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Difficulty: HardCIA Triad and Non-Repudiation

A financial enterprise is upgrading its automated clearing house payment processing system. To prevent fraud, the system requires that submitted wire transfers include a cryptographic control. The lead security architect proposes requiring sender applications to sign transfer payloads using an asymmetric private key rather than generating a Hash-based Message Authentication Code (HMAC) with a pre-shared symmetric key. Which security objective is uniquely satisfied by transitioning to the asymmetric digital signature approach?

  1. Non-repudiation, because any relying third party can independently verify the sender's identity using their public key, preventing the sender from denying transmission.Answer
  2. B
    Data integrity, because HMAC constructs are susceptible to hash collision attacks that allow silent payload modification during transit.
  3. C
    Confidentiality, because asymmetric digital signatures automatically encrypt the underlying transfer payload from unauthorized observers.
  4. D
    Preventive access control, because digital signatures function as an inline control that actively blocks unauthorized networks from connecting to the clearing house.

Answer

Non-repudiation, because any relying third party can independently verify the sender's identity using their public key, preventing the sender from denying transmission.
Asymmetric digital signatures provide non-repudiation because the signing operation uses a unique private key known only to the sender. Anyone with access to the sender's public key can verify the signature's authenticity. Because HMACs use a shared symmetric key, both sender and receiver possess the ability to calculate the message authentication code, preventing either party from mathematically proving to an outside auditor who originated the payload.

Step-by-Step Solution

1
Analyze the cryptographic properties of HMAC vs asymmetric digital signatures.
HMAC relies on a symmetric pre-shared key shared between endpoints. Asymmetric signatures use a private key for signing and a public key for verification.
Understanding key distribution distinguishes bilateral trust from third-party verifiable trust.
2
Evaluate which CIA triad pillar or related property is missing in shared-key HMAC operations.
Because both sender and receiver hold the identical shared secret key in HMAC operations, either party could technically generate a valid HMAC tag. Thus, neither party can prove to an independent third party which entity produced the message.
Non-repudiation requires proof of origin that cannot be forged by the recipient or other key holders.
3
Identify the security objective uniquely met by asymmetric digital signing.
Since only the sender possesses the private signing key, and any auditor or receiver can verify it using the public key, the sender cannot repudiate (deny) sending the payload.
This establishes non-repudiation.

Key Concept

Non-Repudiation vs. Integrity in Cryptographic Controls
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Topics

CIA Triad and Non-Repudiation

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