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Introduction to Pairing

This section teaches how to pair two Bluetooth devices using bluetoothctl - the command-line interface to BlueZ.

What is Pairing

In Bluetooth terminology pairing is the process of making two devices know about each other. The key concept is about exchanging so called link-keys that are used to secure the communication. The pairing process involves authentication however due to the nature and variety of Bluetooth devices there will be different ways of confirming the pairing attempt:

  • Devices such as keyboards or car-kits will require authentication by PIN/passkey code
  • Other devices will provide a yes/no choice to the pairing attempt
  • Devices without an input interface such as headsets or speakers will not require the user to confirm the pairing attempt at all

Pairing with a remote device can be done in two ways due to the fact that it can be initiated from both endpoints. Both ways are described further in this section.

Handling Authentication Requests by BlueZ

The pairing procedure includes an authentication that requires confirmation by the user. If you have ever used Bluetooth previously you probably remeber entering a pin code or answering a “would you like to connect yes/no” question.

To pair with other devices BlueZ uses an agent-style DBus API. See the following links for more details on this:

Within the bluetoothctl utility we can register such an agent with a specific IO capability with the BlueZ service and then process any further pairing operation.

If no agent is registered with BlueZ and a pairing operation happens, BlueZ will try to pair with the remote device without further user interaction.

The agent has to be registered explicitly by typing:

$ sudo bluetoothctl 
[bluetooth]# agent on 
Agent registered

The pairing section will walk you through the pairing procedure with a keyboard. It will require passcode authentication.

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