CAS-004 Security Architecture Practice Question
A company is implementing API security for its web services. Which THREE of the following are considered best practices for securing APIs? (Select THREE).
⚠ Common exam trap
CAS-005 often tests the confusion between encryption at rest and in transit, and between wireless security protocols (WPA3) and transport security (TLS), tricking candidates into selecting irrelevant or incomplete measures when asked for API security best practices.
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
✓
Validate all input
Option B (Validate all input) is correct because input validation defends against injection attacks such as SQL injection and cross-site scripting (XSS) by ensuring data conforms to expected formats, types, and lengths before processing. Option D (Implement rate limiting) is correct because throttling requests per client or API key mitigates brute-force, credential-stuffing, and denial-of-service abuse, and protects backend resources from being overwhelmed. Option E (Use OAuth 2.0 for authorization) is correct because OAuth 2.0 provides delegated, token-based authorization with scoped access, allowing APIs to grant limited permissions without exposing user credentials. Option A does not belong because relying solely on symmetric encryption for data at rest ignores transport security, key management, and other layers of defense. Option C does not belong because WPA3 is a Wi-Fi (802.11) security standard for wireless LANs, not a transport encryption mechanism for web APIs, which should use TLS.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Rely solely on symmetric encryption for data at rest
Why it's wrong here
Symmetric encryption alone protects stored data but not transport or authentication, so it cannot secure API calls in flight or verify callers. It is tempting because encryption at rest is a genuine control, and would be correct for protecting database files or backups rather than API traffic.
- ✓
Validate all input
Why this is correct
Validating all input defends against injection attacks such as SQL injection and cross-site scripting by rejecting malformed or malicious payloads before processing. This directly satisfies the requirement to secure web service APIs against untrusted client-supplied data.
- ✗
Use WPA3 for transport encryption
Why it's wrong here
WPA3 secures Wi-Fi links between clients and access points; it provides no protection for HTTP API transport, which requires TLS. It is tempting because WPA3 is strong wireless encryption, and would be correct for hardening a corporate wireless LAN rather than web service traffic.
- ✓
Implement rate limiting
Why this is correct
Rate limiting caps request frequency per client, mitigating brute-force credential attacks, credential stuffing and denial-of-service abuse. It directly satisfies the API security requirement by preventing excessive or automated request volumes from overwhelming the web services.
- ✓
Use OAuth 2.0 for authorization
Why this is correct
OAuth 2.0 delegates authorisation via scoped access tokens rather than exposing credentials, enforcing least privilege per API call. This satisfies the API security requirement by ensuring clients obtain only the permissions granted, with tokens revocable independently of user passwords.
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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JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official CompTIA exam blueprint
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.