OrganizedProgrammers/3GPPSpecContent · Datasets at Hugging Face

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8ead7ee022fb2d871885d14e20dd07e7	33.714	4.4 Key Issue #4: AIOT device ID protection in DO-A procedure
8ead7ee022fb2d871885d14e20dd07e7	33.714	4.4.1 Key issue details	For AIoT device type 1, all communications between the network and the AIOT device are initiated by the network. Unlike AIOT device type 1, the DO-A AIOT device autonomously initiates communication by sending a message to the network. Due to this change, privacy mechanisms specified in TS 33.369[8] for AIOT device type 1 may not be feasible for DO-A AIOT devices. Therefore, mechanisms for privacy of device ID of DO-A AIOT device contained in the message(s) exchanged between the device and the network should be studied.
8ead7ee022fb2d871885d14e20dd07e7	33.714	4.4.2 Threats	An attacker can identify, monitor and track a DO-A AIoT devices based on the identifiers associated with the AIoT device if the identifiers are not privacy protected.
8ead7ee022fb2d871885d14e20dd07e7	33.714	4.4.3 Potential security requirements	The 5G system shall support mechanisms to prevent privacy threats (e.g., identifying, linking, and tracking) against the identifier of the DO-A capable AIOT device(s).
8ead7ee022fb2d871885d14e20dd07e7	33.714	4.5 Key Issue #5: Amplification of resource exhaustion by exploiting AIoT paging messages
8ead7ee022fb2d871885d14e20dd07e7	33.714	4.5.1 Key issue details	Paging of AIoT devices is different than "regular" paging of regular UEs. In AIOT, one single paging message coming from the reader/network can be used to trigger multiple devices to respond by using, for example, a mask/filter based on target device identification, or by a group ID of the target devices. Once the target devices are triggered, the reader, core network of the PLMN, and the associated AF participate in various steps to accomplish the intended tasks, e.g., inventory reporting and command executing. Unlike regular paging, AIOT paging can happen for devices that are not necessarily already registered in the core network and hence cannot share a session security context with the network. The paging message can include information that the devices and core network of the PLMN can use in successful accomplishment of these tasks in those steps. Therefore, if parts of or the whole paging message is corrupted, the core network of the PLMN and the AF can end up wasting computational resources that leads to no successful accomplishment of the intended tasks. Moreover, the corrupted paging message results in waste of radio resources being used by AIOT over the air interface as well. The above can be used by an adversary that intentionally corrupt the paging message in a way so that many legitimate AIOT devices are triggered by the corrupted paging message, but later, in the core network of the PLMN or in the AF, the responses from the AIOT devices are found invalid. This happens not because the devices computed wrong responses, but because the devices used corrupted paging message in computing their responses. Such an attack can cause the PLMN and the AF wasting computational resources. It also causes the AIOT reader wasting radio resources that can adversely impact the regular UEs in the same network. If devices respond to a corrupted paging message, that should be identified as early as possible, and the responses should not be forwarded any further to the core network or to the AF.
8ead7ee022fb2d871885d14e20dd07e7	33.714	4.5.2 Security threats	An adversary can cause the core network of a PLMN or the AF wasting computational resources by corrupting or spoofing one single paging message, which is surprisingly little work on the adversary’s behalf, that triggers a lot of devices to send a paging response to the legitimate reader. The above attack can also cause the AIOT reader and serving NG-RAN node wasting radio resources that can adversely impact the regular UEs in the same network.
8ead7ee022fb2d871885d14e20dd07e7	33.714	4.5.3 Potential security requirements	Editor’s Note: Potential security requirements are FFS
8ead7ee022fb2d871885d14e20dd07e7	33.714	5 Solutions	Editor’s Note: This clause contains the proposed solutions addressing the identified key issues.
8ead7ee022fb2d871885d14e20dd07e7	33.714	5.1 Mapping of solutions to key issues	Editor’s Note: This clause captures mapping between key issues and solutions. Table 5.1-1: Mapping of solutions to key issues Key Issues Solutions 5.Y Solution #Y: <Solution Name> 5.Y.1 Introduction Editor’s Note: Each solution should list the key issues being addressed. 5.Y.2 Solution details 5.Y.3 Evaluation Editor’s Note: Each solution should motivate how the potential security requirements of the key issues being addressed are fulfilled.
8ead7ee022fb2d871885d14e20dd07e7	33.714	6 Conclusions	Editor’s Note: This clause captures the conclusions of this study. Annex <X>: Change history Change history Date Meeting TDoc CR Rev Cat Subject/Comment New version 10/2025 SA3#124 S3‑253300 Initial draft TR 0.0.1 10/2025 SA3#124 S3‑253732 Incorporated accepted contributions S3‑253822, S3‑253823, S3-253824, S3-253825, S3-253826, S3-253827 0.1.0
d3bf28ab4332aa8f28073a11d4387c3d	33.724	1 Scope	The present document studies the security architecture and security requirements for WAB-nodes, security impacts of potentially compromised WAB nodes and requirements for countermeasures against any compromised WAB nodes.
d3bf28ab4332aa8f28073a11d4387c3d	33.724	2 References	The following documents contain provisions which, through reference in this text, constitute provisions of the present document. - References are either specific (identified by date of publication, edition number, version number, etc.) or non‑specific. - For a specific reference, subsequent revisions do not apply. - For a non-specific reference, the latest version applies. In the case of a reference to a 3GPP document (including a GSM document), a non-specific reference implicitly refers to the latest version of that document in the same Release as the present document. [1] 3GPP TR 21.905: "Vocabulary for 3GPP Specifications". [2] 3GPP TS 23.501: "System architecture for the 5G System (5GS)". [3] 3GPP TS 38.401: "NG-RAN Architecture description". [4] 3GPP TS 33.501: "Security architecture and procedures for 5G System". [5] 3GPP TR 33.745: "Study on security aspects of 5G Next Radio (NR) Femto". [6] 3GPP TS 33.320: "Security of Home Node B (HNB) / Home evolved Node B (HeNB)".
d3bf28ab4332aa8f28073a11d4387c3d	33.724	3 Definitions of terms, symbols and abbreviations
d3bf28ab4332aa8f28073a11d4387c3d	33.724	3.1 Terms	For the purposes of the present document, the terms given in 3GPP TR 21.905 [1] and the following apply. A term defined in the present document takes precedence over the definition of the same term, if any, in 3GPP TR 21.905 [1]. example: text used to clarify abstract rules by applying them literally.
d3bf28ab4332aa8f28073a11d4387c3d	33.724	3.2 Symbols	For the purposes of the present document, the following symbols apply: <symbol> <Explanation>
d3bf28ab4332aa8f28073a11d4387c3d	33.724	3.3 Abbreviations	For the purposes of the present document, the abbreviations given in 3GPP TR 21.905 [1] and the following apply. An abbreviation defined in the present document takes precedence over the definition of the same abbreviation, if any, in 3GPP TR 21.905 [1]. <ABBREVIATION> <Expansion>
d3bf28ab4332aa8f28073a11d4387c3d	33.724	4 Security Architecture and Assumptions	Editor’s Note: This clause contains security architecture and assumptions to be considered for the study (e.g., per work task/KI). Figure 5.49.1.1-1 in TS 23.501[2] shows the MWAB architecture for 5GS. In the architecture. There are two components in MWAB, i.e. MWAB-gNB and MWAB-UE. The WAB-node integration procedure is captured in TS 38.401[3]. From a security point of view, the MWAB architecture rely on the 5G security framework for key management and authorization as captured in TS 33.501 [4].
d3bf28ab4332aa8f28073a11d4387c3d	33.724	5 Key issues	Editor’s Note: This clause contains all the key issues identified during the study.
d3bf28ab4332aa8f28073a11d4387c3d	33.724	5.1 Key Issue #1: Security of the link between WAB-gNB and OAM
d3bf28ab4332aa8f28073a11d4387c3d	33.724	5.1.1 Key issue details	Based on the WAB-node integration procedure, the WAB-gNB will receive the OAM of WAB through the WAB-MT’s network. The link between WAB-gNB and OAM needs to have sufficient security protection for configuration data transmission.
d3bf28ab4332aa8f28073a11d4387c3d	33.724	5.1.2 Security threats	If the link between WAG-gNB and OAM is not well protected, the configuration data will be tampered or disclosure.
d3bf28ab4332aa8f28073a11d4387c3d	33.724	5.1.1 Potential security requirements	The link between the MWAB-gNB and the OAM shall be ciphering and integrity protected.
d3bf28ab4332aa8f28073a11d4387c3d	33.724	5.2 Key Issue #2: Security Protection of Compromised WAB Nodes and Core Network Measures
