Bluetooth® LE peripheral privacy

This code example demonstrates the privacy features available to users in Bluetooth® 5.0 and above using ModusToolbox™ software.

Features demonstrated:

1. Privacy modes as defined in Bluetooth® spec 5.0 and above.
2. Use of persistent storage for bond data management.
3. Management and handling of bond data of multiple peer devices.

View this README on GitHub.

Provide feedback on this code example.

Requirements

• ModusToolbox™ software v2.4 or later (tested with v2.4)

• Board support package (BSP) minimum required version: 3.0.0

• Programming language: C

• Associated parts: AIROC™ CYW20819 Bluetooth® & Bluetooth® LE system-on-chip, AIROC™ CYW20719 Bluetooth® & Bluetooth® LE system-on-chip, AIROC™ CYW20820 Bluetooth® & Bluetooth® LE system-on-chip, AIROC™ CYW20835 Bluetooth® & Bluetooth® LE system-on-chip

Supported toolchains (make variable 'TOOLCHAIN')

• GNU Arm® embedded compiler v9.3.1 (GCC_ARM) - Default value of TOOLCHAIN

Supported kits (make variable 'TARGET')

• CYW920820M2EVB-01 evaluation kit (CYW920820M2EVB-01)- Default value of TARGET
• CYW920835M2EVB-01 evaluation kit (CYW920835M2EVB-01)
• CYW920819M2EVB-01 evaluation kit(CYW920819M2EVB-01)
• CYW989820M2EVB-01 evaluation kit(CYW989820M2EVB-01)
• CYW920819EVB-02 evaluation kit (CYW920819EVB-02)
• CYW920820EVB-02 evaluation kit (CYW920820EVB-02)
• CYW920719B2Q40EVB-01 evaluation kit (CYW920719B2Q40EVB-01)

Hardware setup

This example uses the board's default configuration. See the kit user guide to ensure that the board is configured correctly.

Software setup

Install a terminal emulator if you don't have one. Instructions in this document use Tera Term. All other required software comes bundled with the ModusToolbox™ software.

Using the code example

Create the project and open it using one of the following:

In Eclipse IDE for ModusToolbox™ software

1. Click the New Application link in the Quick Panel (or, use File > New > ModusToolbox Application). This launches the Project Creator tool.

2. Pick a kit supported by the code example from the list shown in the Project Creator - Choose Board Support Package (BSP) dialog.

   When you select a supported kit, the example is reconfigured automatically to work with the kit. To work with a different supported kit later, use the Library Manager to choose the BSP for the supported kit. You can use the Library Manager to select or update the BSP and firmware libraries used in this application. To access the Library Manager, click the link from the Quick Panel.

   You can also just start the application creation process again and select a different kit.

   If you want to use the application for a kit not listed here, you may need to update the source files. If the kit does not have the required resources, the application may not work.

3. In the Project Creator - Select Application dialog, choose the Bluetooth®LE_Peripheral_Privacy application by enabling the checkbox.

4. (Optional) Change the suggested New Application Name.

5. The Application(s) Root Path defaults to the Eclipse workspace which is usually the desired location for the application. If you want to store the application in a different location, you can change the Application(s) Root Path value. Applications that share libraries should be in the same root path.

6. Click Create to complete the application creation process.

For more details, see the Eclipse IDE for ModusToolbox™ software user guide (locally available at {ModusToolbox™ software install directory}/ide_{version}/docs/mt_ide_user_guide.pdf).

In command-line interface (CLI)

ModusToolbox™ software provides the Project Creator as both a GUI tool and the command line tool, "project-creator-cli". The CLI tool can be used to create applications from a CLI terminal or from within batch files or shell scripts. This tool is available in the {ModusToolbox™ software install directory}/tools_{version}/project-creator/ directory.

Use a CLI terminal to invoke the "project-creator-cli" tool. On Windows, use the command line "modus-shell" program provided in the ModusToolbox™ software installation instead of a standard Windows command-line application. This shell provides access to all ModusToolbox™ software tools. You can access it by typing modus-shell in the search box in the Windows menu. In Linux and macOS, you can use any terminal application.

