TI’s BLE stack caches and reuses the LTK’s property for a bonded mobile

TI’s BLE stack caches and reuses the LTK’s property for a bonded mobile. A LTK can be an unauthenticated-and-no-MITM-protection key created by Just Works or an authenticated-and-MITM-protection key created by Passkey Entry, Numeric Comparison or OOB. Assume that a victim mobile uses secure pairing to pair with a victim BLE device based on TI chips and generate an authenticated-and-MITM-protection LTK. If a fake mobile with the victim mobile’s MAC address uses Just Works and pairs with the victim device, the generated LTK still has the property of authenticated-and-MITM-protection. Therefore, the fake mobile can access attributes with the authenticated read/write permission.