d3bf28ab4332aa8f28073a11d4387c3d	33.724	5.2.1 Key issue details	Wireless Access Backhaul (WAB) nodes, consist of a WAB-gNB (gNB-like functionality) and a WAB-MT (UE-like functionality). These nodes operate in non-trusted environments and may serve as moving backhaul nodes for the 5GS, establishing NG, Xn, and OAM interfaces over PDU sessions through 3GPP backhauls. While 3GPP TR 33.745 [5] studied NR Femto security and reused procedures from TS 33.320 [6], security concerns specific to WAB nodes particularly compromised WAB nodes in untrusted environments remain unaddressed. Additionally, core network components may not be equipped to detect anomalous behavior from compromised WAB-gNBs, due to the decentralized and mobile nature of such nodes. The compromised WAB nodes could lead to topology poisoning, signalling storms, or user-plane hijacking. This key issue aims to address the security issues introduced by compromised WAB nodes, where failure to protect the integrity, authenticity, and confidentiality of messages delivered from WAB-gNB and WAB-MT components can expose the 5GS to topology spoofing, rogue signalling, and persistent infiltration.
d3bf28ab4332aa8f28073a11d4387c3d	33.724	5.2.2 Security threats	Potential security threat: • Rogue WAB-gNB Injection: A compromised WAB node may inject unauthorized signalling or reroute traffic maliciously, particularly via spoofed message. Furthermore, a compromised WAB-gNB can attempt to broadcast unauthorized network identifiers or initiate rogue Xn association attempts with neighbouring gNBs causing service disruption. • Topology Manipulation and Signalling Abuse: Moving WAB nodes may falsely report neighbour relationships via Xn or behave inconsistently across locations, leading to incorrect handover decisions, topology poisoning, or signalling loops. • Persistent Threat via Dual Roles: Since WAB-MT behaves like a UE and WAB-gNB like a gNB, a compromised WAB can act in both roles to stage cross-layer attacks, bridging between RAN and CN trust domains.
d3bf28ab4332aa8f28073a11d4387c3d	33.724	5.2.3 Potential security requirements	The 3GPP system shall support security mechanisms to mitigate risks from compromised WAB nodes, preventing topology spoofing, rogue signalling, and mobility-related traceability threats.
d3bf28ab4332aa8f28073a11d4387c3d	33.724	5.3 Key Issue #3: new key issue on enabling NDS/IP for WAB case
d3bf28ab4332aa8f28073a11d4387c3d	33.724	5.3.1 Key issue details	According to the architecture in 23.501[2],the MWAB-gNB establishes the N2 interface with UE’s 5GC, and setup a Xn link with a traditional gNB. Figure 5.3-1: Architecture for MWAB operation support - non-roaming with one PLMN A MWAB may be mounted on a moving vehicle and may serve UEs inside or outside the vehicle. A MWAB cannot provide a connection service to a UE unless it establishes the N2 and Xn connections with UE’s AMF and UE’ NG-RAN. Since the NDS/IP is used for Xn and N2 connection as defined in TS 33.501[4], a credential must be provided in MWAB case in order to build the connection with UE’s network. One existing method is the preconfigure the potential serving UE’s credentials to the MWAB before it starts to connecting to the network. However, this relies on a well and unchanged plan on the MWAB. Since it is very difficult to know where the MWAB will go, it is very difficult to a MWAB vendor to configure everything in advance.
d3bf28ab4332aa8f28073a11d4387c3d	33.724	5.3.2 Security threats	N/A
d3bf28ab4332aa8f28073a11d4387c3d	33.724	5.3.3 Potential security requirements	Credentials for NDS/IP for Xn and N2 connection between WAB and UE’s network shall be provided with confidential protection and integrity protection.
d3bf28ab4332aa8f28073a11d4387c3d	33.724	5.4 Key Issue #4: Protection and binding of MWAB-gNB control plane over BH-PDU sessions
d3bf28ab4332aa8f28073a11d4387c3d	33.724	5.4.1 Key issue details	In MWAB, OAM, N2, Xn and N3 traffic for the MWAB-gNB is carried over backhaul PDU session(s) that the MWAB-UE establishes and modifies based on traffic descriptors and OAM configuration. The MWAB broadcasted PLMN/SNPN may differ from the BH PLMN/SNPN which creates inter-PLMN/SNPN trust boundaries for these control plane and OAM links.
d3bf28ab4332aa8f28073a11d4387c3d	33.724	5.4.2 Security threats	Interception or modification of OAM/N2/Xn control traffic over BH PDU session(s); misclassification of traffic due to descriptor or mapping error; cross-slice leakage; replay during mobility or BH PDU session changes are possible.
d3bf28ab4332aa8f28073a11d4387c3d	33.724	5.4.3 Potential security requirements	Confidentiality and integrity protection for OAM/N2/Xn control traffic over BH PDU session(s), binding MWAB-gNB identity and traffic classes to BH PDU sessions. 5.X Key Issue #X: <Key Issue Name> 5.X.1 Key issue details 5.X.2 Security threats 5.X.3 Potential security requirements
d3bf28ab4332aa8f28073a11d4387c3d	33.724	6 Solutions	Editor’s Note: This clause contains the proposed solutions addressing the identified key issues.
d3bf28ab4332aa8f28073a11d4387c3d	33.724	6.0 Mapping of solutions to key issues	Editor's Note: This clause contains a table mapping between key issues and solutions. Table 6.0-1: Mapping of solutions to key issues Solutions KI#1 KI#2 KI#3 KI#4 #1 X
d3bf28ab4332aa8f28073a11d4387c3d	33.724	6.1 Solution #1: reusing NDS/IP to N2 and Xn interfaces in WAB
d3bf28ab4332aa8f28073a11d4387c3d	33.724	6.1.1 Introduction	This solution proposes a the credential is provided to the WAB by OAM in the phase 2-1 of the WAB-node integration procedure defined in TS 38.401 [3]
d3bf28ab4332aa8f28073a11d4387c3d	33.724	6.1.2 Solution details	Figure 6.1.2-1 Procedure to configure the credential for NDS/IP connection 0. The WAB-node is pre-configured a credential for accessing to the OAM of WAB Phase 1. WAB-MT Setup. It is described in TS 38.401[3]. Phase 2-1. WAB-gNB initialization. Addition to the description in TS 38.401[3], the WAB-gNB uses the pre-configured credential accessing to the OAM of WAB for authentication and security establishment. Then, the OAM of WAB sends the configuration data to the WAB-gNB in the secure link. The configuration data includes the credentials used for establishing Xn and N2 connections for UE. If the WAB servers UEs from different PLMN, the credentials may further bind with PLMN ID information. Phase 2-2. WAB-gNB NG connection setup. Addition to the description in TS 38.401[3], the WAB-gNB uses the credential sent in Phase 2-1 to establish NDS/IP with the potential serving UE’s 5GC. If the WAB-gNB servers more than one PLMN, the WAB-gNB will use the corresponding credentials to establish NDS/IP with each UE’s PLMN’s 5GC. Phase 2-3. WAB-gNB Xn connection setup. Addition to the description in TS 38.401[3], the WAB-gNB uses uses the credential sent in Phase 2-1 to establish NDS/IP with the potential serving UE’s NG-RAN. If the WAB-gNB servers more than one PLMN, the WAB-gNB will use the corresponding credentials to establish NDS/IP with each UE’s PLMN’s NG RAN.
d3bf28ab4332aa8f28073a11d4387c3d	33.724	6.1.3 Evaluation	The solution addresses the situation when the credential of UE’s 5GC or NG-RAN cannot be pre-configured at WAB. The phase 2-1 can be used to configure the credentials of potential serving UEs’ PLMN. 6.Y Solution #Y: <Solution Name> 6.Y.1 Introduction Editor’s Note: Each solution should list the key issues being addressed. 6.Y.2 Solution details 6.Y.3 Evaluation Editor’s Note: Each solution should motivate how the potential security requirements of the key issues being addressed are fulfilled.
d3bf28ab4332aa8f28073a11d4387c3d	33.724	7 Conclusions	Editor’s Note: This clause contains the agreed conclusions that will form the basis for any normative work. Annex <C>: Change History Change history Date Meeting TDoc CR Rev Cat Subject/Comment New version 2025-08 SA3#123 S3-252987 S3-252684 and S3-252686 for endorsed TR Skeleton for WAB Security 0.0.0 2025-10 SA3#124 S3-253741 Included changed from S3-253411, S3-253412, S3-253464, S3-253626, S3-253820 and S3-253821 0.1.0
e97791a0165eb026afd870f9d0c81a3a	33.700-30	1 Scope	The present document …
e97791a0165eb026afd870f9d0c81a3a	33.700-30	2 References	The following documents contain provisions which, through reference in this text, constitute provisions of the present document. - References are either specific (identified by date of publication, edition number, version number, etc.) or non‑specific. - For a specific reference, subsequent revisions do not apply. - For a non-specific reference, the latest version applies. In the case of a reference to a 3GPP document (including a GSM document), a non-specific reference implicitly refers to the latest version of that document in the same Release as the present document. [1] 3GPP TR 21.905: "Vocabulary for 3GPP Specifications". [2] 3GPP TS 23.401: "General Packet Radio Service (GPRS) enhancements for Evolved Universal Terrestrial Radio Access Network (E-UTRAN) access". [3] 3GPP TS 33.401: "3GPP System Architecture Evolution: Security Architecture". [4] 3GPP TS 24.301: " Non-Access-Stratum (NAS) protocol for Evolved Packet System (EPS); Stage 3".
e97791a0165eb026afd870f9d0c81a3a	33.700-30	3 Definitions of terms and abbreviations
e97791a0165eb026afd870f9d0c81a3a	33.700-30	3.1 Terms	For the purposes of the present document, the terms given in 3GPP TR 21.905 [1] and the following apply. A term defined in the present document takes precedence over the definition of the same term, if any, in 3GPP TR 21.905 [1]. example: text used to clarify abstract rules by applying them literally.
e97791a0165eb026afd870f9d0c81a3a	33.700-30	3.2 Abbreviations	For the purposes of the present document, the abbreviations given in 3GPP TR 21.905 [1] and the following apply. An abbreviation defined in the present document takes precedence over the definition of the same abbreviation, if any, in 3GPP TR 21.905 [1]. <ABBREVIATION> <Expansion>
