UE NAS Security Context Storage for Multi-PLMN Registration

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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 potential overwrites and mix-ups of NAS COUNT values, which compromises network registration and security.

Innovation Solution

The Mobile Equipment (ME) component of 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, thereby 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 the UE can securely register in multiple networks, but the USIM storage capacity is insufficient causing context overwrites and security compromises

Engineering Contradiction:

ImprovesecurityVSAvoidstorage capacity

Core Design Contradiction:

ReliabilityVSQuantity of substance

Solution Approach 1:

The patent divides the storage function into two separate locations: the USIM card stores NAS security contexts for the home PLMN, while the ME (mobile equipment) stores NAS security contexts for visited PLMNs. This segmentation allows each component to manage its own storage responsibilities, preventing overwrites and ensuring secure multi-PLMN operation without requiring the USIM to accommodate all contexts.

Inventive Principle:

Principle #1Segmentation

2Adaptability or versatility

If the USIM stores NAS security contexts for multiple PLMNs, then network registration is enabled, but NAS COUNT values may be overwritten or mixed up compromising security

Engineering Contradiction:

Improvemulti-PLMN registrationVSAvoidsecurity

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The patent implements separate storage locations for different PLMN contexts: the USIM maintains contexts for the home PLMN while the ME maintains contexts for visited PLMNs. This segmentation ensures that NAS COUNT values for different PLMNs are stored separately and cannot be overwritten or mixed up, enabling secure multi-PLMN registration.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The ME acts as an intermediary storage layer between the USIM and the network. When the UE needs to register in a visited PLMN, the ME stores the NAS security context there, preventing direct conflicts in the USIM. This intermediary approach allows the system to maintain multiple PLMN contexts without compromising the integrity of NAS COUNT values.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Adaptability or versatility

If the UE stores multiple NAS security contexts in the USIM, then network registration is supported, but the USIM structure becomes more complex

Engineering Contradiction:

Improvemulti-PLMN supportVSAvoidUSIM structure

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The patent segments the storage function by keeping the USIM structure simple for home PLMN contexts while using the ME for visited PLMN contexts. This segmentation avoids complicating the USIM structure while still enabling multi-PLMN support through the distributed architecture.

Inventive Principle:

Principle #1Segmentation

Data Source

PatentUS12507190B2Handling registrations of a user equipment in different communication networks

Publication Date: 2025.12.23 TELEFONAKTIEBOLAGET LM ERICSSON (PUBL)

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.