Examkin

Question

Difficulty: HardCIA Triad and Non-Repudiation

A financial software firm secures its system log repository by encrypting log files with AES-256 and generating an HMAC-SHA256 checksum for each entry using a shared secret key accessible by all system administrators. During an investigation into an unauthorized privilege escalation, a senior administrator is suspected of editing log lines to erase evidence. The administrator claims that another employee with administrative credentials must have altered the logs using the shared key. Which security property is currently lacking in the firm's audit system that prevents proving which specific administrator committed the modification?

  1. A
    Data integrity, because HMAC checksums cannot detect whether log contents were changed after creation.
  2. Non-repudiation, because shared secret keys cannot uniquely attribute actions to a specific individual user.Answer
  3. C
    Confidentiality, because symmetric encryption fails to protect log data against unauthorized internal viewing.
  4. D
    Authorization, because administrators should not have permission to read system log records during an audit.

Answer

The audit system lacks non-repudiation because shared secret keys permit any key holder to create valid HMAC tags, preventing positive cryptographic attribution to a specific individual.
Non-repudiation ensures that a specific subject cannot deny having performed an action or created a message. Because HMAC relies on a symmetric key shared among multiple administrators, any key holder can forge a valid HMAC tag. To achieve non-repudiation, the organization must use asymmetric cryptography (digital signatures) using unique private keys held by each individual administrator.

Step-by-Step Solution

1
Analyze the cryptographic mechanisms used in the logging system.
AES-256 provides confidentiality, and HMAC-SHA256 provides data integrity and group origin verification.
HMAC relies on symmetric shared secrets across all authorized administrators.
2
Evaluate why the administrator can plausibly deny performing the action.
Since all system administrators possess the shared key, any administrator could generate a valid HMAC tag for a modified log entry.
Symmetric keys cannot differentiate between distinct holders of the same secret.
3
Identify the missing security goal required for individual accountability.
Non-repudiation is missing; implementing asymmetric digital signatures with private keys assigned strictly to individual administrators would solve this.
Digital signatures provide non-repudiation by binding an action uniquely to one private key holder.

Key Concept

CIA Triad and Non-Repudiation (Symmetric HMAC vs Asymmetric Digital Signatures)
Rate this question

Topics

CIA Triad and Non-Repudiation

More questions from this topic