- A
MD5
Why wrong: MD5 is a hash function, not a cipher.
- B
AES in ECB mode
Why wrong: ECB is a block cipher mode, not a stream cipher, and is insecure.
- C
ChaCha20
ChaCha20 is a secure stream cipher used in TLS and other protocols.
- D
3DES
Why wrong: 3DES is a block cipher, not a stream cipher, and is considered legacy.
Question 856 of 1,000
SSCP Cryptography Practice Question
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.
Which of the following is a secure alternative to RC4 for stream ciphers?
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
✓
ChaCha20
ChaCha20 is a modern, high-speed stream cipher designed by Daniel J. Bernstein as a secure alternative to RC4, which has known vulnerabilities such as biases in its keystream and susceptibility to attacks like the Fluhrer-Mantin-Shamir attack. ChaCha20 is standardized in RFC 8439 and is widely used in TLS 1.3 and SSH, offering strong security and performance without the weaknesses of RC4.
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.
- ✗
MD5
Why it's wrong here
MD5 is a hash function, not a cipher.
- ✗
AES in ECB mode
Why it's wrong here
ECB is a block cipher mode, not a stream cipher, and is insecure.
- ✓
ChaCha20
Why this is correct
ChaCha20 is a secure stream cipher used in TLS and other protocols.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
3DES
Why it's wrong here
3DES is a block cipher, not a stream cipher, and is considered legacy.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that any symmetric cipher can replace RC4, but the trap here is that candidates confuse block cipher modes (like ECB) or hash functions (like MD5) with stream ciphers, failing to recognize that only a dedicated stream cipher like ChaCha20 provides the same operational paradigm as RC4.
Detailed technical explanation
How to think about this question
ChaCha20 operates on 512-bit blocks using a 256-bit key and a 96-bit nonce, generating a keystream via a quarter-round function that provides high diffusion and resistance to differential cryptanalysis. Unlike RC4, which has a small internal state and biases in the first few bytes, ChaCha20's design avoids such weaknesses and is often paired with Poly1305 for authenticated encryption (ChaCha20-Poly1305). In real-world scenarios, ChaCha20 is preferred on mobile devices due to its software efficiency and lack of hardware acceleration requirements.
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?
Cryptography — This question tests Cryptography — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: ChaCha20 — ChaCha20 is a modern, high-speed stream cipher designed by Daniel J. Bernstein as a secure alternative to RC4, which has known vulnerabilities such as biases in its keystream and susceptibility to attacks like the Fluhrer-Mantin-Shamir attack. ChaCha20 is standardized in RFC 8439 and is widely used in TLS 1.3 and SSH, offering strong security and performance without the weaknesses of RC4.
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.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Last reviewed: Jul 4, 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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