- A
To provide authentication
Why wrong: CBC does not provide authentication; that's MAC.
- B
To increase the key length
Why wrong: IV does not affect key length.
- C
To add randomness and prevent identical ciphertext for repeated plaintext
IV randomizes the first block, causing different ciphertexts.
- D
To enable parallel encryption
Why wrong: CBC is sequential; parallel is possible in other modes like CTR.
Question 759 of 1,000
easyMultiple ChoiceObjective-mapped
SSCP Practice Question: When using CBC mode encryption, what is the…
This SSCP practice question tests your understanding of sscp exam topics. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
When using CBC mode encryption, what is the purpose of the initialization vector (IV)?
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
✓
To add randomness and prevent identical ciphertext for repeated plaintext
Option C is correct because the initialization vector (IV) in CBC mode ensures that each encryption of the same plaintext with the same key produces a different ciphertext. The IV is XORed with the first plaintext block before encryption, introducing randomness that prevents patterns from being exposed in the ciphertext, which is critical for semantic security.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
To provide authentication
Why it's wrong here
CBC does not provide authentication; that's MAC.
- ✗
To increase the key length
Why it's wrong here
IV does not affect key length.
- ✓
To add randomness and prevent identical ciphertext for repeated plaintext
Why this is correct
IV randomizes the first block, causing different ciphertexts.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
To enable parallel encryption
Why it's wrong here
CBC is sequential; parallel is possible in other modes like CTR.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates confuse the IV's role in adding randomness with authentication or key extension, or they mistakenly think CBC supports parallel encryption because they overlook the sequential dependency of ciphertext blocks.
Detailed technical explanation
How to think about this question
In CBC mode, the IV must be unpredictable (often random) to resist chosen-plaintext attacks; reusing the same IV with the same key allows an attacker to detect identical plaintext prefixes across messages. Under the hood, the IV is XORed with the first plaintext block, then encrypted with the block cipher (e.g., AES-128) to produce the first ciphertext block, which then serves as the XOR input for the next block. A real-world scenario: if an attacker observes two ciphertexts with the same IV and key, and the first block of ciphertext is identical, they know the first plaintext blocks are identical, leaking information.
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A developer is choosing between AES-256 (symmetric) and RSA-2048 (asymmetric) for encrypting a large file that will be sent to a partner. Symmetric encryption is fast but requires key exchange; asymmetric is slower but solves the key distribution problem. A hybrid approach — encrypt the file with AES, encrypt the AES key with RSA — is standard. Questions like this test whether you understand when each approach applies.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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FAQ
Questions learners often ask
What does this SSCP question test?
Read the scenario before looking for a memorised answer.
What is the correct answer to this question?
The correct answer is: To add randomness and prevent identical ciphertext for repeated plaintext — Option C is correct because the initialization vector (IV) in CBC mode ensures that each encryption of the same plaintext with the same key produces a different ciphertext. The IV is XORed with the first plaintext block before encryption, introducing randomness that prevents patterns from being exposed in the ciphertext, which is critical for semantic security.
What should I do if I get this SSCP question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 25, 2026
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.
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