How to identify if a previously bonded phone is white listed if the phone removes the pairing information

[jcowfer]

I'm working on a project that requires my device to be able to identify when a phone connects that has been previously bonded and placed in the white list. I need to be able to identify this whether or not the phone still has bond information stored. Is this possible? If so how would I achieve this? I've played some with using central_find_in_db(..) in the on_connect() function (both are part of ble_bondmanager.c), but haven't had any success.

I'm currently using ble_bondmanager from nRF51f SDK 5.2.0 to handle the bonding process and information.

In short: I want to detect if my device has ever seen the phone previously regardless of whether or not the phone has any of the bond information stored. How would I achieve this if possible?

Update 1: I can insert the following lines of code inside on_connect() in ble_bondmanager.c and this works for most scenarios. However in testing I found that this will run into a problem if on iOS the bond information is removed from the phone and Bluetooth is disabled and re-enabled. After disabling and re-enabling the phone is always viewed as a new phone upon re-connection. I'm still investigating how to work around that.

---

device_state.new_phone = true;
   
// For each whitelisted device
for (int i = 0; i < m_centrals_in_db_count; i++)
{
   // check each byte of the device address
   for (int j = 0; j < BLE_GAP_ADDR_LEN; j++)
   {
      // if bytes don't match break
      if (m_central.bond.central_addr.addr[j] != m_centrals_db[i].bond.central_addr.addr[j])
         break;
      
      // If they all match, then this isn't a new phone
      if (j == BLE_GAP_ADDR_LEN-1)
         device_state.new_phone = false;
   }
   
   // If we've determined this isn't a new phone break
   if (!device_state.new_phone)
      break;
}

---

[Petter Myhre]

iOS uses private random resolvable addresses. The addresses used can be resolved if you have the Identity Resolving Key (IRK). The IRK can be put into the whitelist, but it is only shared when you bond, and is only valid as long as the bond exist. So what you are trying to do is not really possible.

[jcowfer]

So there is no way to determine if an iOS device has previously bonded with my device, unless a bond still exists between them?

This seems consistent with what I've seen. Disabling and re-enabling the Bluetooth will cause the phone to be viewed as a new phone, and letting them sit for over a day without disabling Bluetooth also causes the phone to be seem as a new peer.

[Petter Myhre]

This address type is used so that devices can't recognize the iOS device when they don't have a bond. It is a privacy feature.

[jcowfer]

Would there be any other way to identify a previously connected device apart from a BT Address that could be used if bond information is removed? Something that may get transferred during connections or bonding?

[Petter Myhre]

I guess you can implement something in the application space, but the only way to get the IRK (and know that the IRK is valid) is to bond. You need the IRK to do whitelisting.