This tool has the following arguments:

Argument	Description	Required/optional
--board-id	Defined in the <id> field of the BSP manifest	Required
--app-id	Defined in the <id> field of the CE manifest	Required
--target-dir	Specify the directory in which the application is to be created if you prefer not to use the default current working directory	Optional
--user-app-name	Specify the name of the application if you prefer to have a name other than the example's default name	Optional

The following example will clone the "BTSDK Peripheral Privacy" application with the desired name "BTSDKPeripheralPrivacy" configured for the CYW920820M2EVB-01 BSP into the specified working directory, C:/mtb_projects:

project-creator-cli --board-id CYW920820M2EVB-01 --app-id mtb-example-btsdk-peripheral-privacy --user-app-name BTSDKPeripheralPrivacy --target-dir "C:/mtb_projects"

Note: The project-creator-cli tool uses the git clone and make getlibs commands to fetch the repository and import the required libraries. For details, see the "Project creator tools" section of the ModusToolbox™ software user guide (locally available at {ModusToolbox™ software install directory}/docs_{version}/mtb_user_guide.pdf).

In third-party IDEs

Use one of the following options:

• Use the standalone Project Creator tool:

  1. Launch Project Creator from the Windows Start menu or from {ModusToolbox™ software install directory}/tools_{version}/project-creator/project-creator.exe.

  2. In the initial Choose Board Support Package screen, select the BSP, and click Next.

  3. In the Select Application screen, select the appropriate IDE from the Target IDE drop-down menu.

  4. Click Create and follow the instructions printed in the bottom pane to import or open the exported project in the respective IDE.

• Use command-line interface (CLI):

  1. Follow the instructions from the In command-line interface (CLI) section to create the application, and then import the libraries using the make getlibs command.

  2. Export the application to a supported IDE using the make <ide> command.

  3. Follow the instructions displayed in the terminal to create or import the application as an IDE project.

For a list of supported IDEs and more details, see the "Exporting to IDEs" section of the ModusToolbox™ software user guide (locally available at {ModusToolbox™ software install directory}/docs_{version}/mtb_user_guide.pdf).

Operation

1. Connect the board to your PC using the provided USB cable through the USB connector.

2. Open a terminal program and select the COM port. Set the serial port parameters to 8N1 and 115200 baud.

3. Program the board using one of the following:

   Using Eclipse IDE for ModusToolbox™ software

   1. Select the application project in the Project Explorer.

   2. In the Quick Panel, scroll down, and click <Application Name> Program.

   Using CLI

   From the terminal, execute the make program command to build and program the application using the default toolchain to the default target. The default toolchain and target are specified in the application's Makefile but you can override those values manually:

   make program TARGET=<BSP> TOOLCHAIN=<toolchain>
   

   Example:

   make program TARGET=CYW920819EVB-02 TOOLCHAIN=GCC_ARM
   

4. The application runs a custom button service with one custom characteristic that counts the number of button presses on the kit. It can be read or setup for notifications. Each time the button on the kit is pressed, the count value is incremented. If any device is connected and has notifications enabled, the updated value is sent to it. If no device is connected or notifications are disabled a message informing the same is displayed.

NOTE: The button count is incremented on the button press irrespective of whether any device is connected or not.

5. Following instructions appear on the terminal on application start:

   • Press 'l' to check for the number of bonded devices and next empty slot

     • This option allows you to see how many devices are paired to the peripheral and which is the next available slot. This example supports up to four bonded devices after which the oldest devices data is overwritten.

   • Press 'r' to erase all the bond data present in NVRAM

     • This option allows user to clear the memory of all the present bond data.

   • Press 'e' to enter the bonding mode and add devices to bond list

     • This option puts the peripheral into bonding mode allowing it to connect and bond with new devices. After connection and bonding, the incoming device can read and subscribe to the custom button count service.

