How to Implement Secure Key Storage with eFUSE on ESP32 for IoT

Introduction

In this tutorial, we will guide you through the process of implementing secure key storage using eFUSE on the ESP32 for IoT applications. eFUSE is a hardware feature that allows for secure storage of cryptographic keys and other sensitive data, enhancing the security of your IoT devices. By the end of this guide, you will have a clear understanding of how to use eFUSE for secure key management.

Prerequisites

• Basic knowledge of embedded systems and IoT concepts.
• Familiarity with the ESP32 development environment (Arduino IDE or ESP-IDF).
• ESP32 development board.
• USB cable for programming the ESP32.
• Access to a computer with the necessary software installed.

Parts/Tools

• ESP32 Development Board
• USB Cable
• Arduino IDE or ESP-IDF
• Computer with a USB port
• ESP32 eFUSE documentation

Steps

1. Setting up the Development Environment
   1. Install the Arduino IDE or ESP-IDF.
   2. Configure the IDE to support the ESP32 board.
   3. Ensure the ESP32 board drivers are installed on your computer.
2. Understanding eFUSE
   1. Read the ESP32 eFUSE documentation to understand its capabilities.
   2. Identify the eFUSE bits you will use for key storage.
3. Writing Secure Code
   1. Open your Arduino IDE and create a new sketch.
   2. Include the necessary libraries for eFUSE functionality.
   3. Generate a cryptographic key to be stored.

   
   #include "esp_system.h"
   #include "esp_efuse.h"
   
   void generateKey(uint8_t *key, size_t len) {
       for(size_t i = 0; i < len; i++) {
           key[i] = esp_random() % 256; // Generate a random byte
       }
   }
               

   4. Store the generated key in eFUSE.

   
   esp_efuse_write_field_blob(ESP_EFUSE_KEY0, key, sizeof(key));
               

4. Reading the Key from eFUSE
   1. Implement a function to read the key back from eFUSE.

   
   void readKey(uint8_t *key, size_t len) {
       esp_efuse_read_field_blob(ESP_EFUSE_KEY0, key, len);
   }
               

   2. Verify that the read key matches the original key.
5. Testing Your Implementation
   1. Upload the code to the ESP32 board.
   2. Open the Serial Monitor to observe the output.
   3. Confirm that the key is stored and retrieved successfully.

Troubleshooting

• Issue: Keys not being stored correctly
  • Double-check the eFUSE configuration and ensure you are using the correct eFUSE bits.
  • Verify that you have the correct permissions to write to eFUSE.
• Issue: Key retrieval fails
  • Ensure that the reading function is correctly implemented.
  • Check for any errors during the writing process.
• Issue: Random key generation not working
  • Make sure the esp_random() function is working correctly by testing it independently.

Conclusion

By following the steps outlined in this tutorial, you have successfully implemented secure key storage using eFUSE on the ESP32 for your IoT applications. This method enhances the security of sensitive data and is a crucial step in developing secure IoT devices. Be sure to explore further options and configurations available with eFUSE to maximize your device’s security.