Bluetooth pairing and connection

How does Bluetooth pairing work?

This seems to be inaccurate, so would anyone be able to either expand further or actually explain how/what is communicated to result in a successful pairing of the devices?

I was thinking of incorporating some of this research into a final year project (University), but would at least need to know the something of the Bluetooth programming pairing first.

Any help would be much appreciated in describing how these initial communications work.

I’ve heard of terms such as ‘parked mode’, and ‘passive mode’ within my research, but am yet to find any ‘useful’ information in the programming behind the design, (and hence I have asked this question). The likes of googling this type of topic is also quite difficult as it seems to bring up stuff like ‘how to turn your bluetooth on’ pages, and not the design of the programming behind it.

Your question is just so broad I find it difficult to answer. Do you want to know the RF level? The link control level? The higher level protocols? All? But I do have a recommendation for a pretty good book that covers all of these in great detail. It was published in 2002 so doesn’t cover Bluetooth Low Energy. But it does cover the fundamental BT operation from the RF level up. «Bluetooth Operation and Use» by Robert Morrow.

2 Answers 2

Bluetooth Secure Simple Pairing uses Elliptic Curve Diffie Hellman (ECDH) public key cryptography with approximately 95 bits of entropy using the FIPS approved P192 elliptic curve.

The following parameters are given:

• The prime modulus p, order r, base point x-coordinate Gx, base point y- coordinate Gy.
• The integers p and r are given in decimal form; bit strings and field elements are given in hex.

p = 6277101735386680763835789423207666416083908700390324961279 r = 6277101735386680763835789423176059013767194773182842284081 b = 64210519 e59c80e7 0fa7e9ab 72243049 feb8deec c146b9b1 Gx = 188da80e b03090f6 7cbf20eb 43a18800 f4ff0afd 82ff1012 Gy = 07192b95 ffc8da78 631011ed 6b24cdd5 73f977a1 1e794811 

There are five phases of Secure Simple Pairing:

1. Public key exchange

Each device generates its own Elliptic Curve Diffie-Hellman (ECDH) public-private key pair.

2. Authentication Stage 1

1 of 3 protocol options is chosen by the connecting devices based on the IO capabilities of the two devices. These are:

3. Authentication Stage 2

Each device confirms that both devices have successfully completed the exchange as stipulated by which of protocol was chosen and used in the previous step.

4. Link key calculation

A link key is computed from the derived shared key and the publicly exchanged data. This is the numeric code shown to the user.

5. LMP Authentication and Encryption

The encryption keys are generated. The devices are successfully connected.

Further Reading:

• Bluetooth user Interface Flow Diagrams for Bluetooth Secure Simple Pairing Devices (PDF)
• Bluetooth Core Complete Specification v4.0 vol0 (ZIP/PDF)the core specification is 138 pages and to fully answer your question would take at least 20 so to fully answer your question you’ll need to read the references

A trusted relationship is established between the devices using a numerical password, commonly referred to as a passkey. Depending on how often one Bluetooth device connects to another, the user might opt to have the passkey saved for future connection attempts or prompt to enter the passkey each time the devices request communication with each other.

For two devices to have the ability to pair, they must share the same bluetooth profile. The following is from the official Bluetooth website:

Pairing devices

Not all Bluetooth enabled devices are designed to be paired. Logically, there’s no reason to connect a wireless mouse to a wireless headset. You should be able to pair a Bluetooth enabled headset to a Bluetooth enabled phone, or a Bluetooth enabled mouse to a Bluetooth enabled computer.

If you’re not sure whether the two devices you want to connect are designed to be paired with each other, make sure their Bluetooth profiles match.

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Pair a Bluetooth device in Windows

You can pair all kinds of Bluetooth devices with your PC—including keyboards, mice, phones, speakers, and a whole lot more. To do this, your PC needs to have Bluetooth. Some PCs, such as laptops and tablets, have Bluetooth built in. If your PC doesn’t, you can plug a USB Bluetooth adapter into the USB port on your PC to get it.

Before you start, make sure that your Windows 11 PC supports Bluetooth. For more info on how to check, see Fix Bluetooth problems in Windows. If you need help adding a device without Bluetooth capabilities, see Add a device to a Windows PC.

Turn on Bluetooth

After you’ve checked that your Windows 11 PC supports Bluetooth, you’ll need to turn it on. Here’s how:

• In Settings: Select Start >Settings >Bluetooth & devices , and then turn on Bluetooth .
• In quick settings: To find the quick setting for Bluetooth, select the Network, Sound, or Battery icons ( ) next to the time and date on the right side of your taskbar. Select Bluetooth to turn it on. If it’s turned on without any Bluetooth devices connected, it might appear as Not connected .

