How to Implement AES-256 Encryption with STM32 for Secure MQTT Communication

Implementing AES-256 Encryption with the STM32 Hardware Crypto Accelerator using HAL Library for Secure MQTT Communication

This tutorial will guide you through the process of implementing AES-256 encryption using the STM32 hardware crypto accelerator, utilizing the HAL library. We’ll focus on securing MQTT communication, ensuring your messages are protected during transmission.

Prerequisites

• Basic understanding of STM32 microcontrollers
• STM32 development board (e.g., STM32F4 series)
• STM32CubeIDE installed on your computer
• MQTT broker (e.g., Mosquitto) for testing
• Familiarity with C programming language

Parts/Tools

• STM32 development board
• USB to serial converter (if needed)
• MQTT client tool (e.g., MQTT.fx or MQTT Explorer)
• STM32 HAL library
• Crypto libraries for AES (if not included in HAL)

Steps

1. Setup STM32CubeIDE Project
   1. Open STM32CubeIDE and create a new project.
   2. Select your STM32 microcontroller or board.
   3. Configure the necessary peripherals (UART, SPI, etc.) in the .ioc file.
   4. Enable the crypto library in the project settings under middleware.
2. Initialize HAL Library
   1. In your main.c file, initialize the HAL library:

   
   void HAL_Init(void);
               

   2. Configure the system clock to the desired frequency.
3. Setup Crypto Module
   1. Include the necessary headers for the crypto library:

   
   #include "stm32f4xx_hal.h"
   #include "stm32f4xx_hal_cryp.h"
               

   2. Declare and initialize the CRYP handle:

   
   CRYP_HandleTypeDef hcryp;
   hcryp.Instance = CRYP;
               

4. Configure AES-256 Encryption
   1. Set the key size and mode:

   
   hcryp.Init.DataType = CRYP_DATATYPE_8B;
   hcryp.Init.KeySize = CRYP_KEYSIZE_256B;
   hcryp.Init.Algorithm = CRYP_AES_CBC;
               

   2. Initialize the CRYP peripheral:

   
   if (HAL_CRYP_Init(&hcryp) != HAL_OK) {
       // Initialization Error
   }
               

5. Encrypt Data
   1. Define your encryption key and IV:

   
   uint8_t key[32] = { /* 32 bytes key */ };
   uint8_t iv[16] = { /* 16 bytes IV */ };
               

   2. Prepare the plaintext data:

   
   uint8_t plaintext[] = "Hello, secure MQTT!";
               

   3. Perform encryption:

   
   HAL_CRYP_SetKey(&hcryp, key, sizeof(key));
   HAL_CRYP_SetIV(&hcryp, iv, sizeof(iv));
   HAL_CRYP_AES_Encrypt(&hcryp, plaintext, sizeof(plaintext), ciphertext);
               

6. Setup MQTT Communication
   1. Include the MQTT library in your project.
   2. Establish a connection to the MQTT broker:

   
   MQTTClient client;
   MQTTClient_create(&client, "tcp://broker.hivemq.com:1883", clientId, MQTTCLIENT_PERSISTENCE_NONE, NULL);
               

   3. Publish the encrypted message:

   
   MQTTClient_publish(&client, "topic/secure", ciphertext, sizeof(ciphertext), 0, 0, NULL);
               

Troubleshooting

• If the encryption does not work, verify the key and IV lengths are correct (32 bytes for key, 16 bytes for IV).
• Check the configuration of the HAL library and ensure the crypto module is enabled.
• Ensure the MQTT broker is reachable and the client is properly configured.
• Use debugging tools to monitor the data being sent and received.

Conclusion

In this tutorial, we successfully implemented AES-256 encryption on an STM32 microcontroller using the HAL library, enabling secure MQTT communication. This ensures that messages sent over the network are encrypted and safe from unauthorized access. With these steps, you can now secure your IoT applications effectively.