5G-to-4G Handover Key Management for Backward Security
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Solution Overview
Problem
Current wireless communication systems lack an efficient solution for achieving security during handover from Next Generation (5G) to Evolved Packet Core (4G) systems, as existing methods do not provide backward security, allowing the target 4G system to gain knowledge of 5G security information.
Innovation Solution
A key management method is implemented that derives a 4G-master key based on a 5G key and freshness parameter at the source 5G system, forwards this key to the target 4G system, and ensures the freshness parameter is not exposed to the target system, enabling derivation of new 4G-master keys at both the target core network and user equipment, thereby maintaining security.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the target 4G system receives 5G security information during handover, then security management is simplified, but backward security is compromised as the target system gains knowledge of 5G security information
Solution Approach 1:
The patent extracts only the necessary security parameters (freshness parameter and derived 4G-master key) from the 5G security context, excluding the actual 5G security information (5G-master key, 5G-integrity key, 5G-ciphering key) from being transmitted to the target 4G system. This selective extraction maintains backward security while enabling security management during handover.
Solution Approach 2:
The patent introduces a key derivation mechanism as an intermediary between the 5G and 4G security systems. The 4G-master key is derived from the 5G-master key using a one-way function with a freshness parameter, acting as a mediator that allows security context transfer without exposing the original 5G security information to the target 4G system.
2Reliability
If new 4G-master keys are derived at both target core network and user equipment, then forward security is maintained, but key management complexity increases
Solution Approach 1:
The patent performs preliminary key derivation at the source 5G system before handover, generating the 4G-master key and freshness parameter in advance. This preliminary action ensures that both the target core network and user equipment can independently derive the same 4G-master key without requiring complex post-handover key synchronization, thus maintaining forward security while reducing key management complexity.
3Reliability
If the freshness parameter is transmitted to enable key derivation, then key freshness is ensured, but the risk of exposing sensitive 5G keys increases
Solution Approach 1:
The patent changes the parameter being transmitted from static 5G security information to a dynamic freshness parameter that is combined with the 5G-master key in a one-way derivation function. This parameter change ensures key freshness for each handover while the one-way function property prevents reconstruction of the 5G-master key from the transmitted freshness parameter and derived 4G-master key.
Data Source
AI summary
A key management is provided that enables security activation before handing over a user equipment from a source 5G wireless communication system, i.e., a Next Generation System (NGS), to a target 4G wireless communication system, i.e., a Evolved Packet System (EPS)/Long Term Evolution (LTE). The key management achieves backward security, i.e., prevents the target 4G wireless communication system from getting knowledge of 5G security information used in the source 5G wireless communication system.