irk_match when having a BLE_GAP_EVT_CONNECTED

[Marcel Mulder]

Hi all,

I have made my own device manager because the device manager from Nordic is somewhat bloat (in code and resources) and I needed to add a feature, ranking the devices so the less used device is removed when the storage is full and a new devices wants to bond. I was not able to create this feature outside the device manager. Anyway, I want to test the manager and every thing is working well. The only thing I am not able to test is irk. I never see an irk_match. The devices gets identified by means of the address or by means of the diversifier. I find this rather strange be cause the iPhone uses a random address, so it should be identified with an irk. Does anybody knows why I do not get a irk_match in a connect event?

Thanks in advance,

Marcel

[Ulrich Myhre]

Hi,

You will only get an irk_match if you advertise or connect using a whitelist with IRKs in it (irk_count > 0). As a peripheral, the SoftDevice will resolve all devices trying to connect to or scan it and only respond if there is a hit in the address or IRK whitelists. As a central, the SoftDevice will process all connectable advertisers that use resolvable address types and match them before trying to connect

If a connection happens due to a match coming from the IRK part of the whitelist, the index to entry which was matched will be present in the irk_match field of the connected event.

[Ulrich Myhre]

In connection setup, the encryption diversifier plays no role. If you want to identify a device before connecting, you need to know the static peer address or its IRK. If you want to identify a (previously bonded) device by the means of instantly encrypting, then that is a way. The master sends the previously agreed-upon diversifier and you look up the LTK that belongs to it. These are the keys you need to store to be able to identify the master for encryption. A table of LTKs, indexed by the div. The device manager's device_instance_find() is only called when encryption has been started by the master.

In newer variants of the SoftDevice, we abandoned the combined diversifier approach and ask you to instead look up the LTK based on an EDIV and RAND which is sent from the master.