e97791a0165eb026afd870f9d0c81a3a	33.700-30	4 Architecture assumptions	The following architecture assumptions are applied to the study: - The general features and the Split MME architecture of Store and Forward Satellite operation are described in Annex O.2 of TS 23.401 [2] are used as architecture assumptions in this study.
e97791a0165eb026afd870f9d0c81a3a	33.700-30	5 Key issues	Editor’s Note: This clause contains all the key issues identified during the study.
e97791a0165eb026afd870f9d0c81a3a	33.700-30	5.1 Key Issue #1: Authenticated UE to exchange NAS messages with multiple satellites in split-MME architecture
e97791a0165eb026afd870f9d0c81a3a	33.700-30	5.1.1 Key issue details	One of the architectural assumptions for Store and Forward Satellite operation is that when the service link is available, there is no feeder link and inter satellite link. There are two example deployment options for Store and Forward Satellite operation given in Annex O of TS 23.401 [2], i.e. Split MME architecture and Full EPC in each satellite. For the split-MME architecture, S&F Satellite operation may involve multiple satellites allocated by an S&F Monitoring List. In this scenario, the UE context needs to be synchronized between the multiple MME-onboard(s) and the associated MME-ground. The synchronization of UE context between the MME-ground and MME-onboard(s) is out of the scope of 3GPP. According to Annex N of TS 33.401 [3], regular LTE procedures are used to provide security between UE and network for the split-MME architecture. This means that once the UE completes an interaction with a satellite, the UE context in the satellite must be synchronized to other satellites before these satellites can perform any subsequent S&F Satellite operations with the UE. This significantly reduces the data exchange efficiency of the entire system. Ideally, for an IoT device, once it is registered in the network and its UE context has been distributed to the satellites included in the S&F Monitoring List, the UE can exchange data with these satellites without the need for UE context synchronization between the satellites. This key issue focuses on solutions that meet the following conditions: - The UE context of the UE registered in the network has been provided to the satellites included in the S&F Monitoring List; - The UE can perform Mobile Originated (MO) or Mobile Terminated (MT) data transmission with the satellites that have the UE context; - The UE context does not need to be synchronized across the multiple satellites for supporting the MO/MT data transmissions. However, UE context synchronization may still be required for other changes not being associated with the MO/MT data transmission.
e97791a0165eb026afd870f9d0c81a3a	33.700-30	5.1.2 Security threats	If the NAS COUNTs are not synchronized across multiple satellites, an attacker may intercept and replay previously transmitted NAS messages. Since different satellites may accept outdated NAS COUNT values, the replay protection mechanism could be bypassed, leading to unauthorized actions. Key stream may be reused if the security contexts are not well-managed across multiple satellites.
e97791a0165eb026afd870f9d0c81a3a	33.700-30	5.1.3 Potential security requirements	The 3GPP system shall support means to secure NAS messages exchange in the store and forward satellite operations. 5.X Key Issue #X: <Key Issue Name> 5.X.1 Key issue details 5.X.2 Security threats 5.X.3 Potential security requirements
e97791a0165eb026afd870f9d0c81a3a	33.700-30	6 Solutions	Editor’s Note: This clause contains the proposed solutions addressing the identified key issues.
e97791a0165eb026afd870f9d0c81a3a	33.700-30	6.0 Mapping of Solutions to Key Issues	Table 6.0-1: Mapping of Solutions to Key Issues Key Issues Solutions 1 1 X 2 X 3 X 4 X 5 X 6 X 7 X 8 X
e97791a0165eb026afd870f9d0c81a3a	33.700-30	6.1 Solution #1: Derivation of Satellite-Specific NAS keys for S&F Operation
e97791a0165eb026afd870f9d0c81a3a	33.700-30	6.1.1 Introduction	This solution addresses Key Issue #1: Authenticated UE to exchange NAS messages with multiple satellites in split-MME architecture. This solution proposes a mechanism to derive unique NAS integrity and encryption keys for each satellite by using the satellite ID as an additional input parameter during the NAS key derivation.
e97791a0165eb026afd870f9d0c81a3a	33.700-30	6.1.2 Solution details	In this solution, it is proposed to derive distinct set of NAS keys for each satellite from the common root key KASME. The satellite-specific NAS keys are derived by the UE and the network using the KDF as specified in TS 33.220 [x]. For a serving Satellite n, the NAS integrity key KNASint and the NAS encryption key KNASenc are derived from the KASME with the following parameters as input: - FC = 0xxx - P0 = algorithm type distinguisher - L0 = length of algorithm type distinguisher (i.e. 0x00 0x01) - P1 = algorithm identity - L1 = length of algorithm identity (i.e. 0x00 0x01) - P2 = Satellite ID n. - L2: length of Satellite ID n. Where Satellite ID is an identifier uniquely indicating an MME-onboard. The Satellite ID of a given satellite is broadcast by the eNB within the SIB31 and the Satellite ID of the satellites that might be serving a given UE are included within the S&F Monitoring List, which is sent by the MME to indicate the satellite(s) that the UE may (re)-attempt NAS procedures (TS 23.401 clause 4.13.9.1). As a result of using satellite-specific keys, the UE and each MME-onboard maintain independent pairs of NAS COUNT for their mutual communication. The NAS COUNTs are not synchronized with other satellites. Editor’s Note: When the NAS keys are generated in UE and MME-onboard is FFS. Editor’s Note: How to deal with the warp around case is FFS. Editor’s Note: How the MME-ground manages and reconciles the multiple UE security context of the same UE for multiple satellites is FFS. Editor’s Note: How to indicate to the UE whether the solution of the separate NAS keys is implemented or not is FFS.
e97791a0165eb026afd870f9d0c81a3a	33.700-30	6.1.3 Evaluation	TBD Editor’s Note:The impact for key generation on MME-onboard is FFS.
e97791a0165eb026afd870f9d0c81a3a	33.700-30	6.2 Solution #2: NAS Security Context Isolation via Satellite-Specific NAS COUNT
e97791a0165eb026afd870f9d0c81a3a	33.700-30	6.2.1 Introduction	This solution addresses Key Issue #1: Authenticated UE to exchange NAS messages with multiple satellites in split-MME architecture. This solution proposes a mechanism ensuing different satellite using different COUNT to protect NAS message and therefore eliminates the need for real-time NAS COUNT synchronization across satellites.
e97791a0165eb026afd870f9d0c81a3a	33.700-30	6.2.2 Solution details	This solution is based on the following assumptions and principles: - the UE and each MME-onboard maintain independent pairs of NAS COUNTs (one for uplink, one for downlink) for their mutual communication. The NAS COUNTs are not synchronized with other satellites. Based on the above principle, the existing procedures are reused to protect the NAS message between the UE and the network. The NAS integrity and confidentiality protection algorithms are same as defined in TS 33.401 [x], with the following modification to the construction of the 32-bit COUNT input parameter: For a serving Satellite n: COUNT := Satellite ID n \|\| NAS OVERFLOW \|\| NAS SQN Where - Satellite ID n is the 8-bit ID of Satellite n which is an identifier uniquely indicating an MME-onboard coded as a binary coded integer value from 0 to 255 as specified in 3GPP TS 24.301 [x]. The SatelliteID identifier of a given satellite is broadcast by the eNB within the SIB31 and the SatelliteID identifiers of the satellites that might be serving a given UE are included within the S&F Monitoring List, which is sent by the MME to indicate the satellite(s) that the UE may (re)-attempt NAS procedures (TS 23.401 clause 4.13.9.1) - NAS OVERFLOW is a 16-bit value which is incremented each time the NAS SQN is incremented from the maximum value. It is maintained for the connection with Satellite n. - NAS SQN is the 8-bit sequence number carried within each NAS message between UE and MME-onboard n. It is maintained for the connection with Satellite n. All other input parameters (KEY=KNASint/KNASenc, BEARER, DIRECTION, LENGTH) and the algorithm execution remain unchanged. Editor’s Note: How to deal with the warp around case is FFS. Editor’s Note: How the MME-ground manages and reconciles the multiple UE security context of the same UE for multiple satellites is FFS. Editor’s Note: How to indicate to the UE whether the solution of the separate NAS counters is implemented or not is FFS.
e97791a0165eb026afd870f9d0c81a3a	33.700-30	6.2.3 Evaluation	TBD
e97791a0165eb026afd870f9d0c81a3a	33.700-30	6.3 Solution #3: UE context management for S&F operation
e97791a0165eb026afd870f9d0c81a3a	33.700-30	6.3.1 Introduction	This solution addresses Key Issue #1: Authenticated UE to exchange NAS messages with multiple satellites in split-MME architecture. After the UE is authenticated and NAS security is established, the satellite will send a security token to the UE, which contains the UE's current context. When the UE attempts to connect to another satellite, it will provide the security token to that satellite. The satellite will use the content in the security token to reconstruct the UE context and communicate directly with the UE through secure NAS messages.
