Cannot pair with previously bonded peer when key is missing

[helpme]

I am using SDK_11 s130 ble_app_gls on nRF51-dk.

An Android phone running nRF-Connect app was able to pair and bond with nRF51-dk. First time doing pairing and bonding works fine. After the bonding information were deleted from the flash of nRF51-dk, the previously bonded Android phone was not able to connect to nRF51-dk. The bonding link keys are still intact at the phone side.

Here is the output from the UART of nRF51-dk.

Start encryption

link secure failed! error: PM_CONN_SEC_ERROR_PIN_OR_KEY_MISSING

Disconnecting

How can one force ble_app_gls to do pairing and bonding if one of the keys is missing from a previously bonded pair?

[Hung Bui]

Hi helpme,

As stated in the code: "How to handle this error is highly application dependent". It's up to the application and the central on how to deal with the situation.

If you have a look at the ble_app_proximity you can find that when that event happens PM_CONN_SEC_ERROR_PIN_OR_KEY_MISSING, we will not disconnect but request a new bond.

It's upto the central device to accept that or not.

The reason is that it expose a security risk that attacker can spoof the address of the peripheral device and request the central to do a new bond. If the central accepts that, the original authentic bond will be replaced.

The easiest to solve this it to let the end user to manually remove bond information on the phone (Forget this device)

[helpme]

Thanks for the answer. Can the source code of nRF-Connect Android app be modified such that it accepts the new request and replace the original authentic bond? I am worried this behavior is part of Android bluetooth stack and cannot be changed by the app source code.

[Hung Bui]

You are correct, this depends on the OS. I have experience for some Android OS version the bond information is removed automatically and the phone do a new bond. But it's not applied for all version and with all vendor. The app can't do anything with this. You need to tell the end customer to do "Forget this device" manually.

[selim]

What is the behavior on IOS? Can you please tell?