Having Problem with encryption on iOS nRF51822

[Soan]

I am creating an iOS which needs to talk with nRF51822 Soft devices 100.

Problem i am facing is, I am not able to Encrypt the connection properly.

I am using

- security mode = 1 and level = 1 (open) for all custom characteristics, except level = 2 (encryption with no MITM protection) for notifications.

My iOS app can Discover the services/Characteristics.

When i try to Read/Write the data on Characteristics. i am able to do so without any kind of encryption.

When i try to Subscribe to Notifications iOS raises an alert if user wants to pair to Device. And everything works fine if user accepts Pairing.

But once I kill iOS App. i can see inside iOS logs that device adds the Device to RemoveFromWhiteList list. Which from sound of it looks like iOS is throwing away the keys.

And eventually if i try to reOpen the App. App is never able to connect to the BLE device.

iOS App acts like a Central.

BLE Device is Peripheral.

When looking at Wireshark Packets the logs which i can see are

Encrypted packet decrypted incorrectly (bad MIC)

Which is expected as iOS has thrown away the Keys and BLE Peripheral is still using the same keys.

Will appreciate any help regarding to this. It feels to me that some kind of encryption i am doing wrong.

Can i add encryption on connection level so that Pairing alert is raised during connection time.

Or Encryption is only defined on each characteristic.

I am facing this issue on iOS 10.3.3, iPhone 5.

[Soan]

We see the issue across all 3 iOS devices we have used in our testing, but the behaviour is slightly different across devices - they fail at different points. The WireShark logs show the following failure points when our custom app tries to reconnect with the aid:

- iPhone 7 (iOS 12.1.2) fails on CONNECT_REQ (frame 302)

- iPad 4 (iOS 10.3.3) fails on LL_VERSION_IND (frame 524)

- iPhone 5 (iOS 10.3.3) fails on LL_START_ENC_RSP (frame 559)

The test procedure that was followed to produce these logs was as follows:

a. Clear Devices from iOS Bluetooth Settings
b. Run the App
c. Search for Devices
d. Connect to Device
e. Subscribe to Notifications
f. Accept Pairing Alert Raised by iOS Platformg

g. Everything works fine(Read/Write Data)
h. Kill iOS Mobile APP
i. Disconnections Happens
j. Restart App
k. App Tries to Connect again to old Remembered Device.
l. App Never gets Connected

Today we noticed that the issue does not occur most of the time (but not all of the time) if we clear the bond table in the nRF51822 - can you confirm whether an overflowing bond table could be the cause of such re-connection issues?

[Vidar Berg]

Soan said:

Today we noticed that the issue does not occur most of the time (but not all of the time) if we clear the bond table in the nRF51822 - can you confirm whether an overflowing bond table could be the cause of such re-connection issues?

It depends on how it is implemented. Bonds are managed by the application code, not by the bluetooth stack. I think you need to debug the application FW to figure out why the disconnects occur.