The difference between first connection and PM_CONN_SEC_ERROR_PIN_OR_KEY_MISSING?

[Elias]

I'm developing a device that's supposed to establish an encrypted connection with an Android device and I've gotten PM_CONN_SEC_ERROR_PIN_OR_KEY_MISSING during connecting a few times after programming a new app and reprogramming the SoftDevice. How is "this bond" identified?

I understand that I've erased the LTK, but why doesn't the device behave like it's their first-ever connection? AFAIK, I erase the whole chip when I reprogram the SD, but I sometimes still get the event on the very next connection. My device's MAC address should be new after every reset, so what's getting recognized? What information about "this bond" could be sticking around?

[Petter Myhre]

Are you talking about PM_CONN_SEC_ERROR_PIN_OR_KEY_MISSING? Have you erased the bond on the Android device? Have you modified the SDK examples so that the device address is actually changing?

[Elias]

Yes, that's the event I'm talking about. Yes, the device is using BLE_GAP_ADDR_TYPE_RANDOM_PRIVATE_RESOLVABLE. I have not erased the bond on the Android, but I don't understand how the info is still associated with the Peripheral.

[Petter Myhre]

I suspect that the resolvable address are derived from the IRK that was distributed to the Android device. The Android device is able to resolve the address with this IRK and believes that it is bonded. What SDK and SoftDevice version are you using?

[Elias]

The IRK may indeed be what I was looking for. I'm using SDK 12.1, s132 v3.0.0

[Petter Myhre]

I think my suspision is correct. The default IRK used by the SoftDevice will not change (but it will be random for every device). You could try to set the IRK to something else, and check if that changes anything. You can set it with sd_ble_gap_privacy_set().