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SSCP Practice Question: When using CBC mode encryption, what is the…
When using CBC mode encryption, what is the purpose of the initialization vector (IV)?
⚠ Common exam trap
Watch out — candidates often 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.
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
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.
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.
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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.
- ✗
To enable parallel encryption
Why it's wrong here
CBC is sequential; parallel is possible in other modes like CTR.
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JA
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.