Mitigating Cross-Transport Key Derivation Attacks in Bluetooth Communication
Mohammad Ali, Jielun Zhang, Ye Feng · 2023
Bluetooth wireless technology is a communication framework implemented using an open standard. The standard introduces the cross-transport key derivation (CTKD) function in Bluetooth 4.2 to improve redundancy and the security mechanism of the protocol. CTKD allows the creation of pairing keys for both Bluetooth Classic (BT) and Low Energy (BLE) given pairing over one of the protocols. However, unintended sessions and impersonation attacks, e.g., BLUR, can be triggered on an established Bluetooth connection for devices that implement CTKD due to a lack of proper safeguard measures enforced in the Bluetooth standard. To mitigate the threat, we propose modifications to the open-source Android Bluetooth stack to prevent key overwrites across transports from CTKD. Moreover, we propose a framework design that aims to assign more controllability to end users over simultaneous BT and BLE connections. A real-world testbed is also designed and can be further used to evaluate the performance of our proposed countermeasures regarding the mitigation of BLUR attacks through our modified Android Bluetooth stack.