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Difficulty: MediumCIA Triad and Non-Repudiation

An energy distribution company is upgrading its remote terminal unit (RTU) fleet across regional sub-stations. The security engineering team must implement a mechanism for over-the-air (OTA) control command execution. The system must guarantee that once a lead control engineer issues a high-voltage switching instruction, the engineer cannot later deny having authorized the command, and the RTUs can verify both origin authenticity and data integrity. Which of the following technical controls best satisfies this security requirement?

  1. Digitally signing the command payload using the lead control engineer's private keyAnswer
  2. B
    Generating a Hash-based Message Authentication Code (HMAC) using a shared symmetric key
  3. C
    Encrypting the payload with AES-256 in Galois/Counter Mode (GCM) using a shared pre-shared key
  4. D
    Configuring role-based access control (RBAC) permissions on the central SCADA dispatch workstation

Answer

Digitally signing the command payload using the lead control engineer's private key
Digitally signing the payload with a private key provides non-repudiation because only the private key owner could have generated the signature. Anyone with the corresponding public key can verify integrity and authenticity, preventing the sender from denying their action.

Step-by-Step Solution

1
Analyze the core security requirement stated in the scenario.
The requirement asks for origin authenticity, integrity, and non-repudiation (ensuring the author cannot deny issuing the command).
Identifying the required security objective isolates asymmetric digital signatures from simple hashing or symmetric encryption solutions.
2
Evaluate cryptographic mechanisms against the non-repudiation property.
Only asymmetric cryptography (where only the signer holds the private key) provides non-repudiation. Symmetric mechanisms (HMAC/AES) rely on shared keys, allowing either party with the key to produce the payload.
If keys are shared, proof of specific authorship is lost, failing the non-repudiation requirement.

Key Concept

Non-Repudiation through Asymmetric Digital Signatures
Estimated Time:1m 15s
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Topics

CIA Triad and Non-Repudiation

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