e97791a0165eb026afd870f9d0c81a3a	33.700-30	6.3.2 Solution details	UE context management procedure for S&F operation is shown in the following figure. Figure 6.3.2-1: UE context management procedure for S&F operation 0. The security key materials used to provide confidentiality and integrity protection for security tokens used in S&F operations are pre-configured in the satellites. The security tokens are used to transfer UE contexts from one satellite to another satellite. 1. The MME-ground provides UE authentication vectors to the MME-onboards when the feeder link is available. 2. The UE and satellite perform the authentication procedure when the service link is available. 3. The UE and satellite execute the Security Mode Command (SMC) procedure after the authentication procedure. 4. The UE and satellite exchange downlink/uplink data through secure NAS messages. 5. The satellite generates a security token based on the current context of the UE, which is protected by confidentiality and integrity using the security materials received in step 0. NOTE: The detailed information of the security token structure and protection mechanism will be specified during the normative phase. 6. The satellite sends the security token to the UE and ends the connection with the UE. The satellite does not need to store the UE context after ending the connection with the UE. The UE stores the received security token. 7. When the UE connects to another satellite, it sends an attach request to the satellite, which includes the security token. Editor’s Note: The message containing the security token is FFS. 8. The satellite decrypts and verifies the security token using the security materials received in step 0. If the verification is successful, the satellite will attempt to exchange downlink/uplink data directly through secure NAS messages. Editor’s Note: How to address the token replay attack is FFS. 9. The satellite performs the same operation as step 5 10. The satellite and UE performs the same operations as step 6. 11. The MME-onboards and MME-ground exchange downlink/uplink data when the feeder link is available. Editor’s Note: Checking the relation of the solution with NAS_COUNT misuse and related replay attacks is FFS.
e97791a0165eb026afd870f9d0c81a3a	33.700-30	6.3.3 Evaluation
e97791a0165eb026afd870f9d0c81a3a	33.700-30	6.4 Solution #4: Separate NAS COUNT pair per SatelliteID within an EPS Security Context
e97791a0165eb026afd870f9d0c81a3a	33.700-30	6.4.1 Introduction	This solution addresses Key Issue #1. This solution is based on using separate pairs of NAS counters per Satellite ID in the EPS security context when the UE is served by multiple satellites operating in S&F mode and the UE registration remains valid even the serving satellite changes over time (i.e., the UE is not required to attach/detach in each satellite pass). The list of SatelliteID(s) in which the registration is valid is provided to the UE using the S&F Monitoring List.
e97791a0165eb026afd870f9d0c81a3a	33.700-30	6.4.2 Solution details	This solution applies to a satellite network operating in S&F mode and, it’s especially relevant for deployments based on the split MME architecture (see TS 23.402 Annex O.2) in which a UE registration remains valid across multiple satellites (unlike a full EPC deployment, where registration is only valid in one satellite). The solution consists of enabling an option for the UE to use separate pairs of NAS counters (i.e. UL_NAS_Count and DL_NAS_Count) per SatelliteID within its EPS security context, where: • SatelliteID is an identifier uniquely indicating an MME-onboard. The SatelliteID identifier of a given satellite is broadcast by the eNB within the SIB31 and the SatelliteID identifiers of the satellites that might be serving a given UE are included within the S&F Monitoring List, which is sent by the MME to indicate the satellite(s) that the UE may (re)-attempt NAS procedures (TS 23.401 clause 4.13.9.1) • UL_NAS_Count is the uplink NAS counter related to the uplink NAS messages sent to the MME-onboard associated with SatelliteID. • DL_NAS_Count is the downlink NAS counter related to the downlink NAS messages received from the MME-onboard associated with SatelliteID. On the network side, this solution allows each MME-onboard to independently maintain its own pair of NAS counters, which shall no longer to be synchronised across the subset of the MME-onboard instances (identified each by a SatelliteID) that belong to the same logical MME in charge of the registered UE. This is depicted in Figure 6.Y.2-1, which is based on Figure O.2-1: "Split-MME" architecture for supporting Store and Forward Satellite operation for SMS and CP CIoT services” in Annex O.2 in TS 23.401. Figure 6.4.2-1: Illustration of the solution consisting on using separate NAS COUNT pairs per SatelliteID Given Rel-19 UEs will still assume that NAS counters are synchronised across the satellites of the S&F Monitoring List, the proposed solution should be introduced as an optional capability. Therefore, UE is expected to indicate to the network that UE supports separate NAS counters per SatelliteID and the network (NW) should be able to indicate the UE whether this option is activated (i.e. the UE should use separate NAS counters per SatelliteID) or deactivated (i.e. the UE shall assume NAS counters are kept synchronised). Finally, another element to consider in this solution is the use of the “SatelliteID” value as part of the NAS COUNT 32-bit value. For example, the padding bits of the NAS Count can be filled with the SatelliteID, as illustrated in Figure 2. In this way, a NAS message used between the UE and a given satellite cannot be replayed with another satellite. Figure 6.4.2-2: Filling NAS COUNT padding bits with SatelliteID Editor’s Note: FFS whether the solution should also consider the use of the “SatelliteID” value as part of the NAS COUNT 32-bit value so that NAS count values are never reused. Editor’s Note: How to address the wrap-around issue of independent COUNTs is FFS. Editor’s Note: How to activate the security context between the SAT (e.g. SAT#2, SAT#n) and UE is FFS. Editor’s Note: FFS whether the capability to indicate the UE should use separate NAS counters per SatelliteID is optional or mandatory
e97791a0165eb026afd870f9d0c81a3a	33.700-30	6.4.3 Evaluation	Editor’s Note: Each solution should motivate how the potential security requirements of the key issues being addressed are fulfilled.
e97791a0165eb026afd870f9d0c81a3a	33.700-30	6.5 Solution #5: Protection for DL NAS message of authenticated UE in split-MME architecture
e97791a0165eb026afd870f9d0c81a3a	33.700-30	6.5.1 Introduction	This solution is proposed to address Key Issue #1, providing a protection method for exchanging the NAS message in the Store and Forward satellite operations. As specified in TS 33.401 [3], the NAS security is terminated on the MME-onboard, and the ground segment of the network ensures that the latest NAS security context of the UE is available at the MME-onboard. When multiple satellites are involved in the Store and Forward satellite operation, the NAS COUNTs should be synchronized to mitigate the replay attack. This solution proposes that NAS COUNTs are maintained and managed by the UE and MME-ground. When a DL NAS message of authenticated UE is received, the MME-ground is responsible for selecting the MME on-board based on the coverage availability information. In other words, the MME-ground selects the MME on-board that will be available to the UE earliest. For the selected MME on-board, the MME-ground provides the value of DL NAS COUNT together with the DL NAS signaling. Since the selection is based on the coverage availability information, the MME on-board(s) will be available for UE in sequence and the value of DL NAS COUNT will be received in order, which mitigates the replay attack in the Store and Forward satellite operations.
e97791a0165eb026afd870f9d0c81a3a	33.700-30	6.5.2 Solution details	Figure 6.5.2-1: Protection for DL NAS messages of authenticated UE 0. The UE and MME-ground hold the latest NAS COUNTs, including the UL NAS COUNT and DL NAS COUNT. At Time 1: 1. The MME-ground receives the DL NAS signaling #1 of the authenticated UE from another EPS NF. 2. Based on the coverage availability information, the MME-ground selects one of the MME on-board(s) (e.g. MME on-board the SAT1) to transmit the DL NAS signaling #1. 3. The MME-ground sends the DL NAS signaling #1 together with the latest value of DL NAS COUNT (e.g. DL NAS COUNT #1), and increases the DL NAS COUNT by one. If the service link is not available, the MME on-board the SAT1 stores the DL NAS COUNT #1 together with the DL NAS signaling #1. At Time 2: 4. The MME-ground receives the DL NAS signaling #2 of the authenticated UE from another EPS NF. 5. Based on the coverage availability information, the MME-ground selects one of the MME on-board(s) (e.g. MME on-board the SAT2) to transmit the DL NAS signaling #1. 6. The MME-ground sends the DL NAS signaling #2 together with the latest value of DL NAS COUNT (e.g. DL NAS COUNT #2), and increases the DL NAS COUNT by one. If the service link is not available, the MME on-board the SAT2 stores the DL NAS COUNT #2 together with the DL NAS signaling #2. At Time 3 and Time 4, the UE can receive the protected DL NAS message in sequence. 7. Once the service link becomes available (Time 3), the MME on-board the SAT1 generates the integrity-protected and confidentiality-protected NAS signaling #1 and sends it to the UE. NOTE 1: Time 3 may happen before Time 2. In this case, Step #7 is performed before Steps #4-6. 8. Once the service link becomes available (Time 4), the MME on-board the SAT2 generates the integrity-protected and confidentiality-protected NAS signaling #2 and sends it to the UE. Editor’s Note: The NAS count synchronization when the UE receives messages from multiple MME-onboards is FFS. Editor’s Note: How to protect UL NAS messages is FFS.