   • Press 'p' to change privacy mode of bonded device

     • This is used to change the privacy mode setting of the bonded devices i.e., to move devices from device privacy mode to netwok privacy mode and vice versa. For more information about the privacy modes, read the design and implementation section.

   • Press 'h' any time in application to print the menu

     • At any point in the program to look at the available options, user can request the start menu options.

     Use these available commands to interact with the application. Refer Figure 2 for the application flow chart.

Design and implementation

The objective of the application is to demonstrate how the user can make use of privacy features available in the Bluetooth® devices.

Bluetooth® devices implement privacy mainly by using different types of addresses: public, which means no privacy, or random. Random addresses can be static (which don't change) or private (which change periodically, offering privacy protection). Private addresses can be further divided into non-resolvable or resolvable.

The use of resolvable private addresses allows only the devices that are paired to your device to "identify" the device as a known device; all other devices will perceive the device as a new device, making it difficult to track. If the device uses non-resolvable private address, it will be perceived as a new device every time it changes its address. The address is changed at regular intervals and is configurable.

Every privacy-enabled Bluetooth®LE device has a unique address called the identity address and an identity resolving key (IRK). The identity address is the public address or static address of the Bluetooth®LE device. The IRK is used by the BLE device to generate its resolvable private address (RPA) and is used by peer devices to resolve the RPA of the Bluetooth® LE device. Both the identity address and the IRK are exchanged during the pairing process. Privacy-enabled Bluetooth® LE devices maintain a list that consists of the peer device’s identity address, the local IRK used by the Bluetooth® LE device to generate its RPA, and the peer device’s IRK used to resolve the peer device’s RPA. This is called the resolving list. Only peer devices that have the 128-bit identity resolving key (IRK) of a Bluetooth® LE device can determine the device's address.

Maximum resolving list size supported on different devices is:

• CYW20819 : 20 entries

• CYW20820 : 20 entries

• CYW20735B1 : 128 entries

• CYW20719B2 : 128 entries

  Figure 1. Bluetooth® LE address types

  

Apart from this, Bluetooth® 5.0 introduced more options in the form of privacy modes.

There are two modes of privacy: device privacy mode and network privacy mode.

A device in device privacy mode is only concerned about the privacy of the device and will accept advertising/connection packets from peer devices that contain their identity address and a private address, even if the peer device has distributed its identity resolution key (IRK) in the past.

In network privacy mode, a device will only accept advertising/connection packets from peer devices that contain private addresses. By default, network privacy mode is used when private addresses are resolved and generated by the controller.

Table 1 shows the logical representation of the resolving list when a device that is trying to reconnect the controller checks the resolving list for the device. Depending on the result two things can happen as follows:

1. Device is found in the list.

Advertisement/Connection address type	Privacy mode	Request accepted/rejected
Identity address	Network	Rejected
Identity address	Device	Accepted
Resolvable private address	Network	Accepted
Resolvable private address	Device	Accepted

2. Device is not found in the list.

   In this case, the incoming device is treated as a new device and the request is forwarded to the host by the controller for further processing.

Note: A device using non-resolvable private address will be treated as a new device on every reconnection.

Table 1. Logical representation of resolving list entries

Device	Local IRK	Peer IRK	Peer identity address	Identity address type	Privacy mode
1	Local IRK	Peer 1 IRK	Peer 1 identity address	Static/public	Network/device
2	Local IRK	Peer 2 IRK	Peer 2 identity address	Static/public	Network/device
3	Local IRK	Peer 3 IRK	Peer 3 identity address	Static/public	Network/device

The application runs a custom button service with one custom characteristic that counts the number of button presses on the kit. It can be read or setup for notifications. The GATT DB is setup so that the characteristic can be read without pairing/bonding but for enabling and disabling notifications pairing/bonding is required. When the button on the kit is pressed every time, the count value is incremented. If any device is connected and has notifications enabled the updated value is sent to it. If no device is connected or notifications are disabled, a message informing the same is displayed.