To pair a Bluetooth device

1. Turn on your Bluetooth device and make it discoverable. The way you make it discoverable depends on the device. Check the device or visit the manufacturer’s website to learn how.
2. On your PC, select the Network , Sound, or Battery icons ( ) next to the time and date on the right side of your taskbar.
3. Select Manage Bluetooth devices on the Bluetooth quick setting, then select your device under New devices.

Follow additional instructions if they appear, then select Done.

Your Bluetooth device and PC will usually automatically connect anytime the two devices are in range of each other with Bluetooth turned on.

Tip: If you don’t see the Bluetooth device you want displayed in the list, you may need to set the Bluetooth devices discovery setting to Advanced. To learn how, see Fix Bluetooth problems in Windows.

To pair a Bluetooth printer or scanner

1. Turn on your Bluetooth printer or scanner and make it discoverable. The way you make it discoverable depends on the device. Check the device or visit the manufacturer’s website to learn how.
2. Select Start >Settings >Bluetooth & devices >Printers & scanners >Add device. Wait for it to find nearby printers, choose the one you want to use, then select Add device.

If you’re having problems installing your printer or scanner, see either Fix printer problems or Install and use a scanner in Windows.

To pair a Bluetooth device using Swift Pair

Swift Pair in Windows 11 lets you quickly pair a supported Bluetooth device with your PC. If the Bluetooth device supports Swift Pair, you’ll receive a notification when it’s nearby and you put it into pairing mode to make it discoverable.

1. Turn on a Bluetooth device that supports Swift Pair and make it discoverable. The way you make it discoverable depends on the device. Check the device or visit the manufacturer’s website to learn more.
2. If this is your first time using Swift Pair, select Yes when asked if you want to get notifications and use Swift Pair.
3. When a notification appears that a new Bluetooth device was found, select Connect.

Before you start, make sure that your Windows 10 PC supports Bluetooth. For more info on how to check, see Fix Bluetooth problems in Windows 10. If you need help adding a device without Bluetooth capabilities, see Add a device to a Windows 10 PC.

Turn on Bluetooth

After you’ve checked that your Windows 10 PC supports Bluetooth, you’ll need to turn it on. Here’s how:

In Settings: Select Start > Settings > Devices > Bluetooth & other devices, and turn on Bluetooth.

In action center: Action center can be found next to time and date on your taskbar. On the taskbar, select action center ( or ), then select Bluetooth to turn it on. If it’s turned off, it might appear as Not connected.

If you don’t see Bluetooth in your action center, here’s how you can change it:

• Expand quick actions. On the taskbar, select action center ( or ) >Expand. Bluetooth should appear here. It will appear as Bluetooth or Not connected.
• Add Bluetooth to action center. Select Start >Settings >System >Notifications & actions >Quick actions. Go to Add or remove quick actions and turn on Bluetooth.

Note: For more info about how to change the apps and settings that appear in action center, see Change notification and action settings in Windows 10.

To pair a Bluetooth headset, speaker, or other audio device

1. Turn on your Bluetooth audio device and make it discoverable. The way you make it discoverable depends on the device. Check the device or visit the manufacturer’s website to learn how.
2. On your PC, select Start >Settings >Devices >Bluetooth & other devices >Add Bluetooth or other device >Bluetooth. Choose the device and follow additional instructions if they appear, then select Done. Your Bluetooth device and PC will usually automatically connect anytime the two devices are in range of each other with Bluetooth turned on.

To pair a Bluetooth keyboard, mouse, or other device

1. Turn on your Bluetooth keyboard, mouse, or other device and make it discoverable. The way you make it discoverable depends on the device. Check the device or visit the manufactur’s website to learn how.
2. On your PC, select Start >Settings >Devices >Bluetooth & other devices >Add Bluetooth or other device >Bluetooth. Choose the device and follow additional instructions if they appear, then select Done.

To pair a Bluetooth printer or scanner

1. Turn on your Bluetooth printer or scanner and make it discoverable. The way you make it discoverable depends on the device. Check the device or visit the manufacturer’s website to learn how.
2. Select Start >Settings >Devices >Printers & scanners >Add a printer or scanner. Wait for it to find nearby printers, then choose the one you want to use and select Add device.

If you’re having installation issues with your printer or scanner, see either Fix printer problems or Install and use a scanner in Windows 10.

To pair a Bluetooth device using Swift Pair

Swift Pair in Windows 10 lets you quickly pair a supported Bluetooth device with your PC. If the Bluetooth device supports Swift Pair, you’ll receive a notification when it’s nearby and you put it into pairing mode to make it discoverable.

1. Turn on a Bluetooth device that supports Swift Pair and make it discoverable. The way you make it discoverable depends on the device. Check the device or visit the manufacturer’s website to learn more.
2. If this is your first time using Swift Pair, select Yes when asked if you want to get notifications and use Swift Pair.
3. When a notification appears that a new Bluetooth device was found, select Connect.
4. After it’s connected, select Close.

Tip: If you’re a small business owner looking for more information on how to get Microsoft 365 set up, visit Small business help & learning.

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