e97791a0165eb026afd870f9d0c81a3a	33.700-30	6.5.3 Evaluation	Editor’s Note: Each solution should motivate how the potential security requirements of the key issues being addressed are fulfilled.
e97791a0165eb026afd870f9d0c81a3a	33.700-30	6.6 Solution #6: Secure NAS messages via using different NAS keys in multiple satellites
e97791a0165eb026afd870f9d0c81a3a	33.700-30	6.6.1 Introduction	This solution addresses “Key issue #1: Authenticated UE to exchange NAS messages with multiple satellites in split-MME architecture”. This solution is based on split MME architecture. S&F Satellite operation may involve multiple satellites allocated by an S&F Monitoring List. In order to prevent reusing key stream, one possible approach is to use different NAS keys when UE interacts with different satellites. This solution can improve the data exchange efficiency of the entire system.
e97791a0165eb026afd870f9d0c81a3a	33.700-30	6.6.2 Solution details	Based on the existing authentication procedures, this solution proposes to use different NAS keys when UE exchanges data with multiple satellites. Figure 6.6.2-1 Enhanced NAS security for multiple satellites in S&F mode SAT#1 has available Service Link. 1. The UE sends the Attach Request to SAT#1. 2. If SAT#1 does not have context to authenticate the UE, then sends the Attach Reject. SAT#1 has available Feeder Link. 3. SAT#1 sends the Attach Request to the MME-ground. 4. The MME-ground obtains authentication data including KASME, as defined in TS 33.401 [3]. 5. The MME-ground determines to use SAT#1 to serve UE, then the MME-ground calculates KASME1* by using KASME and SAT Id of SAT#1. 6. The MME-ground distributes KASME1* for SAT#1 during the transmission of AV. SAT#1 has available Service Link. 7. The authentication procedure is completed, as defined in TS 33.401 [3]. 8. SAT#1 derives NAS keys based on the KASME1* using existing mechanism as defined in TS 33.401[3] and sends the NAS security mode command integrity protected. 9. The UE calculates KASME1* using the same method as the MME-ground in step5, and further derives the NAS keys using existing mechanism as defined in TS 33.401[3], then the UE verifies the NAS security mode command. 10. If successfully verified, the UE sends the NAS security mode complete to SAT#1. 11. After the NAS SMC procedure, the UE and SAT#1 send protected NAS messages. SAT#2 has available Feeder Link. 12. The MME-ground determines to use SAT#2 to serve the UE, the MME-ground calculates KASME2* by using KASME and SAT Id of SAT#2. 13. The MME-ground distributes KASME2* for SAT#2. Then SAT#2 derives the NAS keys by using KASME2. SAT#2 has available Service Link. 14. The UE calculates KASME2 using the method as the MME-ground in step12, and further derives the NAS keys by using KASME2*. 15. The UE and SAT#2 send protected NAS messages. Editor’s Note: Whether and how to activate the new NAS key between the UE and SAT2 is FFS. Note: As described in TS 23.401[2], the MME-ground together with the associated MME-onboard(s) behave jointly as a single MME entity. For multiple satellites, assume MME-onboards have the same list of ordered NAS security algorithms. After NAS SMC, the selected NAS security algorithms could be synchronized for MME-onboards. Note: Each satellite/UE pair maintains independent COUNTs. Editor’s Note: Wrap-around issue for the independent COUNTs is FFS. Editor’s Note: The detail on securing NAS messages using different NAS keys during handover-like process is FFS.
e97791a0165eb026afd870f9d0c81a3a	33.700-30	6.6.3 Evaluation	Editor’s note: Impact for key separation at UE and MME on ground is FFS. Editor’s note: Whether the UE computes a new NAS security context each time it connects to a new satellite is FFS. TBD.
e97791a0165eb026afd870f9d0c81a3a	33.700-30	6.7 Solution #7: Solution for NAS COUNT synchronization in store-and-forward operations
e97791a0165eb026afd870f9d0c81a3a	33.700-30	6.7.1 Introduction	As per the threat described in the key issue #1, an attacker may intercept and replay previously transmitted NAS messages. This solution proposes the following to address this threat: • A new “Satellite access information” can be included as part of Initial UE message sent from satellite eNB to MME. This information can be used by MME to enable UE context synchronization including NAS COUNT verification and synchronization for the satellites included in the S&F Monitoring List. ◦ A “3GPP satellite access type” in Access type information element (reference : TS 24.501 [X] clause 9.11.2.1A) is included. Considering satellite access as a different access type to enable an independent NAS COUNT for “3GPP satellite access type”. • MME-onboard and MME-onground synchronize the NAS COUNT values for UEs whose security contexts are provided to the satellites included in the S&F Monitoring List. The mechanism of this synchronization across multiple satellites is out of 3GPP scope, however, 3GPP can recommend certain actions as follows: ◦ MME-onboard and MME-onground need to ensure that a given NAS COUNT value shall be accepted at most one time and only if message integrity verifies correctly. This is in accordance with clause 4.4.3.2 from TS 24.501 [X]. ◦ If MME-onboard receives a new message from a UE for which the UE security context is available with the satellite, and the integrity verification is verified successfully, the MME-onboard: ▪ Request MME-onground for NAS COUNT duplicate verification. This can also be done using NAS sequence number verification. ▪ If MME-onground responds indicating that the NAS COUNT is duplicate, OR if there is a timeout because of long delay in obtaining the feeder link, MME-onboard discards that message from UE. ▪ If MME-onground responds indicating that the NAS COUNT is NOT duplicate, MME-onboard consider it as a valid message and proceed to ensure seamless connectivity for the UE.
e97791a0165eb026afd870f9d0c81a3a	33.700-30	6.7.2 Solution details	Figure 6.7.2-1: Message sequence showing NAS COUNT verification at MME As shown in Figure 6.7.2-1: - In Step 2, NAS COUNTs are synchronized between MME-onboard and MME-onground entities. Note that from UE’s perspective, MME is expected to be seen as a single logical entity. Hence, in this solution, the proposal is to ensure NAS COUNT synchronization between MME entities to ensure replay protection. - In Step 3, if a genuine UE sends a NAS message, with UE security context available in Satellite#2, the integrity verification succeeds. The MME-onboard stores the message in the UE security context. Editor’s Note: Step 3 mentions only UL NAS count. Clarification is needed for DL. - In Step 5, MME-onboard requests the NAS COUNT verification with MME-onground. Editor’s Note: It needs to be studied on how the NAS count synchronization happens for messages recieved simulationusly from multiple satelites by MME-onground. - In Step 6, MME-onground responds with the verification status. - In case feeder link is not available for a long time, and there maybe a timeout implemented, the MME-onboard drops this NAS message from the UE. Also, if the NAS COUNT verification status indicates duplicate or old NAS message, the MME-onboard drops it in order to ensure replay protection requirements stated in clause 4.4.3.2 of TS 24.501. - If the NAS COUNT verification status from MME-onground indicates that it is not a duplicate or old message, MME-onboard process it further.
e97791a0165eb026afd870f9d0c81a3a	33.700-30	6.7.3 Evaluation	TBD Editor’s Note: The impact on signaling to mme on-ground needs to be noted
e97791a0165eb026afd870f9d0c81a3a	33.700-30	6.8 Solution #8: New specific rules to handle NAS Counter Overflow in S&F mode
e97791a0165eb026afd870f9d0c81a3a	33.700-30	6.8.1 Introduction	This solution addresses KI#1. In S&F Satellite operation, the subset of satellites operating in S&F Mode in which a given UE registration is valid (i.e. satellites included in the S&F Monitoring List), are expected to maintain a synchronised UE context, even though the synchronisation mechanism is outside the scope of 3GPP. This solution proposes to add an exception with respect to the synchronisation of the NAS counters. Based on the added exception, this solution proposes introducing specific rules for managing the pair of NAS counters stored by the UE and by the MME operating S&F Mode as follows: • When a UE registration is valid in multiple satellites operating in S&F mode, each time the UE interacts with one of these satellites, the UL NAS Overflow Counter (OC) stored in the UE may be higher than the UL NAS OC stored in the MME of the serving satellite. This discrepancy can arise due to previous interactions between the UE and other serving satellites of the same PLMN, where the UL NAS OC in the UE was incremented due to the UL NAS SQN wrap-around. In such a case, if the MME fails to verify the integrity of a received NAS packet using the last stored UL NAS OC, the MME may attempt to validate the message integrity using a series of consecutively incremented UL NAS OC values. If one of the attempts is successful, the MME updates its stored UL NAS OC accordingly. • Similarly, when a UE registration is valid in multiple satellites operating in S&F mode, the DL NAS Overflow Counter (OC) stored in the UE may be higher than the last DL NAS OC stored in the MME of the serving satellite. This can result from prior interactions between the UE and other satellites where the DL NAS OC in the UE was incremented due to the DL NAS SQN wrap-around. In such cases, if the UE fails to verify the integrity of a received NAS packet using the last stored DL NAS OC, it may attempt to validate the message integrity using a series of consecutively decremented DL NAS OC values. To avoid replay attack, the UE can rely on the fact that the Satellite ID is not the same.
