Secure connection between nRF51822 and Android Smartphone?

[Christoph Inhestern]

Hello, i'm programming an android app to connect to the nRF51822 (peripheral). Without any security or pairing settings everything works fine. The Problem: Any kind of authentication and encryption is needed, but in the final Product the nRF51822 has no display or keyboard. Is there any way to establish a secure, authenticated connection to the Chip under that conditions?

In addition to the problem, what is the difference between the "Properties" and the "Permissions" of a Characteristic and what are they used for?

[Christoph Inhestern]

Thank you for your helpful answer, Hung Bui.

Unfortunately I don't get a "Insufficient Authentication" error (Code 5) in the Android app, instead there occurs error code 137 (0x89: GATT_AUTH_FAIL?). Although the solution works anyway it would be interesting to know what's the reason for this!?

I have one more (off topic) question: Is there any way to abort the connection to an already paired device?

[Christoph Inhestern]

I tried it the way you described:

1. Android device tries to read a Characteristic which permissions (read/write) are set to BLE_GAP_CONN_SEC_MODE_SET_ENC_NO_MITM. That returns 137 (sometimes 133 with Connection loss). By the way, I recognized that MasterControlPanel gets the right error.
2. After that a Broadcast Receiver on the Android device is waiting for a BluetoothDevice.ACTION_BOND_STATE_CHANGED with state == BluetoothDevice.BOND_BONDED.
3. By this event the App tires to read the initial Characteristic again. If this returns GATT_SUCCESS, the app state is set to connected.

After the bonding process the user has to identify by a numeric code and if this fails i want to disonnect from the nRF51822 (peripheral). The disconnect has to be initiated by the nRF51822, is that possible?