DAPS Handover COUNT Sequencing to Prevent Keystream Reuse

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Solution Overview

Problem

Existing methods fail to address the issue of keystream reuse during make-before-break handover, which can lead to the exposure of confidential data due to the use of stream ciphers with retained security keys during Dual Active Protocol Stack (DAPS) handovers in wireless communication networks.

Innovation Solution

Maintain sequential incrementation of the DL/UL COUNT value for the Signalling Radio Bearer (SRB1) during both handover to the target cell and fallback to the source cell, irrespective of the cell in which the communication occurs, ensuring that the same keystream is not re-used for a PDCP PDU, thereby ensuring secure communication.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If security parameter is retained during make-before-break handover to reduce re-encryption overhead, then network performance is improved, but keystream reuse occurs leading to exposure of confidential data

Engineering Contradiction:

Improvenetwork performanceVSAvoidexposure of confidential data

Core Design Contradiction:

ProductivityVSObject-affected harmful factors

Solution Approach 1:

The patent changes the COUNT value parameter during handover to prevent keystream reuse. Specifically, when transitioning from source cell to target cell, the COUNT value is adjusted (incremented or reset) so that even though the same security key is retained, the keystream generated by the encryption algorithm differs, thereby preventing exposure of confidential data while maintaining network performance

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent applies preliminary action by pre-adjusting the COUNT value before handover occurs. The source radio network node determines the appropriate COUNT value to use during handover and communicates this to the UE in advance, ensuring that the encryption process is already configured to prevent keystream reuse before the actual handover takes place

Inventive Principle:

Principle #10Preliminary action

2Object-affected harmful factors

If sequential incrementation of COUNT value is maintained during handover and fallback, then keystream reuse is prevented, but device complexity increases

Engineering Contradiction:

Improvekeystream reuse preventionVSAvoiddevice complexity

Core Design Contradiction:

Object-affected harmful factorsVSDevice complexity

Solution Approach 1:

The patent applies self-service by enabling the UE to automatically maintain sequential incrementation of the COUNT value during handover and fallback operations. The UE autonomously manages the COUNT value without requiring complex external coordination, thereby preventing keystream reuse while minimizing the increase in device complexity through self-managed counter incrementation

Inventive Principle:

Principle #25Self-service

Data Source

PatentUS20250344111A1Radio network node, user equipment (UE) and methods performed therein

Publication Date: 2025.11.06 TELEFONAKTIEBOLAGET LM ERICSSON (PUBL)

AI summary

Embodiments herein relate to for example a method performed by a radio network node for handling a communication of a user equipment, UE, in a wireless communication network. The radio network node transmits a handover command for handing over the UE, from a source cell to a target cell, wherein a security parameter for encrypting data communicated between the radio network node and the UE is retained during the handover. Furthermore the radio network node maintains a sequence number status for reception and/or transmission of a signalling radio bearer of the UE during the handover from the source cell to the target cell, and/or at a fallback from the target cell to the source cell, when the UE triggers the fallback to the source cell.