e97791a0165eb026afd870f9d0c81a3a	33.700-30	6.8.2 Solution details	This section provides further details on this solution by analysing the uplink case (UE  MME-onboard) and the downlink case (UE  MME-onboard) when considering (1) UE is served by multiple satellites as per the S&F Monitoring List provided to the UE and (2) UE assumes that NAS counters in the MME-onboard(s) of those satellites are not necessarily synchronised.
e97791a0165eb026afd870f9d0c81a3a	33.700-30	6.8.2.1 Uplink case	Figure 6.8.2.1-1 shows the steps taken by the MME-onboard. Changes introduced by this solution are marked in red. a) Upon receiving an integrity protected NAS uplink message, the MME-onboard retrieves the SQN and the NAS message authentication code (NAS-MAC) which are then used to compute the expected NAS message authentication code (XNAS-MAC) according to 3GPP TS 33.401 clause 8.1 and Annex B.2. Furthermore, the UL NAS Count is increased according to 3GPP TS 24.301 clause 4.4.3. b) The computed XNAS-MAC is compared with the NAS-MAC received in the NAS integrity protected message. c) If the two codes match up, the integrity check is successful and the MME-onboard can process the uplink NAS message. d) If the two codes do not match up, the MME-onboard increases the UL OC by 1 which means increasing the UL NAS Count by 256 units. e) The XNAS-MAC is computed again and compared with the NAS-MAC. If the two codes match up, step c) is executed. Otherwise, step d) is executed. Note that steps d) and e) are repeated up to a number X of times. If the number of attempts exceeds X, the integrity check fails and the NAS message is discarded. A successful integrity check also indicates that the UL NAS OC has been correctly estimated and that the UE and the MME-onboard are aligned, i.e., the UL NAS OC stored by the UE match the UL NAS OC stored by the MME-onboard. Figure 6.8.2.1-1: Handling of UL NAS OC in the MME-onboard.
e97791a0165eb026afd870f9d0c81a3a	33.700-30	6.8.2.2 Downlink case	Figure 6.8.2.2-1 shows the steps taken by the UE. Changes introduced by this solution are marked in red. a) Upon receiving an integrity protected NAS downlink message, the UE retrieves the SQN and the NAS message authentication code (NAS-MAC) which are then used to compute the expected NAS message authentication code (XNAS-MAC) according to 3GPP TS 33.401 clause 8.1 and Annex B.2. Furthermore, the DL NAS Count is increased according to 3GPP TS 24.301 clause 4.4.3. b) The computed XNAS-MAC is compared with the NAS-MAC received in the NAS integrity protected message. c) If the two codes match up, the integrity check is successful and the UE can process the downlink NAS message. d) If the two codes do not match up, and the SatelliteID of the current serving satellite is different from the SatelliteID of the previous serving satellite, the UE decreases the UL OC by 1 which means decreasing the UL NAS Count by 256 units. e) The XNAS-MAC is computed again and compared with the NAS-MAC. If the two codes match up, step c) is executed. Otherwise, step d) is executed. Note that steps d) and e) are repeated up to a number X of times. If the number of attempts exceeds X, the integrity check fails and the NAS message is discarded. A successful integrity check also indicates that the DL NAS OC has been correctly estimated and that the MME-onboard and the UE are aligned, i.e., the DL NAS OC stored by the MME-onboard matches the DL NAS OC stored by the UE. SatelliteID is an identifier uniquely indicating an MME-onboard. The SatelliteID identifier of a given satellite is broadcast by the eNB within the SIB31 and the SatelliteID identifiers of the satellites that might be serving a given UE are included within the S&F Monitoring List, which is sent by the MME to indicate the satellite(s) that the UE may (re)-attempt NAS procedures (TS 23.401 clause 4.13.9.1). Figure 6.8.2.2-1: Handling of DL NAS OC in the UE. Editor’s Note: The impact of repeating integrity verification for X times on the UE side and MME-onboard (i.e., fake messages sent by the attacker require more resources for integrity verification, which increases the risk of attack) is FFS. Editor’s Note: The impact of accepting a range of NAS counters to the overall security of 3GPP system is FFS
e97791a0165eb026afd870f9d0c81a3a	33.700-30	6.8.3 Evaluation	Editor’s Note: Each solution should motivate how the potential security requirements of the key issues being addressed are fulfilled. 6.Y Solution #Y: <Solution Name> 6.Y.1 Introduction Editor’s Note: Each solution should list the key issues being addressed. 6.Y.2 Solution details 6.Y.3 Evaluation Editor’s Note: Each solution should motivate how the potential security requirements of the key issues being addressed are fulfilled.
e97791a0165eb026afd870f9d0c81a3a	33.700-30	7 Conclusions	7.Z Key Issue #Z: <Key Issue Name> Editor’s Note: This clause contains the agreed conclusions of Key Issue #Z. Annex <A>: <Informative annex title for a Technical Report> Annex <X>: Change history Change history Date Meeting TDoc CR Rev Cat Subject/Comment New version 2025-10 SA3#124 S3-253723 Incorporate TR skeleton, new Key Issue and new solutions 0.1.0
53f8772d5c2747defa00fbb998eba7fd	33.746	1 Scope	The present document studies the potential security enhancements for 5G NR Femto. More specifically, the study investigates potential security enhancements in the following areas: - The security requirements and potential solutions to enhance the security of NR Femto devices, to detect misconfigured or compromised NR Femto devices, and to eliminate the security impacts from misconfigured or compromised NR Femto devices. - The security and privacy aspects of local access for NR Femto scenario.
53f8772d5c2747defa00fbb998eba7fd	33.746	2 References	The following documents contain provisions which, through reference in this text, constitute provisions of the present document. - References are either specific (identified by date of publication, edition number, version number, etc.) or non‑specific. - For a specific reference, subsequent revisions do not apply. - For a non-specific reference, the latest version applies. In the case of a reference to a 3GPP document (including a GSM document), a non-specific reference implicitly refers to the latest version of that document in the same Release as the present document. [1] 3GPP TR 21.905: "Vocabulary for 3GPP Specifications". [2] 3GPP TS 23.501: "System architecture for the 5G System (5GS)". [3] 3GPP TS 33.545: "Security aspects of NR Femto".
53f8772d5c2747defa00fbb998eba7fd	33.746	3 Definitions of terms, symbols and abbreviations
53f8772d5c2747defa00fbb998eba7fd	33.746	3.1 Terms	For the purposes of the present document, the terms given in TR 21.905 [1] and the following apply. A term defined in the present document takes precedence over the definition of the same term, if any, in TR 21.905 [1]. example: text used to clarify abstract rules by applying them literally.
53f8772d5c2747defa00fbb998eba7fd	33.746	3.2 Symbols	For the purposes of the present document, the following symbols apply: <symbol> <Explanation>
53f8772d5c2747defa00fbb998eba7fd	33.746	3.3 Abbreviations	For the purposes of the present document, the abbreviations given in TR 21.905 [1] and the following apply. An abbreviation defined in the present document takes precedence over the definition of the same abbreviation, if any, in TR 21.905 [1]. <ABBREVIATION> <Expansion>
53f8772d5c2747defa00fbb998eba7fd	33.746	4 Security Architecture and Assumptions	The following security architecture and assumptions are applied to the present document: - Annex V in TS 23.501[2] captures the architecture for NR Femto. The architecture option of NR Femto with a local UPF is reused as the basis for this study. - The security architectural and requirements captured in TS 33.545 [3] is reused as basis for this study.
53f8772d5c2747defa00fbb998eba7fd	33.746	5 Key issues
53f8772d5c2747defa00fbb998eba7fd	33.746	5.1 Key Issue #1: Detection of misconfigured/compromised 5G NR Femto devices
53f8772d5c2747defa00fbb998eba7fd	33.746	5.1.1 Key issue details	NR Femto devices are deployed outside operator domain and considered to be in un-trusted environments. Un-detected misconfigured or compromised NR Femto devices can lead to disruptions in services to UEs. A misconfigured or compromised NR Femto device with valid credentials and subscription to serve the victim UE can pose various threats including authentication replay attacks, broadcasting CAG IDs that it is not authorized to serve, denial of service attacks, etc.. Besides, misconfigured or compromised NR Femto devices may report false security baseline information to the SeGW and pose potential security threats to the NR Femto MS and the core network. Potential security enhancements to NR Femto security architecture to detect such misconfigured or compromised NR Femto devices are needed to ensure that UEs, the NR Femto MS and the core network do not become victims of such devices.

