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Difficulty: HardCIA Triad and Non-Repudiation

An automated algorithmic trading platform logs high-frequency order requests to an external compliance vault. Following a significant financial anomaly, a senior trader asserts that a series of unauthorized trades attributed to their user account were forged by a malicious internal microservice rather than initiated from their terminal. To resolve the dispute, the security audit team must provide irrefutable proof of the trader's authorship as well as guarantee that the order data was not tampered with after creation. Which of the following security mechanisms best fulfills these requirements?

  1. Digital signatures generated using the trader's asymmetric private key paired with a public key infrastructure timestamping serviceAnswer
  2. B
    AES-256 Galois/Counter Mode (GCM) symmetric encryption applied to trade payloads using a shared vault secret
  3. C
    SHA-256 cryptographic hashes calculated for each order payload and stored in a database protected by role-based access control
  4. D
    Mandatory multi-factor authentication (MFA) at terminal login combined with granular API authorization policies

Answer

Digital signatures generated using the trader's asymmetric private key paired with a public key infrastructure timestamping service
Digital signatures fulfill non-repudiation because they rely on asymmetric cryptography. Only the owner possesses the private key used to sign the transaction payload, creating a unique cryptographic proof of origin. Recipients verify signature validity using the sender's public key. Timestamping further ensures proof of existence at a specific time, preventing the trader from denying trade initiation.

Step-by-Step Solution

1
Analyze the operational security requirement in the compliance scenario
Identified the requirement for non-repudiation (proving authorship so the sender cannot deny originating the transaction) and integrity (ensuring the payload was not altered post-submission).
The trader claims an internal service forged their order, requiring cryptographic evidence that uniquely ties transaction creation to the trader.
2
Evaluate candidate cryptographic controls against non-repudiation principles
Asymmetric digital signatures uniquely bind the transaction payload to the private key owner, which cannot be forged by other services possessing only public keys or shared secrets.
Symmetric encryption and plain cryptographic hashes rely on shared keys or public hash functions, allowing any component with key access to build valid signatures and failing proof-of-origin tests.
3
Select the control combination providing both integrity and non-repudiation
Digital signatures with PKI timestamping satisfy both requirements.
The asymmetric private key guarantees non-repudiation of origin while hash-based digital signing guarantees message integrity.

Key Concept

Non-Repudiation vs Integrity in Asymmetric Cryptography
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Topics

CIA Triad and Non-Repudiation

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