Google PCA Design for security and compliance Practice Question
A startup wants to encrypt data at rest in Cloud Storage using Customer-Managed Encryption Keys (CMEK). They have already created a Cloud KMS key ring and key. What additional step is required to enable CMEK for a new Cloud Storage bucket?
⚠ Common exam trap
A common misconception is that enabling the Cloud KMS API or using Cloud HSM is required for CMEK, when the actual critical step is granting the Cloud KMS CryptoKey Encrypter/Decrypter role to the Cloud Storage service account on the key.
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
✓
Grant the Cloud Storage service account the Cloud KMS CryptoKey Encrypter/Decrypter role on the key.
To use CMEK with Cloud Storage, the Cloud Storage service account must be granted the Cloud KMS CryptoKey Encrypter/Decrypter role on the specific key. This permission allows the bucket's underlying storage system to encrypt and decrypt objects using the customer-managed key. Without this IAM binding, the bucket cannot access the key, and CMEK operations will fail.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Enable the Cloud KMS API in the project where the bucket will reside.
Why it's wrong here
The Cloud KMS API is already enabled, since the key ring and key exist. Enabling APIs is a prerequisite for creating KMS resources, not for attaching an existing key to a bucket; the missing step is granting the Cloud Storage service account encrypt/decrypt permission on the key.
- ✗
Create a Cloud HSM key instead, as CMEK requires HSM.
Why it's wrong here
CMEK accepts any Cloud KMS key, including software-protection-level keys; Cloud HSM is only required when hardware-backed key storage is a compliance mandate. Creating an HSM key adds cost and latency without satisfying the actual requirement, which is IAM authorisation of the Storage service agent.
- ✗
Add a label to the key ring to associate it with the bucket.
Why it's wrong here
Labels are metadata for billing, filtering and organisation; they carry no cryptographic or IAM meaning. The bucket needs the key specified via its defaultKmsKeyName and the service account granted roles/cloudkms.cryptoKeyEncrypterDecrypter, which a key-ring label cannot accomplish.
- ✓
Grant the Cloud Storage service account the Cloud KMS CryptoKey Encrypter/Decrypter role on the key.
Why this is correct
CMEK requires the Cloud Storage service account to hold the CryptoKey Encrypter/Decrypter role on the KMS key, otherwise Cloud Storage cannot wrap and unwrap data encryption keys. Granting this IAM binding is the mandatory step after creating the key ring and key.
Go deeper
Related to this question
Learn chapter
Data Migration and Transfer Services
Key term
Cloud storage
Cloud storage is a service that lets you save data on remote servers accessed over the internet instead of on your computer's hard drive.
Key term
Service
A service is a software component or system that performs a specific function and is available to be used by other programs or users over a network.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This PCA practice question is part of Courseiva's free Google Cloud 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 PCA exam.