DBUS API error "Not paired" when attempting to read GATT characteristic

Hello all.

I was wondering whether someone could possibly help shine some light on an issue I'm having.

Here's the setup:
- Ubuntu 16.04 w/Bluez 5.37 (from the official repos, experimental
mode enabled)
- BBC micro:bit
- "hciconfig -a hci0":
hci0: Type: BR/EDR Bus: USB

	BD Address: XX:XX:XX:XX:XX:XX  ACL MTU: 1022:8  SCO MTU: 183:5
	UP RUNNING PSCAN
	RX bytes:718 acl:0 sco:0 events:54 errors:0
	TX bytes:3731 acl:0 sco:0 commands:54 errors:0
	Features: 0xff 0xfe 0x0d 0xfe 0xd8 0x7f 0x7b 0x8f
	Packet type: DM1 DM3 DM5 DH1 DH3 DH5 HV1 HV2 HV3
	Link policy: RSWITCH HOLD SNIFF
	Link mode: SLAVE ACCEPT
	Name: 'Io'
	Class: 0x4c010c
	Service Classes: Rendering, Capturing, Telephony
	Device Class: Computer, Laptop
	HCI Version: 4.1 (0x7)  Revision: 0x3101
	LMP Version: 4.1 (0x7)  Subversion: 0x1
	Manufacturer: Atheros Communications, Inc. (69)

What I am trying to do:
- Read some bytes from a characteristic on the micro:bit through
BlueZ's DBUS API using a Python script and the dbus module

The error I am getting:
- "org.bluez.Error.NotPermitted: Not paired"

I have paired the micro:bit both from the normal Ubuntu Bluetooth settings menu, and I have also paired it with the bluetoothctl tool, each on separate occasions. Both reported that the pair was successful (no pin was required however, compared to when I pair the micro:bit to my phone I do need the pin), however when I tried running my script (which does not check whether the device is paired or connected: this is performed by the user, and I can verify that both the Ubuntu settings and bluetoothctl reported it as both paired and connected), I get the afore mentioned error ("org.bluez.Error.NotPermitted: Not paired").

Is this, therefore, an error with my program (I have spent hours checking it and cannot find any errors)? Or a possible bug with BlueZ? There are very few resources online for this kind of thing so I ended up resorting to the Bluetooth mailing list - please notify me if this is the wrong kind of stuff to be asking.

The micro:bit is the only LE device which has ever connected to this (laptop) computer, and the characteristic (and its service) which I am reading from do both exist as DBUS objects. My grasp of the DBUS system is rather rudimentary, and so far has just been gained from BlueZ examples.

I have checked using the DBUS API to make sure that the device is both paired and connected - both said yes, but, as previously said I get an error (more specifically, an exception is thrown when I try to call "<DBUS interface to characteristic>.ReadValue()").

Is this my doing, or an issue with something out of my control? Any help will be appreciated :)

Hi Joe,

case BT_ATT_ERROR_AUTHENTICATION:
case BT_ATT_ERROR_INSUFFICIENT_ENCRYPTION:
case BT_ATT_ERROR_INSUFFICIENT_ENCRYPTION_KEY_SIZE:
return btd_error_not_permitted(msg, "Not paired");

So any of these errors could be causing the problem, perhaps it is the device that requires higher security.

How you are actually testing this, perhaps you should try using bluetoothctl:

Luiz Augusto von Dentz

Hello Luiz,

Unfortunately, with the above agent commands the device does not pair, and instead hangs. The btmon logs for the following three scenarios are available at https://gist.github.com/JoeGlancy/a5486660f2f59c627b6da32c810927f9:

- pairing the device through Ubuntu's default Bluetooth manager
- pairing the device through bluetoothctl without issuing the above
agent on/default-agent commands
- pairing the device through bluetoothctl, issuing the above `agent
on/default-agent` commands before issuing the pair command.