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SSCP Practice Question: A security analyst reviews a cryptographic…
A security analyst reviews a cryptographic implementation and notices that the same initialization vector (IV) is used repeatedly with the same key in CBC mode. What is the primary risk?
⚠ Common exam trap
Candidates often confuse confidentiality with integrity or authentication, mistakenly thinking IV reuse primarily enables data tampering (integrity) or impersonation (authentication), when in fact the core cryptographic weakness is the exposure of plaintext patterns, directly violating confidentiality.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Loss of confidentiality
In CBC (Cipher Block Chaining) mode, the initialization vector (IV) is XORed with the first plaintext block before encryption. Reusing the same IV with the same key means that identical plaintext blocks will produce identical ciphertext blocks, revealing patterns in the data. This directly breaks confidentiality, as an attacker can detect repeated plaintext segments, infer message structure, or even recover plaintext through known-plaintext attacks.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Loss of confidentiality
Why this is correct
Reusing an IV with the same key in CBC mode makes identical plaintext blocks produce identical ciphertext blocks, leaking patterns and enabling chosen-plaintext attacks. Confidentiality is lost; integrity is not directly the issue here, so loss of confidentiality is the primary risk.
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Loss of authentication
Why it's wrong here
CBC mode provides confidentiality only; it has no authentication tag, so IV reuse cannot remove authentication that was never present. The risk is that identical plaintext blocks produce identical ciphertext, leaking patterns. Authentication is the domain of modes like GCM or CBC-MAC, which would be chosen when message authenticity is the requirement.
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Non-repudiation is compromised
Why it's wrong here
Non-repudiation requires a digital signature binding a private key to a message, which CBC encryption does not provide regardless of IV handling. Reusing an IV with the same key instead reveals equality of plaintext prefixes through matching ciphertext blocks. Signing schemes such as RSA or ECDSA would be selected when non-repudiation is the actual requirement.
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Loss of integrity
Why it's wrong here
CBC without a MAC offers no integrity protection at all, so IV reuse does not remove it; the concrete failure is deterministic ciphertext, where identical plaintext blocks under the same key and IV yield identical output, enabling pattern analysis. An authenticated mode such as AES-GCM would be chosen when integrity is the requirement.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This SSCP practice question is part of Courseiva's free ISC2 certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the SSCP exam.