UE NAS Security Context Handling Across Multiple PLMNs

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Existing 5G user equipment (UE) devices face security issues due to the inability of Universal Subscriber Identity Modules (USIM) to store multiple Non-Access Stratum (NAS) security contexts for different Public Land Mobile Networks (PLMNs), leading to overwrites and mix-ups of NAS COUNT values, which compromises network registration and security.

Innovation Solution

The Mobile Equipment (ME) in the UE determines the USIM's capability to store multiple NAS security contexts and, if unsupported, stores these contexts in its non-volatile memory, ensuring separate contexts for each PLMN, preventing NAS COUNT value overwrites.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the USIM stores multiple NAS security contexts for different PLMNs, then network registration security is improved, but the USIM storage capacity is insufficient leading to context overwrites

Engineering Contradiction:

Improvenetwork registration securityVSAvoidUSIM storage capacity

Core Design Contradiction:

ReliabilityVSQuantity of substance

Solution Approach 1:

The patent divides the storage of NAS security contexts into two separate locations: the USIM stores only the first NAS security context (K1, Kseaf1), while the second NAS security context (K2, Kseaf2) is stored in the ME's non-volatile memory. This segmentation allows both contexts to be maintained without overlapping storage constraints, preventing overwrites while maintaining security for multiple PLMN registrations.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent introduces non-volatile memory in the ME as an intermediary storage location for the second NAS security context. This intermediary component relieves the USIM of the burden of storing multiple contexts, allowing the USIM to maintain its primary security function while the ME's additional memory handles the extended storage requirements for multiple PLMN contexts.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Adaptability or versatility

If the USIM stores multiple NAS security contexts, then multi-PLMN registration capability is improved, but NAS COUNT value mix-ups occur compromising security

Engineering Contradiction:

Improvemulti-PLMN registration capabilityVSAvoidNAS COUNT value integrity

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The patent segments the storage of NAS security contexts by separating the first context (K1, Kseaf1) in the USIM from the second context (K2, Kseaf2) in the ME's non-volatile memory. This physical separation eliminates the risk of NAS COUNT value mix-ups that would occur if both contexts were stored in the same USIM memory, thereby maintaining integrity while enabling multi-PLMN registration.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The non-volatile memory in the ME serves as an intermediary that isolates the second NAS security context from the USIM's storage environment. This intermediary storage location prevents contamination and mix-ups of NAS COUNT values between different PLMN contexts, ensuring that each context maintains its own integrity independently.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Reliability

If the UE stores multiple NAS security contexts in the USIM, then security contexts for different PLMNs are maintained, but the USIM storage space is exhausted

Engineering Contradiction:

Improvesecurity context maintenanceVSAvoidUSIM storage space

Core Design Contradiction:

ReliabilityVSQuantity of substance

Solution Approach 1:

The patent segments the storage responsibility for NAS security contexts between the USIM and the ME's non-volatile memory. The USIM stores only the first NAS security context, while the second context is stored in the ME's memory. This segmentation allows multiple security contexts to be maintained without exhausting the USIM's storage space, as each context is stored in an appropriate location based on capacity constraints.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The non-volatile memory in the ME acts as an intermediary storage solution that handles the second NAS security context. This intermediary component offloads storage requirements from the USIM, enabling the system to maintain multiple security contexts without the USIM running out of space, while still ensuring secure context maintenance for multi-PLMN operations.

Inventive Principle:

Principle #24Intermediary (Mediator)

Data Source

PatentEP4218278B1Handling registrations of a user equipment in different communication networks

Publication Date: 2025.11.19 TELEFONAKTIEBOLAGET LM ERICSSON (PUBL)

Figure 1~2
Figure 3~6
Figure 7~9

AI summary

A user equipment ("UE") can handle registrations of the UE in different wireless communication networks. The UE can obtain information indicating whether a Universal Subscriber Identity Module ("USIM") of the UE supports storing multiple different Non-Access Stratum ("NAS") security contexts of the UE associated with the different wireless communication networks. The UE can further determine whether the USIM supports storing the multiple different NAS security contexts of the UE associated with the different wireless communication networks based on the obtained information.