RRC Key Security via Hierarchical Counter Segmentation
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Solution Overview
Problem
Current telecommunication systems, particularly in LTE, face complexity in maintaining RRC key security during mobility events like handovers and state transitions, as the hyperframe number (HFN) is used for multiple purposes, including sequence number overflow and mobility events, leading to inefficiencies and additional security-related signaling.
Innovation Solution
Separating sequence number overflow counters from mobility event counters, using hierarchical counters in the UE, eNodeB, and CN, where state transition and handover counters are reset to zero when respective events occur, providing unique inputs to the RRC ciphering and integrity protection algorithm, thereby eliminating the need for additional signaling and ensuring unique sequence numbers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the HFN is used for multiple purposes (sequence number overflow and mobility events), then the system can maintain RRC key security during mobility events, but the device complexity and security-related signaling increase
Solution Approach 1:
The patent segments the counter management by introducing separate counters for different purposes: a HANDOVER counter for mobility events and an OVERFLOW counter for sequence number overflow. This segmentation eliminates the complexity of using a single HFN for multiple purposes while maintaining security, as each counter is independently managed and reset according to its specific event type.
2Reliability
If the HFN is used for multiple purposes, then the system can maintain RRC key security, but the amount of signaling over the radio interface increases
Solution Approach 1:
By segmenting counter management into separate HANDOVER and OVERFLOW counters, the patent reduces signaling overhead. The HANDOVER counter is only updated during handover events and the OVERFLOW counter only during sequence number overflow, eliminating the need for continuous HFN signaling. This segmentation allows each counter to be independently managed with minimal signaling.
3Loss of time
If sequence numbers are not reset after mobility events, then the system avoids regenerating RRC keys, but the same sequence number and RRC key combination may be reused compromising security
Solution Approach 1:
The patent implements preliminary action by resetting the HANDOVER counter to zero at the beginning of each handover event, before any RRC messages are exchanged. This preliminary reset ensures that sequence numbers start from a known state, and combined with RRC key regeneration, prevents reuse of the same sequence number and key combination without requiring time-consuming key regeneration during the handover process.
Solution Approach 2:
The patent changes the parameter state of the HANDOVER counter by resetting it to zero during handover events and when RRC keys are regenerated. This parameter change ensures that the sequence number input to the ciphering algorithm changes accordingly, preventing reuse of the same sequence number and RRC key combination while maintaining efficient key management.
Data Source
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AI summary
The present invention relates to a solution for handling encryption of control messages in a wireless telecommunications network. Key generation is based on sequence numbers and the present invention reduces access to core network devices for updating sequence numbers relating to network events by separating sequence number generation to different parts of the network and different types of network events. This is done by providing a solution where sequence number rollover events and handover events are separated from each other in providing input to radio resource control message encryption. Three different counters may be used for different types of events and all three may be used as input to an encryption algorithm.