hardMultiple ChoiceObjective-mapped
Cloud KMS Automatic Key Rotation — Symmetric Keys Without Re-encryption
A company uses Cloud KMS to protect encryption keys for various applications. They need to ensure that keys are automatically rotated every 90 days and that the rotation does not require re-encrypting all data. Which key type and rotation strategy should they use?
Quick Answer
The answer is a symmetric key with an automatic rotation period set to 90 days. This works because Cloud KMS uses key versions; when automatic rotation is enabled, the service creates a new primary key version at the specified interval while retaining older versions for decryption. Since the key material is never exposed to users, existing ciphertext remains decryptable by its original key version, eliminating any need for re-encryption. On the Google Professional Cloud Security Engineer exam, this scenario tests your understanding that symmetric keys are used for data-at-rest encryption and that automatic rotation is a versioning operation, not a key replacement—a common trap is assuming rotation forces data re-encryption. Remember the mnemonic: "Rotate the version, not the data."
⚠ Common exam trap
Google Cloud often tests the misconception that automatic rotation requires re-encrypting data, or that asymmetric keys are suitable for bulk encryption, leading candidates to choose manual rotation or asymmetric key options.
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 symmetric key with automatic rotation period set to 90 days.
Symmetric keys are used for encryption/decryption of data at rest, and Cloud KMS supports automatic key rotation by creating a new key version at a specified interval (e.g., 90 days). Because Cloud KMS uses key versions and the key material is never exposed, existing ciphertext remains decryptable using the old key version, so no re-encryption is required. This meets the requirement for automatic rotation without data re-encryption.
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 symmetric key with automatic rotation period set to 90 days.
Why this is correct
Symmetric keys support automatic rotation, and old versions remain for decryption.
- ✗
Use an asymmetric key and set the rotation period to 90 days.
Why it's wrong here
Cloud KMS does not support automatic rotation for asymmetric keys.
- ✗
Use an asymmetric key and manually create a new version every 90 days.
Why it's wrong here
Asymmetric keys lack automatic rotation, and manual effort is required.
- ✗
Use a symmetric key and manually create a new version every 90 days.
Why it's wrong here
Manual rotation is not automated and prone to error.
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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Same concept, more angles
1 more way this is tested on PCSE
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. Refer to the exhibit. Based on the exhibit, the corporate security policy requires that all Cloud KMS symmetric keys have automatic rotation enabled. Which statement is true?
hard- A.Both keys are compliant.
- B.Neither key is compliant.
- ✓ C.Only the encryption-key is compliant.
- D.Only the decryption-key is compliant.
Why C: The corporate security policy requires automatic rotation for all Cloud KMS symmetric keys. In the exhibit, the 'encryption-key' has automatic rotation enabled (as indicated by the rotation period being set), while the 'decryption-key' does not have automatic rotation enabled (rotation period is not set or is disabled). Therefore, only the encryption-key is compliant with the policy.
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This PCSE 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 PCSE exam.