HCI bluetooth can pair initially, but re-starting encryption always ends with 0x3D MIC failure
I have been trying to implement a HCI only interface (LL only set) and pass commands to my board (STM32WB55 Nucleo board - BTStack is the bluetooth stack). Everything works except for the following sequence
-> Connect, pair and bond with Just works (LE Secure Connections)
-> Communicate
->Disconnect
-> Reconnect, skip pairing and use LTK from the first session
-> The stack sends the LE_START_ENCRYPTION command with the LTK from the first pairing (fine) but the target immediately shuts down the connection and reports a MIC (Message Integrity Code) failure (0x3D).
Ive tried different stacks and different versions, and it always ends the same way.
This all works perfectly with an off-the-shelf dongle. When I use the LL only flag, do I need to store pairings somehow? Is there security information I need to manage?