, cause the apparatus at least to perform the method of any one of claims 1-10.

18. A user equipment (UE) comprising: at least one processor; and at least one memory storing instructions which, when executed by the processor, cause the UE at least to perform the method of any one of claims 11-16.

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