CV0-004 Security Practice Question
A financial services company runs a multi-tenant SaaS application on AWS. Each tenant has dedicated Amazon RDS for MySQL databases. The security team must ensure that data at rest is encrypted with keys that are unique per tenant and that the company can independently audit key usage. Which approach should be used?
⚠ Common exam trap
The trap here is assuming that a single CMK or AWS managed keys provide sufficient isolation, when the requirement explicitly demands unique keys per tenant and independent auditing.
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
✓
Use a separate customer managed key (CMK) in AWS KMS for each tenant's RDS instance
Using a separate AWS KMS customer managed key for each tenant's RDS instance provides unique encryption keys per tenant, enabling strong isolation and independent auditability. CloudTrail logs each key's usage, so the security team can track which key encrypted which database and when. This meets both the security and compliance requirements without application-level complexity.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Use a single customer managed key (CMK) in AWS KMS for all RDS instances
Why it's wrong here
A single CMK for all tenants does not provide unique keys per tenant. If the key is compromised, all tenant data is at risk. While the company can audit key usage via CloudTrail, the lack of per-tenant key isolation violates the requirement. This approach simplifies management but sacrifices the necessary security granularity.
- ✗
Use client-side encryption with a per-tenant key stored in the application
Why it's wrong here
Client-side encryption would require the application to manage keys and encrypt data before sending to RDS, but it does not integrate with RDS's native encryption at rest. The keys would not be managed in AWS KMS, and auditing key usage would be complex. This approach also adds application overhead and does not leverage RDS's built-in encryption capabilities, making it less suitable than using KMS CMKs.
- ✓
Use a separate customer managed key (CMK) in AWS KMS for each tenant's RDS instance
Why this is correct
Creating a unique CMK per tenant in AWS KMS allows each RDS instance to be encrypted with its own key. The company can audit key usage separately through CloudTrail, meeting the audit requirement. This provides strong isolation: compromise of one key does not affect other tenants. It also enables per-tenant key rotation and access policies.
- ✗
Use AWS managed keys (aws/rds) for each RDS instance
Why it's wrong here
AWS managed keys are shared across all RDS instances in the account and cannot be independently audited per tenant. They are managed by AWS and do not provide the granular control or unique per-tenant keys required. Additionally, key usage logs are not available to the customer. This approach fails to meet the requirements for tenant-specific encryption and auditability.
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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
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