Possibilities to deploy pre Initialized Images (Pre-Set TK or LTK) in BLE

[mario134]

Hello,

A theoretical question at this point, but I read that there are some possibilities to set a Passkey or OoB, but I am more interested in skipping the entire Pairing process and set or change (if the pairing process is also responsible for creating the mesh network) the TK or better yet LTK myself.

Is it possible to create pre Initialized Images to be deployed to the nodes or if not, is it possible to alter the LTK at a later point?

Thanks a lot

[endnode]

It must be, it's the same like if you do pairing&bonding (= provision long-term secrets and save "names"), disconnects and reset nRF5x chip. You then need to start the stack again after next boot and provision all the peers. So you can indeed load these data in front and then just use them. The biggest problem of BLE pairing is "peer-to-peer" topology (the only one supported in Bluetooth - regardless if classic or LE - at the moment until BT SIG standardize some mesh networking or similar architecture) so you need to know name aka MAC address of all the peers, not only LTK. If you know it then fine but I'm afraid you will hardly log all the MAC addresses of all your devices into flash during the production. So using OOB with pre-provisioned "shared" key is usable (although not recommended practice because once someone compromises one device all your devices are compromized at the same moment because of shared symmetric key) for large pool of devices but you still need to pass pairing procedure, otherwise you can pre-provision full pairing/bonding structure but that doesn't scale above few dozens of devices.