This CEH practice question tests your understanding of advanced topics: wireless, cloud, iot, 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.
Which of the following is a symmetric encryption algorithm that uses a block cipher with a fixed block size of 128 bits and key sizes of 128, 192, or 256 bits?
3DES
Why wrong: 3DES has a block size of 64 bits, not 128.
RC4
Why wrong: RC4 is a stream cipher, not a block cipher.
AES
AES meets the description: symmetric, 128-bit block, key sizes 128/192/256.
RSA
Why wrong: RSA is an asymmetric algorithm, not symmetric.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
AES
AES (Advanced Encryption Standard) is a symmetric encryption algorithm that operates as a block cipher with a fixed block size of 128 bits and supports key sizes of 128, 192, or 256 bits. It was established by NIST in 2001 (FIPS 197) and is widely used in modern cryptographic systems, including wireless security (WPA2/WPA3) and TLS.
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.
3DES
Why it's wrong here
3DES has a block size of 64 bits, not 128.
RC4
Why it's wrong here
RC4 is a stream cipher, not a block cipher.
AES
Why this is correct
AES meets the description: symmetric, 128-bit block, key sizes 128/192/256.
Related concept
Read the scenario before looking for a memorised answer.
RSA
Why it's wrong here
RSA is an asymmetric algorithm, not symmetric.
Common exam traps
The trap here is that candidates often confuse AES with 3DES due to both being symmetric block ciphers, but they fail to recall that 3DES uses a 64-bit block size (not 128 bits) and lacks the specific key size options of AES, leading them to select 3DES incorrectly.
Detailed technical explanation
AES operates on a 4x4 column-major order matrix of bytes, with the number of rounds depending on key size: 10 rounds for 128-bit keys, 12 for 192-bit, and 14 for 256-bit. Each round involves SubBytes (S-box substitution), ShiftRows (row-wise permutation), MixColumns (column mixing), and AddRoundKey (XOR with round key). In real-world scenarios, AES is used in modes like GCM (Galois/Counter Mode) for authenticated encryption, which is critical for securing IoT devices and cloud storage against tampering.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A practitioner preparing for the CEH exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
What to study next
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FAQ
Advanced Topics: Wireless, Cloud, IoT, Cryptography — This question tests Advanced Topics: Wireless, Cloud, IoT, Cryptography — Read the scenario before looking for a memorised answer..
The correct answer is: AES — AES (Advanced Encryption Standard) is a symmetric encryption algorithm that operates as a block cipher with a fixed block size of 128 bits and supports key sizes of 128, 192, or 256 bits. It was established by NIST in 2001 (FIPS 197) and is widely used in modern cryptographic systems, including wireless security (WPA2/WPA3) and TLS.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 24, 2026
This CEH practice question is part of Courseiva's free EC-Council 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 CEH exam.
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