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hardEmbedded Systems Engineer interview question

How would you secure an IoT device's firmware against tampering and cloning?

What the interviewer wants to hear

  • Secure boot chain with signature verification from an immutable root of trust
  • Signed and encrypted OTA updates with anti-rollback
  • Disable or lock debug ports in production
  • Unique per-device keys stored in secure hardware
  • Secure communication with TLS and certificate-based identity
  • Follow regulations such as the EU Cyber Resilience Act

Model answer

I start with secure boot: an immutable bootloader in ROM or locked flash holds a public key, or its hash in one-time-programmable memory, and verifies the signature of the next stage before running it. This forms a chain of trust, so only firmware signed with our private key, kept in an HSM, can run. OTA updates are signed, optionally encrypted, and include a version counter in OTP memory for anti-rollback, so attackers cannot install an old vulnerable version. In production, I lock or disable JTAG/SWD and enable flash read-out protection so firmware cannot be dumped. Each device gets a unique key and certificate, ideally generated inside a secure element or TrustZone, so cloning one device does not compromise others. Communication uses TLS with mutual authentication. I also follow standards like PSA Certified and ETSI EN 303 645, and prepare for rules like the EU Cyber Resilience Act, which require vulnerability handling and security updates.

Can you answer it under time pressure?

Take a timed hard round and get scored on every answer.

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