Quick Answer
The primary security concern with ECB mode is that identical plaintext blocks produce identical ciphertext, revealing patterns in the encrypted data. This happens because ECB encrypts each block independently with the same key, so any repetition in the input—such as repeated credit card BIN ranges or fixed-length fields—creates matching ciphertext blocks that an attacker can spot without breaking the encryption. On the Systems Security Certified Practitioner SSCP exam, this question tests your understanding of why ECB is unsuitable for structured data, often appearing alongside questions about CBC or CTR as more secure alternatives. A common trap is thinking ECB’s simplicity makes it safe, but the real weakness is its deterministic output, which leaks data boundaries and frequency. For a memory tip, remember “ECB = Each Ciphertext Block is the same for the same plaintext,” or think of a coloring book where identical shapes get the same color—patterns become obvious.
This SSCP practice question tests your understanding of cryptography. 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.
A security team discovers that a legacy system uses ECB mode to encrypt credit card numbers. What is the primary security concern with this mode?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "primary"
Why it matters: Asks for the main purpose or function, not a secondary benefit. Eliminate answers that describe side-effects or partial functions.
Identical plaintext blocks produce identical ciphertext, revealing patterns
This is the classic weakness of ECB.
It is slow compared to other modes
Why wrong: ECB is actually fast because it's parallelizable.
It is vulnerable to padding oracle attacks
Why wrong: Padding oracle attacks target CBC, not ECB.
It does not provide integrity
Why wrong: No mode without MAC provides integrity, but that's not the main issue.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Identical plaintext blocks produce identical ciphertext, revealing patterns
ECB (Electronic Codebook) mode encrypts each plaintext block independently using the same key. This means identical plaintext blocks produce identical ciphertext blocks, which allows an attacker to detect patterns, data boundaries, and repetitions in the encrypted data. For credit card numbers, which often have predictable formats (e.g., BIN ranges, fixed lengths), this pattern leakage can reveal sensitive information without breaking the encryption key.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
Identical plaintext blocks produce identical ciphertext, revealing patterns
Why this is correct
This is the classic weakness of ECB.
Clue confirmation
The clue word "primary" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
It is slow compared to other modes
Why it's wrong here
ECB is actually fast because it's parallelizable.
It is vulnerable to padding oracle attacks
Why it's wrong here
Padding oracle attacks target CBC, not ECB.
It does not provide integrity
Why it's wrong here
No mode without MAC provides integrity, but that's not the main issue.
Common exam traps
The trap here is that candidates often confuse ECB's lack of diffusion with performance issues or integrity flaws, but Cisco specifically tests whether you recognize that ECB's deterministic block mapping is its fundamental weakness, not speed or padding vulnerabilities.
Detailed technical explanation
Under the hood, ECB splits plaintext into fixed-size blocks (e.g., 16 bytes for AES) and encrypts each block independently with the same key. This deterministic behavior means that if two credit card numbers share the same first 16 bytes (e.g., same BIN and first digits), their ciphertext blocks will match, allowing an attacker to infer structure. In real-world scenarios, this has been exploited in attacks like the ECB byte-at-a-time oracle (e.g., against encrypted cookies) and is why ECB is explicitly discouraged in standards like NIST SP 800-38A.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
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
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FAQ
Cryptography — This question tests Cryptography — Read the scenario before looking for a memorised answer..
The correct answer is: Identical plaintext blocks produce identical ciphertext, revealing patterns — ECB (Electronic Codebook) mode encrypts each plaintext block independently using the same key. This means identical plaintext blocks produce identical ciphertext blocks, which allows an attacker to detect patterns, data boundaries, and repetitions in the encrypted data. For credit card numbers, which often have predictable formats (e.g., BIN ranges, fixed lengths), this pattern leakage can reveal sensitive information without breaking the encryption key.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Yes — watch for: "primary". Asks for the main purpose or function, not a secondary benefit. Eliminate answers that describe side-effects or partial functions.
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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