CAS-004 Security Engineering Practice Question
A security assessor is evaluating an application that uses ChaCha20-Poly1305 for encryption. Which TWO of the following are true about this cryptographic algorithm?
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
✓
It is a stream cipher
ChaCha20-Poly1305 is a stream cipher (ChaCha20) combined with a MAC (Poly1305). It is an AEAD cipher. It is not a block cipher, and it does not require padding.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
It is based on the AES algorithm
Why it's wrong here
ChaCha20 is not related to AES; it is a different design.
- ✗
It requires padding to achieve correct block sizes
Why it's wrong here
Stream ciphers do not require padding.
- ✓
It is a stream cipher
Why this is correct
ChaCha20 is a stream cipher.
- ✓
It provides authenticated encryption with additional data (AEAD)
Why this is correct
Poly1305 provides authentication, making it AEAD.
- ✗
It is a block cipher
Why it's wrong here
ChaCha20 is not a block cipher; it operates on 64-byte blocks but is a stream cipher.
Quick reference
Symmetric Encryption Algorithm Comparison
| Algorithm | Key Size | Block Size | Status | Notes |
|---|---|---|---|---|
| AES-128 | 128-bit | 128-bit | Current standard | NIST approved; WPA3, TLS |
| AES-256 | 256-bit | 128-bit | Current standard | Preferred for sensitive / govt data |
| 3DES | 112-bit effective | 64-bit | Deprecated (2023) | Replaced by AES |
| DES | 56-bit | 64-bit | Broken | Cracked in < 24 h; never deploy |
| ChaCha20 | 256-bit | Stream cipher | Current | TLS 1.3, WireGuard |
Go deeper
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This CAS-005 practice question is part of Courseiva's free CompTIA 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 CAS-005 exam.