In Bluetooth Pairing Part 1: Pairing Feature Exchange, we talked about the pairing feature exchange in Bluetooth® with low energy. The pairing feature exchange is used to make both devices, initiator and responder, understand each other’s pairing features.

The pairing features that can be enabled are:

  • OOB Data Flag bit
  • MITM—Man-In-The-Middle bit
  • SC—LE secure connection indicator bit
  • IO Cap—IO Capabilities

*For an introduction to these features, please refer to Bluetooth Pairing Part 1: Pairing Feature Exchange.

After this exchange, both devices can select which key generation method is used in subsequent phases. Here is the list of key generation methods for Bluetooth LE legacy pairing and Bluetooth LE Secure Connection.

Bluetooth LE Legacy Pairing:

  • Just Works
  • Passkey
  • Out-of-Band(OOB)

Bluetooth LE Secure Connection includes the three methods above and adds one new one:

  • Numeric Comparison

Workflow

Here is the workflow on how a device decides which key generation method to use.

Step 1: Check SC bit in pairing feature exchange frame. If the SC bit is equal to 1 on both sides, an LE secure connection is used, go to step 2. Otherwise, it is LE legacy pairing, and go to step 3.

Step 2: When it is LE secure connection, below is the matrix that initiator and responder will follow.

  • “Use OOB” means Out-of-Band is selected.
  • “Check MITM” means ignore “OOB Data Flag” and check MITM flag, “Man-In-The-Middle” flag.
  • “Use IO Capabilities,” go to step 4 to select the key generation method depending on IO Capabilities of both devices.

Step 3: When it is LE legacy pairing, below is the matrix that initiator and responder will follow.

  • “Use OOB” means Out-of-Band is selected.
  • “Check MITM” means ignore “OOB Data Flag” and check the MITM flag, “Man-In-The-Middle” flag.
  • “Use IO Capabilities”, go to step 4 to select the key generation method depending on IO Capabilities of both device.

Step 4: Below is a mapping of the IO Capabilities to Key Generation Method. With this table, both devices, initiator and responder, will find an appropriate method for connecting depending on their pairing features.

After this, the initiator and responder understand the method that will be used in the key generation phase. In part 3, I will introduce how to generate the corresponding key in Bluetooth® LE legacy pairing by using the Passkey method.

FEATURED DOWNLOAD

Bluetooth 5: Go Faster, Go Further

Download this comprehensive overview to discover how Bluetooth 5 significantly increases the range, speed, and broadcast messaging capacity of Bluetooth applications, making use cases in smart home automation, enterprise, and industrial markets a reality.

INSTANT DOWNLOAD

Designing and Developing Bluetooth® Internet Gateways

Design and implement your own Bluetooth® Internet Gateway (BIG) working prototype and see for yourself how BIGs allow applications to exchange data with Bluetooth devices from anywhere in the world.

Wireless Connectivity Options for IoT Applications - Asset Tracking

If you recall from the previous article in this series, we covered the application…

How Bluetooth Technology Uses Adaptive Frequency Hopping to Overcome Packet Interference

Interference is one of the biggest challenges for any wireless technology in providing reliable…

A Technical Overview of LC3

An Introduction to LE Audio Over the past two decades, since its inception, Bluetooth®…

How Bluetooth Technology Creates Reliability From Unreliable Foundations

Figure 3a – A stack configuration supporting Bluetooth LE with GAP/GATT/ATT Bluetooth® enabled devices…

Bluetooth Mesh and DALI - Under the Hood

In my previous article on Bluetooth Mesh and DALI – the Perfect Match, we…

Bluetooth Mesh and DALI – The Perfect Match

In May 2020, the Bluetooth Special Interest Group (SIG) and DiiA (Digital Illumination Interface…

An Introduction to Bluetooth Low Energy for Swift Developers

All smartphones support Bluetooth® Low Energy (LE) and it is used in all manner…

Building a Sensor-Driven Lighting Control System Based on Bluetooth® Mesh

A technical examination of which Bluetooth mesh models to use in different types of…

Bluetooth Security and Privacy Best Practices Guide

This guide is intended to help implementers better understand why certain available security and…

Advanced Bluetooth for Android Developers

Android developers can take this guided tour of the most recent features and interesting…

How to Deploy BlueZ on a Raspberry Pi Board as a Bluetooth Mesh Provisioner

This step-by-step study guide will teach you: How to rebuild the kernel on a…

Discussing Bluetooth Range

Watch Nordic address some of the most common myths concerning Bluetooth range, discuss the…

The Bluetooth LE Security Study Guide

Learn about fundamental security concepts, the security features of Bluetooth Low Energy, and gain some hands-on experience using those features in device code.

Bluetooth Direction Finding: A Technical Overview

This comprehensive overview examines how two new Bluetooth direction finding methods can enable location services solutions that support high-accuracy.

 Get Help