Can Bonding Info Be Shared?

[c cook]

We are working on a BLE home automation application. It is likely that some homes could have 10 or more of our devices. We also need to allow the homeowner control of which central devices can connect and control our product. We currently are using bonding, the user needs to have physical access to the device to create the bond. That's all working. The issue is this: Let's assume there are 10 of our devices in the home, and the family has 3 smartphones and 2 tablets. Each phone/tablet would have to be individually bonded to each of our devices. That equates to 50 bondings. That could become very tedious, depending on the number of centrals and peripherals the home has.

Is there a way that the user, could take one phone, bond to each of the 10 devices, and then share that information with other phones and tablets, so that the bonding process only has to occur once per peripheral? Thanks

[Hung Bui]

@Ccook: I would say it's possible to do on the nRF51 side to share keys between devices such as same LTK for different central. But I am not sure it's straigh forward to do on the central phone/tablet side. How do you share bond information between phones ? It's not accessible or controllable by the app.

The solution I'm thinking of is to implement your own proprietary security system that you can encrypt and decrypt using your app. Doing so, you can easily share security keys between phones.

[c cook]

Hung Bui - Thanks, and I'm afraid I have to agree with you. I've been unsuccessful in finding anything, that would work. We are looking into the best approach to do our own proprietary method. Another option I'm investigating is - the first phone would bond using a button on the device. After bonding the device would provide the phone a unique passkey. The passkey could be distributed to other phones and tablets. When these new phones connect to the device the first time, they would provide the passkey to bond. iOS requires that they confirm they want to connect to the device, but it would be a much simpler and quicker method than having to physically go to each device and press the button. I should mention, it is possible that some of these devices could be in hard to reach locations, which is another concern.

[Hung Bui]

@ccook: I assume the "passkey" you mentioned here is the key that can trigger the device to allow bonding with the new phone ? Not the passkey needed when doing passkey bonding ( the 6 digit passkey)

If it's the case I don't think it's very safe. First, you can't use whitelist, because if you have whitelisting you won't be able to connect your new phone to the device at the first place.

Second, one can easily sniff the unencrypted trafic and can find your magic passkey and can reuse it later on to bond with your device.

My suggestion is that you have a secret key that the bonded device need to write to the device so that it switch to "open" mode where a new phone can be connected and bond to the device. Your device only start in "open" mode on the first run or when it receives that secret key. The draw back is you always need a bonded device to allow a new bond.