The device can store bond data of up to four peer devices after which the data of the oldest device is overwritten by that of the new incoming device. The incoming device is added in device privacy mode by default which can be changed by issuing 'p' command via terminal.

The peripheral has five states:

1. IDLE_NO_DATA: The device in this state is either waiting for the user input or advertising. No bond data is present in the NVRAM. Directed advertising option is disabled in this state.
2. IDLE_DATA: The device in this state is either waiting for the user input or advertising. Bond data is present in the NVRAM. Directed advertising option is available.
3. IDLE_PRIVACY_CHANGE: The device in this state is not advertising. The device enters this mode when command to change the privacy mode of bonded devices is issued.
4. CONNECTED: In this state, the peripheral is connected to a peer device.
5. BONDED: The peripheral moves into this state once it has paired and bonded with the connected device and the peer bond information has been saved to NVRAM.

The LED1 on the kit is used to represent the current advertising state of the device. Table 2 shows LED behaviour for different advertising states.

Table 2. LED behaviour for advertising states

Advertisement state	LED state
Advertisement ON (undirected):	Slow blinking led (T = 1 sec)
Advertisement ON (directed):	Fast blinking led (T = 20msec)
Advertisement OFF, connected:	LED ON
Advertisement OFF, timed out:	LED OFF

Figure 2. Process flowchart

Resources and settings

This section explains the ModusToolbox™ software resources and their configuration as used in this code example. Note that all the configuration explained in this section has already been done in the code example. Eclipse IDE for ModusToolbox™ software stores the configuration settings of the application in the design.modus file. This file is used by the graphical configurators, which generate the configuration firmware. This firmware is stored in the application’s GeneratedSource folder.

• Device configurator: Used to enable/configure the peripherals and the pins used in the application. See the Device configurator guide.

• Bluetooth® configurator: Used for generating/modifying the Bluetooth® LE GATT database. See the Bluetooth® configurator guide.

Related resources

Resources	Links
Application notes	AN225684: Getting started with CYW208xx
Code examples	Using ModusToolbox™ software on GitHub Using Bluetooth® SDK
Device documentation	CYW20819 device datasheet CYW20820 device datasheet CYW20719 device datasheet CYW89820 device documents
Development kits	Visit https://www.infineon.com/cms/en/product/wireless-connectivity/airoc-bluetooth-le-bluetooth-multiprotocol
Libraries on GitHub	btsdk-drivers – Bluetooth® SDK drivers library btsdk-mesh – Bluetooth® LE mesh libraries btsdk-ota – Bluetooth® LE OTA libraries btsdk-ble – Bluetooth® LE profile libraries
Tools	Eclipse IDE for ModusToolbox™ software – ModusToolbox™ software is a collection of easy-to-use software and tools enabling rapid development with Infineon MCUs, covering applications from embedded sense and control to wireless and cloud-connected systems using AIROC™ Wi-Fi and Bluetooth® connectivity devices. btsdk-utils – Bluetooth® SDK utilities btsdk-peer-apps-ota – Bluetooth® LE OTA peer applications btsdk-host-peer-apps – Bluetooth® LE mesh host and peer applications btsdk-host-apps-bt-ble – Bluetooth® and Bluetooth® LE host applications

Other resources

Infineon provides a wealth of data at www.infineon.com to help you select the right device, and quickly and effectively integrate it into your design.

Document history

Document title: CE228751 - Bluetooth® LE peripheral privacy

Version	Description of change
1.0.0	New code example
1.1.0	Updated to support ModusToolbox™ software v2.1
2.0.0	Major update to support ModusToolbox™ software v2.2, added support for new kits This version is not backward compatible with ModusToolbox™ software v2.1
2.1.0	Updated to support ModusToolbox™ software v2.3.1 and BTSDK 3.1
2.2.0	Added support for 20820 and 20835 kit
2.3.0	Added support for CYW920819M2EVB-01 and CYW989820M2EVB-01

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