How do I secure an MCU from hacking or tampering?

Securing a microcontroller unit (MCU) from hacking or tampering is critical, especially in applications involving sensitive data, financial transactions, or critical infrastructure. Here’s a comprehensive approach to MCU security, categorized into hardware, firmware, and development lifecycle protections:

1. Hardware-Level Protections

a. Secure Boot

• Ensures the MCU boots only trusted, signed firmware.

• Prevents malicious code from executing at startup.

b. Read/Write Protection

• Enable Flash memory readout protection (RDP, in STM32).

• Disable debugging interfaces (JTAG/SWD) after development.

• Lock unused peripherals to avoid exploitation.

c. Physical Tamper Detection

• Use tamper-detection pins or sensors (e.g., for casing, voltage, or temperature anomalies).

• Design with epoxy/resin encapsulation for anti-tamper resistance.

d. Hardware Security Modules (HSM) or Secure Elements

• Some MCUs (e.g., NXP LPC55Sxx, STM32H5, or Microchip Trust Platform) include secure cryptographic co-processors.

• Offload crypto operations to prevent key leakage.

2. Firmware and Software-Level Protections

a. Firmware Encryption and Authentication

• Encrypt firmware at rest and in transit.

• Use digital signatures and cryptographic hashes to verify integrity.

b. Code Obfuscation

• Make reverse engineering more difficult by obfuscating critical parts of your code.

c. Run-Time Protection

• Implement watchdogs and memory integrity checks.

• Use Memory Protection Units (MPU) or TrustZone (if supported) to separate secure and non-secure regions.

d. Over-the-Air (OTA) Update Security

• Encrypt and authenticate all OTA firmware updates.

• Ensure rollback protection (prevent old vulnerable firmware from being reinstalled).

3. Secure Development Lifecycle

a. Threat Modeling and Secure Coding Practices

• Follow secure coding standards (like MISRA for embedded C).

• Perform regular code reviews and penetration testing.

b. Use Static and Dynamic Analysis Tools

• Detect vulnerabilities early using tools like Coverity, Cppcheck, or Valgrind.

c. Key Management

• Never hard-code cryptographic keys.

• Use secure key provisioning during manufacturing.

• Rotate keys periodically and revoke compromised ones.

4. Post-Deployment Considerations

a. Monitoring and Logging

• Log abnormal behavior where feasible.

• Design logging to be tamper-resistant.

b. Regular Updates and Patch Management

• Provide secure update mechanisms to patch vulnerabilities discovered after deployment.

 Example MCU Security Features by Vendor

 Summary Checklist

• Enable Secure Boot

• Protect debug/programming interfaces

• Encrypt and sign firmware

• Implement run-time checks and watchdogs

• Follow secure development practices

• Provision and manage keys securely

• Monitor and maintain after deployment