hardMultiple Choice
CCSP Practice Question: A cloud service provider (CSP) is designing a…
A cloud service provider (CSP) is designing a multi-tenant infrastructure and needs to ensure that a security incident in one tenant's environment does not compromise the confidentiality or integrity of other tenants. The CSP plans to use a combination of network segmentation, hypervisor isolation, and encryption. Which additional control is MOST critical to prevent side-channel attacks that could leak cryptographic keys or other sensitive data across tenants?
⚠ Common exam trap
ISC2 often tests the distinction between network-level isolation (VLANs, firewalls) and microarchitectural side-channel defenses, leading candidates to choose network controls when the question specifically targets side-channel attacks that bypass network segmentation.
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
✓
Ensure cryptographic operations use constant-time algorithms.
Side-channel attacks, such as timing attacks, exploit variations in execution time to infer sensitive data like cryptographic keys. Constant-time algorithms ensure that cryptographic operations execute in a fixed duration regardless of input, eliminating timing variations that could be measured across shared physical hardware. This is critical in multi-tenant environments where tenants share CPU caches and memory buses, as it prevents an attacker from extracting key material through precise timing measurements.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Ensure cryptographic operations use constant-time algorithms.
Why this is correct
Constant-time algorithms eliminate data-dependent timing variations, denying attackers the measurable execution differences that side-channel attacks exploit to infer cryptographic keys. Network segmentation, hypervisor isolation and encryption cannot address timing leakage across shared physical CPUs, so this control directly satisfies the stem's requirement to prevent cross-tenant key disclosure in the multi-tenant infrastructure.
- ✗
Implement virtual LANs (VLANs) and firewall rules between tenants.
Why it's wrong here
VLANs and firewall rules segment network traffic, but side-channel attacks exploit shared CPU caches and memory, which are invisible to layer 2 and 3 controls. It is tempting because segmentation is the correct answer when the risk is lateral movement or unauthorised network reachability between tenants.
- ✗
Use hardware security modules (HSMs) for key management.
Why it's wrong here
HSMs protect key material at rest and during cryptographic operations, but they do not stop a co-resident tenant inferring key bits through cache or timing observations. It is tempting because HSMs are the correct control when the requirement is key custody, rotation, or FIPS-validated cryptographic operations.
- ✗
Enforce strict API rate limiting for each tenant.
Why it's wrong here
Rate limiting throttles request volume per tenant and does nothing to stop cache-timing or speculative-execution leakage across shared CPUs. It is tempting because rate limiting genuinely mitigates API abuse and denial-of-service, and would be the correct control when the threat is resource exhaustion rather than covert-channel data leakage.
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 |
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This CCSP 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 CCSP exam.