Key Separation in UMTS Handover via SGSN AKA
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Solution Overview
Problem
In the UMTS system, the handover process between Home NodeBs (HNBs) and Radio Network Controllers (RNCs) leads to security vulnerabilities due to the lack of key separation, where the Ciphering Key (CK) and Integrity Key (IK) remain unchanged, allowing attackers to acquire target node keys if they obtain the source HNB's key, especially in scenarios where HNBs are vulnerable and lack secure key management.
Innovation Solution
The System GPRS Support Node (SGSN) triggers an Authentication and Key Agreement (AKA) procedure to update CK and IK, ensuring that source and target nodes use different keys by initiating the AKA process when a user equipment (UE) hands over or moves between HNBs or RNCs, thereby separating the keys and enhancing security.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If handover signaling is terminated at the SGSN during hard handover procedure, then the handover can be completed successfully, but the Ciphering Key and Integrity Key will not change, causing security vulnerability where source and target nodes use the same key
Solution Approach 1:
The SGSN triggers an Authentication and Key Agreement (AKA) procedure before or during the handover process to update the CK and IK. This preliminary action ensures that new keys are generated and distributed to both the source and target nodes before the handover is completed, preventing the security vulnerability where both nodes would use the same key.
Solution Approach 2:
The invention changes the key parameters (CK and IK) by initiating an AKA procedure that generates new authentication vectors and updates the cryptographic keys. This parameter change ensures that the target node receives different keys from the source node, eliminating the security risk of key reuse across different network nodes.
2Productivity
If handover signaling is forwarded via the HNB GW and terminated at the HNB GW, then the handover can be optimized, but the security problem of key separation will occur after UE is handed over from source HNB to target HNB
Solution Approach 1:
The SGSN acts as an intermediary that triggers the AKA procedure to ensure key separation. Even though the HNB GW handles the handover signaling, the SGSN intervenes by initiating the key update process, ensuring that the target HNB receives updated keys through the HNB GW, thus maintaining both handover optimization and security.
Solution Approach 2:
The AKA procedure is triggered in advance or during the handover process to update keys before the UE completes the handover to the target HNB. This ensures that when the handover is finalized, the target node already possesses the updated keys, preventing key separation security problems.
3Productivity
If handover signaling is directly transferred via the lur interface between HNBs, then the handover can be optimized, but the security problem of key separation will also occur when UE moves from HNB to another HNB in idle mode
Solution Approach 1:
The SGSN serves as a mediator that triggers the AKA procedure to update keys even when handover signaling is directly transferred between HNBs via the lur interface. This ensures that the key update process is initiated by a trusted core network element, maintaining security while allowing direct handover optimization between HNBs.
Data Source
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AI summary
A key separation method and device are provided in the embodiments of the present invention. The key separation method includes: when a User Equipment hands over from a source node to a target node, or when the User Equipment moves from the source node to the target node in idle state, determining whether or not the source node is a Home NodeB; and if the source node is a Home NodeB, triggering an Authentication and Key Agreement procedure according to the operator's policy, to update Ciphering Key and Integrity Key. By performing Authentication and Key Agreement procedure, the method and device of the embodiments seperate key of the source node from the key of the target node.