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4.4 Key Issue #4: AIOT device ID protection in DO-A procedure

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4.4.1 Key issue details

For AIoT device type 1, all communications between the network and the AIOT device are initiated by the network. Unlike AIOT device type 1, the DO-A AIOT device autonomously initiates communication by sending a message to the network. Due to this change, privacy mechanisms specified in TS 33.369[8] for AIOT device type 1 may not be feasible for DO-A AIOT devices. Therefore, mechanisms for privacy of device ID of DO-A AIOT device contained in the message(s) exchanged between the device and the network should be studied.

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4.4.2 Threats

An attacker can identify, monitor and track a DO-A AIoT devices based on the identifiers associated with the AIoT device if the identifiers are not privacy protected.

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4.4.3 Potential security requirements

The 5G system shall support mechanisms to prevent privacy threats (e.g., identifying, linking, and tracking) against the identifier of the DO-A capable AIOT device(s).

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4.5 Key Issue #5: Amplification of resource exhaustion by exploiting AIoT paging messages

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4.5.1 Key issue details

Paging of AIoT devices is different than "regular" paging of regular UEs. In AIOT, one single paging message coming from the reader/network can be used to trigger multiple devices to respond by using, for example, a mask/filter based on target device identification, or by a group ID of the target devices. Once the target devices are triggered, the reader, core network of the PLMN, and the associated AF participate in various steps to accomplish the intended tasks, e.g., inventory reporting and command executing. Unlike regular paging, AIOT paging can happen for devices that are not necessarily already registered in the core network and hence cannot share a session security context with the network. The paging message can include information that the devices and core network of the PLMN can use in successful accomplishment of these tasks in those steps. Therefore, if parts of or the whole paging message is corrupted, the core network of the PLMN and the AF can end up wasting computational resources that leads to no successful accomplishment of the intended tasks. Moreover, the corrupted paging message results in waste of radio resources being used by AIOT over the air interface as well. The above can be used by an adversary that intentionally corrupt the paging message in a way so that many legitimate AIOT devices are triggered by the corrupted paging message, but later, in the core network of the PLMN or in the AF, the responses from the AIOT devices are found invalid. This happens not because the devices computed wrong responses, but because the devices used corrupted paging message in computing their responses. Such an attack can cause the PLMN and the AF wasting computational resources. It also causes the AIOT reader wasting radio resources that can adversely impact the regular UEs in the same network. If devices respond to a corrupted paging message, that should be identified as early as possible, and the responses should not be forwarded any further to the core network or to the AF.

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4.5.2 Security threats

An adversary can cause the core network of a PLMN or the AF wasting computational resources by corrupting or spoofing one single paging message, which is surprisingly little work on the adversary’s behalf, that triggers a lot of devices to send a paging response to the legitimate reader. The above attack can also cause the AIOT reader and serving NG-RAN node wasting radio resources that can adversely impact the regular UEs in the same network.

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4.5.3 Potential security requirements

Editor’s Note: Potential security requirements are FFS

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5 Solutions

Editor’s Note: This clause contains the proposed solutions addressing the identified key issues.

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5.1 Mapping of solutions to key issues

Editor’s Note: This clause captures mapping between key issues and solutions. Table 5.1-1: Mapping of solutions to key issues Key Issues Solutions 5.Y Solution #Y: <Solution Name> 5.Y.1 Introduction Editor’s Note: Each solution should list the key issues being addressed. 5.Y.2 Solution details 5.Y.3 Evaluation Editor’s Note: Each solution should motivate how the potential security requirements of the key issues being addressed are fulfilled.

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6 Conclusions

Editor’s Note: This clause captures the conclusions of this study. Annex <X>: Change history Change history Date Meeting TDoc CR Rev Cat Subject/Comment New version 10/2025 SA3#124 S3‑253300 Initial draft TR 0.0.1 10/2025 SA3#124 S3‑253732 Incorporated accepted contributions S3‑253822, S3‑253823, S3-253824, S3-253825, S3-253826, S3-253827 0.1.0

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1 Scope

The present document studies the security architecture and security requirements for WAB-nodes, security impacts of potentially compromised WAB nodes and requirements for countermeasures against any compromised WAB nodes.

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2 References

The following documents contain provisions which, through reference in this text, constitute provisions of the present document. - References are either specific (identified by date of publication, edition number, version number, etc.) or non‑specific. - For a specific reference, subsequent revisions do not apply. - For a non-specific reference, the latest version applies. In the case of a reference to a 3GPP document (including a GSM document), a non-specific reference implicitly refers to the latest version of that document in the same Release as the present document. [1] 3GPP TR 21.905: "Vocabulary for 3GPP Specifications". [2] 3GPP TS 23.501: "System architecture for the 5G System (5GS)". [3] 3GPP TS 38.401: "NG-RAN Architecture description". [4] 3GPP TS 33.501: "Security architecture and procedures for 5G System". [5] 3GPP TR 33.745: "Study on security aspects of 5G Next Radio (NR) Femto". [6] 3GPP TS 33.320: "Security of Home Node B (HNB) / Home evolved Node B (HeNB)".

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3 Definitions of terms, symbols and abbreviations

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3.1 Terms

For the purposes of the present document, the terms given in 3GPP TR 21.905 [1] and the following apply. A term defined in the present document takes precedence over the definition of the same term, if any, in 3GPP TR 21.905 [1]. example: text used to clarify abstract rules by applying them literally.

