5G-to-4G Security Context Mapping for Idle Mobility Continuity

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

There is currently no solution for deriving a 4G/EPS security context from a 5G/NGS security context during idle mode mobility, which hinders service continuity when a UE moves out of 5G/NGS coverage into 4G/EPS coverage.

Innovation Solution

A method and arrangement for mapping a 5G/NGS security context to a 4G/EPS security context by obtaining a 5G/NGS security context and deriving a 4G/EPS security context, specifically using a mobility management key KAMF to derive a 4G/EPS master key KASME, ensuring secure and efficient idle mode mobility.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a UE moves out of 5G/NGS coverage into 4G/EPS coverage during idle mode, then service continuity is needed, but there is no solution for deriving 4G/EPS security context from 5G/NGS security context

Engineering Contradiction:

Improveservice continuityVSAvoidinter-system mobility compatibility

Core Design Contradiction:

ReliabilityVSAdaptability or versatility

Solution Approach 1:

The patent applies parameter changes by transforming the security context parameters from 5G/NGS system to 4G/EPS system through key derivation functions. The 5G security keys (KSEAF, KCN) are mathematically transformed into 4G security keys (KASME, CK, IK) using standardized derivation algorithms, enabling the UE to maintain service continuity across different wireless communication systems with incompatible security parameters.

Inventive Principle:

Principle #35Parameter changes

2Reliability

If 5G/NGS security context is mapped to 4G/EPS security context, then service continuity is enabled, but the target core network must not gain knowledge of the source core network's security keys

Engineering Contradiction:

Improveservice continuityVSAvoidsecurity key exposure

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The patent employs an intermediary approach by using key derivation functions as mathematical mediators that transform 5G security keys into 4G security keys without revealing the original keys. The derivation process acts as a one-way transformation where the target network can obtain functional security keys for service continuity but cannot reverse-engineer or learn the source network's master security keys, thus protecting security while enabling mobility.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Productivity

If security context mapping is implemented during idle mode mobility, then seamless handover is achieved, but additional key derivation and management complexity is introduced

Engineering Contradiction:

Improvehandover efficiencyVSAvoidkey management complexity

Core Design Contradiction:

ProductivityVSDevice complexity

Solution Approach 1:

The patent applies preliminary action by pre-configuring the UE with the capability to perform key derivation from 5G to 4G security contexts before actual handover occurs. The UE is pre-programmed with the key derivation algorithms and can autonomously derive 4G security keys from stored 5G security keys when entering idle mode and detecting 4G coverage, eliminating the need for complex real-time key management during the actual handover process.

Inventive Principle:

Principle #10Preliminary action

Data Source

PatentUS12563485B2Management of security contexts at idle mode mobility between different wireless communication systems

Publication Date: 2026.02.24 TELEFONAKTIEBOLAGET LM ERICSSON (PUBL)

AI summary

There is provided a solution for managing security contexts at idle mode mobility of a wireless communication device between different wireless communication systems including a first wireless communication system and a second wireless communication system. The first wireless communication system is a 5G/NGS system and the second wireless communication system is a 4G/EPS system. The solution is based on obtaining (S1) a 5G/NGS security context, and mapping (S2) the 5G/NGS security context to a 4G/EPS security context.