STM32F407 + Plug & Trust + SE050 + mbedTLS TLS Connection Example

This example demonstrates how to establish a TLS connection using:

• STM32F407 microcontroller
• NXP Plug & Trust middleware
• SE050 secure element
• mbedTLS library

The private key operations are performed inside the SE050 secure element, providing enhanced security for TLS communications.

Directory Structure

.
├── Core/                 # Core application files
│   ├── main.c           # Main entry point
│   ├── se05x_init.c     # SE050 initialization
│   └── mbedtls_user_conf.h # mbedTLS configuration
├── Drivers/              # Hardware abstraction layer drivers
│   ├── CMSIS/           # Cortex Microcontroller Software Interface Standard
│   └── STM32F4xx_HAL_Driver/ # STM32F4 HAL drivers
├── Middlewares/          # Middleware components
│   ├── mbedtls/         # mbedTLS library
│   └── plug-and-trust/  # NXP Plug & Trust middleware
│       ├── hostlib/     # Host library
│       ├── sss/         # Secure Subsystem
│       └── se05x/       # SE05x specific implementations
└── board/               # Board support files
    ├── board_I2C.c      # I2C implementation
    └── board_log.c      # Logging functions

How It Works

1. The application initializes the STM32F407 hardware
2. I2C interface is configured for communication with SE050
3. SE050 secure element is initialized via Plug & Trust middleware
4. An ECC key pair is either generated or loaded in the SE050
5. mbedTLS is configured to use the SE050 key via ALT API callbacks
6. A TLS connection is established to a remote server
7. Private key operations (signing) are performed securely within SE050

Key Features

• Secure key storage in SE050 secure element
• Hardware-accelerated cryptographic operations
• mbedTLS integration with SE050 via ALT APIs
• Example TLS client implementation

Building the Project

Prerequisites

1. ARM GCC toolchain
2. CMake 3.15 or higher
3. STM32CubeProgrammer (for flashing)

Build Steps

1. Clone the repository with submodules:

   git clone --recursive https://github.com/your-repo/stm32-se050-tls-example.git
   

2. Create build directory:

   mkdir build && cd build
   

3. Configure with CMake:

   cmake ..
   

4. Build the project:

   make
   

This will generate .elf, .bin, and .hex files that can be flashed to the STM32F407.

Flashing the Application

To flash the application to your STM32F407 board:

STM32_Programmer_CLI -c port=SWD -w build/stm32_se050_tls_client.bin 0x08000000 -v -s

Hardware Requirements

• STM32F407 development board
• SE050 Arduino shield or equivalent
• Proper wiring between STM32F407 and SE050 (typically I2C lines)

Customization

You can customize the following parameters in the code:

1. TLS server endpoint in tls_client.c:

   #define SERVER_NAME "httpbin.org"
   #define SERVER_PORT "443"

2. SE050 key ID in se05x_init.h:

   #define TLS_KEY_ID 0xF0000001

3. mbedTLS configuration in mbedtls_user_conf.h

Troubleshooting

1. If the TLS handshake fails, check:

   • Network connectivity
   • SE050 connection and initialization
   • Certificate validation settings

2. If the SE050 initialization fails, check:

   • I2C wiring
   • Power supply to SE050
   • Correct I2C address (default is 0x48)

3. If you encounter build issues:

   • Ensure all submodules are properly cloned
   • Verify ARM GCC toolchain installation
   • Check that all required dependencies are present