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3.2 Symbols

For the purposes of the present document, the following symbols apply: <symbol> <Explanation>

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3.3 Abbreviations

For the purposes of the present document, the abbreviations given in 3GPP TR 21.905 [1] and the following apply. An abbreviation defined in the present document takes precedence over the definition of the same abbreviation, if any, in 3GPP TR 21.905 [1]. <ABBREVIATION> <Expansion>

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4 Security Architecture and Assumptions

Editor’s Note: This clause contains security architecture and assumptions to be considered for the study (e.g., per work task/KI). Figure 5.49.1.1-1 in TS 23.501[2] shows the MWAB architecture for 5GS. In the architecture. There are two components in MWAB, i.e. MWAB-gNB and MWAB-UE. The WAB-node integration procedure is captured in TS 38.401[3]. From a security point of view, the MWAB architecture rely on the 5G security framework for key management and authorization as captured in TS 33.501 [4].

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5 Key issues

Editor’s Note: This clause contains all the key issues identified during the study.

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5.1 Key Issue #1: Security of the link between WAB-gNB and OAM

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5.1.1 Key issue details

Based on the WAB-node integration procedure, the WAB-gNB will receive the OAM of WAB through the WAB-MT’s network. The link between WAB-gNB and OAM needs to have sufficient security protection for configuration data transmission.

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5.1.2 Security threats

If the link between WAG-gNB and OAM is not well protected, the configuration data will be tampered or disclosure.

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5.1.1 Potential security requirements

The link between the MWAB-gNB and the OAM shall be ciphering and integrity protected.

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5.2 Key Issue #2: Security Protection of Compromised WAB Nodes and Core Network Measures

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5.2.1 Key issue details

Wireless Access Backhaul (WAB) nodes, consist of a WAB-gNB (gNB-like functionality) and a WAB-MT (UE-like functionality). These nodes operate in non-trusted environments and may serve as moving backhaul nodes for the 5GS, establishing NG, Xn, and OAM interfaces over PDU sessions through 3GPP backhauls. While 3GPP TR 33.745 [5] studied NR Femto security and reused procedures from TS 33.320 [6], security concerns specific to WAB nodes particularly compromised WAB nodes in untrusted environments remain unaddressed. Additionally, core network components may not be equipped to detect anomalous behavior from compromised WAB-gNBs, due to the decentralized and mobile nature of such nodes. The compromised WAB nodes could lead to topology poisoning, signalling storms, or user-plane hijacking. This key issue aims to address the security issues introduced by compromised WAB nodes, where failure to protect the integrity, authenticity, and confidentiality of messages delivered from WAB-gNB and WAB-MT components can expose the 5GS to topology spoofing, rogue signalling, and persistent infiltration.

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5.2.2 Security threats

Potential security threat: • Rogue WAB-gNB Injection: A compromised WAB node may inject unauthorized signalling or reroute traffic maliciously, particularly via spoofed message. Furthermore, a compromised WAB-gNB can attempt to broadcast unauthorized network identifiers or initiate rogue Xn association attempts with neighbouring gNBs causing service disruption. • Topology Manipulation and Signalling Abuse: Moving WAB nodes may falsely report neighbour relationships via Xn or behave inconsistently across locations, leading to incorrect handover decisions, topology poisoning, or signalling loops. • Persistent Threat via Dual Roles: Since WAB-MT behaves like a UE and WAB-gNB like a gNB, a compromised WAB can act in both roles to stage cross-layer attacks, bridging between RAN and CN trust domains.

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5.2.3 Potential security requirements

The 3GPP system shall support security mechanisms to mitigate risks from compromised WAB nodes, preventing topology spoofing, rogue signalling, and mobility-related traceability threats.

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5.3 Key Issue #3: new key issue on enabling NDS/IP for WAB case

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5.3.1 Key issue details

According to the architecture in 23.501[2],the MWAB-gNB establishes the N2 interface with UE’s 5GC, and setup a Xn link with a traditional gNB. Figure 5.3-1: Architecture for MWAB operation support - non-roaming with one PLMN A MWAB may be mounted on a moving vehicle and may serve UEs inside or outside the vehicle. A MWAB cannot provide a connection service to a UE unless it establishes the N2 and Xn connections with UE’s AMF and UE’ NG-RAN. Since the NDS/IP is used for Xn and N2 connection as defined in TS 33.501[4], a credential must be provided in MWAB case in order to build the connection with UE’s network. One existing method is the preconfigure the potential serving UE’s credentials to the MWAB before it starts to connecting to the network. However, this relies on a well and unchanged plan on the MWAB. Since it is very difficult to know where the MWAB will go, it is very difficult to a MWAB vendor to configure everything in advance.

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5.3.2 Security threats

N/A

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5.3.3 Potential security requirements

Credentials for NDS/IP for Xn and N2 connection between WAB and UE’s network shall be provided with confidential protection and integrity protection.

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5.4 Key Issue #4: Protection and binding of MWAB-gNB control plane over BH-PDU sessions

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5.4.1 Key issue details

In MWAB, OAM, N2, Xn and N3 traffic for the MWAB-gNB is carried over backhaul PDU session(s) that the MWAB-UE establishes and modifies based on traffic descriptors and OAM configuration. The MWAB broadcasted PLMN/SNPN may differ from the BH PLMN/SNPN which creates inter-PLMN/SNPN trust boundaries for these control plane and OAM links.

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5.4.2 Security threats

Interception or modification of OAM/N2/Xn control traffic over BH PDU session(s); misclassification of traffic due to descriptor or mapping error; cross-slice leakage; replay during mobility or BH PDU session changes are possible.

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5.4.3 Potential security requirements

Confidentiality and integrity protection for OAM/N2/Xn control traffic over BH PDU session(s), binding MWAB-gNB identity and traffic classes to BH PDU sessions. 5.X Key Issue #X: <Key Issue Name> 5.X.1 Key issue details 5.X.2 Security threats 5.X.3 Potential security requirements

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6 Solutions

Editor’s Note: This clause contains the proposed solutions addressing the identified key issues.

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6.0 Mapping of solutions to key issues

Editor's Note: This clause contains a table mapping between key issues and solutions. Table 6.0-1: Mapping of solutions to key issues Solutions KI#1 KI#2 KI#3 KI#4 #1 X

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6.1 Solution #1: reusing NDS/IP to N2 and Xn interfaces in WAB

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6.1.1 Introduction

This solution proposes a the credential is provided to the WAB by OAM in the phase 2-1 of the WAB-node integration procedure defined in TS 38.401 [3]

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6.1.2 Solution details

Figure 6.1.2-1 Procedure to configure the credential for NDS/IP connection 0. The WAB-node is pre-configured a credential for accessing to the OAM of WAB Phase 1. WAB-MT Setup. It is described in TS 38.401[3]. Phase 2-1. WAB-gNB initialization. Addition to the description in TS 38.401[3], the WAB-gNB uses the pre-configured credential accessing to the OAM of WAB for authentication and security establishment. Then, the OAM of WAB sends the configuration data to the WAB-gNB in the secure link. The configuration data includes the credentials used for establishing Xn and N2 connections for UE. If the WAB servers UEs from different PLMN, the credentials may further bind with PLMN ID information. Phase 2-2. WAB-gNB NG connection setup. Addition to the description in TS 38.401[3], the WAB-gNB uses the credential sent in Phase 2-1 to establish NDS/IP with the potential serving UE’s 5GC. If the WAB-gNB servers more than one PLMN, the WAB-gNB will use the corresponding credentials to establish NDS/IP with each UE’s PLMN’s 5GC. Phase 2-3. WAB-gNB Xn connection setup. Addition to the description in TS 38.401[3], the WAB-gNB uses uses the credential sent in Phase 2-1 to establish NDS/IP with the potential serving UE’s NG-RAN. If the WAB-gNB servers more than one PLMN, the WAB-gNB will use the corresponding credentials to establish NDS/IP with each UE’s PLMN’s NG RAN.

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6.1.3 Evaluation

The solution addresses the situation when the credential of UE’s 5GC or NG-RAN cannot be pre-configured at WAB. The phase 2-1 can be used to configure the credentials of potential serving UEs’ PLMN. 6.Y Solution #Y: <Solution Name> 6.Y.1 Introduction Editor’s Note: Each solution should list the key issues being addressed. 6.Y.2 Solution details 6.Y.3 Evaluation Editor’s Note: Each solution should motivate how the potential security requirements of the key issues being addressed are fulfilled.

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7 Conclusions

Editor’s Note: This clause contains the agreed conclusions that will form the basis for any normative work. Annex <C>: Change History Change history Date Meeting TDoc CR Rev Cat Subject/Comment New version 2025-08 SA3#123 S3-252987 S3-252684 and S3-252686 for endorsed TR Skeleton for WAB Security 0.0.0 2025-10 SA3#124 S3-253741 Included changed from S3-253411, S3-253412, S3-253464, S3-253626, S3-253820 and S3-253821 0.1.0