CAS-004 Security Engineering Practice Question
A company is deploying IoT sensors that require secure firmware updates over the air (OTA). To ensure integrity and authenticity of the firmware, which of the following should be implemented?
⚠ Common exam trap
The trap is confusing integrity (hash) with authenticity (signature); candidates often pick hash verification thinking it covers both, but only code signing proves the source.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
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Code signing with a trusted certificate
Code signing with a trusted certificate provides both integrity and authenticity: the firmware is hashed and signed by the vendor's private key, and the device verifies the signature using the vendor's public key. This ensures the firmware has not been tampered with and originates from a trusted source. Hash verification alone only checks integrity, not authenticity.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Code signing with a trusted certificate
Why this is correct
Code signing with a trusted certificate lets each IoT sensor verify the firmware's signature against the vendor's public key before installation, confirming both integrity and origin. Unsigned or tampered images are rejected, satisfying the OTA authenticity requirement.
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Secure boot on the device
Why it's wrong here
Secure boot verifies the bootloader and OS at startup against trusted keys; it does not validate an OTA firmware package before installation. It is tempting because it establishes a root of trust on the device, but the update itself still needs a digital signature checked by the bootloader or updater.
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Hash verification only
Why it's wrong here
A hash verifies integrity but provides no authenticity: an attacker who alters the firmware can simply recompute the hash, so the device cannot tell who signed it. Hashing is tempting as a lightweight checksum, yet it is correct only for detecting accidental corruption, not malicious modification.
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Encryption of the firmware image
Why it's wrong here
Encrypting the firmware image protects confidentiality in transit and at rest, but it does not prove origin; anyone with the key can produce a valid encrypted payload. Encryption is tempting because it sounds like strong protection, yet authenticity requires a digital signature verified against the vendor's trusted public key.
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JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official CompTIA exam blueprint
This CAS-005 practice question is part of Courseiva's free CompTIA certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the CAS-005 exam.