CAS-004 Security Engineering Practice Question

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

• ✓

  Digitally sign the firmware with a private key

  Why this is correct

  Digitally signing firmware with a private key lets devices verify the signature using the corresponding public key before installation, so any tampered or forged image fails validation. This cryptographically ensures only vendor-authorised firmware is accepted.

• ✗

  Compress the firmware to reduce size

  Why it's wrong here

  Compression reduces firmware size for transmission efficiency; it provides no authenticity or integrity check, so a tampered image compresses just as readily. It is tempting where bandwidth or storage is constrained, but secure updates require cryptographic verification, such as a digital signature validated against a trusted key before installation.

• ✗

  Use a hash of the firmware for integrity verification

  Why it's wrong here

  A hash verifies integrity against accidental corruption only when the reference value is trusted; an attacker who alters firmware can simply supply a matching hash. It is tempting because hashing is cheap and detects tampering. Authenticity requires a digital signature, binding the image to the manufacturer's private key.

• ✗

  Encrypt the firmware with a symmetric key

  Why it's wrong here

  Symmetric encryption with a shared key conceals firmware contents but cannot prove origin, since any holder of that key can produce a valid-looking image. It is tempting because it protects confidentiality in transit. Secure updates need asymmetric digital signatures, letting devices verify the manufacturer's private-key signature using a public key.

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